Cl Atom Initiated Photo-oxidation of Mono-chlorinated Propanes To

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A: Kinetics, Dynamics, Photochemistry, and Excited States

Cl Atom Initiated Photo-Oxidation of Mono-Chlorinated Propanes to Form Carbonyl Compounds: A Kinetic and Mechanistic Approach Avinash Kumar, and Balla Rajakumar J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.8b09132 • Publication Date (Web): 03 Jan 2019 Downloaded from http://pubs.acs.org on January 4, 2019

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The Journal of Physical Chemistry

Cl Atom Initiated Photo-Oxidation of Mono-Chlorinated Propanes to Form Carbonyl Compounds: A Kinetic and Mechanistic Approach Avinash Kumar and B. Rajakumar* Department of Chemistry, Indian Institute of Technology Madras, Chennai- 600036, India. *Address for correspondence: [email protected] http://chem.iitm.ac.in/faculty/rajakumar/ http://www.profrajakumar.com Abstract Cl atom initiated photo oxidation of mono-chlorinated propanes to form the carbonyl compounds was investigated. Propionaldehyde and acetone were identified to be major products in the oxidation of 1-chloropropane and 2-chloropropane respectively. The complete product analyses were carried out using Gas chromatography- Mass Spectrometry (GC-MS) and Gas Chromatography – Infra-red spectroscopy (GC-IR) as analytical tools, and an appropriate oxidation mechanism was proposed based on the product analyses. The temperature dependent rate coefficients for the reactions of Cl atoms with 1-chloropropane (1-CP) and 2-chloropropane (2-CP) were measured experimentally in the gas phase, using relative rate method in the temperature range of 268 – 363K and at 1 atm. pressure. Ethane, ethylene and ethyl acetate were used as reference compounds. The obtained rate coefficients for the reactions of Cl atoms with 1CP and 2-CP at room temperature (298K) and at 1 atm pressure are (4.64±0.70) × 10-11 cm3 molecule-1 s-1 and (2.57±0.44) × 10-11 cm3 molecule-1 s-1 respectively. Furthermore, to complement our experimentally obtained results, computational calculations were performed for these reactions using Canonical Variational Transition state theory (CVT) with Small Curvature Tunneling (SCT)

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in combination with CCSD/cc-pVDZ//MP2/6-31+G(d,p) level of theory. Detailed discussion on feasibility of the reactions, branching ratios, degradation mechanism and atmospheric implications are discussed in this manuscript. 1. Introduction In the recent years, many halogenated hydrocarbons are being directly emitted into the Earth’s atmosphere via natural and anthropogenic sources.1 Anthropogenic sources include the extensive use of these halogenated hydrocarbons in different industries 2. Diffusion of these hydrocarbons into the stratosphere makes it as a potential source for halogen atom which disturbs the ozone balance in the stratosphere.3 1-chloropropane (1-CP) has been detected in lava gas and fumaroles from volcanoes in Japan and Italy.4 It has been used as a chemical intermediate which releases it to the environment through various waste streams.5 Allyl chloride is extensively used as a solvent and it mainly contains 1-CP as one of the major impurities.6 Thus, the usage of the allyl chloride results in releasing 1-CP to the environment. 1,2 dichloropropane is used as a solvent for the polystyrene and latex production. It biodegrades anaerobically leading to the formation of 1-CP which can be considered as one of its environmental sources.7 2-chloropropane (2-CP) is known to have anesthetic property. It is primarily used as an industrial solvent, chemical intermediate and extractant.8 2-CP is also produced by landfill leachate which has been treated with chlorine.9 The use of 2-CP is anticipated to increase as it was accepted as a foam blowing agent by the Environmental Protection Agency.10 In accordance with the model of gas/particle portioning of semi-organic compounds in the atmosphere, these chloropropanes exist solely in vapor form in ambient atmospheric condition due to their high vapor pressure.11-12 and the global emissions of chlorinated hydrocarbons have been reported to be 2.4 Tg yr-1.13


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The fate of these hydrocarbons in the troposphere is dominated mainly by their reactions with OH radicals. However, the chlorine chemistry plays important role in polluted mid-continental regions, in industrial locations, in marine boundary layers (MBL)14 and urban polluted areas. Oxidation of chloropropanes in the gas phase are mainly initiated by OH radicals since they photolyze minutely as well as react with O3 and NO3 at a slower rate compared to that of OH radicals.15 Some studies suggests that in the marine boundary layer, the concentration of Cl atoms can be 1 – 10% of the OH radical concentration and a significant production rate of Cl atom is observed in the middle of continental United States.16,17 Raff et al.18 demonstrated the heterogenous reaction of N2O5 with HCl to be a source of tropospheric ClNOx species both experimentally and theoretically. These species generate Cl atoms upon photolyzing in the daytime. Hence, it appears that the main degradation of these chloropropanes occurs via OH radical and Cl atoms. Therefore, in order to assess their impact on the troposphere, there is a requirement for the kinetic parameters and mechanistic details with several oxidizing agents like OH radicals and Cl atoms over the appropriate range of temperatures. In order to investigate the atmospheric impact of the test molecules (1-CP and 2-CP), several groups15, 19-23 have reported the kinetic parameters for the reaction of test molecules with OH radical however, limited studies are available for their reactions with Cl atoms. Donaghy et al.20 reported the rate coefficient for the reactions of the test molecules with Cl atoms and OH radicals using relative rate technique. They have reported the rate coefficients for the reactions of 1-CP and 2-CP with Cl atoms at 298 K to be (4.9±1.5) ×10-11 cm3 molecule-1 s-1 and (2.0±0.6) ×10-11 cm-3 molecule-1 s-1 respectively. Tyndall et al.21 have also reported the rate coefficients for the reactions of Cl atoms with1-CP and 2-CP to be (4.8±0.3) ×10-11 and (2.0±0.1) ×10-11 cm-3 molecule-1 s-1 respectively at 298 K using relative rate technique. Le Crâne et al.22 measured the rate coefficient



for the reaction of 2-CP with Cl atoms using relative rate method. They have used ethylene and ethyl chloride as a reference compounds and reported the rate coefficient at 296 K to be (2.01±0.49) ×10-11 cm3 molecule-1 s-1. Sarzynski et al.23 measured the temperature dependent rate coefficients for the reaction of 2- CP with Cl atoms in the temperature range of 298 – 528.5 K and at 100 Torr of pressure using relative rate technique using ethane as a reference compound. Also, they have measured the rate coefficients for the deuterated 2-CP in the same experimental conditions. They have reported the temperature dependent rate coefficients to be kH = (3.52 ± 0.21) × 10-11 exp[(-184 ± 19)/T] and kD = (1.91±0.16)×10-11 exp[(-185±31)/T] cm3 molecule-1 s-1. To best of our knowledge, no temperature dependent studies are available for reaction of 1-CP with Cl atoms till date. Therefore, in the present investigation, we report the formation of carbonyl compounds and thereby the oxidation mechanism of 1-CP and 2-CP initiated by Cl atoms based on a thorough product analyses. Also we report the temperature dependent rate coefficients for the reactions of 1-CP and 2-CP with Cl atoms in the temperature range of 268 – 363 K using relative rate technique. In order to know the contribution of each individual reaction site to the global rate coefficient and to complement our experimental results, computational calculations were performed at CCSD/ccpVDZ//MP2/6-31+G(d,p) level of theory using Canonical Variational Transition state theory (CVT) with Small Curvature Tunneling (SCT).


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Cl

+

Cl

268 - 363K, Experiment 200 - 400K, Theory

1-chloropropane

268 - 363K, Experiment

Cl

+

Products...................(R1)

Cl

Products ....................(R2)

200 - 400K, Theory

2-chloropropane

2. Methodology 2.1. Experimental The photo-oxidation of 1-CP and 2-CP initiated by Cl atom was carried out using Relative Rate (RR) method to (i) determine the rate coefficients for the title reactions in the temperature range of 268 K–363 K and (ii) understand the mechanism of oxidation by analyzing the reaction products. All the experiments were performed in double-walled Pyrex cell of 100 cm long (~2405 cm3). The cell was equipped with two inches fused silica broadband precision windows (Thorlabs) which allows ultra violet radiation inside the cell to photolyze the organics present inside the cell. The temperature inside the reaction cell was maintained by circulating the cooled/heated fluid (Thermal H5 oil) in the outer jacket of the cell. To calibrate the temperature inside the cell, K-type thermocouple was used and the uncertainty in the measured temperature was found to be ±2K in the studied temperature range (268 K–363 K). The detailed explanation of the complete experimental set up has been reported in our previous publications.24-26



In situ generation of Cl atoms were done via photolyzing oxalyl chloride at 248 nm by using KrF excimer laser (Coherent COMPexPro). The concentration of the oxalyl chloride was varied between (4–6) × 1017 molecules cm-3. The concentration of the sample and the reference compound were maintained in the range of (4–6) × 1016 molecules cm-3. The concentration of the organics were monitored by using Gas Chromatography equipped with Flame Ionization Detector (GCFID, Agilent Technologies, 7890B). The HP- PLOT Q (30 m×0.32 mm×20 μm) capillary column was used to separate the mixture. The oven temperature was optimized to 220 ˚C and the column flow was maintained at 3 mL min-1. The organics were preliminary examined to identify any secondary reactions. The dark reaction was performed by keeping the reaction mixture for 2-3 hours in the absence of any light and the concentrations were measured by GC-FID. No significant change in the concentration of the sample and the reference compound was observed, which confirms the absence of any dark reaction. The sample and the reference compound were irradiated in the absence of precursor and the concentrations were monitored by GC-FID. No significant decrement in the concentrations of sample and reference compound were observed which confirms the absence of any self-reaction between sample and reference via direct photo dissociation. Therefore, any significant variation in the concentration of the sample is solely due to its reaction with Cl atom. Prior to the photolysis in each experiment, the reaction cell was loaded with the definite concentration of the sample, reference and precursor and is pressurized to atmospheric pressure using nitrogen gas. The mixture in the reaction cell was kept undisturbed for an hour to have a uniform composition. On top of it, the contents were mixed with an oil free diaphragm pump and then the samples were tested for consistent concentrations using a gas chromatograph. The reaction mixture was photolyzed by subjecting it to 1000, 1200, 1500, 1800 and 2000 pulses of 248 nm radiation. The energy of the 248 nm light used for photolyzing was ~ 6–7 mJ pulse-1


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cm-3. The samples (~ 0.6 ml) were withdrawn from the reaction cell by gas-tight syringe for the analysis in GC, GC-MS and GC-IR. The rate coefficients at different temperatures were measured by employing the standard relative rate equation.

