Equilibrium Ion Pair Acidities of Polyhalogenated Benzenes in THF. Extrapolation to Benzene1
- 1 January 1996
- journal article
- research article
- Published by American Chemical Society (ACS) in The Journal of Organic Chemistry
- Vol. 61 (9) , 3145-3150
- https://doi.org/10.1021/jo9516401
Abstract
The equilibrium cesium ion pair acidities of six polyfluorobenzenes at 25 °C and six polychlorobenzenes at −20 °C were determined in THF. For fluorinated benzenes the additive (negative) effects of fluorine on pK (partial equilibrium factors) are o = 5.2, m = 3.0, and p = 1.4. From these the cesium ion pair pK (per H) of benzene is extrapolated to be 44.8 at 25 °C. For chlorobenzenes the additive contributions for o-, m-, and p-chlorine are 4.2, 2.7, and 2.1, respectively. The corresponding pK of benzene is 47.0 at −20 °C. Aggregation studies show that in the concentration range 10-3−10-4 M the cesium salt of 1,2,4,5-tetrachlorobenzene and the cesium and lithium salts of 1,2,4,5-tetrafluorobenzene are monomeric. The pK of benzene on the Li scale is extrapolated to be 39.5.Keywords
This publication has 25 references indexed in Scilit:
- Directed lithiation of chlorobenzenes. Regioselectivity and application to a short synthesis of benzocyclobutenesThe Journal of Organic Chemistry, 1990
- Carbon acidity. 73. Conductimetric study of lithium and cesium salts of hydrocarbon acids. A scale of free ion acidities in tetrahydrofuran. Revision of the ion pair scalesJournal of the American Chemical Society, 1988
- Simultaneous use of empirical and semiempirical substituent parameters as a new method of analysis of the ortho effect. Application in reactions via aryl anion intermediatesThe Journal of Organic Chemistry, 1985
- Participation of oligochlorobenzenes in the base-catalyzed halogen danceThe Journal of Organic Chemistry, 1980
- Acidity of hydrocarbons. XLIX. Equilibrium ion pair acidities of fluorinated benzenes for cesium salts in cyclohexylamine. Extrapolation of pK of benzeneJournal of the American Chemical Society, 1972
- Base-catalyzed halogen dance, and other reactions of aryl halidesAccounts of Chemical Research, 1972
- Acidity of hydrocarbons. XXVIII. Hydrogen isotope exchange of polyfluorobenzenes with sodium methoxide in methanolJournal of the American Chemical Society, 1968
- Acidity of hydrocarbons. XXVII. Proton exchange rates of fluorobenzene with lithium cyclohexylamideJournal of the American Chemical Society, 1968
- 622. Aromatic polyfluoro-compounds. Part XI. Pentafluoro-phenyl-lithium and derived compoundsJournal of the Chemical Society, 1962
- Exchange Reactions of Deuterated Benzene Derivatives with Potassium Amide in Liquid Ammonia1aJournal of the American Chemical Society, 1955