Extended Grunwald-Winstein equation

The extended (two-term) Grunwald-Winstein equation has been applied to the solvolyses of ethyl chloroformate (117) and ethyl chlorothioformate (118). For each substrate, there is evidence for two competing reaction channels. " Solvolysis... 

The specific rates of solvolysis of benzyl p-toluenesulfonate and nine benzylic-ring-substituted derivatives (324) have been satisfactorily correlated using Aij and Tots scales within the extended Grunwald-Winstein equation. The reactions of Z-phenylethyl X-benzenesulfonates (325) with Y-pyridines (326) in acetonitrile at 60 °C have been studied at high pressures. The results indicated that the mechanism of the reaction moves from a dissociative 5)vr2 to an early-type concerted 5)vr2 with increasing pressure. 

The application of correlation analysis of solvent effects to mechanistic studies of solvolysis has been reviewed by Takeuchi in Japanese.110 The article mainly covers die behaviour of tertiary chloro compounds. Tins author s research group has continued experimental studies in this area.111-113 Rates of solvolysis of 2-chloro-2,4-trimethylpentane have been measured in 17 solvents and analysed through the extended Grunwald-Winstein equation, which includes a term for nucleophilic participation.111... 

Contrary to earlier suggestions of an SnI pathway for solvolyses of A,A-dimethyl-sulfamoyl chloride (41), the results of an extended Grunwald-Winstein equation treatment of the specific rates of solvolysis of (41) in 32 solvents pointed to an Sn2 pathway. Results of a similar treatment of its rates of solvolysis in a range of solvents supported an SN2 pathway for 2-propanesulfonyl chloride (42).59... 

Application of the extended Grunwald-Winstein equation to solvolyses of propyl chloroformate, PrOCOCl, in a variety of pure and binary solvents indicated an addition-elimination pathway in the majority of the solvents but an ionization pathway in the solvents of highest ionizing power and lowest nucleophilicity. For methanolysis, a solvent deuterium isotope effect of 2.17 was compatible with the incorporation of general-base catalysis into the substitution process.21... 

In Eq. (7-17), k and are the speeifie rate eonstants of SnI solvolysis of the 5-methyl-dibenzothiophenium ion in a given solvent and in a standard solvent (Et0H/H20, 80 20 cL/L At = 0), respeetively. At values are known for 37 pure and binary solvents and span a range from At = -5.26 [(CF3)2CH0H/H20, 97 3 cg/g] to +0.37 (EtOH) [305, 308]. The At solvent nueleophilieity seale ean be used directly to correlate the solvolytic behaviour of other RX+ substrates with a neutral nueleofuge, and also in appHcations of the extended Grunwald-Winstein equation (7-15). Many examples of the use of Nj values in the correlation of specific rates of solvolysis of a variety of RX and RX" " substrates are given in reference [305]. 

The medium influence on the solvolyses of a variety of further substrates, i.e. benzylic [310-313], allylic and propargylic compounds [312], as well as very crowded tertiary haloalkanes [314], has been studied and analyzed in the framework of the extended Grunwald-Winstein equation (7-15). 

A detailed study of the specific rates of solvolysis of N,N,N, N -tetra-methyldiamidophosphorochloridate (80) (TMDAPC) with analysis in terms of the extended Grunwald-Winstein equation has been reported (Scheme 19). The stereochemistry of nucleophilic attack at tetracoordinate phosphorus was also discussed." The initial reaction of bis (2,4-dinitrophenyl) phosphate (BDNPP) (81) with hydroxylamine involves release of 1 mol 2,4-dinitrophen-oxide ion and formation of a phosphorylated hydroxylamine (82), which reacts readily with further NH2OH, giving the monoester (83). The intermediate (82) also breaks down by two other independent reactions one involves intramolecular displacement of aryloxide ion (83) and the other involves migration of the 2,4-dinitrophenyl group from O to N and formation of phosphorylated 2,4-dinitrophenylhydroxylamine (84) (Scheme 20)." ... 

Swain et al. (32) were the first (1955) to use an LFER to quantify solvent nucleophilicity. Their approach was to extend the Grunwald-Winstein equation to include a second term for solvent nucleophilicity. 

This conclusion was supported by Peterson and Waller s data (44) showing that acetic and formic acids reacted at about the same rate with the chlo-ronium ion (VI). Solvent nucleophilicity (N) could then be obtained by rearrangement of the extended Grunwald-Winstein equation (47) ... 

For situations where solvent nucleophilicity may be a factor, Kevill (8) favors the use of the extended Grunwald-Winstein equation (equation 1). Scales of NOTs and OTs values based upon the use of methyl tosylate and 2-adamantyl tosylate as model SN2- and SNl-reacting substrates have been developed (15, 16). Also Y scales have been developed for other anionic leaving groups using 1-adamantyl or 2-adamantyl derivatives (17-19), where Sn2 reaction is impossible or severely hindered. 

DFT studies of the hydrolysis of acetyl and chloroacetyl chloride and of variously substituted benzoyl chlorides supported an S 2 mechanism. An extended Grunwald-Winstein equation correlation for the specific rates of solvolysis of 3,4,5-trimethoxybenzoyl chloride gave sensitivities towards changes in solvent nucleophilic-ity (/-value) of 0.29 and solvent ionizing power (m-value) of 0.54. The low m-value allowed specific rates to be determined in highly ionizing fiuoroalcohol/H20 mixtures. A parallel correlation of the specific rates of solvolysis of 2,4,6-trichlorobenzoyl chloride revealed that solvolyses in 100% and 90% ethanol or methanol did not appreciably follow the ionization pathway indicated for solvolyses in the other solvents and it was proposed that, despite the two or//to-substituents, the addition-elimination pathway had become dominant. ... 