𝐥𝐧

{

[𝒔𝒂𝒎𝒑𝒍𝒆]𝟎 [𝒔𝒂𝒎𝒑𝒍𝒆]𝒕

}

=

𝒌𝒔𝒂𝒎𝒑𝒍𝒆

{

𝐥𝐧

𝒌𝒓𝒆𝒇𝒆𝒓𝒆𝒏𝒄𝒆

[𝒓𝒆𝒇𝒆𝒓𝒆𝒏𝒄𝒆]𝟎 [𝒓𝒆𝒇𝒆𝒓𝒆𝒏𝒄𝒆]𝒕

}

where [sample]0, [sample]t are the concentrations of the sample at times ‘0’ and ‘t’ respectively and [reference]0, [reference]t are the concentrations of the reference compounds at times ‘0’ and ‘t’ respectively, ksample and kreference are the rate coefficients for the reactions of sample and reference compounds with chlorine atoms. Plot of ln([sample]0/[sample]t) versus ln([reference]0/ [reference]t) is expected to give a straight line with zero intercept, in the absence of secondary reactions. The slope of the plot gives the ratio of ksample/kreference. Knowing the kreference, one can calculate ksample at a given temperature.

Chemicals 1-chloropropane (purity 98%, Aldrich), 2-chloropropane (purity >99%, Aldrich), ethylene (purity 99.5%, Praxair), ethane (purity, 99.5%, Praxair), ethyl acetate (purity 99.8%, Aldrich), oxalyl chloride (purity 98%, Spectrochem), Nitrogen (99.995%, Bhuruka, India), Oxygen (98%, Bhuruka, India). These compounds were subjected to repeated freeze-pump-thaw cycles prior to use in experiments. 2.2. Computational Moller-Plesset second order (MP2) level of theory27 with Pople basis set 6-31+G(d,p)28 was used to optimize the geometries of the reactants (1-CP and 2-CP), pre-reactive complexes, transition



states, post reactive complexes and products. Transition states for all the individual abstraction pathways were identified with one imaginary frequency. No such imaginary frequency was identified for the reactants, complexes (pre and post-reactive) and products. Gauss view29 was used to view all the structures and normal mode frequencies of all the reactants, complexes, transition states and products. All the electronic structure calculations were done by using Gaussian 09 program suite.30 All the possible conformations have been optimized while performing geometry optimizations. Among all the conformers, the lowest energy conformer was considered to calculate the rate coefficient for the title reactions. All other conformers were higher in energy than the lowest energy conformer by 2.2 kcal mol-1 and 2.3 kcal mol-1 for 1-chloropropane and 2chloropropane respectively. Thus, they don’t have a significant contribution to the reaction in the studied temperature range. Intrinsic reaction coordinate calculations (IRC)31 were performed at the MP2/6- 31+G(d,p) level of theory to obtain the minimum energy path (MEP) and also to ensure that all the transition states identified follow distinctly different reaction paths. Single point energy calculations were carried out at coupled cluster with single and double, excitation (CCSD) level of theory using cc-pVDZ basis set 32, 33 which gives the accurate kinetics parameters.34

The temperature dependent rate coefficients for the title reactions were calculated theoretically using Canonical Variational Transition state theory (CVT)35-37 with Small Curvature Tunneling (SCT).38, 39 The rate coefficients were calculated by employing the POLYRATE 2008 program40 and GAUSSRATE 2009A.41 The minimum energy pathway is obtained using direct dynamics for a small range of the reaction path with the mass scaled reaction coordinate ‘s’ from − 1.0 to 1.0 Å by using the Page-McIver integrator with a step size of 0.01 Å. A Hessian matrix was calculated for every step and the harmonic frequencies were scaled by 0.9418 along the reaction path.42 The


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minimization of the generalized rate coefficient can be obtained by changing the transition state’s dividing surfaces along the reaction coordinates by employing the following equation 𝑘𝐵𝑇 𝑄𝐺𝑇(𝑇,𝑠) -𝑉𝑀𝐸𝑃(𝑠) 𝑘 (𝑇,𝑠) = 𝜎 ( 𝑅 )exp ( ) 𝑘𝐵𝑇 h ф (𝑇) 𝐺𝑇

𝑘𝐶𝑉𝑇(𝑇) = 𝑚𝑖𝑛𝑠𝑘𝐺𝑇(𝑇,𝑠) = 𝑘𝐺𝑇[𝑇,𝑠𝐶𝑉𝑇(𝑇)] Where kCVT is the rate coefficient calculated using CVT and kGT is the generalized rate coefficient, h= Planck’s constant, σ is the reaction path degeneracy, T= temperature (in Kelvin), kB is the Boltzmann constant, фR and QGT are the partition functions of a generalized reactant at ‘s’ and transition state respectively. SCVT is the reaction coordinates of the canonical variational transition state dividing surface. VMEP(s) is the potential energy of generalized TS at ‘s’. The tunneling corrected rate coefficients (kCVT/SCT) were obtained by multiplying kCVT with temperature dependent transmission coefficient Ƙ𝐶𝑉𝑇/𝑆𝐶𝑇(T). k𝐶𝑉𝑇/𝑆𝐶𝑇(𝑇) = Ƙ𝐶𝑉𝑇/𝑆𝐶𝑇(𝑇)k𝐶𝑉𝑇(𝑇)

3. RESULTS and DISCUSSION 3.1. Relative rate measurements for 1-chloropropane with Cl atom Temperature dependent rate coefficients for the the reaction of 1-CP with Cl atom were measured experimentally over the temperature range of 268–363 K relative to ethane and ethylene. The rate coefficient for the reaction of ethylene with Cl atom reported by Coquet et al.43 was used to determine the rate coefficient for the reaction R1. They reported the rate coefficient at the room temperature to be k = (9.3±0.6) × 10-11 cm3 molecule-1 s-1 and temperature dependent rate coefficient to be kethene + Cl= (0.39±0.22) ×10-11 exp [(950±180)/T] cm3 molecule-1 s-1. They have measured the rate coefficient using relative rate technique and a pressure of 760 Torr with N2 was



maintained throughout the experiments. The IUPAC44 recommended rate coefficients for the reaction of ethylene with Cl atoms is reported to be 1.10 × 10-10 cm3 molecule-1 s-1 at 298 K and is independent of the temperature over the range of 250-300K. The JPL-NASA45 recommended rate coefficient value for the reaction of ethylene with Cl atoms at 300 K is reported to be (3.10 ± 1.51) × 10-10 cm3 molecule-1 s-1 and temperature dependent Arrhenius equation used to calculate rate coefficients at other temperatures is k(T) = k300 (300/T) cm3 molecule-1 s-1. The obtained rate coefficient for reaction R1 at 298 K using IUPAC44 and JPL-NASA45 recommended rate coefficients are obtained to be (6.38 ± 0.99) × 10-11 cm3 molecule-1 s-1 and (1.65 ± 0.81) × 10-10 cm3 molecule-1 s-1 respectively. The obtained rate coefficient for reaction R1 at 298 K using IUPAC44 and JPL-NASA45 recommended rate coefficients are ~30 % and an order magnitude higher than the reported rate coefficients respectively. The obtained rate coefficient with reference to ethylene at 298 K using the rate coefficients reported by Coquet et al.43 is (4.96 ± 0.47) × 10-11 cm3 molecule1 s-1

is in excellent agreement with previously reported rate coefficients. Due to a large deviation

in the rate coefficient for the reaction R1 compared to the previously reported values, when calculated with respect to the IUPAC44 and JPL-NASA45 recommended rate coefficients for the reaction of ethylene with Cl atoms, the rate coefficients values reported by Coquet et al are used throughout the manuscript until specified. The IUPAC

44

recommended rate coefficients for the

reaction of ethane with Cl atoms are used to calculate the rate coefficients for the reactions of 1CP with Cl atoms. It is reported to be (5.90 ± 1.15) × 10-11 cm3 molecule-1 s-1 at 298 K and ― 600 -11 3 -1 temperature dependent Arrhenius equation is 𝑘220 𝐸𝑡ℎ𝑎𝑛𝑒 + 𝐶𝑙= 8.3 × 10 exp (-100/T) cm molecule

s-1. The JPL-NASA45 recommended rate coefficients for the reaction of ethane with Cl at 298 K is reported to be (5.70 ± 1.07) × 10-11 cm3 molecule-1 s-1 and the temperature dependent Arrhenius ― 1400 -11 3 -1 -1 expression is 𝑘48 𝐸𝑡ℎ𝑎𝑛𝑒 + 𝐶𝑙= 7.2 × 10 exp(-70/T) cm molecule s . At 298 K, the obtained rate


