Non-Solvolytic Reactions

For micelle-assisted bimolecular non-solvolytic reactions it is necessary to consider both medium and proximity effects. 

Micellar rate enhancements of bimolecular, non-solvolytic reactions are due largely to increased reactant concentrations at the micellar surface, and micelles should favor third- over second-order reactions. The benzidine rearrangement typically proceeds through a two-proton transition state (Shine, 1967 Banthorpe, 1979). The first step is a reversible pre-equilibrium and in the second step proton transfer may be concerted with N—N bond breaking (17) (Bunton and Rubin, 1976 Shine et al., 1982). Electron-donating substituents permit incursion of a one-proton mechanism, probably involving a pre-equilibrium step. 

This is a useful and informative situation, and solvolytic experiments of this kind have a particular value if an absolute value for the second-order rate constant, ki, for the reaction of the trap with the intermediate is known. In that case, an absolute value of the first-order rate constant, k2, for the conversion of the intermediate into the solvent-derived product maybe obtained, and hence an estimate of its lifetime under the reaction conditions. Measurements yielding values less than the vibrational limit (1.7 x 10 13 s at 25°C) indicate clearly that I has no real lifetime and hence is not a viable intermediate, and an alternative mechanism is required. For non-solvolytic reactions in a solution where the forward reaction of the reactive intermediate (other than with T) is bimolecular/second order, its lifetime will be diffusion controlled and the limit is likely to be closer to 10 10 s (though dependent upon the concentration of its co-reactant). 

Codeine phosphate in a paracetamol-codeine effervescent tablet was found to react at room temperature with the citric acid constituents to form citrate esters of codeine. The esterification was confirmed in a solid-state reaction at an elevated temperature. Tartaric acid also yielded an ester with codeine phosphate in a similar non-solvolytic reaction. 

The advantage of using solvent activity coefficients in a discussion of the transition state for non-solvolytic reactions in mixed solvent media, is that the solvent activity coefficient is a function of state of the system and can be used to infer transition state properties without cognisance of, or concern for, the structure or detailed identity of the solvation sphere. If on the other hand the mechanism of a bimolecular reaction is clearly defined on other grounds, then the solvent activity coefficients should lead to understanding of the solvent reorganisation upon activation. At this stage very few results have been accumulated in binary solvent mixtures. ... 

In contrast, the non-fusible coal requires the solvation (extraction) or solvolytic reaction to be liquefied. The solvation of non-polar organic compounds including the pitch may be rather limitted, so that the solvolytic reaction is necessary for the high liquefaction yield between the coal and the solvent. 

In order to fit solvolytic reactions into the above framework it is important to establish the magnitude of nucleophilic solvent assistance, the extent to which nucleophilic attack by solvent assists heterolytic cleavage of the bond to the leaving group. 2-Adamantyl tosylate [6] was selected as a model for SN 1 behaviour because non-bonded interactions [7] would reduce the possibility of nucleophilic attack (Fry et al., 1970a) extensive experimental evidence... 

Non-additivity of substituent effects has been proposed as a criterion for the operation of the RSR so the linearity argues against its applicability in this system. In a description of transition states by structure-reactivity coefficients (Jencks and Jencks, 1977), two alternative types of behaviour were discussed. In Hammond -type reactions the more endothermic reactions have later transition states, whereas anti-Hammond behaviour is characterized by an adjustment of the transition-state structure to take advantage of favourable substituent effects. These results illustrate that different systems can display quite different behaviour in linear free energy correlations. Thus, in alkene protonations, such correlations cover vast ranges in reactivity with only modest changes in sensitivities, while in solvolytic reactions the selectivity p varies depending on the electron supply at the electron-deficient centre (Johnson, 1978). 

In summary, the limited data available permit no clear-cut decision between the SnI mechanism with charge separation in the transition state, and the SnT mechanism with tight ion-pair intermediates. The fact that ally lie ester isomerizations almost certainly involve ionic intermediates under solvolytic conditions (see below) suggests that the reactions under non-solvolytic conditions probably also occur by an ionic mechanism,... 

