THE PHOTOSENSITIZED OXIDATION OF SULPHIDES

Abstract— The rates of photosensitized oxidation of a number of sulphides were determined under standard conditions in 1, 1, 2,2-tetrachloroethane and in methanol. It was found that the ratio of the rates of reaction in the two solvents was not constant for different sulphides and that t -butyl sulphide does not react in methanol. It is inferred that the presence of an H atom in the α position is essential for reaction in polar solvents and an appropriate mechanism is suggested. The results indicate that reaction in chlorinated solvents may take place by a different mechanism which possibly involves H-abstraction by triplet sensitizer.     

Quenching of fluorescence of solutions of polystyrene and copolymers with methyl methacrylate

Quenching of excimer fluorescence from polystyrene and monomer emission from 5 and 10% methyl methacrylate copolymer with styrene has been studied in solution using dibromoethane and iodine as quenching species. From the measured rate constants along with polarization measurement of the emissions, it is concluded that energy migration does not occur in dilute solution of polystyrene. It is proposed that excimer is formed by rotation of a pendant, excited phenyl group with a face-to-face conformation with its nearest neighbour.     

Additions of enantiopure alpha-sulfinyl carbanions to (S)-N-sulfinimines: asymmetric synthesis of beta-amino sulfoxides and beta-alphamino alcohols

The addition of the lithium anions derived from (R)- and (S)-methyl and -ethyl p-tolyl sulfoxides to (S)-N-benzylidene-p-toluenesulfinamide provides an easy access route to enantiomerically pure beta-(N-sulfinyl)amino sulfoxides. Stereoselectivity can be achieved when the configurations at the sulfur atoms of the two reagents are opposite (matched pair), thus resulting in only one diastereoisomer, even for the case in which two new chiral centers are created. The N-sulfinyl group primarily controls the configuration of the carbon bonded to the nitrogen, whereas the configuration of the alpha-sulfinyl carbanion seems to be responsible for the level of asymmetric induction, as well as for the configuration of the new stereogenic C-SO carbon in the reactions with ethyl p-tolyl sulfoxides. An efficient method for transforming the obtained beta-(N-sulfinyl)amino sulfoxides into optically pure beta-amino alcohols, based on the stereoselective non-oxidative Pummerer reaction, is also reported.     

The photodegradation of poly(vinyl chloride)—V The effect of wavelength of irradiation on the dehydrochlorination reaction

For a purified sample of poly(vinyl chloride), it is found that radiation of wavelength less than 300 nm causes dehydrochlorination. It appears that polychromatic radiation yields a constant ratio of concentrations of polyenes, even from the very early stages of reaction. It is proposed that energy transfer is an important step in the photodecomposition of poly(vinyl chloride).     

The thermal decomposition of hydrocarbon copolymers-V Products and mechanism of decomposition of copolymers incorporating styrene

The products of the thermal decomposition of a series of copolymers of structure with n = 0, 1, 3, 4 and 5, have been investigated. A high proportion of the products consists of low molecular weight analogues of the parent polymers, with styrene the major constituent of the volatile liquids. The copolymers are more stable than head-to-tail polystyrene. Some general conclusions are drawn on the overall mechanism of breakdown.     

(Z)-3-p-tolylsulfinylacrylonitrile as a chiral dienophile: diels-alder reactions with furan and acyclic dienes

The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles.     

Structures of neat and hydrated 1-octanol from computer simulations

Molecular dynamics computer simulations of 1-octanol and its mixtures with water have been performed. The liquid is composed of regions enriched in either hydrocarbons or hydroxyl groups. In neat octanol, the hydroxyl groups form clusters of long, thin chains. Upon the addition of water, the clusters become longer and more spherical, forming a structure that can be described as consisting of "overlapping elongated inverse micelles". The structures of the mixtures obtained at different hydration levels are consistent with those of experimental diffraction studies of water/octanol mixtures and previous computer simulations of neat and water-saturated octanol. The saturation point of the model has been calculated using the cavity-bias particle insertion method. The solubility of water in octanol is slightly too low compared to experimental results, and suggestions for possible improvements to the force field are made.     

Quartic equations and classification of Riemann tensors in general relativity

For space-times in general relativity, the Petrov classification of the Weyl conformai curvature and the Plebaski or Segre classification of the Ricci tensor each depend on the properties of the roots of quartic equations. The coefficients in these quartic equations are in general complicated functions of the space-time coordinates. We review the general theory of quartic equations, and discuss algorithms for determining the existence and values of multiple roots. We consider practical implementation of an algorithm and the consequent Petrov classification. Tests of programs embodying this algorithm, using the computer algebra system CLASSI based on SHEEP, are reported.