Preparation and properties of isocyanic acid

Belson, David J.; Strachan, Alec N.

doi:10.1039/cs9821100041

Cited by 73 publications

(53 citation statements)

References 2 publications

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“…The slope in Fig. 3a also allows us to determine HNCO's acid dissociation constant, K a , which at 298 K is 2.1 ± 0.2 × 10 −4 M. Our K a value also agrees well with previously reported K a for HNCO (Amell, 1956;Belson and Strachan, 1982). …”

Section: Ph Dependence Of K Eff Hsupporting

confidence: 80%

“…Once HNCO partitions to the aqueous phase, three mechanisms for its hydrolysis are possible. The first (Reaction R1) is acidcatalyzed and is therefore termolecular, whereas the second (Reaction R2) and third (Reaction R3) are bimolecular reactions involving either the protonated or deprotonated form of HNCO (Scheme 1) (Amell, 1956;Belson and Strachan, 1982;Jensen, 1958). In 1958, Jensen determined the hydrolysis rate of the three mechanisms through addition of AgNO 3 to buffered solutions at different time points to precipitate unreacted isocyanate as AgNCO, followed by back titration of excess AgNO 3 with NH 4 SCN.…”

Section: Henry's Law Coefficient Experiments 16mentioning

confidence: 99%

“…Until recently, the interest in studying HNCO was from a fundamental science perspective with research conducted on its structure, preparation and physical properties (Belson and Strachan, 1982) and on its theoretical rovibrational spectra (Mladenović and Lewerenz, 2008). Both theoretical and experimental data indicate that HNCO is the most stable CHNO isomer with a near-linear π -bond system (Hocking et al, 1975;Jones et al, 1950;Poppinger et al, 1977).…”

Section: Introductionmentioning

confidence: 99%

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Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere

et al. 2016

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Abstract.A growing number of ambient measurements of isocyanic acid (HNCO) are being made, yet little is known about its fate in the atmosphere. To better understand HNCO's loss processes and particularly its atmospheric partitioning behaviour, we measure its effective Henry's Law coefficient K eff H with a bubbler experiment using chemical ionization mass spectrometry as the gas phase analytical technique. By conducting experiments at different pH values and temperature, a Henry's Law coefficient K H of 26 ± 2 M atm −1 is obtained, with an enthalpy of dissolution of −34 ± 2 kJ mol −1 , which translates to a K eff H of 31 M atm −1 at 298 K and at pH 3. Our approach also allows for the determination of HNCO's acid dissociation constant, which we determine to be K a = 2.1 ± 0.2 × 10 −4 M at 298 K. Furthermore, by using ion chromatography to analyze aqueous solution composition, we revisit the hydrolysis kinetics of HNCO at different pH and temperature conditions. Three pH-dependent hydrolysis mechanisms are in play and we determine the Arrhenius expressions for each rate to be k 1 = (4.4 ± 0.2) × 10 7 exp(−6000 ± 240/T ) M s −1 , k 2 = (8.9 ± 0.9) × 10 6 exp(−6770 ± 450/T ) s −1 and k 3 = (7.2 ± 1.5) × 10 8 exp(−10 900 ± 1400/T ) s −1 , where k 1 is for HNCO + H + + H 2 O → NH + 4 + CO 2 , k 2 is for HNCO + H 2 O → NH 3 + CO 2 and k 3 is for NCO − + 2 H 2 O → NH 3 + HCO − 3 . HNCO's lifetime against hydrolysis is therefore estimated to be 10 days to 28 years at pH values, liquid water contents, and temperatures relevant to tropospheric clouds, years in oceans and months in human blood. In all, a better parameterized Henry's Law coefficient and hydrolysis rates of HNCO allow for more accurate predictions of its concentration in the atmosphere and consequently help define exposure of this toxic molecule.

