108-90-7 Chlorobenzene

Chlorobenzene is used in chemical and pesticide production. It is classified as a probable human carcinogen (EPA Group B2) or possible human carcinogen (EPA Group C). 

Chlorinated benzenes, otherwise known as DCBs, are used in the production of organic chemicals (e.g., herbicides, pesticides, and fungicides). Chronic exposures can result in liver injury. 

Chlorobenzene was one of the first basic organic chemicals produced on a large scale it was already manufactured in 1909 by United Alkali Co, Wipnes/USA. The importance of chlorobenzene rose dramatically during World War I, since it was needed as an intermediate in the production of phenol for the manufacture of picric acid. Other uses, now principally of historic importance, are the production of DDT (l,l,l-trichloro-2,2-di(4-chlorophenyl)ethane) from chlorobenzene and chloral in the presence of sulfuric add, first synthesized in 1874 by Othmar Zeid-ler, and the ammonolysis to produce aniline. 

The reaction of benzene and chlorine is carried out with Friedel-Crafts catalysts such as FeCls or HCl, under very mild conditions. Low molar ratios of chlorine to benzene favor monosubstitution. The production of monochlorobenzene is therefore performed with a chlorine/benzene molar ratio of 0.6, at temperatures of 30 to 80 °C. 

For the industrial application of the reaction it is necessary to use dry reactants, since water deactivates the catalyst and causes corrosion damage as a result of the formation of hydrochloric acid. 

Benzene, which is pre-dried to a residual water content of 35 ppm, is brought into contact with dry HCl gas, produced in the chlorination process, in a spray 

1 Benzene drying (Hausmann column) 2 Adiabatic HCl absorption 3 Reactor 4 and 5 Benzene and HCl stripping columns 6 Chlorobenzene main column 7 Chlorobenzene side column 8 p-Dichlorobenzene column 9 o-Dichloro-benzene column 10 Crystallizer 

Place 50 g. (57 ml.) of dry A.R. benzene and 0 5 ml. of dry p rridine (1) (dried over potassium hydroxide pellets) in a 500 ml. round-bottomed flask. Attach a reflux condenser to the flask and an inverted funnel (just dipping into some water in a beaker) to the top of the condenser (Fig. II, 13, 8, b). Partially immerse the flask in a bath of cold water, supported upon a tripod and gauze. Carefully pour 125 g, (40 ml.) of bromine (for precautions to be taken with bromine, see Section 111,35, Note 1) through a condenser and immediately insert the absorption device into the upper end of the condenser. A vigorous reaction soon occurs and hydrogen bromide is evolved which is absorbed by the water in the beaker when the reaction slackens, warm the bath to 25-30° for 

I hour. Finally raise the temperature of the bath to 65-70° for a further 45 minutes or until all the bromine has disappeared (no red vapours visible) and the evolution of hydrogen bromide has almost ceased. Keep the solution of hydrogen bromide in the beaker (2). 

Method 1. Arrange the flask containing the reaction mixture for steam distillation as in Fig. II, 40, 1. Proceed with the steam distillation until crystals of p-dibromobenzene appear in the condenser. Change the receiver and continue with the distillation until all the p-dibromobenzeiie has passed over from time to time run out the water from the condenser so that the crystals melt and run down into the receiver. Reject the residue in the flask. Transfer the first distillate to a separatory funnel, wash it with a httle water, and dry the lower layer with a little anhydrous magnesium sulphate or anhydrous calcium chloride filter. Distil slowly from a small distilling flask use a wire gauze or an air bath (Fig. II, 5, 3). Collect the fraction which passes over at 150-170° pour the residue (R), while it is still hot, into a small beaker or porcelain basin for the isolation of p-dibromobenzene. Redistil the fraction of b.p. 150-170° and collect the bromobenzene at 154-157° (3). The yield is 60 g. 

