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Aromatic hydrocarbons rate constants with

G.6.2.3 Aromatic Hydrocarbons Rate constants for the reaction of hydroxyl and nitrate radicals with some aromatic hydrocarbons are compiled in Table 6.23, and it is clear that with a few exceptions, that the hydroxyl radical is the more... [Pg.244]

FIGURE 1.22. Solvent reorganization energies derived from the standard rate constants of the electrochemical reduction of aromatic hydrocarbons in DMF (with n-Bu4N+ as the cation of the supporting electrolyte) uncorrected from double-layer effects. Variation with the equivalent hard-sphere radii. Dotted line, Hush s prediction. Adapted from Figure 4 in reference 13, with permission from the American Chemical Society. [Pg.60]

In contrast to the results of Bossmann et al., Lindsey and Tarr [31,32] observed equivalent rate constants for polycyclic aromatic hydrocarbon (PAH) degradation with Fenton systems as had been previously observed for PAH reaction with hydroxyl radicals as generated by pulse radiolysis techniques [33], Such kinetic agreement suggests, but does not confirm, equivalent mechanisms. PAHs, unlike 2,4-dimethylaniline, are not expected to directly coordinate iron in aqueous solutions. [Pg.179]

Figure 6.13 Electron transfer between organic compounds. Correlation of rate constant with standard free-energy change (AG ) for reactions of amine donors with aromatic hydrocarbons in acetonitrile (see text). After D. Rehm and A. Weller, Ref. [27,c]. Figure 6.13 Electron transfer between organic compounds. Correlation of rate constant with standard free-energy change (AG ) for reactions of amine donors with aromatic hydrocarbons in acetonitrile (see text). After D. Rehm and A. Weller, Ref. [27,c].
That the reaction with a lower rate constant is taking place preferentially and that the rate increases during the reaction are phenomena that can also occur with parallel reactions. As an example, Wauquier and Jungers (48), when studying competitive hydrogenation of a series of couples of aromatic hydrocarbons on Raney-nickel, have observed these phenomena for the couple tetraline-p-xylene (Table I). The experimental result was... [Pg.11]

If, for the purpose of comparison of substrate reactivities, we use the method of competitive reactions we are faced with the problem of whether the reactivities in a certain series of reactants (i.e. selectivities) should be characterized by the ratio of their rates measured separately [relations (12) and (13)], or whether they should be expressed by the rates measured during simultaneous transformation of two compounds which thus compete in adsorption for the free surface of the catalyst [relations (14) and (15)]. How these two definitions of reactivity may differ from one another will be shown later by the example of competitive hydrogenation of alkylphenols (Section IV.E, p. 42). This may also be demonstrated by the classical example of hydrogenation of aromatic hydrocarbons on Raney nickel (48). In this case, the constants obtained by separate measurements of reaction rates for individual compounds lead to the reactivity order which is different from the order found on the basis of factor S, determined by the method of competitive reactions (Table II). Other examples of the change of reactivity, which may even result in the selective reaction of a strongly adsorbed reactant in competitive reactions (49, 50) have already been discussed (see p. 12). [Pg.20]

It has been proposed that aromatic solvents, carbon disulfide, and sulfur dioxide form a complex with atomic chlorine and that this substantially modifies both its overall reactivity and the specificity of its reactions.126 For example, in reactions of Cl with aliphatic hydrocarbons, there is a dramatic increase in Ihe specificity for abstraction of tertiary or secondary over primary hydrogens in benzene as opposed to aliphatic solvents. At the same time, the overall rate constant for abstraction is reduced by up to two orders of magnitude in the aromatic solvent.1"6 The exact nature of the complex responsible for this effect, whether a ji-coinplex (24) or a chlorocyclohexadienyl radical (25), is not yet resolved.126- 22... [Pg.34]

