Quantitative study of the acidity of HCl in a molten chloroaluminate system (AlCl3/1-ethyl-3-methyl-1H-imidazolium chloride) as a function of HCl pressure and melt composition (51.0-66.4 mol % AlCl3)

The acidity of HCl in Lewis acid mixtures of AlCl{sub 3} and 1-ethyl-3-methyl-1H-imidazolium chloride (EMIC) has been determined as a function of HCl pressure (P{sub HCl}) and melt composition at ambient temperatures. The equilibrium constant (K{prime}{sub b}) for the protonation of arene bases (B)...

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Bibliographic Details
Published in:Journal of the American Chemical Society 1989-07, Vol.111 (14), p.5075-5077
Main Authors: SMITH, G. P, DWORKIN, A. S, PAGNI, R. M, ZINGG, S. P
Format: Article
Language:English
Subjects:
400000 - Chemistry
400201 - Chemical & Physicochemical Properties
ALKYLATED AROMATICS
AROMATICS
BENZENE
CHEMICAL ANALYSIS
CHEMICAL REACTION KINETICS
Chemistry
CONDENSED AROMATICS
DATA
DATA ANALYSIS
Exact sciences and technology
EXPERIMENTAL DATA
HYDROCARBONS
HYDROCHLORIC ACID
HYDROGEN COMPOUNDS
INFORMATION
INORGANIC ACIDS
Inorganic chemistry and origins of life
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
KINETICS
Kinetics and mechanism of reactions
LEWIS ACIDS
MEASURING INSTRUMENTS
MEASURING METHODS
NAPHTHALENE
NUMERICAL DATA
ORGANIC COMPOUNDS
QUANTITATIVE CHEMICAL ANALYSIS
REACTION KINETICS
TOLUENE
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Summary:The acidity of HCl in Lewis acid mixtures of AlCl{sub 3} and 1-ethyl-3-methyl-1H-imidazolium chloride (EMIC) has been determined as a function of HCl pressure (P{sub HCl}) and melt composition at ambient temperatures. The equilibrium constant (K{prime}{sub b}) for the protonation of arene bases (B) according to the reaction HCl + B {r reversible} BH{sup +} + Cl{sup {minus}} was determined from the relation log K{prime}{sub B} = H{prime} + log ((BH{sup +})/(B)) with the protonation ratio measured spectrophotometrically and the acidity function, H{prime} = log ((Cl{sup {minus}})/P{sub HCl}), evaluated by using the thermodynamic model of Dymek et al. to calculate (Cl{sup {minus}}). Values of log K{prime}{sub B} were determined for chrysene, fluorene, 2-methylnaphthalene, and mesitylene over a range of HCl pressures and melt compositions, while estimates for benzene, toluene and naphthalene were obtained at a single pressure and composition (1 atm, 66.4 mol % AlCl{sub 3}). The correlation between log K{prime}{sub B} for these arenes in HCl/AlCl{sub 3}-EMIC and log K{sub B} for the same arenes in HF/BF{sub 3} suggests that H{prime} {minus} H{sub 0} {approx equal} 0.4, where H{sub 0} is the Hammett acidity function. According to this criterion H{sub 0} for 0.01 atm HCl in 51 mol % AlCl{sub 3} has a value of {minus}12.6 (a superacid comparable to 100% H{sub 2}SO{sub 4}). At 1 atm HCl, a melt saturated with AlCl{sub 3} at ambient temperatures ({approximately} 67 mol % AlCl{sub 3}) is a much stronger superacid with a value of H{sub 0} on the order of {minus}18.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja00196a009