Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

Rates of hydrolysis, k_H⁺, of methyl 2-chloro-2,3,3,3-tetrafluoro-(III), 2,3-dichloro-2,3,3-trifluoro-(IV), 2,2,3-trichloro-3,3-difluoro-(V), 2,3,3,3-tetrafluoro-(VI) and 3-chloro-2,3,3-trifluoropropanoate (VII) were measured in 0.5M-HCl in aqueous methanol (80% vol; 76% wt) at 40, 50 and 60 °C. The relative rate constants, k_rel (50 °C), (for the propanoate III, k_H⁺ = 4.3 . 10^-5 l mol^-1 s^-1; k_rel = 100) are 311, 100, 38, 9.4, 44 and 15 for the esters II, III, IV, V, VI and VII, respectively (experimental error ±9%). It was found that k_rel = αβ where α and β are the following factors for groups in the position 2 and 3: CClF 10, CHF 4.2, CCl₂ 2.8, CF₃ 10 and CClF₂ 3.6. The rate constants obey the isokinetic relationship. For the ester III the dependence of log k_obs on logarithm of hydrogen chloride concentration is linear at concentrations 0.08-2.4 mol l^-1 which, together with high activation entropy ΔS^≠ for the esters III-VII (-167 to -217 J mol^-1 K^-1), shows that the hydrolysis proceeds by an A_AC2 mechanism.