Dimethoxypropane, water scavenger

With aldehydes, primary alcohols readily form acetals, RCH(OR )2. Acetone also forms acetals (often called ketals), (CH2)2C(OR)2, in an exothermic reaction, but the equiUbrium concentration is small at ambient temperature. However, the methyl acetal of acetone, 2,2-dimethoxypropane [77-76-9] was once made commercially by reaction with methanol at low temperature for use as a gasoline additive (5). Isopropenyl methyl ether [116-11-OJ, useful as a hydroxyl blocking agent in urethane and epoxy polymer chemistry (6), is obtained in good yield by thermal pyrolysis of 2,2-dimethoxypropane. With other primary, secondary, and tertiary alcohols, the equiUbrium is progressively less favorable to the formation of ketals, in that order. However, acetals of acetone with other primary and secondary alcohols, and of other ketones, can be made from 2,2-dimethoxypropane by transacetalation procedures (7,8). Because they hydroly2e extensively, ketals of primary and especially secondary alcohols are effective water scavengers. 

Chemical methods are very effective for getting rid of water. Lorette and Brown [12] introduced 2,2-dimethoxypropane as a water scavenger. It reacts in acid solution to yield acetone ... 

Perhaps classical for the protection of 1,2- and 1,3-cis-diols is the isopropyl-idene (acetonide) function. This acid labile ketal may be formed by reaction of a ribonucleoside with acetone in the presence of an acid (HCl, p-toluene-sulfonic, H2SO4) and water scavenger (2,2-dimethoxypropane, ethyl orthoformate). Other similar protecting groups include the benzylidene and cyclohexylidene functions. 

The ability of 2,2-dimethoxypropane to act as a water scavenger has resulted in its use (in conjunction with acetone and an acid catalyst) in the protection of the 2, 3 -hydroxy groups of purine and pyrimidine nucleosides. Here again, the formation of acetone and methanol serves to drive the equilibrium towards the product. 

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