kinetics and mechanism for the thermal chlorination of chloroform in the gas phase: inclusion of hcl...

Kinetics and Mechanism forthe Thermal Chlorination ofChloroform in the GasPhase: Inclusion of HClElimination from CHCl3LI ZHU, JOSEPH W. BOZZELLI

Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, NJ 07102

Received 22 October 2002; accepted 17 July 2003

DOI 10.1002/kin.10159

ABSTRACT: HCl elimination from chloroform is shown to be the lowest energy channel forinitiation in the thermal conversion of chloroform to CCl4, with chlorine gas in the temper-ature range of 573–635 K. Literature data on this reaction is surveyed and we further estimateits 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 tem-perature using quantum RRK theory for k(E) and master equation analysis for fall-off. Thehigh-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 re-actions of 1CCl2 with itself, with CCl3, and with CHCl3 are incorporated in a detailed mecha-nistic analysis for the CHCl3 + Cl2 reaction system. Inclusion of these reactions does not sig-nificantly 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 rangeof 573–635 K; but Cl2, CHCl3, C2Cl6 species profiles are significantly different at elevated tem-peratures. 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 experimentaldata, is discussed. C© 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 647–660, 2003

INTRODUCTION

Several recent studies of CHCl3 conversion to CCl4in presence of chlorine have considered Cl2 dissocia-tion to two Cl atoms as the important chain initiationreaction [1]. We note that at least one dissociation re-action of chloroform has a lower reaction barrier and

Correspondence to: Joseph W. Bozzelli; e-mail: [email protected]© 2003 Wiley Periodicals, Inc.

endothermicity than that of Cl2 dissociation. Paths forchloroform decomposition include

CHCl3 → 1CCl2 + HCl

�Hrxn,298 = 56.9 kcal/mol (a)

CHCl3 → CHCl2 + Cl

�Hrxn,298 = 74.5 kcal/mol (b)

CHCl3 → CCl3 + H

�Hrxn,298 = 94.8 kcal/mol (c)

648 ZHU AND BOZZELLI

CHCl3 → 1CHCl + Cl2

�Hrxn,298 = 100.8 kcal/mol (d)

Data for chlorine molecules dissociation:

Cl2 + M → 2Cl + M �Hrxn,298 = 58.0

The �Hrxn are computed from the thermochemicalparameters presented in this article. Chloroform, be-ing a larger molecule than Cl2, will have its disso-ciation in the fall-off or high-pressure limit, whereCl2 will be in the low-pressure limit. A number ofresearchers have considered the pathways of chloro-form decomposition and reaction processes in chlo-roform conversion to CCl4. Semeluk and Bernstein[2] investigated the decomposition kinetics of gaseousCHCl3 and CDCl3 from 725 to 800 K in 1957.They did not consider HCl elimination, reaction(a), and they estimated a rate constant of 6.3 ×108 exp(−37.2 kcal/mol/RT ) s−1 for reaction (b). TheC Cl bond dissociation energy was estimated to be≤72 kcal/mol.

In 1957, Shilov and Sabirova [3] measured therate constant for CHCl3 → 1CCl2 + HCl at 758–923 Kas 2.63 × 1011 exp(−47 ± 2 kcal/mol/RT ) s−1. HCland C2Cl4 were the principal products, and smallamounts of C2Cl6 and C2HCl5 were observed. Shilovand Sabirova [4] concluded that the decompositiondoes not have a radical mechanism and that the firststep in the mechanism is the biradical CHCl3 →1CCl2 + HCl, which is the rate-determining step of thereaction.

Benson and Spokes [5] reported an Arrhenius pre-exponential A factor of 5.0 × 1013 s−1 with an Ea

greater than 56 kcal/mol for HCl elimination fromchloroform, which they studied in a very low-pressurepyrolysis apparatus. Schug et al. [6] also pointedout that the molecular elimination of HCl was thedominant path of CHCl3 pyrolysis, and the high-pressure limit rate constant was determined to be1.82 × 1014 exp(−54.49 kcal/mol/RT ) s−1 at 1050–1380 K. Herman et al. [7] examined pulsed CO2 lasermultiple-photon dissociation of CDCl3 in a molecu-lar beam and reported that the only observed CHCl3reaction channel was hydrogen chloride elimination(greater than 99.1%), with no evidence of simple chlo-rine atom cleavage (less than 0.9%).

In 1986, Chuang and Bozzelli [8] studied CHCl3reactions in H2 and in water vapor at 828–1473 K,where HCl, C(s), CH4, and C2H2 were observed as themajor products from the reaction of CHCl3 with H2.The primary products from the reaction of chloroformwith water vapor were identified as HCl, C(s), C2H2,

CO, and CO2. Taylor and Dellinger [9] evaluated thethermal degradation characteristics of the chlorinatedmethanes as pure compounds and within mixtures ofvarying Cl content as a function of waste feed com-position and fuel/air equivalence ratio. Results indi-cated chloroform was the most active molecule andchloromethane was the most stable under both py-rolytic and oxidative conditions. In 1992, Won andBozzelli [10] studied pyrolysis of 1% CHCl3 in 1 atmAr at 808–1073 K with residence time of 0.3–2 s. Theydeveloped a detailed mechanism containing 67 reac-tions and 31 species to describe the reaction system.The high-pressure limit rate constant for primary dis-sociation of CHCl3 → CCl2 + HCl was estimated as1.6 × 1014 exp(−56 kcal/mol/RT ) s−1.

Kumaran et al. [11] report the thermal decompo-sition of CHCl3 based on the laser schlieren densitygradient study in 101–365 torr Kr bath at a higher tem-perature range (1282–1878 K). They also applied twounimolecular rate theories (Troe and RRKM) usingab initio determinations, CCSD(T)/cc-pvDZ//MP2/6-31G(d), for both the transition states and molecules.The 〈�E〉down from Troe and RRKM calculations are787 and 850 cm−1, respectively. Their experimentalresults agree with RRKM theory calculations withan Ea of reaction (a) at 0 K of 56 kcal/mol, sug-gesting that the barrier for back reaction of (a) at0 K is 3.8 kcal/mol if �Hrxn,0K = 52.2 kcal/mol wasadopted. Their high-pressure limit rate constant byRRKM analysis was log10 k∞ (in s−1) = 15.21–58.97(kcal/mol)/(2.303 RT ).

