Other reactions of the carboxyl group

A carboxyl group raises the activity of the adjacent CH2 group above that of other CH2 groups in a long-chain acid. It is thus possible to functionalize the a-methylene group in a number of ways. Some reactions of this type are useful only for saturated acids (or esters) because double bonds sometimes promote similar reactions at their allylic positions leading to mixed or more complex products. Reference has already been made to a-halo-genation (Section 10.5) and this account deals with sulphonation and the formation and reactions of a-anions. Some of these reactions are accompanied or followed by decarboxylation so the whole sequence can be summarized  

Sulphonation of saturated fatty acids (or esters) can be effected with oleum, stabilized sulphur trioxide, dilute vaporized sulphur dioxide or chlorosulphonic acid. Trichloromethane, tetrachloromethane, tetra-chloroethene and liquid sulphur dioxide have been used as reaction solvent. 

Saturated and monoene acids form dianions when treated with lithium di-isopropylamide and hexa-methylphosphoramide and these undergo further 

RCH2CHO (HCOOH and decarboxylation) RCH2NO2 (Pr0N02 and decarboxylation) RCHCH2CH2 (ethylene oxide). 

Bluestein, B.R. and Kapur, B.L. (1979) Fatty Acids (ed. E.H. Pryde), American Oil Chemists Society, Champaign, p. 260. 

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