Ozonization methylene groups

The close structural similarities between polychloroprene and the natural rubber molecule will be noted. However, whilst the methyl group activates the double bond in the polyisoprene molecule the chlorine atom has the opposite effect in polychloroprene. Thus the polymer is less liable to oxygen and ozone attack. At the same time the a-methylene groups are also deactivated so that accelerated sulphur vulcanisation is not a feasible proposition and alternative curing systems, often involving the pendant vinyl groups arising from 1,2-polymerisation modes, are necessary. 

U.S. producers and capacities, 2 800t Methylene fluoride, 13 720-721 Methylene groups, reaction with ozone, 17 781... 

Ready addition of 2-nitrosopyridine to 1,3-dienes gives 3,6-dihydro-1,2-oxazines, e.g. (774) — (773), and condensation with aromatic amines gives azo compounds, e.g. (774) — (775). Nitroso compounds are oxidized by ozone or sodium hypochlorite to the corresponding nitro compounds. 5-Nitrosopyrimidines can be reduced to the 5-amino derivatives or condensed with activated methylene groups. 

Regioselectlve oxidation of methylene groups. Ozonation of cyclododecyl acetate adsorbed on silica gel results in formation of only three keto iicetates, 5-keto-, 6-keto-, and 7-ketocyclododecyI acetate in yields of 15, 27, and 9%, respectively. This same regioselectivity is observed in microbiological hydroxylation of the substrate by various fungi. ... 

The original purpose was to cyclize this compound to a cyclitol derivative by treatment with potassium in xylene. However, a crystalline diene derivative (115) was formed which, after hydrolysis of the methylene groups, gave crystalline l,6-dideoxy-D-(/ireo-2,5-hexodiulose (116). It showed no indications of the presence of a double bond and reduced Fehling solution in the cold. The location of the two keto groups at C-2 and C-5 in this compound and in the diulose (118), obtained later, was proved by ozonization of their parent diene compound (115) to yield D-threaric acid. The compound (116) showed no mutarotation and was converted into a crystalline bis[(p-nitrophenyl)hydrazone] and di-(p-nitrobenzoate). 

The presence of an exocyclic methylene group in ignavine is indicated by the IR spectrnm (1645 and 892 cm i) and by formation of formaldehyde on ozonization. That the exocyclic methylene is involved in a secondary allylic alcohol system as in atisine was demonstrated by catalytic isomerization to a methyl ketone (1692 cm i) and by oxidation to a conjugated enone (1615, 1687 cm i) (72). 

Selective oxidations. Dry ozonization of cyclododecyl acetate (1) gives a mixture of three keto acetates, 2, 3, and 4. Methylene groups remote from the binding site are attacked preferentially. This behavior is similar to oxidation of 1 by fungi. ... 

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