H atom cleavage and molecular chlorine elimina-tions, reactions (c) and (d) in the chloroform reac-tions listed earlier, are of relatively low importance inchloroform decomposition because of the high barri-ers compared with reactions (a) and (b). The CCl3 Hbond is 94.8 kcal/mol. The barrier for a four-centeredelimination reaction of Cl2 from 1,2-dichloroethanehas been calculated as 93.4 kcal/mol at CBS-Q//B3LYP/6-31++G(d) level [12], or 89.8 kcal/molat PMP4(SDTQ,Full)/6-311++G(d,p)//MP2(FC)/6-31+G(d,p) level [13] (from reverse addition Ea =36.3 kcal/mol and other data provided in Ref. 13).

In 2000, Huybrechts et al. [1] published a paperon the thermal chlorination of chloroform in the gasphase, where they did not consider the HCl elimina-tion from chloroform. In this work, we want to add thisreaction plus several reactions related to the singlet andtriplet CCl2 to their mechanism, and observe the dif-ference in the modeling results relative to their exper-iments. We identify their mechanism as “HuybrechtsMechanism,” and the mechanism we present, whichincludes Huybrechts’ plus the added reactions, as“NJIT.”

THERMAL CHLORINATION OF CHLOROFORM IN THE GAS PHASE 649

KINETIC PARAMETERS OF CHCl3 ANDCCl2 REACTIONS

CHCl3 → 1CCl2 + HCl

We have calculated the rate constant of CHCl3 →1CCl2 + HCl using three different calculation methods.

The three different composite calculations forthe transition state energies of CHCl3 → CCl2 + HClare G3 (TS-a1), G3//MP2/6-311G(d,p) (TS-a2), andG3//B3LYP/6-311G(d,p) (TS-a3). The three calcu-lation levels for the optimized geometries of theseTS’s shown in Table I are HF/6-31G(d), MP2(FC)/6-311G(d,p), and B3LYP/6-311G(d,p). The bond dis-tances in the cleaving C H and C Cl bonds of the threeTS’s are 1.34, 1.32, 1.44, and 2.80, 2.71, 2.85 A, respec-tively. The corresponding frequencies are also listed.The calculated MP2/6-311G(d,p) frequencies for theTS of CHCl3 → 1CCl2 + HCl are in good agreementwith the frequencies at the CCSD(T)/cc-pvDZ//MP2/6-31G(d) level of Kumaran et al. [11]. The total energiescorrected by zero-point energies and thermal correc-tions are summarized in Table II. The �H ◦

f,298 for tran-sition states TS-a1, TS-a2, and TS-a3 are determinedfrom �H ◦

f,298 of CHCl3 plus the calculated total energydifferences between the TS and CHCl3 at the respectivelevels. S◦

298 and C◦p (T) of TS-a1, TS-a2, and TS-a3 are

calculated from vibrational frequencies and momentsof inertia at corresponding level using “SMCPS” pro-gram [15].

Table III lists the thermochemical properties of thespecies involved in this study. We use the thermochem-ical properties available in Huybrechts mechanism inthis study, since they are close to our own data, andthis avoids differences in model predictions because ofdifferences in thermochemical parameters. The valuesfor species not considered in Huybrechts mechanismare calculated in this study or taken from literature asnoted in Table III.

The high-pressure limit rate constant of CHCl3 →1CCl2 + HCl in three-parameter Arrhenius expressionis then determined from the above thermochemical pa-rameters using canonical transition state analysis in a“THERMKIN” [15] code. The results over a tempera-ture range of 300–2000 K are as follows:

1.20 × 1013T 0.516 exp(−58.1 kcal/mol/RT )

at the G3 level

2.14 × 1012T 0.731 exp(−57.2 kcal/mol/RT )

at G3//MP2/6-311G(d,p) level

9.09 × 1011T 0.941 exp(−57.1 kcal/mol/RT )

at G3//B3LYP/6-311G(d,p) level

Application of these three rate constants separatelyin the NJIT mechanism shows that the three methodsgave very similar results; the G3//B3LYP/6-311G(d,p)result is chosen.

CHCl3 → 1CCl2 + HCl is determined to be themost important channel for decomposition of chlo-roform at low to moderate temperature; the bar-rier of ∼57 kcal/mol from the above calculations is∼16 kcal/mol lower than that of the Cl atom elimina-tion reaction. The �Erxn of CHCl3 → 1CCl2 + HCl is56.3 kcal/mol at 298 K by “THERMKIN” [15], whichresults in an activation energy for the reverse insertionreaction to be 0.8 kcal/mol at 298 K. By adopting the(�H ◦

f,298 − �H ◦f,0) as 0.3 [26], −1.2 [16], and −0.8

[16] kcal/mol for 1CCl2, HCl, and CHCl3 respectively,we estimated the �Hrxn for CHCl3 → 1CCl2 + HClat 0 K to be 56.2 kcal/mol. This value suggests thatthe reverse insertion barrier at 0 K is also around 0.9kcal/mol. Although the barrier of 56 kcal/mol (0 K)from Kumaran et al. [11] is only 0.2 kcal/mol lower thanours, they adopted �Hrxn,0K as 52.2 kcal/mol (impliedby JANAF [30] and Kohn et al. [29]), which results intheir insertion barrier (reverse reaction) of 3.8 kcal/molat 0 K.

Our calculated high-pressure limit rate constantsfor CHCl3 → 1CCl2 + HCl at three levels are com-pared with that of Kumaran et al. [11] in Table IV,which shows that the values are in good agreement. Theabove high-pressure limit rate constant for CHCl3 →1CCl2 + HCl at G3//B3LYP/6-311G(d,p) level is usedas input to a kinetic analysis [31,32] for decomposi-tion of CHCl3 as functions of temperature and pres-sure (Table V). For this multichannel system, this anal-ysis uses quantum Rice–Ramsperger–Kassel (QRRK)analysis for k(E) and master equation for fall-off; theoutputs are listed as R11 to R14 in the NJIT mechanism(Table VI).

The uncertainty of the HCl elimination barrier fromchloroform is ±1.5 kcal/mol from variations in dataof Table IV. We have tried the upper and lower limitsof this rate constant in our mechanism and the modelresults are indistinguishable.

