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N-bromosuccinimide

N-bromosuccinimide

N-Bromosuccinimide or NBS is a chemical reagent which is used in radical substitution and electrophilic addition reactions in organic chemistry. NBS can be considered a convenient source of bromine.

Reactions of N-Bromosuccinimide

Addition to alkenes

NBS will react with alkenes 1 in aqueous solvents to give bromohydrins 2. The preferred conditions are the portionwise addition of NBS to a solution of the alkene in 50% aqueous DMSO, DME, THF, or tert-butanol at 0°C. Formation of a bromonium ion and immediate attack by water gives strong Markovnikov addition and anti stereochemical selectivities. Markovnikov addition Side reactions include the formation of α-bromo-ketones and dibromo compounds. These can be minimized by the use of freshly recrystallized NBS.

Allylic and benzylic bromination

Standard conditions for using NBS in allylic and/or benzylic bromination involves refluxing a solution of NBS in anhydrous CCl₄ and dibenzoyl peroxide, irradiation, or both to effect radical initiation. This is also called the Wohl-Ziegler reaction. Wohl-Ziegler reaction The carbon tetrachloride must be maintained anhydrous throughout the reaction, as the presence of water may likely hydrolyze the desired product. Barium carbonate is often added to maintain anhydrous and acid-free conditions.

Bromination of carbonyl derivatives

NBS can α-brominate carbonyl derivatives via either a radical pathway (as above) or via acid-catalysis. For example, hexanoyl chloride 1 can be brominated in the alpha-position by NBS using acid catalysis. carbonyl The reaction of enolates, enol ethers, or enol acetates with NBS is the prefered method of α-bromination as it is high-yielding with few side-products.

Bromination of aromatic derivatives

Electron-rich aromatic compounds, such as phenols, anilines, and various aromatic heterocycles, can be brominated using NBS. Using DMF as the solvent gives high levels of para-selectivity.
- Organic Syntheses, Vol. 81, p.98 ([http://www.orgsyn.org/orgsyn/prep.asp?prep=v81p0098 Article])

Preparation of NBS

To a well-stirred ice-water solution of succinimide is added sodium hydroxide and then bromine. The product, NBS, precipitates out and can be collected by filtration. To purify the NBS, it can be recrystallized from water.

Precautions

Although NBS is easier and safer to handle than bromine, precautions should be taken to avoid inhalation. NBS should be stored in a refrigerator. NBS will decompose over time giving off bromine. Pure NBS is white, but it is often found to be off-white or brown colored by bromine. In general, reactions involving NBS are exothermic. Therefore, extra precautions should be taken when used on a large-scale.

References

# Organic Syntheses, Coll. Vol. 6, p.560; Vol. 56, p.112 ([http://www.orgsyn.org/orgsyn/prep.asp?prep=cv6p0560 Article]) # Beger, J.; J. Prakt. Chem. 1991, 333(5), 677-698. # Djerassi, C.; Chem. Rev. 1948, 43, 271. # Organic Syntheses, Coll. Vol. 4, p.108; Vol. 38, p.8 ([http://www.orgsyn.org/orgsyn/prep.asp?prep=cv4p0108 Article]) # Wohl, A. Ber. 1919, 52, 51. # Ziegler, K.; et al. Ann. 1942, 551, 30. # Binkley, R. W.; Goewey, G. S.; Johnston, J; J. Org. Chem. 1984, 49, 992. # Organic Syntheses, Coll. Vol. 6, p.190; Vol. 55, p.27 ([http://www.orgsyn.org/orgsyn/prep.asp?prep=cv6p0190 Article]) # Stotter, P. L.; Hill, K. A.; J. Org. Chem. 1973, 38, 2576. # Lichtenthaler, F. W.; et al. Synthesis 1992, 179. # Gilow, H. W.; Burton, D. E.; J. Org. Chem. 1981, 46, 2221. # Mitchell, R. H.; Lai, Y.-H.; Williams, R. V.; J. Org. Chem. 1979, 44, 4733.

External links

- [http://www.jtbaker.com/msds/englishhtml/b5332.htm N-bromosuccinimide External MSDS] Category:Bromine compounds Category:Reagents for organic chemistry

Chemical reagent

When purchasing or preparing chemicals, reagent describes chemical substances of sufficient purity for use in chemical analysis, chemical reactions or physical testing. Purity standards for reagents are set by organizations such as ASTM International. For instance, reagent-quality water must have very low levels of impurities like sodium and chloride ions, silica, and bacteria, as well as a very high electrical resistivity. category:chemistry

Electrophilic addition

In organic chemistry, an electrophilic addition reaction is an addition reaction where in chemical compound a pi bond is removed by the creation of two new covalent bonds. In electrophilic additions common substrates have a carbon-carbon double bond or triple bond. Y-Z + C=C → Y-C-C-Z The driving force for this reaction is the formation of an electrophile Y⁺ that forms a covalent bond with a electron-rich unsaturated system (-C=C-) (step 1). The positive charge on Y is transferred to the carbon - carbon bond. step (1) Y⁺ + -C=C- → Y-C-C⁺- In step 2 of an electrophilic addition the positively charged intermediate combines with (Z) that is electron-rich to form the second covalent bond. step (2) Y-C-C⁺- + Z → Y-C-C-Z Step 2 is also found in a SN1 reaction. The exact nature of the electrophile and the nature of the positively charged intermediate is not always clear and depends on reactants and reaction conditions. In all asymmetric addition reactions to carbon regioselectivity is important and often determined by Markovnikov's rule. Organoborane compounds give anti-Markovnikov additions. Electrophilic attack to an aromatic system results in electrophilic aromatic substitution rather than an addition reaction.

Typical electrophilic additions

- dihalo addition reaction
- Hydrohalogenation
- Hydration reaction
- Hydrogenation
- Oxymercuration reaction
- Hydroboration-oxidation reaction

Bromine

Bromine (from Gr. βρωμος (brómos), meaning "stench"), is a chemical element in the periodic table that has the symbol Br and atomic number 35. A halogen element, bromine is a red volatile liquid at room temperature which has a reactivity between chlorine and iodine. This element is harmful to human tissue in a liquid state and its vapor irritates eyes and throat.

Notable characteristics

Bromine is the only liquid nonmetallic element at room temperature. It is a heavy, mobile, reddish-brown liquid, that evaporates easily at standard temperature and pressures in a red vapor (its color resembles nitrogen dioxide) that has a strong disagreeable odor resembling that of chlorine. A halogen, bromine resembles chlorine chemically but is less active (it is more active than iodine however). Bromine is slightly soluble in water, and highly soluble in carbon disulfide, aliphatic alcohols (such as methanol), and acetic acid. It bonds easily with many elements and has a strong bleaching action. Bromine is highly reactive and is a powerful oxidizing agent in the presence of water. It reacts vigorously with amines, alkenes and phenols as well as aliphatic and aromatic hydrocarbons, ketones and acids (these are brominated by either addition or substitution). With many of the metals and elements, anhydrous bromine is less reactive than wet bromine; however, dry bromine reacts vigorously with aluminium, titanium, mercury as well as alkaline earth metals and alkaline metals. Bromine is used in the film used in older cameras.

