Rate of hydrogenation

Truong T N 1997 Thermal rates of hydrogen exchange of methane with zeolite a direct ab initio dynamics study on the importance of quantum tunneling effects J. Rhys. Chem. B 101 2750... 

The uncatalyzed addition of hydrogen to an alkene although exothermic is very slow The rate of hydrogenation increases dramatically however m the presence of cer tain finely divided metal catalysts Platinum is the hydrogenation catalyst most often used although palladium nickel and rhodium are also effective Metal catalyzed addi tion of hydrogen is normally rapid at room temperature and the alkane is produced m high yield usually as the only product... 

Each act of proton abstraction from the a carbon converts a chiral molecule to an achi ral enol or enolate ion The sp hybridized carbon that is the chirality center m the start mg ketone becomes sp hybridized m the enol or enolate Careful kinetic studies have established that the rate of loss of optical activity of sec butyl phenyl ketone is equal to Its rate of hydrogen-deuterium exchange its rate of brommation and its rate of lodma tion In each case the rate determining step is conversion of the starting ketone to the enol or enolate anion... 

The mechanism and rate of hydrogen peroxide decomposition depend on many factors, including temperature, pH, presence or absence of a catalyst (7—10), such as metal ions, oxides, and hydroxides etc. Some common metal ions that actively support homogeneous catalysis of the decomposition include ferrous, ferric, cuprous, cupric, chromate, dichromate, molybdate, tungstate, and vanadate. For combinations, such as iron and... 

A mathematical model of the operating characteristics of a modem HLW storage tank has been developed (60). This model correlates experimental data for the rate of radiolytic destmction of nitric acid, the rate of hydrogen generation owing to radiolysis of water, and cooling coil heat transfer. These are all functions of nitric acid concentration and air-lift circulator operation. 

Alternatively, there are also iuhibitors that decrease the rate of hydrogen generation and thus decrease corrosion. Mercury, effective at inhibiting 2iac corrosion, has long been used as an additive to 2iac anodes. More recentiy, however, because of iacreased iaterest ia environmental issues, the amount of mercury ia alkaline cells has been reduced. 

The quaHty of the feedstock is important since it affects not only the product quaHty but the rate of hydrogenation. Some of the impurities that affect the rate are sulfur, phosphoms, haHdes, polyethylene, and moisture. Impurities are usually removed by clay treatment or by distillation (30). 

The resulting melt is cooled lapidly to prevent reversion to calcium cyanamide. The product is marketed in the form of flakes, dark gray because of the presence of carbon. Typical composition is shown in Table 7. Because the rate of hydrogen cyanide evolution is relatively high, it is readily adaptable to fumigation. Specific gravity of the product is 1.8 to 1.9. The price of black cyanide is generally lower than sodium cyanide it is manufactured in Canada and South Africa. 

When hydrogen recovery is unsafe or otherwise impractical it is vented into the cell room or tank house. The light weight and high diffusion rate of hydrogen and good cell room ventilation have made this an accepted practice. 

FIG. 23-34 Effeot of reaction pressure and temperature on tLe rate of hydrogenation of soybean oil. (Swern, ed., Baileys Industrial Oil and Fat Products, ijol 2, Wiley, 1979. )... 

Poly(butadiene-l>-vinyl pyridine) or poly(isoprene-l>-vinyl pyridine) Ni/Et3Al catalysis BF3 and CFAlEt used to complex vinyl pyridine to increase rate of hydrogenation BFj released by NH4OH... 

Bodenstein and Lind [3] first studied the thermal reaction over the temperature range of 500-600 K. The relative reaction rates of hydrogen and bromine and the formation of hydrogen bromide are ... 

A container of hydrogen at 2 bar at 27 F is damaged causing a 1 cm" sharp-edged opening What is the rate of hydrogen discharge into the atmosphere ... 

In general the rates of hydrogenation of steroidal double bonds can be roughly classified as follows a) readily hydrogenated A, A, A", A , A14 A diene, A , A ° and 19-vinyl (Z>) moderately difficult ... 

The rate of hydrogen (or deuterium) uptake with homogeneous catalysts is usually faster in benzene-alcohol (methanol or ethanol) solvent systems or in acetone than in tetrahydrofuran or in benzene alone. Whereas... 

Quantitative studies of the effect of pyridine on the rate of hydrogenation of imns-crotonic acid in the presence of a platinum catalyst have been carried out by Maxted and Walker who concluded that... 

The rate of reaction is variable requiring from 1-4 days. Fresh catalyst is added whenever the rate of hydrogen uptake markedly decreases. Added catalyst must first be wet with solvent. The hydrogen must be well evacuated, for opening the mixture to the atmosphere without such evacuation will produce a mixture that may explode on contact with fresh catalyst, t A eutectic mixture of diphenyl and diphenyl ether, available from Dow Chemical Co. 

Temperature can have an important influence on rate, selectivity, and catalyst life. In general, the rate of hydrogenation rises with increasing temperature the rate increase will be much larger when the reaction is... 

Hydrogenation of aromatic nitro compounds is very fast, and the rate is limited often by the rate of hydrogen transfer to the catalyst. It is accordingly easy to use inadvertently more catalyst than is actually necessary. Aliphatic nitro compounds are reduced much more slowly than are aromatic, and higher catalyst loadings (6,11) or relatively lengthy reduction times may be... 

Phenylhydroxylamine rearranges in sulfuric acid to give mainly p-aminophenol. Industrial routes to this compound have been developed in which phenylhydroxylamine, formed by hydrogenation of nitrobenzene in sulfuric acid over platinum-on-carbon, is rearranged as it is formed. Conditions are adjusted so that the rate of rearran ment is high relative to the rate of hydrogenation of hydroxylamine to aniline (15,17,86). An easy way to obtain a favorable rate ratio is to carry out the reduction with about 1% DMSO present in the sulfuric acid (79,81). 

Although the reactants have only limited solubility in the catalyst phase, the rates of hydrogenation in [BMIM][SbFg] are almost five times faster than for the comparable reaction in acetone. All ionic catalyst solutions tested could be reused repeatedly. The loss of rhodium through leaching into the organic phase lay below the detection limit of 0.02 %. These results are of general importance for the field of... 

Guo et al. [70,71,73] recently attempted to hydrogenate NBR in emulsion form using Ru-PCy complexes. However, successful hydrogenation can only be obtained when the emulsion is dissolved in a ketone solvent (2-butanone). A variety of Ru-phosphine complexes have been studied. Crosslinking of the polymer could not be avoided during the reaction. The use of carboxylic acids or first row transition metal salts as additives minimized the gel formation. The reactions under these conditions require a very high catalyst concentration for a desirable rate of hydrogenation. 

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