4-Hydroxy-benzaldehyde prodn. from 4-benzyloxy-benzaldehyde or acetal - by treatment with aq. hydrohalic acid, used in prodn. of semi-synthetic antibiotic

摘要

In a new process for the prodn. of p-hydroxybenzaldehyde, p-benzyloxy-benzaldehyde derivs. of formula PhCH2OAr are treated with an aq. hydrohalic acid at 70-130 degrees C: Ar is p-formyl-phenyl or its acetal with 1-3C alkyl gps. Reaction temp. is pref. 90-120 degrees C. Suitable hydrohalic acids are HCl and HBr with a concn. of e.g. 5-30 wt.% (the concn. pref. being less than that of the constant boiling mixt. with water). The aq. hydrohalic acid is generally used in an amt. of 3-20 times the wt. of benzoaldehyde deriv. Reaction time is generally 3-20 hrs. Benzyl halide formed as byproduct is advantageously removed from the reaction mixt. by azeotropic distn. with the aq. hydrohalic acid. The single-step process gives prod. of excellent quality in good yields.