The enthalpy change for the three-centered Cl2molecular elimination CHCl3 → 1CHCl + Cl2 [reac-tion (d)] is high, 100.8 kcal/mol, where �H ◦

f,298 of1CHCl is 76.1 [17] kcal/mol. The transition state struc-ture for this reaction is obtained at B3LYP/6-31G(d,p)level in this study (TS-b in Table I). The activationenergy for this Cl2 elimination is 107.5 kcal/mol atCBS-Q//B3LYP/6-31G(d,p) level. This results in anEa for the reverse reaction, 1CHCl insertion to Cl2,of 6.7 kcal/mol, and indicates that the reverse reac-tion will occur, should 1CHCl be present. CHCl3 →1CHCl + Cl2 is considered in NJIT mechanism


Table I Geometries of Transition States

Transition States and Bond Length Bond Angle Dihedral Angle FrequencyCalculation Levels Structure (A) (degree) (degree) (cm−1)

TS-a1: CHCl3 r21 1.645 −135 1007→ 1CCl2 + HCl r31 1.645 〈312 119.88 65 1061

r41 2.910 〈412 118.37 〈4123 −159.14 269 1475HF/6-31G(d) freq r51 1.173 〈512 119.78 〈5123 −171.60 388 1915

for G3 method 739


r41 2.711 〈412 110.86 〈4123 −127.35 186 1178MP2(FC)/6-311G(d,p) r51 1.323 〈512 117.44 〈5123 −145.86 367 1342

658

CHCl3 → 1CCl2 + −520 774HCl at CCSD(T)/ 85 885cc-pvDZ//MP2/6- 176 114831G(d) (Ref. [11]) 343 1253

587 (scaled)


r41 2.853 〈412 115.01 〈4123 136.79 152 1039B3LYP/6-311G(d,p) r51 1.441 〈512 118.63 〈5123 148.36 346 1057

712

TS-b: CHCl3 r21 1.754 −265 707→ 1CHCl + Cl2 r31 2.278 〈312 107.53 58 853

r43 2.100 〈431 99.66 〈4312 −104.98 149 1149B3LYP/6-31G(d,p) r51 1.115 〈512 104.54 〈5123 89.56 197 2899

386

r21 2.591 −775 378TS-c: CCl2 r31 1.774 〈312 109.29 5 474

+ CHCl3 →C2HCl5 r41 1.766 〈412 106.12 〈4123 121.92 70 568r51 1.761 〈512 102.15 〈5123 −119.56 93 757

B3LYP/6-31G(d,p) r62 1.725 〈621 105.04 〈6213 −151.58 129 784r72 1.722 〈721 103.46 〈7213 88.20 150 792r82 1.172 〈821 21.39 〈8213 −33.00 270 856

276 1371335 2255

TS-d: C2HCl5 r21 1.481 −939 384→ C2Cl4 + HCl r31 1.780 〈312 114.93 35 598

r41 1.780 〈412 114.94 〈4123 −132.68 96 674B3LYP/6-31G(d,p) r51 1.172 〈512 97.41 〈5123 113.67 139 805

r62 1.687 〈621 121.30 〈6213 153.30 189 811r72 1.687 〈721 121.29 〈7213 −20.74 190 1009r85 1.891 〈851 142.88 〈8512 0.07 236 1217

307 1226327 1938

TS-e: CCl4 r21 1.713→ 1CCl2 + Cl2 r31 1.714 〈312 116.06 −455 278

r41 2.499 〈412 120.73 〈4123 173.88 59 342B3LYP/6-31G(d,p) r54 2.460 〈541 61.41 〈5412 −87.62 116 671

127 837186


Table II Total Energies at 298 Ka

//B3LYP/6-31G(d,p)

Species B3LYP/6-31G(d,p) B3LYP/6-311+G(3df,2p) QCISD(T)/6-31+G(d′) CBS-Q ZPVEb,c H298 − H0c

CHCl3 −1419.25545 −1419.37254 −1417.44351 −1417.86388 12.23 3.401CCl2 −958.37477 −958.45962 −957.14528 −957.425 2.46 2.753CCl2 −958.34797 −958.43218 −957.11436 −957.39220 2.71 2.74HCl −460.79088 −460.82847 −460.20395 −460.34379 4.14 2.071CHCl −498.74738 −498.79891 −498.06919 −498.24212 6.88 2.43Cl2 −920.34526 −920.41945 −919.20513 −919.45598 0.73 2.21C2HCl5 −2377.72654 −2377.92453 −2374.69475 −2375.40569 17.62 5.61C2Cl4 −1916.92692 −1917.09164 −1914.46518 −1914.44467 9.43 4.67CCl4 −1878.83854 −1878.99192 −1876.48155 −1877.01446 5.73 4.13TS-b −1419.08864 −1419.21412 −1417.26424 −1417.69263 8.97 3.97TS-c −2377.61100 −2377.81172 −2374.57056 −2375.28240 13.36 6.24TS-d −2377.64579 −2377.84627 −2374.59285 −2375.30580 14.28 5.86TS-e −1878.66851 −1878.82106 −1876.28139 −1876.80943 3.67 4.75

G3 G3//MP2/6-311G(d,p) G3//B3LYP/6-311G(d,p)

CHCl3 −1418.82321 −1418.82333 −1418.82292TS-a −1418.73088 −1418.73341 −1418.734101CCl2 −958.08118 −958.08110 −958.08066HCl −460.65121 −460.65110 −460.65123

aTotal energies (ZPVE and thermal corrections are included) in hartree, 1 hartree = 627.51 kcal/mol.bScaled by 0.9806 (Ref. [14]).cIn units of kcal/mol.

although it will not be important because of the highbarrier.

Abstraction of a Cl atom in CHCl3 by Cl is listed asR15 in Table VI; the CHCl3 + Cl → HCl + CCl3 ab-straction reaction has been considered by Huybrechtset al.

Reactions of 1CCl2

Two 1CCl2 molecules can combine to form C2Cl4. Thehigh-pressure limit association rate constant is esti-mated as 9.12 × 1012 cm3/(mol s), using the genericreaction, CHCl2 + CHCl2 association [19]. The in-put parameters of QRRK-master equation calculationfor 1CCl2 + 1CCl2 association are shown in Table Vand the result of this calculation is listed as R16 inTable VI. We have also used the termolecular rate con-stant, 1CCl2 + 1CCl2 + Kr → C2Cl4 + Kr as 1.26 ×1015 exp(12.6 kcal/mol/RT ), reported by Kumaranet al. [11] from a RRKM analysis and have obtainedthe same model results (not shown).

