FREE-RADICAL ADDITION OF 2-(PERFLUOROALKYL)ETHANETHIOLS TO ALKENES, ALKADIENES, CYCLOALKENES, ALKYNES AND VINYL MONOMERS

The free-radical addition of 2-(perfluoroalkyl)ethanethiols (RFCH2CH2SH) to alkenes, cycloalkenes, alkadienes and alkynes has been studied to determine: (1) the mode of reaction, i.e. the stereochemistry, regiochemistry and any skeletal changes; (2) the relative reactivity towards unsaturates of differing structures and classes as affected by the presence of the R(F) group; and (3) the influence of the reaction conditions on the rate of addition or selectivity for different products. Adducts from 2-(F-hexyl)ethane thiol (1) and alkenes have been obtained in high yield, but containing small amounts of regio isomers. For example, compound 1 with 1-heptene gave 1-[2-(F-hexyl)ethanethio]heptane (3, 96% yield) as well as 2-[2-(F-hexyl)ethanethio]heptane (4, 0.61%) and 3-[2-(F-hexyl)ethanethio]heptane (5, 2.22%). 1,6-Hexadiene and 1,7-octadiene gave chiefly linear adducts, i.e. RFCH2CH2S(CH2)nCH = CH2 (7, n = 4; or 12, n = 6, respectively) and RFCH2CH2S(CH2)nSCH2CH2RF (8, n = 6; or 14, n = 8, respectively). A small amount (2-3%) of cis- and trans-1-methyl-[2-(F-hexyl)ethanethiomethyl]cyclohexane (13) isomers were present in 12. Compound 1 with 1,6-heptadiene gave 7-[2-(F-hexyl)ethanethio]-1-heptene (9), the bis adduct, 1,7-bis-[2-(F-hexyl)ethanethio]heptane (11) and the cyclic adducts, cis- and trans-1-methyl-2-12-(F-hexyl)-ethanethio]methylcyclopentane (10). The relative amounts of cyclic isomers depended on the reactant ratio. Compound 1 added readily with free-radical initiation to vinyl monomers such as styrene and vinyl acetate, and to phenyl acetylene, propargyl acetate and ethyl propynoate. These new addition products are useful as models for further study.