Radical reaction of methallyl chloride and polychloromethanes withβ-elimination of chlorine atom

Conclusions A study was made of the radical reaction of methallyl chloride with CCl₄ and CHCl₃ in the presence of peroxide initiators. On the basis of the structures of the isolated products and certain kinetic data a reaction mechanism was proposed with the postulated-elimination of the chlorine atom from the intermediate radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1331–1337, June, 1972.     

CIDNP study of the Ni(acac)2-catalyzed reaction of triethylaluminum with chloroform

CIDNP effects were found in the Ni(acac)₂-catalyzed reaction of Et₃Al with CHCl₃. The effects appear in the products of transformation of the diffusion radical pair of the ethyl and dichloromethyl radicals. The radical route is a side process in this reaction, and the main products, Et₂AlCl, ethane, and ethylene, are formed by a nonradical route. A general mechanism of the reactions of Et₃Al with CHCl₃ and CCl₄ including radical and ioncoordination processes was suggested. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1003–1006, May, 1999.     

FTIR study of the Cl- and Br-atom initiated oxidation of trichloroethylene

The Cl- and Br- initiated oxidations of CHCl(DOUBLEBOND)CCl₂ in 700 torr of air at 296 K have been studied using a Fourier transform infrared spectrometer. Rate constants k(Cl+CHCl(DOUBLEBOND)CCl₂)=(7.2±0.8)×10⁻¹¹ and k(Br+CHCl(DOUBLEBOND)CCl₂)=(1.1±0.4)×10⁻¹³ cm³ molecule⁻¹ s⁻¹ were determined using a relative rate technique with ethane and ethylene as references, respectively. The major products observed were CHXClC(O)Cl, (X=Cl or Br), CHClO, and CCl₂O. Combining results obtained for the Cl-initiated oxidation of CHCl₂(SINGLEBOND)CHCl₂, we deduced that Cl-addition on trichloroethylene occurs via channel 1a, Cl+CHCl(DOUBLEBOND)CCl₂→ CHCl₂(SINGLEBOND)CCl₂, (100±12)%. Self-reaction of the subsequently generated peroxy radicals CHCl₂(SINGLEBOND)CCl₂O₂ leads to CHCl₂CCl₂O radicals which were found to decompose via channel 8a, CHCl₂C(O)Cl+Cl, (91±11)% of the time, and channel 8b, CHCl₂+CCl₂O, (9±2)%. The reaction Br+CHCl(DOUBLEBOND)CCl₂→CHBrCl(SINGLEBOND)CCl₂ (17a) accounted for ≥(96±11)% of the total reaction. Decomposition of the CHBrCl(SINGLEBOND)CCl₂O radicals proceeds (≥93±11)% via CHBrClC(O)Cl+Cl. As part of this work, k(Cl+CHCl₂C(O)Cl)=(3.6±0.6)×10⁻¹⁴ and k(Cl+CHCl₂(SINGLEBOND)CHCl₂)=(1.9±0.2)×10⁻¹³ cm³ molecule⁻¹ s⁻¹ were measured. Errors reported above include statistical uncertainties (2σ) and estimated systematic uncertainties. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet: 29: 695–704, 1997.     

Kinetics and mechanism of the thermal chlorination of chloroform in the gas phase

The gas‐phase thermal chlorination of CHCl₃ has been studied up to high conversions by photometry and gas chromatography in a conditioned static quartz reaction vessel between 573 and 635 K. The initial pressures of both CHCl₃ and Cl₂ ranged from about 10–100 Torr, and the initial total pressure was varied between about 30–190 Torr. The reaction is rather complex because the produced CCl₄ is not stable. The rate of consumption of Cl₂ therefore increases in the course of time. This acceleration is explained quantitatively in terms of a radical mechanism and its kinetic and thermodynamic parameters. This reaction model is based on a known model for the pyrolysis of CCl₄ to which only one reaction couple involving CHCl₃ has been added. Analyses of the rates of the homogeneous elementary steps show that the primary source of Cl atoms is the second‐order dissociation of Cl₂, which is rapidly superseded by a secondary source, the first‐order dissociation of the CCl₄ primary product. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 466–472, 2000     

Radiolytic generation and photochemistry of 9-xanthenyl radicals in halogenated solvents