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Section: Ph Dependence Of K Eff Hsupporting

confidence: 80%

Section: Henry's Law Coefficient Experiments 16mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere

et al. 2016

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“…2b). Thermal decomposition of solid cyanuric acid at 210 • C provides a convenient and relatively clean source of HNCO (Belson and Strachan, 1982), which then diffuses through a capillary (1 mm i.d., 5 cm length) and is mixed with a small flow (50 sccm) of zero air. The system was designed so that the entire capillary was kept at temperature and the gas stream allowed to cool only after mixing to lower concentrations since HNCO is known to polymerize at high concentrations (Fischer et al, 2002).…”

Section: Ni-pt-cimsmentioning

confidence: 99%

Measurement of HONO, HNCO, and other inorganic acids by negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS): application to biomass burning emissions

et al. 2010

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Abstract. A negative-ion proton-transfer chemical ionization mass spectrometric technique (NI-PT-CIMS), using acetate as the reagent ion, was applied to the measurement of volatile inorganic acids of atmospheric interest: hydrochloric (HCl), nitrous (HONO), nitric (HNO 3 ), and isocyanic (HNCO) acids. Gas phase calibrations through the sampling inlet showed the method to be intrinsically sensitive (6-16 cts/pptv), but prone to inlet effects for HNO 3 and HCl. The ion chemistry was found to be insensitive to water vapor concentrations, in agreement with previous studies of carboxylic acids. The inlet equilibration times for HNCO and HONO were 2 to 4 s, allowing for measurement in biomass burning studies. Several potential interferences in HONO measurements were examined: decomposition of HNO 3 ·NO − 3 clusters within the CIMS, and NO 2 -water production on inlet surfaces, and were quite minor (≤1%, 3.3%, respectively). The detection limits of the method were limited by the instrument backgrounds in the ion source and flow tube, and were estimated to range between 16 and 50 pptv (parts per trillion by volume) for a 1 min average. The comparison of HONO measured by CIMS and by in situ FTIR showed good correlation and agreement to within 17%. The method provided rapid and accurate measurements of HNCO and HONO in controlled biomass burning studies, in which both acids were seen to be important products.

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“…The hypothesis of hydrolysis of HNCO taking place in gas phase [26] seems not to be realistic since HNCO(g) is quite stable in the gas phase [27][28][29]. However, in solution, cyanate can be readily hydrolyzed to ammonia and carbon dioxide according to the sequence of reactions Carbamate NH 2 CO 2 -ion was identified by Schoppelrei et al [30].…”

Section: Introductionmentioning

confidence: 99%

Detailed modeling of the evaporation and thermal decomposition of urea‐water solution in SCR systems

2011

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This work aims to develop a multi-component evaporation model for droplets of urea-watersolution (UWS) and a thermal decomposition model of urea for automotive exhausts using the Selective Catalytic Reduction (SCR) systems. In the multi-component evaporation model, the influence of urea on the UWS evaporation is taken into account using a NRTL activity model. The thermal decomposition model is based on a semi-detailed kinetic scheme accounting not only for the production of ammonia (NH 3 ) and isocyanic acid (HNCO), but also for the formation of heavier solid by-products (biuret, cyanuric acid and ammelide). This kinetics model has been validated against gaseous data as well as solid-phase concentration profiles obtained by Lundstroem et al. (2009) andSchaber et al. (2004). Both models have been implemented in IFP-C3D industrial software in order to simulate UWS droplet evaporation and decomposition as well as the formation of solid by-products. It has been shown that the presence of the urea solute has a small influence on the water evaporation rate, but its effect on the UWS temperature is significant. In addition, the contributions of hydrolysis and thermolysis to urea decomposition have been assessed. Finally, the impacts of the heating rate as well as gas-phase chemistry on urea decomposition pathways have been studied in detail. It has been shown that reducing the heating rate of the UWS causes the extent of the polymerization to decrease because of the higher activation energy.

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Preparation and properties of isocyanic acid

Cited by 73 publications

References 2 publications

Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere

Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere

Measurement of HONO, HNCO, and other inorganic acids by negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS): application to biomass burning emissions

Detailed modeling of the evaporation and thermal decomposition of urea‐water solution in SCR systems

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