Applications

Elemental bromine is used to manufacture a wide variety of bromine compounds used in industry and agriculture. Traditionally the largest use of bromine was in the production of 1,2-Dibromoethane which in turn was used as a gasoline anti-knock agent for leaded gasolines before they were largely phased out due to environmental considerations. Bromine is also used in making fumigants, flameproofing agents, water purification compounds, dyes, medicinals, sanitizes, inorganic bromides for photography, etc. It is also used to form intermediates in organic synthesis, where it is preferred to iodine due to its much lower cost. Bromine is used to make brominated vegetable oil, which is used as an emulsifier in many citrus-flavored soft drinks. Aqueous bromine is orange and can be used in tests for alkenes and phenols.
- When added to an alkene it will lose its color as it reacts forming a colorless bromoalkane.
- When added to phenol a white precipitate (2,4,6-tribromophenol) will form.

History

Bromine was discovered by Antoine Balard at salt marshes of Montpellier in 1826 but was not produced in quantity until 1860. The French chemist and physicist Joseph-Louis Gay-Lussac suggested the name bromine due to the characteristic smell of the vapours.

Occurrence

Bromine occurs in nature as bromide salts in very diffuse amounts in crustal rock. Due to leaching bromide salts have accumulated in sea water (85 ppm), and may be economically recovered from brine wells and the Dead Sea (up to 5000 ppm). Approximately 500 million kilograms ($350 million USD) of bromine are produced per year (2001) worldwide with the United States and Israel being the primary producers. The largest bromine reserve in the United States is located in Columbia and Union County, Arkansas.

Precautions

Elemental bromine is a strong irritant and, in concentrated form, will produce painful blisters on exposed skin and especially mucous membranes. Even low concentrations of bromine vapor (from 10 ppm) can affect breathing, and inhalation of significant amounts of bromine can seriously damage the respiratory system. Accordingly, one should always wear safety goggles and ensure adequate ventilation when handling bromine.

Recycling

Because of its high cost, bromine is usually recycled rather than disposed of into the environment.

Compounds

Aluminium bromide (AlBr₃), Ammonium bromide (NH₄Br), Bromine pentafluoride (BrF₅), Bromine trifluoride (BrF₃), Tetrabromomethane (CBr₄), Hydrobromic acid (HBr), Iron(III) bromide (FeBr₃), Lithium bromide (LiBr), Phosphorus pentabromide (PBr₅), Phosphorus tribromide (PBr₃), Potassium bromide (KBr), Potassium bromate KBrO₃), Silver bromide (AgBr), Sodium bromide (NaBr), Sodium bromate (NaBrO₃), Bromine Monofluoride (BrF)

References

- [http://periodic.lanl.gov/elements/35.html Los Alamos National Laboratory – Bromine]

External links

- [http://www.webelements.com/webelements/elements/text/Br/index.html WebElements.com – Bromine] Category:Halogens ko:브로민 ja:臭素 th:โบรมีน

Halohydrin formation reaction

A halohydrin formation reaction is an chemical reaction in which a halogen is added to an alkene in aqueous solution to form a halohydrin. The reaction is similar to the halogen addition reaction. The basic chemical equation for this reaction is as follows: :C=C + X₂ + H₂O → X-C-C-OH (X represents a halogen, either Cl or Br). The reaction occurs with anti addition, leaving the newly added X and OH groups in a trans configuration. The reaction is a form of electrophilic addition. N-Bromosuccinimide is preferable to bromine in that fewer side-products are produced. bromine

Reaction mechanism

In the first step, a halogen attacks the pi bond of the alkene, forming a bromonium ion. Addition of water give the desired halohydrin with high anti stereoselectivity and Markovnikov addition preference. Category:Organic reactions

Dimethylsulfoxide

: Dimethyl sulfoxide

Tetrahydrofuran

:THF is also the IATA airport code for Tempelhof International Airport Tetrahydrofuran is a heterocyclic organic compound. It is a clear, low-viscosity liquid with an diethyl ether-like smell. It is one of the most polar ethers and is used as a solvent of intermediate polarity in chemical reactions. THF is the fully hydrogenated analog of the aromatic compound furan.

Precautions

THF tends to form peroxides on storage. As a result, THF should not be distilled to dryness, which can leave a residue of highly-explosive peroxides. Commercial THF is therefore often inhibited with BHT. Alternatively, THF can be stored in air-tight bottles in the dark over sodium hydroxide.

External links

- [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc05/icsc0578.htm International Chemical Safety Card 0578]
- [http://www.cdc.gov/niosh/npg/npgd0602.html NIOSH Pocket Guide to Chemical Hazards]
-
- THF usage on [http://www.orgsyn.org/orgsyn/chemname.asp?nameID=35996 Organic Syntheses]
- [http://www.camd.lsu.edu/msds/t/tetrahydrofuran.htm THF info]
- [http://www.osha-slc.gov/SLTC/healthguidelines/tetrahydrofuran/ U.S. OSHA info on THF]

Markovnikov's rule

In chemistry, Markovnikov's rule is an observation based on Zaitsev's Rule. It was formulated by the Russian chemist Vladimir Vasilevich Markovnikov . It states that, in chemical reactions found particularly in organic chemistry, when a hydrogen halide reacts with the carbon-carbon double bond of an unsymmetrical alkene, giving an alkyl halide, the hydrogen adds to the carbon of the alkene functional group that has the greater number of hydrogen substituents, and the halogen adds to the carbon on the other end of the double bond which has a smaller number of hydrogen substituents. However, the real reason that the hydrogen adds on to the carbon with the most hydrogens ("the rich get richer") is because the positive charge wants to be in the most stable form. The positive charge sits comfortably in the center of the molecule because of induction. This form of the molecule is known as the most stable Carbo-Cat Ion. Therefore when a molecule of the form HX (where X is more electronegative than H) is added in an addition reaction to a carbon-carbon double bond, the H is added to the less substituted carbon atom, while the X is added to the more substituted. The stability of the carbocation reactive intermediate directly causes this rule. The rule may be summed up by quoting that the rich get richer and the poor get poorer, in that a carbon rich in substituents will get more substituents and the carbon with more hydrogens attached will get the hydrogen in case of many different organic addition reactions. Mechanisms which avoid the carbocation intermediate may react through other mechanisms that are regioselective, against what Markovnikov's rule predicts: such as free radical addition. Such reactions are said to be anti-Markovnikov, since the halogen adds to the least substituted carbon. Again, like the positive charge, the radical prefers to be in the center of the molecule where it is most stable. Category:Organic chemistry ja:マルコフニコフ則

