Thiolates of arsenic(III), antimony(III), and bismuth(III) with dl-α-dihydrolipoic acid

Abstract

Lipoic acid can be reduced to dihydrolipoic acid free of lipoic acid without using deoxygenated solvents. Dihydrolipoic acid reacted with phenylarsine oxide, As2O3, and AsCl3, SbCl3 but not Sb2O3, and Bi2O3, BiCl3, and Bi(NO3)3·5H2O in various solvents giving thiolates. When the reactions were done in methanol, the HCl and HNO3 released caused esterification of the –COOH group. The reaction with As(III) compounds was sensitive to dioxygen, leading to production of lipoic acid derivatives as well, arsenite being particularly active for the autoxidation. Physical (1H NMR) and chemical [reactivity of >M–Cl and >Bi(NO3)] properties of the adducts are described. The six-membered dihydrolipoic acid complexes reacted with stoichiometric amounts of British Anti-Lewisite releasing the dihydrolipoic acid by forming the corresponding complexes of British Anti-Lewisite.