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The chloride-chloride exchange reaction in arenesulfonyl chlorides was investigated experimentally and theoretically by density functional theory (DFT) calculations. The second order rate constants and activation parameters of this identity reaction were determined for 22 variously substituted arenesulfonyl chlorides using radio-labeled Et4N36Cl. The chloride exchange rates of 11 sulfonyl chlorides bearing para-and meta-substituents (σ constants from −0.66 to +0.43) in the aromatic ring followed the Hammett equation with a ρ-value of +2.02. The mono- and di-ortho-alkyl substituted sulfonyl chlorides exhibit an enhanced reactivity although both inductive and steric effects lower the reaction rate. The DFT calculations of their structures together with X-ray data showed that an increased reactivity is mainly due to a peculiar, rigid, strongly compressed and sterically congested structure. The DFT studies of the title reaction revealed that it proceeds via a single transition state according to the SN2 mechanism. The analogous fluoride exchange reaction occurs according to the addition–elimination mechanism (A–E) and formation of a difluorosulfurandioxide intermediate. The reliability of the calculations performed was supported by the fact that the calculated relative rate constants and activation parameters correlate well with the experimental kinetic data.

The kinetics of the chlorine isotopic exchange reaction between tetraethylammonium ~hloride-3~Cl and 0,O-diarylphosphorochloridates ( p -RCsH40)2POC1 or 0,O-diarylphosphorochloridothionates (p-RCsH40)2PSCl has been studied in acetonitrile solution. Good Hammett's correlations of the rate constants with Taft's u" constants were obtained. The values of the reaction constants p were found identical for phosphoryl and thiophosphoryl compounds. In comparison with oxygen in the phosphoryl group, the sulfur atom exhibits an electron-donating effect (Ago N 0.80). No correlation has been found for the enthalpg and entropy of activation. The effect of the substituents aryloxy groups, oxygen, or sulfur atoms in the phosphoryl group on the kinetics of the sN2-P reaction is discussed. The reactivity of the investigated compounds is determined by the extent of the positive charge localized on the phosphorus atom. The positive charge is formed by the direct interactions of the substituents with the reaction center and the indirect-intramolecular interactions revealed in the structure of the compound.