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coefficient for the reaction R1 with reference to ethane by using IUPAC44 recommended and JPLNASA45 recommended values are (4.66 ± 1.03) × 10-11 cm3 molecule-1 s-1 and (4.50 ± 0.96) × 1011

cm3 molecule-1 s-1 which are in very good agreement with the previously reported values within

the experimental uncertainties. The overall rate coefficient for R1 at 298 K using JPL-NASA45 recommended and Coquet et al.43 reported rate coefficient for the reaction of Cl atom with ethane and ethylene respectively rate coefficient is (4.73 ± 1.11) × 10-11 cm3 molecule-1 s-1. The overall rate coefficient for reaction R1 at 298 K with reference to IUPAC44 recommended and Coquet et al.43 reported rate coefficient for the reaction of Cl atom with ethane and ethylene respectively is (4.81 ± 1.15) × 10-11 cm3 molecule-1 s-1. The rate coefficients obtained for R1 with reference to JPL-NASA45 and IUPAC44 recommended rate coefficient for the reaction of ethane with Cl atoms are in excellent agreement with the reported rate coefficients at 298 K within the experimental uncertainties with a maximum deviation of 3% and 2% respectively. Since both the obtained rate coefficients are close to each other, we have computed the temperature dependent rate coefficients for R1 with reference to IUPAC44 recommended and Coquet et al.43 reported rate coefficients for the reaction of ethane and ethylene with Cl atoms respectively and are given in Table1. The rate coefficients obtained from these Arrhenius expressions were used in the present study to measure the rate coefficients at 268, 283, 298, 313, 343 and 363K and depicted in Table 1. The pressure was maintained at 760 Torr of N2 throughout the experiment. To ensure the reproducibility, each experiment was repeated three times at every temperature. For each experiment, the data were fit by linear least square method to get the slope and the error associated with it. The relative decrement in the concentration of 1-CP with respect to ethylene and ethane is given in Figure 1. The obtained rate coefficients relative to ethane and ethylene are close to each other in the measured temperature range. Hence, they were averaged and are given in Table 1. The



-11 3 -1 -1 average rate coefficient obtained at 298 K is 𝑘𝐸𝑥𝑝𝑡 𝑅1 ― 298𝐾= (4.81±1.15) × 10 cm molecule s . The

average rate coefficients at individual temperature were used to fit the Arrhenius equation and the obtained temperature dependent equation for the reaction R1 is 𝑘𝐸𝑥𝑝𝑡 𝑅1 ― (268 ― 363𝐾)= (4.09±3.22)×10 18T2.26exp[(1013±73)/T]cm3

molecule-1 s-1.The Arrhenius plot for the reaction is shown in Figure

2 and the negative temperature dependency was observed, vide infra. 3.2. Relative rate measurements for 2-chloropropane with Cl atom For the reaction of 2-CP with Cl atom, temperature dependent rate coefficients were measured experimentally over the temperature range of 268–363 K with reference to ethane and ethyl acetate. The IUPAC 44 recommended rate coefficients for the reaction of ethane with Cl atoms are used to calculate the rate coefficients for the reactions of 2-CP with Cl atoms. It is reported to be (5.90 ± 1.15) × 10-11 cm3 molecule-1 s-1 at 298 K and temperature dependent Arrhenius equation is ― 600 -11 3 -1 -1 45 recommended rate 𝑘220 𝐸𝑡ℎ𝑎𝑛𝑒 + 𝐶𝑙= 8.3 × 10 exp (-100/T) cm molecule s . The JPL-NASA

coefficients for the reaction of ethane with Cl at 298 K is reported to be (5.70 ± 1.07) × 10-11 cm3 ― 1400 -11 molecule-1 s-1 and the temperature dependent Arrhenius expression is 𝑘48 𝐸𝑡ℎ𝑎𝑛𝑒 + 𝐶𝑙= 7.2 × 10 exp(-

70/T) cm3 molecule-1 s-1. At 298 K, the obtained rate coefficient for the reaction R2 with reference to ethane by using IUPAC44 recommended and JPL-NASA45 recommended values are (2.26 ± 0.45) × 10-11 cm3molecule-1s-1 and (2.34 ± 0.48) × 10-11 cm3 molecule-1 s-1 which are in very good agreement with the previously reported values within the experimental uncertainties. Cuevas et al.46 reported the temperature dependent rate coefficient for the reaction of ethyl acetate with Cl atom, which was used in this study. They have used pulsed laser photolysis – resonance fluorescence technique to obtain the rate coefficient for the reaction of ethyl acetate with Cl atoms in the temperature range of 265–383 K. They have reported the rate coefficient at room temperature to be k = (1.37±0.20) ×10-11 cm3 molecule-1 s-1 and the temperature dependent rate coefficient to


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be kethyl

acetate + Cl=

(4.35±0.65)×10-12exp[(342±92)/T] cm3 molecule-1 s-1. The rate coefficients

obtained from these Arrhenius expressions were used in the present study to measure the rate coefficients at 268, 283, 298, 313, 343, 363 K and at 760 Torr of pressure and the obtained rate coefficients are depicted in Table 2. The rate coefficients obtained for reaction R2 with reference to JPL-NASA45 recommended rate coefficient for the reaction of ethane with Cl atoms and ethyl acetate are in excellent agreement with the reported rate coefficients at 298 K within the experimental uncertainties with a maximum deviation of 31%. The rate coefficients obtained for reaction R2 with reference to IUPAC

44

recommended rate coefficient for the reaction of ethane

with Cl atoms and ethyl acetate are in excellent agreement with the reported rate coefficients at 298 K within the experimental uncertainties with a maximum deviation of 32%. Since both the obtained rate coefficient are close to each other, we have computed the temperature dependent rate coefficients for R2 with reference to IUPAC44 recommended temperature dependent rate coefficients for the reaction of ethane with Cl atoms and ethyl acetate and are given in Table2. For each experiment, the data were fit using linear least square method to get the slopes and the error associated with it. The relative decrement in the concentration of 2-CP with respect to ethane and ethyl acetate is shown in Figure 3. The obtained rate coefficients relative to ethane and ethyl acetate are close to each other in the studied temperature range. Hence, they were averaged and are given in Table 2. The obtained averaged rate coefficient for the reaction R2 is 𝑘𝐸𝑥𝑝𝑡 𝑅2 ― 298𝐾. = (2.65±0.66) ×10-11 cm3 molecule-1 s-1 at 298 K and deduced temperature dependent rate coefficient -19 2.50exp{(1079±80)/T}cm3 molecule-1 s-1 . The Arrhenius is 𝑘𝐸𝑥𝑝𝑡 𝑅2 ― (268 ― 363𝐾)=(4.89±1.28)×10 T

plot for the reaction of 2-CP with Cl atoms in the temperature range of 268–363 K is shown in Figure 4. Similarly, like reaction R1, negative temperature dependency is observed for the reaction of 2-CP with Cl atom, vide infra.



Page 14 of 56

3.3. Error Analysis The reaction chamber was associated with very small uncertainties in temperature (± 2K) and pressure (± 1 Torr) which negligibly contribute to the rate coefficient. The uncertainty in the concentration of the test molecules and the references measured by GC is less than 5%. Linear least square method was used to obtain slopes and the associated errors (95% confidence level) for each experiment. The uncertainties on the weighted average slopes are determined in accordance with the error propagation method, which is described below:

[( ) ( )

∆𝑎 ∆𝑦 = 𝑦 𝑎

Where,

∆𝑦 𝑦

2

∆𝑏 + 𝑏

2

+ …….

is the relative error on the average slope and

]

∆𝑎 𝑎

1 2

∆𝑏 𝑏

( ) and ( ) are the relative errors on the

individual slopes. The errors associated with the rate coefficients which incorporates the errors in the rate coefficients of the reference reactions are calculated by using standard error propagation method following the equation.47-50 1

∆𝑘𝑠𝑎𝑚𝑝𝑙𝑒 = 𝑘𝑠𝑎𝑚𝑝𝑙𝑒 ×

[ ( )] ( ) ( ) ( ) ∆𝑘𝑟𝑒𝑓 𝑘𝑟𝑒𝑓

∆

2

+

𝑘𝑠𝑎𝑚𝑝𝑙𝑒

2

2

𝑘𝑟𝑒𝑓

𝑘𝑠𝑎𝑚𝑝𝑙𝑒 𝑘𝑟𝑒𝑓

The uncertainties associated with the averaged weighed rate coefficient was calculated by employing the following equation


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[( ) ( ) ]

∆𝑙 ∆𝑘𝑎𝑣𝑒𝑟𝑎𝑔𝑒 = 𝑘𝑎𝑣𝑒𝑟𝑎𝑔𝑒 × 𝑘𝑙

2

∆𝑚 + 𝑘𝑚

2

1 2

Where, Δl and Δm correspond to the uncertainty on the individual rate coefficients with particular reference reactions. The absolute uncertainties associated with the rate coefficient of the reference reaction contribute significantly to the systematic errors in the determination of the rate coefficient of the title reaction. 3.4. Computational discussion 3.4.1. Reaction of 1-CP + Cl atom (TS4) H4

(TS1) Cl

H1 H2

H5

(TS2) H3 (TS5) H7 (TS7) (TS3)

