Product yields, free radical experiment

In 1988, Terry and coworkers attempted to homopolymerize ethylene, 1-octene, and 1-decene in supercritical C02 [87], The purpose of their work was to increase the viscosity of supercritical C02 for enhanced oil recovery applications. They utilized the free radical initiators benzoyl peroxide and fert-butyl-peroctoate and conducted polymerization for 24-48 h at 100-130 bar and 71 °C. In these experiments, the resulting polymers were not well studied, but solubility studies on the products confirmed that they were relatively insoluble in the continuous phase and thus were not effective as viscosity enhancing agents. In addition, a-olefins are known not to yield high polymer using free radical methods due to extensive chain transfer to monomer. 

Photolytic. When synthetic air containing gaseous nitrous acid and 4-methyl-2-pentanone was exposed to artificial sunlight k = 300-450 nm), photooxidation products identified were acetone, peroxyacetal nitrate, and methyl nitrate (Cox et al, 1980). In a subsequent experiment, the OH-initiated photooxidation of 4-methyl-2-pentanone in a smog chamber produced acetone (90% yield) and peroxyacetal nitrate (Cox et al, 1981). Irradiation at 3130 A resulted in the formation of acetone, propyldiene, and free radicals (Calvert and Pitts, 1966). 

The olefin 3,3-dimethyl-l-butene (III) was studied since it gave almost exclusively the expected product 3,3-dimethyl-l-buten-2-yl acetate (VII) with only traces of ketone or 3,3-dimethyl-l-buten-l-yl acetate. With a single product the test of material balance was simplified since it was possible to run a blank on the wet separation and then check the yield of VII by isotope dilution using (CH3)3CC(OCOCD3)=CH2. Experiments with III are not complicated by isomerization or allylic palladium complex formation and are unlikely to involve free radical reactions. 

In 1994, the free-radical bromination of toluene (and other alkylaro-matics) in sc C02 was reported (Tanko and Blackert, 1994 Tanko et al., 1994). Product yields were similar to those obtained with conventional solvents. The relative reactivity of the secondary hydrogens of ethylbenzene versus the primary hydrogens of toluene on a per hydrogen basis, r(2°/l°), were assessed via competition experiments and (a) did not vary with pressure, (b) were nearly identical to what is observed in conventional solvents. 

The roles of leukotrienes and cytochrome P450 products in the human kidney are currently speculative. Recently, the 5,6-epoxide has been shown to be a powerful vasodilator in animal experiments. Another recent discovery is that free radicals attack arachidonic acid-containing phospholipids to yield an 8-ep/-PGF2[J that has powerful thromboxane-like properties. Synthesis is not blocked by COX inhibitors but can be blocked by antioxidants. This vasoconstrictor, which is present in humans, is thought to be another important mediator causing renal failure in the hepatorenal syndrome. 

A limitation of both methods is that the second component must be liquid at the temperature of-the reaction, which is 5-10° for the diazohydroxide reaction and room temperature or slightly higher for the nitrosoacetylamine reaction. Experiments with solid reactants in solution have not been very successful, because of the difficulty of finding a suitable solvent. The solvent should be neutral and immiscible with water, have a high solvent action and reasonably low boiling point, and be inert to the free radicals which result from the diazo compound. The last qualification is the most difficult one to satisfy. Of the solvents which have been tried, carbon tetrachloride and chloroform appear to be the most suitable.18 From diazotized aniline and biphenyl in these solvents, some p-terphenyl is obtained, and from diazotized p-nitroaniline and biphenyl a small amount of 4-nitro-4 -phenylbiphenyl is formed. In these reactions an appreciable amount of tfie aryl halide (chlorobenzene and p-nitrochlorobenzene) is produced as a by-product. In general, the yields of products obtained by coupling with reactants in solution are extremely low. 

Gravimetric Results of Catalytic Cracking. Experiments were conducted to assess the effects of temperature, cat-to-oil ratio, and feedstock composition. In addition to the effect of variables on product yields, it was also important to identify the relative influence of thermal reactions, since free-radical reactions may adversely affect product quality. A series of experiments was conducted in the temperature range of 412°-415°C because this is the temperature of maximum increase in production from thermal cracking and catalytic vs. thermal effects are more easily discernible at this temperature. 

Since the cage effect is less than 100 % in most cases (Table 1), some of the radical pairs exit the micelle and become water solubilized free radicals. At some later time, the free radicals recombine to form DPE. This has been verified by Cu2+ quenching experiments (Fig. 6)13,19). The disappearance of DBK is not dependent upon the concentration of Cu2+. However, the yield of DPE drops very rapidly with increasing copper concentration and then levels off. The leveling off region is directly related to the amount of cage reaction. The products formed by reaction with copper are benzyl chloride (4), and benzyl alcohol (5) (Scheme V)20). 

The relative importance of various free radicals in the photolysis has been determined by the photolysis of i-CsD j in the presence of H2S. The relative yields of the monoprotonated products indicates the relative importance of free radicals. Thus it was found that H CH3 C2HJ C3H7 are present in the proportion 1 1.1 0.42 0.10. These experiments also point to the importance of free-radical processes in the photolysis of isopentane, relative to the molecular eliminations. 

The effect of electrical fields on the radiolysis of ethane has been examined by Ausloos et and this study has shown that excited molecules contribute a great deal to the products. The experiments were conducted in the presence of nitric oxide, and free-radical reactions were therefore suppressed. The importance of reactions (12)-(14) was clearly demonstrated by the use of various isotopic mixtures. Propane is formed exclusively by the insertion of CH2 into C2H6 and the yield is nearly equal to the yield of molecular methane from reaction (14). Acetylene is formed from a neutral excited ethane, probably via a hot ethylidene radical. Butene and a fraction of the propene arise from ion precursors while n-butane appears to be formed both by ionic reactions and by the combination of ethyl radicals. The decomposition of excited ethane to give methyl radicals, reaction (15), has been shown by Yang and Gant °° to be relatively unimportant. The importance of molecular hydrogen elimination has been shown in several studies ° °. ... 

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