Sodium salt of 1-menthyloxycarbonyl 1-hydroxy methanesulphonic acid, its preparation process and its use for obtaining L(-)menthyl glyoxylate

Preparation process for the product of formula (I), ##STR4## wherein an aqueous solution of glyoxylic acid is reacted, at a temperature higher than or equal to 50.degree. C., in an acid medium, with an excess of the corresponding menthol with elimination by azeotropic distillation of the water present and formed with a C.sub.6 -C.sub.10 hydrocarbon, then the reaction medium, cooled down and diluted with water, is decanted, then the organic phase is treated at a pH of about 5 with an excess of a sulphurous acid derivative of sodium metabisulphite or sodium hydrogensulphite in order to obtain a corresponding product of formula (I).