Explicit mechanisms attempt to include all nonmethane hydrocarbons believed present in the system with an explicit representation of their known chemical reactions. Atmospheric simulation experiments with controlled NMHC concentrations can be used to develop explicit mechanisms. Examples of these are Leone and Seinfeld (164), Hough (165) and Atkinson et al (169). Rate constants for homogeneous (gas-phase) reactions and photolytic processes are fairly well established for many NMHC. Most of the lower alkanes and alkenes have been extensively studied, and the reactions of the higher family members, although little studied, should be comparable to the lower members of the family. Terpenes and aromatic hydrocarbons, on the other hand, are still inadequately understood, in spite of considerable experimental effort. Parameterization of NMHC chemistry results when NMHC s known to be present in the atmosphere are not explicitly incorporated into the mechanism, but rather are assigned to augment the concentration of NMHC s of similar chemical nature which the... [Pg.90]

Quenching rate constants for dienes and quadricyclenes have similar sensitivities to the electronic and structural features of the excited aromatic hydrocarbon. However, during this process quadricyclene isomerizes to nor-boraadiene with a quantum yield of 0.52, whereas dienes usually remain unchanged/10 Hammond has suggested that vibrational energy which is partitioned to the acceptor upon internal conversion of the exciplex can lead to isomerization(10a,103) ... [Pg.457]

Lloyd, A.C., Darnall, K.R., Winer, A.M., Pitts, Jr., J.N. (1976) Relative rate constants for reaction of the hydroxyl radical with a series of alkanes, alkenes, and aromatic hydrocarbons. J. Phys. Chem. 80, 189-794. [Pg.400]

Ohta, T., Ohyama, T. (1985) A set of rate constants for the reactions of hydroxyl radicals with aromatic hydrocarbons. Bull. Chem. Soc. Jpn. 58, 3029-3030. [Pg.612]

However, in contrast to the VE system discussed in the previous section, we have no information on c for this system, but since the yield of ions from a given dose-rate depends mainly on the dielectric constant, it can be assumed that in the mixtures of aromatic hydrocarbons with which we are dealing here, the c and the rate constants are independent of m, so that we can use (5.10) and (5.14), treating c as constant. [Pg.382]

The above considerations should bear some relationship with the stereochemistry of the reaction. As indicated earlier (8ection 2 Hebert et ai, 1985), in the reaction of anthracene anion radicals with optically active 2-octyl bromide, racemization is mostly observed together with a small but distinct amount (ca. 10%) of inversion. In the context of the ET-8n2 mixed mechanism sketched above, this can be rationalized in terms of a minor contribution of the latter pathway that would not detectably affect the overall rate constant of the reaction. The weakness of the bonded interactions in the transition state derives from the relatively poor affinity of the alkyl radical for the aromatic hydrocarbon. This is consistent with the fact that in those of the radical-anthracene pairs that were not favourably oriented for the 8, 2 reaction to occur, the alkyl radical escapes from the... [Pg.111]

Atkinson, R., and J. N. Pitts, Jr. Temperature dependence of the absolute rate constants for the reaction of 0( P) atoms with a series of aromatic hydrocarbons over the range 299-392 K. J. Phys. Chem. 79 295-297, 1975. [Pg.112]

The rate of volatilization will also increase with an increase in temperature, ten Hulscher et al. (1992) studied the temperature dependence of Henry s law constants for three chlorobenzenes, three chlorinated biphenyls, and six polynuclear aromatic hydrocarbons. They observed that within the temperature range of 10 to 55 °C, Henry s law corrstant doubled for every 10 °C increase in temperature. This temperature relationship should be corrsidered when assessing the role of chemical volatilization from large surface water bodies whose temperatines are generally higher than those typically observed in groimdwater. [Pg.16]

