Mixed cellulose ether and preparation thereof

Claim 1

A PROCESS FOR PREPARING A MIXED CARBOXY AND HYDROXY-LOWER ALKYL CELLULOSE ETHER COMPRISING FIRST INTRODUCING INTO CELLULOSE AT LEAST ABOUT 0.05 HYDROXYALKYL GROUP PER ANJYDROGLUCOSE UNIT BY REACTING CELLULOSE WITH A LOWER HYDROXYALKYLATING AGENT, AND SUBSEQUENTLY, WITHOUT SEPARATING THE HYDROXYALKYL CELLULOSE THUS FORMED FROM THE REACTIONS MIXTURE, INTRODUCING INTO SAID HYDROXYALKYL CELLULOSE AT LEAST ABOUT 0.05 CARBOXYALKYL GROUP PER ANHYDROGLUCOSE UNIT BY REACTING SAID HYDROXYALKYL CELLULOSE WITH A LOWER CARBOXYALKYLATING AGENT, THE TOTAL AMOUNT OF HYDROXYALKYL AND CARBOXYALKYL SUBSTITUENT GROUPS THUS INTRODUCED BEING AT LEAST ABOUT 0.5 PER ANHYDROGLUCOSE UNIT TO PRODUCE A WATERSOLUBLE CARBOXYALKYL HYDROXYALKYL CELLULOSE ETHER, THE ENTIRE PROCESS BEING CARRIED OUT IN THE PRES ENCE OF AT LEAST ONE ORGANIC SOLVENT OF THE GROUP CONSISTING OF THE 3- AND 4-CARBON ALIPHATIC ALCOHOLS, DIOXANE, TETRAHYDROFURAN AND THE DIETHYL ETHER OF ETHYLENE GLYCOL IN A QUANTITY SUFFICIENT TO MAINTAIN THE CELLULOSE ETHER IN A SOLID, UNDISSOLVED STATE THROUGHOUT THE PROCESS.