The photochemistry of 9-xanthenyl radicals produced by pulse radiolysis of xanthene in halocarbon was studied by means of a successive laser flash photolysis in the presence and absence of oxygen. In deaerated solutions rapid (during 6 ns laser pulse) and permanent photobleaching due to chlorine atom transfer from solvents to the excited 9-xanthenyl radical was observed with quantum yields of 0.04 and 0.26 in 1,2-dichloroethane and CCl₄, respectively. In the solutions containing oxygen, equilibrium between 9-xanthenyl radicals and peroxyl radicals was established and recovery of the photobleached 9-xanthenyl radicals was observed, which was accounted for by dissociation of peroxyl radicals. The whole reaction scheme of formation and decay of 9-xanthenyl radicals in CCl₄ is discussed based on the kinetic simulations.     

Radical addition of polychloromethanes toα,α-dichlorovinyl compounds

Conclusions The reaction of CCl₄ and CHCl₃ with CCl₂=CHR, where R=(CH₂)₃H (I) and (CH₂)₃Cl (II), gives compounds of type HCCl₂CH(CCl₃)R, and the adducts HCCl₂CH(CCl)₂CH₂CH₂CH₂Cl (V) from (I) and HCCl₂CH·(CCl₃)CH₂CH₂CHCl₂ (VIII) from (II).From CCl₄ and CC1₂=CHCH₂CH₂CH=CH₂, besides the usual addition product CCl₂=CHCH₂CH₂CHClCH₂· CCl₃, is formed 1,1-dichloro-2-(trichIoromethyl)-5-(chloromethyl)cyclopentane due to stabilization of the CCl₂CH(CCl₃)R radical by intramolecular addition to the CH=CH₂ group and the subsequent cleavage of chlorine.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1569–1574, July, 1975.     

Abstraction of chlorine atoms from chloroalkanes. V. The liquid-phase reaction between Et3SiH radicals and CH2Cl2, CHCl3, CCl4, and CCl3CN

The kinetics of chlorine transfer from CH₂Cl₂, CHCl₃, CCl₄, and CCl₃CN to the triethylsilyl radical was studied in the liquid phase by a competitive method. Br abstraction from 1-bromopentane was used as a reference. The following Arrhenius parameters were determined: where the error limits are two standard deviations (2σ). Based on these results, the observed reactivity trends in the chlorine transfer reactions of Et₃Si radicals appear to primarily reflect the variation in entropy of activation rather than in activation energies.     

Kinetics and mechanism for the thermal chlorination of chloroform in the gas phase: Inclusion of HCl elimination from CHCl3

HCl elimination from chloroform is shown to be the lowest energy channel for initiation in the thermal conversion of chloroform to CCl₄, with chlorine gas in the temperature range of 573–635 K. Literature data on this reaction is surveyed and we further estimate its kinetic parameters using ab initio and density functional calculations at the G3//B3LYP/6‐311G(d,p) level. Rate constants are estimated and reported as functions of pressure and temperature using quantum RRK theory for k( E ) and master equation analysis for fall‐off. The high‐pressure limit rate constant of this channel is k(CHCl₃ → ¹CCl₂ + HCl) = 5.84 × 10⁴⁰ × T ^?8.7 exp(?63.9 kcal/mol/ RT ) s^?1, which is in good agreement with literature values. The reactions of ¹CCl₂ with itself, with CCl₃, and with CHCl₃ are incorporated in a detailed mechanistic analysis for the CHCl₃ + Cl₂ reaction system. Inclusion of these reactions does not significantly change the mechanism predictions of Cl₂ concentration profiles in previous studies (Huybrechts, Hubin, and Van Mele, Int J Chem Kinet 2000, 32, 466) over the temperature range of 573–635 K; but Cl₂, CHCl₃, C₂Cl₆ species profiles are significantly different at elevated temperatures. Inclusion of the ¹CCl₂ + Cl₂ → CCl₃ + Cl reaction (abstraction and chain branching), which is found to have dramatic effects on the ability of the model to match to the experimental data, is discussed. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 647–660, 2003     

Stereoselektivität diastereogener CC-Verknüpfungen II Eine Carben/Carbenoid-Kaskade und «Hypermechanismen»

