Patent ID: 7411095

Claim:
A method of producing a highly pure compound having a formula (3) wherein R 1 and R 2 are the same or different and each represents a hydrogen atom, an unsubstituted C 1 -C 6 alkyl group, a C 1 -C 6 alkyl group substituted with at least one substituent selected from the group consisting of a Substituent group α and a Substituent group β, an unsubstituted C 6 -C 14 aryl group or a C 6 -C 14 aryl group substituted with at least one substituent from Substituent group α, R 3 and R 4 are the same or different and each represents an unsubstituted C 1 -C 6 alkyl group, a C 1 -C 6 alkyl group substituted with a C 1 -C 6 alkoxy group or a C 3 -C 6 cycloalkyl group, Substituent group α is selected from the group consisting of a hydroxyl group, a nitro group, a cyano group, a halogen atom, a C 1 -C 6 alkyl group, a C 1 -C 6 alkoxy group, a C 1 -C 6 alkylthio group and a di(C 1 -C 6 alkyl)amino group, and Substituent group β is selected from the group consisting of an unsubstituted C 6 -C 14 aryl group and a C 6 -C 14 aryl group substituted with at least one substituent from Substituent group α, which comprises (a) reacting a compound having a formula (1) wherein R 1 and R 2 have the same meanings as those indicated hereinbefore, with a compound having a formula (2) R 3 —(NH)—R 4 (2) wherein R 3 and R 4 have the same meanings as those indicated hereinbefore, wherein the compound of the formula (2) is in an amount which is more than one equivalent of the compound of the formula (1), (b) treating the resulting reaction mixture from step (a) with an acidic aqueous solution selected from the group consisting of a dilute aqueous solution of mineral acid and an aqueous solution of an organic acid, at a temperature between 0° C. and 30° C. and (c) carrying out a treatment on the resulting reaction mixture from step (b) with a basic aqueous solution.