Reactions of hexafluorobenzene and pentafluorophenylamino compounds with amides and anilides (steric effects)

Contrary to N-lithium-N-methylanilide and N-lithium-diphenylamide, trimethyl-N-lithium-N-phenyl-silylamide gave with hexafluorobenzene in molar ratio 2:1, only the monosubstituted compound. Competitive reactions gave the following order of reactivity toward N-lithiumanilide: 2,3,4,5,6-pentafluorotriphenylamine > 2,3,4,5,6-pentafluoro-N-methyl-diphenylamine > hexafluorobenzene ? trimethyl-2,3,4,5,6-pentafluoro-N,N-diphenyl-silylamine. A reason for the low reactivity of trimethyl-2,3,4,5,6-pentafluoro-N,N-diphenyl-silylamine against aromatic amides has been proposed.Some new aromatic amines have been synthesized, among them hexamethyl-N-pentafluorophenyl-disilylamine.     

Solvent effects upon reactions between ions: hexacyanoferrate(II)-peroxodisulphate and sulphite-hexacyanoferate(III)

Summary Different approaches to the interpretation of solvent effects on reactions between ionic reactants are analysed, taking as a basis the kinetic data corresponding to the sulphite-hexacyanoferrate(III) and peroxodisulphate-hexacyanoferrate(III) oxidations. It is concluded that the approach based on the use of solvent parameters is the more promising, although knowledge of the transfer chemical potentials of the reactants may also be useful in the interpretation of kinetic behaviour.     

Solvent effects in lipase-catalysed transesterification reactions

Porcine pancreatic lipase-catalysed transesterifications of 2,2,2-trifluoroethyl butyrate with racemic 2-octanol and 1-phenylethanol have been studied in different organic solvents. Solvent hydrophobicity (log P -1.1 to 3.3) has only a minor effect on the reaction rate. Independently of the solvent used as the reaction medium, both (R)-2-octyl and (R)-1-phenylethyl butyrates were obtained in high optical purity (ee greater than 90%). Candida cylindracea lipase is active only in the most hydrophobic solvents studied.     

Solvent effects in gold-catalysed A-coupling reactions

Gold-catalysed A³-reactions proceed efficiently when conducted in 2,2,2-trifluoroethanol as solvent. The rates of these reactions are accelerated considerably when conducted in a microwave reactor.     

Solvent effects on hydrogen abstraction reactions from lactones with antioxidant properties

Solvent effects on the kinetics for hydrogen abstraction from a lactone antioxidant were determined for alkoxyl and nitroxyl radicals; their reactivity differ by about 7 orders of magnitude. A decrease by approximately 12 and approximately 35 were determined for H-abstraction by tert-butoxyl and nitroxyl radicals, respectively, upon changing the solvent from hexane to acetonitrile. Results of solvent and isotope studies indicate that the antioxidant properties of lactone antioxidants should be attributed to the enol, not the lactone. [reaction: see text]     

Thermal and autoxidation reactions of poly-3-methylenecyclobutene and poly-1-methyl-3-methylenecyclobutene

The thermal ring-opening reactions, autoxidation and hydrogenation of polymethy-lenecyclobutene (PMCB) and poly-1-methyl-3-methylenecyclobutene (PMMCB), were investigated. Both polymers were prepared by cationic polymerization and consisted almost entirely of 1,5-repeating units containing cyclobutene rings in the polymer backbone. Both polymers showed well behaved exothermic processes at elevated temperatures which apparently resulted in crosslinking. These processes were investigated by differential scanning calorimetry and interpreted to involve thermal ring-opening reactions. Autoxidation occurred very rapidly in PMCB but much more slowly in PMMCB as predicted by Bolland's rules. Attempts to hydrogenate the cyclobutene rings in both polymers resulted in the occurrence of hydrogenolysis in PMCB and little or no reaction with PMMCB for a Pd-catalyzed reaction and partial hydrogenation of the latter for a diimide reaction.     

Solvent polarity effects on the regioselectivity of photoaddition reactions of arene-ethene systems

Use of polar solvents in the $\text{ortho}$ protocycloaddition of ethenes to anisole greatly increases the regioselectivity of the process and the major adducts reflect 1,2-attack onto the arene.     

Preparation and properties of poly-(N-butylmethacrylamide) networks

The gel-effect influences the copolymerization of N-butylmethacrylamide with methylene-bis-acrylamide similarly to other vinyl-divinyl copolymerizations. The fraction of crosslinks wasted in cycles is very high at the gel point, reaching 0.84–0.95; it decreases with increasing content of the crosslinking agent and with decreasing content of dimethylsulphoxide (DMSO) in the polymerization mixture. The effect of residual time processes on the mechanical characteristics in the rubberlike region decreases with increasing concentration of elastically active network chains, ν_e. The equilibrium deformational behaviour obeys the kinetic theory of rubber elasticity. With increasing dilution of the system, the efficiency of the cross-linking reaction decreases and so does the effect of trapped entanglements. A comparison of the gel points and the mechanical characteristics for poly(N-butylmethacrylamide) and poly(N-ethylmethacrylamide) networks swollen in DMSO indicates that the substituent at the amide nitrogen atom has a dilution effect depending on its size. The interaction parameter of the system poly(N-butylmethacrylamide)-DMSO increases linearly with the volume fraction of the polymer in the swollen gel, ν₂; χ = 0.498 + 0.362 ν₂ for ν₂? (0.1, 0.33) and 25°.     

