由二卤甲基或二卤亚甲基合成醛酮

将二卤甲基或二卤亚甲基化合物在酸性或碱性条件下水解,则生成相应的醛酮。比如9，9-二溴芬在醋酸中，于醋酸钠存在下加热回流即可以良好的收率生成芬酮。

p-Clorobenzal cloride was added to a 4-1.wide-mouthed bottle containing 400 cc.ofconcentrated sulfuric acid,and stirred vigorously(Hood)for five hours.The viscous mixtureis then transferred to a separatory funnel and allowed to stand overnight,after which the lowerlayer is run slowly,with stirring,into a 3-1.beaker three-quarters filled with cracked ice.The cream-colored solid obtained when the ice has melted is filtered by suction,washed withwater,pressed dry on the funnel,and divided into three equal parts.Each portion is dissolvedin a minimum of ether,and the ether solution is repeatedly shaken with 2 per cent sodiumhydroxide solution until acidification of the washings gives no precipitate of p-chlorobenzoicacid.After removal of the ether by distillation on a steam bath,the residue is distilled underdiminished pressure from a Claisen flask.The yield of p-chlorobenzaldehyde distilling at108-111/25 mm.and melting at 46-47°is 76-84 g.(54-60 per cent of the theoreticalamount).