由于氰基很容易由卤代烃或重氮盐与无机氰化物反应引入，因此腈水解是制备羧酸的很重要的方法。腈水解也有酸水解和碱水解两种情况。腈的酸水解一般都是用浓硫酸在水或水-乙醇的溶剂中进行，若用浓盐酸，经常会停留在酰胺一步。在某些特殊情况下，腈水解也会停留在酰胺这一步，此时为了水解完全，可以加入亚硝酸钠促进水解反应的进行。直接将腈水解为酸的反应条件相当苛刻，因此并不是一个很好的办法，一般来说，是将腈在HCl/MeOH 中转化为甲脂，而后再水解，这样条件就要温和了很多。

1、腈的酸水解示例

A mixture of water (1150mL), commercial sulfuric acid (840 mL) and benzyl cyanide (700 g, 6 mol) was heated under a reflux condenser and stirred for three hours, cooled slightly, and then poured into 2 L of cold water. The mixture should be stirred so that a solid cake was not formed; the phenylacetic acid was then filtered off. The crude material was melted under water and washed by decantation several times with hot water. These washings, on cooling, deposited a small amount of phenylacetic acid which was filtered off and added to the main portion of material. The last of the hot water was poured off from the material while it was still molten, and it was then transferred to a Claisen distilling flask and distilled under reduced pressure. A small amount of water came over first and was rejected; about 20 mL, containing an appreciable amount of benzyl cyanide, then distils. This fraction was used in the next run. The distillate boiling at 176–189°/50 mmHg was collected separately and solidified on standing to give the product (630 g, 77.5%) which melts at 76~76.5°C.

Reference: Organic Syntheses Coll. Vol. 1, 436。

2、腈的碱水解示例

A mixture of 2-phenylpropanenitrile (13.2 g, 0.1 mol) and an aqueous solution of sodium hydroxide (10%, 60 mL) was heated with magnetic stirring in an oil bath at reflux temperature for 4.5 hr. The course of the reaction was monitored by gas-chromatographic analysis. After the solution was cooled to room temperature, it was extracted with diethyl ether to remove nonacidic material (primarily traces of amide). An aqueous solution of hydrochloric acid (15%, 50 mL) was added portionwise. The suspension that formed was poured into a separatory funnel and extracted with diethyl ether (3 × 50 mL). The combined organic extracts were washed with water (60 mL) and dried over sodium sulfate (25 g). After filtration, the solvent was removed by rotary evaporation, and the yellow liquid residue was

distilled under reduced pressure to afford 2-phenylpropionic acid (14.3 g, 93%) as a pale-yellow liquid.

Reference: Organic Syntheses Coll. Vol. 10, 640

3 、亚硝酸钠促进的腈的酸水解示例

A mixture of compound 1 (6.6 g, 35 mmol), conc. H2SO4 (29 ml), AcOH ( 58 ml) and water (115 ml) was heated at 120°C for 1h, then a solution of NaNO2 (4.0 g), in water (30 ml) was added at 90~100°C. After the mixture had been heated for 1 h, NaCl (40 g) was added to the hot mixture and the whole was cooled in an ice-bath. The precipitate was collected to give the crude free acid (6.2 g, 62%).

Reference: Chem. Pharm. Bull.; EN; 33; 8; 1985; 3336-3348.

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