Hydrocarbons relative reactivities

Wax usually refers to a substance that is a plastic solid at ambient temperature and that, on being subjected to moderately elevated temperatures, becomes a low viscosity hquid. Because it is plastic, wax usually deforms under pressure without the appHcation of heat. The chemical composition of waxes is complex all of the products have relatively wide molecular weight profiles, with the functionaUty ranging from products that contain mainly normal alkanes to those that are mixtures of hydrocarbons and reactive functional species. 

Table 12.10. Relative Reactivities of Some Aromatic Hydrocarbons toward Oxygen"...

Unsaturated hydrocarbons are quite reactive —in contrast to the relatively inert saturated hydrocarbons. This reactivity is associated with the double bond. In the most characteristic reaction, called addition, one of the bonds of the double bond opens and a new atom becomes bonded to each of the carbon atoms. Some of the reagents that will add to the double bond are... 

Rate Constants k (mmole min g ) of Isolated Reactions, and Relative Reactivities S from Competitive Reactions Obtained in the Hydrogenation of Aromatic Hydrocarbons... 

The competition between dilution of NMHQ (here [NMHCJq represents the initial hydrocarbon concentration) and its reaction with HO to generate an oxidant molecule enters through the dimensionless parameter S fcd/k25[HO ] that compares the rate of the HO reaction to the rate of dilution. Also important is the relative reactivity of the oxidation product PROD to the parent hydrocarbon as defined by the dimensionless parameter If the oxidation products... 

Therefore, the measurement of the relative reactivities in separate and in competitive experiments will permit the evaluation of either K jK or KiK IK K depending upon whether the principal surface species are the TT-complexed multiply unsaturated hydrocarbons or the respective half-hydrogenated states. If the former situation exists, the evaluated ratios might be expected to correlate with the association constants of the hydrocarbons with silver ion (78), but not if the main surface species are the half-hydrogenated states. Apparently, it is the latter condition which prevails. 

Table VI shows the relative reactivities of various asym DAMs. An equi-molecular mixture of two kinds of asym DAMs was fed as a 5% benzene solution and hydrogenolyzed in order to check the effect of the methyl group on the reactivity. Two kinds of asym DAMs having similar reactivities were selected as a combination. The reaction conditions were temperature, 400°C H2/hydrocarbons molar ratio, 2. The contact time was changed since the reactivities of asym DAMs differed considerably according to their structures this made it possible to evaluate the different reactivities. Side reactions such as demethylation, isomerization, and disproportionation were negligible under these reaction conditions. The relative values for the reactivities of the asym DAMs shown in Table VI are determined when the value of 2,5-DMeDPM as a standard material is fixed at 100.

Relative Reactivities of Cyclic Hydrocarbons with 4-7 Membered Rings" (78)... 

Stephens, E. R., and W. E. Scott. Relative reactivity of various hydrocarbons in polluted atmospheres. Proc. Amer. Petrol. Inst. 42(Section III Refining) 665-670, 1%2. 

Table III. Relative Reactivities of Hydrocarbons Toward Various Radicals"...

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. 

Tphe original objectives of this work were to determine how much the relative reactivity of two hydrocarbons toward alkylperoxy radicals, R02, depends on the substituent R—, and whether there are any important abnormalities in co-oxidations of hydrocarbons other than the retardation effect first described by Russell (30). Two papers by Russell and Williamson (31, 32) have since answered the first objective qualitatively, but their work is unsatisfactory quantitatively. The several papers by Howard, Ingold, and co-workers (20, 21, 23, 24, 29) which appeared since this manuscript was first prepared have culminated (24) in a new and excellent method for a quantitative treatment of the first objective. The present paper has therefore been modified to compare, experimentally and theoretically, the different methods of measuring relative reactivities of hydrocarbons in autoxidations. It shows that large deviations from linear rate relations are unusual in oxidations of mixtures of hydrocarbons. 

Early this year, Middleton and Ingold (29) reported relative rates of chain propagation of a primary, secondary, and tertiary peroxy radical (from allylbenzene, Tetralin, and a-methylstyrene, respectively) with a series of nine hydrocarbons. By using a large excess of one of the first three hydrocarbons, they dealt almost entirely with one chain carrier in each co-oxidation. Relative reactivities were determined by a GLPC method like that of Russell and Williamson (31, 32). They concluded that the average relative reactivities of the primary, secondary, and tertiary peroxy radicals toward the nine hydrocarbons were 5.2/2.2/1.0 but that the relative reactivities of the nine hydrocarbons were about the same toward each type of radical. These results are acceptable as semi-quantitative. However, despite numerous replicate analyses, their experimental method suffers from the same limitations as that of Russell and Williamson, and they give no primary data—only the calculated results. 

A subsequent paper (23) gives propagation and termination constants for numerous additional hydrocarbons and deals mostly with relative reactivities of active hydrogen atoms and with effects of structure on termination constants. A comparison of relative reactivities of hydrocarbons toward alkylperoxy, tert-butoxy, and phenyl radicals uses a different alkyl in each alkylperoxy radical in spite of the differences in reactivity among different alkylperoxy (29) radicals. 

Reactivity Ratios and Relative Rates of Oxidation. Table VI summarizes reactivity ratios for all combinations of butadiene, styrene, Tetralin, and cumene reported here and by Hendry (12) for butadiene. The underscored r values in the table are calculated from the base point in the same column (1.00) and the reciprocals (because of the definition of r in Equation 2) of the relative reactivities of the hydrocarbons toward an average R02 radical, B S T C = 1.0 2.2 4.5 5 30 (all underscored values in the butadiene column). The calculated and experimental values always agree within 50%, and in seven out of 12 systems, within 15%. Thus, among these four hydrocarbons a change of R— in RC>2 affects relative reactivities by less (often much less) than 50%. 

Reactivity of Hydrocarbons. - Each homologous series in a liquid fuel can exhibit different kinetics upon reforming under similar reaction conditions. For example, aromatic compounds are the most difficult to reform and require higher temperatures and lower space velocities. Aromatics also contribute significantly to carbon formation, compared to paraffins and naphthenes. At the same reaction conditions, the H2 production rates are typically in the order aromatics naphthenes. ° The relative reactivities of various higher hydrocarbons are summarized in Table 12. 

---