Haouas Mohamed, Walspurger Stéphane, Taulelle Francis, Sommer Jean
RMN et Chimie du Solide, UMR 7140 CNRS, Université Louis Pasteur, 4 rue Blaise Pascal, 67070 Strasbourg Cedex, France.
J Am Chem Soc. 2004 Jan 21;126(2):599-606. doi: 10.1021/ja0377549.
In situ solid-state NMR spectroscopy was employed to study the kinetics of hydrogen/deuterium exchange and scrambling as well as (13)C scrambling reactions of labeled propane over Al(2)O(3)-promoted sulfated zirconia (SZA) catalyst under mild conditions (30-102 degrees C). Three competitive pathways of isotope redistribution were observed during the course of the reaction: (1) a regioselective H/D exchange between acidic protons of the solid surface and the deuterons of the methyl group of propane-1,1,1,3,3,3-d(6), monitored by in situ (1)H MAS NMR; (2) an intramolecular H/D scrambling between methyl deuterons and protons of the methylene group, without exchange with the catalyst surface, monitored by in situ (2)H MAS NMR; (3) a intramolecular (13)C scrambling, by skeletal rearrangement process, favored at higher temperatures, monitored by in situ (13)C MAS NMR. The activation energy of (13)C scrambling was estimated to be very close to that of (2)H scrambling, suggesting that these two processes imply a common transition state, responsible for both vicinal hydride migration and protonated cyclopropane formation. All pathways are consistent with a classical carbenium ion-type mechanism.
采用原位固态核磁共振光谱法研究了在温和条件（30 - 102℃）下，标记丙烷在Al₂O₃促进的硫酸化氧化锆（SZA）催化剂上的氢/氘交换、重排以及（¹³）C重排反应的动力学。在反应过程中观察到三种同位素重新分布的竞争途径：（1）通过原位¹H MAS NMR监测，固体表面酸性质子与丙烷-1,1,1,3,3,3-d₆甲基的氘核之间的区域选择性H/D交换；（2）通过原位²H MAS NMR监测，甲基氘核与亚甲基质子之间的分子内H/D重排，不与催化剂表面交换；（3）通过原位¹³C MAS NMR监测，在较高温度下有利于通过骨架重排过程进行的分子内（¹³）C重排。估计（¹³）C重排的活化能与²H重排的活化能非常接近，这表明这两个过程意味着一个共同的过渡态，负责邻位氢化物迁移和质子化环丙烷的形成。所有途径均与经典的碳正离子型机理一致。