1CCl2 can also associate with CCl3 to form C2Cl5(�Hrxn = −63 kcal/mol) and the activated C2Cl∗5 canundergo �-scission to C2Cl4 + Cl with a low barrier of12 kcal/mol (relative to the stabilized C2Cl5 adduct).The input for the QRRK-master equation calculation

and the pressure- and temperature-dependent resultsare shown in Tables V and VI, respectively. C2Cl5 canassociate with Cl to form C2Cl6 or abstract Cl from Cl2to also form C2Cl6, both of which are included in theNJIT mechanism.

Another path for 1CCl2 is insertion reaction to chlo-roform, 1CCl2 + CHCl3 → C2HCl5; the TS geometryfrom B3LYP/6-31G(d,p) calculation is shown as TS-cin Table I. The activation energy (10.3 kcal/mol) of thisreaction is higher than the zero barrier for recombina-tion reactions of 1CCl2 + 1CCl2 and 1CCl2 + CCl3. The1CCl2 insertion to CHCl3 and subsequent reactions ofthe products are included in the NJIT mechanism.

The four-centered molecular HCl elimination fromC2HCl5 is calculated at CBS-Q//B3LYP/6-31G(d,p)level (TS-d in Table I). Our result for the Ea, 62.7kcal/mol, is 3 kcal/mol higher than the data by Bensonand Weissman (59.7 [38]) and our preexponential Afactor at 500 K, 0.98 × 1014 cm3/(mol s), is close totheir value (1.26 × 1014 for 300–700 K).

Cl2 elimination from CCl4 resulting in 1CCl2 iscalculated at B3LYP/6-31G(d,p) level and is shownas TS-e in Table I. The Ea of this reaction is high,128.5 kcal/mol at CBS-Q//B3LYP/6-31G(d,p), whichis expected from our evaluations of the Cl2 eliminationreactions of chloroform and 1,2-dichloroethane [12].


Table III Standard Gas-Phase Thermochemical Propertiesa ,b

C◦p (K)

Species �H◦f,298 S◦

298 300 400 500 600 800 1000 1500 Note

Cl2 0.0 53.30 8.12 8.37 8.58 8.73 8.88 Huybrechts et al. [1]HCl −22.1 44.70 6.99 6.99 7.02 7.09 7.31 Huybrechts et al. [1]CHCl3 −24.7 70.80 15.29 17.20 18.77 19.98 21.38 Huybrechts et al. [1]CCl4 −22.2 73.80 20.06 21.71 22.98 23.85 24.45 Huybrechts et al. [1]C2Cl6 −33.2 95.20 32.96 35.99 38.35 40.05 41.45 Huybrechts et al. [1]Cl 29.0 39.50 5.23 5.33 5.40 5.43 5.37 Huybrechts et al. [1]CCl3 18.0 71.20 15.32 16.57 17.55 18.23 18.77 Huybrechts et al. [1]H 52.1 27.39 4.97 4.97 4.97 4.97 4.97 4.97 4.97 Ref. [16]1CHCl 76.1 56.19 8.83 9.50 10.07 10.54 11.28 11.83 12.70 Ref. [17] and DFT freq calc. [18]1CCl2 54.3c 63.51 11.21 12.09 12.63 12.97 13.35 13.54 13.74 Ref. [17] and DFT freq calc. [18]3CCl2 77.4 65.29 10.95 11.80 12.37 12.76 13.21 13.44 13.69 Ref. [17] and DFT freq calc. [18]CHCl2 20.8 64.98 11.03 12.20 13.10 13.77 14.71 15.37 16.38 DFT calc. [19]C2HCl3 −4.2 77.73 19.24 21.80 23.68 25.07 26.95 28.16 29.83 Refs. [20] and [21]C2Cl4 −5.8 81.48 22.71 25.09 26.71 27.84 29.26 30.05 30.96 Ref. [22] and DFT freq calc. [18]C2Cl3 54.4 78.31 18.62 20.45 21.69 22.57 23.70 24.35 25.11 Ref. [22] and DFT freq calc. [18]C2Cl2 53.9 65.92 15.96 16.88 17.53 18.03 18.76 19.28 20.01 Ref. [24]CHCl2C·Cl2 6.6 90.65 23.88 26.74 28.78 30.23 32.15 33.31 34.89 Refs. [21] and [25]C2Cl5 9.1 95.83 27.16 30.18 32.05 33.17 34.35 35.36 35.97 Refs. [21] and [25]C2HCl5 −37.3 91.25 28.25 31.99 34.55 36.38 38.75 40.21 42.03 Refs. [20] and [21]TS-a1 33.2 76.71 15.36 17.09 18.48 19.55 21.00 21.85 22.87 G3TS-a2 32.5 76.09 15.73 17.60 19.03 20.09 21.45 22.21 23.07 G3//MP2/6-311G(d,p)TS-a3 32.4 77.13 16.14 18.17 19.64 20.65 21.87 22.52 23.23 G3//B3LYP/6-311G(d,p)TS-b 82.8 78.82 16.83 18.19 19.17 19.88 20.87 21.55 22.54 CBS-Q//B3LYP/6-31G(d,p)TS-c 40.7 102.92 29.54 32.53 34.55 25.99 27.84 38.96 40.33 CBS-Q//B3LYP/6-31G(d,p)TS-d 25.4 95.78 28.11 31.29 33.60 35.29 37.49 38.77 40.28 CBS-Q//B3LYP/6-31G(d,p)TS-e 105.8 87.76 20.46 21.57 22.25 22.58 23.15 23.39 23.64 CBS-Q//B3LYP/6-31G(d,p)

a�H ◦f,298 in kcal/mol; S◦

298 and C◦p (T ) in cal/(mol K).

bSpecies in bold are new species introduced in NJIT mechanism.cOther literature on �H ◦

f,298 of 1CCl2 are 54.7 ± 1.0 [26], 57.0 [27], 52.1 ± 3.4 [28], and 51.0 ± 2.0 [29] kcal/mol.