Stereoselectivity of Diastereogenic CC-Linking Reactions II. A Carbene/Carbenoid-Cascade and «Hypermechanisms» In a systematic study four pairs of dihalocarbene precursors were treated with methyllithium in the presence of 2-methyl-2-pentene. Each pair was made up of a tetrahalomethane and a trihalomethane, namely CCl₄ vs. CHCl₃, CCl₃F vs. CHCl₂F, CCl₂F₂ vs. CHClF₂ and CClF₃ vs. CHF₃. Since all the tetrahalomethanes reacted exclusively by chlorine/lithium exchange and all the trihalomethanes by hydrogen/lithium exchange, each pair gave rise (at least formally) to an identical ‘carbenoid’. Two different carbenoids may always undergo elimination of LiCl or LiF and thus collapse generating the same carbene. A comparison of the product composition (ratios of straight-forward cycloaddition vs. consecutive substitution reactions, ratios of diastereoisomers) reveals more or less marked, but always significant discrepancies in the outcome of ‘carbene-convergent’ as well as ‘carbenoid-convergent’ reactions.     

Determination of the Rate Constant of the Reaction of CCl2 with HCl

The rate constant of the reaction between CCl₂ radicals and HCl was experimentally determined. The CCl₂ radicals were obtained by infrared multiphoton dissociation of CDCl₃. The time dependence of the CCl₂ radicals' concentration in the presence of HCl was determined by laser‐induced fluorescence. The experimental conditions allowed us to associate the decrease in the concentration of radicals to the self‐recombination reaction to form C₂Cl₄ and to the reaction with HCl to form CHCl₃. The rate constant for the self‐recombination reaction was determined to be in the high‐pressure regime. The value obtained at 300 K was (5.7 ± 0.1) × 10^?13 cm³ molecule^?1 s^?1, whereas the value of the rate constant measured for the reaction with HCl was (2.7 ± 0.1) × 10^?14 cm³ molecule^?1 s^?1.     

A new cataluminescence sensor for carbon tetrachloride using its catalytic reduction by hydrogen on palladium/carbon surface

A new cataluminescence (CTL) sensor was developed based on the chemiluminescence (CL) emission from the catalytic hydrodechlorination of carbon tetrachloride on the surface of palladium/carbon catalyst. The factors influencing the CTL signal, such as the catalyst, carrier gas, gas flow rate, temperature and the CL wavelength, were investigated in detail. Under the optimal conditions, the linear range of the CTL intensity versus concentration of carbon tetrachloride was 4.7–235 μg/mL (R = 0.9944, n = 7), with a limit of detection of 0.7 μg/mL (σ = 3). GC/MS results suggest that the possible CTL mechanism of the reduction is the formation of CCl₃ radicals. The CCl₃ radicals combine with H free atoms or capture hydrogen atoms from H₂ molecules to form excited CHCl₃ intermediates, which decay from the excited-state to the ground giving CTL emission for the detection. It is also found that some benzene derivatives with α-H of branched-chain, such as toluene, ethylbenzene and xylenecan, can play a role of catalyst in the reaction.     

Reaction of α,α,ω-trichloroalkenes with 1,1,1-trichloroethane and 1,1,1,3-tetrachloropropane,accompanied by rearrangement of radicals

Conclusions In the reaction of CCl₃CH₃ with CCl₂=CHCH₂CH₂CH₂Cl, and of CCl₃CH₂CH₂Cl with CCl₂= CHCH₂Cl, initiated by Fe(CO)₅+DMF, the main addition products are respectively compounds of structure HCCl₂CH(CCl₂CH₃)CH₂CH₂CHCl₂ and HCCl₂CH(CCl₂CH₂CHCl₂)CH₂C1. The formation of these compounds was explained by the isomeriza'tion of the radical-adducts CCl₂CH(CCl₂CH₃)CH₂CH₂CH₂Cl and CCl₂CH(CCl₂CH₂CH₂Cl)CH₂Cl, with migration of a hydrogen atom from the CH₂Cl groups found in the 5 position to the radical center.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1857–1861, August, 1980.     

