Polymerizations of ethylenic monomers initiated by superacids—II: Complexation of some trifluoromethanesulphonates by their conjugate acid |
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Authors: | D Souverain A Leborgne G Sauvet P Sigwalt |
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Institution: | Laboratoire de Chimie macromoléculaire associé au C.N.R.S. Université Pierre et Marie Curie, 4, Place Jussieu, 75230 Paris Cedex 05, France |
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Abstract: | Ionic trifluoromethanesulphonates (triflates) are strongly solvated with their conjugate acid in dichloromethane (Ph3C+, n-Bu4N+, Ag+) and acetonitrile (Na+, Ag+). A 1H and 19F NMR study of the chemical shifts of various acid-salt mixtures show that in CH2Cl2 three homoconjugates A? · HA, A?. (HA)2 and A?(HA)3 were formed with large formation constants whereas in acctonitrile only the 1:1 homoconjugate was formed with an equilibrium constant K1 ~ 4 1 · M?1. This result explains why the protonation by CF3SO3H of non-polymerizable olefins such as 1,1-diphenylethylene and 3-phenylindene is always incomplete ( and respectively) in CH2Cl2. Conditions in which covalent triflates could be obtained have been investigated. As a consequence of homoconjugation, reaction of Ph3COH with triflic anhydride led to Ph3C+ CF3SO?3 HOSO2CF3. Other tertiary alcohols were dehydrated by triflic anhydride and led to ethylenic compounds (1,1-diphenylethanol) or ethers (2-phenyl 2-propanol). Esters were only observed in the case of benzyltriflate (at ?20°) and in the case of 1-phenylethyltriflate which is a model of polystyryltriflate (stable at room temperature). |
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