Extent of Nucleophilic Participation in the Solvolyses of Alkyl Chloromethyl Ethers and Sulfides

Abstract

The specific rates of solvolysis have been determined for chloromethyl ethyl ether (3) and chloromethyl octyl ether (4) at -10.0 °C and for chloromethyl methyl sulfide (5) at 25.0 °C in a variety of pure and binary solvents. These values were used for a correlation analysis treatment using the extended Grunwald-Winstein equation incorporating literature values for solvent nucleophilicity (N T ) and solvent ionising power (Y Cl ). Appreciable values were found for the sensitivities towards changes in both N T and Y Cl values. Using a literature specific rate of hydrolysis at 25.0 °C for fluoromethyl methyl ether (2), the required value for chloromethyl methyl ether (1) was obtained from use of N T and Y Cl values and the sensitivities for 3 to changes in their values, to adjust an experimental specific rate value for 1 in 100% ethanol to the corresponding value in 100% water. In this way, an estimated k Cl /k F of 1.2 x 10 5 was obtained, essentially identical to values for the solvolyses of tert-butyl halides. A unimolecular mechanism for the solvolyses, with appreciable nucleophilic solvation of the developing carbocation, is proposed. Electronic supplementary information provides, for several solvents, specific rates of solvolysis for 3, 4, and 5 at additional temperatures and the calculated activation parameters.

Extent of Nucleophilic Participation in the Solvolyses of an Aryl Chloromethyl Ether, α,p-Dichloroanisole

“…1), has been discussed previously. 27 For the correlation of the 24 remaining solvents, the l value of 0.68 and m value of 0.59 were very similar to the corresponding values of 0.71 and 0.62 for the chloromethyl ethyl ether, 12 suggesting that the extents of nucleophilic and electrophilic assistance varied little on changing the oxygenbonded group accompanying the chloromethyl group in the ether from alkyl to aryl. Indeed the l/m ratios, a measure of the balance between the two effects, were identical at 1.15 and the l/m ratio remains at this value when all 28 solvents are considered for the solvolysis of 1 ( Table 3).…”

“…12 This observation suggests that the transition-state structures are very similar for both aryl and alkyl chloromethyl ether solvolyses. The m values are only a little lower than those for the corresponding sulfides, with values of 0.67 for both chloromethyl phenyl sulfide and its p-chloro derivative 11 and 0.71 for chloromethyl methyl sulfide 12 having been reported.…”

“…When the values for the α-chloroethers and α-chlorosulfides within this paper together with the preceding papers 11,12 are compared to each other (Table 3), a range of l/m values of from 0.33 to 1.15 (value from the present study at the high end) is obtained. The l/m values for sulfides of 0.33 to 0.79 can be seen to be lower than for ethers, 1.06 to 1.15, consistent with the lower degrees of nucleophilic assistance for solvolyses of sulfides shown by the respective l values.…”

“…E-mail: dkevill@niu.edu Previously, we have reported on corresponding studies of the solvolyses of (arylthio)methyl chlorides and derivatives 11 and of the solvolyses of alkyl chloromethyl ethers and sulfides. 12 The present report completes the matrix as regards correlation studies of the solvolyses of alkyl or aryl chloromethyl ethers or sulfides.…”

A comprehensive N+ scale of nucleophilicity in an equation including a Swain‐Scott response/selectivity parameter

“…6 ) were shown from both Swain‐Scott correlations and secondary deuterium kinetic isotope effects to involve ‘exploded’ S N 2 transition states, with small extents of bond formation between nucleophile and electrophile . Also, solvolyses of EtOCH 2 Cl have recently been shown to give a Grunwald‐Winstein l value of 0.7, compared with the defined value of 1.00 for methyl tosylate 7 , Z = Me) . Consequently, the implication from Eqn ( that reactions of 6 ( s E = 0.59) are more sensitive than 7 , Z = NO 2 ( s E = 0.30) to changes in nucleophilicity emphasises the unreliability of Eqn .…”