The formation of the alkyl hydrogen sulfate arises from initial protonation on the double bond,and the intermediate carbocation is trapped by the bisulfate anion.(Markovnikov addition). CH3 CHa CH3 HO3SO-H →H+CHs HOSO3- H CH3 CH3 CH3 CH3 CH3 H CH H CH H :OSO3H H OSO H The alkyl hydrogen sulfate can be converted to an alcohol by boiling in water. This proceeds usually by SI substitution where water is the nucleophile and bisulfate is the leaving group. CH3CH3 CH3 CH3 CH3CH3 →H 车CH →HCHs HOSO3H H /:02H H OH2 HOSO3 H CH3CH3 H-CHs H OH The product has the same regiochemistry as an alcohol formed by direct hydration of the same alkene (Markovnikov orientation). Ch08 Reacns of Alkenes (landscape) Page 11
Ch08 Reacns of Alkenes (landscape) Page 11 The formation of the alkyl hydrogen sulfate arises from initial protonation on the double bond, and the intermediate carbocation is trapped by the bisulfate anion. (Markovnikov addition). The alkyl hydrogen sulfate can be converted to an alcohol by boiling in water. This proceeds usually by SN1 substitution where water is the nucleophile and bisulfate is the leaving group. The product has the same regiochemistry as an alcohol formed by direct hydration of the same alkene. (Markovnikov orientation). H3C H CH3 CH3 H CH3 H CH3 CH3 H CH3 H CH3 CH3 H CH3 H CH3 CH3 OSO3H HO3S O H + HOSO3 - - :OSO3H + H CH3 H CH3 CH3 OSO3H H CH3 H CH3 CH3 HOSO3 - + :O2H H CH3 H CH3 CH3 OH2 + -H + H CH3 H CH3 CH3 OH
Oxymercuration-Demercuration This is another alternative for converting alkenes to alcohols with Markovnikov orientation.This method has the advantage of not involving free carbocationic species,and thus removes the possibility of rearrangements CC=C Hg(OAc)2 H20 HO HgOAc HO H (Markovnikov orientation) The reagent is called mercuric acetate,and is usually abbreviated to Hg(OAc)2In solution it ionizes into acetate ion and a positively charged mercury species which is very electrophilic. 0 0 CH,-C-O一Hg-O-C-CH, CH-C-O-Hg+ + CH-C-O Hg(OAc) +Hg(OAc) -OAc 2013 Prson Educalion ine OAc mercurinium ion Oxymercuration is the +Hg(OAc) electrophilic attack of this species on a double bond, giving a 3 membered ring compound called a mercurinium ion. Cho8 Reacns of Alkenes (landscape) Page 12
Ch08 Reacns of Alkenes (landscape) Page 12 Oxymercuration-Demercuration This is another alternative for converting alkenes to alcohols with Markovnikov orientation. This method has the advantage of not involving free carbocationic species, and thus removes the possibility of rearrangements. The reagent is called mercuric acetate, and is usually abbreviated to Hg(OAc)2 In solution it ionizes into acetate ion and a positively charged mercury species which is very electrophilic. Oxymercuration is the electrophilic attack of this species on a double bond, giving a 3 membered ring compound called a mercurinium ion