H6

(TS6)

All the optimized structure of the reactants, pre-reactive complexes, transition states, post reactive complexes and products are shown in Figure 5. The structural parameters and frequencies are given in the supporting information (Table S1 and S2). As shown in the above structure, there is a possibility of abstraction of hydrogen by Cl atom in seven pathways. Our calculations reveal that transition states, TS1 and TS3, formed by abstracting H1 and H3 are equivalent. Transition states, TS4 and TS5 which are formed by abstracting H4 and H5 respectively are equivalent. Similarly, the abstraction of H6 and H7 by chlorine atom leads to the formation of transition states, TS6 and TS7 respectively are equivalent. Transition state TS2 is formed by abstracting H2 by Cl atom. Therefore, there are four possible independent transition states for the hydrogen abstraction pathway for the reaction R1. Hereafter, for reaction R1, transition states obtained from H1, H2,



H4 and H6 are TS1, TS2, TS3 and TS4 respectively until specified. The transition states, TS1 to TS4 are formed via formation of pre-reactive complexes, RC1 to RC4 respectively. All the transition states leads to the formation of products via product complexes. In TS1 and TS2, the fissionable C-H bond length elongates by 27% and 26% respectively. Similarily, the elongation in the fissionable C-H bond for TS3 and TS4 are 25% and 20% respectively. The nature of the transition state whether it is a reactant-like (early transition state) or product-like (late transition state) can be determined by calculating the L parameter.51 L parameter is the ratio of the change in the C-H bond in a transition state with respect to the normal C-H bond length in a reactant and the change in the H-Cl bond length in a transition state with respect to the normal H-Cl bond length in HCl molecule. The L parameter of all the transition states for the reaction R1 is given in Table 3. The transition state resembles reactant-like character if the value of L-parameter is less (usually lesser than one) whereas it resembles product-like character if the value of L-parameter is more (usually greater than one). In case of R1, the transition states, TS3 and TS4 are early transition state or reactant-like transition state since their values are less than one (0.88 and 0.91 for TS3 and TS4 respectively). The transition states, TS1 and TS2 are late transition states or product-like transition state since their values are greater than one (1.68 and 1.65 for TS1 and TS2 respectively). Thus, according to Hammonds postulates,52 if the transition state is early or reactant-like, then the reaction proceeding via this particular transition state will be exergonic and if the reaction proceeding via transition state which is late or product-like transition state, will be endergonic in nature. Thus, hydrogen abstraction reaction proceeding via TS1 and TS2 for the reaction R1 will be endergonic and the hydrogen abstraction proceeding via TS3 and TS4 are exergonic. To predict the feasibility of the reaction, standard enthalpy and standard Gibbs free energy were calculated at MP2/6-31+G(d,p) level of theory and are summarized in Table 4. The abstraction channel (TS3)


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is found to be most exothermic (ΔH0 = 0.71 kCal mol-1) and most feasible pathway (ΔG0 = -2.16 kCal mol-1). The potential energy diagram for the reaction of 1-CP with Cl atoms obtained at CCSD/cc-pVDZ//MP2/6-31+G(d,p) level of theory is shown in Figure 6. The internal rotation modes are treated using the hindered rotor approximation (McClurg et al.)53 whereas the remaining vibrations are treated harmonically. The rate coefficient for reaction R1 over the temperature range of 200-400 K is given in Table 5. The obtained rate coefficient was -11 cm3 molecule-1 s-1 at 298 K and deduced temperature calculated to be 𝑘𝑇ℎ𝑒𝑜𝑟𝑦 𝑅1 ― 298𝐾 = 4.32×10 -18 T2.27 exp[(849±22)/T] dependent Arrhenius expression is 𝑘𝑇ℎ𝑒𝑜𝑟𝑦 𝑅1 ― (200 ― 400𝐾)= (5.97 ± 3.22)×10

cm3 molecule−1 s-1 and is shown in Figure 2. The radicals formed in the process of abstraction of H atoms from 1-CP at various positions viz. via transition states TS1-TS4 are C●H2CH2CH2(Cl), C●H2CH2CH2(Cl), CH3C●HCH2(Cl)and CH3CH2C●H(Cl) respectively. The formation of the products via these radicals is explained in the product analysis section of this manuscript. 3.4.2. Reaction of 2-CP + Cl atom (TS1)

Cl

H1 H2 (TS2)

H3 (TS3)

H4

(TS4)

(TS5) H5 H6 (TS6) H7 (TS7)

The optimized structures of reactants, pre-reactive complexes, transition states, post reactive complexes and products at CCSD/cc-pVDZ//MP2/6-31+G(d,p) level of theory are shown in Figure 7. The structural parameters and frequencies are given in the supporting information (Table S3 and S4). There is a possibility of abstraction of hydrogen by Cl atoms in seven pathways. The transition



state, TS1 formed by abstracting H1 is equivalent to the transition state, TS5 formed by abstracting H5. The transition state, TS2 formed by abstracting H2 is equivalent to the transition state, TS6 formed by abstracting H6. The transition state, TS3 formed by H3 is equivalent to the transition state, TS7 formed by abstracting H7. The transition state, TS4 is formed by abstracting H4. Therefore, there are four independent hydrogen abstraction channels. All the transition states, TS1 to TS4 are formed via pre-reactive complexes RC1 to RC4 respectively. All the transition states forms the corresponding products via formation of corresponding product complexes. In TS1, TS2 and TS3, the fissionable C-H bond length elongates by 27%, 29% and 28% respectively. In TS4, the fissionable C-H bond length elongates by 15%. The L-parameter for all the transition states are given in Table 3. The transition state TS4 is early transition state or reactant-like transition state since their L values are less than one (0.59). The transition states, TS1, TS2 and TS3 are late transition states or product like transition states since their values are greater than one (1.73, 2.11 and 1.09 for TS1, TS2 and TS3 respectively). Thus, according to Hammonds postulates,52 hydrogen abstraction reactions proceeding via TS1, TS2, and TS3 for the reaction R2 are endergonic and the hydrogen abstraction proceeding via TS4 is exergonic. To predict the feasibility of the reaction, standard enthalpy (ΔH0) and standard Gibbs free energy (ΔG0) are calculated at MP2/6-31+G(d, p) level of theory and are summarized in Table 6.The abstraction channel, TS4 is found to be most exothermic (ΔH0 = -0.67 Kcal mol-1 ) and most feasible pathway (ΔG0 = -3.51 Kcal mol-1) among all the abstraction channels. The potential energy level diagram for reaction R2 at the same level of theory is shown in Figure 8. The internal rotation modes are treated using the hindered rotor approximation (McClurg et al.),53 whereas the remaining vibrations are treated harmonically. The rate coefficient for reaction R2 over the temperature range of 200-400 K is given in Table 7. At room temperature, the rate


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-11 3 -1 -1 coefficient was calculated to be 𝑘𝑇ℎ𝑒𝑜𝑟𝑦 𝑅2 ― 298𝐾 = 2.93 ×10 cm molecule s and deduced Arrhenius -20 T2.93 exp{(1338 ± 20)/T} cm3 molecule−1 expression is 𝑘𝑇ℎ𝑒𝑜𝑟𝑦 𝑅2 ― (200 ― 400𝐾)= (1.78 ± 0.86) × 10

s−1and is shown in Figure 4. The radicals formed in the process of abstraction of H atoms from 2-CP at various positions viz. via transition states TS1-TS4 are C●H2CH(Cl)CH3, C●H2CH(Cl)CH3, C●H2CH(Cl)CH3 and CH3C●(Cl)CH3 respectively. The formation of the products via these radicals is explained in the product analysis section of this manuscript. 3.5. Kinetic Analysis: The experimentally measured rate coefficient for the reaction R1 at 298 K is 𝑘𝐸𝑥𝑝𝑡 𝑅1 ― 298𝐾= (4.81± 1.15)×10-11 cm3 molecule-1 s-1 and the computationally calculated value at 298 K is 𝑘𝑇ℎ𝑒𝑜𝑟𝑦 𝑅1 ― 298𝐾 = 4.32×10-11 cm3 molecule-1 s-1, are in reasonable agreement with each other. Both experimentally measured and computed rate coefficients are in reasonably good agreement with the rate coefficients reported by Donaghy et al.20 [(4.90 ± 1.5) × 10-11 cm3 molecule-1 s-1] and Tyndall et al.21 [(4.80±0.3) ×10-11 cm3 molecule-1 s-1] within the experimental uncertainties (maximum deviation between experimentally obtained and reported values was found to be around 2.5%). Negative temperature dependency was observed both experimentally and computationally over the studied temperature range. This is due to the formation of the pre-reactive complexes, which are more stabilized. The experimentally measured rate coefficient for the reaction R2 at 298 K is 𝑘𝐸𝑥𝑝𝑡 𝑅2 ― 298𝐾. = (2.65 ± 0.66) × 10-11 cm3 molecule-1 s-1 and computationally calculated value at 298 K is 𝑘𝑇ℎ𝑒𝑜𝑟𝑦 𝑅2 ― 298𝐾 =2.93×10-11 cm3 molecule-1 s-1, are in excellent agreement with each other. Both experimentally measured and computed rate coefficients are in reasonably good agreement with the rate



coefficients reported by Donaghy et al.20 [(2.0±0.6) ×10-11 cm3 molecule-1 s-1], Tyndall et al.21 [(2.0±0.1) ×10-11 cm3 molecule-1 s-1], Le Crâne et al.22 [(2.01±0.49) ×10-11 cm3 molecule-1 s-1] and Sarzynki et al.23 [ (1.97±0.06) ×10-11 cm3 molecule-1 s-1] within the experimental uncertainties (maximum deviation between experimentally obtained and reported values was found to be around 34 %). Similar to reaction R1, negative temperature dependency was observed for the reaction R2 both experimentally and computationally over the studied temperature range, which is due to the formation of more stabilized pre-reactive complexes. Sarzynki et al.23 measured the rate coefficient for the reaction R2 and observed a positive temperature dependency which is contradicting with our reported results. They also have studies R2 using RR method with ethane as reference. This is quite surprising, as ethane was used as reference compound in our present investigation as well. In our studies we have used ethyl acetate as second reference compound and the results were found to be very close to the ones obtained using ethane. In addition, our computational results were also found to be in very good agreement with our experimentally measured kinetic parameters, across the studied temperature range, with a negative temperature dependence. They have measured the rate coefficient for the reaction R2 in the cylindrical quartz cell of volume 150 cm3 and the total pressure maintained in the reaction cell was 100 Torr throughout the experiment. Chlorine gas was used as a precursor of Cl atoms, which was photolyzed with 330 nm radiation. The concentration of chlorine gas was maintained in the range of (0.8 – 1.7) × 1017 molecules cm-3. The concentration of sample and reference compound was maintained in the range of (0.3-0.7) ×1017 molecules cm3.

