O- and p-Nitrochlorobenzene

An accurate melting point curve of mixtures of o- and p-nitrochlorobenzenes has been given by Holleman and de Bruyn.2 From this curve, it is possible to determine directly the composition of ai mixture. 

The alkyl ethers of o- and p-nitrophenols can also be prepared from o- and p-nitrochlorobenzenes bv the action of sodium alcoholates (see page 97). 

Chlorobenzenes remain important intermediates for the production of nitrated chlorine compounds, particularly o- and p-nitrochlorobenzene. 

Four nucleophilic aromatic substitution reactions with amines have been studied for deuterium isotope effects. Hawthorne (81) found that the rates of reaction of o- and p- nitrochlorobenzene with piperidine in xylene are not altered by substitution of deuterium for hydrogen on the amino group of the nucleophile. Similarly, 2,4-dinitrochlorobenzene reacts at identical rates with -butylamine and with iV,iV-dideuterio-n-butylamine containing 0.75% ethanol (76). Under the conditions of the rate measurements the deuterated amine does not undergo exchange with either the chloroform or the ethanol present. Finally, the reaction of trichloro-s-triazene with aniline shows no isotope effect with AT,JV-dideuterioaniline in benzene as well as in benzene saturated with deuterium oxide (82). 

Sandmeyer in 1884 found that replacement of the diazonium group by halogen was catalyzed by cuprous chloride or bromide. It is a good route to o- and p-chlorotoluenes and m-nitrochlorobenzene. Gattermann in 1890 used copper powder to permit milder conditions. Methods were available for synthesis of benzidine and its congeners, a variety of aminoanthraquinones and acyl derivatives of aryl amines. 

A variety of isomeric or closely related mixtures of organic compounds are often found when manufacturing chemical and pharmaceutical products. However, it is usually necessary to separate these molecules in order to obtain the expected functionality of the products. Conventional methods such as distillation, extraction and crystallization might be difficult to use since the molecules to be separated might have very close chemical and physical properties. Hydrotropes are known to be selective in the solubilization of compounds and as mentioned earlier, do not perform so generally as surfactants. It has been found that the solubility enhancement in water by adding the hydrotrope sodium xylene sulfonate (SXS) will vary for different isomers such as o- and /7-nitrochlorobenzene, as well as for o- and p-dichlorobenzene (24). In this case, the c -isomer is more soluble than the p-isomer. Higher solubilities have also been reported for aromatic compounds when compared to aliphatic and alicyclic compounds (24). This selective... 

From 13.1 g of N-preduction with Raney-nickel and hydrogen, in which reaction the substance may be suspended in methanol or dissolved in methanol-ethyl acetate at normal pressure and at about 40°C with combination of the theoretical quantity of hydrogen, 12.2 g are obtained of o-emino-N-pfrom aqueous methanol hasaMPof90°C. 

The potential energy surfaces for the fragmentation of the radical anions of p-nitrochlorobenzene and p- and m-chloroacetophenones have been explored using first principle methods215. The presence of n and a radical anions and the intramolecular ET from the ji to the o surface are reported therein. 

Analogous Sulfonations. Exactly the same method can be used for sulfonating p-nitrochlorobenzene, p-nitrotoluene, o-m trochlorobenzene, chlorobenzene, and many other compounds. On the other hand, it is usually not possible to sulfonate dinitaro compounds in this way. Dinitrochlorobenzene and dinitrotoluene are decomposed explosively by treatment with fuming sulfuric acid. If dinitrochloro-benzenesulfoitic acid is to be prepared, for example, one starts with p-nitrochloro-benzene/ This is sulfonated, as described previously, and the sulfonic acid is converted to dinitrochlorobenzenesulfonic acid by treatment with mixed acid (50 50 sulfuric and nitric acids) at low temperatures. This product yields, on replacement of the chlorine by —OH and partial reduction, 4-nitro-2-aminophenol-6-sulfonic acid (nitro acid III), which is used in preparing chrome dyes. 

Nitrochlorobenzene-4-sulfonic acid can be prepared ako by sulfonation of o-nitrochlorobenzene (see Table III).This method,however,is inherently more costly and less reliable than the one given above (nitration of chlorobenzene-4-sulfonic acid), because it requires the isolation of o-nifrochlorobenzene and its separation from the para isomer. Nevertheless, the second method may be preferable technically under those circumstances where the demand for p-nitrochlorobenzene is so large that a use for the by-product ortho isomer is need. At the present time, the situation is reversed. The manufacture of o-nitroanisole uses so much o-nitrochloroben-zene that the accumulated para compound is partly used in making p-nitroaniline. 

Reduction of 2-nitrochIorobenzene-4-sulfonic acid gives o-chlorometanilic acid which is used in making azo dyes. The real technical value of nitrochlorobenzene-sulfonic acid, however, lies in the ability of its chlorine atom to be replaced by various groups. For example, o-nitrophenol-p-sulfonic acid is obtained by treatment wiui sodium hydroxide, and this product, on reduction, yields o-aminophenol-p-sulfonic acid. An ogously, nitrochlorobenzenesulfonic acid gives o-nitroanisole-p-sulfonic acid by treatment with alcoholic methanol, and from this is obtained o-anisidine-p-sulfonic acid. The action of ammonia on nitrochlorobenzenesulfonic acid produces o-nitroaniline-p>sulfonic acid aniline and its derivatives produce o-nitrodiphenylamine-p Sulfonic acids (cf. Table II). 

Synonyms and trade names 4-chloronitrobenzene p-chloronitrobenzene PCNB PNCB p-nitrochlorobenzene l-chloro-4-nitrobenzene 4-nitro-chlorobenzene 4-chloronitrobenzene C6H4CINO2 (nitrobenzol, oil of mir-bane) nitrobenzene C6H5NO2 (nitrobenzol, oil of mirbane) o-nitrotolnene CH3C6H4NO2 (m-nitrotolnene, p-nitrotolnene)... 

Chlorination of p-nitrochlorobenzene followed by reduction yields 3,4-dichloroaniline, though the process suffers from the presence of p-chloroaniline and 2,5-dichloroaniline (from o-nitrochlorobenzene in the starting material). A purer product is formed by nitration of o-dichlorobenzene followed by reduction. 

Fluorinated aromatic compounds. Finger and Kruse found that an aromatic chlorine or bromine atom activated by an o- or p-nitro group is subject to nucleophilic displacement by fluoride ipn on reaction with potassium fluoride in solvents such as succinonitrile, dimethyl formamide, or dimethyl sulfoxide. Unpublished work at Olin Mathieson Chemical Corporation indicates that best results are obtained with dimethyl sulfoxide as solvent and with potassium fluoride that has been finely ground (<100 mesh) and dried in a vacuum oven at 100° for at least 4 hrs. prior to use. In a typical case a mixture of p-nitrochlorobenzene, potassium fluoride, and dimethyl sulfoxide is stirred under reflux at 180° for 8-9 hrs., the cooled mixture... 

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