Kinetics of aminolysis of 2,4-dinitrophenyl acetate

757-760The second order rate constants for the reaction of 2,4-dinitrophenyl acetate with aniline and p- and o-substituted anilines have been reported in 10% acetonitrile-90% water (v/v) mixture at 25°, 30°, 35° and 40°C. In the reaction of p-substituted anilines, electron-releasing groups facilitate the reaction while electron-withdrawing groups retard it. The ρ-value is evaluated to be - 2.33 ± 0.16. The Bronsted plot is also linear with βN = 0.792 ± 0.027 at 30°C. The S≠ values are all negative as expected for bimolecular nucleophilic substitution reactions. In the case of o-substituted anilines, the rate data have been analysed in terms of electronic and steric effects

Kinetics of reaction of 2,4-dinitrophenyl acetate with 3- and 4-substituted Pyridines and 4’-susbstituted 4-styrylpyridines

852-855Second order rate constants have been de ermined for the reaction of 2,4-dinitrophenyl acetate with 3- and 4-substituted pyridines and 4'-substituted 4’-styrylpyridines in acetonitrile-water (50%, v/v) mixture at 25°, 30°, 35° and 40°C. Activation parameters have been evaluated. Electron-releasing substituents increase the rate while electron-withdraw in substituents retard it. In both the reaction series linear free energy relationship is found to exist between the logarithms of rate constants and σ constants with ρ = -3.39 ± 0.38 (r = 0.989; s = 0.163;  n= 12 for 3- and 4-substituted pyridines and ρ = -0.390 ± 0.080 (r = 0.984; s = 0.028; n = 8) for 4'-substituted 4-styrylpyridines at 30°C. The ratio of effectiveness of transmission of substituent effect in styryl system relative to pyridine system in this reaction is 0.115. The Bronsted plot obtained is linear and βN is found to be 0.692 ± 0.056 (r = 0.990; s= 0.146; n = 16) indicating the extensive bond formation between pyridine and the reaction centre in the transition state

Kinetics of reaction of <i>para</i>-substituted β-nitrostyrenes and β -methyl- β-nitrostyrenes with <i>n</i>-butylamine

609-613The kinetics of addition of n-butylamine to β nitrostyrene and β -methyl- β-nitrostyrene and their para- substitutedderivatives in acetonitrile at four different temperatures have been followed spectrophotometrically. The order in [substrate] is unity and in [n-butylarnine] it is non-integral. On the basis of the observed kinetic data, a stepwise mechanism involving the formation of zwitterionic addition complex in an equilibrium step followed by conversion into the reaction product via proton transfer in catalytic route by the amine has been proposed. The study of effect of substituents in these reactions shows that the electron-withdrawing substituents accelerate the reaction and electron releasing substituents retard it. Good Hammett correlations have been observed in both the reaction series

Structure-reactivity correlations in the reaction of substituted N-methyl- 2-styrylpyridinium iodides with alkaline hydrogen peroxide

666-669The kinetics of reaction between N-methyl-2-styrylpyridinium iodides and alkaline hydrogen peroxide have been studied spectrophotometrically in 1:1 (v/v) water-methanol mixture. The reaction is first order in [substrate], [H2O2] and [OH-]. Structure-reactivity study with various 2'- and 4'-substituted N-methyl-2-styrylpyridinium iodides shows that the reaction is accelerated by electron-withdrawing substituents and retarded by electron-releasing substituents. A Hammett &rho;-value of +0.916 &plusmn; 0.064 (r = 0.988; s = 0.063) is obtained. A suitable mechanism involving the attack of hydroperoxide ion on the &beta;-carbon atom of the substrate to form epoxide in a slow step followed by cleavage of epoxide is proposed. Analysis of ortha-effects using multiparameter extensions of the Hammett equation in the reaction of 2'-substituted-N-methyl-2-styrylpyridinium iodides with alkaline hydrogen peroxide shows that both localised and delocalised effects are important and the steric effect is insignificant

Kinetics of addition of <i>n</i>-butylamine to 4'-substituted N-methyl2-styrylpyridinium iodides

417-419The kinetics of addition of n-butylamine to 4'-substituted N-methyl-2-styrylpyridinium iodides in acetonitrile have been followed spectrophotometrlcally. The reaction is first order with respect to the substrate and the order in n-butylamine is non-integral. A mechanism involving the formation of the zwitterionic addition complex in the first equilibrium step with subsequent proton transfer in a slow step is proposed. Structure-reactivity study with various 4'-substituents shows that the rate of proton transfer is accelerated by electron-releasing substituents and retarded by electron-withdrawing substituents

Non-linear structure-reactivity correlation in the addition reaction of <i>n- </i> butylamine to <i>para-</i> substitutedethyl <i>α</i>-cyanocinnamates

401-407The study of kinetics of addition of n-butylamine to a number of para- substitutedethyl a-cyanocinnamates in acetonitrile reveals that the reaction is first order in the substrate and the order In nucleophile varies with the nature of the para-substituent. The analysis of the rate data of the various para- substituted ethyl α-cyanocinnamates in terms of the Hammett equation gives a non-linear concavedown type of curve. A stepwise mechanism involving the formation of zwitterionic addition complex in an equilibrium step followed by conversion into the reaction product via a proton transfer In two routes, viz., non-catalytic and by amine catalysed, has been proposed. The non-linear structure-reactivity correlation has been accounted for by the change in rate-controlling step

Kinetic study of charge transfer interaction of substituted pyridines and substituted 4-styrylpyridines with <em>p-</em>bromanil

402-405Kinetics of charge transfer interaction of various 3- and 4-substituted pyridines and 4' –substituted 4-styrylpyridines with p-bromanil has been studied spectrophotometrically in carbon tetrachloride at three different temperatures and thermodynamic parameters have been evaluated. The reaction between pyridine and p-bromanil follows second order kinetics, first order in each reactant. Electron-releasing substituents in pyridine ring increase the rate of the charge-transfer interaction while electron- withdrawing substituents retard it. Good Hammett correlations have been observed in both the reaction series. The ratio of effectiveness of transmission of substitutent effect in styrylpyridine system relative to pyridine system in this reaction is computed to be 0.167

Photochemistry of squaraine dyes. 5. Aggregation of bis(2,4-dihydroxyphenyl)squaraine and bis(2,4,6-trihydroxyphenyl)squaraine and their photodissociation in acetonitrile solutions

The equilibrium constants and thermodynamic parameters for aggregate formation of bis(2,4-dihydroxyphenyl)- squaraine and bis(2,4,6-trihydroxyphenyl)squaraine have been studied by absorption spectroscopy. The values of the equilibrium constant, K, for the dimerization of SQ1 and SQ2 in acetonitrile at 300 K are (3.1 &#177; 0.3) &#215; 105 M-1 and (2.2 &#177; 0.1) &#215; 105 M-1, respectively. Iodine enhances the aggregation process. This has been attributed to the formation of charge-transfer complexes between iodine and the dyes and the stronger tendency of these complexes to form aggregates. Excitation of the squaraine dimer with a 532-nm laser pulse leads to the formation of the excited singlet state of monomeric dye as the excited dimer dissociates within the laser pulse duration of 18 ps