Chloral

Properties of Chloral (SECTIONS 329, 331).—(a) Preparation from chloral hydrate.—Shake in a small test-tube about 3 grams of chloral hydrate and 3 cc. of concentrated sulphuric acid. (Eq.) Separate by means of a pipette the oil which floats on the sulphuric acid, and add it to one-half its volume of water. (Eq.) 

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CCls CHO. A colourless oily liquid with a pungent odour b.p. 98°C. Manut actured by the action of chlorine on ethanol it is also made by the chlorination of ethanal. When allowed to stand, it changes slowly to a white solid. Addition compounds are formed with water see chloral hydrate), ammonia, sodium hydrogen sulphite, alcohols, and some amines and amides. Oxidized by nitric acid to tri-chloroethanoic acid. Decomposed by alkalis to chloroform and a methanoate a convenient method of obtaining pure CHCI3. It is used for the manufacture of DDT. It is also used as a hypnotic. 

CCl3CH(OH)2, C3H3CI3O2. Crystallizes in large, colourless prisms having a peculiar odour m.p. 57"C, b.p. 91-5 C. Manufactured by adding the calculated amount of water to chloral. For other properties see chloral. Its chief use is as a hypnotic. 

Dichloroethanoic acid, CHCljCOOH. Low-melting solid, m.p. 5-6 "C, b.p. 194°C. Prepared by the action of copper powder on trichloroethanoic acid or by the action of sodium cyanide on chloral hydrate. 

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. 

Telluric acid, TefOH), is formed from Te in aqua regia and a chlorale(V). Forms tellurales, e.g. Na[TeO(OH)s], Na2[Te02(0H)4]. 

Liquids are occasionally purified by removing impurities as constant-boiling mixtures, or by shaking with concentrated sulphuric acid and subsequently separating the dried liquid from the acid the second method is therefore limited to liquids which are insoluble in, and chemically unaffected by, the strong acid e.g., benzene, anhydrous chloral). 

When chlorine is passed into boiling ethanol, both chlorination of the methyl group and oxidation of the primary alcohol group to an aldehyde occur, giving trichloro-acetaldehyde or chloral ... 

CHjCHoOH + 4CI2 CCI3CHO 5HCI When chloral is treated with caustic alkali, fission of the C-C linkage occurs, giving chloroform and a formate ... 

In addition to chloroform, many other compounds containing the trichloro-methyl group, CI3C-, show marked physiological action. Thus trichloro-acetaldehyde or chloral hydrate, Cl3C CH(OH) (p. 342), and trichloro-tertiary-butanol or chloretone, CUC CfCHaliOH, are both hypnotics. Similarly, tribromo-ethanol or avertin, BraC-CHjOH, has strong anaesthetic properties. 

Aldehydes. Formaldehyde, metaformaldehyde, acetaldehyde, paraldehyde, chloral hydrate, benzaldehyde, salicylaldehyde (and other substituted benzaldehydes). 

Aniline.—Burns with a very smoky flame, clouds of soot being produced. Typical of many aromatic substances. i,2 Dibromoethane.—Does not burn until vapour becomes hot and then burns with a slightly smoky flame. Typical of substances rich in halogens such as cldoroform, chloral hydrate, and carbon, tetrachloride. (Note, however, that iodoform evolves copious fumes of iodine when heated in this way.)... 

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

Acetaldehyde, CH3CHO, b.p. 21°, is generally used in aqueous solution, which has also a characteristic odour paraldehyde, (CH3CHO)3, is a liquid polymer, b.p. 124°, slightly soluble in water, odour similar to that of acetaldehyde, but less intense. Chloral, CCI3CHO, a liquid, is almost invariably encountered as the stable solid hydrate , CCl3CH(OH)2, m.p. 57 . Both have a characteristic odour the hydrate is readily soluble in water. 

Bisulphite addition compound. To 0 2 g. of powdered chloral hydrate add 2 ml. of saturated NaHSOj solution and stir. The hydrate dissolves and the white addition product separates. Stale or slightly diluted solutions of NaHSO, do not give this product. 

Action of sulphuric add. To 0-5 g. of powdered chloral hydrate add 2 ml. of cone. H2SO4, shake well and allow to stand. Liquid chloral gradually separates out as an oil on the surface of the acid. 

Isocyanide reaction. Since chloral hydrate is readily converted into chloroform by alkali, it will give the isocyanide reaction. To a few crystals of the solid add about 5 ml. of alcoholic NaOH solution and a few drops of aniline, and heat the disagreeable odour of phenyl isocyanide, C H(NC, is rapidly detected. 

Derivatives. The precise identification of a compound normally depends upon the preparation of a derivative and the determination of physical constants such as m.p. in the case of a solid. Many simple compounds can, however, be identified with a fair degree of certainty by intelligently-selected qualitative tests alone, e.g., formates, oxalates, succinates, lactates, tartrates, chloral hydrate. 

Monohydric alcohols, aldehydes (including chloral hydrate), ketones, cinnamic acid, amines (2-naphthylaminc is odourless), nitrophenols (resemble both phenol and nitro-compound),... 

Chloral hydrate Acid halides Halogeno-hydrocarbons Ammonium salts )... 

Aldehydes (including chloral hydrate) formates and lactates some esters chloroform and iodoform reducing sugars some phenols. 

Formation of silver mirror or precipitate of silver indicates reducing agent. (This is often a more sensitive test than I (a) above, and some compounds reduce ammoniacal silver nitrate but are without effect on Fehling s solution.) Given by aldehydes and chloral hydrate formates, lactates and tartrates reducing sugars benzoquinone many amines uric acid. 

TEST Formaldehyde (solution) Acetal d yde (solution) Paraldehyde Chloral hydrate Benzaldehyde Salicylaldehyde... 

The student is recommended to carry out the following reactions with chloral hydrate in order to familiarise himself with its general properties. 

Confirm this by treating 0 5 g. of chloral hydrate with 3 ml. of dilute sodium hydroxide solution and warming gently. 

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