Recrystallize

Recrystallization is an essentially physical process that has meanings in chemistry and geology. In chemistry, recrystallization is a procedure for purifying compounds. A typical situation is that a desired compound X is contaminated by a small amount of compound Y. A chemist can prepare a saturated solution of the mixture X+Y in a warm solvent and subsequently lower the temperature. For most compounds, the solubility decreases with decreasing temperature. If X is not soluble in the solvent at lower temperatures, and Y is soluble at lower temperatures, then X will precipitate as the temperature decreases, while Y stays in solution. The precitipate now has a much higher purity than the original mixture. The cost of this purification method is the loss of the part of compound X that stays in solution. Successful recrystallization depends on finding the right solvent. This is a combination of prediction and trial/error. The solvent must be soluble with X+Y at higher temperatures, and must be insoluble with either X or Y at lower temperatures to force the product to either precipitate out (while the impurity stays in solution), or stay in solution (while the impurity precipitates out). This separates the desired product from the impurity. In geology, solid-state recrystallization is a metamorphic process that occurs under situations of intense temperature and pressure where grains, atoms or molecules of a rock or mineral are packed closer together, creating a new crystal structure. The basic composition remains the same. This process can be illustrated by observing how snow recrystallizes to ice without melting. As opposed to metasomatism, which is a chemical change caused by metamorphism, recrystallization is a physical process. However, recrystallization can occur when a local migration of chemicals results in the chemical change of the rock or mineral with no external addition of materials. Limestone is a sedimentary rock that undergoes metamorphic recrystallization to form marble, and clays can recrystallize to muscovite mica. In metallurgy, recrystallization is the growth of particular grain fragments in a metal or alloy at the expense of others. This occurs when the metal or alloy is severely worked, as by cold rolling. Recrystallization results in greater, strain-free grains. Recrystallization can occur dynamic as well as static. Category:Chemical processes Category:Geological processes Category:Materials science

Anhydrous

Liquids and solids are anhydrous if they are without water, i.e., dry. A hydrate can be made anhydrous by eliminating the water from its structure. End products are sold as anhydrous when they have been processed to remove water. This should be bigger. Category:Chemical properties

Carbon tetrachloride

Carbon tetrachloride (CCl₄), also known as tetrachloromethane, is a synthetic chemical compound formerly widely used in fire extinguishers and refrigeration, but now largely abandoned due to its toxicity. At room temperature and pressure, it is a clear, colorless liquid with a "sweet" smell that can be detected at low levels. Both carbon tetrachloride and tetrachloromethane are acceptable names under IUPAC nomenclature, depending on whether it is seen as an inorganic or an organic compound. It is also called carbon chloride, methane tetrachloride, perchloromethane or benziform. Colloquially, it is called "carbon tet". Trade names include Benzinoform, Freon 10, Halon 104, Tetraform, and Tetrasol.

Production

Most carbon tetrachloride is produced by reacting carbon disulfide with chlorine. At 105 to 130 °C, these chemicals react to produce carbon tetrachloride according to the chemical equation :CS₂ + 3Cl₂ → CCl₄ + S₂Cl₂ A smaller quantity of carbon tetrachloride is produced as a byproduct in the synthesis of methylene chloride and chloroform in reaction: :CH₄ + 4Cl₂ → CCl₄ + 4HCl

Chemistry

In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedral geometry, joined to a carbon atom in the center by single covalent bonds. This symmetrical configuration results in the molecule having no net dipole moment. Therefore, carbon tetrachloride is a non-polar solvent, best at dissolving other non-polar compounds. It is somewhat volatile, giving off vapors having a smell characteristic of other chlorinated solvents, somewhat similar to the perchloroethylene smell reminiscent of some dry cleaner shops. Pure carbon tetrachloride has little or practically no flammability at lower temperatures. Because it has no hydrogen atoms, it is sometimes useful as an ¹H NMR spectroscopy solvent for non-polar samples. Because of its health risks, its use as a solvent, etc. has been minimized in the past decades.

Uses

In the early 20th century, carbon tetrachloride was widely used as a dry cleaning solvent, as a refrigerant, and in fire extinguishers. However, once it became apparent that carbon tetrachloride exposure had severe adverse health effects, safer alternatives were found for these applications, and its use in these roles declined from about 1940 onward. Carbon tetrachloride persisted as a pesticide to kill insects in stored grain, but in 1970, it was banned in consumer products in the United States. Prior to the Montreal Protocol, large quantities of carbon tetrachloride were used to produce the freon refrigerants R-11 and R-12. However, these refrigerants are now believed to play a role in ozone depletion and have been phased out of use. However, carbon tetrachloride is still used to manufacture less destructive refrigerants. Carbon tetrachloride has also been used in the detection of neutrinos. Carbon tetrachloride, like chloroform, is a useful source of chlorine in the Appel reaction.

Safety

Exposure to high concentrations of carbon tetrachloride (including vapor) can affect the central nervous system, including the brain. Victims may feel intoxicated and experience headaches, dizziness, sleepiness, and nausea and vomiting. These effects may subside if exposure is stopped, but in severe cases, coma and even death can occur. Chronic exposure to carbon tetrachloride can cause liver and kidney damage. When exposed, the liver swells, and its cells can be damaged or destroyed. The risk of liver damage is greater when one is exposed to carbon tetrachloride while under the influence of alcohol. Kidneys may also be damaged, causing a buildup of wastes in the blood. If exposure is low and then stops, the liver and kidneys can repair the damaged cells and function normally again. Chronic ingestion of carbon tetrachloride has been linked to liver cancer in animals. It is not known if breathing carbon tetrachloride vapors causes cancer in animals, or if carbon tetrachloride exposure causes cancer in humans. However, the US Department of Health and Human Services holds that carbon tetrachloride may reasonably be anticipated to be a human carcinogen. There have been no studies in people on carbon tetrachloride's effects on reproduction or development, but studies in rats showed no adverse effects. Several tests are available to measure the amount of carbon tetrachloride in a person's breath, blood, urine, and body tissues. Because carbon tetrachloride leaves the body quickly, the tests cannot tell you how much carbon tetrachloride the subject was exposed to if there is a substantial delay between exposure and testing. Typical recommended limits are 0.005 parts of carbon tetrachloride per million parts of drinking water (0.005 ppm). Drinking water exposures should not exceed 0.3 ppm for adults and 0.07 ppm for children for long periods of time (7 years). There are limits on how much carbon tetrachloride can be released from an industrial plant into waste-water and the outside air. A typical maximum concentration limit in workplace air is 10 ppm for an 8-hour workday over a 40-hour working week. Repeated sub-toxic doses of carbon tetrachloride may allow an individual to build up a partial, short-term "immunity" to toxic doses. This may be related to induction of cytochrome P450 enzymes, and is linked to the phenomenon of hormesis.

