The invention discloses a method for preparing 7-phenylacetamido-3-chloromethyl-4-
carboxylic acid p-
meth-oxybenzyl ester. The method comprises the following steps of: adding
nitrogen heterocyclic
butanone sulfinic acid which is a
primary standard substance, a
chlorinated solvent and a catalyst which is 1 to 5 percent of the
primary standard substance by weight into a reaction kettle; starting a recycle pump to cycle materials through a film chlorinator; aerating
chlorine gas into the film chlorinator by using air as a carrier to perform a chlorination reaction; stopping the
aeration of the
chlorine gas, and withdrawing and reclaiming
chlorinated solvent, when the reaction is completed; adding a ring closure
solvent and dropping a ring closed agent into the film chlorinator, and adding a pH
regulator into the film chlorinator at a temperature of between 20 and 25 DEG C to regulate the pH value to between 4 and 6; keeping on stirring, feeding, centrifugalizing the materials, washing the materials with
solvent, and
drying to produce the product. The whole process is performed at normal temperature, thereby avoiding a harsh condition of deep cooling below 40 DEG C below zero, and facilitating the industrial operation. The method reduces the investment of a deep cooling unit, reduces the equipment investment, reduces
electrical load, reduces the production cost of the product, and improves market competitiveness.