Chloronitrobenzene from nitrobenzene

As can be seen from Table 4-2, the relative rates of chlorine substitution in nitrochlorobenzenes under the action of different nucleophilic reagents are in agreement with af of the anion radicals. The constants af and af of the 4-chloronitrobenzene anion radical are close to the af and af constants of the nitrobenzene anion radical. The pair of anion radicals of 2-chloronitrobenzene and nitrobenzene show the same agreement between af and af. In the anion radical of nitrobenzene, af is larger than af. The substitution of ethoxyl for chlorine in 4-chloronitrobenzene proceeds much more easily and requires a lower activation energy than the same substitution in 2-chloronitrobenzene. The spin density in position 4 of the anion radical of 1,3-dinitrobenzene is greater than that in position 2 (af > af). Therefore, l,3-dinitro-4-chlorobenzene is more active in nucleophilic substitution than l,3-dinitro-2-chlorobenzene. 

In the reaction of chloronitrobenzene and nitraniline with alkali the halogen atom or the amino group is only mobile in the 0 andp isomers and is replaceable by OH (also by CN, CNS etc.) much more readily than in chlorobenzene or aniline. This is a reaction of the nucleophilic OH- ion. 0-Nitrophenol and some -nitrophenol, but no meta, can indeed be produced from nitrobenzene with alkali also, though with difficulty. 

Table 9.7 contains recent data on the nitration of polychlorobenzenes in sulphuric acid. The data continue the development seen with the diehlorobenzenes. The introduetion of more substituents into these deactivated systems has a smaller effect than predicted. Whereas the -position in ehlorobenzene is four times less reactive than a position in benzene, the remaining position in pentachlorobenzene is about four times more reactive than a position in 1,3,4,5-tetraehlorobenzene. The chloro substituent thus activates nitration, a circumstance recalling the faet that o-chloronitrobenzene is more reactive than nitrobenzene. As can be seen from table 9.7, the additivity prineiple does not work very well with these compounds, underestimating the rate of reaction of pentachlorobenzene by a factor of nearly 250, though the failure is not so marked in the other cases, especially viewed in the circumstance of the wide range of reactivities covered. 

Where does the hydrogen atom in the product of hydro-de-diazoniation, 2-chloro-nitrobenzene (8.66), come from in CH3OD It was found (Bunnett and Takayama, 1968 b Broxton and Bunnett, 1979) that in the reaction of Scheme 8-47 the deuterium content of 2-chloronitrobenzene was 79%, a figure which is not close to either zero or 100%. For other substituted benzenediazonium ions a very wide range of D incorporation was observed. This range is consistent with hydro-de-diazoniation by both homolytic and a competitive anionic mechanism. The anionic pathway is favored by an increase in methoxide ion concentration. 

The ONSH reaction of the carbanion of 2-phenylpropionitrile (45 c) with nitrobenzene in liquid ammonia at -70 °C involves rate-limiting Carom—H bond breaking, as evidenced by the 9.8 times faster rate than for reaction of the analogous substitution of deuterium in 4-<7-nitrobenzene and perdeuterionitrobenzene. Reactions of the carbanion derived from (45c) with 4-chloro-3-trifluoromethylnitrobenzene and 4-chloronitrobenzene in toluene under phase transfer catalysis has also been studied." ... 

As seen from Table 4.2, activation energies of chlorine substitution in nitrochlorobenzenes under the action of diverse nucleophilic reagents are in agreement with a, of anion-radicals. Constants and of 4-chloronitrobenzene anion-radical are close to the and constants of nitrobenzene... 

The above process was applied initially [142,144] to destroy 100 ppm aniline and 4-chloroaniline in alkaline solutions of pH between 11 and 13 by anodic oxidation in the presence of H202 electrogenerated at an ODC (54 mM H202 at 600 mA). Both substrates presented pseudo first-order decays with half-lives less than 30 min at 600 mA. After 11 hr of electrolysis at 300 mA, a TOC decay >95% was found (see Table 4). Nitrobenzene and p-chloronitrobenzene were detected, respectively, as intermediates, which degraded via maleic acid. Cl was quantitatively released from 4-chloroaniline, and NH3 was a final product of both substrates. General reaction pathways involving oxidation of organics by OH and H02 were proposed. 

The nitration of chlorobenzene with a mixed acid reagent comprising around 35% nitric acid, 53% sulfuric acid and 12% water, at temperatures of from 40 to 80 °C and a HNOa/chlorobenzene molar ratio of around 1 gives a 98% yield of an isomeric mixture consisting of around 33% o-chloronitrobenzene, 66% p-chloro-nitrobenzene and 1% m-chloronitrobenzene. 

---