Acid-Base Behavior of Organic Compounds in Supercritical Water

Xiang, Tao; Johnston, Keith P.

doi:10.1021/j100083a027

Cited by 76 publications

(84 citation statements)

References 13 publications

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“…9 A second high-pressure cell, constructed from grade 2 Tico titanium fitted with three sapphire windows, was used to collect fluorescence spectra. 9 A second high-pressure cell, constructed from grade 2 Tico titanium fitted with three sapphire windows, was used to collect fluorescence spectra.…”

Section: Methodsmentioning

confidence: 99%

Absorption and Fluorescence Studies of Acridine in Subcritical and Supercritical Water

et al. 1997

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The isobaric acid/base equilibrium between acridine and the acridinium cation was measured from ambient temperature to 380°C (above the critical temperature of water, T c ) 374°C) using absorption spectroscopy. At 3500 psia, the isobaric protonation of acridine is shown to be exothermic up to approximately 315°C. Above 315°C, protonation becomes endothermic due to changes in the dielectric constant of water with temperature, which has a profound influence on the solvation of ions. The results are interpreted using a modified Born equation to account for the temperature-dependent changes in acridinium cation and proton solvation. The absorption and fluorescence spectra and the fluorescence lifetime of acridine are sensitive to changes in solvent-solute hydrogen bonding. Hydrogen bonding between acridine and water is observed to decrease from ambient temperature to the critical temperature. A relatively rapid change in hydrogen bonding occurs between 100 and 200°C.Acridine in Subcritical and Supercritical Water

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Section: Methodsmentioning

confidence: 99%

Absorption and Fluorescence Studies of Acridine in Subcritical and Supercritical Water

et al. 1997

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“…This influences chemical reactions. As a rule of thumb, weak acids like dissolved CO 2 become stronger [67,68] and strong acids like HCl become weaker [69]. From the thermodynamic perspective the reason is that the dissociation of weak acids is usually endothermic [67].…”

Section: Properties Of Watermentioning

confidence: 99%

Water – A magic solvent for biomass conversion

Kruse

Dahmen

2015

The Journal of Supercritical Fluids

271

148

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“…This analysis is based on the recently reported values for the temperature-dependent ionization constants for acridine (Ryan et al, 1997) and 2-naphthol (Xiang and Johnston, 1994). The acid dissociation of acridinium ion to acridine can be represented by the expression HAcr…”

Section: Spectroscopic Analysismentioning

confidence: 99%

Ionization constants of aqueous amino acids at temperatures up to 250°C using hydrothermal pH indicators and UV-visible spectroscopy: Glycine, α-alanine, and proline

Clarke

Collins

Roberts

et al. 2005

Geochimica et Cosmochimica Acta

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Abstract-Ionization constants for several simple amino acids have been measured for the first time under hydrothermal conditions, using visible spectroscopy with a high-temperature, high-pressure flow cell and thermally stable colorimetric pH indicators. This method minimizes amino acid decomposition at high temperatures because the data can be collected rapidly with short equilibration times. The first ionization constant for proline and ␣-alanine, K a,COOH , and the first and second ionization constants for glycine, K a,COOH and K a,NH4ϩ , have been determined at temperatures as high as 250°C. Values for the standard partial molar heat capacity of ionization, ⌬ r C p o , COOH and ⌬ r C p o , NH4ϩ , have been determined from the temperature dependence of ln (K a,COOH ) and ln (K a,NH4ϩ ). The methodology has been validated by measuring the ionization constant of acetic acid up to 250°C, with results that agree with literature values obtained by potentiometric measurements to within the combined experimental uncertainty.We dedicate this paper to the memory of Dr. Donald Irish (1932-2002 of the University of Waterloofriend and former supervisor of two of the authors (R.J.B. and P.R.T.).

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Acid-Base Behavior of Organic Compounds in Supercritical Water

Cited by 76 publications

References 13 publications

Absorption and Fluorescence Studies of Acridine in Subcritical and Supercritical Water

Absorption and Fluorescence Studies of Acridine in Subcritical and Supercritical Water

Water – A magic solvent for biomass conversion

Ionization constants of aqueous amino acids at temperatures up to 250°C using hydrothermal pH indicators and UV-visible spectroscopy: Glycine, α-alanine, and proline

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