Phase-transfer catalysis has been used for substitution reactions using sodium phenyl sulfinate to produce phenyl sulfones. We show such a substitution in the course “Industrial Phase-Transfer Catalysis” published in Synthesis in 1987 that cites that the high yield uses PTC and replaced DMSO and DMF for this reaction.
The reaction shown in the diagram could be improved in at least two ways.
The first improvement would be to choose a better solvent. The inventors chose to use acetonitrile. While acetonitrile promotes the reaction, it is not a good solvent for workup. In fact, workup included water washes and extraction into ethyl acetate. Most PTC systems use water-immiscible solvents, especially for nucleophilic substitutions that liberate NaCl since the byproduct salt and excess starting material salt can be washed away from the product into water. It is usually best to use a nonpolar water-immiscible solvent in combination with a phase-transfer catalyst to transfer the phenyl sulfinate into the organic phase and activate its nucleophilicity. As long as the product is soluble in toluene (which we expect this product to be), then water washing would likely easily remove the NaCl, excess phenyl sulfinate and even the tetrabutylammonium chloride (TBAC) phase-transfer catalyst. Instead, the TBAC remained with the product at the end of the reaction and required further unit operations including recrystallization followed by chromatography.
A second improvement for this process would be to use TBAB (bromide) instead of TBAC. TBAB supplies the bromide ion that would co-catalyze the reaction by forming a small amount of allyl bromide in-situ from the allyl chloride starting material. Considering that the inventors post-reacted for 2 days, they could have benefitted from the extra push of the bromide co-catalyst. In addition TBAB is less expensive than TBAC for reasons we explained elsewhere on our PTC website.
Other process improvements can be suggested, but these two are a good start.
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