Excess acidities

Cox, Robin A.

doi:10.1016/s0065-3160(00)35011-0

Cited by 43 publications

(19 citation statements)

References 228 publications

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“…Equilibrium constants were adjusted to 220 K using available enthalpy values. The protonation of acetaldehyde was treated with the excess acidity method [ Cox , 2000]. This approach to strongly acidic solutions depends upon two variables: the excess acidity, X , and the slope factor, m *.…”

Section: Resultsmentioning

confidence: 99%

“…According to our thermodynamic model (discussed in the previous section), the solubility of enolized acetaldehyde ( H e ) decreases slightly from 298 to 220 K, and so does the activity of water. (Note that the activity of water at 298 K is from Cox [2000], while the values at 220 K are from Knopf et al [2003].) The solubility of protonated acetaldehyde ( H a ), however, is higher by almost three orders of magnitude at the lower temperature.…”

Section: Resultsmentioning

confidence: 99%

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Dissolution, speciation, and reaction of acetaldehyde in cold sulfuric acid

2004

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[1] The uptake of gas-phase acetaldehyde [CH 3 CHO, ethanal] by aqueous sulfuric acid solutions was studied under upper tropospheric/lower stratospheric (UT/LS) conditions. The solubility of acetaldehyde was found to be low, between 2 Â 10 2 M atm À1 and 1.5 Â 10 5 M atm À1 under the ranges of temperature (211-241 K) and acid composition (39-76 weight percent, wt%, H 2 SO 4 ) studied. Under most conditions, acetaldehyde showed simple solubility behavior when exposed to sulfuric acid. Under moderately acidic conditions (usually 47 wt% H 2 SO 4 ), evidence of reaction was observed. Enhancement of uptake at long times was occasionally detected in conjunction with reaction. The source of these behaviors and the effect of acetaldehyde speciation on solubility are discussed. Implications for the uptake of oxygenated organic compounds by tropospheric aerosols are considered.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Dissolution, speciation, and reaction of acetaldehyde in cold sulfuric acid

2004

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“…Water activities in the aqueous sulfuric acid medium [50] are very accurately known [51], but this is not the case for HCl [52–54] and, particularly, HClO 4 [55–58]. All of the plots fit the appropriate lines more closely than was previously found by treating the process as a traditional A1 reaction [48]. …”

Section: Resultsmentioning

confidence: 97%

“…The preferable method to use for this is the excess acidity correlation analysis [48], which is used here. The applicable rate equation is shown as Equation 2.…”

Section: Resultsmentioning

confidence: 99%

A Greatly Under-Appreciated Fundamental Principle of Physical Organic Chemistry

Cox

2011

IJMS

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If a species does not have a finite lifetime in the reaction medium, it cannot be a mechanistic intermediate. This principle was first enunciated by Jencks, as the concept of an enforced mechanism. For instance, neither primary nor secondary carbocations have long enough lifetimes to exist in an aqueous medium, so SN1 reactions involving these substrates are not possible, and an SN2 mechanism is enforced. Only tertiary carbocations and those stabilized by resonance (benzyl cations, acylium ions) are stable enough to be reaction intermediates. More importantly, it is now known that neither H3O+ nor HO− exist as such in dilute aqueous solution. Several recent high-level calculations on large proton clusters are unable to localize the positive charge; it is found to be simply “on the cluster” as a whole. The lifetime of any ionized water species is exceedingly short, a few molecular vibrations at most; the best experimental study, using modern IR instrumentation, has the most probable hydrated proton structure as H13O6+, but only an estimated quarter of the protons are present even in this form at any given instant. Thanks to the Grotthuss mechanism of chain transfer along hydrogen bonds, in reality a proton or a hydroxide ion is simply instantly available anywhere it is needed for reaction. Important mechanistic consequences result. Any charged oxygen species (e.g., a tetrahedral intermediate) is also not going to exist long enough to be a reaction intermediate, unless the charge is stabilized in some way, usually by resonance. General acid catalysis is the rule in reactions in concentrated aqueous acids. The Grotthuss mechanism also means that reactions involving neutral water are favored; the solvent is already highly structured, so the entropy involved in bringing several solvent molecules to the reaction center is unimportant. Examples are given.

