Comparison of the mechanisms of the bromination and oxymercuration reactions of alkenes

Selective Conversion of Enol Ethers into Alcohols in the Presence of Alkenes Using Hg(OAc)2-NaBH4

“…Formation of the mercurinium intermediate is believed to be very rapid with nucleophilic attack of H 2 O as the rate-determining step. 12 It has also been observed that electron donation to an alkene increases and electron withdrawal from an alkene decreases the rate of nucleophilic attack on the mercurinium ion intermediate and, thus, affects the rate of oxymercuration reactions. [13][14][15] And, in Boeckman's use of solvomercuration-demercuration to convert alkyl enol ethers into mixed acetals, olefinic alcohols and alkyl enol ethers were combined in the presence of Hg(OAc) 2 and only alkoxymercuration of the enol ether, not of the alkene, was reported.…”

Mercury(II) Acetate

“…Thus the rate-limiting step for mercuration is the cleavage of the intermediate mercuronium ion by a nucleophile; in contrast, bromination proceeds by the rate-limiting formation of the bromonium ion. 15 Mercuration is very sensitive to steric factors in which it parallels hydroboration. 16 The following reactivity of alkenes has been observed: terminal disubstituted > terminal monosubstituted > internal disubstituted > > trisubstituted > tetrasubstituted (eq 4); 17 cis-alkenes are more reactive than their trans counterparts 17 and enol ethers are much more reactive than any other alkene.…”

Kinetics and Mechanism of Acetoxymercuration and Acid-Catalysed Hydration of α-Alkylstyrenes

“…Solvent effects on alkoxymercuration of styrenes were dealt with in several papers [3][4][5]; however, in all the cases they referred to alcohols or their mixtures with other solvents. Within their research work on kinetics and mechanism of methoxymercuration of styrenes [1][2][3][4][5][6][7][8] and other alkenes [8][9][10][11][12][13][14][15][16], the authors have focused their attention especially on substituent effects [2,3,6,8,10,12], including the steric ones [10,12]; furthermore, to salt effects [14,15], temperature dependences of the reaction rate constant [1,2,6] and in the context with the abovementioned areas, also to the structure of the addition intermediate [3,4,[8][9][10][13][14][15][16]. From these studies it follows that methoxymercuration is an electrophilic reaction, whose rate-limiting step involves formation of an intermediate with an acetylmercuric cation asymmetrically bound to the carbon atoms of the styrene vinyl group.…”