POLYHYDRIC ALCOHOLS, FATS AND SOAPS

Polyhydric alcohols are compounds containing two or more hydroxyl groups in the molecule. The two most important are ethylene glycol HOCHjCHjOH (a dihydric alcohol) and glycerol HOCHjCH(OH)CH. OH (a trihydric alcohol). Ethylene glycol may be obtained by the hydrolysis of ethylene dibromide or ethylene dichloride with dilute aqueous sodium hydroxide or sodium carbonate solution  

BrCHisCHjBr + 2NaOH — HOCHjCHisOH + 2NaBr Industrially, it is produced directly from ethylene by the addition of hypo, chlorous acid, followed by treatment of the resulting ethylene chlorohydrin with sodium bicarbonate solution  

ClCHjCHjOH + NaHCOj — HOCHjCHjOH + COj + NaCl When ethylene chlorohydrin is heated with sodium hydroxide solution, the highly reactive cyclic ether, ethylene oxide, is formed  

Upon reaction with an alcohol in the presence of a catalyst, the monoalkyl ether of ethylene glycol is obtained  

The monoalkyl ethers with R = CHj, CjHj and C4H, , known respectively as methyl ceUoaolve, ceUosolve and hutyl cellosolve, are of great commercial value, particularly as solvents, since they combine the properties of alcohols and ethers and are miscible with water. Equally important compounds are the carbitols (monoalkyl ethers of diethyleneglycol) prepared by the action of ethylene oxide upon the monoethers of ethylene glycol  

Thus with R = CH3, C2H5 and C4H , the compounds are called methyl carbitol, carbitol and butyl carbitol respectively. None of these compounds can be conveniently prepared in the laboratory by elementary students they are, however, readily available commercially. The preparation of one glycol, pinacol or tetramethylene glycol from acetone, has already been described (Section 111,77). 

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