Carbazoles partial rate factors

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... 

These trends have been quantified for some reactions. Nitration studies showed carbazole to react 222,000 times faster than benzene, with nitric acid-acetic anhydride having partial rate factors of 32,100 (C-1), 1,100 (C-2), 77,600 (C-3), and too small to measure (C-4). Carbazole reacts about 20 times more slowly than diphenylamine. The partial rate factor for nitration at C-3 can be compared with a value of 50,100 found for the perchloric add protodesilylation of 3-trimethylsilylcarbazole. ... 

Chlorination of 9-acetylcarbazole in acetic acid produced values of 4,300 (C-1), 8,600 (C-2), 122,000 (C-3), and 8,600 (C-4) for the partial rate factors. Chlorination of carbazole itself gave values of > 10 and > 10 for the 1- and 3-positions chlorination of carbazole was found to be six times slower than that of diphenylamine. ... 

Nitration in acetic anhydride of 9-(p-tosyl)carbazole gave the 1-, 2-, and 3-isomers in 28, 19, and 53% yields, respectively, and for 9-acetyl- and 9-nitrosocarbazole these became, correspondingly, 10, 48, and 42%, and 24, 0, and 66% (84T1857). Nitration of carbazole itself under those conditions gave partial rate factors of/, = 32,100 /2 = 1100 and/3 = 77,600 (58JCS3079). 

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