Oxidative cleavage determining products

Oxidation indices, 656-72 peroxide determination, 762-3 peroxide value, 656, 657-64 colorimetry, 658-61 definition, 657 direct titration, 657 electrochemical methods, 663-4 IR spectrophotometry, 661-3 NIR spectrophotometry, 663 UV-visible spectrophotometry, 658-61 secondary oxidation products, 656, 665-72 tests for stability on storage, 664-5, 672 thermal analysis, 672 Oxidative amperometiy, hydroperoxide determination, 686 Oxidative cleavage alkenes, 1094-5 double bonds, 525-7 Oxidative couphng, hydrogen peroxide determination, 630, 635 Oxidative damage... 

The MMA homopolymer and the unreacted PVA are removed from the reaction product by the selective extraction method. The grafted branch PMMA is separated from the backbone by oxidative cleavage of all 1,2-glycols of PVA (about 2 mole%)29 Molar masses of the isolated graft copolymers and the separated branches are osmo-metrically determined, after acetylation of hydroxyl groups in benzene. The chemical composition of the graft copolymers is determined from the saponification value of the acetylated sample. 

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). 

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. 

Chemically, oxidative cleavage of the benzoquinone ring with H2O2 under basic or acidic conditions was effective to determine the structure as shown in the example of AQ-C-1 (114) (Scheme 19). In this reaction, the presence of methox-yl and isopentenyl groups causes a decrease in yield of the degradative products. Hierefore, it is desirable to use pigments which have been hydrogenated in the side chain and demethylated prior to oxidation. 

EIEs provide invaluable information concerning both molecular structure and the determination of reaction mechanisms. EIEs are traditionally defined as the ratio of equilibrium constants for unlabeled and labeled reactants and products (EIE = A h/A d Figure 2). For oxidative addition and reductive elimination reactions, the presence of intermediates along the reaction coordinate, such as alkane cr-complexes and agostic interactions, make these reactions multistep processes and hence, additional terms are necessary in order to more fully describe the overall mechanism. Thus, reductive elimination may consist of a reductive coupling (rc) step followed by dissociation (d), whereas the microscopic reverse, oxidative addition, could consist of ligand association (a) followed by oxidative cleavage (oc), as illustrated in Scheme 6. 

Ketones are cleaved oxidatively by Cr(VI) or Mn(VIII) reagents. The reaction is sometimes of utility in the synthesis of difunctional molecules by ring cleavages. The mechanism for both reagents is believed to involve reaction of an enolic intermediate, although in neither case have all the details been established. A study involving both kinetic data and accurate product-yield determination has permitted a fairly complete description of the Cr(VI) oxidation of benzyl phenyl ketone (desoxybenzoin). The products include both oxidative-cleavage products and... 

An attempt to determine the absolute stereochemistry of natural eucomol (10) by chemical degradation to a product of known chirality led to a series of new transformations (64). It was anticipated that reduction of (10) to the deoxo derivative (58) followed by oxidative cleavage of ring A would lead to the lactone (59). From this intermediate the key compound (61) should be obtained by subsequent reduction. The derivative (61) is easily prepared from eucomic acid (60) whose absolute stereochemistry has been elucidated recently (34, 36). 

Oxidative cleavages of selected alcohols and oximes to the corresponding carbonyl compounds in CHCI3 by BCC, PCC, MCC, ICC, and QFC have shown similar reactivity and mechanism. The phen-catalysed BTEACC oxidation of cychc ketones in 40% AcOH is fractional order in ketones, H ion, and phen, with reactivity order Cs > Cg > C5 > C7. Disproportionation of the BTEACC-protonated ketone complex is the rate-determining step, followed by fast steps leading to the final products (1,2-diketones). ... 

To determine the product of oxidative cleavage, replace C=C withC=0 0=C. 

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