Electrochemical activation and dehalogenation of freons in low-temperature ionic liquids

The effect of various factors (the nature of the medium and the electrode material, the electronic structure of the Freons, etc.) on the electrochemical activation and dehalogenation of a series of Freons [F113 (CF₂ClCFCl₂), F13B1 (CF₃Br), F114B2 (CF₂BrCF₂Br), and F113B2 (CFClBrCF₂Br)] in various low-temperature ionic liquids (LTIL) [1-butyl-3-methylimidazolium, 1-butyl-1-methylpyrrolidinium, and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imides and 1-butyl-3-methylimidazolium hexafluorophosphate, tetrafluoroborate, and trifluoroacetate] at various electrodes (glassy carbon, Pt, Ag) was studied. It was established in particular that the investigated processes are affected substantially by the electrical conductivity and viscosity of the medium. With decrease of the latter the peak potential in the cyclic voltammetry of the electrochemical reduction of the Freons is shifted toward less negative values while the current increases. It was found that a silver cathode has a specific effect on the electrochemical activation of the Freons in the LTILs, and this may be due to the formation of complexes Ag⋯Hal⋯R_f between the Freons and silver atoms on the electrode surface, in which cleavage of the C—Hal bond is facilitated. Such processes are compared with the processes realized in the traditional solvent dimethylformamide. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 67–74, March–April, 2007.     

Electrochemical reduction of 4-methyl-4-(trichloromethyl)cyclohexa-2,5-dien-1-one

The properties of 4-methyl-4-(trichloromethyl)cyclohexa-2,5-dien-1-one which contains the trichloromethyl substituent at a quaternary carbon atom have been studied by cyclic voltammetry, rotating disk electrode voltammetry, and preparative electrolysis. Reductive dehalogenation involves initial two-electron reductive elimination of one of the geminal chlorine atoms followed by consecutive addition of proton, simultaneous elimination of the two residual halogen atoms to form carbene, and rearrangement of cyclohexadienone into the corresponding 4-methylcyclohepta-2,4,6-trien-1-one.     

Reaction of 4-methyl-4-tribromomethylcyclohexa-2,5-dien-1-one with zinc metal

4-Methyl-4-tribromomethylcyclohexa-2,5-dien-1-one reacts with zinc dust in absolute DMF to give a mixture of 4-bromo-5-methylcyclohepta-2,4,6-trien-1-one, 4-methyl-cyclohepta-2,4,6-trien-1-one, and 4-dibromomethyl-4-methylcyclohexa-2,5-dien-1-one. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 177–178, January, 1998.     

Redox troponization of 4-methyl-4-dibromomethyl-2,5-cyclohexadien-1-one by the action of Pd(PPh3)4

Conclusions The feasibility of using gem-dihalomethyl-substituted cyclohexadienones in redox troponization reactions was shown in the case of the reaction of 4-methyl-4-dibromomethyl-2,5-cyclohexadien-1-one with Pd(PPh₃)₄, leading to the formation of 4-methy1-2,4,6-cycloheptatrien-1-one.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2345–2346, October, 1987.     

Electrochemical reductive cleavage of carbon-halogen bonds in 5-bromo-1,3-dichloro-2-iodobenzene

The electrochemical reduction of carbon-halogen bonds in 5-bromo-1,3-dichloro-2-iodobenzene follows quadratic activation-driving force relationship except in one of the carbon-chlorine bonds. The variation of the transfer coefficient with the electrode potential has been estimated using the voltammetric data coupled with the convolution analysis. The standard potentials pertaining to the reduction of carbon-halogen bonds are evaluated using the Marcus theory of outer sphere electron transfer.     

An unusual dehalogenation in the Suzuki coupling of 4-bromopyrrole-2-carboxylates

An unusual dehalogenation of 4-bromopyrrole-2-carboxylates under Suzuki coupling conditions has been observed. This dehalogenation can be suppressed by protection of the pyrrole nitrogen. Using a BOC protecting group, not only is dehalogenation suppressed, but the protecting group is also removed under the reaction conditions.     

Spirocyclohexadienones. 5. Synthesis of 2-R-7a-methyl-3-(spirocyclohexa-2,5-dien-4-one)perhydro-1-indolines

2-R-7a-Methyl-3-(spirocyclohexa-2,5-dien-4-one)perhydro-1-indolines were obtained by the reactions of 1-(4-ethoxyphenyl)-2-methylcyclohexanol with nitriles (RCN) in dichloromethane in the presence of concentrated sulfuric acid.     

