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Rate Coefficients for the Reactions of OH Radicals with a Series of Alkyl Substituted Amines Ian Barnes, Peter Wiesen, and Michael Gallus J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.6b08713 • Publication Date (Web): 18 Oct 2016 Downloaded from http://pubs.acs.org on October 19, 2016
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Rate Coefficients for the Reactions of OH Radicals with a Series of Alkyl
2
Substituted Amines
3 Ian Barnesa,*, Peter Wiesena, Michael Gallusa
4 5 6
a
Bergische Universität Wuppertal, Fakultät Mathematik und Naturwissenschaften,
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Physikalische & Theoretische Chemie, Gauss Strasse 20, 42119 Wuppertal,
8
Germany
9 10
* Author to whom correspondence should be addressed
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Tel.: +49 202 439 2510
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Fax: +49 202 4392505
13
Email;
[email protected] 14 15 16
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Abstract
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Rate coefficients have been determined at (298 ± 2) K and atmospheric pressure for
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the reaction of OH radicals with two primary mono-alkyl, one secondary di-alkyl and
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five tertiary tri-alkyl substituted amines in a large volume photoreactor using the
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relative kinetic technique. The following rate coefficients (in cm3 molecule-1 s-1 units)
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have been obtained:
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1,2-dimethylpropylamine, CH3C(CH3)HC(CH3)H)NH2: (5.08 ± 1.02) × 10-11; tert-amylamine (tert-pentylamine), CH3CH2C(CH3)2NH2: (0.86 ± 0.17) × 10-11; diethylamine, (CH3CH2)2NH: (7.36 ± 1.47) × 10-11 N,N-dimethylethylamine, (CH3)2NCH2CH3: (7.37 ± 1.47) × 10-11; N,N-dimethylpropylamine, (CH3)2NCH2CH2CH3: (10.97 ± 1.78) × 10-11; N,N-dimethylisopropylamine, (CH3)2NCH(CH3)2: (9.79 ± 1.75) × 10-11; N,N-diethylmethylamine, (CH3CH2)2NCH3: (8.92 ± 1.54) × 10-11; triethylamine, (CH3CH2)3N: (10.86 ± 1.88) × 10-11.
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The quoted errors are the 2σ deviations from least-squares linear analyse of the
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kinetic date plus a contribution to take into account uncertainties associated with the
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reference compounds. With the exception of diethylamine this study represents the
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first determinations of the rate coefficients for reaction of the compounds with OH
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radicals. The results are compared with rate coefficients available in the literature for
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smaller alkyl substituted amines and also the values predicted for the compounds
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investigated using a structure activity relationship (SAR). With the exception of tert-
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amylamine the SAR predicted OH rate coefficients are in good agreement with the
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experimental values. 2 ACS Paragon Plus Environment
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Introduction
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Amines are derivatives of ammonia (NH3) where one, two or three of the hydrogen
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atoms are replaced by organic groups to produce primary, secondary and tertiary
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amines, respectively. Amines are emitted to the atmosphere from natural sources
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such as oceans, biomass burning, vegetation and geologic activities and a number
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of current and proposed large scale industrial processes make use of amines which
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will result in fugitive emissions. For example, they are used to a large extent in the
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pharmaceutical industry and are widely used in developing chemicals for crop
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protection, medication and water purification. Amines are used in a diverse array of
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end-use applications such as personal care products, agricultural chemicals,
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cleaning products, gas treatment, petroleum, water treatment, pharmaceuticals, and
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food processing. Amines are also used extensively in the foundry industry whereby
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their first use dates back to the 1960s with the introduction of the Phenolic Urethane
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Cold Box Process (PUCB).1 The PUCB process utilizes an amine gas to catalyze the
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reaction between a phenolic resin and an isocyanate resin to produce a urethane
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bond. In the process no by-products are produced and curing takes place at the
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same rate throughout. Amines such as trimethylamine (TEA), dimethylethylamine
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(DMEA) and dimethylisopropylamine (DMIPA) are commonly used to cure the
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phenolic urethane cold box binders. The anthropogenic and natural sources of
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atmospheric amine emissions have been reviewed recently by Ge et al.2
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The possible large-scale use of amines such as monoethanol amine (MEA) in
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carbon capture technologies3 and the associated potential of
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anthropogenic amine emission to the atmosphere has helped to kindle interest in the
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atmospheric chemistry of amines.
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industry and market studies estimate that the size of the market will grow from USD
large-scale
The amine global market is a billion dollar
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13.35 Billion in 2015 to USD 19.90 Billion by 2020.4 The large scale employment of
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amines in the diverse array of applications in which they are used will unavoidably
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result in direct and fugitive emissions of amines to the atmosphere. Amine
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emissions, including both anthropogenic and natural sources, are an important
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component of VOC emissions and have impacts on important environmental topics
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such as aerosol formation and the production of potential carcinogens. To date,
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approximately 150 amines have been identified in the atmosphere whereby
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according to Ge et al.2 the most common and abundant are low-molecular weight
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aliphatic amines with carbon numbers of 1-6.
