Chromium-carbon bond cleavage

Reaction of O2 with the complex [(H20)5CrCH(CH3)2] to give [Cr(H20)6] and acetone proceeds by a chain mechanism initiated by chromium-carbon bond cleavage with a rate of 1.74 x 10 s at 25°C and 1.0 M ionic strength. Inhibition studies suggest the organic radicals (CH3)2CH and (CH3)2CH02 are chain intermediates involved in the reaction... 

Oxidations. WChlorosuccinimide-dimethyl sulfide (NCS-DMS) is one of several reagents for converting alcohols to alkoxydtmethylsulfonium salts, which in the presence of base convert to the corresponding carbonyl compounds via intramolecular proton transfer and loss of dimethyl sulfoxide. These oxidations are among the mildest and most selective for conversions of alcohols to aldehydes and ketones. This reaction does not suffer the overoxidation to acids or the carbon-carbon bond cleavages which are often encountered in chromium(VI) or manganese(VII) oxidations (eq 1). ... 

Mikami M, Hatano M, Akiyama K (2005) Active Pd(II) Complexes as Either Lewis Acid Catalysts or Transition Metal Catalysts. 14 279-322 Minatti A, DOtz KH (2004) Chromium-Templated Benzannulation Reactions. 13 123-156 Miura M, Satoh T (2005) Catalytic Processes Involving b-Carbon Elimination. 14 1-20 Miura M, Satoh T (2005) Arylation Reactions via C-H Bond Cleavage. 14 55-84 Mizobe Y, see Hidai M (1999) 3 227-241... 

The main applications of oxidation with chromium trioxide are transformations of primary alcohols into aldehydes [184, 537, 538, 543, 570, 571, 572, 573] or, rarely, into carboxylic acids [184, 574], and of secondary alcohols into ketones [406, 536, 542, 543, 575, 576, 577, 578, 579, 580, 581, 582, 583, 584]. Jones reagent is especially successful for such oxidations. It is prepared by diluting with water a solution of 267 g of chromium trioxide in a mixture of 230 mL of concentrated sulfuric acid and 400 mL of water to 1 L to form an 8 N CrOj solution [565, 572, 579, 581, 585, 556]. Other oxidations with chromic oxide include the cleavage of carbon-carbon bonds to give carbonyl compounds or carboxylic acids [482, 566, 567, 569, 580, 587, 555], the conversion of sulfides into sulfoxides [541] and sulfones [559], and the transformation of alkyl silyl ethers into ketones or carboxylic acids [590]. 

Chromium sulfide is a selective catalyst of THT dehydrogenation minimizing the C-S bond cleavage. The activity seems to be correlated to the reducibility of chromium into Cril species. Carbon is an excellent support promoting both the dispersion of the active phase and favoring the creation of coordinatively unsaturated chromium species (probably CrII species). However further inve.stigations are required to improve its stability. 

Mechanism 15.3 outlines the mechanism of chromic acid oxidation of 2-propanol to acetone. The alcohol reacts with chromic acid in the first step to give a chromate ester. A carbon-oxygen double bond is formed in the second step when loss of a proton from carbon accompanies cleavage of the bond between oxygen and chromium. The second step is rate-determining as evidenced by the fact that (CH3)2CHOH reacts 6.7 times faster than (CH3)2CDOH. If the second step were faster than the first, no deuterium isotope effect (Section 5.17) would have been observed. 

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