Generation and characterization of aliphatic selenothioic acid salts

The reaction of thioic acid O-methyl esters with in situ generated aluminum 2-(trimethylsilyl)ethylselenolate gave selenothioic acid Se-(2-trimethylsilyl)ethyl esters in 56–78% yields. The resulting four esters were treated with a THF solution of tetrabutylammonium fluoride (TBAF) to generate selenothioic acid ammonium salts in low to good yields. The efficiency of the generation of the salts depended on the substituents α to the selenocarbonyl group. Fluoride ion in TBAF partly worked as a base to deprotonate from the esters to generate ammonium enethiolates as by-products. Methylation of the acid salts with methyl iodide took place selectively at the selenium atom to give selenothioic acid Se-methyl esters in 48–68% yields. Instead of TBAF, Me4NF and KF/18-crown-6 were used to generate the salts with other counter cations. The spectroscopic properties of the esters and salts suggested that resonance structures involving carbon–selenium double bonds also contribute to the resonance hybrids of the salts.