Vibrational analysis of alkyl xanthates

Rotational isomers are indicated in the Raman spectra of sodium ethyl and other xanthates. Vibrational bands useful for characterizing xanthate solids and aqueous solutions are given. Vibrational analyses are reported for sodium ethyl xanthate, trans and gauche forms, and the methyl and isopropyl analogs using a Cartesian coordinate force field derived from ab initio molecular orbital calculations.     

Studies on the HPLC determination of xanthates via copper(I) xanthates and dixanthogens

Summary Two HPLC methods for the determination of individual alkyl xanthates in mixtures are described. They are based on the formation of copper xanthate complexes and the oxidation of xanthates to dixanthogens, respectively. The reversed-phase chromatographic behaviour of both types of compounds together with the optimization of separation and determination conditions are discussed in detail. It is shown by several determinations of synthetic and practical flotation samples that the two methods provide an identical reliability for the analysis of xanthates and could complement each other. The detection limits (301 resp. 240 nm) are as low as 3.1 · 10^–8 mol/l (metal xanthate complexes) and 1.6 · 10^–8 mol/1 (dixanthogens). The methods described are suitable for flotation, chemical industry and environmental analysis.

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Untersuchungen zur HPLC-Bestimmung von Xanthaten über Kupfer(I)-xanthate und Dixanthogene

     

Solvent extraction of metal xanthates

The solvent extraction of metal xanthates is reviewed with emphasis on the characteristics and analytical uses of ethyl xanthate complexes. Elements reviewed include As, Sb, Bi, Cd, Co, Cu. Cr, Ga, Au, In, Fe, Pb, Mn, Hg, Mo, Ni, Pd, Pt, Re, Ag, Se, Te, Tc, Tl, Sn, U, V and Zn.     

beta-Nitro xanthates as olefin precursors

[reaction: see text] Potassium O-ethyl xanthate readily adds to alpha,beta-unsaturated nitro compounds to give stable beta-nitro xanthates, which undergo tin-free elimination to form olefins in good yield and good E selectivity upon simple heating with lauroyl peroxide in refluxing 1,2-dichloroethane.     

Anionic polymerization of vinyl monomers with xanthates

The polymerization of vinyl monomers with various xanthates (potassium tert-butylxanthate, potassium benzylxanthate, zinc n-butylxanthate, etc.) were carried out at 0°C in dimethylformamide. N-Phenylmaleimide, acrylonitrile, methyl vinyl ketone, and methyl methacrylate were found to undergo polymerization with potassium tert-butylxanthate; however, styrene, methyl acrylate, and acrylamide were not polymerized with this xanthate. In the anionic polymerization of methyl vinyl ketone with potassium tert-butylxanthate, the rate of the polymerization was found to be proportional to the catalyst concentration and to the square of the monomer concentration. The activation energy of methyl vinyl ketone polymerization was 2.9 kcal/mole. In the polymerization, the order of monomer reactivity was as follows: N-phenylmaleimide > methyl vinyl ketone > acrylonitrile > methyl methacrylate. The initiation ability of xanthates increased with increasing basicity of the alkoxide group and with decreasing electronegativity of the metal ion in the series, lithium, sodium, and potassium tert-butylxanthate. The relative effects of the aprotic polar solvents on the reactivity of potassium tert-butylxanthate was also determined as follows: diethylene glycol dimethyl ether > dimethylsulfoxide > hexamethylphosphoramide > dimethylformamide > tetrahydrofuran (for methyl vinyl ketone); dimethyl sulfoxide > hexamethylphosphoramide > dimethylformamide ? diethylene glycol dimethyl ether (for acrylonitrile).     

Thermal studies on palladium alkyl xanthates

Eleven palladium(II) alkylxanthates: Pd(ROCSS)₂ [RMe, Et, nPr, iPr, nBu, iBu, tBu, nAm, iAm, nHex and cyclohex], have been prepared and their thermal properties investigated by thermogravimetric analysis. The complexes, although volatile under vacuum (10^?2 mm Hg), decompose without volatilization at normal atmospheric pressure leaving a residue of palladium metal at 950°C. The intermediate decomposition products were identified mass spectrometrically and a thermal decomposition mechanism is proposed.     

计算光化学

本文从光化学的最基本概念入手,简要介绍了计算光化学理论方法的发展历程和典型应用,并对不同时期的工作做简要评述,以期读者对整个计算光化学有一个整体的了解。本文还介绍了计算机硬件的发展对计算光化学的影响。最后指出目前计算光化学研究的困难和存在问题以供同行讨论。     

Photochemistry of bromofluorobenzenes

The photochemistry of low lying excited states of six different fluorinated bromobenzenes has been investigated by means of femtosecond laser spectroscopy and high level ab initio CASSCF/CASPT2 quantum chemical calculations. The objective of the work was to investigate how and to what extent light substituents, position on the benzene ring and number, would influence the dissociation mechanism of bromobenzene. In general, the actual position of a fluorine atom affects the dissociation rate to a less extent than the number of fluorine atoms. A clear connection between a lowering of a repulsive pisigma relative to a bound pipi state and the number of fluorine substituents exists, and the previously suggested model of coupling between dissociation rate and relative location of bound and repulsive state still holds for these molecules. A more elaborate examination of the electronic structure of the excited states in bromobenzenes than previously reported is presented.     

Photochemistry of o-fluoranil

Initial exploration of the photochemical behavior of o-fluoranil has revealed dimer formation, cycloaddition to alkenes, and hydrogen abstraction from hydrocarbons, aldehydes, and ethers.     

Photochemistry of dicyanopyridines

The photochemistry of a variety of dicyanopyridines (2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-dicyanopyridine) in solution at room temperature was investigated. Pulsed UV (308 nm) laser irradiation in deoxygenated acetonitrile yields the triplet state with lifetimes between 4 and 10 μs and absorption bands in the 400 and 320 nm regions. In the presence of added HCl an air-insensitive transient (τ ≈ 10–12 μs, λ_max ≈ 360–380 nm) was observed, suggesting the formation of a protonated excited state.

Irradiation in the presence of amines resulted in the production of the pyridyl radical anion (τ ≈ 40–80 μs, air sensitive, λ_max ≈ 360–380 nm) formed by electron transfer from the amine to the pyridine triplet excited state. Stern-Volmer analysis gave electron transfer rate constants in the range (1–8) × 10⁻⁸ M⁻¹ s⁻¹.

In methanol solvent, irradiation yielded an air-insensitive transient assigned as the neutral pyridyl radical (τ ≈ 30–200 μs, λ_max ≈ 370–385 nm). The formation of these transients is discussed in the context of previous photochemical electron spin resonance and product studies.