Studies of acyl and thioacyl isocyanates—XII : The reactions of benzoyl and thiobenzoyl isocyanates with sulfonium ylides and with diazoalkanes

Benzoyl isocyanates react with ethyl (dimethylsulfuranilidene) acetate, dimethyl sulfonium phenacylide and dimethyloxosulfonium methylide to give the corresponding stable benzoylcarbamoyl- sulfonium ylides which on pyrolysis, are converted into oxazoles. However, with dimethylsulfonium phenacylide, thioacyl isocyanate affords the thiazole derivative. In connection with the formation of oxazoles, the reaction of benzoyl isocyanates with some diazoalkanes was also investigated: the products are not 1,2,3-triazolones as reported by Neidlein, but instead benzoylcarbamoyldiazo compounds which were thermally decomposed to oxazoles.     

Optical emission spectroscopy with a microwave-induced plasma in a sealed microtube

A microwave system is used to induce a plasma inside a sealed microtube containing a sample or standard, and the emission from the analyte is measured. The detection limits are about 4 ng for S, Cl and Br, and 100 ng for Cd and Sn, in approximately 30-mul samples. Both gaseous and liquid samples can be analysed.     

Photochemistry of heterocyclic compounds—II : The photochemical reaction of 2,5-disubstituted 1,3,4-oxadiazoles with furan

The photochemical reaction of 2,5-disubstituted 1,3,4-oxadiazoles with furan has been studied. With or without benzophenone as a sensitizer, irradiation of 2,5-diphenyl-1,3,4-oxadiazole with furan in benzene solution gives the 1 : 1 cycloadduct, tetrahydrofuro[2·3-b]azetidino[2·1-b]-1,3,4-oxadiazole. However in the presence of iodine 3-acylfurans and their acylhydrazones are formed. A reaction pathway of this novel photo-induced acylation has been suggested.     

Reaction of sulfonium ylides complexed with tricarbonylchromium

Oxiranes and olefins are obtained from the reactions of free and complexed phenylmethylsulfonium methylides with tricarbonylchromium with benzophenone, benzaldehyde and cyclohexanone. Good yields of olefins are obtained from the Cr(CO)₃ complexes with benzophenone, but yields of 0.1-0.5% are obtained with benzaldehyde and cyclohexanone.     

Reaction of thiobenzophenones with the manganese pentacarbonyl anion

The first study of the reactions of thioketones with metal carbonyl anions is described. Reaction of thiobenzophenones with the manganese pentacarbonyl anion and methyl iodide or benzyl bromide in methanol affords the complexes [Ar₂CHSMn(CO)₄]₂, identified on the basis of analytical and ir, as well as nmr (¹H, ¹³C) spectral data. The reaction is proposed to occur via charge-transfer and radical intermediates.     

Reaction of urates and other antioxidants with galvinoxyl

Uric acid, 3-ribosyluric acid, 1-methyluric acid, 1,3,7-trimethyluric acid, 2,8-dihydroxyadenine, and 2-imidazolone reacted with galvinoxyl, a stable free radical, to form galvinol. The reaction was followed by the decrease in absorbance at 550 nm of an ethanolic solution of galvinoxyl. Related compounds such as inosine, xanthosine, 2-hydroxybenzimidazole, lumichrome, and lumazine did not react with galvinoxyl. The data reported support the proposal that urates are important antioxidants and free-radical scavengers.     

Substituent effects in the reaction of phenols with polyacrylonitrile radicals

Substituent effects in the reactivities of phenols towards polyacrylonitrile radicals have been studied in terms of Swain and Luptons' field (F_k) and resonance (R_k) components of the substituent parameters and the unique positional weighting factors (f_j and r_j) proposed by Williams and Norrington, with the aid of the following equation:

$\text{P}{}_{\mathrm{i}}\text{= x}{}_{\mathrm{i}}\text{?}{}_{\mathrm{i}}\text{F}{}_{\mathrm{k}}\text{+ ß}{}_{\mathrm{i}}\text{r}{}_{\mathrm{j}}\text{K}{}_{\mathrm{i}}\text{+ e}{}_{\mathrm{i}}\text{+}\text{P}\text{i}\text{o}$

P_i′s are the rate parameters, P_i⁰ being that for a standard reference compound. Two types of rate parameters have been employed—one, suggested by Simonyi, Tüdös and Pospisil (β) and another, suggested by us, (K), which is obtained from a plot of [Monomer]/(rate of polymerisation) vs [Phenol]. The correlations have been found to be quite satisfactory with both β and K. An attempt has been made to ascertain the nature of the transition state from the reaction parameters α_i and β_i; a dipolar transition state is suggested. The anomalous kinetic behaviour of hydroxy phenols has been discussed.     

