p-Clorobenzal cloride was added to a 4-l. wide-mouthed bottle containing 400 cc. of concentrated sulfuric acid, and stirred vigorously (Hood) for five hours. The viscous mixture is then transferred to a separatory funnel and allowed to stand overnight, after which the lower layer is run slowly, with stirring, into a 3-l. beaker three-quarters filled with cracked ice. The cream-colored solid obtained when the ice has melted is filtered by suction, washed with water, pressed dry on the funnel, and divided into three equal parts. Each portion is dissolved in a minimum of ether, and the ether solution is repeatedly shaken with 2 per cent sodium hydroxide solution until acidification of the washings gives no precipitate of p-chlorobenzoic acid. After removal of the ether by distillation on a steam bath, the residue is distilled under diminished pressure from a Claisen flask. The yield of p-chlorobenzaldehyde distilling at 108–111°/25 mm. and melting at 46–47° is 76–84 g. (54–60 per cent of the theoretical amount).

Preparation of 4-Fluoro-2-methylbenzaldehyde

    n-BuLi (2.6M in hexane, 57 ml, 143 mmol) was added over 15 minutes to a THF solution(200 ml) of 2-methyl-4-fluorophenylbromide (24.5 g, 130 mmol), cooled to -78.deg. C. and allowed to stir 1 hour at -78.deg. C. DMF (26.61 gm, 364 mmol) was then added over 2 minutes, and the solution was allowed to stir another hour. The reaction was quenched with NH4Cl and warmed to room temperature. 10% HCl was added until the solution became acidic. The mixture was diluted with ether and the organic layer washed with water and brine, then dried over MgSO 4 , filtered and concentrated to give an orange oil. The oil was purified by distillation (bp=69℃，at 7 mm Hg) to afford aldehyde 4-fluoro-2-methylbenzaldehyde as a clear liquid (13.3 g, 74%). TLC: Rf 0.30 (10% EtOAc in hexane)。