1. Derived from the reaction of p-chlorobenzyl chloride and sodium cyanide. Add p-chlorobenzyl chloride and neocerizin into the reaction pot, heat to 100°C, slowly add sodium cyanide aqueous solution, and react at 100-104°C for 5h (add sodium cyanide for 3h, keep for 2h). Then add water to dissolve the sodium chloride and separate the water layer to obtain the crude p-chlorobenzyl cyanide, which is distilled under reduced pressure to collect the 160°C (2.66kPa) fraction to obtain the finished product. The yield is over 81%. Benzyl chloride and sodium cyanide reflux in ethanol at 83-85 ℃ for 4h, the product can also be obtained. The industrial intermediate is a slightly yellow liquid, containing p-chlorobenzyl cyanide ≥90%. Raw material consumption quota: p-chlorobenzyl chloride (92%) 1432kg/t, sodium cyanide (95%) 450kg/t, and promethazine (above 90%) 18kg/t.

2. The preparation method is to add solid sodium cyanide and water into the reactor, heat to 40°C to dissolve the sodium cyanide, add a phase transfer catalyst, and then add p-chlorobenzyl chloride dropwise at a temperature of 40-60°C. After dripping, the reaction was stirred at 85°C for 4h, and after cooling, it was processed to obtain p-chlorobenzyl cyanide.