Defining a quantitative metric for sulfenamide–sulfur interaction in rubber compounds

A set of one hundred sulfenamide molecules, spanning commercially used vulcanization accelerators and hypothetical analogues, was examined through molecular modeling using the PM3 semiempirical method and AMBER force fields. The goal was to identify chemically meaningful descriptors capable of predicting their specific interaction with elemental sulfur. A multivariate regression model was developed using the hardness difference between each sulfenamide and sulfur as the response variable. The analysis identified S–N bond length (L ₂ ), electronic charge on sulfur in Bz–S–N (τ ₁ ), Bz–S–N bond angle (θ), dipole moment (μ), and electrophilicity index (ω) as the statistically dominant descriptors. Except for μ, which contributes positively, increases in all other parameters decrease Δη, thereby enhancing the predicted interaction with sulfur. The electrophilicity index (ω) appears as the sole quadratic term in a model devoid of interaction terms. An optimal Δη range was identified, encompassing hypothetical sulfenamides with predicted performance between CBS and DCBS. The model, however, requires further validation using more robust molecular modeling approaches, such as ab initio methods.