PURPOSE: To easily obtain a high purity ascorbic acid deriv. that is an alternative application form of vitamin C at a low cost in a high yield by esterifying ascorbic acid with a carboxylic acid halide in the presence of a specified amide.

CONSTITUTION: When ascorbic acid is esterified with an aliphatic 2-20C carboxylic acid halide, the objective ascorbic acid deriv. is obtd. by carrying out the esterification in the presence of an N,Ndialkyl-alkanecarboxylic acid amide of formula I, a cyclic amide of formula II, a tetraalkyl carbamide of formula III, a cyclic carbamide of formula IV (where R1 is a 1-5C alkyl; each of R2-R10 is methyl or ethyl; 3≤m≤5: 2≤n≤4) or a phosphoric acid triamide of formula V (where R11 is methyl or ethyl and two R11' s may form piperidino in combination with N to which they bond).