The Ea of reverse reaction, 1CCl2 insertion to Cl2, is51.5 kcal/mol. This reaction is included in the mech-anism although it is not important because of its highbarrier. The rate constant of R35 in Table VI is obtained

Table IV Comparison for the Rate Constant of CHCl3 → 1CCl2+ HCl

k (s−1) atMethod Source Rate Expression (s−1) T = 1600 Ka

Chemmaster with TS by G3 This work 6.88 × 1039 × T −8.4 exp(−64.5 kcal/mol/RT )b 1.04 × 104

Chemmaster with TS by This work 7.24 × 1039 × T −8.4 exp(−63.9 kcal/mol/RT )b 1.24 × 104

G3//MP2/6-311G(d,p)Chemmaster with TS by This work 5.23 × 1040 × T −8.7 exp(−63.9 kcal/mol/RT )b 1.50 × 104

G3//B3LYP/6-311G(d,p)Fit of experimental data Kumaran et al. [11] 3.98 × 1016 exp(−44.7 kcal/mol/RT ) × [M], 3.07 × 104

[M] ≈ 10−6 mol/cm3c

aThis temperature is chosen since the mechanism of Kumaran et al. is for the range of 1282–1878 K.bSingle channel Chemmaster [31,32] at 300–2000 K and 0.13 atm, using �Edown = 1000 cm−1. If using �Edown = 850 cm−1, the resulting

k will be ∼10% lower.cAt 1651 K and 101.6 torr; see Table II of Ref. 11.

from a “THERMKIN” [15] code using theoretical cal-culation data as input. The Cl2 elimination reactionsfrom C2Cl4, C2Cl5, and C2Cl6 are estimated to havehigh barrier and are not included in our modeling.


Table V Input Parameters for the QRRK-Master Equation Analysisa (k = A × T n exp(−Ea/RT) Between 300 and 2000 K)

A∞ (in cm3, mol−1, s−1) n Ea (kcal/mol)

Set I: CHCl3 dissociation reactions1 CHCl3 → 1CCl2 + HCl 9.09E+11 0.941 57.12 CHCl3 → CHCl2 + Cl 2.92E+15 0 70.83 CHCl3 → CCl3 + H 1.58E+15 0 93.64 CHCl3 → 1CHCl+Cl2 6.86E+12 0.788 107.8

286.4 (×3.372), 931.3 (×4.449), 2836.6 (×1.179)b

σ = 5.389 A, e/k = 340.2 Kc

Set II: 1CCl2 + 1CCl2 chemical activation1 1CCl2 + 1CCl2 → C2Cl4 9.12E+12 0 0

−1 C2Cl4 → 1CCl2 + 1CCl2 1.03E+17 0 109.72 C2Cl4 → C2Cl3+Cl 2.43E+14 0 86.6

316.2 (×8.203), 990.8 (×3.285), 1893.6 (×0.511)b

σ = 5.64 A, e/k = 541.9 Kc

Set III: C2Cl3 dissociation reactions1 C2Cl3 → C2Cl2+Cl 2.57E+14 0 26.2

368.3 (×6.591), 1117.5 (×1.86), 1848.1 (×0.549)b

σ = 4.76 A, e/k = 450 Kc

Set IV: 1CCl2+CCl3 chemical activation reactions1 1CCl2+CCl3 → C2Cl5 5.37E+12 0 0

−1 C2Cl5 → 1CCl2+CCl3 2.37E+15 0 58.92 C2Cl5 → Cl + C2Cl4 4.78E+13 0 12.1

100.7 (×4.510), 568.9 (×9.400), 1912.6 (×0.590)b

σ = 6.14 A, e/k = 556.0 Kc

Set V: 1CCl2+CHCl3 chemical activation reactions1 1CCl2 + CHCl3 → C2HCl5 0.202 2.289 10.3

−1 C2HCl5 → 1CCl2+CHCl3 2.06E+12 1.218 77.92 C2HCl5 → C2Cl4 + HCl 1.78E+11 1.016 62.73 C2HCl5 → CHCl2CCl2 + Cl 3.07E+16 0 70.44 C2HCl5 → CHCl2 + CCl3 2.61E+16 0 70.4

227.9 (×8.373), 401.0 (×3.613), 1500.2 (×5.514)b

σ = 6.14 A, e/k = 556.0 Kc

Set VI: Cl2 dissociation reaction1 Cl2 (+M) → Cl + Cl (+M) 8.71E+15 0 55.9

561.1 (×1) from JANAF [16]σ = 5.389 A, e/k = 340.2 Kc

I1: From transition state study (TST) using G3//B3LYP/6-311G(d,p) calculation levels, see text; I2: Via I−2 and microscopic reversibility(MR); AI-2 = 5.70E+13 and EaI-2 = 0 [19]; I3: Via I−3 and MR, AI-3 = 1.20E+14 and EaI-3 = 0 [35]; I4: From transition state study (TST)using CBS-Q//B3LYP/6-31G(d,p) calculation levels, see text; II1: km from the analysis for CHCl2 + CHCl2 recombination [19]; II−1: Via II1

and MR; II2: Via II−2 and MR; AII-2 = 7.24E+11 and EaII-2 = 0 from the analysis for Cl + chloro vinyl radical recombination [19]; III1: ViaIII−1 and MR, AIII-1 = 6.92E+13 and EaIII-1 = 0 from the analysis for Cl + 1,2-dichloroethene addition [19]; IV1: AIV1 taken as CHCl2 + CCl3

and EaIV1 = 0 [19]; IV−1: Via IV1 and MR; IV2: Via IV−2 and MR; AIV-2 = 3.47E+13 and EaIV-2 = 0 [19]; V1, V−1, V2: all from TST usingCBS-Q//B3LYP/6-31G(d,p) calculations; V3: Via V−3 and MR; V−3 from the analysis for Cl + chloromethyl radical recombination [19]; V4:Via V−4 and MR; V−4 from the analysis for chloromethyl + chloromethyl radical recombination [19]; VI1: From Huybrechts et al. [1].

a�Edown = 1000 cal/mol.bThree reduced frequency sets (frequency in cm−1, degeneracy) from CPFIT [33].cLennard–Jones parameters [34].

The rate constant of Cl + 1CCl2 ↔ CCl3 is esti-mated as 5.70 × 1013 cm3/(mol s) from Cl + CHCl2using the trends of rate constants of chlorinated hy-drocarbons [19]. The interconversion between 1CCl2and 3CCl2 and the subsequent abstraction reaction3CCl2 + Cl2 → CCl3 + Cl are also considered.

