Formation rate, straight chain

Also, pyridine or substituted pyridines as solvents, for example, y-picoline (4-methyl pyridine), enhanced the catalytic activity of unmodified or phosphine-modified rhodium catalysts [23]. Yields of >90% of HOCH2CHO were achieved within 4 h at 70 °C. Above 100 °C, the reaction was complicated by the formation of straight-chain polyols. Interestingly, the addition of protonic acids enhanced the rate, and almost perfect chemoselectivity was noted (only 1.9% methanol). 

Figure 3. Correlation between the rate of formation of straight chain paraffins plus a-olefins (r ) and carbon number n (catalyst C-II, F(CO) = 3.5 bar, V(H,) = 3.7 bar)...

The duration of the inhibition period of a chain-breaking inhibitor of autoxidation is proportional to its efficiency. Indeed, with an increasing rate of chain termination, the rates of hydroperoxide formation and, hence, chain initiation decrease, which results in the lengthening of the induction period (this problem will be considered in a more detailed manner later). It should be noted that when initiated oxidation occurs as a straight chain reaction, the induction period depends on the concentration of the inhibitor, its inhibitory capacity, and the rate of initiation, but does not depend on the inhibitor efficiency. 

Preliminary kinetic studies indicate that X4 hydrolysis was extremely slow, while larger straight-chain substrates were cleaved at rates that increased with increasing chain length. It is possible that branched-chain xylo-oligosaccharides were formed during incubation with Xylanase II their rates of formation and hydrolysis are as yet unknown. 

Interestingly, the 5-hexenyl radical, which is believed to cyclize quickly, with a rate constant on the order of k = 10 sec [73,74], had led to a high yield of cyclized product when generated in solution [75]. For example, reduction of 110 with tri-n-butyltin hydride provides 112 in 78% yield and only 7% of the straight-chain olefin 111. This contrasts with what was actually observed in formation of the Grignard reagent by reaction of 110 with magnesium, in spite of the fact that the 5-hexenyl radical is involved in both instances. 

At high partial pressure of carbon monoxide the but3trylcobalt tetracarbonyl precursor is mainly the product from the kinetically favored n-isomer of the addition of HCo(CO)4 to the olefin double bond of propene. This conclusion was further supported by the comparison of rates of propene hydroformylation with the rates of n-butyrylcobalt tetracarbonyl isomerization at 0.25 MPa and at 9.0 MPa of carbon monoxide partial pressure. The data in Table 18 show that at 0.25 MPa partial pressure of carbon monoxide, the rate of acyl isomerization is indeed higher than the rate of the overall aldehyde formation, and this makes an equilibration of the acyl isomers prior to the irreversible aldehyde formation conceivable vm-der these conditions. At 9.0-MPa partial pressure of carbon monoxide, however, the rate of acyl isomerization is 29 times slower than the rate of the aldehyde formation, and this severally hampers the isobutyrylcobalt formation from the primarily formed straight-chain acyl isomer. 

The rate of ester formation depends on the carboxylic acid and the alcohol used. The lowest members, i.e. methanol and formic acid, react most readily. Primary alcohols react faster than secondary alcohols and the latter react faster than tertiary ones. Within each series, the reaction rate generally decreases with increasing molecular mass. Straight-chain acids react more readily than branched ones particularly branching in the a-position lowers the rate of esterification. Esterification of aromatic acids, e.g. benzoic... 

Straight and branched chain reactions almost invariably have complex rate expressions, as shown by -d[H2]/df = A [H2]° [02]° [N2]° for the H2 + O2 reaction in aged boric-acid-coated vessels at 500 Torr and 773 K [6]. Change of pressure can have striking effects even when achieved by addition of an inert gas such as N2. Hydrocarbon combustion reactions proceed through the formation of many intermediates, both radical and molecular, prior to formation of the final products CO2 and H2O. Another striking feature is the sensitivity of chain reactions to traces of impurities and to changes in surface properties. This is particularly pronounced in the case of some explosion boundaries or limits where parts per million quantities of an impurity may completely subdue the explosion. 

A detailed study of the same aromatic polysulphone (PS) has been reported by Davis [296]. The gas composition does not change with the time of heating. Volatile liquid and solid products have been separated and identified by gas chromatography and mass spectrometry the results are given in Table 24. After three hours heating, a gel is formed. The amount of gel is not affected by the presence of the volatile pyrolysis products. If the theory of Charlesby-Pinner is applied to the gel formation data, a straight line with a positive intercept of 0.35 is obtained. This means that chain scission also occurs. The rate of S02 evolution is in agreement with the results of Levy and Ambrose [297] on the pyrolysis... 

Straight lines are obtained in this plot excepting for an observable increase in the reaction rate in the initial part of the polymerizations carried out at the two lower temperatures. It is concluded from these results that the chain propagation reaction is first-order in monomer concentration. An apparent activation energy of 13.7 + 0.8 kcal/mole was calculated for the chain propagation reaction involving the formation of poly (propylene ether) diol. This value compares very well with that of ll<-.7 kcal/mole reported by Shigematsu and coworkers (l5) for the sodium hydroxide catalyzed addition of propylene oxide to isopropyl alcohol. 

---