Etherifying Agents

Cellulose in the form of cotton linters, wood pulp or regenerated cellulose is used as the raw material for the commercial production of cellulose ethers. The advantage which linters possess over wood pulp in the manufacture of cellulose esters is not so apparent in the case of the ethers. 

The usual etherifying agents are the alkyl chlorides or sulfates. The advantage, usually found in organic reactions, of using the alkyl iodides and bromides because of their greater reactivity as compared to the chlorides is overshadowed by their much slower diffusion rate, lower solubility in the alkali and greater rate of saponification. The sulfates are relatively costly. Alkyl sulfites have also been proposed  

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The hydroxyl groups of the cellulose appear to be somewhat acidic. While studies of the composition of alkali cellulose and adsorption of sodium hydroxide have not clearly proved the presence of any sodium compound in alkali cellulose, the reactions of alkali cellulose with carbon disulfide and with etherifying agents would seem to justify the assumption that such an intermediate exists or that the hydroxyl hydrogen at least ionizes. This view is strengthened by the fact that the rate of etherification is proportional to a high power of the concentration of alkali.19... 

TBA and isobutene have been compared as the etherifying agent at 60 °C. The initial molar ratio of isobutene to glycerol was 4.0 with Amberlyst A35 as the catalyst. The conversion of glycerol is lower when etherified with TBA than when etherified with isobutene. More hydrocarbons are formed with isobutene than with TBA. But, with TBA, mainly monoethers are formed and valuable triethers are formed only in small amounts. In addition, TBA dehydrates to water, which has an inhibition effect on ion-exchange resin catalysts [23],... 

The hexitols form the typical derivatives of alcohols and glycols— esters, ethers, acetals and ketals, and metallic complexes. Because of the multiplicity of reactive groups and because of stereoisomerism, the number of theoretically possible derivatives of a given type is enormous. For example, D-mannitol on reacting with a mono reagent such as an etherifying agent or an acid, can form 35 different compounds ... 

In contrast to esterification, etherification is carried out in an alkaline medium and the etherifying agents are alkyl halides. The general reaction is termed aliphatic nucleophilic substitution and, employed under normal conditions, is of the bimolecular type. 

Fully alkylated starches are insoluble in water but are soluble in many polar nonaqueous and nonpolar solvents. Starch alkylated to a lower extent retains its water solubility but is also soluble in alcohols and chloroform. The solutions have a micellar character.741 Decrease in the softening points of alkyl starch ethers as the length of the alkyl chains increased is observed.706 The solubility of etherified starches depends also on which etherifying agent is applied. 

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