- Mixed tetrahaloborate ions. Detection and study by nuclear magnetic resonance
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BF4-, BCl4-, BBr4-, and BI4- undergo halogen exchange in methylene chloride solution to form the mixed tetrahaloborate ions, for which 19F and 11B nmr data are presented. A previous report of very rapid halogen exchange in the BF4--BCl4- system is incorrect. Only in the BF4--BI4- system is halogen redistribution so rapid that separate nmr signals are not observed for the mixed-halogen anions. Exchange with methylene halide solvents gives rise to ternary-halogen species such as BF2ClBr-. Additional methods of preparation of mixed tetrahaloborate anions are investigated. The nmr parameters of the mixed tetrahaloborate anions show trends which resemble those of the mixed boron trihalides. The trends can be interpreted in terms of the presence of boron-fluorine π bonding. The results of CNDO/2 calculations provide an alternative interpretation of the trends in chemical shifts. The 11B and F19 chemical shifts of the tetrahaloborate anions are found to fit Malinowski's criteria of pairwise additivity. .
- Hartman,Schrobilgen
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- Synthesis of Fluorine-Containing Aryl(halo)boranes from Potassium Aryl(fluoro)borates
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Fluorine-containing aryldihalogenoboranes have been obtained by the reaction of boron and aluminum chlorides and bromides with potassium aryltrifluoroborates K[ArBF3] under mild conditions. In a similar way, bis(pentafluorophenyl)halogenoboranes have been synthesized by the reaction with K[(C6F5)2BF2]. The reaction of K[C6F5BF3] with AlBr3 affords a mixture of C6F5BF2 and C6F5BCl2 due to fast conversion of AlBr3 to AlBrCl2. The inductive and resonance parameters of BCl2 and BBr2 groups were calculated.
- Bardin,Prikhod’ko,Shmakov,Shabalin, A. Yu.,Adonin, N. Yu.
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- Facile continuous process for gas phase halogen exchange over supported alkyl phosphonium salts
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Chloride-bromide halogen exchange was realized when a mixture of an alkyl chloride and an alkyl bromide were reacted over a supported molten alkyl phosphonium catalyst. Conversion was found to be near equilibrium in a tubular flow reactor at 150 °C and 1500 GHSV. The catalyst was prepared by impregnation of alumina or silica support and found to be highly stable for relatively long periods of time. A pathway for the catalytic cycle is proposed.
- Sharma, Priti,Sasson, Yoel
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p. 2824 - 2828
(2018/02/06)
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- Kinetics of the R + HBr ? RH + Br (R = CH2Br, CHBrCl or CCl3) equilibrium. Thermochemistry of the CH2Br and CHBrCl radicals
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The kinetics of the reaction of the CH2Br, CHBrCl or CCl3 radicals, R, with HBr have been investigated separately in a heatable tubular reactor coupled to a photoionization mass spectrometer. The CH2Br (or CHBrCl or CCl3) radical was produced homogeneously in the reactor by a pulsed 248 nm exciplex laser photolysis of CH2Br2 (or CHBr2Cl or CBrCl3). The decay of R was monitored as a function of HBr concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature. The reactions were studied separately over a wide ranges of temperatures and in these temperature ranges the rate constants determined were fitted to an Arrhenius expression (error limits stated are 1σ + Student's t values, units in cm3 molecule-1 s-1): k(CH2Br + HBr) = (7.5 ± 0.9) × 10-13 exp[- (2.53 ± 0.13) kJ mol-1/RT], k(CHBrCl + HBr) = (4.9 ± 1.1) × 10-13 exp[-(8.2 ± 0.3) kJ mol-1/RT] and k(CCl3 + HBr) -15 at 787 K. The kinetics of the reverse reactions, Br + R′H → HBr + R′ (R′ = CH2Br or CHBrCl), were taken from the literature and also calculated by ab initio methods at the MP2(fc)/6-31G(d,p)//MP2(fc)/6-31G(d,p) level of theory in conjunction with the thermodynamic transition state theory to calculate the entropy and the enthalpy of formation values of the radicals studied. The thermodynamic values were obtained at 298 K using a second-law method. The results for entropy values are as follows (units in J K-1 mol-1): 263 ± 7 (CH2Br) and 294 ± 6 (CHBrCl). The results for enthalpy of formation values at 298 K are (in kJ mol-1): 171.1 ± 2.7 (CH2Br) and 143 ± 6 (CHBrCl). The C-H bond strength of analogous halomethanes are (in kJ mol-1): 427.2 ± 2.4 (CH3Br) and 406.0 ± 2.4 (CH2BrCl). Thermodynamic properties of the CH2Br radical were calculated by statistical thermodynamic methods over the temperature range 100-1500 K.