Flammability and Combustion of Polymeric Compositions Reactivity of Polymer Solutions Analytical Calorimetry Ions and Ion Pairs in Non-Solvolytic Organic Reactions Fibers of Thermally Resistant Organic Polymers Chemistry of Polyurethanes Water Vapor Transport in Polymers... 

Solvolytic experiments specifically designed to test Bartell s theory were carried out by Karabatsos et al. (1967), who were primarily interested in an assessment of the relative contributions of hyperconjugation and non-bonded interactions to secondary kinetic isotope effects. Model calculations of the (steric) isotope effect in the reaction 2- 3 were performed, as well as that in the solvolyses of acetyl chloride... 

The present authors studied the solvolytic liquefaction process ( ,7) from chemical viewpoints on the solvents and the coals in previous paper ( 5). The basic idea of this process is that coals can be liquefied under atmospheric pressure when a suitable solvent of high boiling point assures the ability of coal extraction or solvolytic reactivity. The solvent may be hopefully derived from the petroleum asphaltene because of its effective utilization. Fig. 1 of a previous paper (8) may indicate an essential nature of this process. The liquefaction activity of a solvent was revealed to depend not only on its dissolving ability but also on its reactivity for the liquefying reaction according to the nature of the coal. Fusible coals were liquefied at high yield by the aid of aromatic solvents. However, coals which are non-fusible at liquefaction temperature are scarcely... 

These aquation reactions follow the same general mechanism as for non-cyclic amines, even though the rates can be many orders of magnitude less.35 The rate expression can show acid independent (solvolytic) and/or acid dependent pathways. For secondary amine/imine macrocycles with less than 16 members, reactions with Ni2+ are usually first order in [H+] (cleavage of first M—N bond rate-determining), while for Cu2+ they are second order in [H+] (cleavage of second... 

This chapter deals with silyl-substituted carbocations. In Section II results of quantum chemical ab initio calculations of energies and structures of silyl-substituted carbocations are summarized1. Throughout the whole chapter results of ab initio calculations which relate directly to the experimental observation of silyl-substituted carbocations and their reactions are reviewed. Section m reports on gas phase studies and Section IV on solvolytic investigations of reactions which involve silyl-substituted carbocation intermediates and transition states. Section V summarizes the structure elucidation studies on stable silyl-substituted carbocations. It includes ultra-fast optical spectroscopic methods for the detection of transient intermediates in solution, NMR spectroscopic investigations of silyl-substituted carbocations in superacids and non-nucleophilic solvents, concomitant computational studies of model cation and X-ray crystallography of some silyl-substituted carbocations which can be prepared as crystals of salts. 

There have been a very large number of investigations of carbocationic reactions of cyclobutyl, cyclopropylcarbinyl and allylcarbinyl derivatives under so-called stable-ion as well as solvolytic conditions. Bartlett (1965) has stated Among nonclassical ions the ratio of conceptual difficulty to molecular weight reaches a maximum with the cyclopropylcarbinyl-cyclobutyl system . The term nonclassical was first used by Roberts and Mazur (1951) to describe the nature of tricyclobutonium ion [32] suggested to be involved in reactions of cyclopropylcarbinyl derivatives. Later Roberts and coworkers (Mazur et al., 1959) favoured a set of rapidly equilibrating nonclassical bicyclo-butonium ions [34] instead of a single non-classical species. Essentially all experimental evidence on indicates that the species is a nonclassical... 

Sensitivity precludes the use of concentrated acid nitrating mixtures. Reaction of furan, or substituted furans" with acetyl nitrate produces non-aromatic adducts, in which progress to a substimtion product has been interrupted by nucleophilic addition of acetate to the cationic intermediate, usually at C-5. Aroma-tisation, by loss of acetic acid, to give the nitro-substitution product, will take place under solvolytic conditions, but is better effected by treatment with a weak base, like pyridine. " Further nitration of 2-nitrofuran gives 2,5-dinitrofuran as the main product. ... 

---