The reaction of p-nitrophenyl disulfide and auranofin, a gold(I) drug used to treat rheumatoid arthritis, has been carried out in solvents of varying dielectric constant. This reaction can be monitored by UV-vis spectroscopy since it results in formation of p-nitrophenylthiolate bound to gold(I), which gives rise to an intensely yellow solution. The data shows that the rate in DMSO, a solvent with a high dielectric constant, is more than 25 times faster than in the low dielectric solvent THF. Non-metal mediated thiol-disulfide exchange reactions show the reverse dependency on solvent dielectric, i.e. the reaction occurs faster in a low-dielectric medium than in water. The implications for medicinal activity of auranofin will be presented.