Dimethyl sulfate hydrolyzes slowly in cold water but rapidly in warm water and acidic solutions. The hydrolysis occurs stepwise, initially forming methyl sulfuric acid, then sulfuric acid and methanol. It can be calculated that DMS hydrolyzes to methyl sulfuric acid with 99.9% completion as follows:1
Complete conversion to sulfuric acid occurs at a much slower rate. Salts of methyl sulfuric acid are formed when DMS is hydrolyzed in aqueous alkali (see Figure 4 ). Hydrolysis is rapid in aqueous ammonia. (Dilute ammonia solutions [less than 5%] are commonly used to neutralize spills and residues. Caution is necessary. Do not use concentrated aqueous ammonia. This can react with DMS with explosive violence.2 Dry soda ash [Na2CO3 ] or dilute [less than 10%] caustic soda solution may also be used for neutralizing spills.
Dimethyl sulfate is a strong methylating agent that reacts with active hydrogen and alkali metal salts to form substituted oxygen, nitrogen, and sulfur compounds. Usually, DMS releases only one methyl group to the reactant. Higher temperatures and concentrations are required for the second methyl group to react. Typical reactions include the preparation of tetramethyl glucosides from glucose, anisole (C6H5OCH3 ) from phenol, N-methyl-p-aminophenol from p-aminophenol, and caffeine (1,3,7-trimethylxanthine) from theobromine (3,7-dimethylxanthine). Tertiary amines and DMS form quaternary ammonium compounds (see "Uses & Applications").
1 The Hydrolysis of Dimethyl Sulfate and Diethyl Sulfate in Water. R.E. Robertson and S.E. Sugamon, Canadian Journal of Chemistry, Vol. 44 (1966) pp 1728–1730.
2 P. Claesson and C.F. Lundvall, Ber. 13, 1700 (1880); H. Lindlar, Angew. Chem. 75, 297 (1963) and Angew. Chem. Int’l Ed. in Eng. 2, 262 (1963).