Reduction of Carboxylic Acids Containing Substituents or Other

REDUCTION OF CARBOXYLIC ACIDS CONTAINING SUBSTITUENTS OR OTHER FUNCTIONAL GROUPS 

Carboxylic acids containing halogens are easily reduced to halogenated alcohols 

Refluxing with zinc in ethanol reduced a-bromocinnamic acid to cinnamic acid in 80% yield [997]. Allylic chlorines in y,y,y-trichlorocrotonic acid were partly or completely hydrogenolyzed by zinc and sodium amalgam [5/9]. Hydrogenolysis of allylic bromine in oc, -unsaturated esters with zinc in acetic acid gave predominantly, y-unsaturated esters in 65-97% yields [998]. 

The biochemical reduction of a, -unsaturated -haloaliphatic acids by means of Clostridium kluyveri yielded halogen-free satmated acids. The same products were obtained from saturated -halo acids. However, the same microorganism converted ix, -unsaturated a-halo acids to saturated a-halo acids with R configuration. Yields of reduction of a-fluoro-, a-chloro- and a-bromocrotonic acid ranged from 30% to 100% [330]. 

In carboxylic adds containing nitro groups borane reduced only the carboxyl group [738, 977] whereas ammonium sulfide reduced only the nitro group [239]. 

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