Pentadiene radicals produced

Lipoxygenases (Lox) are selective towards polyunsaturated fatty acids containing the c/, c/ -l,4-pentadiene moiety to produce either the 9(5)-hydroperoxide, 13(i )-hydroperoxide, or a mixture of both from linoleic and linolenic acids. These enzymes contain an iron atom in their active center. They are activated by hydroperoxides, and the Fe + is oxidized to Fe +, according to a scheme in which the pentadiene radical of linoleic acid becomes bound to the enzyme, reacts with oxygen, and the peroxyl radical formed is reduced by the enzyme to produce a hydroperoxide after reaction with a proton (1). 

Oxidation to CO of biodiesel results in the formation of hydroperoxides. The formation of a hydroperoxide follows a well-known peroxidation chain mechanism. Oxidative lipid modifications occur through lipid peroxidation mechanisms in which free radicals and reactive oxygen species abstract a methylene hydrogen atom from polyunsaturated fatty acids, producing a carbon-centered lipid radical. Spontaneous rearrangement of the 1,4-pentadiene yields a conjugated diene, which reacts with molecular oxygen to form a lipid peroxyl radical. 

Zimmerman and Hoffacker also observed a regioselective reaction subjecting various aryl-substituted 1,4-pentadienes to photoinduced electron transfer using DCN and DCA. The radical cations produced underwent a regioselective cyclization wherein one electron-deficient aryl group of one diarylvinyl moiety bonds to the (3-carbon of the second diarylvinyl group (Scheme 30) [41]. 

One of the issues that concern liquid feedstock cracking operations is a higher rate of fouling. This is not only a consequence of heavier coke forming precursors, but also as a consequence of long lived free radicals which act as agents for the formation of a polymer (often referred to as pop-corn polymer) in the primary fractionator and downstream units. For instance, free radicals based on styrene or indene have sufficiently long half-lives to pass from the pyrolysis section into the primary fractionator. These can concentrate in this unit and produce polymer (free radical polymerisation) when sufficient amounts of suitable olefins are present, in particular styrene itself and di-olefins such as cyclo-pentadiene or butadiene. 

By using rare earth metals or radicals it is possible to copolymerize 1,3-butadiene and other dienes with cis-, A linkage [3,498]. Polymers of 1,3-butadiene and isoprene at any ratio can be obtained. Copolymes of 1,3-butadiene and 1,3-pentadiene can be produced with catalysts on the basis of vanadium chelates. 1,3-Butadiene is almost completely converted to trans-, A units, whereas 1,3-pentadiene yields 50 to 60% 1,4-addition and 40 to 50% 1,2-addition products. At a 1,3-pentadiene content of 26 to 45wt%, the copolymers are amorphous, featuring high rigidity [499-501]. Diethylaluminum chloride, nickel naphthenate, and water catalyze the copolymerization of 1,3-butadiene and acetylene. The low-molecular-weight copolymers contain mostly cis-Q-Q double bonds [502]. 

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