Oxidation by Vanadium Compounds

Hydrogen Atom Abstraction by Metal−Oxo Complexes: Understanding the Analogy with Organic Radical Reactions

“…t Bu • is then oxidized by CrO 2 Cl 2 primarily to isobutylene, plus some t BuCl and t BuOH. The alkenes formed in these reactions are rapidly oxidized by CrO 2 Cl 2 , consistent with previous studies (including Sharpless' pioneering suggestion of organometallic intermediates in olefin oxidations 25 ) indicating that epoxides and chlorohydrins are the initial products. ,, …”

“…For aqueous solutions with E vs NHE, we find C = 57 ± 2 kcal/mol, both from tabulated thermochemical values as in Scheme and using phenol and aniline as benchmarks . Wiberg and Foster used a similar cycle in 1961 to estimate the enthalpy of R 3 CH + H + + HCrO 4 - → R 3 C • + H 3 CrO 4 as +19 kcal/mol 21b 5 Calculation of the O−H Bond Strength in [O 3 MnO−H] - 35,41 …”

“…, Scheme ), is known as the Étard reaction and dates from the 19th century. In the 1960s, Wiberg and co-workers argued convincingly for radical intermediates though carbocation and concerted pathways have been more recently advanced . Wiberg suggested that Cr VI complexes abstract hydrogen atoms from substrates but also considered radical chain paths in which another oxidant performed the initial abstraction.…”

Advances in Homogeneous and Heterogeneous Catalytic Asymmetric Epoxidation

“…The asymmetric epoxidation of homoallylic alcohols was difficult to conduct with the other metal-based catalysts reported previously. − However, vanadium complexes could effectively catalyze the occurrence of this reaction to yield the corresponding epoxy alcohols with good to high stereoselectivities . Yamamoto et al prepared a chiral vanadium complex 23 from vanadium triisopropoxide and an α-amino acid-based hydroxamic acid, which was a rather efficient catalyst for the epoxidation of disubstituted allylic alcohols with up to 96% ee in high yields (almost >95%). ,, In 2003, they reported again that this chiral catalyst could also be used for the asymmetric epoxidation of 3-monosubstituted homoallylic alcohols with high enantioselectivities (84−91% ee) in moderate yields (42−89%), as shown in Table .…”

An Efficient and Selective Solvent-free Oxidation of Alcohols by Shaking with Chromium Trioxide Supported on Aluminium Silicate

“…One of the most important reactions of alcohols, which have long been the objective of many research papers, is their oxidation to the corresponding carbonyl compounds. Chromium (VI)-based reagents have been extensively used in organic synthesis [ 2 , 3 , 4 ]. The utility of chromium (VI) reagents in the above oxidative transformation is compromised due to their inherent toxicity, cumbersome preparation, and potential danger in terms of product isolation and waste disposal.…”