Xenon arc lamp was used as a source of radiation. The photolyzing time and band width of the

radiation source was varied depending upon the temperature and the decrement in the concentration of reactant and reference compounds. In the present experiments we have used a reaction cell with ca. 2000 cm3 volume, An excimer laser (KrF, 248nm) as a light source and oxalyl


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chloride a s precursor. While the room temperature rate coefficients are in reasonable agreement with the present values, the positive temperature dependence may be attributed to any of the mentioned differences in the experimental conditions. Also, Sarzynki et al.23 theoretically explored the mechanism for the hydrogen abstraction of 2-CP by Cl atoms. In their investigation, the rate coefficient for the abstraction of hydrogen attached to the secondary carbon, they observed it to be decreasing with increase in temperature. Thus, it shows a negative temperature dependency whereas other abstraction channels (i.e, for hydrogen attached to the primary carbon) shows a positive temperature dependency. According to our calculations, the abstraction channel from secondary carbon is the most contributing channel. It is conspicuous from the branching ratio calculations. Therefore, the abstraction of hydrogen from secondary carbon i.e, TS4, plays a major role in the reaction and governs the overall Arrhenius parameters. Nelson et al.54 and Teton et al.55 have also suggested an indirect H-atom transfer mechanism with the formation of an aduct between the incoming radical and the test molecule at low temperatures. Sarzynki et al.23, as well as our calculations, suggest the formation of pre-reactive complex and therefore negative temperature dependency may be attributed to the tunneling of the reactants via pre-reactive complexes in the reaction R2. Murray et al.56 studied the dynamics of halomethanes CH3X; X = F, Cl, Br, I) with Cl atoms both experimentally and computationally. Their calculations have shown the formation of pre and post reactive complexes during the hydrogen abstraction reaction with a significant positive barrier height. 3.6. Reactivity Trend The rate coefficients for the reactions of OH radicals and Cl atoms with halogenated propanes are given in Table 8. The rate coefficients for the reaction of Cl atoms with propane57, 1-CP (present study) and 2-CP (present study) are 1.20×10-10, (4.81 ± 1.15) ×10-11, (2.65 ± 0.66) ×10-11 cm3



molecule-1 s-1 respectively at 298K. The rate coefficients for the reactions of Cl atoms with 1bromopropane20 and 2-bromopropane20 are 6.1×10-11 and 2.7×10-11cm3 molecule-1 s-1respectively at 298K. The rate coefficient seems to be decreases if the halogen substitution is at middle carbon (kR1 is nearly 1.8 times to that of kR2 at 298K). Cl substituted propane has more deactivating effect than the bromine substituted propane which can be observed by comparing the rate coefficients for the Cl atom reactions with chlorinated and brominated substituted propanes. There is a decrease in the reactivity by ~50 % and ~75 % for the reaction of 1-bromopropane and 2-brompropane with Cl atoms when compared to that of the reactivity of propane with Cl atoms. This is due to the larger size and less electronegativity of Br atom when compared to Cl atom. Same trend was observed for the reaction of OH radicals. The decrement in the rate coefficient was less pronounced in case for OH radical reactions. A similar trend is observed for the reaction of chloropropanes with OH radicals. The rate coefficient for the reaction of OH radicals with propane58, 1-CP15, 2-CP15, 1,2-dichloropropane15 and 1,2,3-trichloropropane15 are 1.10×10-12, 9.8×10-13, 7.0×10-13, 4.6×10-13, 4.6×10-13 cm3 molecule-1 s-1 respectively at 298K. The rate coefficient for the reaction of OH radical with 1bromopropane20 and 2-bromopropane20 are 1.18×10-12 and 8.8×10-13 cm3 molecule-1 s-1 respectively at 298K. The rate coefficient for the reaction of OH radicals with 1-CP is nearly 1.4 times to that of the rate coefficient of OH radical with 2-CP. Similar behavior is shown for the OH radical and Cl atom reactions with 1-bromopropane and 2-bromopropane. There is a decrease in the reactivity of chloropropanes towards Cl atoms when compared with propane (nearly 60 % in case of 1-CP and ~80 % in case of 2-CP) and is attributed to the repelling effect caused due to the electronegativity of both the substituted Cl atom as well as the attacking Cl atoms. 3.7. Branching ratio


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To find out the contribution of a particular pathway to the global rate coefficient, branching ratios have been calculated in the temperature range of 200- 400 K. The branching ratios (kTS1/k), (kTS2/k), (kTS3/k), (kTS4/k) for the reaction R1 is shown in Figure 9. At 298K, the values of branching ratios, (kTS1/k), (kTS2/k), (kTS3/k) and (kTS4/k) are 0.40%, 0.08%, 5.10% and 94.50% respectively. Branching ratios of all the pathways for the reaction R1 in the temperature range of 200-400K are given in Table 9. From Figure 9, it can be seen that, the reaction pathway forming TS4 is kinetically most favorable pathway. With an increase in temperature, there is a decrement in the branching ratio for TS4 whereas the branching ratio for TS3 increases with increase in temperature and becomes prominent. The contribution from other two reaction pathways (TS1 and TS2) seems to be negligible. Figure 10 represents the branching ratios, (kTS1/k), (kTS2/k), (kTS3/k), (kTS4/k) for all the pathways for the reaction R2. At 298K, the branching ratio for (kTS1/k), (kTS2/k), (kTS3/k) and (kTS4/k) are 0.06%, 0.05%, 0.06% and 99.65% respectively. Branching ratio for all the different pathways for the reaction R2 in the temperature range of 200 – 400K is given in Table 10. It can be observed that, the reaction pathway proceeds via TS4 is the most dominant channel. With an increase in temperature, the branching ratio (kTS4/k) decreases, whereas other pathways increases insignificantly. The individual rate coefficients for each transition state involved in the calculations for the reactions R1 and R2 is given in Table S5 and Table S6 respectively in the supporting information. For the reaction of 1-CP with Cl atoms, abstraction pathway via TS3 is more thermodynamically feasible when compared to abstraction pathway via TS4 which is more kinetically favorable. In the abstraction channel via TS3, there will be more hyperconjugation structures (five hyperconjugation structures) when compared to abstraction pathway via TS4 (two hyperconjugation structures). Thus, TS3 having more hyperconjugation structure stabilizes the



radical and makes it more thermodynamically feasible pathway compared to TS4. Another reason for TS3 to be more thermodynamically feasible pathway is the formation of secondary radical after abstracting the H-atom whereas, in TS4, primary radical is formed after abstraction of H-atom. But TS4 is the most kinetically favorable pathway due to the prominent electron donatingresonance effect (+R) of Cl atom directly attached to the radical carbon. Due to its +R effect, electron density increases on the radical carbon and makes it more kinetically labile when compared to TS3. For the reaction of 2-CP with Cl atoms, it is clear from the computational calculations that the abstraction of H atom will be either from -CH3 (TS1 or TS2 or TS3) or from -CHCl (TS4). The radical formed via TS1 is primary radical and it has one hyperconjugation structure. The radical formed via TS4 is a secondary radical and it has six hyperconjugation structures. Thus, TS4 is more stabilized due to secondary radicals and more hyperconjugation structures when compared with TS1. TS4 is also more kinetically favorable pathway when compared to other pathways (TS1 or TS2 or TS3) because of the electron-donating resonance effect (+R) of directly attached Cl atom along with the +I effect of two methyl group attached to radical carbon, which increases the electron density and makes it more kinetically labile. 3.8 Product Analysis. To understand the degradation mechanism of 1 CP and 2-CP on reaction with Cl atoms, products were analyzed using GC-MS (7890B-5977A MSD) and GC-IR (7890B-iS50) as analytical tools. HP-PLOT’Q’ column was used with helium and N2 as carrier gas for MS and IR respectively. For the reaction of 1-CP with Cl atoms, the oven temperature was maintained at 150 0C. The column flow was maintained at 1.2 mL min-1 and He and N2 were used as a carrier gas for the analysis in


