Copper catalyzed oxidation of tetralin to 1-(tert-butylperoxy)-tetralin by aqueous tert-butylhydroperoxide under phase transfer conditions
摘要:
Selective alpha-peroxidation of tetralin by TBHP is catalyzed by copper salts with the aid of quaternary ammonium compounds in an aqueous-organic biphasic system.
Electronic Absorption Spectra of Some Alkoxyl Radicals. An Experimental and Theoretical Study
摘要:
The visible and UV absorptions of a variety of alkoxyl radicals have been examined by experiment and theory. In most solvents, the tert-butoxyl radical shows only a weak ''tail-end'' absorption in the UV region of the spectrum and no absorption in the visible region. However, a visible absorption band has been observed (lambda(max) = 440 nm) in the presence of 1,3,5-trimethoxybenzene. This absorption band provides the first unequivocal evidence for the existence of alkoxyl radical/electron-rich aromatic pi-complexes. By way of contrast, a solvent-independent absorption in the visible is observed for (arylcarbinyl)oxyl radicals, e.g., benzyloxyl (lambda(max) = 460 nm, epsilon = 1300 M(-1) cm(-1)) and cumyloxyl (lambda(max) = 485 nm, epsilon = 1300 M(-1) cm(-1)). Electron-donating substituents on the aromatic ring shift the visible absorption to the red by 25-30 nm for a 4-methyl group and by 100-105 nm for a 4-methoxy group. However, alpha-substitution has only a minor effect on lambda(max), e.g., 530 and 535 nm for diphenylmethoxyl and 1,1-diphenylethoxyl, respectively. The visible absorption appears to be virtually uninfluenced by the (calculated) magnitude of the dihedral angle, theta, between the C-O-. bond and the plane of the aromatic ring, e.g., indan-1-oxyl, theta - 51 degrees, lambda(max) = 530 nm, and Tetralin-1-oxyl, theta similar to 33 degrees (major conformer), lambda(max) = 520 nm, vs benzyloxyl and cumyloxyl, both of which have theta similar to 0 degrees. All of these experimental observations are well-matched by theory, which reveals that the visible absorptions of (arylcarbinyl)oxyl radicals are due to D-0(A '')-->D-2(A '') (pi-->pi*) transitions which increase the negative charge on the oxygen atom and have respectable oscillator strengths. The unpaired electron is largely localized in the oxygen 2p orbital which is perpendicular to the plane of the aromatic ring.
Allylic and benzylic alcohols were oxidized in good yields to the respective ketones by tert-butylhydroperoxide (TBHP) in the presence of copper salts under phase-transfer catalysis conditions. This dehydrogenation was found to proceed via a heterolytic mechanism. CuCl2, CuCl, and even copper powder were equally facile as catalysts, as they were all transformed in situ to Cu(OH)Cl which was extracted
在相转移催化条件下,在铜盐存在下,叔丁基氢过氧化物(TBHP)将烯丙醇和苄醇以良好的产率氧化为相应的酮。发现该脱氢是通过杂化机理进行的。CuCl 2,CuCl甚至铜粉同样容易用作催化剂,因为它们都可以原位转化得到Cu(OH)Cl,其被相转移催化剂(PTC)萃取到有机相中。氘标记实验证明了在速率测定步骤中苄基CH键的断裂。在醇底物的存在下未观察到非生产性TBHP分解。相反,发现在同一介质中的π-活化的亚甲基的氧合是一个自由基过程,主要产物是合适的叔丁基过氧化物。讨论了催化剂的失活,溶剂作用和萃取作用。通过应用的Minisci的关于TBHP分子朝着相对反应性的假定叔-质子和非质子环境中的-丁氧基自由基,可以解释均解和杂化途径的共存。提出了一种完整的反应机理,其中自由基氧化遵循高知的机理,并且杂合脱氢基于高价Cu IV O物种或[Cu(OH)Cl] 2物种。
N-Heterocyclic Carbene Dirhodium(II) Complexes as Catalysts for Allylic and Benzylic Oxidations
作者:Jaime A. S. Coelho、Alexandre F. Trindade、Riccardo Wanke、Bruno G. M. Rocha、Luis F. Veiros、Pedro M. P. Gois、Armando J. L. Pombeiro、Carlos A. M. Afonso
DOI:10.1002/ejoc.201201300
日期:2013.3
conditions (solvent, base, temperature and oxidant) for allylic and benzylicoxidation reactions catalyzed by dirhodium(II)/N-heterocyclic carbene (NHC) complexes were optimized for the first time in this work. The oxidations of cyclohexene and fluorene were used as model reactions. Two optimized experimental conditions for both types of oxidations were found, which resulted in their ketone [aerobic conditions
Green Organic Solvent-Free Oxidation of Alkylarenes with tert-Butyl Hydroperoxide Catalyzed by Water-Soluble Copper Complex
作者:Abdelaziz Nait Ajjou、Ateeq Rahman
DOI:10.1515/chem-2020-0018
日期:2020.3.24
Abstract Different benzylic compounds were efficiently oxidized to the corresponding ketones with aqueous 70% tert-butylhydroperoxide (TBHP) and the catalytic system composed of CuCl2.2H2O and 2,2’-biquinoline-4,4’-dicarboxylic acid dipotassium salt (BQC). The catalytic system CuCl2/BQC/TBHP allows obtaining high yields at room temperature under organic solvent-free conditions. The interest of this
Structural Effects on the β-Scission Reaction of Alkoxyl Radicals. Direct Measurement of the Absolute Rate Constants for Ring Opening of Benzocycloalken-1-oxyl Radicals
The absoluterateconstants for β-scission of a series of benzocycloalken-1-oxyl radicals and of the 2-(4-methylphenyl)-2-butoxyl radical have been measured directly by laser flash photolysis. The benzocycloalken-1-oxyl radicals undergo ring opening with rates which parallel the ring strain of the corresponding cycloalkanes. In the 1-X-indan-1-oxyl radical series, ring opening is observed when X =