Gas-Phase Reaction of Methyl Isothiocyanate and Methyl Isocyanate with Hydroxyl Radicals under Static Relative Rate Conditions

Lü, Zhou; Hebert, Vincent R.; Miller, Glenn C.

doi:10.1021/jf404526t

Cited by 14 publications

(20 citation statements)

References 11 publications

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“…The atmospheric chemistry of CH 3 NCO is less well studied than HNCO. There is a single reported measurement of the reaction rate of CH 3 NCO with OH by relative rates which gave k = 3.6 × 10 −12 cm 3 mole −1 s −1 (Lu et al, 2014); however recent work indicates that secondary chemistry may have made this rate high by a significant amount (Papanastasiou et al, 2019). In addition, there are likely condensedphase reactions that are faster than the simple hydrolysis reactions consider in this work.…”

Section: Ch 3 Ncomentioning

confidence: 99%

“…There have only been a few studies on the gas-phase loss rates of CH 3 NCO including reaction with OH radicals, which appears to be slow based on the most recent measurements (Lu et al, 2014;Papanastasiou et al, 2019), re-action with chlorine atoms (Cl), which might be as much as 20 % of OH under some atmospheric conditions (Papanastasiou et al, 2019), and UV photolysis, which has a negligible contribution to atmospheric loss (Papanastasiou et al, 2019). Thus, heterogeneous uptake might compete with these gas-phase loss processes.…”

Section: Introductionmentioning

confidence: 99%

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Solubility and solution-phase chemistry of isocyanic acid, methyl isocyanate, and cyanogen halides

Roberts

Liu

2019

Atmos. Chem. Phys.

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Abstract. Condensed-phase uptake and reaction are important atmospheric removal processes for reduced nitrogen species, isocyanic acid (HNCO), methyl isocyanate (CH3NCO), and cyanogen halides (XCN, X = Cl, Br, I); yet many of the fundamental quantities that govern this chemistry have not been measured or are not well studied. These nitrogen species are of emerging interest in the atmosphere as they have either biomass burning sources, i.e., HNCO and CH3NCO, or, like the XCN species, have the potential to be a significant condensed-phase source of NCO− and therefore HNCO. Solubilities and the first-order reaction rate of these species were measured for a variety of solutions using a bubble flow reactor method with total reactive nitrogen (Nr) detection. The aqueous solubility of HNCO was measured as a function of pH and had an intrinsic Henry's law solubility of 20 (±2) M atm−1 and a Ka of 2.0 (±0.3) × 10−4 M (pKa = 3.7±0.1) at 298 K. The temperature dependence of HNCO solubility was very similar to other small nitrogen-containing compounds, such as HCN, acetonitrile (CH3CN), and nitromethane, and the dependence on salt concentration exhibited the “salting out” phenomenon. The rate constant of reaction of HNCO with 0.45 M NH4+, as NH4Cl, was measured at pH = 3 and found to be 1.2 (±0.1) × 10−3 M−1 s−1, faster than the rate that would be estimated from rate measurements at much higher pHs. The solubilities of HNCO in the non-polar solvents n-octanol (n-C8H17OH) and tridecane (C13H28) were found to be higher than aqueous solution for n-octanol (87±9 M atm−1 at 298 K) and much lower than aqueous solution for tridecane (1.7±0.17 M atm−1 at 298 K), features that have implications for multi-phase and membrane transport of HNCO. The first-order loss rate of HNCO in n-octanol was determined to be relatively slow, 5.7 (±1.4) × 10−5 s−1. The aqueous solubility of CH3NCO was found to be 1.3 (±0.13) M atm−1 independent of pH, and CH3NCO solubility in n-octanol was also determined at several temperatures and ranged from 4.0 (±0.5) M atm−1 at 298 K to 2.8 (±0.3) M atm−1 at 310 K. The aqueous hydrolysis of CH3NCO was observed to be slightly acid-catalyzed, in agreement with literature values, and reactions with n-octanol ranged from 2.5 (±0.5) to 5.3 (±0.7) × 10−3 s−1 from 298 to 310 K. The aqueous solubilities of XCN, determined at room temperature and neutral pH, were found to increase with halogen atom polarizability from 1.4 (±0.2) M atm−1 for ClCN and 8.2 (±0.8) M atm−1 for BrCN to 270 (±54) M atm−1 for ICN. Hydrolysis rates, where measurable, were in agreement with literature values. The atmospheric loss rates of HNCO, CH3NCO, and XCN due to heterogeneous processes are estimated from solubilities and reaction rates. Lifetimes of HNCO range from about 1 day against deposition to neutral pH surfaces in the boundary layer, but otherwise can be as long as several months in the middle troposphere. The loss of CH3NCO due to aqueous-phase processes is estimated to be slower than, or comparable to, the lifetime against OH reaction (3 months). The loss of XCNs due to aqueous uptake is estimated to range from being quite slow, with a lifetime of 2–6 months or more for ClCN and 1 week to 6 months for BrCN to 1 to 10 days for ICN. These characteristic times are shorter than photolysis lifetimes for ClCN and BrCN, implying that heterogeneous chemistry will be the controlling factor in their atmospheric removal. In contrast, the photolysis of ICN is estimated to be faster than heterogeneous loss for average midlatitude conditions.

