SODIUM ATOM AS AN INTERMEDIATE IN THE RADIOLYSIS OF CONCENTRATED ALKALINE METHANOLIC SOLUTIONS

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Solvent effects on the photochemistry of dimethyl sulfoxide-Cl complexes studied by combined pulse radiolysis and laser flash photolysis

Photolysis of complexes of dimethyl sulfoxide (DMSO) with chlorine atoms results in rapid and permanent photobleaching which may be due to intramolecular hydrogen abstraction. The effects of solvent polarity were examined in a wide variety of DMSO–carbon tetrachloride mixed solvents. The quantum yields of photobleaching decreased from 0.27 to 0.08 as the solvent polarity increased, while significant changes were observed in the low DMSO concentration range (<0.2 mol dm−3). This cannot be accounted for by simple solvent polarity effects. The effects of polar and nonpolar additives were also examined and it is concluded that the specific solvation effect of DMSO was the main cause of the significant change in quantum yields in the low concentration range of DMSO

Reaction of CS2/Cl complexes with alcohols studied by pulse radiolysis

The reactivity and selectivity of carbon disulfide-chlorine atom complex (CS2/Cl) for hydrogen atom abstraction from various alcohols were studied by pulse radiolysis technique in carbon tetrachloride at room temperature. The measured absolute rate constants were in the range from 4.0×106 for methanol to 3.5×107 dm3 mol−1 s−1 for cyclopentanol. The hydrogen abstraction selectivity was calculated based on the analysis of partial reactivities. The tertiary/primary selectivities were determined to be 8.2 for α-position and 6.8 for β-position of alcohols

Pulse radiolysis studies of the reactions of bromine atoms and dimethyl sulfoxide-bromine atom complexes with alcohols

Dimethylsulfoxide (DMSO)–Br complexes were generated by pulse radiolysis of DMSO/bromomethane mixtures and the formation mechanism and spectral characteristics of the formed complexes were investigated in detail. The rate constant for the reaction of bromine atoms with DMSO and the extinction coefficient of the complex were obtained to be 4.6×109 M−1 s−1 and 6300 M−1 cm−1 at the absorption maximum of 430 nm. Rate constants for the reaction of bromine atoms with a series of alcohols were determined in CBrCl3 solutions applying a competitive kinetic method using the DMSO–Br complex as the reference system. The obtained rate constants were 108 M−1 s−1, one or two orders larger than those reported for highly polar solvents. Rate constants of DMSO–Br complexes with alcohols were determined to be 107 M−1 s−1. A comparison of the reactivities of Br atoms and DMSO–Br complexes with those of chlorine atoms and chlorine atom complexes which are ascribed to hydrogen abstracting reactants strongly indicates that hydrogen abstraction from alcohols is not the rate determining step in the case of Br atoms and DMSO–Br complexes

Photochemistry of CS2/Cl complexes-combined pulse radiolysis-laser flash photolysis studies

Complexes of chlorine atoms and carbon disulfide (CS2) were produced by pulse radiolysis of CS2 in halocarbons and photochemical reactions were studied by laser flash photolysis. Excitation of CS2/Cl complexes resulted in rapid and permanent photobleaching. The photobleaching of CS2/Cl complexes is due to intermolecular chlorine atom abstraction in CCl4 with a quantum yield of 0.04, while that ascribed to hydrogen atom abstraction in 1,2-dichloroethane has a quantum yield of 0.21. The effects of additives are discussed based on the bond dissociation energy