- Seetula, Jorma A.
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p. 849 - 855
(2007/10/03)
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- Kinetics of the Reactions of Halogenated Methyl Radicals with Molecular Bromine
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The kinetics of seven reactions of halogenated methyl radicals (CH2Cl, CHCl2, CFCl2, CF2Cl, CF3, CH2Br, and CH2I) with molecular bromine were studied by using a heatable tubular reactor coupled to a photoionization mass spectrometer.Rate constants were measured as a function of temperature, typically between 296 and 532 K.Arrhenius activation energies were found to be small negative values (typically -2 kJ mol-1) for all reactions studied with the exception of that of the CF3 + Br2 reaction (whose activation energy is positive, but which could not determined accurately).The pattern of reactivity among 11 reactions of substituted methyl radicals with Br2 (which includes the 7 reactions studied here and 4 C(H)x(CH3)3-x + Br2 reactions (x = 0-3) studied earlier) has been accounted for by the inductive effect of the substituent atoms or groups.The sum of the Pauling electronegativities of these substituents provides a useful measure of their total inductive effect on the reaction rate constant.
- Timonen, R. S.,Seetula, J. A.,Niiranen, J.,Gutman, D.
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p. 4009 - 4014
(2007/10/02)
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- Kinetics of the Reactions of Partially Halogenated Methyl Radicals (CH2Cl, CH2Br, CH2I, and CHCl2) with Molecular Chlorine
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The gas-phase kinetics of the reactions of four partially halogenated methyl radicals (CH2Cl, CH2Br, CH2I, and CHCl2) with Cl2 have been studied as a function of temperature using a tubular reactor coupled to a photoionization mass spectrometer.Radicals were homogeneously generated by pulsed 193- and/or 248-nm laser photolysis.Decays of the radical concentrations were monitored in time-resolved experiments as a function of to obtain bimolecular rate constants for the R + Cl2 -> RCl + Cl reactions studied.The following Arrhenius expressions (k = A exp(-E/RT)) were obtained (the numbers in brackets are log(A/(cm3 molecule-1 s-1)), E/(kJ mol-1); the temperature ranges are also indicated): R = CH2Cl ; R = CH2Br ; R = CH2I ; R = CHCl2 .Errors are 1?, including both random and an estimated 20percent systematic error in the individual bimolecular rate constants.The Arrhenius parameters of these and two other R + Cl2 reactions are compared with theoretical determinations based on semiempirical AM1 calculations of transition-state energies, structures, and vibration frequencies.The calculations qualitatively reproduce the observed trends in both the Arrhenius A factors and in the activation energies.The use of molecular properties to account for reactivity differences among all the R + Cl2 reactions which have been studied to date are also explored using free-energy correlations with these properties.
- Seetula, J. A.,Gutman, D.,Lightfoot, P. D.,Rayes, M. T.,Senkan, S. M.
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p. 10688 - 10693
(2007/10/02)
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- Fe3O4-Catalyzed Halogen-Exchange Reactions of Polyhalomethanes
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Triiron tetraoxide pretreated by polyhalomethane was shown to catalyze the halogen-exchange reaction of polyhalomethanes CHlBrmCln (l=1 or 2).The exchange proceeds consecutively giving, for example, CHBrCl2, CHBr2Cl, and C
- Nakada, Masahiro,Tokumoto, Sei-ichi,Hirota, Minoru
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p. 3979 - 3984
(2007/10/02)
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- Substituted pyrimidin-2-ones and the salts thereof
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Compounds of the general formula: STR1 (wherein X represents a halogen atom or a trifluoromethyl group; R1 and R2 independently represent a hydrogen atom or a lower alkyl group; Z is --O--, --S--, --SO--, --SO2 -- or the group --NR4 -- wherein R4 is as defined for R hereinafter or represents the group COR5 in which R5 represents a hydrogen atom or an optionally substituted aryl, heterocyclic, aralkyl, lower alkyl or lower alkoxy group; R represents a C6-10 carbocyclic aromatic group or a heterocyclic group containing a 5-9 membered unsaturated or aromatic heterocyclic ring which ring contains one or more heteroatoms selected from O, N and S and optionally carries a fused ring which carbocyclic or heterocyclic group may carry one or more C1-4 alkyl or phenyl groups, said groups being optionally substituted; or, where Z represents the group >NR4, the group --ZR may represent a heterocyclic ring optionally carrying a fused ring and/or optionally substituted as defined for R; and R3 represents a hydrogen atom or a lower alkyl, lower alkenyl, lower alkynyl, lower alkanoyl, lower alkenoyl, C7-16 aralkyl or C6-10 arly group or a 5-9 membered unsaturated or aromatic heterocyclic ring); and, where acid or basic groups are present, the salts thereof; are useful in combating abnormal cell proliferation. The compounds of the invention are prepared by inter alia alkylation, ring closure and oxidation.