To isolate pure p-dibromobenzene, filter the second portion of the steam distillate through a small Buchner funnel with suction press the crystals as dry as possible. Combine these crystals with the residue (R) and recrystaliise from hot ethyl alcohol (for experimental details, see Section IV,12) with the addition of 1-2 g. of decolourising charcoal use about 4 ml. of alcohol (methylated spirit) for each gram of material. Filter the hot solution through a fluted filter paper, cool in ice, and filter the crystals at the pump. The yield of p-dibromobenzene, m.p. 89°, is about 12 g. 

Method 2. Transfer the dark-coloured reaction product to a separatory funnel and shake successively with water, with sufficient 5-10 per cent, sodium hydroxide solution to ensure that the washings are alkaline to litmus, and finally with water. Dry with anhydrous magnesium sulphate or calcium chloride. Filter through a fluted filter paper into a small distilling flask and distil slowly. Collect the crude bromobenzene at 150-170° pour the residue whilst still hot into a small porcelain basin. Redistil the hquid of b.p. 150-170° (3) and collect the bromobenzene at 154-157° the yield is about 60 g. 

Water Less than 0.03% by Karl Fischer titration Ultraviolet absorbance  

Refractive Index 1.5249 0.0007 at 20 C Bolling range 131-132 C Residue Less than one mg/1 

SPECIFICATIONS Packed under nitrogen Preservative Anylene 

Refractive index 1.4457 0.0003 at 20 C Boiling range 61-62 0 Residue Less than one mg/l 

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M.p. I08-5 C. Ordinary DDT contains about 15% of the 2,4 -isomer, and is prepared from chloral, chlorobenzene and sulphuric acid. It is non-phytotoxic to most plants. It is a powerful and persistent insecticide, used most effectively to control mosquitoes in countries where malaria is a problem. It is stored in the bodies of animals and birds. 

A mixture of the two mononitro-chlorobenzenes is prepared by nitration of chlorobenzene. Further nitration of the mixture or of either of the mononitro-compounds gives 2,4-dinitrochlorobenzene, m.p. 5 C, b.p. 315"C. 

Obtained synthetically by one of the following processes fusion of sodium ben-zenesulphonate with NaOH to give sodium phenate hydrolysis of chlorobenzene by dilute NaOH at 400 C and 300atm. to give sodium phenate (Dow process) catalytic vapour-phase reaction of steam and chlorobenzene at 500°C (Raschig process) direct oxidation of cumene (isopropylbenzene) to the hydroperoxide, followed by acid cleavage lo propanone and phenol catalytic liquid-phase oxidation of toluene to benzoic acid and then phenol. Where the phenate is formed, phenol is liberated by acidification. 

Students should carry out the purification by steam distillation of (a) crude nitrobenzene or chlorobenzene, or of (b) crude naphthalene, o-nitrophenol (p. 170) or />-tolunitrile (p. 194) as examples of solid compounds which may also be purified in this way. When the distillation is complete, disconnect the tubing (Fig. 15) between C and D before removing the flame from under D, otherwise the contents of C will be sucked back into D as the latter cools. 

Chlorobenzene may be obtained from an aqueous solution of benzenediazo-nium chloride by two methods ... 

Chlorobenzene is a stable colourless liquid having b.p. 132° and d, i-ii it is insoluble in water. 

Prepare a solution of benzencdiazonium chloride from 20 ml, (20 5 g.) of aniline precisely as in the preparation of chlorobenzene (p. 189), i.e, by dissolving the aniline in a mixture of 50 ml. of concentrated hydrochloric acid and 50 ml. of water, cooling to 5°, and then cautiously adding a solution of 17 g. of sodium nitrite in 40 ml. of water to the well-cooled and stirred aniline hydrochloride solution so that the temperature of the mixture remains between 5° and 10°. 

Methyl iodide, ethyl bromide and iodide, higher alpihatic halides chloroform, iodoform, carbon tetrachloride chlorobenzene, bromobenzene, iodobenzene benzyl chloride. 

Halogen, Chloral hydrate, sodium chloroacetate, chlorobenzene, />-chlorophenol, dichlorhydrin, bromobenzene, iodobenzene. 

Chlorobenzene, CjHjCl, bromobenzene, CgHgBr, and iodobenzene possess aromatic odours. Benzyl chloride, CgHjCHgCl, has a sharp irritating odour and is lachrymatory. 

