Synthesis of fluoro-substituted acrylic monomers bearing a functionalized lateral chain: Part 1. Preparation of sulfur-containing monomers
The synthesis of sulfur-containing fluoroacrylic monomers CmF2m+1(CH2)2S(CH2)n OC(O)CH=CH2 (where m=6, 8 and n=2-4, 11) is presented from a two-step procedure. The first deals with the radical addition of fluorinated mercaptans CmF2m+1(CH2)2SH onto ω-unsaturated alcohols leading to new ω-perfluorinated alcohols containing various polymethylene spacers CmF2m+1(CH2)2S(CH2)n OH according to the nature of the unsaturated alcohols. By-products were noted, resulting from the β-addition of the thiyl radical onto the more hindered side of the alcohol. The proportion of linear and branched isomers is discussed according to the stability of the radical intermediates. These minor products were obtained selectively from other routes to confirm their presence in the reaction media. The second step deals with the acrylation reaction that occurred either in the presence of acryloyl chloride or from a Fisher esterification. Both reactions are described and discussed taking into account the nature of the starting alcohols. The formation of thiiranium ions as intermediates in the esterification of β-sulfur-containing alcohols in acidic medium is established and the formation of regioisomers described according to this thiiranium moieties interposition.