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Section: Ch 3 Ncomentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Solubility and solution-phase chemistry of isocyanic acid, methyl isocyanate, and cyanogen halides

Roberts

Liu

2019

Atmos. Chem. Phys.

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“…In addition to its toxicological importance, HNCO measurements are useful as the criteria of [HNCO]/ [CO] has been used to define the separation of flaming from smoldering combustion phases (Roberts et al, 2011). Methyl isocyanate (MIC) is a homologue of HNCO and a known secondary pollutant with precursors originating from both biogenic and anthropogenic sources (Lu et al, 2014;Woodrow et al, 2014) MIC has been measured as a direct emission from industrial processes and the burning of common building materials (Blomqvist et al, 2003;Henriks-Eckerman et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Observations of Isocyanate, Amide, Nitrate, and Nitro Compounds From an Anthropogenic Biomass Burning Event Using a ToF‐CIMS

et al. 2018

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Anthropogenic biomass burning is poorly represented in models due to a lack of observational data but represents a significant source of short‐lived toxic gases. Guy Fawkes Night (bonfire night) is a regular UK‐wide event where open fires are lit and fireworks are set off on 5 November. Previous gas phase studies of bonfire night focus on persistent organic pollutants primarily using off‐line techniques. Here the first simultaneous online gas phase measurements of several classes of compounds including isocyanates, amides, nitrates, and nitro‐organics are made during bonfire night (2014) in Manchester, UK, using a time‐of‐flight chemical ionization mass spectrometer (ToF‐CIMS) using iodide reagent ions. A shallow boundary layer and low wind speeds favor pollutant buildup with typical HCN, HNCO, and CH3NCO concentrations of tens of parts per thousand increasing by a factor of 13 to potentially harmful levels >1 ppb. Normalized excess mixing ratios relative to CO for a range of isocyanates and amides are reported for the first time. Using a HNCO:CO ratio of 0.1%, we distinguish emissions from flaming and smoldering combustion and report more accurate normalized excess mixing ratios for the distinct burning phases. While bonfire night is a highly polluting event, NO2 concentrations measured at this location are higher at other times, highlighting the importance of traffic as an NO2 emission source at this location. A risk communication methodology is used to equate enhancements in hourly averaged black carbon and NO2 concentrations caused by bonfire night as an equivalent of 26.1 passively smoked cigarettes.

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“…The atmospheric chemistry of CH3NCO is less well studied than HNCO. There is a single reported measurement of the reaction rate of CH3NCO with OH by relative rates which gave k = 3.6 ×10 -12 molec cm -3 sec -1 (Lu et al, 2014). The uptake coefficients estimated for CH3NCO in Figure 8 are relatively low with only a slight increase at the lowest pHs in atmospheric media.…”

Section: B Ch3ncomentioning

confidence: 88%

“…There have been only a few studies of the gas phase loss rates of CH3NCO including reaction with OH radical (Lu et al, 2014), which appears to be slow based on the mostly recent measurements (Papanastasiou et al, in preparation, 2018), reaction with chlorine atoms (Cl) which might be as much as 20% of OH under some atmospheric conditions (Papanastasiou et al, in preparation, 2018), and UV photolysis which has a negligible contribution to atmospheric loss (Papanastasiou et al, in preparation, 2018). Thus, heterogeneous uptake might compete with these gas phase loss processes.…”

mentioning

confidence: 99%

Solubility and Solution-phase Chemistry of Isocyanic Acid, Methyl Isocyanate, and Cyanogen Halides