Structure-reactivity relationships in reactions of alkane radical cations: Study of the proton transfer from alkane radical cations to alkane molecules in γ-irradiated disordered CCl3F/alkane systems by ESR spectroscopy at cryogenic temperatures

A summary is presented of ESR results obtained in γ-irradiated disordered CCl₃F/alkane systems at cryogenic temperatures, with respect to proton-donor site selectivity in the proton transfer from alkane radical cations to alkane molecules. The nature of the alkyl radicals formed by proton transfer is indicative for the site of proton donation and is derived unambiguously from ESR results by comparison with powder spectra of authentic isomeric alkyl radicals, obtained by γ-irradiation of various chloro and bromoalkanes in perdeuterated cis-decalin. The experiments can be divided into two main classes. (i) Experiments on n-alkane radical cations in the extended all-trans conformation, i.e. ESR results on the system CCl₃F/heptane. The ESR spectrum of γ-irradiated CCl₃F/heptane consists of a triplet due to heptane radical cations in the extended all-trans conformation. In this conformation, the unpaired electron is delocalized over the carbon-carbon σ-bonds as well as the two chain-end carbon-hydrogen bonds that are in the plane of the C---C skeleton. Superimposed on the ESR triplet is a low-intensity spectrum due to heptyl radicals, which increases drastically with increasing heptane concentration. The formation of these heptyl radicals can be attributed unambiguously to proton transfer from heptane radical cations to heptane molecules, taking place in small heptane clusters to which positive-hole transfer still occurs efficiently. At the onset of proton transfer with increasing heptane concentration only primary heptyl radicals are present, clearly showing that the proton transfer takes place selectively from a chain-end position, in accordance with the electronic structure of the reacting radical cations. At higher heptane concentration secondary heptyl radicals also appear as a result of intermolecular radical-site transfer, i.e. the nature of the heptyl radicals becomes governed by their thermodynamic stability. (ii) Experiments on n-alkane radical cations in the gauche-at-C₂ conformation, i.e. ESR results on the system CCl₃F/octane. The ESR spectrum of γ-irradiated CCl₃F/octane indicates that octane radical cations are largely in the gauche-at-C₂ conformation in this matrix, with large unpaired-electron (and positive-hole) density on one planar chain-end C---H bond and one planar penultimate C---H bond at the other side of the radical cation. Careful investigation of ESR spectra with increasing octane concentration clearly reveals that in this case secondary octyl radicals are present from the very onset of proton transfer, in accordance with the electronic structure of the reacting radical cations. The results clearly point to proton-donor site selectivity in the proton transfer from alkane radical cations to alkane molecules and to a strict dependence of the site of proton donation on the electronic structure and conformation of the reacting radical cations.     

The reaction of cyclopentyl radicals with carbon tetrachloride

The photolysis of azocyclopentane in the presence of cyclopentane–carbon tetrachloride mixtures has been investigated in the gas phase. Product analysis data have been used to determine the Arrhenius parameters for the reactions The rate data for chlorine atom abstraction from CCl₄ by the cyclopentyl radical were compared with available data for other alkyl radicals in both the gas and the solution phases. The results indicate that the rate constant for chlorine atom abstraction in the gas phase is fairly insensitive to the nature of the attacking alkyl radical and that the activation energy for a secondary radical is about 4 kcal/mol higher than the corresponding reaction in the solution phase.     

Spectral,kinetics, and redox properties of the transients formed on one‐electron oxidation of 4,4′‐thiodiphenol: A pulse radiolysis study

The transient absorption bands (λ_max = 330, 525 nm, k_f = 5 × 10⁹ dm³ mol⁻¹ s⁻¹) obtained on pulse radiolysis of N₂O‐saturated neutral aqueous solution of 4,4′‐thiodiphenol (TDPH) are due to the reaction of TDPH with ^·OH radicals and are assigned to phenoxyl radical formed on fast deprotonation of the solute radical cation. The reaction of specific one‐electron oxidants (Cl₂^·−, Br₂^·−, N₃^·, TI²⁺, CCl₃OO^·) with TDPH also produced similar transient absorption bands. The phenoxyl radicals are also produced on pulse radiolysis of N₂‐saturated solution of TDPH in 1,2‐dichloroethane. The nature of transient absorption spectrum obtained on reaction of ^·OH radicals with TDPH is not affected in acidic solutions, showing that OH‐adduct is not formed in neutral solutions. The oxidation potential for the formation of phenoxyl radical is determined to be 0.98 V. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 603–610, 1999     

Vanadium Chloroperoxidases: The Missing Link in the Formation of Chlorinated Compounds and Chloroform in the Terrestrial Environment?