Comparisons of our calculated forward rate con-stants of CHCl3 ↔ CCl2 + HCl (R11) and CHCl3 ↔CHCl2 + Cl (R12) with the rate constant recommendedby Huybrechts et al. for Cl2 + M → 2Cl + M (R1) areshown in Figs. 1a and 1b. The QRRK-calculated rateconstant of Cl2 + M → 2Cl + M (R1′) is also shown


Table VI Kinetics Model for CHCl3 + Cl2 Systema

A Ea

Reactions (in cm3, mol−1, s−1) n (kcal/mol) Reference

Cl2 + M → 2Cl + M (R1) 8.71E+15 0 55.85 Huybrechts et al. [1]2Cl + M → Cl2 + M (R2) 1.29E+12 0 −1.63 Huybrechts et al. [1]Cl + CHCl3 → HCl + CCl3 (R3) 5.37E+12 0 3.65 Huybrechts et al. [1]HCl + CCl3 → Cl + CHCl3 (R4) 2.40E+11 0 11.79 Huybrechts et al. [1]CCl3 + Cl2 → CCl4 + Cl (R5) 5.01E+11 0 5.10 Huybrechts et al. [1] Huybrechts

MechanismCCl4 + Cl → CCl3 + Cl2 (R6) 6.01E+13 0 15.66 Huybrechts et al. [1]

CCl3 + Cl → CCl4 (R7) 7.24E+13 0 0 Huybrechts et al. [1]CCl4 → CCl3 + Cl (R8) 6.61E+16 0 68.04 Huybrechts et al. [1]CCl3 + CCl3 → C2Cl6 (R9) 4.68E+12 0 0 Huybrechts et al. [1]C2Cl6 → CCl3 + CCl3 (R10) 2.51E+17 0 67.09 Huybrechts et al. [1]CHCl3 ↔ 1CCl2 + HCl (R11) 5.84E+40 −8.7 63.9 Table V (I)b

CHCl3 ↔ CHCl2 + Cl (R12) 1.03E+40 −10.9 72.3 Table V (I)b

CHCl3 ↔ CCl3 + H (R13) 2.43E+26 −10.3 94.4 Table V (I)b

CHCl3 ↔ 1CHCl + Cl2 (R14) 7.15E+16 −9.3 108.5 Table V (I)b

CHCl3 + Cl ↔ CHCl2 + Cl2 (R15) 1.33E+14 0 20.2 Ref. [25]1CCl2 + 1CCl2 ↔ C2Cl4 (R16) 2.72E+54 −14.2 9.2 Table V (II)b

1CCl2 + 1CCl2 ↔ C2Cl3 + Cl (R17) 2.69E+21 −2.6 3.2 Table V (II)b

C2Cl4 ↔ C2Cl3 + Cl (R18) 4.36E+31 −5.5 91.7 Table V (II)b

C2Cl4 + Cl ↔ C2Cl3 + Cl2 (R19) 1.78E+14 0 29.6 Ref. [25] NJITMechanismC2Cl3 ↔ C2Cl2 + Cl (R20) 4.87E+35 −7.9 29.2 Table V (III)b

1CCl2 + CCl3 ↔ C2Cl5 (R21) 1.66E − 04 −1.2 −0.6 Table V (IV)b

1CCl2 + CCl3 ↔ C2Cl4 + Cl (R22) 6.51E+12 0 0.0 Table V (IV)b

C2Cl5 ↔ C2Cl4 + Cl (R23) 9.31E+22 −4.3 10.7 Table V (IV)b

C2Cl5 + Cl ↔ C2Cl6 (R24) 3.66E+13 0 0.0 Ref. [19]C2Cl6 + Cl ↔ C2Cl5 + Cl2 (R25) 2.66E+14 0 15.6 Ref. [25]1CCl2 + CHCl3 ↔ C2HCl5 (R26) 9.73E+49 −14.4 23.4 Table V (V)b

1CCl2 + CHCl3 ↔ C2Cl4 + HCl (R27) 1.08E+09 −0.9 16.2 Table V (V)b

1CCl2 + CHCl3 ↔ CHCl2CCl2 + Cl (R28) 4.58E+07 −0.2 16.0 Table V (V)b

1CCl2 + CHCl3 ↔ CHCl2 + CCl3 (R29) 3.38E+07 −0.1 16.0 Table V (V)b

C2HCl5 ↔ C2Cl4 + HCl (R30) 9.27E+38 −7.8 70.8 Table V (V)b

C2HCl5 ↔ CHCl2CCl2 + Cl (R31) 1.82E+54 −12.2 80.9 Table V (V)b

C2HCl5 ↔ CHCl2 + CCl3 (R32) 1.91E+54 −12.2 81.0 Table V (V)b

CHCl2CCl2 ↔ C2HCl3 + Cl (R33) 1.49E+14 0 16.4 Ref. [19]C2HCl5 + Cl ↔ C2Cl5 + HCl (R34) 5.78E+12 0 4.1 Ref. [36]CCl4 ↔ 1CCl2 + Cl2 (R35) 1.98E+15 0.4 128.5 b

Cl + 1CCl2 ↔ CCl3 (R36) 5.70E+13 0 0.0 Ref. [19]3CCl2 + M ↔ 1CCl2 + M (R37) 1.00E+13 0 0.0 Estimatedc

3CCl2 + Cl2 ↔ CCl3 + Cl (R38) 6.89E+11 0 0.0 Ref. [25]1CCl2 + Cl ↔ CCl3 + Cl2 (R39) 7.83E+12 0 0.6 Ref. [37]Cl2(+M) ↔ 2Cl (+M) (R1′) 1.21E+17 −2.8 56.0 Table V (VI)b

aReactions R1–R10 are irreversible (from Huybrechts et al. [1]); reactions in bold (with double arrows ↔) are reversible, the reverse rateconstants are calculated from thermodynamic and microscopic reversibility.

bThis study, for 0.1 atm and 300–2000 K.cR37 is written in exothermic (∼−23 kcal/mol) direction.

in these two figures. At a pressure of 0.1 atm (Fig. 1a),the HCl molecular elimination for CHCl3 is faster thanthe Cl elimination from CHCl3 and the Cl2 dissociationover the temperature range of 500–2000 K. Compar-isons of these three reactions at different pressures and600 K (Fig. 1b) show that the HCl molecular elim-ination is faster than other paths between 10−5 and100 atm.

