Molar Refractivity and Connectivity Index Correlations for Henry's Law Virial Coefficients of Odorous Sulfur Compounds on Carbon and for Gas-Chromatographic Retention Indices

Abstract

Gas–solid chromatography was used to obtain values of the second gas–solid virial coefficient, B2s, in the temperature range from 392 to 511 K for 10 volatile, malodorous organic sulfur compounds; ethanethiol, 1-propanethiol, methyl sulfide, 2-propanethiol, 1-methyl-1-propanethiol, 2-methyl-1-propanethiol, 2-methyl-2-propanethiol, ethyl sulfide, ethyl methyl sulfide, and tert-butyl methyl sulfide. Carbopack C (Supelco Inc.), a graphitized carbon black powder, was used as the adsorbent. Beginning with a theoretical equation for the second gas–solid virial coefficient, it was shown how a quantitative structure–retention relation (QSRR) could be developed to correlate ln B2s and hence chromatographic retention times with calculated molar refractivity and connectivity index values for the thiols and thioethers. It was found that both the gas–solid interaction energies and the ln B2s values could be correlated with calculated adsorbate molar refractivity (r2=0.951) and (r2=0.961), respectively. Connectivity index and molar refractivity together provide a r2=0.989 correlation of the ten ln B2s values at 403 K. A set of 373 organic compounds with retention indices taken from the literature was used to further test our approach. The 373 molecules were divided into 10 structural subgroups and molar refractivities and connectivity indices were calculated and used to correlate their retention index values. An overall correlation of r2=0.982 for the retention indices of the 373 molecules was found.