Oxidative cleavage products

Ketones are oxidatively cleaved by Cr(VI) or Mn(VII) reagents. The reaction is sometimes of utility in the synthesis of difunctional molecules by ring cleavage. The mechanism for both reagents is believed to involve an enol intermediate.206 A study involving both kinetic data and quantitative product studies has permitted a fairly complete description of the Cr(VI) oxidation of benzyl phenyl ketone.207 The products include both oxidative-cleavage products and benzil, 7, which results from oxidation a to the carbonyl. In addition, the dimeric product 8, which is suggestive of radical intermediates, is formed under some conditions. 

Kim, S. J. et al. (2005). Oxidative cleavage products derived from phytofluene by pig liver homogenate. Food Sci. Biotech. 14(3) 424-427. 

Hoffman, G. 1962. l-Octen-3-ol and its relation to other oxidative cleavage products from esters of linoleic acid. J. Am. Oil Chemists Soc. 39, 439-444. 

With a molar ratio of propylene glycol to H2O2 of 2.5, the selectivity to hydroxyacetone at 32% conversion of the glycol was 94%, and the selectivity based on H202 was 85%. Small amounts of acetic acid and formic acid were detected. The initial oxidation proceeds with high selectivity for the secondary alcohol group. Further oxidation affords oxidative cleavage products rather than pyruvic acid, as is observed when the oxidation of hydroxyacetone is carried out with 02 and noble metal catalysts. 

In nonprotic solvents, alkenes are stoichiometrically oxidized by Vv-peroxo complexes to epoxides and consecutive oxidative cleavage products in a nonstereoselective fashion. For example, cis-2-butene gave an approximately 2 1 mixture of cis- and trans-epoxides (equation 37). The reactivity of alkenes increases with their nucleophilic nature. Alkenes containing phenyl substituents such as styrene, a- and jS-methylstyrene are also very reactive and mainly give oxidative cleavage products. 

Ruthenium tetroxide is a four-electron oxidant which directly transforms alkenic compounds into oxidative cleavage products, i.e. carbonyl compounds and carboxylic acids.288 The reaction can be visualized as proceeding according to a [4 + 2] cycloaddition of the cis-dioxo moiety with the alkene, resulting in the formation of a RuVI cyclic diester which decomposes to ruthenium(IV) dioxide and oxidative cleavage products (equation 114).288 This reaction can be made catalytic... 

Figure 16 Molecular structures of a thymine dimer (TT) model compound and of its oxidative cleavage products. Here bimolecular oxidation of the cis-syn 1,3-dimethyl-thymine dimer (DMTADMT) yields two 1,3-dimethylthymine monomers (DMT).

Eleven apo-carotenoids (1-11), including five new compounds, 4, 6, 9,10 and 11, were isolated from the fruits of the red paprika collected from Japan by Maoka et al. (2001b). The structures of new apocarotenoids were determined to be apo-14 -zeaxanthinal (4), apo-13-zeaxanthinone (6), apo-12 -capsorubinal (9), apo-8 -capsorubinal (10) and 9,9 -diapo-10,9 -retro-carotene-9,9 -dione (11) by spectroscopic analysis. The other six known apocarotenoids were identified to be apo-8 -zeaxanthinal (1), apo-lO -zeaxanthinal (2), apo-12 -zeaxan-thinal (3), apo-15-zeaxanthinal (5), apo-11-zeaxanthinal (7) and apo-9-zeaxanthinone (8), which had not been found previously in paprika. These apocarotenoids were assumed to be oxidative cleavage products of C40 carotenoid, such as capsanthin in paprika. 

Another control experiment was done to determine the importance of water in this oxidative cleavage reaction. Water was found to be a necessary reagent for the reaction to occur since no p-hydroxybenzaldehyde was obtained when the sodium salt of chlorostilbene 5b was heated in neat nitrobenzene with or without solid sodium hydroxide and a crown ether phase transfer catalyst. Another set of controls was done to evaluate the formation of p-hydroxybenzaldehyde by a nonoxidative reaction, such as the loss of X-PI1-CH2 in a retrograde-type Aldol reaction. No p-hydroxybenzaldehyde was formed when the chlorostilbene 5b was heated at 155 °C for 5 hours in the presence of 2N NaOH but without the presence of nitrobenzene and atmospheric oxygen. Finally, in all of the above control experiments, no oxidized cleavage products were observed from the nonphenolic side of the alcohols 4 or stilbenes 5 (Dershem, S. M., et al., Holzforschung, in press). 

Another possibility is the use of tungsten, which has led to excellent results for the conversion of cyclohexene to adipic acid (see Fig. 4.23) [48]. For linear olefins using the Venturello-system, oxidative cleavage products can be obtained in around 80% yield [96]. 

Oxidative cleavage is a valuable tool for structure determination of unknown compounds. The ability to determine what alkene gives rise to a particular set of oxidative cleavage products is thus a useful skill, illustrated in Sample Problem 12.4. 

Problem 12,21 What alkene yields each set of oxidative cleavage products ... 

An achiral hydrocarbon A of molecular formula C7H12 reacts with two equivalents of H2 in the presence of Pd-C to form CH3CH2CH2CH2CH(CH3)2. One oxidative cleavage product formed by the treatment of A with O3 is CH3COOH. Reaction of A with H2 and Lindlar catalyst forms B, and reaction of A with Na, NH3 forms C. (a) Identify compounds A, B, and C. (b) Explain why A does not react with NaH. 

The high chemical yield of the oxidative cleavage product argues for efficient interception of a cation radical (Eq. 2), perhaps by superoxide produced by surface trapping of the conduction band electron. 

Radical cations are probably involved in the photooxidation of olefins [1-7, 24, 50-54, 56, 61, 66] (Eqs. 2 and 5). Many oxidizable arenes and dienes are, similarly, oxidatively cleaved or rearranged by routes consistent with initial formation of a radical cation. As we saw above, the observed oxidative cleavage product probably derives from the combination of a surface-bound radical cation with superoxide or adsorbed oxygen. With alkanes or simply substituted alkenes, however, the capture of a photogenerated hole is often thermodynamically forbidden. Thus, instead of radical cations, radicals formed by hydrogen atom abstraction by an activated oxygen species dominate the observed chemistry. With alkanes, oxygenation at sites... 

When 3,4-diethyl-3-hexene is treated with potassium permanganate and aqueous hydroxide, the expected product is a diol. It is possible for oxidative cleavage of the C=C unit to occur if the solution is too concentrated or heated too much. Draw the expected diol and the oxidative cleavage product or products and use IR and proton NMR spectroscopic differences to distinguish them. 

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