MODEL COMPARISON TO EXPERIMENT

The complete NJIT mechanism for the chlorination ofchloroform is listed in Table VI. Reactions 1–10 orig-inate from Huybrechts et al. [1]. Reactions 11–38 arethe results of our QRRK-master equation calculations,from theoretical calculations, and in some cases esti-mations from generic reactions.


Figure 1 Comparison of rate constants for reactions R1, R11, R12, and R1′ (Table VI) at different temperatures and pressures.(a) k vs. T (K) at 0.1 atm; (b) k vs. pressure at 600 K.

We use the CHEMKIN II [39] program with mi-croscopic reversibility (MR) for all reactions in themechanism; Huybrechts used separate reverse reac-tions. The thermochemical properties in Table IV areused to determine the reverse rate constants of reac-tions R11–R38. The modeling conditions are takenas the experimental conditions of Huybrechts et al.[1], i.e. various CHCl3/Cl2 ratios at 573, 615, and635 K. The modeling results on Cl2 profiles fromthe NJIT mechanism are compared and show goodagreement with the experimental data of Huybrechtset al. [40]. In Fig. 2a we note that this mechanismanalysis does not include the chain-branching re-action of 1CCl2 + Cl2 ↔ CCl3 + Cl (see discussionbelow).

For comparison, we also show the Huybrechtsmechanism results in Fig. 2b. This figure is almostidentical to Fig. 2a, which suggests that the amendedreactions R11–R38 in the NJIT mechanism do not alterthe product distribution profiles under the experimentalconditions of Huybrechts et al., i.e. 0.038–0.251 atmand 573–635 K.

The reason for the near complete lack of any dif-ference in the two mechanisms lies in the secondaryreactions of the products from chloroform dissocia-tion. HCl elimination from CHCl3 is the lowest en-ergy and highest rate initiation channel in this chlori-nation of CHCl3. It is about three orders of magnitudefaster in the temperature range (575–635 K) than thesecond-order Cl2 dissociation (Cl2 + M → 2Cl + M,Ea = 58 kcal/mol) as shown in Fig. 1. The singlet1CCl2 diradical and the HCl products are, however, notactive species compared to Cl radical. We consider, inthis analysis, that the singlet 1CCl2 undergoes insertion,but not abstraction. Singlet 1CCl2 needs ∼23 kcal/mol(endothermic) to form triplet 3CCl2 where the tripletwill readily undergo conventional radical abstractionwith Cl2,

3CCl2 + Cl2 → CCl3 + Cl

resulting in chain propagation.Considering no abstraction reactions by the sin-

glet 1CCl2, the chloroform dissociation to 1CCl2 + HCl


requires 56 kcal/mol and 1CCl2 conversion to 3CCl2needs 23 kcal/mol resulting in 79 kcal/mol for chainpropagation to occur. This is 23 kcal/mol higher thanthe Cl2 + M → 2Cl + M reaction and providing theassumption that 1CCl2 does not abstract from Cl2, theHCl elimination channel is not important in chlorinat-ing chloroform at the temperatures and pressures ofHuybrechts experiments.

The concentration of chloroform is higher than Cl2in some cases, and 1CCl2 can undergo insertions withchloroform to form C2HCl5 and then eliminate HCl toC2Cl4. This overall process is, however, a chain termi-nation and Cl2 + M → 2Cl + M is the most importantreaction as predicted by Huybrechts et al. with the notabstraction assumption.

1CCl2 Abstraction of Cl from Cl21CCl2 is a singlet diradical with one empty orbital,and singlets are usually considered to undergo insertion

(a)

Figure 2 (a) Comparison of NJIT model (lines) versus experimental data of Huybrechts et al. (points) for Cl2 profiles with timeat varied total pressure (CHCl3 + Cl2); (b) Comparison of Huybrechts et al. model (lines) versus experiment (points) at variedtotal pressure (CHCl3 + Cl2); (c) NJIT model results (lines) including 1CCl2 + Cl2 → CCl3 + Cl (R39) versus experiment(points) at varied total pressure. Note poor agreement and change from Fig. 2a.

(Continued )

reactions. We have analyzed 1CCl2 insertion into HCl,Cl2, and CHCl3 where barriers of 0.8, 51.5, and 10.3kcal/mol were calculated, respectively (see earlier).

It is possible that 1CCl2 will undergo abstractionas the singlet may have some diradical character. In-deed, Kostina et al. [37] have recently reported ex-perimental results on the reaction of CCl2 + Cl2 →Cl3 + Cl. Their rate constant for this abstraction isdetermined by monitoring the CCl2 loss in a flowreactor with laser/photoionization mass spectrometryrepresenting a near barrierless rate constant, 7.83 ×1012 exp(−0.558 kcal/mol/RT ). If we put this reaction(R39) into our mechanism with 1CCl2 as the abstract-ing species, the modeling results for [Cl2] decay areso fast, due to the chain propagation, that the modelprediction for [Cl2] profiles has no similarity with theexperimental data of Huybrechts et al. [1] (Fig. 2c).The chain propagation effects immediate conversionof Cl2 and chloroform. The results with the abstractionpath clearly indicate a major discrepancy between the


(b)

(c)

Figure 2 (Continued ).


model and the experimental data. This leaves the cur-rent manuscript with a need for further work. Whichis correct—Huybrechts data and mechanism, or use ofKnyazev’s rate constant for singlet CCl2 + Cl2? Oneanswer to this problem is that the CHCl3 dissociationbarrier is ca. 10 kcal/mole higher than that reportedhere and in the several other studies referenced; thiswould make the Cl2 dissociation dominant, as in theHuybrechts mechanism. We feel that the significantnumber of literature studies on the CHCl3 dissocia-tion refute this possibility. We look forward to morescientific studies on this abstraction reaction and thechloroform—chlorine reaction system in the future.