CASRN 24157-81-1 molecular formula C10H2O FW 212.33 Photolytic. Fukuda et al. (1988) studied the photolysis of 2,6-diisopropylnaphthalene and other polycyclic aromatic hydrocarbons in distilled water using a high pressure mercury lamp. After 96 h of irradiation, a rate constant of 0.045/h with a half-life of 16.0 h was determined. When the experiment was replicated in the presence of various NaCl concentrations, they found that the rate of photolysis increased proportionately to the concentration of NaCl. The photolysis rates of 2,6-diisopropylnaphthalene at aqueous NaCl concentrations of 0.2, 0.3, 0.4, and 0.5 M following 3 h of irradiation were 33.8, 44.7, 46.4, and 54.6%, respectively. It appeared that the presence of NaCl, the main component in seawater, is the cause for the increased rate of degradation. [Pg.1576]

The cation-radicals ArH+ were detected, but they originated from the fast reaction of a one-electron transfer, which does not affect kinetic constants of the oxidation. The rate constant depends linearly on Brown s a constants of substituents (Dessau et al. 1970). All these data are in agreement with the formation of the strong polar dication of an aromatic hydrocarbon as an intermediate. Because PF salts (in particular the diacetate) are not reductants, the two-electron transfer reaction proceeds irreversibly. [Pg.71]

For nitration of aromatic hydrocarbons with acetylnitrate, there is a clear linear correlation between the IPs of these hydrocarbons and rate constants relative to benzene (Pedersen et al. 1973). Table 4.4 jnxtaposes spin densities of cation-radicals and partial rate factors of ring attacks in the case of nitration of isomeric xylenes with nitric acid in acetic anhydride. [Pg.253]

The results obtained by liquid-phase oxidation or co-oxidation of various hydrocarbons are reviewed, and new results are reported for new kinds of compounds such as alkyl-aromatics, alcohols, and ethers, which were also systematically studied by co-oxidation. Gathering all kinetic data and discussing them in connection with data on absolute termination constants, obtained by other groups through physical measurements, enables us to estimate the termination and propagation rate constants for about 40 compounds and to present characteristic values for some new classes of compounds. Examples demonstrate that co-oxidation studies make it possible to explain the behavior of complex compounds reacting by different kinds of bonds, and more particularly the behavior of polymers oxidized in solution. [Pg.71]

As seen in Table 6.1, the reactions of the nitrate radical with the simple aromatic hydrocarbons are generally too slow to be important in the tropospheric decay of the organic. However, one of the products of the aromatic reactions, the cresols, reacts quite rapidly with NO,. o-Cresol, for example, reacts with N03 with a room temperature rate constant of 1.4 X 10 " cm3 molecule-1 s-1, giving a lifetime for the cresol of only 1 min at 50 ppt N03. This rapid reaction is effectively an overall hydrogen abstraction from the pheno-... [Pg.212]

Chlorine atoms react with aromatic hydrocarbons, but only at a significant rate with those having saturated side chains from which the chlorine atom can abstract a hydrogen or unsaturated side chains to which it can add. For example, the rate constant for the Cl atom reaction with benzene is 1.3 X 10"15 enr3 molecule-1 s-1 (Shi and Bernhard, 1997). On the other hand, the rate constants for the reactions with toluene and p-xylene are 0.59 X 10-10 and 1.5 X 10-l() enr3 molecule"1 s"1, respectively (Shi and Bernhard, 1997), and that for reaction with p-cymene is 2.1 X 10"10 cm3 molecule"1 s-1 (Finlayson-Pitts et al., 1999). Hence... [Pg.212]

The rate constant kTD for fluorescence of the pyrene intermolecular solution excimer has been found to follow the relation kFD = n2(kFD)n=I, where n is the the refractive index of the solvent69 . The values of kTO for the 1-methylnaphthalene excimer in ethanol at various temperatures are also consistent with the above relation 76). The fact that (kFD)n=I is independent of solvent and temperature indicates that the excimer has a specific structure, according to Birks 69,71). Experimentally, it was observed much earlier that kFM = n2(kFM)n=i for the polycyclic aromatic hydrocarbons, and that k /kp is independent of solvent and temperature. Table 5 shows that agreement between independent investigators of the excimers of naphthalene compounds is not always good, as in the case of 1-methylnaphthalene. [Pg.46]


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