Free-radical addition of 2-(perfluoroalkyl)ethanethiols to alkenes, alkadienes, cycloalkenes, alkynes and vinyl monomers

The free-radical addition of 2-(perfluoroalkyl)ethanethiols (R F CH 2 CH 2 SH) to alkenes,cycloalkenes, alkadienes and alkynes has been studied to determine: (1) the mode ofreaction, i.e. the stereochemistry, regiochemistry and any skeletal changes; (2) the relativereactivity towards unsaturates of differing structures and classes as affected by the presenceof the R F group; and (3) the influence of the reaction conditions on the rate of additionor selectivity for different products. Adducts from 2-( F -hexyl)ethane thiol ( 1 ) and alkeneshave been obtained in high yield, but containing small amounts of regio isomers. Forexample, 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 chieflylinear adducts, i.e. R F CH 2 CH 2 S(CH 2 ) n CHCH 2 ( 7 , n = 4; or 12 , n = 6, respectively) andR F CH 2 CH 2 S(CH 2 ) n SCH 2 CH 2 R F ( 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 werepresent 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-[2-( F -hexyl)-ethanethio]methylcyclopentane ( 10 ). The relativeamounts of cyclic isomers depended on the reactant ratio. Compound 1 added readilywith free-radical initiation to vinyl monomers such as styrene and vinyl acetate, and tophenyl acetylene, propargyl acetate and ethyl propynoate. These new addition productsare useful as models for further study.