Raman spectroscopy of carbon fibres

Investigations of coated carbon fibres are reported using Raman spectroscopy. Relationships between different process parameters (for example precursor concentration, reactor temperature and various precursors) and the resulting types of carbon fibres are discussed.     

Photodecomposition of several compounds commonly used as sunscreen agents

The photolysis reactions of three compounds commonly used as a sunscreen agents, Parsol 1789 (1-[4-(1,1-dimethylethyl)phenyl]-3-(4-methoxyphenyl)-1,3- propanedione), Oxybenzone ((2-hydroxy-4-methoxyphenyl)phenyl-methanone) and Padimate O (2-ethylhexyl-4-(dimethylamino)benzoate), were investigated to provide a chemical background to aid in the understanding of the photosensitization of the sunscreen agents. Photolysis was carried out in cyclohexane for 70–140 h using a mercury vapor lamp (450W) without excluding oxygen.

Irradation of Parsol 1789 in cyclohexane yielded tert-butylbenzene, p-tert-butylbenzoic acid and p-methoxybenzoic acid; products obtained from the combination of the sunscreen with the solvent included the cyclohexyl esters of p-methoxybenzoic acid, p-tert-butylbenzoic acid and methanoic acid; products obtained from the solvent included cyclohexanol, cyclohexanone and dicyclohexyl ether.

Irradiation of Oxybenzone in the cyclohexane for 100 h produced no detectable products by either gas or liquid chromatographic analysis. Oxybenzone was recovered unchanged and no products were observed from the photoinitiated reaction of oxygen with the solvent.

Irradiation of Padimate O in cyclohexane yielded the ethylhexyl esters of p-aminobenzoic acid, p-monomethylaminobenzoic acid and p-dimethylamino (o/m)-methylbenzoic acid, as well as products from the photoinitiated reaction of oxygen with the solvent.     

Regiochemistry of the addition of mercury salts to bornylene

The dependence of the regiochemistry of the mercuration of bornylene on the nature of the mercurating reagent and on the solvent has been found. The structures of the intermediate and transition state in these reactions have been proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 501–505, March, 1994.     

Sorption characteristics of polyfluorocarboxamides

The dependence of the variations in the differential molar free energy of sorption of polyfluorocarboxamides R_FC(O)NR₂ (R_F = CF₃(CF₂) _i ,i=0 to 5, R=H or Me) on capillary columns on the molecular structure of the amides, the temperature of analysis, and the nature of the stationary phases (OV-101, XE-60, and PEG-40M) were investigated by GLC. The peculiarities of the variation of the sorption characteristics of amides in XE-60 and PEG-40M polar phases, which cause the inversion of the order of retention of the members of pseudohomologous series, were found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 868–871, May, 1994.We are grateful to R. V. Golovnya and D. N. Grigor'eva (Institute of Food Substances of the RAS, Moscow) for their participation in the discussion of the results obtained.     

Reactions of mercury salts with benzo- and tetrafluorobenzobarrelenes

Regiochemistry and stereochemistry of the addition of mercury salts to benzobarrelene and tetrafluorobenzobarrelene have been studied in acetic acid and methanol. The effect of the substrate structure on the regiochemistry of the reaction is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1105–1108, June, 1994.     

Electrochemical co-oxidation of C-H acids and methanol as a new route to functionalized cyclopropanes

Electrolysis of dimethyl malonate or methyl cyanoacetate in methanol in the presence of LiCl in an undivided cell leads to formation of 1,1,2,2-cyclopropanetetracarboxylic derivatives.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1835–1836, October, 1994.This work was supported by the International Science Foundation (Grant No MHY 000).     

A high sensitivity titration calorimeter using pyroelectric sensor

A new sensitive isothermal titration microcalorimeter using polyvinylidene difluoride (PVDF) as detector has been developed. Heat pulses of less than 0.4 μJ can be detected and the baseline noise level (p-p) is 40 nW. The calorimeter is constructed with one reaction cell (0.7 ml) insulated by several radiation shields inside a vacuum chamber. The performance of the instrument was examined by measuring the heat of protonation of Tris with HCl. The enthalpy of reaction was found to be ?49±1 kJ·mol^?1, in good agreement with the reported value of ?47.5 kJ·mol^?1.     

Fluctuation conductivity in superconducting MgB2

According to the crystal structure of MgB₂ and band structure calculations, quasi-two-dimensional (2D) boron planes are responsible for the superconductivity. We report on critical-field and resistance measurements of 5.6-μm-thick MgB₂ films grown on a sapphire single-crystal substrate. Resistivity measurements yield a temperature dependence of the fluctuation conductivity above the critical temperature, which agrees with the Aslamazov-Larkin and Maki-Thompson theory of fluctuations in layered superconductors, indicating a quasi-two-dimensional nucleation of superconductivity in MgB₂.