Electrochemically induced transformation of 4(6)-dihalomethyl-4(6)-methylcyclohexa-2,5(2,4)-dien-1-ones into 4(2)-methyltropones

Electrochemical investigation of 4(6)-dihalomethyl-4(6)-methylcyclohexa-2,5(2,4)-dien-1-ones using cyclic voltammetry (CVA) and rotating disc electrode (RDE) methods has been performed. The reductive dehalogenation of cyclohexa-2,5(2,4)-dien-1-ones having a dihalomethyl substituent at the tertiary carbon atom was shown to proceed as a two-electron reductive elimination of the geminal halogen atoms with the intermediate formation of carbene and subsequent rearrangement of cyclohexadienone with the ring expansion to the corresponding 4- or 2-methylcyclohepta-2,4,6-trien-1-one.     

Synthesis of 1,3-Benzoxathiol-2-one Derivatives from N-(4-Oxocyclohexa-2,5-dien-1-ylidene)ureas

Russian Journal of Organic Chemistry - 1,3-Benzoxathiol-2-one derivatives were synthesized by reactions of N-(4-oxocyclohexa-2,5-dien-1-ylidene)ureas with potassium thiocyanate or thiourea. In most...     

Redox troponization of (η5-cyclopentadienyl)(η4-4-menthyl-4-exo-trichloromethylcyclohexa-2,5-dien-1-one)rhodium as a novel approach to the synthesis of metal-coordinated nonbenzenoid aromatics of the tropone seriesas a novel approach to the synthesis of metal-coordinated nonbenzenoid aromatics of the tropone series

The possibility of redox troponization of a gem-polyhalomethylated semiquinoid system, π-coordinated to a metal atom, was shown in relation to the reaction of (η⁵-cyclopentadienyl)(η⁴-4-menthyl-4-exo-trichloromethylcyclohexa-2,5-dien-1-one)rhodium with Pd(PPh₃)₄. The reaction occurs with retention of the metal coordination affording a sevenmembered organometallic derivative of the nonbenzoid aromatic series, namely, (η⁵-cyclopentadienyl)(η⁴-4-chloro-5-menthylcyclohepta-2,4,6-trien-1-one)rhodium, whose structure was established by means of elemental analysis, NMR, and mass-spectral data. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1255–1256, June, 1998.     

Theoretical study of the microhydration of 1-chloro and 2-chloro ethanol as a clue for their relative propensity toward dehalogenation

This work reports a computational analysis of hydrogen-bonded clusters of mono-, di-, tri-, and tetrahydrates of the chlorohydrins CH₃CHClOH (1ClEtOH) and CH₂ClCH₂OH (2ClEtOH). The goal of the study is to assess the role of the water solvent into the facilitation of the initial step for dehalogenation of these compounds, a process of interest in several contexts. Molecular orbital methods (MP2), density functional methods (B3LYP, M06, and ωB97X-D), and composite model chemistries (CBS-QB3, G4) were employed to investigate the structure, electronic distribution, and hydrogen-bonded structure of seven monohydrates, six dihydrates, five trihydrates, and five tetrahydrates of both species. Standard reaction enthalpy and standard Gibbs free reaction energy () were computed for all aggregates with respect to n independent water molecules and with respect to the dimer, trimer, and tetramer of water, respectively, in order to evaluate stability and hydrogen bonding network. The influence of the water chains on the length and vibrational frequencies, especially of the C Cl and O H bonds, was evaluated. Hydrogen bonding in the complexes is discussed at length.     

On the reaction of 4-chloromethylene-2,6-di-tert-buthylcyclohexa- 2,5-dien-1-one with P(III) acids esters

Russian Journal of General Chemistry -     

4-Hydroxy-2-quinolones 137. Synthesis,structure, and spectroscopic characteristics of diethyl 2,2′-dioxo-1,2,3,4,1′,2′,3′,4′-octahydro[4,4′]biquinolinyl-3,3′-dicarboxylate

Treatment of the ethyl esters of 1-R-4-chloro-2-oxo-1,2-dihydroquinoline-3-carboxylic acids with zinc dust in glacial acetic acid gives high yields of diethyl 2,2′-dioxo-1,2,3,4,1′,2′,3′,4′-octahydro[4,4′]biquinolinyl-3,3′-dicarboxylates. The structural features of the synthesized compounds together with their NMR and mass spectra are discussed. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1799–1807, December, 2007.     

