Hydrogen styrene ratio

PS-HF = poly(styrene-co-4-vinylpyridine)-supported hydrogen fluoride. Ratio 75 25, Ratio 74 26. 

A molar equivalent of hydrogen peroxide to monomer and horseradish peroxidase is a well-known redox system that catalyzes the free radical polymerization of phenol, anilines, and their derivatives [6-14]. Horseradish peroxidase-mediated polymerization of styrene and methyl methacrylate, with a monomer (styrene or methyl methacrylate) to hydrogen peroxide ratio of 40 1, did not occur in the absence of 2,4-pentanedione. Therefore, it is likely that this compound is involved in the initiation of free radical formation. A reasonable hypothesis for the horseradish peroxidase-catalyzed polymerization of vinyl monomers is that the enzyme is oxidized by hydrogen peroxide and passes from its native state through two catalytically active forms (Ez and Ezz). Each of these active forms oxidizes the initiator (b-diketone, 2,4-pentanedione) while the enzyme returns to the native form. The Ezz state of enzyme is oxidized by hydrogen peroxide to produce inactive enzyme, Ezzz, which spontaneously reverts to the native form of enzyme. The free radicals produced from the initiator generate radicals in the vinyl monomer to form polymer (Fig. 2). 

Assisted transfers of a hydrogen atom from two other atoms— sulfur and oxygen—might be mentioned to demonstrate the variety of MAH processes. Hiatt and Bartlett (24) have shown that ethyl thioglycolate and styrene react to produce radicals. At high thiol/styrene ratios, the rate of radical production is too fast to be accounted for by the thermal reaction of styrene with itself, and we (2,7) have suggested that the reaction is a direct MAH of an S-H bond, eq 21. 

Acetophenone is separated for hydrogenation to 1-phenylethanol, which is sent to the dehydrator to produce styrene. Hydrogenation is done over a fixed-bed copper-containing catalyst at 115—120°C and pressure of 8100 kPa (80 atm), a 3 1 hydrogen-to-acetophenone ratio, and using a solvent such as ethylbenzene, to give 95% conversion of the acetophenone and 95% selectivity to 1-phenylethanol (186,187). 

Most rubbers used in adhesives are not resistant to oxidation. Because the degree of unsaturation present in the polymer backbone of natural rubber, styrene-butadiene rubber, nitrile rubber and polychloroprene rubber, they can easily react with oxygen. Butyl rubber, however, possesses small degree of unsaturation and is quite resistant to oxidation. The effects of oxidation in rubber base adhesives after some years of service life can be assessed using FTIR spectroscopy. The ratio of the intensities of the absorption bands at 1740 cm" (carbonyl group) and at 2900 cm" (carbon-hydrogen bonds) significantly increases when the elastomer has been oxidized [50]. 

Hydrogenation of styrene oxide over palladium in methanol 66 gives exclusively 2-phenylethanol, but in buffered alkaline methanol the product is l-phenylelhanol. If alcoholysis of the epoxide by the product is troublesome, the problem can be eliminated by portion-wise addition of the epoxide to the reaction, so as always to maintain a high catalyst-to-substrate ratio. The technique is general for reactions in which the product can attack the starting material in competition with the hydrogenation. 

The results of chain transfer studies with different polymer radicals are compared in Table XIV. Chain transfer constants with hydrocarbon solvents are consistently a little greater for methyl methacrylate radicals than for styrene radicals. The methyl methacrylate chain radical is far less effective in the removal of chlorine from chlorinated solvents, however. Vinyl acetate chains are much more susceptible to chain transfer than are either of the other two polymer radicals. As will appear later, the propagation constants kp for styrene, methyl methacrylate, and vinyl acetate are in the approximate ratio 1 2 20. It follows from the transfer constants with toluene, that the rate constants ktr,s for the removal of benzylic hydrogen by the respective chain radicals are in the ratio 1 3.5 6000. Chain transfer studies offer a convenient means for comparing radical reactivities, provided the absolute propagation constants also are known. 

Finally, the only example of a polynuclear homogeneous catalyst is the dinuc-lear complex [Pt P sH ]4- [66], which catalyzed the hydrogenation of styrene, phenylacetylene, 1-octyne, and 1-hexyne (i-PrOH, 60°C, 20.7 atm H2 pressure, Pd substrate ratio 1 1800) to the corresponding alkanes within 10 h of reaction. 

Catalytic studies and kinetic investigations of rhodium nanoparticles embedded in PVP in the hydrogenation of phenylacetylene were performed by Choukroun and Chaudret [90]. Nanoparticles of rhodium were used as heterogeneous catalysts (solventless conditions) at 60 °C under a hydrogen pressure of 7 bar with a [catalyst]/[substrate] ratio of 3800. Total hydrogenation to ethylbenzene was observed after 6 h of reaction, giving rise to a TOF of 630 h 1. The kinetics of the hydrogenation was found to be zero-order with respect to the al-kyne compound, while the reduction of styrene to ethylbenzene depended on the concentration of phenylacetylene still present in solution. Additional experi-... 

The first highly enantioselective asymmetric hydroformylation was the asymmetric hydroformylation of styrene.120 In 1991, Stille et al.121 reported the achievement of up to 96% ee using a chiral bisphosphine complex of PtCl2 as the catalyst in combination with SnCl2. However, the Pt(II)-catalyzed hydroformylation of arylethenes and some functionalized olefins has several disadvantages, such as low reaction rates, a tendency for the substrates to undergo hydrogenation, and poor branched-to-linear ratio. 

Reactivity ratios for all the combinations of butadiene, styrene, Tetralin, and cumene give consistent sets of reactivities for these hydrocarbons in the approximate ratios 30 14 5.5 1 at 50°C. These ratios are nearly independent of the alkyl-peroxy radical involved. Co-oxidations of Tetralin-Decalin mixtures show that steric effects can affect relative reactivities of hydrocarbons by a factor up to 2. Polar effects of similar magnitude may arise when hydrocarbons are cooxidized with other organic compounds. Many of the previously published reactivity ratios appear to be subject to considerable experimental errors. Large abnormalities in oxidation rates of hydrocarbon mixtures are expected with only a few hydrocarbons in which reaction is confined to tertiary carbon-hydrogen bonds. Several measures of relative reactivities of hydrocarbons in oxidations are compared. 

The formation of benzocyclobutene and styrene in different ratios from the three isomeric tolylcarbenes is not easily explained by the Baron mechanism, and led to more than one clever (but ultimately wrong) alternative proposal. The question is best resolved by assuming that in the ortho system hydrogen atom transfer in the diazo compound leads to extra benzocyclobutene... 

Reaction of AT-fluorobis(trifluoromethylsulfonyl)amine (Id) with alkenes gives various products, depending on the reaction conditions and the structure of the substrate. In solvents of higher nucleophilicity such as water, acetic acid, aqueous hydrochloric acid, and 70 % hydrogen fluoride/pyridine, a-fluorohydrins or their acetates, a-chloro-fl-fluoroalkanes or a,/ -difluoroal-kanes, e.g. 14. are obtained.146 Reaction of styrene and ( >l-phenylpropene with Id in dich-loromethane/acetic acid gives l-acetoxy-2-fluoro-l-phenylethane and -propane, in 92 and 99 % yield, respectively, the latter product in a ratio (erythrojthreo) 1 l.146... 

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