External links

- [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc00/icsc0024.htm International Chemical Safety Card 0024]
- [http://www.cdc.gov/niosh/npg/npgd0107.html NIOSH Pocket Guide to Chemical Hazards]
- [http://www-cie.iarc.fr/htdocs/monographs/vol71/011-carbontetrac.html IARC Monograph: "Carbon Tetrachloride"]
-
- [http://ull.chemistry.uakron.edu/erd/chemicals/7/6256.html Carbon tetrachloride MSDS at Hazardous Chemical Database] Category:Inorganic carbon compounds Category:Chlorides Category:Nonmetal halides Category:Organochlorides Category:Solvents Category:Aerosol propellants Category:Greenhouse gases Category:Insecticides Category:Refrigerants ja:四塩化炭素

Initiation (chemistry)

In chemistry initiation is a chemical reaction that triggers one or more secondary reactions. Often the initiation reaction generates a reactive intermediate from a stable molecule which is then involved in secondary reactions. In polymerisation, initiation is followed by a chain reaction and termination. Category:Chemical kinetics Category:Polymer chemistry

Carbon tetrachloride

Production

Chemistry

Uses

Safety

External links

Water

:This article focuses on water as it is experienced in everyday life. See water (molecule) for information on the chemical and physical properties of pure water (H₂O, hydrogen oxide). Water (from the Old English word wæter; c.f German "Wasser", from PIE
- wod-or, "water") is a tasteless, odorless, and nearly colorless (it has a slight hint of blue) substance in its pure form that is essential to all known forms of life and is known also as the most universal solvent. Water is an abundant substance on Earth. It exists in many places and forms. It appears mostly in the oceans and polar ice caps, but also as clouds, rain water, rivers, freshwater aquifers, and sea ice. On the planet, water is continuously moving through the cycle involving evaporation, precipitation, and runoff to the sea. Water fit for human consumption is called potable water. This natural resource is becoming more scarce in certain places as human population in those places increases, and its availability is a major social and economic concern.

Molecular properties

Forms of water

potable water] Water takes many different shapes on earth: water vapor and clouds in the sky, waves and icebergs in the sea, glaciers in the mountain, aquifers in the ground, to name but a few. Through evaporation, precipitation, and runoff, water is continuously flowing from one form to another, in what is called the water cycle. Because of the importance of precipitation to agriculture, and to mankind in general, different names are given to its various forms: while rain is common in most countries, other phenomena are quite surprising when seen for the first time. Hail, snow, fog or dew are examples. When appropriately lit, water drops in the air can refract sunlight to produce rainbows. Similarly, water runoffs have played major roles in human history as rivers and irrigation brought the water needed for agriculture. Rivers and seas offered opportunity for travel and commerce. Through erosion, runoffs played a major part in shaping the environment providing river valleys and deltas which provide rich soil and level ground for the establishment of population centers. Water also infiltrates the ground and goes into aquifers. This groundwater later flows back to the surface in springs, or more spectacularly in hot springs and geysers. Groundwater is also extracted artificially in wells. Because water can contain many different substances, it can taste or smell very differently. In fact, humans and other animals have developed their senses to be able to evaluate the drinkability of water: animals generally dislike the taste of salty sea water and the putrid swamps and favor the purer water of a mountain spring or aquifer.

Water in biology

From a biological standpoint, water has many distinct properties that are critical for the proliferation of life that set it apart from other substances. Water carries out this role by allowing organic compounds to react in ways that ultimately allows replication. It is a good solvent and has a high surface tension, and thus allows organic compounds and living things to be transported in it. Fresh water has its greatest density at 4°C, then becoming less dense as it freezes or heats up from this point. As a stable, polar molecule prevalent in the atmosphere, it plays an important atmospheric role as an absorber of infrared radiation, crucial in the atmospheric greenhouse effect without of which, the average surface temperature would be −18° Celsius. Water also has an unusually high specific heat, which plays many roles in regulating global and regional climate, such as the Gulf Stream climate, allowing life to survive. Water is a very good solvent, chemically not unlike ammonia, and dissolves many types of substances, such as various salts and sugar, and facilitates their chemical interaction, which aids complex metabolisms. Some substances, however, do not mix well with water, including oils and other hydrophobic substances. Cell membranes, composed of lipids and proteins, take advantage of this property to carefully control interactions between their contents and external chemicals. This is facilitated somewhat by the surface tension of water. Water drops are stable due to the high surface tension of water caused by the strong intermolecular forces called cohesive forces. This can be seen when small quantities of water are put onto a nonsoluble surface such as polythene: the water stays together as drops. On extremely clean glass the water may form a thin film because the molecular forces between glass and water molecules (adhesive forces) are stronger than the cohesive forces. This property plays a key role in plant transpiration. A simple but environmentally important and unique property of water is that its common solid form, ice, floats on the liquid. This solid phase is less dense than liquid water, due to the geometry of the strong hydrogen bonds which are formed only at lower temperatures. For almost all other substances and for all other 11 uncommon phases of water ice except ice-XI, the solid form is more dense than the liquid form. Fresh water is most dense at 4°C, and will sink by convection as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4°C. This effectively insulates a lake floor from the cold. While this behavior may seem obvious, even intuitive, it should be noted that almost all other chemicals are denser as solids than they are as liquids, and freeze from the bottom up. Life on earth has evolved with and adapted itself to the important features of water. The existence of abundant liquid, vapor and solid forms of water on Earth has been an important factor in the abundant colonization of Earth's various environments by life-forms adapted to those varying and often extreme conditions. Civilizations have historically flourished around rivers and major waterways; Mesopotamia, the so-called cradle of civilization, is situated between two major rivers. Large metropolises like London, Paris, New York, and Tokyo owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore and Hong Kong, have flourished for precisely this reason. In places such as North Africa and the Middle East, where water is scarcer, access to clean drinking water was and is a major factor in human development.

Astronomical position of Earth and impact on its water

Mesopotamia The coexistence of the solid, liquid, and gaseous phases of water on Earth is vital to the origin, evolution, and continued existence of life on Earth. However, if the Earth's location in the solar system were even marginally closer or further from the Sun (ie, a million miles or so), the conditions which allow the three forms to be present simultaneously would be far less likely to exist. Earth's mass allows gravity to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provides a greenhouse effect which helps maintain a relatively steady surface temperature. If Earth were less massive, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in polar ice caps (as on Mars). According to the solar nebula model of the solar system's formation, Earth's mass may be largely due to its distance from the Sun. The distance between Earth and the Sun and the combination of solar radiation received and the greenhouse effect of the atmosphere ensures that its surface is neither too cold nor too hot for liquid water. If Earth were more distant, most water would be frozen. If Earth were nearer to the Sun, its higher surface temperature would limit the formation of ice caps, or cause water to exist only as vapor. In the former case, the low albedo of oceans would cause Earth to absorb more solar energy. In the second case, a runaway greenhouse effect and inhospitable conditions similar to Venus would result. It has been proposed that life itself may maintain the conditions that have allowed its continued existence. The surface temperature of Earth has been relatively constant through geologic time despite varying solar flux, indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.

