cinnamic acid containing a metallic catalyst which is a mixture prepared by the synthetic reaction of a cinnamic acid ester a disclosed purifying means is the combination of alkali hydrolysis active carbon adsorption solvent extraction and precipitation with an acid application_number US 78229991 A description a cinnamic acid ester to which a method of the present invention can be applied is a cinnamic acid ester represented by the formula i str1 wherein r 1 is hydrogen a halogen a hydroxyl group an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms n is an integer of from 1 to 5 r 2 and r 3 may be identical or different and each of them is hydrogen or an alkyl group having 1 to 6 carbon atoms and r 4 is an alkyl group or an alkenyl group which may have substituents typical examples of the cinnamic acid ester represented by the formula i include methyl cinnamate ethyl cinnamate propyl cinnamate butyl cinnamate ethyl u03b1 methyl u03b2 phenylacrylate methyl u03b1 propyl u03b2 chlorophenylacrylate methyl u03b2 3 4 dimethoxyphenylacrylate methyl u03b2 4 methoxyphenylacrylate benzyl cinnamate cinnamyl cinnamate and guaiacol cinnamate each of these esters can be obtained by reacting a styrene an alcohol carbon monoxide and oxygen in the presence of a catalyst in a solvent and examples of the.