1. A carboxylate represented by formula (1) or (2) ##STR11## wherein a ring X is an unsubstituted aromatic residue or an aromatic residue substituted with a halogen atom, alkyl group, alkoxy group, aryloxy group, alkylcarbonyl group, arylcarbonyl group, alkylthio group, arylthio group, nitro group, dialkylamino group, amino group, alkylsilyl group, alkylsilyloxy group or trifluoromethyl group; A is .dbd.NH or (--OR.sup.3 and --OR.sup.4) (wherein each of R.sup.3 and R.sup.4 is independently an alkyl group having 1 to 8 carbon atoms which is unsubstituted or substituted with an allyloxy group or hydroxy group, and R.sup.3 and R.sup.4 may bond to each other to form a ring); R.sup.1 is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms which is unsubstituted or substituted with a halogen atom, hydroxy group, alkoxy group having 1 to 4 carbon atoms, aryloxy group, alkylthio group having 1 to 4 carbon atoms, alkoxycarbonyl group having 2 to 20 carbon atoms, amino group or amide group, an aralkyl group which is unsubstituted or substituted with a halogen atom, hydroxy group, alkyl group having 1 to 4 carbon atoms, alkoxy group having 1 to 4 carbon atoms, alkylthio group having 1 to 4 carbon atoms, amino group, carboxyl group, acyl group or nitro group, or an aryl group which is unsubstituted or substituted with a halogen atom, hydroxy group, alkyl group having 1 to 4 carbon atoms, alkoxy group having 1 to 4 carbon atoms, alkylthio group having 1 to 4 carbon atoms, amino group, carboxyl group, acyl group or nitro group, but when A is .dbd.NH, R.sup.1 is a residue of benzoic acid, chlorobenzoic acid, hydroxybenzoic acid, anisic acid, toluic acid or nitrobenzoic acid; and R.sup.2 is an alkyl group having 1 to 8 carbon atoms which is unsubstituted or substituted with an allyloxy group or hydroxy group.