Synthesis of Sulfonate and Phosphate Esters by PTC

The formation of both sulfonate esters and phosphate esters have been achieved under phase transfer conditions. Good yields of sulfonate esters were obtained when 3-hydroxy steroids (aromatic A ring) were reacted with dialkylaminosulfonyl chlorides in a two phase system consisting of benzene and aqueous base. A typical acylation using pyrrolidine sulfonyl chloride in the presence of catalytic benzyl-triethylammonium chloride is formulated in equation 6.12 [30]. 

Phenols have been phosphorylated under phase transfer conditions in the presence of a nucleophilic catalyst [31, 32]. The reaction of 4-nitrophenol with dimeth-oxythiophosphoryl chloride is ordinarily slow and leads to a mixture of the desired methyl parathion and hydrolysis products. Addition of N-methylimidazole enhanced the rate but the best results were obtained when both the imidazole and a quaternary ammonium salt (TBAB) were used at the same time. The co-catalysis was accounted for in terms of nucleophilic activation of the acylating agent by imidazole and solubilization of the phenoxide by ion pairing with the quaternary ion. The overall transformation is formulated in equation 6.13. 

Brandstrom, A. Preparative Ion Pair Extraction , pp. 109-111, 155-156. L emedel, Sweden Apotekarsocieteten/Hassle 1974. 

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