Human uses of water

Gaia hypothesis All known forms of life depend on water. Water is a vital part of many metabolic processes within the body. Significant quantities of water are used during the digestion of food. (Note however that some bacteria and plant seeds can enter a cryptobiotic state for an indefinite period when dehydrated, and come back to life when returned to a wet environment) About 72% of the fat free mass of the human body is made of water. To function properly the body requires between one and seven litres of water per day to avoid dehydration, the precise amount depending on the level of activity, temperature, humidity, and other factors. It is not clear how much water intake is needed by healthy people. However, for those who do not have kidney problems, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) dangerous to drink too little. People do often drink far more water than necessary while exercising, however, putting them at risk of water intoxication, which is frequently fatal. The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source. However, leading dieticians and nutritionists will tell you that this is the RDI (Recommended Daily Intake) of water. [http://ajpregu.physiology.org/cgi/content/full/283/5/R993]. The latest dietary reference intake report by the National Research Council recommended 2.7 liters of water total (including food sources) for women and 3.7 liters for men[http://www.iom.edu/report.asp?id=18495]. Water is lost from the body in urine and feces, through sweating, and by exhalation of water vapor in the breath. Humans require water that does not contain too much salt or other impurities. Common impurities include chemicals and/or harmful bacteria, such as crypto sporidium. Some solutes are acceptable and even desirable for perceived taste enhancement and to provide needed electrolytes.

Water as a precious resource

:See water resources for information about fresh water supplies. fresh water Because of the growth of world population and other factors, the availability of drinking water per capita is shrinking. The issue of water shortage can be solved through more production, better distribution and less waste of it. For this reason, water is a strategic resource for many countries. Many battles and wars, such as the Six-Day War in the Middle East, have been fought to gain access to it. Experts predict more trouble ahead because of the world's growing population, increasing contamination through pollution, and global warming. UNESCO's World Water Development Report (WWDR, 2003) from its World Water Assessment Program indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30%. 40% of the world's inhabitants currently have insufficient fresh water for minimal hygiene. More than 2.2 million people died in 2000 from diseases related to the consumption of contaminated water or drought. In 2004, the UK charity WaterAid reported that a child dies every 15 seconds due to easily preventable water-related diseases. Some have predicted that clean water will become the "next oil", making Canada, with this resource in abundance, possibly the richest country in the world.

Regulating water distribution

Drinking water is often collected at springs or extracted from artificial borings in the ground, or wells. Building more wells in adequate places is thus a possible way to produce more water assuming the aquifers can supply an adequate flow. Other water sources are the rainwater and river or lake water. This surface water, however, must be purified for human consumption. This may involve removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant ocean or seawater is a more expensive solution used in coastal arid climates. The distribution of drinking water is done through municipal water systems or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge. Others argue that the market mechanism and free enterprise are best to manage this rare resource, and to finance the boring of wells or the construction of dams and reservoirs. Reducing waste, that is using drinking water only for human consumption, is another option. In some cities, such as Hong Kong, sea water is extensively used for flushing toilets citywide in order to conserve fresh water resources. Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the pollutor. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable.

The impact of water on human culture

Water is considered a purifier in most religions, including Christianity, Islam, Judaism, and Shinto. For instance, baptism in Christian churches is done with water. In addition, a ritual bath in pure water is performed for the dead in many religions including Judaism and Islam. In Islam, the daily Salah can only be done after ablution (Wodoo), that is, washing parts of the body in clean water. In Shinto, water is used in almost all rituals to cleanse a person or an area. Water is often believed to have spiritual powers. In Celtic mythology, Sulis is the local goddess of thermal springs; in Hinduism, the Ganga is also personified as a goddess. Alternatively, gods can be patrons of particular springs, river or lakes: for example in Greek and Roman mythology, Peneus was a river god, one of the three thousand Oceanids. The Greek philosopher Empedocles held that water is one of the four classical elements along with fire, earth and air, and was regarded as the ylem, or basic stuff of the universe. Water was considered cold and moist. In the theory of the four bodily humours, water was associated with phlegm. Water was also one of the Five Elements in traditional Chinese philosophy, along with earth, fire, wood, and metal. A common misconception about water is that it is a powerful conductor of electricity. Any electrical properties observable in water are due to the ions of mineral salts and carbon dioxide dissolved in it. Water does self-ionize (two water molecules become one hydroxide anion and one hydronium cation), but only at a very slight, almost immeasurable level. Pure water can also be electrolized into oxygen and hydrogen gases but without any dissolved ions, this is a very slow process and thus very little current is conducted. Many bottled water companies exploit another common misconception, advertising both purity and taste, even though pure water is tasteless.

External links

- [http://www.lsbu.ac.uk/water/phase.html Phase diagrams of water]
- [http://www.publicforuminstitute.org/issues/oceans/index.htm Oceans and Water Issues Page]
- [http://www.greenfacts.org/water-disinfectants/index.htm Scientific Facts on Water disinfectants] A faithful summary by GreenFacts of a leading scientific consensus report on Drinking Water Disinfectants published by the International Programme on Chemical Safety of the WHO.
- [http://www.hkc22.com/residentialwater.html Residential water problems and markets] Study paper from Helmut Kaiser Consultancy
- [http://www.hkc22.com/watermarketsworldwide.html Water markets worldwide] Study paper from Helmut Kaiser Consultancy
- [http://www.worldwaterforum.org/ World Water Forum]
- [http://www.unesco.org/water/wwap/ World Water Assessment Program]
- [http://unesdoc.unesco.org/images/0012/001295/129556e.pdf United Nations' World Water Development Report]
- [http://www.gemswater.org/ United Nations GEMS/Water Programme]
- [http://www.lsbu.ac.uk/water/ Water Structure and Behaviour]
- [http://www.wateraid.org/ WaterAid]
- [http://www.sahra.arizona.edu/newswatch/ SAHRA—Global Water Newswatch]
- [http://www.siwi.org/ Stockholm International Water Institute] (SIWI)
- [http://www.c-win.org/ California Water Impact Network (C-WIN)]
- [http://news.bbc.co.uk/2/hi/science/nature/3752590.stm BBC: The water debate]
- [http://www.geocities.com/tapvsbottled/ Tap Water Vs Bottled Water] - Interesting site providing facts about tap and bottled water.
- [http://www.emagazine.com/september-october_2003/0903feat1.html E the Environmental Magazine piece on bottled water] (Oct 2003).
- [http://www.iapws.org/ International Association for the Properties of Water and Steam]
- [http://ga.water.usgs.gov/edu/watercycle.html US Geological Survey: Comprehensive discussion of the water cycle, in many languages]
- [http://www.dartmouth.edu/~etrnsfer/water.htm Why is water blue?]
- [http://www.water.org.uk/home/resources-and-links/water-for-health/ask-about/adults Water requirements in adults]
- [http://www.hkc22.com/environmentaltechnology.html/ Climate change raises markets for environmental technology, drinking water and clean energies]

References

- OA Jones, JN Lester and N Voulvoulis, Pharmaceuticals: a threat to drinking water? TRENDS in Biotechnology 23(4): 163, 2005
- Category:Beverages Category:Hydrology Category:Materials Category:Natural resources Category:Nutrition zh-min-nan:Chúi als:Wasser ko:물 ja:水 ms:Air simple:Water th:น้ำ

Hydrolyze

Hydrolysis is a chemical process in which a molecule is cleaved into two parts by the addition of a molecule of water. This is distinct from a hydration reaction, in which water molecules are added to a substance, but no cleavage occurs. In inorganic chemistry, the word is often applied to solutions of salts and the reactions by which they are converted to new ionic species or to precipitates (oxides, hydroxides, or salts). In the discussion below, the focus is on hydrolysis of organic compounds. Some of them are explained below.

