Jones oxidation mechanism

Mechanism The mechanism of the Jones oxidation proceeds through a chromate ester intermediate which undergoes an E2-like elimination to the carbonyl product (Scheme 7.2). Since chromate reagents are of dark orange-red colour (Cr in VI oxidation state) and Cr(III) compounds are normally green, the progress of these oxidations is easily observed. Indeed, this is the chemical transformation on which the Breathalizer test is based. 

Romine, R.R. Hansen, J.L. Jones, R.L. Aldicarb oxidation mechanism studies, Union Carbide Agricultural Products Company, Inc., Preliminary Draft, 1984. 

Finally, we discuss the oxidation of CS2 and COS. Jones et al. (1982, 1983) and Barnes et al. (1983) have studied the OH-induced oxidation of CS2 in air at atmospheric pressure and observed as products S02 and COS in equal amounts. The rate-accelerating effect of 02 then suggests the following simple oxidation mechanism ... 

Penkett and Jones (1979), Daniel and Jacob (1986), and Deminsky et al. (1990). The oxidation mechanism in droplets depends on their acidity, which can be presented through the following kinetic schemes ... 

The reason for these apparently contradictory results is the different conditions used to perform the radical cyclisation. In Jones studies, 1.2 equiv. of BusSnH and trace amounts of AIBN were used, while in Tsuge s work, 1.5 equiv. of BusSnH and 0.25 equiv. of initiator were used. This difference could explain the disparity, since the initiator probably takes part in the oxidation mechanism. 

You met methods for this reaction in Chapter 9, where you met the use of Cr(VI) in the form of CrOs. One common version of this reaction is the Jones oxidation, shown in the margin. The mechanism starts with the formation of HCrOj ions, that is, Cr(VI), from dichromate ion in solution. In acid, these Cr(VI) species form chromate esters with alcohols. Chromate esters decompose by elimination of a Cr(IV) species, which subsequently reacts with Cr(VI) to yield 2 X Cr(V). These Cr(V) species can oxidize alcohols in the same way and are thereby reduced to Cr(III) (the final metal-containing by-product). Cr(VI) is orange and Cr(III) is green, so the progress of the reaction is easy to follow by colour change. 

In an aptly titled paper Herz et describe unexpected rearrangements of photolevopimaric acid derivatives. Among a wealth of chemical reactions discussed it appears that the exo-bicyclo[2,2,0]hexanol (575), derived from methyl levopimarate by hydroboration-oxidation, is rearranged during Jones oxidation to the bicyclo[2,l,l]-hexanone (576), contrary to a previous report. A mechanism is proposed. 

Variable valence transition metal ions, such as Co VCo and Mn /Mn are able to catalyze hydrocarbon autoxidations by increasing the rate of chain initiation. Thus, redox reactions of the metal ions with alkyl hydroperoxides produce chain initiating alkoxy and alkylperoxy radicals (Fig. 6). Interestingly, aromatic percarboxylic acids, which are key intermediates in the oxidation of methylaromatics, were shown by Jones (ref. 10) to oxidize Mn and Co, to the corresponding p-oxodimer of Mn or Co , via a heterolytic mechanism (Fig. 6). 

The risk of developing colonic cancer is raised in UC, particularly in those with long-standing extensive disease (Lennard-Jones et al., 1990). The mechanism of this increased susceptibility is unknown, although it is tempting to speculate that it is related to inflammation and resulting oxidative damage to DNA. As yet there is little evidence to support this contention. Markowitz et al. (1988) have reported a decrease in constituent and oxidant-induced adenosine diphosphate ribosyl... 

Inhibition and stimulation of LOX activity occurs as a rule by a free radical mechanism. Riendeau et al. [8] showed that hydroperoxide activation of 5-LOX is product-specific and can be stimulated by 5-HPETE and hydrogen peroxide. NADPH, FAD, Fe2+ ions, and Fe3+(EDTA) complex markedly increased the formation of oxidized products while NADH and 5-HETE were inhibitory. Jones et al. [9] also demonstrated that another hydroperoxide 13(5)-hydroperoxy-9,ll( , Z)-octadecadienoic acid (13-HPOD) (formed by the oxidation of linoleic acid by soybean LOX) activated the inactive ferrous form of the enzyme. These authors suggested that 13-HPOD attached to LOX and affected its activation through the formation of a protein radical. Werz et al. [10] showed that reactive oxygen species produced by xanthine oxidase, granulocytes, or mitochondria activated 5-LOX in the Epstein Barr virus-transformed B-lymphocytes. 

The mechanism of the oxidation of tertiary cyclobutanols with Jones reagent is believed to involve the intermediate lactols (Eq. (18)) and the cleavage of the lactol to ketol and its subsequent oxidation to diketone when R1 = H157). 

There is ample evidence that the reductive elimination of alkanes (and the reverse) is a not single-step process, but involves a o-alkane complex as the intermediate. Thus, looking at the kinetics, reductive elimination and oxidative addition do not correspond to the elementary steps. These terms were introduced at a point in time when o-alkane complexes were unknown, and therefore new terms have been introduced by Jones to describe the mechanism and the kinetics of the reaction [5], The reaction of the o-alkane complex to the hydride-alkyl metal complex is called reductive cleavage and its reverse is called oxidative coupling. The second part of the scheme involves the association of alkane and metal and the dissociation of the o-alkane complex to unsaturated metal and free alkane. The intermediacy of o-alkane complexes can be seen for instance from the intramolecular exchange of isotopes in D-M-CH3 to the more stable H-M-CH2D prior to loss of CH3D. 

Turner, P. S., Jones, C. F., Myhra, S., Neall, F. B., Pham, D. K. Smart, R. St. C. 1989. Dissolution mechanisms of oxides and titantate cermics - electron microscope and surface analytical studies. In Dufour, L.-C., Monty, C. Petot-Ervas, G. (eds) Surfaces and Interfaces of Ceramic... 

The Jones reagent851 and < rt-BuOOH in the presence of chromium(VI) complexes852,853 were found to be particularly useful in the oxidation of tetralins and indans. Oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) occurs with an exceptional mechanism.854 In contrast with the radical processes observed in other oxidations DDQ generates a carbocation by hydride abstraction that is trapped by water to form an alcohol ... 

The mechanism of the oxidation of alcohols with Jones reagent is often depicted as given below.4... 

E2. Eiserich, J. P., Cross, C. E., Jones, A. D., Halliwell, B., and van derVliet, A., Formation of nitrating and chlorinating species by reaction of nitrite with hypochlorous acid. A novel mechanism for nitric oxide-mediated protein modification. J. Biol. Chem. 271,19199—19208 (1996). 

L. L. Shipman, in Polynuclear Aromatic Hydrocarbons, R. Freudenthal and P. W. Jones, Eds., Raven Press, New York, 1976. Ab Initio Quantum Mechanical Characterization of the Ground Electronic State of Benzo[ ]pyrene. Implications for the Mechanism of Polynuclear Aromatic Hydrocarbon Oxidation to Epoxides by Cytochrome P-450. 

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