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GC-MS and GC-IR respectively. For the reaction of 2-CP with Cl atoms, all the parameters were kept same except the oven temperature. The oven temperature was maintained at 150 0C up to 5 minutes and the temperature was increased at the rate of 10 0C min-1. The source temperature for MS was maintained at 230 0C and the MS-quad temperature was maintained at 150 0C throughout our analysis. The transfer line temperature was maintained at 200 0C in the GC-MS analysis. The MS was made to run in scan mode using the settings from the atune.u file with an electron multiplier offset of 200 eV. For GC-IR analysis, the parameters for GC was kept same as that of GC-MS. The temperature for the transfer line and flow cell was maintained at 200 0C throughout the analysis. The eluted sample was scanned at a resolution of 4 cm-1 using a highly sensitive mercury cadmium telluride (MCT) detector. The same reaction cell, which was employed for RR experiment, was used to analyze the products formed in the title reactions. The temperature of the reaction cell was maintained at (298 ± 2) K. The concentration of the test molecules, oxalyl chloride and oxygen was maintained in the range of (4-6) × 1016 molecules cm-3, (4-6) × 1017 molecules cm-3 and (6-8) × 1016 molecules cm-3 respectively and was pressurized to 1 atm by nitrogen. The reaction mixture was irradiated with 3000 pulses of 248 nm radiation and allowed to mix uniformly. The samples were withdrawn from the reaction cell by gas tight syringe for the analysis in GC-MS and GC-IR. For the reaction of 1-CP with Cl atoms in the presence of oxygen, propionaldehyde and propylene were observed to be major products. The gas chromatogram illustrating the products is given in Figure 11. When a hydrogen atom is abstracted from CH2 group attached to Cl atom via TS4, CH3CH2C●H(Cl) radical is formed. This radical in the presence of molecular oxygen forms corresponding peroxy radical i.e, CH3CH2C(OO●)H(Cl), which recombines with itself and forms two molecules of the corresponding alkoxy radical i.e, CH3CH2C(O●)H(Cl) along with oxygen



molecule. This alkoxy radical further rearranges to form propionaldehyde with the elimination of Cl radical. Another pathway to abstract the hydrogen atom by Cl atom is from β- carbon via transition state TS3, which from CH3C●HCH2Cl radical. This radical undergoes rearrangement to form propylene as a product. There is also a probability of forming propylene through the major contributing channel i.e, TS4. After abstracting the H-atom via TS4, CH3CH2CH(Cl)● radical is formed. This radical undergoes 1, 2 H-shift to form a secondary radical. This secondary radical rearranges to form propylene with the elimination of the Cl radical. The individual IR spectra and mass spectra of the products are given in Figure S3 (SI). The degradation mechanism for the reaction of R1 is proposed based on the product formation and is given in Figure 12. For the reaction of 2-CP with Cl atom in the presence of oxygen, acetone and propylene were observed to be major products. The gas chromatogram illustrating the products is given Figure 13. When a hydrogen is abstracted from middle carbon by Cl atom via TS4, CH3C●(Cl)CH3 radical is formed. This radical on further reaction with molecular oxygen form the corresponding peroxy radical, CH3C(OO●)(Cl)CH3 which recombines with itself and forms two molecules of corresponding alkoxy radical i.e, CH3C(O●)(Cl)CH3 along with oxygen molecule. This alkoxy radical further rearranges to from acetone with the elimination of Cl radical. Another pathway by which Cl atom can abstract the hydrogen atom from the terminal carbon atom to form C●H2CH(Cl)CH3 radical. On rearrangement, it forms propylene along with Cl radical. The individual IR spectra and mass spectra of the products are given in Figure S4 (SI). The degradation mechanism for the reaction of R2 is given in Figure 14. Carbonyl compounds are the major oxygenated Volatile Organic Compounds (VOCs) which are formed as oxidation products of hydrocarbons and other organic species in the Earth’s atmosphere. They plays an important role in altering the chemical composition of troposphere and are important


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precursor for the generation of ozone molecules and free radicals.59 Propionaldehyde is the major product during the photo oxidation of 1-CP with Cl atoms. Its atmospheric lifetime is estimated to be 15 hours.60 It serves as a major source for the production of peroxypropionyl nitrate (PPN) which produces ozone on further oxidation. PPN concentrations were measured to be 4 ppb in urban regions.61 Acetone is the major product formed during the photo-oxidation of 2-CP with Cl atoms. Its mean atmospheric lifetime is estimated to be between 14 to 35 days.62-64 It serves as a precursor for hydrogen oxide radicals (HOx) and peroxyacetylnitrate (PAN).65, 66 It draws a major attention just below the tropopause, where it generates ozone molecule rapidly.67, 68 3.9. Atmospheric Implication The rate at which a molecule reacts with the oxidizing species such as Cl atoms and OH radicals decides its atmospheric lifetime in the Earth’s atmosphere. The cumulative atmospheric lifetimes of the test molecules were calculated with respect to their reactions with Cl atoms and OH radicals using the following equation. 𝟏 𝝉𝒆𝒇𝒇

=

𝟏 𝟏 + 𝝉𝑶𝑯 𝝉𝑪𝒍

where, τeff is the cumulative lifetime of the chemical species, τCl and τOH are the lifetimes of the chemical species due to its reaction with Cl atoms and OH radicals respectively. The typical concentrations of OH radicals69 and Cl atoms70,71 used in this calculation are 1×106 radical cm-3 and 1.3×105 atom cm-3 (in the MBL) respectively. The rate coefficients for the reaction of 1-CP and 2-CP with OH radicals15 at 298K are (9.8±1.0) ×10-13 cm3 molecule-1 s-1 and (7.0±0.7) ×10-13 cm3 molecule-1 s-1 respectively. From Table11 it is obvious that, the reaction of the test molecules with Cl atoms is much faster (nearly two order of magnitude) than the reaction with OH radicals.



However, the main degradation processes happen due to its reaction with OH radicals. This can attributed to the fact that the concentration of OH radicals in the Earth’s atmosphere is more when compared to that of Cl atoms. The calculated effective lifetime of 1-CP is 1.60 days and 2-CP is 2.80 days. As the effective lifetime of both the test molecules are very short their contribution to the global warming is very negligible. The degradation of VOCs leads to the formation of peroxy and alkoxy radicals in presence of oxygen. These peroxy and alkoxy radicals oxidizes NO to NO2, which in the presence of light and oxygen generates ozone molecule. Since 1-CP and 2-CP are emitted into Earth’s atmosphere in sufficient quantity, it is necessary to determine its ozone formation potential. The method developed by Jenkin et al.72 was used to calculate the ozone formation potential. The maximum number of ozone molecules which can be formed from one hydrocarbon depends on the sum of the number of C-C and C-H bonds (nB) present in the substrate. The number of C-C and C-H bonds are 9 for both 1-CP and 2-CP. The estimated photochemical ozone formation potential (POCPE) for 1-CP and 2-CP were calculated using the following equation and was found to be 13 and 10 respectively. (POCP)E = (A× γs × R × S × F) + P + Ro3 -Q Where, A, γs, R and S are the core parameters used for all the VOCs whereas F, P, Ro3 and Q are the parameters used for specific sets of compounds (usually unsaturated, carbonyls and hydroxy arenes). “γs” is the structural parameter related to the number of oxidizable bonds per unit mass and the molecular weight of VOCs relative to ethylene. It is directly proportional to ozone formation and is defined by the following relation 𝛾𝑠 =

𝑛𝐵

28.05

6

𝑀

( )×( )


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M= molecular weight of the VOCs. “R” is the element related to the reactivity of VOCs with OH radical and is given by the following relation 𝑅 = 1 ― (𝐵.𝛾𝑅 + 1) ―1 𝛾𝑅 =

( )×( ) 𝑘𝑂𝐻

6

𝑘0𝑂𝐻

𝑛𝐵

Where, 𝑘0𝑂𝐻 is the rate coefficient for the reaction of ethylene with OH radical i.e, 8.64 × 10-12 cm3molecule-1s-1. 𝑘𝑂𝐻 is the rate coefficient of OH radical reaction with 1-CP and 2-CP ((9.8±1.0) ×10-13 cm3 molecule-1 s-1 and (7.0±0.7) ×10-13 cm3 molecule-1 s-1 for respectively)15. Therefore, the degradation of 1-CP and 2-CP would form negligible amount of ozone in the troposphere. 4. Conclusion The rate coefficient for the reaction of 1-CP and 2-CP with Cl atoms were measured by relative rate experimental technique with reference to ethane, ethylene and ethyl acetate in the temperature range of 268–363K. Rate coefficients for the title reactions were also calculated computationally employing CVT/SCT at CCSD/cc-pVDZ//MP2/6-31+G(d,p) level of theory in the temperature range of 200 –400K. For both the reactions, experimentally measured rate coefficients are in very good agreement with the computationally calculated and previously reported rate coefficients at 298K. Negative temperature dependency was observed for the title reactions both experimentally and computationally. Abstraction of hydrogen attached to the carbon to which the Cl atom is attached, is the most labile pathway for both R1 and R2 reactions. Thermodynamically, the hydrogen abstraction from the middle carbon (-CH2-) is the most feasible pathway irrespective to the position of the Cl atom. On photo-oxidation, these mono halogenated propanes generates carbonyl compounds (propionaldehyde and acetone) which are the source for PPN and PAN and



