Carboxylic acids halides, degradation with

Silver salts of carboxylic acids react with bromine or chlorine in an inert solvent to give carbon dioxide, a silver halide, and the halide containing one less carbon atom than the acid. The method has been reviewed. " Both low- and high-molecular-weight aliphatic bromides have been prepared. "t i i The degradation of silver salts of aromatic acids is complicated by nuclear halogenation." The procedure is valuable as a step in the synthesis of oi-bromo esters (C, to C,) from dicarboxylic acids. ... 

Sodium hypochlorite is used for the epoxidation of double bonds [659, 691] for the oxidation of primary alcohols to aldehydes [692], of secondary alcohols to ketones [693], and of primary amines to carbonyl compounds [692] for the conversion of benzylic halides into acids or ketones [690] for the oxidation of aromatic rings to quinones [694] and of sulfides to sulfones [695] and, especially, for the degradation of methyl ketones to carboxylic acids with one less carbon atom [655, 696, 697, 695, 699] and of a-amino acids to aldehydes with one less carbon [700]. Sodium hypochlorite is also used for the reoxidation of low-valence ruthenium compounds to ruthenium tetroxide in oxidations by ruthenium trichloride [701]. 

The degradation of carboxylic acids to alkyl halides using mercuric oxide and halogens involves the initial formation of the mercuric salt of the acid, followed by a normal Hunsdiecker reaction of the salt with halogen. The relative insensitivity of the reaction to water is a consequence of the solubility of the mercury salts in the solvent (CC14). There are two limitations tertiary acids are not degraded, and use of iodine as the halogen frequently leads to the ester RCOOR as the major product. The yields in the modified reaction are usually lower than those obtained with the silver salt method.2... 

In the Barbier-Wieland degradation, the alpha-methylene group in an aliphatic carboxylic acid is removed in a sequence of reaction steps, effectively a chainshortening. The inverse procedure is the Amdt-Eistert synthesis, where an acid is converted into acyl halide and reacts with diazomethane to give the highest homolog. 

In general, hydrazides may be prepared by many of the methods analogous to those used in the preparation of amides. For example, hydrazine salts of carboxylic acids and reactions of hydrazine with esters, acyl halides, acyl anhydrides, and amides may be used to produce hydrazides. A reaction analogous to the Hofmann degradation is the formation of hydrazides from ureides (acylureas) [54] (Eq. 4). 

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