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|Type:||Artigo de periódico|
|Title:||Transacetalization of 1,3-dioxane with acylium and sulfinyl cations in the gas phase|
|Abstract:||Transacetalization occurs extensively In gas phase ion-molecule reactions of 1,3-dioxane with a variety of acylium ions [R-C+=O; R = CH3, C2H5, Ph, CH3O, Cl, CH2=CH, (CH3)(2)N] and a sulfur analogue, the thioacetyl ion CH3-C+=S. Six-membered 1,3-dioxanylium ions and analogues, i.e. cyclic 'ionic (thio)ketals', are formed, as evidenced by pentaquadrupole triple-stage collision-dissociation mass spectra and MP2/6-311G(d,p)//6-311G(d,p) + ZPE ab initio calculations, as well as by O-18 labelling experiments. Transacetalization with 1,3-dioxane is not a general reaction for sulfinyl cations (R-S+=O). They react either moderately (CH3-S+=O) or extensively (CH2=CH-S+=O) by transacetalization, form abundant intact adducts (Ph-S+=O) or undergo mainly proton transfer and/or hydride abstraction reactions (Cl-S+=O, CH3O-S+=O and C2H5O-S+=O). Competitive MS2 experiments are employed to compare the transacetalization reactivity of different acylium ions, and that of two cyclic neutral acetals, that is 1,3-dioxane and 1,3-dioxolane. All the cyclic 'ionic ketals) dissociate exclusively under low-energy collision conditions to regenerate the original reactant ion species, a simple dissociation chemistry that is amply demonstrated to be a very general characteristic of the transacetalization products. The cyclic 'ionic thioketal' formed in transacetalization with CH3-C+=S is found, however, to dissociate exclusively to the oxygen analogue ion CH3-C+=O, a triple-stage mass spectrometric(MS3) experiment that constitutes a novel gas-phase strategy for conversion of thioacylium ions into acylium ions.|
|Editor:||Royal Soc Chemistry|
|Appears in Collections:||Artigos e Materiais de Revistas Científicas - Unicamp|
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