Rates of solvolysis of cinnamoyl chloride and its 4-chloro and 4-nitro derivatives were analysed using the simple and extended Grunwald-Winstein equations. Studies of solvent effects in the solvolysis of isopropenyl, isobutyl,and propargyl chloroformate " and of 1- and 2-naphthyl chloroformate were reported. 

The cr-substituent effects and solvent effects (extended Grunwald-Winstein equation) for solvolyses of / -X-substituted benzoyl chlorides (X = OMe, Me, H, and Cl) in 97% wt/wt hexafluoroisopropanol/water was explained by two competing pathways. Plots of log k versus a were consistent with a cationic path and explained by an 5 n2-5n1 spectrum of mechanism. Electron-donating groups favoured the reaction and values of p increased in the order AcOH < HCO2H < TEE < HFIP. A benzoyl cation intermediate was trapped in hexafluoroisopropanol. Ab initio calculations of heterolytic bond dissociation energies of various chloro- and fluoro-substituted and other benzoyl chlorides were correlated with log k for solvolyses... 

The extended Grunwald-Winstein equation has been applied to the 5 nI solvolyses of p- and o-bromomethylphenylacetic acids. Rates increase with solvent nucleophilicity and water content, for both substrates. Activation parameters are given. 

Solvolysis rate constants of 5-nitro-2-furoyl chloride in 27 different solvents were well correlated with the extended Grunwald-Winstein equation, with sensitivity values of 1.20 0.05 and 0.37 0.02 for I and m, respectively. These data, the range of values found for A// and AS, and the solvent kinetic isotope effect (SKIE, MeOH MeOD) of 2.65 were in accord with an 5 2 mechanism. ... 

The specific rates of solvolysis of the acid anhydride, acetyl p-toluenesulfonate (30) were measured by a rapid-response conductivity technique at temperatures in the range 263-218 K. For 13 solvents at 233.4 K, an extended Grunwald-Winstein equation correlation led to sensitivities to changes in solvent nucleophilicity of 0.65 and to changes in solvent ionizing power of 0.61. In 89.1 % acetone at 253 K, the comparison with acetyl bromide solvolysis led to a koj /k ratio of 1.4. In methanol and methanol-d at 233.4 K, the solvent deuterium isotope effect A MeOH MeOD was 0.99. These results are consistent with an 5 1 reaction with appreciable nucleophilic solvation or an 5 2 reaction with a loose TS. ... 

The specific rates of solvolysis of methyl chloroformate, MeOCOCl, are very well correlated by the extended Grunwald-Winstein equation over a wide range of solvents the pathway is believed to be predominantly addition-elimination, except that a positive deviation for solvolysis in 90% l,l,l,3,3,3-hexafiuoropropan-2-ol suggests an 80% contribution from an ionization mechanism. " ... 

The specific rates of solvolysis of phenyl chlorothionoformate (PhOCSCl) were found to be remarkably similar to those reported previously for phenyl chlorothioformate (PhSCOCl). When analysed using the extended Grunwald-Winstein equation over the usual range of solvent types, these solvolyses showed essentially identical divisions... 

The specific rates of solvolysis of benzenesulfonyl chloride and a series of 4-and 2,4,6-substituted derivatives (Scheme 25) have been very well correlated using the extended Grunwald-Winstein equation, with incorporation of A/r solvent nucle-ophilicity and Tq solvent ionizing power values. In two instances, it was shown that almost identical correlations were obtained after the incorporation of methyl groups into the 2- and 6-positions of the benzene ring. No evidence was found for a dissociative (5n1) mechanism or for a duality of mechanism. All of the results could be rationalised in terms of a concerted bimolecular displacement (5n2) mechanism, involving attack by solvent at sulfur. ... 

The solvolyses of p-methoxybenzyl chloride in 39 solvents are well correlated by an extended Grunwald-Winstein equation involving terms in Tci (solvent ionizing power), At (solvent nucleophilicity) and I (Kevill s aromatic ring parameter). A claim by Liu that nucleophilic participation is greater than in the solvolyses of the corresponding bromide is discussed and said to be disproved. 

The rate constants for the solvolysis of chloromethyl ethyl ether, chloromethyl octyl ether, and chloromethyl methyl sulfide have been determined in several pure and binary solvents. Application of the extended Grunwald-Winstein equation, logffe/fe, ) = /Nj + mY + c, gave appreciable T values (0.55-0.71) for the three substrates indicating that there is significant nucleophilic solvation of the developing carbenium ion in the transition states of these reactions. The kQ lkp = 1.2 x 10 found for the hydrolysis of chloromethyl methyl ether in water is virtually identical to that observed for the uni-molecular solvolyses of t-butyl chloride and trityl halides confirming the unimolecular mechanism for these reactions. 

Figure 11 Extended Grunwald-Winstein plot for the solvolysis of isopropyl tosylate , plot of the data against , improved plot when bilinear equation is...

---