New version of redox-troponization — oxidative expansion of apara-semiquinoid ring in the reaction of 4-methyl-4-bromomethyl-2,5-cyclohexadien-1-one with tetrakis(triphenylphosphine)palladium

4-Methyl-4-bromomethyl-2,5-cyclohexadien-1-one reacts with Pd(PPh₃)₄ in benzene to give 4-methyl-2,4,6-cycloheptatrien-1-one. The reaction occurs as intramolecular carbometallation of the enone fragment of the starting dienone followed by rearrangement—dehydrometallation or involves a sequence of steps,viz., homolytic abstraction of the halogen atom, cyclization, recyclization, and dehydrogenation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1836–1837, September, 1995.This work was carried out with financial support from the Russian Foundation for Basic Research (Project No. 95-03-09784) and the International Science Foundation (Grants MHW 000 and MHW 300).     

Water-catalyzed dehalogenation reactions of the isomer of CBr4 and its reaction products and a comparison to analogous reaction of the isomers of di-and trihalomethanes

A combined experimental and theoretical study of the UV photolysis of a typical tetrahalomethane, CBr4, in water and acetonitrile/water was performed. Ultraviolet photolysis of low concentrations of CBr4 in water mostly leads to the production of four HBr leaving groups and CO2. Picosecond time-resolved resonance Raman (Ps-TR3) experiments and ab initio calculations indicate that water-catalyzed O-H insertion/HBr elimination of the isomer of CBr4 and subsequent reactions of its products lead to the formation of these products. The UV photolyses of di-, tri-, and tetrahalomethanes at low concentrations in water-solvated environments are compared to one another. This comparison enables a general reaction scheme to be deduced that can account for the different products produced by UV photolysis of low concentrations of di-, tri-, and tetrahalomethanes in water. The fate of the (halo)formaldehyde intermediate in the chemical reaction mechanism is the key to determining how many strong acid leaving groups are produced and which carbon atom final product is likely formed by UV photolysis of a polyhalomethane at low concentrations in a water-solvated environment.     

X-ray structural and spectral study of 1:2 solvate of 2,7-dinitro-4-bromo-10,10-dihydroxyphenanthren-9-one with dimethylformamide

An x-ray structural study showed the total similarity of the behavior of 2,4,7-trinitro- and 2,7-dinitro-4-bromo-9,10-phenanthrenequinones dissolved in aqueous DMF: addition of a molecule of water at one of the two carbonyl groups with formation of the corresponding 10,10-dihydroxyphenanthren-9-ones takes place in both cases in soft conditions. These products of hydration exist as hydrogen-bonded solvates with molecules of the solvent whose crystals are isostructural to each other. The results of the x-ray structural study are in agreement with the data from the IR absorption and electron absorption spectra; their comparison suggests the existence of equilibrium between the starting compounds and the products of hydration, and the equilibrium position is a function of the polarity of the basic solvent.A. N. Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Sciences, Moscow 117813. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 910–916, April, 1992.     

Pyrolysis of 5-chloropentan-2-one and 4-chloro-1-phenylbutan-1-one. Participation of the carbonyl group

The rates of elimination of 5-chloropentan-2-one and 4-chloro-1-phenylbutan-1-one in the gas phase have been determined in a static system, seasoned with allyl bromide, and in the presence of the chain inhibitor propene. The reactions are unimolecular and follow a first-order rate law. The working temperature and pressure ranges were 339.4–401.1°C and 46–117 torr, respectively. The rate coefficients for the homogeneous reactions are given by the following Arrhenius equations: for 5-chloropentan-2-one, log k₁(s^?1) = (13.12 ± 0.88) - (207.8 ± 11.0)kJ/mol/2.303RT; and for 4-chloro-1-phenylbutan-1-one, log k₁(s^?1) = (12.28 ± 1.09) - (185.2 ± 12.0)kJ/mol/2.303RT. The carbonyl group at the γ position of the C? Cl bond of haloketones apparently participates in the rate of pyrolysis. The five-membered conformation appears to be a favorable structure for anchimeric assistance of the C?O group in the gas-phase elimination of chloroketones.