Reaction of 2,6-dinitroanisole with cyclohexylamine in toluene–octanol binary solvents. Further support for the ‘dimer nucleophile mechanism’ in aromatic nucleophilic substitution

Abstract

The reaction of 2,6-dinitroanisole with cyclohexylamine in toluene, octanol and toluene-octanol mixtures has been studied at several amine concentrations. The reactions in toluene and in octanoltoluene mixtures up to 30% octanol show a third-order kinetic dependence on [amine]. Although the reaction rates in toluene and octanol are very similar, addition of small amounts of octanol to the toluene solution diminishes the rate of reaction, reaching a minimum value at 30-50% octanol, after which the rate increases almost linearly w i t h the octanol content. These and other results, here described, are satisfactorily explained b y the previously proposed 'dimer nucleophile mechanism'. Previously reported similar observations in methanol-benzene mixtures were criticised as being due to the reversibility of the reaction. The present results confirm the previously reported mechanism and the irreversibility of the reaction under the reaction conditions. Paper 2103755F

S N Ar Reactions of Amines in Aprotic Solvents

“…In the reactions of 2,6-DNA with cyclohexylamine [B] D 0.264 M in toluene and in octanol at 35, 45 and 60°C, it was observed that at 35°C the reaction is slightly faster in toluene than in octanol, whereas at 45 and 60°C the inverse is observed 177 . These results show, once more, the difficulties of studying related reaction rates at a single temperature.…”

“…Although this argument could be refuted by the observation of the 'dimer nucleophile' in other systems 10 , it was of interest to examine the effect of addition of a hydrogenbond donor(HBD) co-solvent different from methanol, to the reaction of a substrate where the nucleofuge is methoxide, such as the reaction of 2,6-DNA with cyclohexylamine in toluene octanol binary mixtures 177 . As regards octanol: (a) it would not compete with the product (methanol) in case of a reversible reaction; (b) its dipolarity Ł D 0.37 is between that of toluene and methanol 178 ; (c) its hydrogen-bond donor ability (˛D 0.30 179 is greater than that of toluene or cyclohexylamine (˛D 0 for both) but smaller than that of methanol (˛D 0.69 179 .…”

“…A very low enthalpy of activation is observed for the reactions in toluene consistently with the operation of the 'dimer' nucleophile mechanism. The reaction in octanol shows a higher enthalpy of activation and also a slightly higher entropy of activation 177 .…”

“…Overall second-order rate coefficients over cyclohexylamine (CHA) concentration, k A /[B], for the reaction of 2,6-dinitroanisole with cyclohexylamine in:°, toluene; and , 5; Ł, 20; , 30; x, 100% octanol toluene binary solvents, as a function of [B]177 …”

Kinetic studies on the aminolysis of someO-aryl oximes in benzene

“…These reactions generally show second [1][2][3][4][5] and third order [6][7][8][9][10][11][12] dependence on amine in dipolar and nonpolar solvents, respectively. Further in nonpolar solvents these reactions exhibit an inverse temperature effect [13][14][15][16].…”