Triplet—triplet absorption of some azanaphthalenes

Experimetnal and theoretical studies of TT spectra, previously restricted mostly to D_2h and C_2v hydrocarbons, are extended to C_s heterocyclics. The TT spectrum of quinoline and isoquinoline can be interpreted as resulting from a dilution of the naphthalene ³B^?_1g state over near lying levels in the azanaphthalenes.     

Reaction of (bromodifluoromethyl)phenyldimethylsilane with organometallic reagents

A new fluorine-containing organosilicon compound, (bromodifluoromethyl)-phenyldimethylsilane (II), was synthesized by the N-bromosuccinimide (NBS) bromination of difluoromethyl)phenyldimethylsilane (I), which was prepared from phenyldimethylsilyllithium and chlorodifluoromethane. Compound II reacted with dimethyl sulfoxide to give dimethyl sulfide and phenyldimethylfluorosilane in quantitative yield. The reaction of II with nucleophiles, such as sodium ethoxide, Grignard or lithium reagents, afforded products arising from cleavage of the carbonsilicon bond. In contrast, the reaction of II with Grignard reagents in the presence of appropriate catalysts (Group VIII transition metal salts or complexes) afforded the homo-coupling product of II, 1,2-bis-(phenyldimethylsilyl)-1,1,2,2-tetrafluoroethane (IV), in excellent yield. The silver(I) salt-catalyzed reaction of II with ethylmagnesium bromide gave the cross-coupling product, (1,1-difluoropropyl)phenyldimethylsilane (V) as well as III and IV. When cuprous bromide was employed as catalyst, the reaction of II with ethylmagnesium bromide afforded 1-phenyldimethylsilyl-1-propene (VI) and 3-phenyldimethylsilyl-2-pentene (VII) as main products.     

Synthesis and structure of polynuclear carbonylphosphine clusters of palladium

Reductive condensation of Pd(OAc)₂ in dioxane in the presence of CO and PR₃ (R = Et, Buⁿ) with addition of CF₃COOH leads to the formation of decanuclear Pd₁₀(μ₃-CO)₄(μ₂-CO)₈(PBuⁿ₃)₆ (I) and Pd₁₀(CO)₁₄(PBuⁿ₃) (II) at Pd(OAc)₂:PR₃ molar ratios of 1:4–1:10 and 1:1.5–1:2.5, respectively. The use of CH₃COOH instead of CF₃COOH results in tetranuclear clusters Pd₄(CO)₅(PR₃)₄ (III) and Pd₄(μ₂-CO)₆(PBuⁿ₃) (IV). I ? III and III → IV transformations occur in organic media. The structures of I (space group P2₁/n, Z = λMo, 12125 independent reflections, R = 0.047) and IV (Pz:3, Z = λMo, 3254 reflections, R = 0.098) were established by X-Ray diffractions analysis. Cluster I is a 10-vertex Pd₁₀ polyhedron, an octahedron with four unsymmetrically centered non-adjacent faces. The average PdPd distances in the octahedron are 2.825 Å, in the eight short Pd_oct.Pd_cap. bonds with the “equatorial” Pd atoms of the inner octahedron, bridged by the μ₂-CO ligands, are 2.709 Å, and in the four elongated (without bridging CO groups) bonds with the apical Pd atoms of the octahedron are 3.300–3.422 Å. The PBuⁿ₃ ligands are coordinated to the apical Pd atoms and the capping atoms (PdP 2.291–2.324 Å). Cluster IV is tetrahedral, with the CO ligands symmetrically bridged; PdPd 2.778–2.817; PdP 2.232–2.291; PdC 2.06 Å (average).     

