Free radical routes to functional fluorine-containing organic compounds

Abstract

Free radical additions of functional hydrocarbons such as alcohols, aldehydes and ethers to the highly fluorinated alkenes 2H-pentafluoropropene and hexafluoropropene have been studied. In particular, reactions involving 2H-pentafluoropropene have given rise to a series of new fluorinated alcohols and ketones. For the purpose of synthesising the 1:1 adducts, γ-ray initiation was shown to provide a superior method to ultra violet radiation or peroxides. Competition reactions were carried out between homologous alcohols and between different species, viz alcohol, aldehyde, amine, ether. These reactions enabled reactivity series to be established. Chemistry of the derived polyfluorinated alcohols was investigated, and it has been shown that these compounds may be reacted with a broad spectrum of electrophiles to give new esters, carbonates, sulphonates and ethers, including the first reported such reactions with perfluorinated aromatic and heteroaromatic compounds as electrophiles. Interestingly, it was observed that tosylated polyfluoroalcohols would not undergo nucleophilic displacement, in contrast to the situation which exists with non-fluorinated analogues.2-(1,1,2,3,3,3- exafluoropropyl)oxolane was chlorinated selectively at the 5-position, and subsequently reacted with a range of different types of nucleophile. This study gave a number of novel compounds, and reasons were proposed for the variation in reactivity of nucleophiles under study. Direct chlorination of this ketone gave rise to the chloromethyl and dichloromethyl ketones, as did direct chlorination of 3,3,4,5,5,5- hexafluoropentan-2-ol. A pathway for the latter reaction is proposed, involving 1,1,1,2,3,3-hexafluoropentan-2-one as an intermediate.