Kinetics of proton and deuteron transfer reactions of 4-nitrophenylnitromethane with triethylamine and tri-n-butylamine in acetonitrile solvent

Abstract

The second-order rate constants for the proton and deuteron transfer reactions between 4-nitrophenylnitromethane and the organic bases triethylamine and tri-n-butylaniine have been determined at eight different temperatures between 0 and 35"C, using the stopped-flow technique. The four reactions are characterized by low enthalpies of activation and large negative entropies of activation. The isotope effects give values for (AD: -AH$) of 1.02 and 0.74 kcal mol-' and (AS," -AS;) of 1.2 and 0.9 cal mol-l K-l for triethylamine and tri-n-butylamine respectively. The rate ratios are small for primary deuterium effects ; k ~/ k ~ for Et3N at 0°C is 3.56 and for n-Bu3N at 0°C is 2.41. These reaction constants are used to elucidate the type of energy barrier involved in the reaction and the nature of the transition state.The reaction of 4-nitrophenylnitromethane with the strong organic bases triethylamine and tri-n-butylamine in acetonitrile gives a reddish-brown solution. Proton magnetic resonance and visible-spectroscopic measurements indicate that this reaction is a reversible proton transfer whose product is a coloured ion-pair : 1-NO2C6H4CH,No2 + R3N=[NO2C6H4CHNO,]-HNR3.

Kinetics, isotope effects of the reaction of 1-(4-nitrophenyl)-1-nitroalkanes with DBU in tetrahydrofuran and chlorobenzene solvents

“…We found that this bimole-'~u t h o r to whom correspondence may be addressed. cular proton transfer reaction gave a dissociated product in MeCN to a large extent, contrary to earlier reports (2)(3)(4)(5). Therefore the applicability of the Benesi-Hildebrand method (6) has been carefully discussed, to explain why it gave incorrect results in previous papers, published by different authors ( 1 ) .…”

“…4.0]undec-7-ene (DBU) has already been examined in acetonitrile (MeCN) solvent (1). We found that this bimole-'~u t h o r to whom correspondence may be addressed.…”

Influence of steric hindrance in molecules of substituted 2-phenyl-1,1,3,3-tetramethylguanidines on the kinetics and isotope effects of their proton transfer reactions with 4-nitrophenylnitromethane in acetonitrile solvent

“…The reaction of 4-nitrophenylnitromethane with three phenyl substituted derivatives of 2-phenyl-l , 1,3,3-tetramethylguanidine: 2- (4'-chloropheny1)-1,1,3,3-tetramethylguanidine, (1 The equilibrium measurements gave a linear plot of a/A (a, the initial concentration of acid; A , the equilibrium absorbance of the reaction mixture) with l l b (b, initial concentration of base), a relation expected for products existing in the form of ion pairs (29). The relation of a/A against A l b , expected to be linear when the product is in the form of separate ions (29), shows a distinct upward curvature so that the form of product is certain and in agreement with previous measurements (1,29).…”

“…The relation of a/A against A l b , expected to be linear when the product is in the form of separate ions (29), shows a distinct upward curvature so that the form of product is certain and in agreement with previous measurements (1,29). A molecular extinction coefficient of the order of The value of the molecular extinction coefficient, about 2 x lo4 dm3 mol-' cm-', is in good agreement with values found in previous measurements for reactions with 4-NPNM as an acid (1).…”

“…29. Values of the absorbance for solutions of 4-NPNM and base, with known initial concentration, were determined.…”