Arylamines reaction with nitrous acid

Sec. 24.8) from arylamines by reaction with nitrous acid... 

We have seen that primary arylamines react with nitrous acid to form stable arene-diazonium salts (Section 16.12). Arenediazonium salts are useful to synthetic chemists because the diazonium group can be replaced by a wide variety of nucleophiles. This reaction allows a wider variety of substituted benzenes to be prepared than can be prepared solely from electrophilic aromatic substitution reactions. 

Tertiary arylamines react with nitrous acid to form C-nitroso aromatic compounds. Nitrosation takes place almost exclusively at the para position if it is open and, if not, at the ortho position. The reaction (see Practice Problem 20.9) is another example of electrophilic aromatic substitution. 

Primary arylamines react with nitrous acid, HNOg, to yield stable arenediazo-nium salts, Ar—N=N X , a process called a diazotization reaction. Alkylamines also react with nitrous acid, but the corresponding alkanediazonium products... 

Arylamines are converted by diazotization with nitrous acid into arenediazonium salts, ArN2+ X-. The diazonio group can then be replaced by many other substituents in the Sandmeyer reaction to give a wide variety of substituted aromatic compounds. Aryl chlorides, bromides, iodides, and nitriles can be prepared from arenediazonium salts, as can arenes and phenols. In addition to their reactivity toward substitution reactions, diazonium salts undergo coupling with phenols and arylamines to give brightly colored azo dyes. 

The most useful reaction of amines with nitrous acid is the reaction of arylamines to form arenediazonium salts. We consider next how these diazonium salts may be used as synthetic intermediates. 

The most useful reaction of arylamines is conversion by diasiotization with nitrous acid into arenediazonium aatte. X. The diaxonio... 

Salts of primary aromatic amines react with nitrous acid to produce diazonium salts. The reaction is usually performed by adding a cold solution of sodium nitrite to a cold solution of the arylamine in aqueous mineral acid. The end point of the reaction is conveniently determined by the detection of excess nitrous acid with potassium iodide-starch paper. Sulfamic acid has long been used both in industry and in the laboratory to remove excess nitrous acid. It has been found to react with the more active diazo compounds. In most cases, high temperatures are avoided to prevent the formation of phenols and the decomposition of the unstable nitrous acid. An excess of mineral acid is necessary to prevent coupling between the diazonium salt and unreacted amine (cf. method 494). If the amine salt is somewhat insoluble, a fine crystalline form, which is produced by rapid crystallization from a warm aqueous solution, may be employed. ... 

Primary arylamines rea t with nitrous acid, HNOg, to yield stable arene-diazonium salts, Ar-NsNX". This diazotization reaction is compatible with the presence of a wide variety of substituents on the aromatic ring. 

B Reactions of Primary Arylamines with Nitrous Acid... 

The most important reaction of amines with nitrous acid, by far, is the reaction of primary arylamines. We shall see why in Section 20.7. 

The most important reaction of amines with nitrous acid, by far, is the reaction of primary arylamines. We shall see why in Section 20.7. Primary arylamines react with nitrous add to give arenediazonium salts. Even though arenediazonium salts are unstable, they are still far more stable than aliphatic diazonium salts they do not decompose at an appreciable rate in solution when the temperature of the reaction mixture is kept below 5°C ... 

Aliphatic primary amines also give diazonium salts with nitrous acid. However, in this case the diazonium ion is not stabilized by resonance structures as in the case of arylamine, and decomposition to nitrogen and carbo-nium ions takes place. During the performance of the reaction the evolu-... 

Sandmeyer-type reactions are a useful route to polynitroarylenes with unusual substitution patterns. In these reactions an arylamine is treated with a source of nitrous acid to form an intermediate diazonium salt which is readily displaced on reaction with a suitable nucleophile. Many substituents can be incorporated into the aromatic ring via this method, including the nitro group. 

Nitrous acid reacts with 1 ° alkylamines and arylamines to form diazonium salts. This reaction is called diazotization. 

The optimum temperature for simple arylamines is 0-2°, for m-haloaryl-amines 0-5°, and for benzidines, naphthylamines, and o- and / -haloarylamines 10-12°. In isolated cases higher temperatures are used, e.g., 34° for / -nitro-aniline and 40° for o-anisidine. The end-point of the reaction is determined by testing for an excess of nitrous acid with potassium iodide-starch paper. Amino sulfonic acids are no longer used to remove the excess of nitrous acid since they react with reactive diazo compounds.244... 

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