Isoprene inhibition

SYNS ISOPRENE, INHIBITED (DOT) P-METHYLBIVINYL 2-METHYLBUTADIENE 2-METHYI 1,3-BUTADIENE pOT)... 

Rudzinski K.J. and W. Pasiuk-Bronikowska Isoprene inhibition of S(IV) autoxidation initiated by peroxydisulphate, in P.M. Midgley, M. Reuther, M. Williams (eds). Transport and chemical transformation in the troposphere. Proc. EUROTRAC-2 Symposium 2000, Springer Verlag, Berlin (2001) 1-4 (CD). 

Rudzinski K.J., W. Pasiuk-Bronikowska and J. Krolik Mechanistic study of isoprene inhibition of S(IV) autoxidation in aqueous phase, in M.J. Rossi, E.-M. Rossi (eds). Chemical Processes and Mechanisms -Chemical Mechanism Development. Proc. EC/EUROTRAC-2 Joint Workshop, EPFL, Lausanne (2000) 148-151. 

Copolymers with acrylonitrile, butadiene, isoprene, acrylates, piperjiene, styrene, and polyethylene have been studied. The high cost of sorbic acid as a monomer has prevented large-scale uses. The abiUty of sorbic acid to polymerize, particularly on metallic surfaces, has been used to explain its corrosion inhibition for steel, iron, and nickel (14). 

Inhibition of olefin polymerization occurred when its basicity was not sufficient to produce an appreciable displacement of initiator from the aldehyde-acid complex isoprene, cyclopentadiene and styrene were in this category. 

Coenzyme Qio (ubiquinone) is a coenzyme in the mitochondrial respiratoiy chain. It has a side chain made up of 10 isoprene units. Its synthesis can be inhibited by... 

Aerobic biodegradation of trichloroethylene occurs by cometabolism with aromatie eompounds (Ensley 1991) and thus requires a cosubstrate such as phenol (Nelson et al. 1987, 1988) or toluene (Fan and Scow 1993). Trichloroethylene degradation by toluene-degrading baeteria has been demonstrated in the presence, but not absence, of toluene (Mu and Scow 1994). Isoprene, a structural analog of trichloroethylene, has also been used as a cosubstrate for triehloroethylene oxidation by some bacteria (Ewers et al. 1990). One source of inhibition of degradation in the absence of cosubstrate may be the toxieity of triehloroethylene itself to indigenous bacteria. 

Mechanisms depending on carbanionic propagating centers for these polymerizations are indicated by various pieces of evidence (1) the nature of the catalysts which are effective, (2) the intense colors that often develop during polymerization, (3) the prompt cessation of sodium-catalyzed polymerization upon the introduction of carbon dioxide and the failure of -butylcatechol to cause inhibition, (4) the conversion of triphenylmethane to triphenylmethylsodium in the zone of polymerization of isoprene under the influence of metallic sodium, (5) the structures of the diene polymers obtained (see Chap. VI), which differ. both from the radical and the cationic polymers, and (6)... 

Phenanthroline in the presence of heavy metals acts as an activator of the polymerization of vinyl compounds558,559 and other olefins.560-564 It also assists the dimerization of olefins in the presence of titanium catalysts.565,566 It enhances the metal catalyzed oxidation of ascorbic acid567 and dimethyl sulfoxide.568 On the other hand, on its own it can inhibit several polymerization processes.545,569 It also stabilizes butadiene and isoprene and prevents their dimerization.570 It prevents peroxide formation in ether,571 inhibits the vinylation of alcohol572 and stabilizes cumyl chloride.573 It accelerates the vulcanization of diene rubbers574 and copolymers.575 1,10-Phenanthroline catalyzes the autooxidation of linoleic and ascorbic acids in the absence of metals.567... 

The dithiocarbamates have the pentacoordinate binuclear structure (44). The diamyl- and diethyl-dithiocarbamate complexes have been found to inhibit the hardening of asphalt, but the effect appears too weak to be useful.127 The latter complex is an effective antioxidant for polyethylene,128 polypropylene,129 polystyrene,130 poly(methyl methacrylate)130 and an isoprene-styrene copolymer.131 The di-n-butyldithiocarbamate complex is important in the vulcanization and injection moulding of rubber,132 as a stabilizer against photolytic and thermal degradation. 

Low concentrations of S02 and TBHP were used to initiate the polymerization of MMA and other vinyl monomers. DPPH and hydroquinone do not inhibit this MMA polymerization. End-group analysis indicates the incorporation of sulfonate and hydroxyl end groups in the polymers, and copolymerization results (MMA-isoprene and MMA-acrylic acid) with this S02-TBHP initiator system and AIBN are in good agreement. The over-all polymerization appears to be primarily radical in nature. Inert solvents (benzene, toluene, and xylene) enhance the rate of polymerization of MMA but not of other vinyl monomers (AN, Sty, V A, EM A, MA, etc.). An initiation mechanism involving monomer and solvent appears to be predominant in the case of MMA, while with other monomers an initiation reaction involving only the monomer is predominant. 

Radioactive isoprene was liberated from leaf surfaces of Hamamelis virginiana and Quercus borealis when labelled intermediates of the glycolate pathway and labelled mevalonate were fed to them.55 It is not clear whether MVA was an obligate precursor of isoprene, although inhibition studies showed a distinct similarity between the biosynthetic pathway to isoprene and that to /3-carotene. 

Figure 2. Decay of oxygen dxuing autoxidation of Na2S03 initiated by thermal decomposition of K2S2O8 (a) or by Mn(lll) (b), and inhibited by isoprene. Initial concentrations of reactants were K2S2O8 1 mM or MnS04 0.01 mM Na2SOs 1.02 mM O2 0.22-0.25 mM for isoprene -...

We followed the extent of autoxidation by measuring the concentration of dissolved oxygen versus the reaetion time (Figure 2). The plots and the formulas approximating the rates of autoxidation (Eqs 2, 3) elearly show the inhibiting role played by isoprene. 

Bilimoria et al. investigated the inhibition of radical initiated polymerization of vinyl acetate by tobacco smoke and some PAHs in 1973 (329). Their results indicated that vapor phase of smoke is an efficient inhibitor of vinyl acetate polymerization and that conjugated dienes like isoprene are responsible for the inhibition. There were no free radicals from tobacco smoke specifically identified in this research. Nisbet and Schmeller presented the results of this research at the 27th Tobacco Chemists Research Conference (TCRC) in 1973 (2789a). 

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