Derivatives with Oxygen

Oxides, hydroxides, phenoxides and carboxylates of organogermanium-tin compounds are listed in this chapter. The derivatives all compiled in Table 80 are prepared by methods from the following scheme. 

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Villar, J. C., Caperos, A., and Garcia-Ochoa, F., Oxidation of hardwood kraft-lignin to phenolic derivatives with oxygen as oxidant. Wood Sci Technol 2001, 35 (3), 245 255. 

G.l.c.-m.s. data are reported" for a series of C19O3 (androstane) derivatives with oxygen substituents at either C-2, -6, -7, -11, or -16 in addition to those at C-3 and C-17. Field desorption mass spectra are reported for some saponins (kryptogenin 3-0-/8-D-glucopyranoside, dioscin, etc.) Progress is reported towards the computer-aided recognition of structural features of steroids from low-resolution mass spectra. ... 

VI.2.1 Reactions of Acylpalladium Derivatives with Oxygen, Nitrogen, and Other Group 15,16, and 17 Atom Nucleophiles... 

All photosynthetic tissues, as well as some nonphotosynthetic tissue and Protista, contain carotenoids. It is said that over 400 carotenoids have been identified, but that most are xanthophylls. As noted above, xanthophylls are carotenoid derivatives with oxygen substitutions in the ring or side chain and have reduced or no vitamin A activity (Simpson and Chichester, 1981). Vitamin A activity for vertebrates requires that a carotenoid have at least the unaltered p-ionone ring with an attached polyene side chain containing 11 carbon atoms. Although some compounds with chemical modifications in the P-ionone ring still... 

Kobayashi, M. (1994b) Marine terpenes and terpenoids Part 18. First natural 4-tocopherol and A—tocopheryl quinone derivatives with oxygenated side chain, isolated from soft coral Sinularia mayi. J. Chem, Res, (S), 494- 95. 

The achiral triene chain of (a//-rrans-)-3-demethyl-famesic ester as well as its (6-cis-)-isoiner cyclize in the presence of acids to give the decalol derivative with four chirai centres whose relative configuration is well defined (P.A. Stadler, 1957 A. Escherunoser, 1959 W.S. Johnson, 1968, 1976). A monocyclic diene is formed as an intermediate (G. Stork, 1955). With more complicated 1,5-polyenes, such as squalene, oily mixtures of various cycliz-ation products are obtained. The 18,19-glycol of squalene 2,3-oxide, however, cyclized in modest yield with picric acid catalysis to give a complex tetracyclic natural product with nine chiral centres. Picric acid acts as a protic acid of medium strength whose conjugated base is non-nucleophilic. Such acids activate oxygen functions selectively (K.B. Sharpless, 1970). 

Cyclopentene derivatives with carboxylic acid side-chains can be stereoselectively hydroxy-lated by the iodolactonization procedure (E.J. Corey, 1969, 1970). To the trisubstituted cyclopentene described on p. 210 a large iodine cation is added stereoselectively to the less hindered -side of the 9,10 double bond. Lactone formation occurs on the intermediate iod-onium ion specifically at C-9ot. Later the iodine is reductively removed with tri-n-butyltin hydride. The cyclopentane ring now bears all oxygen and carbon substituents in the right stereochemistry, and the carbon chains can be built starting from the C-8 and C-12 substit""" ... 

Oxidation. Acetaldehyde is readily oxidised with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid and derivatives). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the Hquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is beheved to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21 -0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or osone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directiy by Hquid-phase oxidation at 5—50°C with a cobalt salt catalyst (37) (see Peroxides and peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of /)-xylene to terephthaHc acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

Oxidation. As a 7t-excessive heterocycle, indole is susceptible to oxidation a variety of oxidation intermediates and products have been observed. With oxygen as the oxidant, the key intermediate is normally a 3-hydroperoxy-3ff-indole. These intermediates ate observable for 2,3-disubstituted indoles but are unstable for less substituted derivatives. Figure 1 indicates typical reactivity patterns toward oxygen. 

A number of chemiluminescent reactions may proceed through unstable dioxetane intermediates (12,43). For example, the classical chemiluminescent reactions of lophine [484-47-9] (18), lucigenin [2315-97-7] (20), and transannular peroxide decomposition. Classical chemiluminescence from lophine (18), where R = CgH, is derived from its reaction with oxygen in aqueous alkaline dimethyl sulfoxide or by reaction with hydrogen peroxide and a cooxidant such as sodium hypochlorite or potassium ferricyanide (44). The hydroperoxide (19) has been isolated and independentiy emits light in basic ethanol (45). 

Weak to moderate chemiluminescence has been reported from a large number of other Hquid-phase oxidation reactions (1,128,136). The Hst includes reactions of carbenes with oxygen (137), phenanthrene quinone with oxygen in alkaline ethanol (138), coumarin derivatives with hydrogen peroxide in acetic acid (139), nitriles with alkaline hydrogen peroxide (140), and reactions that produce electron-accepting radicals such as HO in the presence of carbonate ions (141). In the latter, exemplified by the reaction of h on(II) with H2O2 and KHCO, the carbonate radical anion is probably a key intermediate and may account for many observations of weak chemiluminescence in oxidation reactions. 

Such solvent-derived radicals can induce the decomposition of the hydroperoxide or react with oxygen in the system to form peroxidic solvent molecules. They may also react with other radicals either by coupling or disproportionation. 

Other miscellaneous compounds that have been used as inhibitors are sulfur and certain sulfur compounds (qv), picryUiydrazyl derivatives, carbon black, and a number of soluble transition-metal salts (151). Both inhibition and acceleration have been reported for styrene polymerized in the presence of oxygen. The complexity of this system has been clearly demonstrated (152). The key reaction is the alternating copolymerization of styrene with oxygen to produce a polyperoxide, which at above 100°C decomposes to initiating alkoxy radicals. Therefore, depending on the temperature, oxygen can inhibit or accelerate the rate of polymerization. 

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