MODELING COMPARISON OF SPECIESPROFILES (ASSUMPTION: 1CCl2 DOESNOT ABSTRACT Cl FROM Cl2)

It is seen from Figs. 2a (NJIT mechanism) and 2b(Huybrechts mechanism) that the HCl elimination fromchloroform channel (R11) and subsequent reactions(R12–R38) have little effect on the Cl2 profiles in thetemperature range of 573–635 K. The effects on otherproduct profiles, such as CHCl3, HCl, CCl4, C2Cl6,Cl, and CCl3, are also small (not shown); the absolutedifferences between two mechanisms in mole fractionare less than 10% at concentrations and times of theexperimental data. At a somewhat elevated tempera-ture, such as 773 K, data shown in Figs. 3a–3c indi-cate that the inclusion of reactions R11–R38 results insignificant differences between predictions of the twomechanisms. Figures 3a–3c show species profiles ofthe same reaction system at 773 K and total pressure of0.133 atm. The pressure and mole fractions in Figs. 3a–3c are the same as the two curves labeled with 0.133atm in Figs. 2a and 2b, but the temperature is 200 Khigher. The units of Y -axis in Figs. 3a–3c are all inmole fraction. The time range in our modeling study is10−5 to 150,000 s.

Both Huybrechts and the NJIT mechanisms (Fig. 3a)predict that CHCl3 decreases from 0.896 slowly at earlytimes, then CHCl3 in Huybrechts mechanism holdsnear constant (∼0.7) after 500 s, but in the NJIT mech-anism it decays fast and then stabilizes at 10−4–10−5.The Huybrechts experiments monitored only the con-centration changes of the Cl2 molecules. The differ-ence between these two mechanisms results from theinclusion of HCl elimination reaction of chloroformand subsequent reactions of 1CCl2. HCl is predictedhigher in the NJIT mechanism than in the Huybrechtsmechanism.

Cl atom (Fig. 3b) is the primary active radical in thissystem when considering the dissociation of Cl2 only.

The mole fractions of Cl atom in both mechanisms in-crease from the dissociation of Cl2 and then decreasewhen Cl starts to react (abstract H) with CHCl3. This Clconcentration stabilizes at 10−9 in Huybrechts mech-anism, where as in the NJIT mechanism it increasesto 2 × 10−6 at longer times. This recovery of Cl atomin the NJIT mechanism comes from the association of1CCl2 and CCl3 and then �-scission of Cl atom fromC2Cl5. Two other evidences are as follows: (1) the pre-diction of C2Cl4 (Fig. 3c, self-association product of1CCl2) is 0.3 after 2000 s by the NJIT mechanism; (2)Cl2 in the NJIT mechanism shows a recovery to 0.02at 2000 s.

CCl3 as shown in Fig. 3b increases monotonicallyto 10−5 in both mechanisms. C2Cl6 in the same fig-ure follows the same trends as CCl3 for the twomechanisms since it comes from association of twoCCl3. The increased drop of CCl3 and C2Cl6 inthe NJIT mechanism is understandable because CCl3starts to react with 1CCl2 produced from chloroformdissociation.

CCl4 (Fig. 3a) comes from CCl3 via two reactions:CCl3 + Cl association and CCl3 + Cl2 abstraction,which are all considered by Huybrechts et al. Thetwo mechanisms show similar behavior for a two-stagechange of CCl4 mole fraction between 1 and 10 s: (1)CCl4 increases to 0.1 when Cl and CCl3 are also in-creasing, (2) CCl4 decreases to 0.01 at 1000 s whereCCl3 association with 1CCl2 becomes important. After1200 s, CCl4 decays to 0.001 in Huybrechts mech-anism, while it is 0.05 in the NJIT mechanism. Thehigher CCl4 yield in final stage of the NJIT mechanismis due to the much higher Cl and Cl2 concentrations inthe NJIT than in the Huybrechts mechanism.

1CCl2 from HCl elimination of chloroform becomesthe highest concentration active intermediate in ourstudy. 1CCl2 in Fig. 3c reaches its highest concentra-tion of 10−5 at ∼0.01 s, then decreases to 10−11 after2000 s after reaction with CCl3 to form C2Cl5.

C2Cl2 (Fig. 3c) is predicted by the NJIT mecha-nism to have mole fraction up to 0.001 at 1200 s inFig. 3c; its formation results from loss (elimination)of a Cl atom from the C2Cl3 vinylic radical. C2HCl3and C2HCl5 are the next species in high concentrationin Fig. 3c and they are results of CHCl3 + 1CCl2 ↔[C2HCl5]∗ → C2HCl3 + HCl. The elimination of HClis the lowest channel for unimolecular dissociation ofC2HCl5. Another path, fission of the weak C Cl bondresulting in CHCl2C·Cl2, is shown to be much slowerin the same figure; this product will rapidly undergo�-scission to form C2HCl3 + Cl.

At times longer than 5000 s, the concentra-tions appear to have reached equilibrium at 773 K(see Figs. 3a–3c).


(a) (b)

(c)

Figure 3 (a) Comparison of NJIT model (thick)N and Huybrechts (thin)H at 773 K and 0.133 atm. Initial mole fractions are0.896 (CHCl3) and 0.104 (Cl2); (b) Comparison of NJIT (thick)N and Huybrechts (thin)H models at conditions of Fig. 3a; (c)Comparison of NJIT (thick)N and Huybrechts (thin)H models at conditions of Fig. 3a for species introduced in this study.

SUMMARY

The rate constant of primary dissociation of chloro-form, CHCl3 → 1CCl2 + HCl, is calculated and esti-mated as a function of pressure and temperature us-ing QRRK-master equation analysis; results are inagreement with previous studies. Inclusion of this re-action and subsequent reactions of 1CCl2 does notsignificantly change the Cl2 mole fraction in chlori-nation of chloroform under the experimental condi-tions of Huybrechts et al. (573–635 K and 0.038–0.251 atm, Ref. [1]), provided 1CCl2 does not abstractCl from Cl2. At higher temperatures the chloroform

dissociation to 1CCl2 + HCl, and subsequent reactionsof 1CCl2 + 1CCl2, 1CCl2 + CCl3, 1CCl2 + CHCl3, etc.,have a significant effect on CHCl3, Cl2, CCl4, C2Cl6,etc. species profiles. The modeling results cannot matchthe experimental data for [Cl2] decay, if the recentlypublished CCl2 + Cl → CCl3 + Cl abstraction reac-tion is included in the mechanism.

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kinetics and mechanism for the thermal chlorination of chloroform in the gas phase: inclusion of hcl...

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