Showing papers on "Elementary reaction published in 1969"

A flash photolysis study of intermediates in photochemical reactions of chlorophyll

Abstract: — The photochemical reactions of chlorophyll intermediates in vitro have been studied by the flash photolysis method. The flash excitation of pigment solutions has been shown to involve the population of a chlorophyll triplet state where the oxidation-reduction processes occur. The mechanism and kinetics of pigment triplet decay have been investigated from 20°to — 50°C and the ability of chlorophyll molecules to carry out triplet-triplet energy transfer has been established. The latter phenomenon has been used to show up the role of chlorophyll triplets in the reversible photooxidation reaction with P-quinone. There have been studied initial products of pigment photoreduction with ascorbic acid and phenylhydrazine. Experimental data of the mechanism of the initial oxidation and reduction in chlorophyll photosensitized reactions have been analysed. There have been also obtained the differential spectra of chlorophyll triplets and radicals. A calculation has been made of rate constants for a few elementary reactions.

Kinetics of Multidentate Ligand Substitution Reactions. VI. The Substitution Reaction of Diethylenetriaminepentaacetic Acid with the Nitrilotriacetato Nickelate(II) Chelate

Abstract: The kinetics of the substitution reaction of diethylenetriaminepentaacetic acid (DTPA) with the nitrilotriacetato nickelate(II) chelate have been studied polarographically in both acid and alkaline media. The reaction was found to be first-order with respect to DTPA and also first-order with respect to the nitrilotriacetato nickelate(II) chelate with 1-to-1 composition. In an acid solution the reaction proceeds mainly through tervalent and quadrivalent DTPA anions. On the other hand, in an alkaline solution the reaction proceeds through quadrivalent and quin-quevalent DTPA anions. The heat of activation and the entropy of activation for the three elementary reactions were estimated, and the effect of the protonation of the quinquevalent DTPA anion on the reaction rate was discussed.

Elementary Reactions of Metal Alkyl in Anionic Polymerizations. V. Reaction of Di-n-butylzinc and Tri-n-butylaluminum witna α, β-Unsaturated Ketones

Abstract: The reactions of n-Bu2Zn and n-Bu3Al with α,β-unsaturated ketones were studied. The elementary reactions were found to be conjugate addition and hydrogen abstraction reactions. One n-butyl group of metal alkyl was consumed in the conjugate addition, in contrast to the hydrogen abstraction reaction, all n-butyl groups being consumed in the latter elementary reaction. Conjugate addition rate constants were calculated regarding the conjugate addition as a second-order reaction with metal alkyl. On the basis of the kinetic data, infrared spectra of the reaction system, and the relative reactivity of the homologous vinyl ketones (α-methyl-substituted > unsubstituted > β-methyl-substituted), a four-centred mechanism was presented for the conjugate addition reaction of the metal alkyl with α, β-unsaturated ketone.

The Effect of Acetate Ion on the Rate of the Reaction between Cobalt(II) and Manganese(II)-Ethylenediaminetetraacetate Complexes

Abstract: The kinetics of the substitution reactions of cobalt(II) ions and manganese(II)-ethylene-diaminetetraacetate complexes have been studied in acetate buffer solutions at 25°C and at ionic strength of 0.2. The reaction was treated as to proceed through both hydrated metal ions and monoacetato complexes. The rate constants for six elementary reaction paths, three of which involve hydrated cobalt(II) ions and the others, monoacetatocobalt(II) complexes, were determined. The values obtained indicate that all the reactions proceeding through monoacetatocobalt(II) complexes are about three times faster than the corresponding reactions proceeding through hydrated cobalt(II) ions.

Kinetics and mechanism of nucleophilic halogen exchange in furan derivatives

Abstract: Studies are made of the reaction of 5-bromofurfurylidenaniline with aromatic amines (reaction 1), of the disproportionation of 5-bromofurfurylidenaniline (reaction 2), and of the reaction of 5-bromofurfurylidenaniline and 5-bromofurfural with saturated secondary amines (reaction 3). It is shown that these reactions are of the autocatalytic type (the catalyst being a reaction product, the hydrobromide of the amine), that addition of acid accelerates them, while they are retarded by addition of alkali. The hypothesis is advanced that in these reactions the active form of the substrate is the salt containing the fragment . The latter arises by protonation of the Schiff's base (reactions 1 and 2), or by quaternization of aminoacetals (which are products formed by addition of a secondary amine across the (double) bonds in through the action of the hydrohalide salt of the amine (reaction 3).

Graphical Evaluation of the Rate Constants of the Elementary Reactions in the Acrolein Polymerization with the Potassium Persulfate-Silver Nitrate Redox System

Abstract: A quantitative study was made of the redox-polymerization of acrolein initiated by the potassium persulfate-silver nitrate system. The reaction mechanism of this polymerization was proposed on the basis of the results of the time-conversion, time-molecular weight curves, and also on the basis of the characteristic features of this polymerization, reported in a previous paper. The rate constants of the elementary reactions in this polymerization were estimated by a graphical method. In the early stage, neither the termination nor the transfer reaction is very remarkable as the initiation reaction, but in the later stage the termination reaction by a recombination of the polymer radical and the transfer reaction increase with the reaction time, as does the initiation reaction also.