Abstract: Process for the synthesis of a cyclic diester of an alpha-hydroxyacid, comprising the following steps: an alkalino-earth salt of the corresponding alpha-hydroxyacid is mixed with said alpha-hydroxyacid and water; the mixture is treated by evaporation-crystallization, so that a hydrate of the alkalino-earth salt of the linear dimer of the corresponding alpha-hydroxyacid precipitates; the hydrated salt is dehydrated to give the corresponding anhydrous salt; and the anhydrous salt is pyrolyzed, releasing the cyclic diester of the corresponding alpha-hydroxyacid and leaving the alkalino-earth hydroxide as solid residue.

Abstract: Process for the synthesis of a cyclic diester of an alpha-hydroxyacid, comprising the following steps: an alkalino-earth salt of the corresponding alpha-hydroxyacid is mixed with said alpha-hydroxyacid and water; the mixture is treated by evaporation-crystallization, so that a hydrate of the alkalino-earth salt of the linear dimer of the corresponding alpha-hydroxyacid precipitates; the hydrated salt is dehydrated to give the corresponding anhydrous salt; and the anhydrous salt is pyrolyzed, releasing the cyclic diester of the corresponding alpha-hydroxyacid and leaving the alkalino-earth hydroxide as solid residue.

Abstract: Process for manufacturing a cyclic diester of an ?-hydroxy acid comprising the following steps: a substantially anhydrous salt of a divalent metal and of an ?-hydroxy acid is mixed with a strong acid, the pKa of which is less than that of the ?-hydroxy acid and the salt of which with the divalent metal is hygroscopic; and the mixture is left to react for a sufficient time in order to obtain the cyclic diester dispersed in the hygroscopic salt.