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It is only fairly recently that the atmospheric gas-phase chemistry of low-molecular
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weight alkylated primary, secondary and tertiary amines (mainly methylated) has
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received attention. Reviews of the presently available gas-phase amine chemistry
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can be found in Nielsen et al.
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reviews emphasize the need for additional kinetic and mechanistic data in this area.
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The multiphase chemistry of atmospheric amines has been reviewed by Qiu and
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Zhang.9
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Studies to date indicate that the main atmospheric fate of amines will be competition
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between reaction with the OH radical7 and heterogeneous uptake.10,11
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Room temperature rate coefficients have been reported in the literature for the
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reaction of the OH radical with a number of aliphatic amines including methylamine
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(CH3NH2)12,13,14 dimethylamine ((CH3)2NH)13,14,15, trimethylamine ((CH3)3N)13,14,15,
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ethylamine ((CH3CH2)NH2)13,14,15, diethylamine ((CH3CH2)2NH)7,16, methylethylamine
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(CH3(CH3CH2)NH)7 and methylpropylamine (CH3(CH3CH2CH2)NH).7 There have
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been three kinetic investigations of the reaction of OH with the carbon capture
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technology
important
5,6,7
and Lee and Wexler.8 The authors of these
monoethanol
amine.17,18,19
For
reactions
where
the
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temperature dependency of the rate coefficients has been investigated, it has been
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found to be negative in all cases.12,14,15,17 Reaction of OH with the amines will occur
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via H-atom abstraction from the alkyl chains attached to the nitrogen atom and in the
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case of primary and secondary amines also from the N-H site. Onel et al.20 have
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recently investigated the branching ratios for αC-H and N-H abstraction in the
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reactions of OH with methylamine, dimethylamine and ethylamine.
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In this study we present determinations of rate coefficients for the reaction of the OH
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radical with two primary mono-alkyl, one-dialkyl and five tertiary tri-alkyl substituted
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amines many of which are either used or are under consideration as catalysts in the
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PUCB process, i.e. 1,2-dimethylpropylamine, tert-amylamine (tert-pentylamine),
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diethylamine,
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dimethylisopropylamine, N,N-diethylmethylamine and triethylamine, reactions (1) to
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(8) below:
N,N-dimethylethyl
amine,
N,N-dimethylpropylamine,
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OH + CH3C(CH3)HC(CH3)H)NH2
→ products (1)
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OH + CH3CH2C(CH3)2NH2
→ products (2)
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OH + (CH3CH2)2NH
→ products (3)
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OH + (CH3)2NCH2CH3
→ products (4)
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OH + (CH3)2NCH2CH2CH3
→ products (5)
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OH + (CH3)2NCH(CH3)2
→ products (6)
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OH + (CH3H2)2NCH3
→ products (7)
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OH + (CH3CH2)3N
→ products (8)
N,N-
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The rate coefficients have been measured in a large volume photoreactor at room
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temperature using the relative kinetic technique and, with the exception of
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diethylamine for which there is some uncertainty in the rate coefficient, represent the
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first determinations of the rate coefficients. 6 ACS Paragon Plus Environment
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Experimental
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The experiments were performed in a large volume (1080 L) quartz-glass reaction
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chamber at a total pressure of 760 Torr (760 Torr = 101.325 kPa) of synthetic air and
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(298 ± 2) K. The reactor is described in detail elsewhere21 and only a basic
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description is given here. The chamber can be evacuated by a pumping system
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consisting of a turbo-molecular pump backed by a double stage rotary fore pump to
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10-3 Torr. Magnetically coupled Teflon mixing fans are mounted inside the chamber
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to ensure homogeneous mixing of the reactants. The chamber is surrounded by two
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types of lamps: 32 super actinic fluorescent lamps (Philips TL 05/40 W:
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320N- reported in Nielsen et
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al.7 which are all lower than those used in the Kwok and Atkinson24 SAR, in
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particular, for the R3N parameter which is around 30% lower. The revised SAR
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parameters of Nielsen et al.7 thus obviously result in lower rate coefficient estimates
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for the reactions of OH with the amines investigated in this work and consequently
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also in a poorer agreement between predicted and experimental values compared to
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the Kwok and Atkinson24 SAR, especially for the tertiary amines.
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It is interesting to consider why tert-amylamine is so much less reactive toward OH
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than predicted by the Kwok and Atkinson24 SAR which functions reasonably well for
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the other aliphatic amines. In contrast to all of the other aliphatic amines which have
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been investigated here (Table 1) and also most of those reported in the literature
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(Table 2) tert-amylamine has a tertiary carbon atom (>CCH-. It would appear
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that in such a case the RNH2 parameter of 21 × 10-12 cm3 molecule-1 s-1 presently
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used in the Kwok and Atkinson SAR is significantly over estimated. A value of only 7
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to 8 × 10-12 cm3 molecule-1 s-1 for the RNH2 parameter would be required to match
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the experimentally determined rate coefficient for OH with tert-amylamine
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determined in this work. To our knowledge the only other alkyl amine to be
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investigated which has a tertiary carbon atom (>C