Types

Hydrolysis of an ester link In a hydrolysis reaction that involves breaking an ester link, one hydrolysis product contains a hydroxyl functional group, while the other contains a carboxylic acid functional group. The fragment of the parent molecule that was originally a carboxylate gains a hydrogen ion from the additional water molecule. The fragment that was originally an alkyl group collects the remaining hydroxyl group from the water molecule. This effectively reverses the esterification reaction, yielding the original alcohol and carboxylic acid again. An important example of this reaction is the release of fatty acids from glycerol in triglyceride hydrolysis. Hydrolysing peptide link of amino acids In other hydrolysis reactions, such as hydrolysing the peptide links of amino acids, only the carboxylic acid product has a hydroxide group derived from the water. The amine product gains the remaining hydrogen ion. Hydrolysis can be considered as the opposite of condensation, in which two fragments are joined for each water molecule produced. As hydrolysis is a reversible reaction, condensation and hydrolysis can take place at the same time the position of equilibrium determining the amount of each product.

Irreversibility of hydrolysis under physiological conditions

Under physiological conditions (i.e. in dilute aqueous solution), a hydrolytic cleavage reaction, where the concentration of a metabolic precursor is low (on the order of 10^-3 to 10^-6 molar), is essentially thermodynamically irreversible. To give an example: :A + H₂O → X + Y :

K_d = \frac

Assuming that x is the final concentration of products, and that C is the initial concentration of A, and W = [H₂O] = 55.5 molar, then x can be calculated with the equation: :

\frac = K_d

let K_d×W = k then

x = \frac

For a value of C = 0.001 molar, and k = 1 molar, x/C > 0.999. Less than 0.1% of the original reactant would be present once the reaction is complete. This theme of physiological irreversibility of hydrolysis is used consistently in metabolic pathways, since many biological processes are driven by the cleavage of anhydrous pyrophosphate bonds.

Barium carbonate

Barium carbonate (Ba CO₃), also known as witherite, is a chemical compound used in rat poison, bricks, and cement. Witherite crystallizes in the orthorhombic system. The crystals are invariably twinned together in groups of three, giving rise to pseudo-hexagonal forms somewhat resembling bipyrarnidal crystals of quartz, the faces are usually rough and striated horizontally. The color is dull white or sometimes greyish, the hardness is 3.5, and the specific gravity is 4.3. The mineral is named after W. Withering, who in 1784 recognized it to be chemically distinct from barytes. It occurs in veins of lead ore at Hexham in Northumberland, Alston in Cumbria, Anglezarke, near Chorley in Lancashire, and a few other localities. Witherite is readily altered to barium sulfate by the action of water containing calcium sulphate in solution, and crystals are therefore frequently encrusted with harytes. It is the chief source of barium salts, and is mined in considerable amounts in Northumberland. It is used for the preparation of rat poison, in the manufacture of glass and porcelain, and formerly for refining sugar. Barium carbonate reacts with many acids to soluble barium salts, for example barium chloride: BaCO₃(s) + 2 HCl(aq) → BaCl₂(aq) + CO₂(g) + H₂O(l) However the reaction with sulfuric acid is poor, because of the fact that barium sulphate is highly insoluble. Category:Barium compounds Category:Carbonates

Carbonyl

In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom. The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex (e.g., nickel carbonyl); in this situation, carbon is triple-bonded to oxygen. A carbonyl group characterizes the following types of compounds (and a representation of the full group, where -CO means a C=O group):
- aldehyde- (R-CHO)
- ketone- (R-CO-R₁)
- carboxylic acid- (R-COOH)
- ester- (R-CO-O-R₁)
- amide- (R-CO-NH₂ or R-CO-NHR₁ or R-CO-NR₁R₂)
- enone- R₂-C=CR−CO−R
- acyl chloride- (R-CO-Cl)
- anhydride- (R-CO-O-CO-R)

Reactivity

Oxygen is more electronegative than carbon, and thus pulls electron density away from carbon to increase the bond's polarity. Therefore, the carbonyl carbon becomes electrophilic, and thus more reactive with nucleophiles. Carbonyl groups can be reduced by reaction with hydride reagents such as NaBH₄ and LiAlH₄, and by organometallic reagents such as organolithium reagents and Grignard reagents. Other important reactions include:
- Wolff-Kishner Reduction
- Clemmensen reduction
- Conversion into thioacetals
- Hydration to hemiacetals and hemiketals, and then to acetals and ketals
- Reaction with ammonia and primary amines to form imines
- Reaction with hydroxylamines to form oximes
- Reaction with cyanide to form cyanohydrins

α,β-unsaturated carbonyl compounds

α,β-unsaturated carbonyl compounds are an important class of carbonyl compounds with the general structure C_β=C_α-C=0. In these compounds the carbonyl group is conjugated with an alkene (hence the adjective unsaturated), from which they derive special properties. Examples of unsaturated carbonyls are acrolein, mesityl oxide, acrylic acid and maleic acid. Unsaturated carbonyls can be prepared in the laboratory in an aldol reaction and in the perkin reaction. The carbonyl group, be it an aldehyde or acid, draws electrons away from the alkene and the alkene group in unsaturated carbonyls are therefore deactived towards an electrophile such as bromine or hydrochloric acid. As a general rule with unsymmetric electrophiles hydrogen attaches itself at the α position in an electrophilic addition. On the other hand, these compounds are activated towards nucleophiles in nucleophilic conjugate addition.

Spectroscopy

- IR spectroscopy: the C=O double bond absorbs infrared light at wavenumbers between approximately 1680–1750 cm^-1. This absorption is known as the "carbonyl stretch" when displayed on an infrared absorption spectrum.
- Nuclear magnetic resonance: the C=O double-bond exhibits different resonances depending on surrounding atoms.
- Mass spectrometry

References

- William Reusch. (2004) [http://www.cem.msu.edu/~reusch/VirtualText/aldket1.htm Aldehydes and Ketones] Retrieved 23 May 2005.
- ILPI. (2005) [http://www.ilpi.com/msds/ref/anhydride.html The MSDS Hyperglossary- Anhydride].

