Enhancement of the Oxidizing Power of an Oxoammonium Salt by Electronic Modification of a Distal Group
Enhancement of the Oxidizing Power of an Oxoammonium Salt by Electronic Modification of a Distal Group
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DOI：
10.1021/acs.joc.7b01965
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发表时间：
2017-11-03
影响因子：
3.6
通讯作者：
Bailey, William F.
中科院分区：
文献类型：
--
作者：
Lambert, Kyle M.;Stempel, Zachary D.;Bailey, William F.
报道了一种新的TEMPO基氧铵盐2，2，6，6-tetramethy1-4-(2，2，2-trifluoroacetamido)-1-oxopiperidinium四氟硼酸盐(5)及其相应的氮氧化物(4)的多克合成和表征。5在通常用于乙醇氧化的溶剂中的溶解度分布与博比特盐4-acetamido-2，2，6，6-tetramethyl-1-oxopiperidinium四氟硼酸盐有很大不同(1)。测定了一系列具有代表性的伯醇、仲醇和苄醇在乙腈溶剂中的氧化速率，发现氧铵盐5比1氧化醇快。间位和对位取代苄醇的氧化速率与Hammett参数(r>；0.99)呈很强的线性相关，斜率(P)分别为-2.7和-2.8，表明氧化的限速步骤涉及从醇底物的甲醇碳中抽出氢化物。
The multigram preparation and characterization of a novel TEMPO-based oxoammonium salt, 2,2,6,6-tetramethy1-4-(2,2,2-trifluoroacetamido)-1-oxopiperidinium tetrafluoroborate (5), and its corresponding nitroxide (4) are reported. The solubility profile of 5 in solvents commonly used for alcohol oxidations differs substantially from that of Bobbitt's salt, 4-acetamido-2,2,6,6-tetramethyl-1-oxopiperidinium tetrafluoroborate (1). The rates of oxidation of a representative series of primary, secondary, and benzylic alcohols by 1 and 5 in acetonitrile solvent at room temperature have been determined, and oxoammonium salt 5 has been found to oxidize alcohols more rapidly than does 1. The rate of oxidation of meta- and para-substituted benzylic alcohols by either 1 or 5 displays a strong linear correlation to Hammett parameters (r > 0.99) with slopes (p) of -2.7 and -2.8, respectively, indicating that the rate limiting step in the oxidations involves hydride abstraction from the carbinol carbon of the alcohol substrate.