Preparation of dimethyl and diethyl phthalate from phthalic anhydride

Claim 1

METHOD OF EFFECTING THE SUBSTANTIALLY COMPLETE CONVERSION OF THE ANHYDRIDE OF AN ACID SELECTED FROM THE GROUP CONSISTING OF PHTHALIC AND HYDROGENATED PHTHALIC ACIDS INTO A DIALKYL ESTER OF THE ACID, THE ALKYL GROUP CONTAINING UP TO TWO CARBON ATOMS, WHICH COMPRISES HEATING AN INITIAL MIXTURE OF THE ANHYDRIDE, THE CORRESPONDING MONO-ALKYL ESTER AND THE ALKANOL WITH AN ESTERIFICATION CATALYST TO A TEMPERATURE OF 90 TO 100* C., THE MONO-ESTER REPRESENTING 25 TO 35 MOLE PERCENT OF THE ANHYDRIDE AND THE QUANTITY OF THE ALKANOL BEING AT THE MOST SUFFICIENT TO CONVERT ALL THE ANHYDRIDE AND MONO-ESTER INTO DIESTER, CONTINUING THE HEATING UNTIL EQUILIBRIUM IS SUBSTANTIALLY ATTAINED, RAISING THE TEMPERATURE 10 TO 30* AND DISTILLING OFF WATER AND UNCHANGED ALKANOL, SLOWLY INTRODUCING INTO THE REACTION MIXTURE MAINTAINED AT THE HIGHER TEMPERATURE A FURTHER QUANTITY OF ALKANOL EQUAL AT THE MOST TO 50% OF THE QUANTITY IN THE INITIAL MIXTURE, WHILE DISTILLING OFF WATER TOGETHER WITH SOME OF THE ALKANOL TO LEAVE A PRODUCT COMPRISING THE DIESTER AND THE MONO-ESTER IN QUANTITIES SUBSTANTIALLY EQUIVALENT RESPECTIVELY TO THE ANHYDRIDE AND THE MONO-ESTER PRESENT IN THE INITIAL MIXTURE.