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- REACTIONS OF BrCl WITH ALKYL RADICALS.
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It is demonstrated that photohalogenation of low reactivity substrates with BrCl occurs mainly with Cl. selectivity.With tertiary or benzylic hydrogens in the substrate, mainly Br. selectivity is observed.These observations are rationalized, taking into account the relative concentrations of halogen atoms and their respective rates of hydrogen abstractions.The resultant radicals react with BrCl to make (RBr/RCl) in ratios between 1 and 15.
- Skell, P. S.,Baxter, H. N.,Tanko, J. M.
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p. 5181 - 5184
(2007/10/02)
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- 3-Mercaptomethyl-2-oxo-1-pyrrolidine acetic acids and use for hypertension
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This invention provides for certain lactam derivatives, their pharmaceutical formulations, and a method of treating hypertension.
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- Catalytic Interconversion of Alkyl Halides by Gas-liquid Phase-transfer Catalysis
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High halogen exchange conversions are achieved when a gaseous mixture of alkyl halides (chlorides, bromides, iodides) is passed over a solid bed consisting of porous inorganic supports bearing a phase-transfer catalyst under gas-liquid phase-transfer catalysis (g.l.-p.t.c.) conditions.The process is catalytic since the bed undergoes no changes once it reaches operating conditions.For example, a methylene dichloride and bromoethane mixture is converted into all the halogen-exchange products, and their statistical distribution at equilibrium depends on the original ratio of the halogens in the organic reagents.Catalytic activity is high: 200 ml of such a mixture can be converted in 1 h by passage through 200 g of alumina coated with 10 percent tetrabutylphosphonium bromide.The catalytic process is promoted by the halide anions present as Q(1+)X(1-) in the liquid phase constituted by the molten catalyst and as Na(1+)X(1-) in the solid inorganic support; the halide anions partition themselves between the liquid and solid phases as a function of their respective affinities.This catalysis depends on the diffusion, partition, and adsorption of the alkyl halides between the gaseous, liquid, and solid phases, as well as on their intrinsic nucleophilic reactivity.Mechanistic aspects and industrial applicability are discussed.
- Tundo, Pietro,Venturello, Paolo,Angeletti, Enrico
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p. 485 - 492
(2007/10/02)
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- Catalytic Halide Exchange in Hydrocarbons Promoted by Aluminas Coated with Phosphonium Salts
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Passing a mixture of two different alkyl halides, in the gas phase, through a column filled with alumina and a phosphonium salt, gives halide-exchange products which are collected at the outlet by condensation; the process is catalytic and allows transformations to be carried out in a continuous flow process.
- Angeletti, Enrico,Tundo, Pietro,Venturello, Paolo
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p. 1127 - 1128
(2007/10/02)
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- Group VIII metal complex catalyzed halogen exchange reaction
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Alkyl halide exchange may be catalyzed under mild conditions in homogeneous solution by ligand stabilized, low valent, coordinatively unsaturated d6 or d8 Group VIII metal complexes of the formula wherein M is a metal of Group VIII of the Periodic Table; X is chloride, bromide or iodide; n is 1 or 2; L is a neutral ligand such as CO; trialkyl or triaryl- phosphines, arsines, amines, or stibines and the like; x is an integer from 2-4 and Lx represents x neutral ligands which may be the same or different. In this manner the halide group of one alkyl halide may be replaced by the halogen of another alkyl halide by a process of alkyl halide exchange.
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