Alkylation by dialkyl sulfates

Alcohols and phenols can be alkylated by use of alkyl sulfates (contrast the use of alkyl halides in many other cases). Particular importance attaches to the preparation of methyl ethers by means of dimethyl sulfate.683 

Phenols are generally etherified by Ullmann s method,684-686 reaction occurring in two stages  

Dimethyl sulfate is highly poisonous. Work with it should always be in a fume cupboard, and all glass vessels should be rinsed with methanohc ammonia after use. 

For etherification of alkali-sensitive substances such as polyphenols it is advisable to treat the derived acetate with dimethyl sulfate and alkali (if necessary, with addition of acetone), which achieves simultaneous hydrolysis 

Alkali-sensitive compounds can be methylated by adding the alkali solution to the stirred mixture of dimethyl sulfate and the substance to be alkylated, taking care that each portion is rapidly consumed.690 Another procedure for alkylation of alkali-sensitive compounds is to add the dimethyl sulfate and ca. 30% sodium hydroxide solution from two separate dropping funnels to a vigorously stirred solution of the hydroxy compound in water, in such a way that the mixture never becomes acid or strongly alkaline. 

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Benzoselenadiazole (1) is alkylated by dialkyl sulfates and dialkyl 2,4-dinitrobenzene sulfonates to give 1-alkyl 2,1,3-benzoselenadiazolium salts <89SC1381>. 2,1,3-Benzoselenadiazole (1) reacts with I2, KI and HCl in CHCI3 to give the quasi-polymeric structure (9) <85ZAAC(523)33> (see Section 4.21.3.1). 

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