Possible dimers from oxidative

Scheme 2. Possible dimers from oxidative coupling of phenol.

Chloroprene is a monomer used almost exclusively for the production of polychloroprene elastomers and latexes. It readily forms dimers and oxidizes at room temperature. Occupational exposures occur in the polymerization of chloroprene and possibly in the manufacture of products from polychloroprene latexes. 

Dihydromorphine undergoes the same oxidative dimerization as morphine, but a mixture of both alkaloids yields a mixed dimer. The three possible dimers were separated by HPLC and from the relative peak areas the morphine concentration could be determined. The retention time of a series of dimers is given in Table 7.12. For a large number of drugs it was reported that no interference was observed when this method was used. The absolute sensitivity determined by the detection limit of the fluorimeter was 4 ng. 

Since it appears that anthocyanins and tannins condense in wine to form secondary wine pigments, the nature of the linkage between these compounds has been the focus of many investigations. There are a large number of possibilities but this chapter will discuss only two for historical purposes. Others will be discussed by other authors in this book. Based upon the structure of a natural compound, Jurd synthesized a dimer from catechin and a synthetic anthocyanidin (Figure 1). The flavylium form of the anthocyanidin has an electrophilic carbon at C-4 that will condense with the phloroglucinol ring of catechin. The new product, a flavene, will be oxidized by a second flavylium... 

Shegansu B, the isorhapontigenin dimer from Belameanda chinensis, was synthesized from 5 with FeCk as oxidant [22]. In the reaction procedure, seven compounds (109-115) of dimeric, trimeric and tetrameric polymers were obtained. Their possible formation mechanisms were also deduced respectively [80, 81]. For instance, the mechanism of 115 was described as shown in Fig. (8). 

Sorbic acid is oxidized rapidly in the presence of molecular oxygen or peroxide compounds. The decomposition products indicate that the double bond farthest from the carboxyl group is oxidized (11). More complete oxidation leads to acetaldehyde, acetic acid, fumaraldehyde, fumaric acid, and polymeric products. Sorbic acid undergoes Diels-Alder reactions with many dienophiles and undergoes self-dimerization, which leads to eight possible isomeric Diels-Alder stmctures (12). 

It is apparent from DTA studies [1021] of the decompositions of Group IA formates in inert or oxidizing atmospheres that reaction is either preceded by or accompanied by melting. Anion breakdown leading to carbonate production may involve formation of the oxalate, through dimerization [1022] of the postulated intermediate, C02, especially during reaction of the Na and K salts in an inert atmosphere and under isothermal conditions. Oxalate production is negligible in reactions of the Li and Cs formates. Reference to oxalate formation is included here since this possibility has seldom been considered [1014] in discussions of the mechanisms of decompositions of solid formates. 

The HPLC-MS/MS assay was also successfully applied to the measurement of UV-induced dimeric pyrimidine photoproducts [123, 124]. The latter lesions were released from DNA as modified dinucleoside monophosphates due to resistance of the intra-dimer phosphodiester group to the exonuclease activity during the hydrolysis step [125, 126]. The hydrolyzed photoproducts exhibit mass spectrometry and chromatographic features that allow simultaneous quantification of the three main classes of photolesions, namely cyclobutane dimers, (6-4) photoproducts, and Dewar valence isomers, for each of the four possible bipyrimidine sequences. It may be added that these analyses are coupled to UV detection of normal nucleosides in order to correct for the amount of DNA in the sample and obtain a precise ratio of oxidized bases or dimeric photoproducts to normal nucleosides. 

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