Correlation of the Rate of Solvolysis of 2-Chloro-thioacetophenones

Abstract

According to the recent results of Kevill et al. 1-3 from kinetic data for solvolyses, they reported that the introduction of S-atom adjacent to a reaction center caused a partial shift away from the addition-elimination (AdE) through dual reaction channel (DC) to the ionization channel (IC) for solvolysis of acid chloride [ie: PhOCOCl 1 (AdE) → PhSCOCl 1b,2 ≈ PhOCSCl 3 (DC) → PhSCSCl 3 (IC)]. And more recent results of Ryu et al. 4 the results of the rates of solvolysis of α-methylthioacetyl chloride (1) and phenylthioacetyl chloride (2) in more than 33 aqueous solvent system including 2,2,2-trifluoroethanol (TFE)-ethanol (EtOH) solvent can be explained by the same mechanism with the same structure of transition state (TS), controlled by the contribution from strong nucleophilic participation (third order reaction model for TFE-EtOH system) 5 by the molecule of solvent as well as weakly solvent polarity (ionization), regardless of the different neighboring groups containing an S-atom [even if these are far away the reaction center, (C=O)] Results and Discussion Accordingly, we have conducted the further research to investigate how S-methyl and S-phenyl groups influence the reaction center as well as the variation of reaction mechanism in solvolysis of 2-chloro-2-methylthioacetophenone (3) 6 and 2-chloro-2-phenylthioacetophenone (4) 7 (not acid chlorides), respectively at 25 o C and 50 o C, for more than 40 solvent mixtures containing hexafluoro-iso-propanol (HFIP)water system and TFE-EtOH system (kinetic data in Table 1 and 2), by using the same regression analysis such as those