Abstract
AbstractA combination of collisional activation mass spectrometry and low‐temperature infrared spectroscopy has been used to monitor the production and isomerization of vinyl‐ and methylene‐ketenes. Vinyl‐ and 2‐propenyl‐ketenes were produced by flash vacuum pyrolysis of β,γ‐unsaturated acid chlorides. Vinyl(carboxyl)ketenes, vinylketenes and methyleneketenes were obtained from Meldrum's acid derivatives (5‐alkylidene‐1,3‐dioxane‐4,6‐diones). The formation of methyleneketenes by pyrolysis of α, β‐unsaturated acid chlorides is only indicated in the mass spectrometry experiments. Carbonylcyclopropane was obtained by pyrolysis of cyclopropylcarbonyl chloride or the corresponding Meldrum's acid derivative. The methyleneketenes isomerize to vinylketenes in the gas phase, particularly under conditions involving long contact times. Carbonylcyclopropane thermally decarbonylates to allene, not methylacetylene. Molecular ions of vinylketenes are obtained via pyrolysis of either acid chlorides or Meldrum's acid derivatives. Molecular ions of alkylmethyleneketenes are obtained pure only by electron impact induced fragmentation of Meldrum's acid derivatives.
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