generates ozone in the troposphere. As these mono-chlorinated propanes have less atmospheric lifetime, they are degraded close to the emission source and have an impact on mainly local scale which suggests inconsiderable global warming potential for the change of climate. Supporting information: The optimized parameters and frequencies for the reactants, pre-reactive complexes, transition states and products are given in Tables S1 to S4 and the mass spectra and IR spectra for all the product for the reactions of Cl atoms with 1-CP and 2-CP are given in Figure S3 to S4. Acknowledgement The authors cordially thank the Department of Science and Technology (DST), Government of India, for the financial support. We also thank Mr. V. Ravichandran, High Performance Computing Environment (HPCE), IIT Madras for the help in providing the computational resources to carry out the calculations. References 1. Laine, P.L.; Nicovich, J.M.; Wine, P.H. 2011. Kinetic and mechanistic study of the reactions of atomic chlorine with CH3CH2Br, CH3CH2CH2Br, and CH2BrCH2Br. The J. Phy. Chem. A. 2011, 115,1658-1666. 2. Van Agteren, M.H.; Keuning, S.; Janssen, D. 2013. Handbook on biodegradation and biological treatment of hazardous organic compounds (Vol. 2). Springer Science and Business media. 2013 3. Rowland, F. S. Stratospheric ozone depletion. Philos Trans R Soc Lond B Biol Sci. 2006, 361, 769-790. 4. Jordan, A.; Harnisch J.; Borchers, R.; Guern F L.; Shinohara, H. Volcanogenic halocarbons. .Environ. Sci. Technol. 2000, 34, 1122 – 1124. 5. von Rymon Lipinski GW; Ullmann's encyclopedia of industrial chemistry. 7th ed. 1999-2013. New York, NY: John Wiley & Sons.


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Table 1: Relative rate measurements for the reaction of Cl atoms with 1-Chloropropane over the temperature range of 268-363K at 760 Torr in N2 relative to ethane and ethylene . T (K)

Reference compound Ethane

268 ± 2 Ethylene

Ethane 283 ± 2 Ethylene

Ethane 298 ± 2

(ksample / kreference) ± 2σ 0.93 ± 0.08 0.89 ± 0.03 0.95 ± 0.02 0.42 ± 0.02 0.40 ± 0.04 0.43 ± 0.04 0.82 ± 0.02 0.85 ± 0.04 0.79 ± 0.05 0.49 ± 0.03 0.46 ± 0.02 0.50 ± 0.03 0.79 ± 0.02 0.78 ± 0.06 0.80 ± 0.05

(ksample / kreference)Average ± 2σ

(k ± 2σ) × 1011 (cm3 molecule-1 s-1)

0.92 ± 0.09

5.27 ± 1.20

0.42 ± 0.06

5.63 ± 0.86

0.82 ± 0.07

4.78 ± 1.03 5.10 ± 1.24

0.48 ± 0.05

5.41 ± 0.60

0.79 ± 0.08

4.67 ± 1.03 4.81 ± 1.15

Ethylene

0.53 ± 0.02 0.53 ± 0.03 0.65 ± 0.08

0.53 ± 0.09

4.96 ± 0.47

Ethane

0.70 ± 0.08

0.69 ± 0.15

4.14 ± 1.19

0.71 ± 0.10

4.44 ± 1.47

0.59 ± 0.03 Ethylene

0.60 ± 0.08 0.56 ± 0.02 0.66 ± 0.03

0.58 ± 0.09

4.74 ± 0.77

Ethane

0.60 ± 0.08

0.63 ± 0.10

3.91 ± 0.91

0.63 ± 0.04

343 ± 2

4.21 ± 1.08

0.71 ± 0.04 Ethylene

0.72 ± 0.01

0.72 ± 0.04

4.51 ± 0.48

0.59 ± 0.10

3.73 ± 0.92

0.81 ± 0.09

4.34 ± 0.65

0.74 ± 0.01 0.62 ± 0.08 Ethane

363 ± 2

0.59 ± 0.04 0.57 ± 0.02 0.83 ± 0.03

Ethylene

0.80 ± 0.06

Reported.k×1011 (cm3 molecule-1 s-1) at 298K

5.45 ± 1.49

0.54 ± 0.01

313 ± 2

(kaverage ± 2σ) ×1011 (cm3 molecule-1 s-1)

0.81 ± 0.06


4.04 ± 1.17

4.90 ± 1.50 [20] 4.80 ± 0.40 [21]


Page 40 of 56

Table 2: Relative rate measurements for the reaction of Cl atoms with 2-Chloropropane over the temperature range of 268-363K at 760 Torr in N2 relative to ethane and ethyl acetate.

Temp (K)

Reference compound

Ethane 268 ± 2 Ethyl acetate

Ethane 283 ± 2 Ethyl acetate

Ethane 298 ± 2

(ksample / kreference) ± 2σ 0.54 ± 0.02 0.55 ± 0.06 0.54 ± 0.02 2.22 ± 0.04 2.26 ± 0.06 2.23 ± 0.02 0.49 ± 0.04 0.50 ± 0.02 0.51 ± 0.04 2.19 ± 0.04 2.20 ± 0.02 2.19 ± 0.03 0.38 ± 0.01 0.40 ± 0.02 0.41 ± 0.01

(ksample / kreference)Average ± 2σ

(k ± 2σ) × 1011 (cm3 molecule-1 s-1)

0.54 ± 0.07

3.10 ± 0.75

2.24 ± 0.07

3.49 ± 0.48

0.50 ± 0.06

2.92 ± 0.68 3.05 ± 0.83

2.19 ±0.05

3.18 ± 0.44

0.40 ± 0.02

2.34 ± 0.48 2.65 ± 0.66

Ethyl acetate

2.17 ± 0.02 2.16 ± 0.02 0.43 ± 0.02

2.17 ± 0.05

2.97 ± 0.44

Ethane

0.41 ± 0.02

0.42 ± 0.11

2.55 ± 0.56

0.43 ± 0.04 Ethyl acetate

Ethane

2.13 ± 0.06 2.15 ± 0.01 2.16 ± 0.01 0.43 ± 0.07 0.40 ± 0.06

2.66 ± 0.72 2.15 ± 0.06

2.77 ± 0.44

0.41 ± 0.11

2.52 ± 0.81

0.39 ± 0.06

343 ± 2

2.52 ± 0.91

2.12 ± 0.09 Ethyl acetate

2.14 ± 0.04

2.12 ± 0.10

2.51 ± 0.42

0.40 ± 0.10

2.50 ± 0.77

2.11 ± 0.02 Ethane 363 ± 2 Ethyl acetate

0.38 ± 0.06 0.40 ± 0.02 0.41 ± 0.08 2.10 ± 0.05 2.07 ± 0.03 2.10 ± 0.06

Reported .k×1011 (cm3 molecule-1 s-1) at 298K

3.29 ± 0.91

2.18 ± 0.04

313 ± 2

(kaverage ± 2σ) × 1011 (cm3 molecule-1 s-1)

2.42 ± 0.86 2.09 ± 0.08

2.34 ± 0.41


2.00 ± 0.60 [20] 2.00 ± 0.30 [21] 2.01 ± 0.49 [23] 1.97 ± 0.06 [22]

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Table 3. L-parameter for the reaction of 1-chloropropane and 2-chloropropane with Cl atoms calculated at MP2/6-31+G(d, p). Transition states

L- parameter R1 R2 1.68 1.73 1.65 2.11 0.88 1.09 0.91 0.59

TS1 TS2 TS3 TS4

Table 4: Enthalpy of reaction [ΔH0 (298K) Gibbs free energy [ΔG0 (298K), kcal mol−1] for the reaction of Cl atoms with 1-Chloropropane at the MP2/6-31+G(d,p) level of theory TSs TS1 TS2 TS3 TS4

ΔH0 (kcal mol-1 ) 3.77 3.85 0.71 0.75

ΔG0 (kcal mol-1) 0.77 0.32 -2.16 -1.86

Table 5: Calculated total CVT/SCT rate coefficients (cm3 molecule-1 s-1) for the reaction of Cl atoms with 1-chloropropane obtained at the CCSD/cc-pVDZ//MP2/6-31+G(d,p) level of theory.

200

k (cm3 molecule-1 s1) 7.04 × 10-11

225

5.77 × 10-11

250

5.03 × 10-11

275

4.57 × 10-11

298

4.32 × 10-11

300

4.31 × 10-11

325

4.15 × 10-11

350

4.07× 10-11

375

4.07 × 10-11

400

4.10 × 10-11

Temperature (K)



Table 6: Enthalpy of reaction [ΔH0 (298K) Gibbs free energy [ΔG0 (298K), kcal mol−1] for the reaction of Cl atoms with 2-chloropropane at the MP2/6-31+G(d,p) level of theory. TSs TS1 TS2 TS3 TS4

ΔH0 (kcal mol-1 ) 4.09 4.09 4.09 -0.67

ΔG0 (kcal mol-1) 1.51 1.51 1.51 -3.51

Table 7: Calculated total CVT/SCT rate coefficients (cm3 molecule-1 s-1) for the reaction of Cl atoms with 2-chloropropane obtained at the CCSD/cc-pVdz//MP2/6-31+G(d,p) level of theory.

