Effect of pressure on the rates of hydrolysis of allyl chlorides

Abstract

The pressure dependence of the rates of hydrolysis of allyl chloride and a-, P-, and I-methyl ally] chlorides has been examined. The significance of the activation volumes, AV*, and their pressure dependence, dAV4/dP, is discussed. These activation parameters indicate an SN2 mechanism for allyl and 13-methyl allyl chloride and an SN1 or intermediate character mechanism for the other methyl substituted allyl chlorides investigated. The results are compared with the corresponding AHY and ACp* measurements of Robertson and co-workers. The temperature dependence of the activation volunie, dA VY/dT, for the solvolysis of the parent ailyl chloride has been measured and found to be small and negative.

Solvation Effects on Alternative Nucleophilic Substitution Reaction Paths for Chloride/Allyl Chloride and γ-Methylated Congeners

“…There are some limited experimental data with which to compare the present calculations. The bulk of the experimental data available for allyl chloride has been interpreted to suggest that it reacts primarily via the S N 2 mechanism in most organic solvents. ,,, This is consistent with our calculations; a very large dielectric constant, like that for water, is required to bring the free energy of activation for the S N 1 process below that for the S N 2. We note that Brubacher et al studied the hydrolysis of allyl chloride in water in 1968, and reported a 298 K Δ G ⧧ of 25.5 ± 2 kcal mol -1 for this process.…”

“…In the majority of nonaqueous solvents, experimental studies have been interpreted to indicate that crotyl chloride also seems to prefer the S N 2 pathway, ,, consistent with the CCl 4 predictions in Table (as an example of a nonpolar medium) and Figure . In aqueous solvents, however, it has been variously reported that crotyl chloride hydrolyses can be S N 2, , S N 1, , or a mixture of both. , The predictions in Table suggest, however, that the S N 1 pathway should strongly dominate over the S N 2 for crotyl chloride in water. Brubacher et al .…”

“…Though there have been no prior computational studies on the effects of solvation on the preferred pathways for nucleophilic substitution of chloride/allyl chloride and its methylated congeners, there have been many experiments performed on these or analogous systems in a range of solvents to assess the mechanism(s) of reaction. ,− The general consensus from the full scope of experiments is that allyl chloride reacts via S N 2 substitution, ,,, isoprenyl chloride reacts via S N 1 substitution, − , and crotyl chloride may react by both S N 1 and S N 2 pathways, ,,,,,,− although the S N 2' pathway can be forced with appropriate steric bias. ,, Sneen et al proposed a particularly detailed ion-pair mechanism to rationalize the mixed S N 1/S N 2 results observed for the crotyl system. ,− …”

“…57,[67][68][69][70][71][72][73][74] Though there have been no prior computational studies on the effects of solvation on the preferred pathways for nucleophilic substitution of chloride/allyl chloride and its methylated congeners, there have been many experiments performed on these or analogous systems in a range of solvents to assess the mechanism(s) of reaction. 2, [75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94] The general consensus from the full scope of experiments is that allyl chloride reacts via S N 2 substitution, 83,85,87,88 isoprenyl chloride reacts via S N 1 substitution, [83][84][85]92 and crotyl chloride may react by both S N 1 and S N 2 pathways, 75,76,78,82,83,85,[87][88][89] although the S N 2' pathway can be forced with appropriate steric bias. 82,89,…”

The Temperature Dependence of Transition State Volumes in Hydrolysis Reactions

“…The hydrolysis of benzyl chloride (8), isopropyl bromide (I), and ally1 chloride (2) have been studied by previous workers and their ratelpressure data were used in the determinations of dVt/dTfor these compounds.…”