It is well established that the majority of chlorinated organic substances found in the terrestrial environment are produced naturally. The presence of these compounds in soils is not limited to a single ecosystem. Natural chlorination is also a widespread phenomenon in grasslands and agricultural soils typical for unforested areas. These chlorinated compounds are formed from chlorination of natural organic matter consisting of very complex chemical structures, such as lignin. Chlorination of several lignin model compounds results in the intermediate formation of trichloroacetyl‐containing compounds, which are also found in soils. These decay, in general, through a haloform‐type reaction mechanism to CHCl₃. Upon release into the atmosphere, CHCl₃ will produce chlorine radicals through photolysis, which will, in turn, lead to natural depletion of ozone. There is evidence that fungal chloroperoxidases able to produce HOCl are involved in the chlorination of natural organic matter. The objective of this review is to clarify the role and source of the various chloroperoxidases involved in the natural formation of CHCl₃.     

Abstraction of chlorine atoms from chloroalkanes. III. The kinetics of liquid phase reactions of trichlorosilyl radicals with chloromethanes

The kinetics of chlorine atom abstraction from the chloromethanes (ClM), CCl₄, CHCl₃, CH₂Cl₂, and CH₃Cl by radiolytically generated trichlorosilyl radicals was studied in the liquid phase by a competitive method. Arrhenius parameters of chlorine atom abstraction from chloromethanes relative to that of bromine atom abstraction from cyclohexyl bromide (RBr) were as follows: The error limits are two standard deviations (2σ) from least mean square Arrhenius plots. From the linear correlation between E_cl values derived from the reactions of SiCl₃ and cyclohexyl radicals with the ClM series it is estimated that E_cl (R + CH₃Cl) ? 16 kcal/mole. In addition the relative Arrhenius parameters for the hydrogen atom abstraction from SiHCl₃ and chlorine atom abstraction from CCl₄ by cyclohexyl radicals were obtained log A_H/A_cl = 0.12 ± 0.15 and E_H ? E_cl = 0.24 ± 0.26. The E_H ? E_cl value was combined with existing data on E(R + CCl₄) to yield the E_H(R + SiHCl₃) value.     

Kinetics and mechanism for the oxidation of 1,1,1-trichloroethane

The reaction mechanisms for oxidation of CH₃CCl₂ and CCl₃CH₂ radicals, formed in the atmospheric degradation of CH₃CCl₃ have been elucidated. The primary oxidation products from these radicals are CH₃CClO and CCl₃CHO, respectively. Absolute rate constants for the reaction of hydroxyl radicals with CH₃CCl₃ have been measured in 1 atm of Argon at 359, 376, and 402 K using pulse radiolysis combined with UV kinetic spectroscopy giving ??(OH + CH₃CCl₃) = (5.4 ± 3) 10^?12 exp(?3570 ± 890/RT) cm³ molecule^?1 s^?1. A value of this rate constant of 1.3 × 10^?14 cm³ molecule^?1 s^?1 at 298 K was calculated using this Arrhenius expression. A relative rate technique was utilized to provide rate data for the OH + CH₃ CCl₃ reaction as well as the reaction of OH with the primary oxidation products. Values of the relative rate constants at 298 K are: ??(OH + CH₃CCl₃) = (1.09 ± 0.35) × 10^?14, ??(OH + CH₃CClO) = (0.91 ± 0.32) × 10^?14, ??(OH + CCl₃CHO) = (178 ± 31) × 10^?14, ??(OH + CCl₂O) < 0.1 × 10^?14; all in units of cm³ molecule^?1 s^?1. The effect of chlorine substitution on the reactivity of organic compounds towards OH radicals is discussed.     

Mechanistic insights into the reaction of CF3CCl3 with SO3: Theory and experiment

Reaction mechanism of 1,1,1-trifluorotrichloroethane (CF₃CCl₃) and sulphur trioxide (SO₃) in the presence of mercury salts (Hg₂SO₄ and HgSO₄) was studied applying the density functional theory (DFT) at the UB3LYP/6-31+G(d,p) level. It was found that this reaction occurs in the free radical chain path as follows: mercury(I) sulphate free radical is generated by heat, causing CF₃CCl₃ to produce the CF₃CCl₂ free radical which reacts with SO₃ leading to the formation of CF₃CCl₂OSO₂ decomposing into CF₃COCl and SO₂Cl. The SO₂Cl free radical triggers CF₃CCl₃ to regenerate CF₃CCl₂ which recycles the free radical growth reaction. This elementary reaction has the highest energy barrier and it is therefore the rate control step of the whole reaction path. Experiment data can confirm the existence of the mercury(I) salt free radical and the free radical initiation stage. So, mercury salts play the role of initiators not that of catalysts. The results agree well with our hypothesis.