Roberts¹,

Liu²

2018

Preprint

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Abstract. Condensed phase uptake and reaction are import atmospheric removal processes for reduced nitrogen species, isocyanic acid (HNCO), methyl isocyanate (CH3NCO) and cyanogen halides (XCN, X =Cl, Br, I), yet many of the fundamental quantities that govern this chemistry have not been measured or are understudied. Solubilities and first-order reaction rate of these species were measured for a variety of solutions using a bubble flow reactor method with total reactive nitrogen (Nr) detection. The aqueous solubility of HNCO was measured as a function of pH, and exhibited the classic behavior of a weak acid, with an intrinsic Henry's law solubility of 20 (&#177;2)&#8201;M/atm, and a Ka of 2.0 (&#177;0.28)&#8201;&#215;&#8201;10&#8722;4&#8201;M (which corresponds to pKa&#8201;=&#8201;3.7&#8201;&#177;&#8201;0.06) at 298&#8201;K. The temperature dependence of HNCO solubility was very similar to other small nitrogen-containing compounds and the dependence on salt concentration exhibited the &#8220;salting out&#8221; phenomenon that was also similar to small polar molecules. The rate constant of reaction of HNCO with 0.45&#8201;M&#8201;NH4+ was measured at pH&#8201;=&#8201;3, and found to be 1.2 (&#177;0.1)&#8201;&#215;&#8201;10&#8722;3&#8201;M&#8722;1&#8201;sec&#8722;1, which is much faster than the rate that would be estimated from rate measurements at much higher pHs, and the assumption that the mechanism is solely by reaction of the un-dissociated acid with NH3. The solubilities of HNCO in the non-polar solvents n-octanol (n-C8H17OH) and tridecane (C13H28) were found to be higher than aqueous solution for n-octanol (87&#8201;&#177;&#8201;3&#8201;M/atm at 298&#8201;K) and much lower than aqueous solution for tridecane (1.7&#8201;&#177;&#8201;0.17&#8201;M/atm at 298&#8201;K), but the first-order loss rate of HNCO in n-octanol was determined to be relatively slow 5.7 (&#177;1.4)&#8201;&#215;&#8201;10&#8722;5sec&#8722;1. The aqueous solubility of CH3NCO was measured at several pHs and found to be 1.3 (&#177;0.13)&#8201;M/atm independent of pH, and CH3NCO solubility in n-octanol was also determined at several temperatures and ranged from 4.0 (&#177;0.5) to 2.8 (&#177;0.3)&#8201;M/atm. The aqueous hydrolysis of CH3NCO was observed to be slightly acid-catalyzed, in agreement with literature values, and reactions with n-octanol ranged from 2.5 (&#177;0.5) to 5.3 (&#177;0.7)&#8201;&#215;&#8201;10&#8722;3&#8201;sec&#8722;1 from 298 to 310&#8201;K. The aqueous solubilities of XCN was determined at room temperature and neutral pH were found to increase with halogen atom polarizability from 1.4 (&#177;0.2)&#8201;M/atm for ClCN, 8.2 (&#177;0.8)&#8201;M/atm for BrCN, to 270 (&#177;41)&#8201;M/atm for ICN. Hydrolysis rates where measurable, were in agreement with literature values. The atmospheric loss rates of HNCO, CH3NCO, and XCN due to heterogeneous processes are estimated from solubilities and reaction rates. Lifetimes of HNCO range from about 1 day against deposition to neutral pH surfaces in the boundary layer, but otherwise can be as long as several months in the mid troposphere. The loss of CH3NCO due to aqueous phase processes is estimated to be slower than, or comparable to, the lifetime against OH reaction (3 months). The loss of XCNs due to aqueous uptake are estimated to range from quite slow, lifetime of 2&#8211;6 months or more for ClCN, 1 week to 6 months for BrCN, to 1 to 10 days for ICN. These characteristic times are shorter than photolysis lifetimes for ClCN, and BrCN, implying that heterogeneous chemistry will be the controlling factor in their atmospheric removal. In contrast, the photolysis of ICN is estimated to be faster than heterogeneous loss for average mid-latitude conditions.

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Gas-Phase Reaction of Methyl Isothiocyanate and Methyl Isocyanate with Hydroxyl Radicals under Static Relative Rate Conditions

Cited by 14 publications

References 11 publications

Solubility and solution-phase chemistry of isocyanic acid, methyl isocyanate, and cyanogen halides

Solubility and solution-phase chemistry of isocyanic acid, methyl isocyanate, and cyanogen halides

Observations of Isocyanate, Amide, Nitrate, and Nitro Compounds From an Anthropogenic Biomass Burning Event Using a ToF‐CIMS

Solubility and Solution-phase Chemistry of Isocyanic Acid, Methyl Isocyanate, and Cyanogen Halides

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