Solvent extraction of silver and thallium picrates with poly- and bis-(crown ether)s

Summary Solvent extraction of silver and thallium picrates by new poly- and bis(crown ether)s, which contain benzo-15-crown-5 or benzo-18-crown-6 moieties, was carried out in water-chloroform system. The poly- and bis(crown ether)s showed higher extractability for both metals than the corresponding monocyclic crown ethers.Especially poly- and bis(benzo-15-crown-5) were found to be quite effective extracting agents for Tl⁺.The extraction equilibrium constants and the complexation constants for the chloroform phase were also estimated.

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Lösungsmittelextraktion von Silber- und Thalliumpikraten mit Poly- und Bis-Kronenethern

Zusammenfassung Die Extraktion der Pikrate wurde in Wasser/Chloroform mit neuen Poly- und Bis-Kronenethern durchgeführt, die Benzo-15-Krone-5- oder Benzo-18-krone-6-Komponenten enthielten. Die Poly- und Bis-Kronenether wiesen für beide Metalle eine bessere Extrahierbarkeit auf als die entsprechenden monocyclischen Kronenether. Insbesondere Poly- und Bis(benzo-15-krone-5) erwiesen sich als wirkungsvolle Extraktionsmittel für Thallium(I). Die Extraktions-Gleichgewichtskonstanten und die Komplexbildungskonstanten für die Chloroformphase wurden bestimmt.

     

The reactions of aromatic compounds with bromine trifluoride(I): hexafluorobenzene and its derivatives

The reactions of mixtures of bromine trifluoride and bromine with hexa-, penta- and bromopenta-fluorobenzene, with octafluorotoluene and decafluoro -p-xylene and 2,3,4,5,6-pentafluorotoluene and -anisole have been investigated. The initial products were polyfluorocyclohexa-1,4-dienes, substituent groups being in the 1-position for electron withdrawing and the 3-position for electron donating groups respectively. The dienes then reacted further to add bromine monofluoride across one or both of the diene double bonds to give bromofluorocyclohexene or polybromofluorocyclohexane isomer mixtures. In the absence of added bromine, no reaction occurred with hexafluorobenzene and reaction was less vigorous and complete with pentafluorobenzene and 2,3,4,5,6-pentafluoroanisole. The mechanism of reaction has been discussed in terms of the ionization potential of the aromatic substrates and the formation of radical cations.     

Solvent effects on the oxidative free radical reactions of 2-amino-1,4-naphthoquinones

Solvent effects on the manganese (III) initiated oxidative free radical reactions of 2-amino-1,4-naphthoquinones are described. This free radical reaction provides a novel method for the synthesis of benzo[f]indole-4,9-diones, benzo[f]indole-2,4,9-triones, benzo[b]carbazole-6,11-diones and benzo[b]acridine-6,11-diones. High chemoselectivity was observed in different solvents.     

Solvent and temperature effects on the reduction and amination reactions of electrophiles by lithium dialkylaminoborohydrides

The influence of temperature and solvent effects on the reduction and amination mechanisms of iodomethane by lithium N,N-diisopropylaminoborohydride (iPr-LAB) was examined in varying concentrations of THF and dioxane. The reactions of benzyl chloride and trimethylsilyl chloride with iPr-LAB in THF were also studied. The amination of iodomethane is favored over reduction at low and room temperatures in pure THF and with increasing the amount of dioxane in THF. At higher temperatures, the reduction reaction appears to compete with the amination. In dioxane solvent, however, iodomethane yields exclusively the amination product regardless of temperature. On the other hand, reduction by iPr-LAB to the aminoborane is the only product observed in THF when benzyl chloride and trimethylsilyl chloride are used. To understand the solvent effects on the product distribution, ab initio and density functional theory (DFT) calculations were used to examine the mechanisms of reduction and amination of chloromethane and bromomethane by lithium dimethylaminoborohydride (LAB) in THF and dioxane. The results of these calculations show that the relative reaction barrier heights are significantly affected by the nature of the coordinated solvent molecule and thus lend support to the experimental observations.     

Solvent effects on electron transfer reactions. The system iron(III)-phenothiazine in water-alcohol mixtures

Summary The effect of solvent composition (aqueous mixtures of methanol, ethanol, propan-1-ol and propan-2-ol) on the rate constants and activation parameters of the electron transfer between iron(III) and phenothiazine has been investigated. The dependence of the kinetic parameters on the solvent composition is discussed with reference to previously investigated systems.