M. Ya. Botnikov

Effect of pressure on the bromination of ring-substituted toluenes by N-bromosuccinimide

1. Study has been made of the effect of pressures ranging up to 6000 kgf/cm2 on the bromination of ring-substituted toluenes by N-bromosuccinimide. Increase of pressure increases the rate of benzyl H atom detachment by Br atoms, the effect being most pronounced in systems in which the bromination rate at atmospheric pressure is low. 2. A linear correlation has been established (for the first time) between the substituent a constant and the difference in the activation volume effects (ΔVR≠-ΔVT≠) in the substituted and unsubstituted toluenes. It is clear that this difference in volume effects does not arise from solvation processes. 3. The Hammett equation applies to the bromination of substituted toluenes by N-bromosuccinimide at all pressures, theρ value for any such reaction falling off sharply as the pressure rises.

Bromination of hydrocarbons by N-bromosuccinimide at high pressures

1. The competing bromination of a number of hydrocarbons using N-bromosuceinimide at high pressures made it possible to establish that in reactions of the type Br + RH → Br ... H ... R → BrH + R the rule is retained, according to which the reactions that proceed most easily are accelerated most strongly by pressure. 2. The obtained rule is explained if we start with the concept of a variable elongation of the bonds in the formation of the transition state.

Electrochemical adamantylation of carbonyl derivatives of thiophene

Conclusions1.The fundamental possibility of the electrochemical adamantylation of carboxy (carbonyl) derivatives of thiophene in a nonaqueous medium was demonstrated.2.The selectivity of the cathode coupling of carboxy (carbonyl) derivatives of thiophene with adamantyl bromide is determined by the distribution of the spin density in the electrochemically generated anion radical.

Influence of the pressure on the rate constants of the elementary stages of the homolytic decomposition of organic compounds

Summary1.An equation describing the influence of the pressure on the rate constant of liquid-phase homolytic bond-cleavage reactions has been obtained.2.A difference in the values of (∂ΔV≠/∂p)p=0/ΔV0≠ in addition and homolytic bond cleavage reactions and in diffusional processes has been found which is explained by the different contribution of the free volume to the volume effect of activation (ΔV0≠). In addition reactions and reactions involving the radical detachment of a hydrogen atom the values of (∂ΔV≠/∂p)p=0/ΔV0≠ are close to one another, and the contributions of the free volume to ΔV0≠ are approximately the same.3.An equation has been proposed for describing the influence of the pressure on the viscosity of liquids. It has been shown that a linear relationship of free energies with a change in the pressure is inapplicable for this process.

Homolytic addition of aliphatic alcohols to tetrachloroethylene in the liquid phase

ConclusionsAs the result of a radical reaction between tetrachloroethylene and aliphatic alcohols in liquid phase, not only products of the substitution of hydrogen at theα-C atom of the alcohol for the trichlorovinyl group, but also isomers with a trichlorovinyl group at other C atoms, preferably in theω-1 position, are formed.

Effect of high pressure on rearrangement of organosilicon peroxides

The thermal rearrangement of organosilicon peroxides to alkoxysiloxanes proceeds with a substantial decrease in the volume activation effect.

Effect of high pressure on “cage” reactions of radicals during decomposition of azobisisobutyronitrile

1. The efficiency of initiation during the decomposition of azobisisobutyronitrile in toluene is practically independent of the temperature and decreases noticeably with pressure. 2. The reaction rate of the cyanoisopropyl radicals in the toluene “cage” decreases with the pressure, which indicates the diffusion character of this reaction.

Bromination of p-methoxytoluene by N-bromosuccinimide at atmospheric pressure and above

1. Study has shown that the reaction between p-methoxytoluene and N-bromosuccinimide leads not only to benzyl bromination but also to ring bromination, the latter process becoming more significant as the pressure rises. 2. The mechanism of bromination of p-methoxysuccinimide is quite different from the mechanism of bromination of the other substituted toluene, and relative rate constants for benzyl bromination calculated from equations based on the latter are not tenable here.

Effect of high pressure on radical isomerization of 2-isopropyl-1,3-dioxolane

1. Pressure decreases the rate of forming ethyl isobutyrate during the homolytic liquid-phase isomerization of 2-isopropyl-1,3-dioxolane. 2. The volume effect for the activation of the decomposition of di-tert-butyl peroxide to 2-isopropyl-1,3-dioxolane at 130° is characterized by a substantial value (11 cm3/mole).

Chlorination of certain monoalkylbenzenes with tert-butyl hypochlorite at high pressures

1. In the reaction of radical-chain chlorination of alkylaromatic compounds (cumene, ethylbenzene) by tert-butyl hypochlorite, with increasing pressure the content of theα-isomer, formed in a larger amount than theβ-isomer at atmospheric pressure, increases. 2. In the competitive chlorination of alkyl aromatic compounds by tert-butyl hypochlorite, the ratio of the monochlorosubstituted compounds formed is determined chiefly by the reaction of stripping of hydrogen atoms by the chlorine atoms present in theπ-complex with the aromatic ring. 3. The accelerating effect of pressure in the stripping of hydrogen atoms is greater, the higher the rate constant of the reaction. 4. When chlorination is conducted in the presence of trichloroethylene, the mechanism of the process is changed, which was noted according to the change in the ratio of the chlorination products at atmospheric pressure and according to the decrease in the influence of the pressure on the composition of monochloro-substituted compounds.