| 摘要 |
Prepn. of isovanillin comprises selective dealkylation in position 3 of a 3-alkoxy-4-methoxybenzaldehyde with a strong acid, the alkoxy gps. contg. at least 2C. The strong acid has a pKa of ≤ 3 and is pref. a halogenic acid, an opt. halogenated oxyacid or an opt. halogenated sulphonic acids. The alkylating agent is a halomethyl, pref. CH3Cl or dimethylsulphate. The 3-alkoxy-4-methoxy-benzaldehyde is prepd. by O-methylation of the corresp. 4-hydroxy cpd. at 80-95 degrees C and at a pH of 9, by addn. of an aq. alkali metal base, partic. sodium hydroxide, carbonate or hydrogencarbonate. The 4-hydroxy deriv. is pref. treated with a basic soln., the temp. is then adjusted, the alkylating agent and an optional base are added and the organic phase is recovered and separated. Both reaction steps are carried out under inert gas, pref. a noble gas or N2. In the dealkylation step, . 95-99 wt.% H2SO4 or 30-50 wt.% HCl or HBr is used, and in an acid to 3-alkoxy-4-methoxybenzaldehyde molar ratio of 4-10. |
