Benzene competitive nitration studies

Dewar and his co-workers, as mentioned above, investigated the reactivities of a number of polycyclic aromatic compounds because such compounds could provide data especially suitable for comparison with theoretical predictions ( 7.2.3). This work was extended to include some compounds related to biphenyl. The results were obtained by successively compounding pairs of results from competitive nitrations to obtain a scale of reactivities relative to that of benzene. Because the compounds studied were very reactive, the concentrations of nitric acid used were relatively small, being o-i8 mol 1 in the comparison of benzene with naphthalene, 5 x io mol 1 when naphthalene and anthanthrene were compared, and 3 x io mol 1 in the experiments with diphenylamine and carbazole. The observed partial rate factors are collected in table 5.3. Use of the competitive method in these experiments makes them of little value as sources of information about the mechanisms of the substitutions which occurred this shortcoming is important because in the experiments fuming nitric acid was used, rather than nitric acid free of nitrous acid, and with the most reactive compounds this leads to a... 

Very important from both theoretical and practical points of view were experiments on the influence of substituents on the rate and the yield of nitration. For that purpose the method of competitive nitration was used. It was originally developed by Wibaut [17] to study the rate of nitration with nitric acid-acetic anhydride of toluene, chlorobenzene and bromobenzene in relation to benzene. The experiments established a higher rate of nitration of toluene and a lower rate of chloro- and bromobenzene ... 

Olah and Lin studied the boron trlfluoride-catalyzed reaction of methyl nitrate with aromatic compounds in nltromethane.2 Using competition methods they found that the toluene to benzene rate ratio was 25 and that the rate ratios for the methylben-zenes. Table IX, reached a limiting value, about 1000. Unfortunately, kinetic rate data were not obtained. However, the leveled reactivity of the polymethylbenzenes suggests that these compounds react at the encounter controlled diffusion limit. 

In order to study this problem, Olah and Lin carried competitive studies of nitration of benzene and toluene with nitry chloride, catalyzed by Lewis acid halides. When carbon tetrachloride or excess aromatics were used as solvent, the data summarized in Table XII were obtained. The data show that the ortho para ratios are smaller than in nitrations with nitio-nium salts. The observed changes point to the fact that the nitrating agents arc the conesponding donor acceptor complexes and not the nitronium ion itself. The lower orthojpara ratios than those obtained in case of NOj, particularly point to bulkier nitrating agents. 

In the present study, competition kinetics was used to determine the rate constant for the reaction of OH with BPA. Phenol was produced by the reaction of benzene with OH (Russi et al, 1982 Arakaki and Faust, 1998). When benzene as a trapping agent for OH is added to the experimental solution containing nitrate and BPA, the photoformation rate of OH (J oh) and the fraction of OH that reacts with benzene (Fbenzene.ou) are... 

Relative rate constants of the nitration were obtained by direct competition between two aromatic hydrocarbons. The rate constants depend markedly on substrate structure, with >10 difference in values between the least reactive (benzene) and most reactive (perylene) compounds studied. The more reactive (and more easily ionised) polycyclic aromatic hydrocarbons interact with NO in solution by an electron transfer mechanism. 

---