Process for preparing E-isomer of triazolyl styryl ketone derivative

A novel process for preparing E-isomer of triazolyl styryl ketone derivative of the formula (I): which comprises treating Z-isomer of the said derivative which may contain E-isomer of the said derivative with an acid and an isomerization catalyst in an organic solvent, precipitating and separating the resulting salt of E-isomer from the solution, and decomposing the resulting precipitate to obtain E-isomer of the said derivative free from the acid. Said E-isomer is useful for preparing E-isomer of triazolyl styryl carbinol of the formula (II): which is useful as an antimicrobial, a herbicide, a plant growth regulator, or the like.