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“…The values of log{c H + } and X are available for aqueous H 2 SO 4 [29]. The data for H 0 are calculated using the equations (7) [20]:…”

Section: Determination Of the Protonation Parametersmentioning

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Determination of protonation constants and structural correlations for some tertiary formamides and acetamides in sulfuric acid with UV spectroscopy

Dimitrieska-Stojković

Popovski

2015

Maced. J. Chem. Chem. Eng.

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The protonation of ten aliphatic amides in sulfuric acid media was studied by UV spectroscopy. (-0.57, -0.29, -0.32 and 0.36, respectively), analogous acetamides were more basic than formamides. Applying the Hammett's equation, satisfactory correlation could be gained only for some formamides, the basicities of which increased linearly with the inductive effect of the electron donating groups. From Taft's approach, it can be concluded that the polar effect slightly dominates over the steric one. Excellent correlation between pK BH + and solvation parameters m* was achieved for formamide, dimethylformamide and diethylformamide. At half-and fullprotonation, better correlation was obtained for formamides than for acetamides.Keywords: UV spectroscopy; formamides; acetamides; protonation constants; Hammett-Taft correlations ОПРЕДЕЛУВАЊЕ НА КОНСТАНТИТЕ НА ПРОТОНИРАЊЕ И СТРУКТУРНИ КОРЕЛАЦИИ НА НЕКОИ ТЕРЦИЈАРНИ ФОРМАМИДИ И АЦЕТАМИДИ ВО СУЛФУРНА КИСЕЛИНА СО УЛТРАВИОЛЕТОВА СПЕКТРОСКОПИЈАПротонирањето на десет алифатични амиди во сулфурна киселина е проучувано со примена на ултравиолетова спектроскопија. Вредностите за pK BH+ и солватационите параметри се пресметани според методот на Yates и McClelland, методот на вишок на киселост и Bunnett-Olsen-овиот метод. Вредностите за pK BH + изнесуваат -1.44, -1.15, -0.80, -0.32, -1.13 и -0.80 за формамид, диметилформамид, диетилформамид, диизопропилформамид, диизобутилформамид и дибутилформамид, соодветно. Според вредностите на pK BH+ определени за ацетамид, диметилацетамид, диетилацетамид и диизопропилацетамид (-0.57, -0.29, -0.32 и 0.36, соодветно) аналогните ацетамиди се побазни од формамидите. Со примена на Hammett-овата равенка добиени се задоволителни резултати само за некои формамиди, чија базност линеарно расте со индуктивниот ефект на електронодонорната група. Од Taft-овскиот пристап може да се заклучи дека поларниот ефект е незначително поголем од стерниот. Постигната е одлична корелација помеѓу вредностите на pK BH + и солватационите параметри m* за формамид, диметилформамид и диетилформамид. Кај полу-и целосна протонација, подобра корелација е добиена за формамиди отколку за ацетамиди.Клучни зборови: UV спектроскопија; формамиди; ацетамиди; константи на протонирање; Hammett-Taft-овски корелации G. Stojković, E. Dimitrieska-Stojković, E. Popovski Maced. J. Chem. Chem. Eng. 34 (2), 255-265 (2015) 256

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Excess acidities

Cited by 43 publications

References 228 publications

Dissolution, speciation, and reaction of acetaldehyde in cold sulfuric acid

Dissolution, speciation, and reaction of acetaldehyde in cold sulfuric acid

A Greatly Under-Appreciated Fundamental Principle of Physical Organic Chemistry

Determination of protonation constants and structural correlations for some tertiary formamides and acetamides in sulfuric acid with UV spectroscopy

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