Enolate

Enol (or, more officially, but less commonly: alkenol) is an alkene with hydroxyl group on one of the carbon atoms of the double bond. Enols and carbonyl compounds (such as ketones and aldehydes) are in fact isomers; this is called keto-enol tautomerism: center The enol form is shown on the left. It is usually unstable, does not survive long and changes into the keto (ketone) form, shown on the right. This is because oxygen is more electronegative than carbon and thus forms stronger multiple bonds. Hence, a carbon-oxygen (carbonyl) double bond is more than twice as strong as a carbon-oxygen single bond, but a carbon-carbon double bond is weaker than two carbon-carbon single bonds. Only in 1,3 dicarbonyl and 1,3,5 tricarbonyl compounds does the (mono)enol form predominate. This is because resonance and intramolecular hydrogen bonding occur in the enol form but are not possible for the keto form. Thus, propanedial (OHCCH₂CHO) exists to an extent of over 99 percent as the monoenol. The proportion is lower for 1,3 aldehyde ketones and diketones. The words enol and alkenol are combinations of the words alkene (or just en(e), the suffix given to alkenes) and alcohol (which represents the enol's hydroxyl group).

Enolate ion

When the hydroxyl group (−OH) in an enol loses a hydrogen ion (H⁺), a negative enolate ion is formed as shown here: Image:Formation_of_Enolate.PNG 1.3 dicarbonyl and 1,3,5 tricarbonyl compounds are quite acidic because of the strong resonance stabilisation created when one of the hydrogens is removed (from either the keto or enol forms). The resonance from the enol is exactly analgous to that used to explain the acidity of phenols and consists of the delocalisation of the negative charge of the enolate ion to the alpha-carbon. These enolate ions are very valuable in synthesis of complicated alcohols and carbonyl compounds (aldol additions). Category:Functional groups

Phenol

Phenol, also known under the old name carbolic acid, is a colorless crystalline solid with a typical sweet tarry odor. Its chemical formula is C₆H₅O H and its structure is that of a hydroxyl group (-OH) bonded to a phenyl ring; it is thus an aromatic compound. The word phenol is also used to refer in general to an aromatic compound in which a hydroxyl group (-OH) is bonded directly to a six-membered aromatic ring. In effect, phenols are a class of organic compounds of which the phenol discussed in this article is the simplest member. For more information on this class, see Phenols. Phenol has a limited solubility in water (8.3 g/100 ml). It is slightly acidic: the phenol molecule has weak tendencies to lose the H+ ion from the hydroxyl group, resulting in the highly water-soluble phenolate anion C₆H₅O⁻. Phenol can be made from the partial oxidation of benzene, by the cumene process, or by the Raschig process. It can also be found as a product of coal oxidation. Phenol has antiseptic properties, and was used by Sir Joseph Lister in his pioneering technique of antiseptic surgery, though the skin irritation caused by continual exposure to phenol eventually led to the substitution of aseptic (germ-free) techniques in surgery. It is one of the main components of the commercial antiseptic TCP. It is also used in the production of drugs (it is the starting material in the industrial production of aspirin), weedkillers, and synthetic resins (Bakelite, one of the first synthetic resins to be manufactured, is a polymer of phenol with formaldehyde). Exposure of the skin to concentrated phenol solutions causes chemical burns which may be severe; in laboratories where it is used, it is usually recommended that polyethylene glycol solution is kept available for washing off splashes. Washing with large amounts of plain water (most labs have a safety shower or eye-wash) and removal of contaminated clothing are required, and immediate ER treatment for large splashes; particularly if the phenol is mixed with chloroform (a commonly used mixture in molecular biology for DNA purification). Notwithstanding the effects of concentrated solutions, it is also used in cosmetic surgery as an exfoliant, to remove layers of dead skin. Compared to aliphatic alcohols, phenol shows higher acidity. This is due to the mesomeric effect: : mesomeric effect : Mesomeric structures of phenol, resulting in a partial positive charge δ⁺ on the oxygen atom. This together with the mesomeric stabilization of the phenolate anion causes an enhanced acidity.

External link

- [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc00/icsc0070.htm International Chemical Safety Card 0070]
- [http://www.cdc.gov/niosh/npg/npgd0493.html NIOSH Pocket Guide to Chemical Hazards]
- [http://www-cie.iarc.fr/htdocs/monographs/vol71/027-phenol.html IARC Monograph: "Phenol"]
-
- Category:Antiseptics Category:IARC Group 3 carcinogens ja:フェノール

Aniline

Aniline, phenylamine or aminobenzene (C₆H₅N H₂) is an organic chemical compound which is a primary aromatic amine consisting of a benzene ring and an amino group. The chemical structure of aniline is shown at the right.

Synthesis

Aniline can be produced from benzene in two steps. First, benzene is nitrated (reacted with nitric acid, a form of electrophilic substitution reaction) to give nitrobenzene. Second, the nitrobenzene is reduced to give aniline. A variety of reducing agents are effective for the reduction, including H₂ (with a catalyst), hydrogen sulfide, iron, zinc, or tin. Many derivatives of aniline can be prepared similarly.

Properties

Aniline is oily and, although colourless, it can be slowly oxidized and resinified in air to form impurities which can give it a red-brown tint. Its boiling point is 184 °C and its melting point is -6 °C. It is a liquid at room temperature. Like most volatile amines, it possesses a somewhat unpleasant odour of rotten fish, and also has a burning aromatic taste; it is a highly acrid poison. It ignites readily, burning with a large smoky flame. Chemically, aniline is a weak base. Aromatic amines such as aniline are generally much weaker bases than aliphatic amines. Aniline reacts with strong acids to form salts containing the anilinium ion (C₆H₅-NH₃⁺), and reacts with acyl halides (such as acetyl chloride, CH₃COCl) to form amides. The amides formed from aniline are sometimes called anilides, for example CH₃-CO-NH-C₆H₅ is acetanilide. The sulphate forms beautiful white plates. Although aniline is but feebly basic, it precipitates zinc, aluminium and ferric salts, and on warming expels ammonia from its salts. Aniline combines directly with alkyl iodides to form secondary and tertiary amines; boiled with carbon disulphide it gives sulphocarbanilide (diphenyl thio-urea), CS(NHC₆H₅)₂, which may be decomposed into phenyl mustard-oil, C₆H₅CNS, and triphenyl guanidine, C₆H₅N: C(NHC₆H₅)₂. Sulphuric acid at 180° C gives sulphanilic acid, NH₂.C₆H₄.SO₃H. Anilides, compounds in which the amino group is substituted by an acid radical, are prepared by heating aniline with certain acids; antifebrin or acetanilide is thus obtained from acetic acid and aniline. The oxidation of aniline has been carefully investigated. In alkaline solution azobenzene results, while arsenic acid produces the violet-colouring matter violaniline. Chromic acid converts it into quinone, while chlorates, in the presence of certain metallic salts (especially of vanadium), give aniline black. Hydrochloric acid and potassium chlorate give chloranil. Potassium permanganate in neutral solution oxidizes it to nitrobenzene, in alkaline solution to azobenzene, ammonia and oxalic acid, in acid solution to aniline black. Hypochlorous acid gives para-amino phenol and para-amino diphenylamine. Like phenols, aniline derivatives are highly reactive in electrophilic substitution reactions. For example, sulfonation of aniline produces sulfanilic acid, which can be converted to sulfanilamide. Sulfanilamide is one of the sulfa drugs which were widely used as antibacterials in the early 20th century. Aniline and its ring-substituted derivatives react with nitrous acid to form diazonium salts. Through these, the -NH₂ group of aniline can be conveniently converted to -OH, -CN, or a halide.

