Amines nitrous acid test

Nitrous acid test. The conditions of the test are similar to those described for the classification of primary amines (Section 9.5.2, p. 1215), but using acetic acid in place of hydrochloric acid. An a-amino acid yields nitrogen and an a-hydroxy acid. 

Two common qualitative tests for amines are the Hinsberg test and the nitrous acid test. The nitrous acid test is not included here because the N-nitroso derivatives of some secondary amines are carcinogenic. The risk of producing an as-yet-unrecognized carcinogenic material in this procedure outweighs any possible benefit of a test that can also be misleading and difficult to interpret. The modified sodium nitroprusside test has been included as an alternative. 

Some acylated arylamines (e.g. anilides) give misleading results in the nitrous acid test for amines (page 69). 

The Reaction has the following limitations (i) a compound that can liberate nitrous acid in acid solution is required (e.g., a metallic nitrite or a nitroso-amine, p. 204). (2) Nitrophenols and />-substituted phenols do not give the test. (3) Among the dihydroxyphenols. only resorcinol gives a satisfactory positive test. 

Primary aromatic amines differ from primary aliphatic amines in their reaction with nitrous acid. Whereas the latter yield the corresponding alcohols (RNHj — ROH) without formation of intermediate products see Section 111,123, test (i), primary aromatic amines 3neld diazonium salts. Thus aniline gives phcnyldiazonium chloride (sometimes termed benzene-diazonium chloride) CjHbNj- +C1 the exact mode of formation is not known, but a possible route is through the phenjdnitrosoammonium ion tlius ... 

The experimental conditions necessary for the preparation of a solution of a diazonium salt, diazotisation of a primary amine, are as follows. The amine is dissolved in a suitable volume of water containing 2 5-3 equivalents of hydrochloric acid (or of sulphuric acid) by the application of heat if necessary, and the solution is cooled in ice when the amine hydrochloride (or sulphate) usually crystallises. The temperature is maintained at 0-5°, an aqueous solution of sodium nitrite is added portion-wise until, after allowing 3-4 minutes for reaction, the solution gives an immediate positive test for excess of nitrous acid with an external indicator—moist potassium iodide - starch paper f ... 

For preparative diazotisations it is important to use a sufficient excess of acid and to keep the temperature down. Two moles of acid are required for each mole of amine, one for salt formation and one for liberating the nitrous acid from the nitrite. As a rule 2-5-3-0 moles are used. The excess is required to prevent condensation of the diazonium salt with unchanged base to diazoamino-compound such condensations take place in a faintly acid medium. The test for unchanged amine, accordingly, consists in buffering the free mineral acid with sodium acetate, and so providing a solution faintly acid with acetic acid, under which conditions the diazoamino-compound is formed. The latter is decomposed by mineral acids into diazonium salt and amine salt, e.g. 

Amines are easily identified because they re readily soluble in dilute acid. Sodium fusion converts the cimine to the cyanide ion, which is detectable by a Vciriety of methods. The ready formation and decomposition of diazonium salts (discussed in the earlier section Reactions with nitrous acid ) leads to the identification of primary amines. The Hinsberg test (see the nearby sidebcir) is useful in identifying amines. 

In Table 1 is a list of the environmental secondary and tertiary amines which have been tested by feeding to rats together with nitrite. Of these, several react very readily with nitrite in acid solution, but some, for example phenmetrazine (2 , 27), give rise to a noncarcinogenic N-nitroso derivative. On the other hand, aminopyrine reacts extremely readily with nitrous acid, although it is a tertiary amine, and forms the potent carcinogen nitrosodimethylamine in high yield (28, ). The other amines vary considerably in the extent to which they form N-nitroso derivatives by reaction with nitrous acid, especially at the relatively low concentrations which model human exposure more closely... 

Lecorche-Jovinet Sensitivity Test. Test for the stability of proplnts contg NG. Any nitrous acid present is absorbed by diethyldiphenyl-urea to form ethylphenylnitrosamine, which can be detected by testing with os-naphthyl-amine-HCl... 

If the sodium nitrite is not of the highest technical purity it may be necessary to employ more than the indicated quantity. It is essential that the test for nitrous acid be permanent if any unchanged amine remains, a precipitate of the diazoamino compound is formed on neutralization. A moderate excess of nitrite does not appear to interfere with the reaction, especially since the greater portion of the free nitrous acid is removed by the carbon dioxide liberated on neutralization. 

G) Action of Nitrous Acid on Amines. (1) Primary Amines. To 3 ml of methylamine solution in a test tube, add 3 ml of water and 2 g of solid sodium nitrite. Add slowly in small portions 2 ml of dilute sulfuric acid. After a few minutes, warm, and note the effect. What product remains behind By what test may its presence be detected ... 

In order now to diazotise an amine, the cooled solution is first treated with a small portion of the nitrite solution it is well stirred, and a drop of it transferred with a clean glass rod to the starch-potassium-iodide paper. If the nitrous add is already used up in the diazotisation, no dark spots appear, and further portions of the sodium nitrite may be added, the test is again repeated, and so on. But if a dark spot is formed at once, the nitrous acid is still present and in this case, before more of the nitrite is added, one waits until the reaction has been completed, and so on. After the addition of three-fourths of the nitrite solution, larger quantities may be added at one time, but toward the end of the reaction small quantities must again be employed. The diazotisation is ended when, after standing some time, the mixture shows the presence of nitrous add- Since the diazotisation of the last portions of the amine often requires some time, the addition of the nitrite is not discontinued at once, even if after one minute the test for nitrous add is obtained, but the solution is allowed to stand 5-10 minutes, and is then tested again. At times, it happens that the... 

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