The formation and reduction of anodic films on electrodeposited ruthenium

The formation and reduction of anodic films on bright ruthenium was investigated using substrates prepared by electrodeposition onto gold-plated platinum from a commercial ruthenium bath operated at 70°C. Anodic films formed on the ruthenium may be reduced by maintaining the electrode at potentials below 0.2 V. The reduction behaviour was markedly affected by the anodization potential and, at short times, by the period of anodization. The bell-shaped cathodic current-time curves observed with films produced at potentials in the region of 1.2 V, suggest that the process in this case involves nucleation of reduction centres on a relatively stable surface layer. The influence of potential, time, and both the concentration and nature of the electrolyte on the extent of anodic film formation was investigated. The results are discussed in terms of the formation of stable phase oxides in the relatively thick anodic film produced on the ruthenium surface.     

Studies on membrane concentration potentials across heavy metal soap discs

The electrostatic effect of specifically adsorbed electroinactive ions upon electrode processes involving adsorbed reactants with a time of adsorption greater than the characteristic time of surface-diffusion jumps is considered. The validity of the most general form of the Frumkin correction term for double-layer effects, with ψ₁ equal to the local potential ₃ at the position occupied by the reactant in the transition state, is first examined on the basis of current molecular theories of electrode kinetics. Subsequently, approximate expressions of ₃ are derived for the case in which adsorbed reactant and adsorbed supporting ion are charged both of equal and of opposite sign. In both cases the logarithm Φ of the rate constant for the electrode reaction at constant applied potential, as corrected for diffuse-layer effects only, is expected to vary linearly with the charge density q_i due to the adsorbed supporting ion. |ΔΦ/Δq_i| is, however, much greater in the case of electrostatic attraction between reactant and adsorbed supporting ion than in the case of electrostatic repulsion. The influence of reactant adsorption with partial charge transfer upon the magnitude of ΔΦ/Δq_i is considered.     

The structure of the carbon dioxide dimer

The structure of the carbon dioxide dimer is discussed theoretically in terms of two empirical potentials and using CNDO/2 and ab initio quantum mechanical calculations. All these methods support the conclusion that there are two structures of comparable energy, the lower one being non-polar.     

Gas permeability of various block copolyether—urethanes

The effect of chemical structure and fabrication variables on the gas permeability of several block copolyether—urethane—urea and copolyether—urethane membranes was determined. It was found that the gas permeability of the copolyether—urethane—ureas increased in a linear manner with an increase in the polypropylene glycol segment molecular weight. Copolymers with a polyethylene glycol segment were found to be less permeable than those with propylene glycol segments. This may be due to the ability of polyethylene glycol to crystallize. For both copolymer systems, the type of chain extender used affected gas permeability. Again, these effects may be due to the degree of phase separation and to the nature of chain packing with the different extenders (i.e., the better the packing the lower the permeability). Changes in casting solvent, or the addition of salts such as LiBr or urea, had only minor effects on gas permeability.     

A potential—Time relationship for the reversible re-oxidation of an insoluble product by current reversal chronopotentiometry

An equation is presented for the potential—time dependence for the reversible re-oxidation of an insoluble product using current reversal chronopotentiometry with an inert electrode. The relationship presented accounts for unequal forward and reverse current densities. Experimental verification is presented with results from a study of silver and lead ions in molten LiCl?KCl eutectic at 710 K using a glassy carbon working electrode.     

Photo-induced homolysis of alkyltricyclopentadienyluranium(IV) complexes: an example of a successful UIV → UIII reduction

Photo-induced reduction of two organouranium complexes of the type Cp₃UR (R = CH₃ and n-C₄H₉) was studied in toluene and THF solution at various temperatures. Optimal conditions for the production of Cp₃U . THF as the final product involve UV/VIS irradiation in THF at ca. 60°C. Spin trap experiments indicate that, at least in THF, intermediate free radicals participate. The results, including gas chromatographic, mass spectroscopic and ¹H NMR spectroscopic measurements, are discussed in terms of a virtually first order multi-step process involving discrete radical pairs kept together efficiently by solvent cages so that H-atom abstraction from a Cp ligand followed by decomposition of the organometallic product is largely avoided.