Uses

Originally the great commercial value of aniline was due to the readiness with which it yields, directly or indirectly, valuable dyestuffs. The discovery of mauve in 1858 by William Perkin was the first of a series of dyestuffs which are now to be numbered by hundreds. Reference should be made to the articles dyeing, fuchsine, safranine, indulines, for more details on this subject. In addition to dyestuffs, it is a starting-product for the manufacture of many drugs, such as antipyrine, antifebrin, etc. Aniline is manufactured by reducing nitrobenzene with iron and hydrochloric acid and steam-distilling the product. The purity of the product depends upon the quality of the benzene from which the nitrobenzene was prepared. In commerce three brands of aniline are distinguished—aniline oil for blue, which is pure aniline; aniline oil for red, a mixture of equimolecular quantities of aniline and ortho- and para-toluidines; and aniline oil for safranine, which contains aniline and ortho-toluidine, and is obtained from the distillate (échappés) of the fuchsine fusion. Monomethyl and dimethyl aniline are colourless liquids prepared by heating aniline, aniline hydro-chloride and methyl alcohol in an autoclave at 220°C. They are of great importance in the colour industry. Monomethyl aniline boils at 193-195°C; dimethyl aniline at 192°C. Currently the largest market for aniline is preparation of 4,4'-MDI, some 85% of aniline serving this market. Other uses include rubber processing chemicals (9%), herbicides (2%), and dyes and pigments (2%). ¹

History

Aniline was first isolated from the destructive distillation of indigo in 1826 by Otto Unverdorben (Pogg. Ann., 1826, 8, p. 397), who named it crystalline. In 1834, Friedrich Runge (Pogg. Ann., 1834, 31, p. 65; 32, p. 331) isolated from coal tar a substance which produced a beautiful blue colour on treatment with chloride of lime; this he named kyanol or cyanol. In 1841, C. J. Fritzsche showed that by treating indigo with caustic potash it yielded an oil, which he named aniline, from the specific name of one of the indigo-yielding plants, Indigofera anil, anil being derived from the Sanskrit nīla, dark-blue, and nīlā, the indigo plant. About the same time N. N. Zinin found that on reducing nitrobenzene, a base was formed which he named benzidam. August Wilhelm von Hofmann investigated these variously prepared substances, and proved them to be identical (1855), and thenceforth they took their place as one body, under the name aniline or phenylamine. Its first industrial-scale use was in the manufacture of mauveine, a purple dye discovered in 1856 by William Henry Perkin. p-toluidine, an analine derivitive, can be used in qualitative analysis to prepare carboxylic acid derivitives.

Toxicology

Oil mixtures containing rapeseed oil denatured with aniline have been clearly linked by epidemiological and analytic chemical studies to the toxic oil syndrome that hit Spain in the spring and summer of 1981, in which 20,000 became acutely ill, 12,000 were hospitalized, and more than 350 died in the first year of the epidemic. The precise etiology though remains unknown. Some authorities class aniline as a carcinogen, although the IARC lists it in Group 3 (not classifiable as to its carcinogenicity to humans) due to the limited and contradictary data available.

References

# [http://www.the-innovation-group.com/ChemProfiles/Aniline.htm ChemProfiles of Aniline] updated January 12, 2002.

External links

- [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc00/icsc0011.htm International Chemical Safety Card 0011]
- [http://www.cdc.gov/niosh/npg/npgd0033.html NIOSH Pocket Guide to Chemical Hazards]
- [http://www-cie.iarc.fr/htdocs/monographs/suppl7/aniline.html IARC Monograph "Aniline"]
-
- [http://www.compchemwiki.org/index.php?title=Aniline Computational Chemistry Wiki entry] Category:Aromatic amines Category:Dyes Category:IARC Group 3 carcinogens Category:Arabic words ja:アニリン

Dimethylformamide

Dimethylformamide is a clear liquid, miscible with water and majority of organic solvents. It is a common solvent that is often used in chemical reactions. Pure dimethylformamide is odorless while technical grade or degraded dimethylformamide often has a fishy smell due to dimethylamine impurities. Its name is derived from the fact that it is formamide (the amide of formic acid) with two methyl group substitutions, both of them on the N (nitrogen) atom. Dimethylformamide is a polar (hydrophilic) aprotic solvent with a high boiling point. It facilitates the S_N2 reaction mechanism. Dimethylformamide is synthesized from formic acid and dimethylamine. Dimethylformamide is not stable in the presence of strong bases like sodium hydroxide or strong acids like hydrochloric acid or sulfuric acid and is hydrolyzed back into formic acid and dimethylamine, especially at elevated temperatures.

Uses

The primary use of dimethylformamide is as a solvent with low evaporation rate. Dimethylformamide is used in the production of acrylic fibers and polyurethane plastics. Additionally, it is found in the pharmaceutical industry, in the development and production of pesticides, and in the manufacture of

N-bromosuccinimide

Reactions of N-Bromosuccinimide

Addition to alkenes

Allylic and benzylic bromination

Bromination of carbonyl derivatives

Bromination of aromatic derivatives

Preparation of NBS

Precautions

References

See also

External links

Chemical reagent

Electrophilic addition

Typical electrophilic additions

See also

Bromine

Notable characteristics

Applications

History

Occurrence

Precautions

Recycling

Compounds

References

External links

Halohydrin formation reaction

Reaction mechanism

Dimethylsulfoxide

Tetrahydrofuran

Precautions

External links

See also

Markovnikov's rule

Recrystallize

Anhydrous

Carbon tetrachloride

Production

Chemistry

Uses

Safety

See also

External links

Initiation (chemistry)

Carbon tetrachloride

Production

Chemistry

Uses

Safety

See also

External links

Water

Molecular properties

Forms of water

Water in biology

Astronomical position of Earth and impact on its water

Human uses of water

Water as a precious resource

Regulating water distribution

The impact of water on human culture

See also

External links

References

Hydrolyze

Types

Irreversibility of hydrolysis under physiological conditions

See also

Barium carbonate

Carbonyl

Reactivity

α,β-unsaturated carbonyl compounds

Spectroscopy

See also

References

Further Reading

Enolate

Enolate ion

Phenol

See also

External link

Aniline