Competing base-promoted E2 and E1 reactions of an acidic tertiary substrateElectronic supplementary information (ESI) available: the effect of base concentration on rate constant and product composition. See http://www.rsc.org/suppdata/p2/b2/b200758d/
作者:Xiaofeng Zeng、Alf Thibblin
DOI:10.1039/b200758d
日期:2002.6.27
The solvolysis of 4-chloro-4-(4′-nitrophenyl)pentan-2-one (1-Cl) in aqueous acetonitrile yields the alcohol 4-hydroxy-4-(4′-nitrophenyl)pentan-2-one (1-OH) and the elimination products 4-(4′-nitrophenyl)-2-oxopent-4-ene (2), (E)-4-(4′-nitrophenyl)-2-oxopent-3-ene (3), and (Z)-4-(4′-nitrophenyl)-2-oxopent-3-ene (4). Addition of thiocyanate ion does not increase the total reaction rate in 25 vol% acetonitrile in water, but gives rise to the substitution products 1-SCN and 1-NCS, at the expense of 1-OH, and a small increase in the fraction of alkene 3. Addition of acetate ion and other weak bases gives rise to base-promoted E2 (or E1cB) to give alkene 3 (and 4).
The Brønsted parameter for this reaction was measured as β
= 0.76. Water-promoted E2 (or E1cB) reaction was not observed.
4-氯-4-(4'-硝基苯基)戊-2-酮 (1-Cl) 在乙腈水溶液中溶剂分解,得到醇 4-羟基-4-(4'-硝基苯基)戊-2-酮 (1 -OH) 和消除产物 4-(4'-硝基苯基)-2-氧代戊基-4-烯 (2)、(E)-4-(4'-硝基苯基)-2-氧代戊基-3-烯 (3) ,和(Z)-4-(4'-硝基苯基)-2-氧代戊-3-烯(4)。添加硫氰酸根离子不会增加 25 vol% 乙腈水溶液中的总反应速率,但会产生取代产物 1-SCN 和 1-NCS,以 1-OH 为代价,并且 1-OH 的分数略有增加烯烃3。加入乙酸根离子和其他弱碱产生碱促进的E2(或E1cB),得到烯烃3(和4)。
该反应的布朗斯台德参数测量为 β
= 0.76。未观察到水促进的 E2(或 E1cB)反应。