Temperature (K)

k (cm3 molecule-1 s-1)

200

8.20×10-11

225

5.54×10-11

250

4.17×10-11

275

3.39×10-11

298

2.93×10-11

300

2.90×10-11

325

2.60×10-11

350

2.42×10-11

375

2.30×10-11

400

2.23×10-11


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Table 8: Reactivity of series of halogenated propanes with Cl atoms and OH radicals at 298K. Molecules

kCl (cm3 molecule-1 s-1)

kOH (cm3 molecule-1 s-1)

1.20 × 10-10

1.1 × 10-12

Cl

4.81 × 10-11

9.8 × 10-13

Cl

Br

2.65 × 10-11

7.0 × 10-13

6.1×10-11

1.18×10-12

2.7 × 10-11

0.88 × 10-12

_

4.6 × 10-13

_

4.6 × 10-13

Br

Cl Cl Cl Cl

Cl

Table 9: Branching ratios for the reactions of Cl atoms with 1-chloropropane in the range of 200 – 400 K. Temperature(K)

Branching ratio (%) RP1

RP2

RP3

RP4

200

3.32×10-2

4.35×10-3

1.57

98.34

225

7.65×10-2

1.16×10-2

2.31

97.60

250

1.49×10-1

2.57×10-2

3.17

96.60

275

2.59×10-1

4.96×10-2

4.15

95.53

298

3.96×10-1

8.28×10-2

5.10

94.50

300

4.09×10-1

8.62×10-2

5.21

94.24

325

6.09×10-1

1.40×10-1

6.35

92.91

350

8.49×10-1

2.11×10-1

7.52

91.39

375

1.14

3.03×10-1

8.76

89.72

400

1.48

4.16×10-1

10.05

88.11



Page 44 of 56

Table 10: Branching ratios for the reactions of Cl atoms with 2-chloropropane in the range of 200 – 400 K. Temperature(K)

Branching Ratio(%) RP1

RP2

RP3

RP4

200

1.77×10-3

1.33×10-3

1.77×10-3

99.990

225

5.97×10-3

4.40×10-3

5.97×10-3

99.967

250

1.57×10-2

1.15×10-2

1.57×10-2

99.914

275

3.46×10-2

2.51×10-2

3.46×10-2

99.811

298

6.38×10-2

4.58×10-2

6.38×10-2

99.653

300

6.72×10-2

4.83×10-2

6.72×10-2

99.634

325

1.17×10-1

8.37×10-2

1.17×10-1

99.363

350

1.89×10-1

1.34×10-1

1.89×10-1

98.977

375

2.85×10-1

2.03×10-1

2.85×10-1

98.454

400

4.10×10-1

2.91×10-1

4.10×10-1

97.776

Table 11: Atmospheric lifetimes (τ) calculated for 1-chloropropane and 2- chloropropane with different atmospheric oxidizing agents at 298K.

Molecule 1-chloropropane 2-chloropropane

Cl atoms

OH radicals

[Cl] = 1.3 × 105 atom cm-3,

[OH] = 1×106 radical cm-3.

MBL70,71

Diurnal69

Cumulative life times

kCl ×1011 3 (cm molecule-1s-1)

τ (days)

kOH ×1013 3 (cm molecule-1s-1)

τ (days)

τeff (days)

4.81

1.85

9.80

11.81

1.60

2.65

3.36

7.00

16.53

2.80


Page 45 of 56

ln ([sample]0/[sample]t)

1.4 1.2 1.0 0.8 0.6

with reference to ethane with reference to ethylene

0.4 0.2 0.0 0.0

0.5

1.0 1.5 2.0 ln ([reference]0/[reference]t)

2.5

3.0

Figure 1: Plot of the relative decrease in the concentration of 1-chloropropane due to its reaction with Cl atoms relative to ethane and ethylene at 298K.

500

400

300

250

200

-22.5 This work (Experimental) This work(Theory) Tyndall et al. Donaghy et al.

-23.0

-23.5

3

-1 -1

ln (k(cm molecule s ))

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-24.0

-24.5 2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

-1

1000/T (K )

Figure 2: Arrhenius plot of experimentally measured rate coefficients between 268 and 363 K, computed CVT/SCT rate coefficients at CCSD/cc-pVDZ//MP2/6-31+G(d,p) level of theory between 200 and 400 K for the reaction of Cl atoms with 1-chloropropane.


Page 46 of 56

with reference to ethane with reference to ethyl acetate

1.5

1.0

0.5

0.0 0.0

0.5

1.0 1.5 2.0 ln([reference]0/[reference]t)

2.5

Figure 3: Plot of the relative decrease in the concentration of 2-chloropropane due to its reaction with Cl

atoms relative to ethane and ethyl acetate at 298 K.

600 500 -22.5 -23.0 -23.5

400

300

250

200

4

5

This work (Experimental) This work (Theory) Donaghy et al Tyndall et al Sarzynski et al Le Crâne et al.

-24.0

3

-1 -1

ln(k(cm molecule s ))

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ln([sample]0/[sample]t)


-24.5 -25.0 -25.5 2

3 1000/T(K)

Figure 4: Arrhenius plot of experimentally measured rate coefficients between 268 and 363 K, and computed CVT/SCT rate coefficients at CCSD/cc-pVDZ//MP2/6-31+G(d, p) level of theory between 200 and 400 K for the reaction of Cl atoms with 2-chloropropane.


Page 47 of 56 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1-chloropropane

TS1

RC4

TS2

TS4

TS3

P1

P3

P2

PC1

PC2

P4

PC4 PC3


HCl


Figure 5: Optimized geometries of the reactants, pre-reactive complexes, transition states and products for the reaction of Cl atoms with 1-chloropropane obtained at MP2/6-31+G(d,p) level of theory. Black color represents carbon atoms, blue color represents hydrogen atoms and green color represents Cl atoms.

+12 TS2 (10.58) +10

TS1(9.75) TS3 (8.37)

+8

Relative Energy (kCal/mol)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 48 of 56

(P1+ HCl ) (7.47) (P2 + HCl) (7.37)

TS4 (7.76)

+6

PC2(5.42) +4

PC1(5.18)

(P3 + HCl) (3.65) (P4 + HCl) (3.45)

+2 PC4 (0.82) 0

-2

(R1 + R2)

PC3(0.14)

RC1, RC2 RC3, RC4(-1.97)

-4 -6

Figure 6: Potential energy diagram for the reaction of Cl atoms with 1-chloropropane obtained at CCSD/cc-pVDZ//MP2/6-31+G(d,p) level of theory at 298K.


Page 49 of 56 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2-Chloropropane

RC2

RC1

TS1

RC4

RC3

TS3

TS2

TS4

PC1 PC2

PC3

P1 P2

P3

HCl P4 Figure 7: Optimized geometries of the reactants, pre-reactive complexes, transition states and products for the reaction of Cl atoms with 2-chloropropane obtained at MP2/6-31+G(d,p) level of theory. Black color represents carbon atoms, blue color represents hydrogen atoms and green color represents Cl atoms.



TS3 (12.32) +12

TS2(11.91)

+10

TS1 (10.24)

(P1, P2,P3) + HCl (7.19)

+8

+6 Relative Energy (kCal/mol)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 50 of 56

TS4 (5.05)

PC1 (5.18) PC3 (3.41)

+4

PC2 (3.33) +2

0

P4 + HCl (1.86)

(R1 + R2) RC1(-0.65) RC3(-2.02) RC4(-2.03)

-2 RC2 (-2.08) -4 -6

Figure 8: Potential energy diagram for the reaction of Cl atoms with 2-chloropropane obtained at CCSD/ccpVDZ//MP2/6-31+G(d,p) level of theory at 298K.


Page 51 of 56

Branching Ratio (%)

100 80

kTS4/ktotal kTS3/ktotal kTS2/ktotal kTS1/k

60 40 20 0 200

250

300 Temperature (K)

350

400

Figure 9: Calculated branching ratios vs temperature for the reaction of Cl atoms with 1-chloropropane.

100

Branching Ratio (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


80

kTS1/kTotal kTS2/kTotal kTS3/kTotal kTS4/kTotal

60 40 20 0 200

250

300 Temperature (K)

350

400

Figure 10: Calculated branching ratios vs temperature for the reaction of Cl atoms with 2-chloropropane.



6

22x10

A 1-chloropropane + Cl B

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 52 of 56

F

21

D

E

20 C 19

2

4

6

8 10 12 Retention Time (min)

14

16

Figure 11: GC-MS chromatogram for the reaction of 1-chloropropane with Cl atoms in the presence of oxygen. A: Nitrogen, B: carbon dioxide, C: propylene, D: propionaldehyde, E:1-chloropropane, F: HCl.


Page 53 of 56 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Cl

1-chloropropane

Cl

.

Cl

Cl 1,2 H-shift

.

Cl

O2 Cl Cl

+

propylene

Cl

.

propylene

OO Cl

Cl Cl

+

2

O

.

O

.O

O

Cl

O

O

.

O

.

O2

propionaldehyde Cl

Figure 12: Degradation mechanism for the reaction of 1-chloropropane with Cl atoms in the presence of oxygen.



6

20.5x10

20.0

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 54 of 56

A

2-chloropropane + Cl

B

19.5 19.0

C E

18.5

F

D 18.0 2

4 6 Retention time (min)

8

Figure 13: GC-MS chromatogram for the reaction of 2-chloropropane with Cl atoms in the presence of oxygen. A: Nitrogen, B: carbon dioxide, C: acetone, D: propylene, E:2-chloropropane, F: HCl.


Page 55 of 56 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2-chloropropane Cl Cl

CH2.

.

Cl

Cl O2

+

OO.

Cl

propylene Cl O

O.

O

O

O

2

+ Cl

O2

Cl

O.

Cl

Cl

O

Cl

Acetone

Figure 14: Degradation mechanism for the mechanism for the reaction of 2-chloropropane with Cl atoms in the presence of oxygen.



TOC Graphic


Page 56 of 56

Cl Atom Initiated Photo-oxidation of Mono-chlorinated Propanes To

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