Preparation of alkali metal and alkaline earth metal salts of L-ascorbic acid-2-monophosphate of formula (I) comprises reacting L-ascorbic acid-2-polyphosphate compounds (II) with an alkali or alkaline earth metal salt of L-ascorbic acid (III) in the presence of an alkaline earth metal hydroxide in concentrated aqueous solution. The amount of (III) and base is chosen to give a pH of 8-11. The reaction involves a step-wise transfer of each phosphate group (-P(=O)(O<->M<+>)-O-) from (II) to (III). M<+> = an alkali metal ion or an equivalent of an alkaline earth ion; n = 2 or more.
