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

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 behavior, we measure its effective Henry's Law solubility coefficient KHeff 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 KH of 26 ± 2 M atm-1 is obtained, with an enthalpy of dissolution of −34 ± 2 kJ mol-1. Our approach also allows for the determination of HNCO's acid dissociation constant, which we determine to be Ka = 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 k1 = (4.4 ± 0.2) × 107 exp (−6000 ± 240/T) M s-1, k2 = (8.9±0.9) × 106 exp (−6770 ± 450/T) s-1 and k3 = (7.2±1.5) × 108 exp (−10 900 ± 1400/T) s-1 where k1 is for HNCO + H+ + H2O → NH4+ + CO2, k2 is for HNCO + H2 O → NH3 + CO2 and k3 is for NCO- + 2H2 O → NH3 + HCO3-. 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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Solubility and reactivity of HNCO in water: insights into HNCO's fate in the atmosphere

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-703-2016 ◽

2016 ◽

Vol 16 (2) ◽

pp. 703-714 ◽

Cited By ~ 25

Author(s):

N. Borduas ◽

B. Place ◽

G. R. Wentworth ◽

J. P. D. Abbatt ◽

J. G. Murphy

Keyword(s):

Acid Dissociation ◽

Enthalpy Of Dissolution ◽

Ionization Mass ◽

Acid Dissociation Constant ◽

Henry's Law ◽

Analytical Technique ◽

Henry’S Law ◽

Ph Values ◽

Ambient Measurements

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 KHeff 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 KH of 26 ± 2 M atm−1 is obtained, with an enthalpy of dissolution of −34 ± 2 kJ mol−1, which translates to a KHeff 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 Ka = 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 k1 = (4.4 ± 0.2)  ×  107 exp(−6000 ± 240∕T) M s−1, k2 = (8.9 ± 0.9)  ×  106  exp(−6770 ± 450∕T) s−1 and k3 =  (7.2 ± 1.5)  ×  108 exp(−10 900 ± 1400∕T) s−1, where k1 is for HNCO + H++ H2O → NH4++ CO2, k2 is for HNCO + H2O → NH3 + CO2 and k3 is for NCO−+ 2 H2O → NH3+ HCO3−. 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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Chromatographic Determination of Thermodynamic Acid Dissociation Constants of Tetracycline Antibiotics and Their Epimers

Journal of Chromatographic Science ◽

10.1093/chromsci/bmz051 ◽

2019 ◽

Vol 57 (8) ◽

pp. 745-750

Author(s):

İlkay Konçe ◽

Ebru Çubuk Demiralay ◽

Hülya Yılmaz Ortak

Keyword(s):

Experimental Data ◽

Dissociation Constant ◽

Binary Mixtures ◽

Dissociation Constants ◽

Reversed Phase ◽

Acid Dissociation ◽

Acid Dissociation Constant ◽

Chromatography Method ◽

Ph Values

Abstract The presented study describes the development of reversed-phase liquid chromatography method using a core-shell particle column with a pentafluorophenyl stationary phase for the dissociation constant (pKa) determination of the tetracycline group antibiotics (tetracycline, oxytetracycline, chlortetracycline) and their epimers (4-epitetracycline, 4-epioxytetracycline, 4-epichlortetracycline). The pH values were measured in the acetonitrile (ACN)–water binary mixtures, used as mobile phases, instead of in water and take into account the effect of the activity coefficients. Thermodynamic acid dissociation constant (pKa1) values of studied antibiotics and their epimers were calculated using retention factor (k) at different mobile phase pH values in studied binary mixtures with ACN percentages of 20, 25, 30 and 35% (v/v). Experimental data were analyzed by using an Origin 7.0 program to fit experimental data to the nonlinear expression derived. From calculated pKa1 values, the aqueous pKa values of studied compounds were calculated by different approaches and these values were compared.

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Dissociation of imino proton(s) of a highly water-soluble metal-free phthalocyanine and determination of its pKa value in water

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424613500235 ◽

2013 ◽

Vol 17 (06n07) ◽

pp. 447-453 ◽

Cited By ~ 2

Author(s):

Hiroaki Isago ◽

Harumi Fujita

Keyword(s):

Aqueous Media ◽

Thermal Reaction ◽

Water Soluble ◽

Acid Dissociation ◽

Acid Dissociation Constant ◽

Metal Free ◽

Imino Proton ◽

Pka Value ◽

Triton X

Dissociation of imino proton(s) in the cavity of the macrocycle of a highly water-soluble, metal-free phthalocyanine ( H 2( H 4 tsppc ); where H 4 tsppc denotes tetrakis{(2′,6′-dimethyl-4′-sulfonic acid)phenoxy}phthalocyaninate) in ethanolic and aqueous solutions has spectrophotometrically been investigated. The spectral changes associated with reaction with NaOH have been found to involve one-proton transfer process in aqueous media while two-protons process in ethanolic media. The acid-dissociation constant of the first imino proton in water (in the presence of Triton X-100) has been determined to be 12.5 ± 0.2 (as pKa) at 25 °C. The doubly deprotonated species in EtOH has been easily converted to its corresponding cobalt(II) derivative by thermal reaction with anhydrous CoCl 2.

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