GB623607A - Preparation of cellulose ethers - Google Patents

Abstract

Cellulose is subjected to etherification in the presence of alkali and a viscosity-regulating agent selected from the group consisting of hydrogen peroxide, an alkali-metal hypobromite, hypochlorite, hypoiodite, peroxide and periodate. In an example, high viscosity cellulose is heated with ethyl chloride, sodium hydroxide, sodium hypochlorite and water, to 140 DEG C. over a period of 8 hours, followed by maintenance at 140 DEG C. for a further 8 hours. Volatile constituents are then removed by distillation under reduced pressure, so that the ethyl cellulose is precipitated from the remaining aqueous medium. The product dissolves in benzene-alcohol mixtures to give solutions of much lower viscosity than products prepared in a similar manner, but with omission of the hypochlorite. In another example, cellulose is heated with sodium hydroxide, sodium hypochlorite, monochloracetic acid, and water, to form a carboxymethyl cellulose of reduced viscosity characteristics. It is soluble in water. The proportion of hypochlorite or other viscosity-regulating agent is varied according to the desired reduction in viscosity, and it may be 0.01-0.25 moles. per glucose unit of the cellulose. The cellulose used may be cotton linters, wood-pulp, wood flour, or sawdust. The etherifying agent may be dimethyl or diethyl sulphate; methyl, ethyl, butyl, or benzyl chloride; ethylene chlorhydrin, ethylene oxide, or propylene oxide; or a halogenated lower fatty acid such as monochloracetic acid or its sodium salt. The alkali used may be sodium, potassium or lithium hydroxide, or a quaternary ammonium base. The etherification may be carried out at 25-200 DEG C. in the case of ethyl cellulose. For carboxymethyl cellulose the temperature may be 20-75 DEG C.