1-Chloronitrobenzene reactions mechanism

Place 50 g. of o-chloronitrobenzene and 75 g. of clean dry sand in a 250 ml. flask equipped with a mechanical stirrer. Heat the mixture in an oil or fusible metal bath to 215-225° and add, during 40 minutes, 50 g. of copper bronze or, better, of activated copper bronze (Section 11,50, 4) (1), Maintain the temperature at 215-225° for a further 90 minutes and stir continuously. Pour the hot mixture into a Pyrex beaker containing 125 g. of sand and stir until small lumps are formed if the reaction mixture is allowed to cool in the flask, it will set to a hard mass, which can only be removed by breaking the flask. Break up the small lumps by powdering in a mortar, and boil them for 10 minutes with two 400 ml. 

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. 

We use the reaction of 3-chloronitrobenzene with the hydroxide ion to illustrate in Figure 8-1 the mechanism for a nucleophilic substitution reaction. 

Reactions of 2-lithio-l,3-dithiane (161) with nitroarenes gave 1,4- and 1,6-addition products whereas 2-methyl and 2-phenyl-l,3-dithiane derivatives provide only 1,6-addition products. These conjugate-addition products are transformed into the respective nitroaromatic compounds by in situ oxidation with oxygen or DDQ. In the case of 4-chloronitrobenzene, the 1,4-addition product with respect to the nitro group was mainly obtained242. A SET mechanism was proposed242, as in the case of alkyl iodides243. 

In a S-1. round-bottomed flask equipped with a reflux condenser and a mechanical stirrer are placed 236 g. (1.5 moles) of / chloronitrobenzene, 960 g. (4 moles) of sodium sulfide nona-hydrate, and 2.5 1. of water. With rapid agitation, the reaction mixture is slowly heated to the reflux temperature (Note 1). Heating is continued over a period of 20 hours. 

The photochemistry of 4-chloroanilines in methanol, dioxane-water and diox-ane-methanol solvents has been investigated for more than thirty years by Latowski185,186. Large quantum yields of HC1 formation (hci) have been observed for the photolysis of 91a in protic solvents (e.g. Hci = 0.78 in methanol at 254 nm). However, the values of 4>hx are relatively small for 4-bromoaniline (HBt = 0.19), 4-iodoaniline (cbm = 0.29), 2-chloroaniline (hci < 0.02) and 3-chloroaniline (hci = 0.02) under the same condition. N-Acetylation of 91a to 4-chloroacetanilide also inhibits the photolytic process. In conjunction with the solvent- and concentration-dependent photolysis rates of 91a, these results indicate an electron-transfer mechanism for the photochemical reaction electron transfer occurred from an excited 91a to an unexcited 91a molecule, followed by ionization reactions. However, recent analysis of photoproducts from 91a in water/methanol mixtures has shown that benzidine (92) is a major product along with aniline (equation 29)187. As a result, a carbene mechanism that leads to the formation of aniline radicals was put forward in analogy to the photochemistry of 4-halophenols188,189. For example, the photolysis of 91a in aqueous solution first results in the transient species carbene 93 followed by the formation of the aniline radical 94 that was observed as the primary product (Scheme 13)190. In addition to la and 92, other identified secondary products include 4-aminodiphenylamine, 2-aminodiphenylamine, hydrazobenzene, 4-chloronitrosobenzene and 4-chloronitrobenzene, but they are all in low yields191. 

The reason this reaction is suitable is that it involves nucleophilic aromatic substitution by the addition-elimination mechanism on ap-nitro-substituted aryl halide. Indeed, this reaction has been carried out and gives an 80-82% yield. A reasonable synthesis would therefore begin with the preparation of p-chloronitrobenzene. 

VNS hydroxylation of nitroarenes with alkylhydroperoxides proceeds according to mechanism similar to that of the reaction with a-halocarbanions— reversible nucleophiUc addition, followed by the base-induced p-ehmination of alcohols from the intermediate a"-adducts. These mechanistic features were established by detramination of effects of base on the rate of the reaction, namely, on the competition between VNS hydroxylation and S Ar of chlorine in 4-chloronitrobenzene and 2,4-dinitrochlorobenzene. For instance, the reaction of these hydropaoxides with 2,4-dinitrochlorobenzene carried out in the presence of an excess of f-BuOK proceeds exclusively as VNS to give 2,4-dinitro-5-chlorophenol, whereas in the presence of equimolar amount of f-BuOK substantial quantity of 2,4-dinitrophenol, product of S,.jAr is formed (Scheme 11.43) [66]. 

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