Solvation And Steric Effects On Electrophilic Reactivity Of Ethylenic Compounds .4. Bromination Of Oct-1-Ene In Anionic Microemulsions

The kinetics and product distribution of the bromination of oct-1 -ene in anionic sodium dodecylsulfate (SDS)-butanol-hexane-water and sodium bis(2-ethylhexyl)sulfosuccinate (AOT)-isooctane-water microemulsions are reported. Dibromide and solvent-incorporated products are formed. In both kinds of microemulsion, the dibromide yield decreases smoothly from 100% to 10% as the water content of the reaction medium increases from 0% to 65%, whereas in pure water or butanol it is greater than 80%. The regioselectivity of the water- or butanol-incoporated products is 70:30 Markownikoff:anti-Markownikoff, a ratio identical with that found in pure methanol, butanol or water. Kinetic bromide-ion effects on the reaction in a water-rich (75%) SDS microemulsion, show that bromination occurs in the interfacial oil-water region, and not in one of the two microphases, the only brominating agent being molecular bromine and not the tribromide ion. The overall bromination rate constant in this SDS microemulsion (k = 1.6 x 10(4) dm3 Mol-1 s-1) is smaller than that in pure water (2.3 x 10(7) dM3 Mol-1 s-1) and in SDS micelles (2 x 10(5) dM3 Mol-1 s-1), in the same range as that in a 80-20 methanol-water mixture, and greater than that in butanol (2 x 10(2) dM3 Mol-1 s-1). These results are discussed in terms of the particular characteristics (ionization and dissociating abilities, aquation and water properties) of the microemulsion interfaces.