Excess acidities. A generalized method for the determination of basicities in aqueous acid mixtures

Cox, Robin A.; Yates, Keith

doi:10.1021/ja00480a033

Cited by 200 publications

(190 citation statements)

References 19 publications

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“…Certainly the very large negative entropies of activation, -40 to -55 eu, only seem consistent with a highly structured transition state such as the one shown. The observed very small extent of 1 T+, in eq. [5], were formed directly in the ratedetermining step, rather than subsequently as in eq.…”

Section: Discussionmentioning

confidence: 88%

The hydrolyses of benzamides, methylbenzimidatium ions, and lactams in aqueous sulfuric acid. The excess acidity method in the determination of reaction mechanisms

Cox¹,

Yates²

1981

Can. J. Chem.

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The excess acidity method has been applied to hydrolysis rate data for a number of benzamides, methylbenzimidatium ions, and lactams, obtained as a function of sulfuric acid concentration and temperature. All of the substrates studied except β-propiolactam (8) and methyl-2,6-dimethylbenzimidatium ion (7) were found to follow the AOT2 mechanism at all acidities. The excess acidity method provided considerable mechanistic detail; in dilute acid the transition state contains O-protonated (or methylated) substrate and three water molecules (large negative ΔS≠), but in more concentrated solutions a one-water-molecule mechanism takes over (smaller negative ΔS≠). In strong acid bisulfate ion acts as the nucleophile (positive ΔS≠). N-protonated intermediates are not involved for "normal" substrates, being observed in this work only for 8, which follows the AND1 pathway. Observed differences between benzamide and methylbenzimidatium ion (4) hydrolyses are due to their differing activity coefficient behaviour, the mechanism being the same for both. The hydrolysis of 7 involves a one-water-molecule SN2 displacement at the O-methyl group. Comparison with 7 shows that this displacement is not likely to occur under the reaction conditions for 4; however, for the N-methyl and N,N-dimethyl derivatives studied it is probably an important reaction pathway. A comprehensive mechanistic framework for amide hydrolyses in strong acid media is given.

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Section: Discussionmentioning

confidence: 88%

The hydrolyses of benzamides, methylbenzimidatium ions, and lactams in aqueous sulfuric acid. The excess acidity method in the determination of reaction mechanisms

Cox¹,

Yates²

1981

Can. J. Chem.

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“…Tables 1 and 2 report the hydrolysis lifetimes (τ hyd = 1 k S n ) previously determined for primary organosulfates as well as the new hydrolysis lifetimes (τ hyd = 1 k N n ) determined for the primary and secondary organonitrates in the present work for reactions in 55 wt % D 2 SO 4 solutions. For these highly concentrated acid solutions, k S eff and k N eff are best interpreted through the excess acidity framework (Cox and Yates, 1978), rather than Eq. (6).…”

Section: Kinetics Of Hydrolysis Of Primary and Secondary Organonitratesmentioning

confidence: 99%

Thermodynamics and kinetics of the hydrolysis of atmospherically relevant organonitrates and organosulfates

2011

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Abstract. The presence of alcohol, organonitrate, and organosulfate species related to the gaseous precursor isoprene in ambient secondary organic aerosol (SOA) has stimulated investigations of the nature of SOA-phase chemical processing. Recent work has suggested that certain isoprene-derived organonitrates are able to efficiently convert to organosulfates and alcohols on ambient SOA. In order to better understand the structure activity relationships previously observed for the isoprene-derived organonitrates and organosulfates, the hydrolysis reactions of a number of monofunctional and difunctional organonitrates and organosulfates with varying carbon substitution properties were investigated. Nuclear magnetic resonance techniques were used to study the bulk phase aqueous reactions of these organonitrates and organosulfates in order to determine hydrolysis reaction rate and, in some cases, thermodynamics information. Electronic structure calculations were also carried out to determine the enthalpy of hydrolysis for these species, and for the previously studied isoprene-derived species. The results suggest that while organonitrates and organosulfates are thermodynamically unstable with respect to the corresponding alcohols at standard state, only the tertiary organonitrates (and perhaps some tertiary organosulfates) are able to efficiently hydrolyze on SOA timescales and acidities.

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“…On substituting Equations (3)- (5) into Equation (2) and rearranging, a linear equation was obtained as below (Cox and Yates 1978).…”

Section: Equilibrium Of An Indicator In the Acidic Aerosolmentioning

confidence: 99%

Aerosol Acidity Measurement Using Colorimetry Coupled With a Reflectance UV-Visible Spectrometer

Jang

2012

Aerosol Science and Technology

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In this study, aerosol acidity was measured using colorimetry integrated with a Reflectance UV-Visible spectrometer (C-RUV). An inorganic aerosol comprising NH 4 + −H + −SO 4 2− −H 2 O was generated using an atomizer and introduced into a 2-m 3 indoor Teflon film chamber. The produced aerosol was collected on the Tefloncoated glass fiber filter dyed with metanil yellow (MY) as an indicator for measuring proton concentrations in aerosol. A calibration curve for measuring aerosol acidity using the C-RUV technique was obtained through the relationship between the absorbance of the UV-Visible spectrum of the filter sample vs. theoretically calculated proton concentrations using the E-AIM Model II. To develop the C-RUV method under various humidities, the aerosol filter sample was mounted inside a small optical flow chamber controlled for humidity in situ. The humidity effect on the equilibrium thermodynamics of the indicator was theoretically described by inclusion of excess acidity (X) into the calibration curve. The calibration curve obtained from relatively highly acidic aerosols (e.g., H 2 SO 4 , NH 4 H 3 (SO 4 ) 2 , and (NH 4 ) 7 H 13 (SO 4 ) 10 ) was extrapolated to estimate proton concentrations for weakly acidic aerosols (e.g., NH 4 HSO 4 and (NH 4 ) 3 H(SO 4 ) 2 ), which is more relevant to the ambient aerosol acidity but has been poorly predicted with typical inorganic thermodynamic models due to the limited experimental data. The C-RUV technique of this study permits one to estimate aerosol acidity for a variety of compositions of the NH 4 + −H + −SO 4 2− −H 2 O system including both ammonia-poor and ammonia-rich sulfate aerosols.

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Excess acidities. A generalized method for the determination of basicities in aqueous acid mixtures

Cited by 200 publications

References 19 publications

The hydrolyses of benzamides, methylbenzimidatium ions, and lactams in aqueous sulfuric acid. The excess acidity method in the determination of reaction mechanisms

The hydrolyses of benzamides, methylbenzimidatium ions, and lactams in aqueous sulfuric acid. The excess acidity method in the determination of reaction mechanisms

Thermodynamics and kinetics of the hydrolysis of atmospherically relevant organonitrates and organosulfates

Aerosol Acidity Measurement Using Colorimetry Coupled With a Reflectance UV-Visible Spectrometer

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