For an actual determination, first place in J some stable liquid the boiling-point of which is at least 50 above that of the organic liquid the pour density of which is to be measured. This difference in boiling-point is important, because it is essential that the organic liquid, when nbsequently dropped into the bottom of T, should volatilise rapidly nd so push out an equivalent volume of air before the organic vapour can diffuse up the tube T and possibly condense in the cooler ttppcr portion of the tube. Suitable liquids for use in the jacket are ter, chlorobenzene (132°), rym-tetrachloro-ethane (147 ), P ... 

Vapour Density of Carbon Tetrachloride, chlorobenzene being used as the heating liquid. 

The following liquids may be used (boiling points are given in parentheses) — chlorobenzene (132-3°) bromobenzene (155°) p cymene (176°) o-dichloro-benzene (180°) aniline (184°) methyl benzoate (200°) teti-alin (207°) ethyl benzoate (212°) 1 2 4-trichlorobenzene (213°) iaopropyl benzoate (218°) methyl salicylate (223°) n-propyl benzoate (231°) diethyleneglycol (244°) n-butyl benzoate (250°) diphenyl (255°) diphenyl ether (259°) dimethyl phth ate (282°) diethyl phthalate (296°) diphenylamine (302°) benzophenone (305)° benzyl benzoate (316°). 

Repeat the boiling point determination with the following pure liquids (a) carbon tetrachloride, A.R. (77°) (6) ethylene dibromide (132°) or chlorobenzene (132°) (c) aniline, A.R. (184-6°) and (d) nitrobenzene, A.R. (211°). An air condenser should be used for (c) and (d). Correct the observed boiling points for any appreciable deviation from the normal pressure of 760 mm. Compare the observed boiling points with the values given in parentheses and construct a calibration curve for the thermometer. Compare the latter with the curve obtained from melting point determinations (Section 111,1). 

Chlorobenzene. Prepare a solution of phenyldiazonium chloride from 31 g. (30 -5 ml.) of aniUne, 85 ml. of concentrated hydrochloric acid, 85 ml, of water, and a solution of 24 g. of sodium nitrite in 50 ml. of water (for experimental details, see Section IV,60). Prepare cuprous chloride from 105 g. of crystallised copper sulphate (Section 11,50,1), and dissolve it in 170 ml. of concentrated hydrochloric acid. Add the cold phenyl diazonium chloride solution with shaking or stirring to the cold cuprous chloride solution allow the mixture to warm up to room temperature. Follow the experimental details given above for p-chlorotoluene. Wash the chlorobenzene separated from the steam distillate with 40 ml. of 10 per cent, sodium hydroxide solution (to remove phenol), then with water, dry with anhydrous calcium chloride or magnesium sulphate, and distil. Collect the chlorobenzene (a colourless liquid) at 131-133° (mainly 133°), The yield is 29 g. 

Equip a 1 Utre three-necked flask or a 1 litre bolt- head flask with a reflux condenser and a mercury-sealed stirrer. Dissolve 50-5 g. of commercial 2 4-dinitro-l-chlorobenzene in 250 ml. of rectified spirit in the flask, add the hydrazine solution, and reflux the mixture with stirring for an hour. Most of the condensation product separates during the first 10 minutes. Cool, filter with suction, and wash with 50 ml. of warm (60°) rectified spirit to remove unchanged dinitrochlorobenzene, and then with 50 ml. of hot water. The resulting 2 4-dinitrophenylhydrazine (30 g.) melts at 191-192° (decomp.), and is pure enough for most purposes. Distil oflF half the alcohol from the filtrate and thus obtain a less pure second crop (about 12 g.) recrystallise this from n-butyl alcohol (30 ml. per gram). If pure 2 4-dinitrophenylhydrazine is required, recrystallise the total yield from n-butyl alcohol or from dioxan (10 ml. per gram) this melts at 200° (decomp.). 

Dinitroaniline. This preparation is another illustration of the mobile character of the chlorine atom in 2 4-dinitro-l-chlorobenzene ... 

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