Substituted aliphatic monobasic acids

SUBSTITUTED ALIPHATIC MONOBASIC ACIDS Acetic acid can be chlorinated by gaseous chlorine in the presence of red phosphorus as catalyst to yield successively mono-, di-, and tri-ohloroacetic acid the reaction proceeds better in bright sunlight. If the chlorination is stopped when approximately one molecule of chlorine per molecule of acetic acid is absorbed the main product is monochloroacetic acid  

CH3COOH + Cl — CHjClCOOH -b HCl Bromination of fatty acids in the a-position can be effected quite readily in the presence of phosphorus trichloride, red phosphorus or pyridine as catalysts or halogen carriers with acetic acid, the addition of acetic anhydride (to ensure the absence of water) improves the yield and facilitates the bromination. Examples are — 

The conversion of an aliphatic carboxylic acid into the a-bromo- (or a-chloro-) acid by treatment with bromine (or chlorine) in the presence of a catalytic amount of phosphorus tribromide (or trichloride) or of red phosphorus is known as the Hell-Volhard-Zelinsky reaction. The procedure probably involves the intermediate formation of the acyl halide, since it is known that halogens react more rapidly with acyl hahdes than with the acids themselves  

COOH-b PX3 —3RCH,COX + HjPOj RCHjCOX -b X — RCHXCOX -b HX RCHXCOX -b RCHjCOOH — RCHXCOOH -b RCH,COX Dichloroacetic acid is conveniently prei ared by the action of calcium carbonate in the presence of a little sodium cyanide upon chloral hydrate, followed by acidification with concentrated hydrochloric acid  

Trichloroacetic acid is best prepared by the oxidation of chloral hydrate with fuming nitric acid  

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NAPHTHENIC ACIDS. The term naphthenic acid, as commonly used in the petroleum industry, refers collectively to all of the carboxylic adds present m crude oil. Naphthenic adds are classified as monobasic carboxylic acids of the general formula RCOOH, where R represents the naphthene moiety consisting of cyclopentine and cyclohexane derivatives. Naphthenic adds are composed predominantly of alkyl-substituted cycloaliphatic carboxylic adds, with smaller amounts of acyclic aliphatic (paraffinic or fatty) acids. Aromatic, okfinic. hydroxy, and dibasic acids are considered to be minor components. Commercial naphthenic aads also contain varying amounts of unsaponifiable hydrocarbons, phenolic compounds, sulfur compounds, and water. The complex mixture of adds is derived from straight-run distillates of petroleum, mostly from kerosene and diesel fractions. See also Petroleum. 

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