14 ноября, 2015 
Pokraskin 1. Aniline. A solution of 9.3 grams (0.1 mole) of aniline (purified by redistillation if necessary) in 125 cc. 2 N hydrochloric acid is cooled in a beaker surrounded by ice and stirred with a turbine or electric motor. (The quantities given in all examples assume 100 per cent material; the quantities must be increased, of course, if the material is impure (see page 240.) When the solution is cold, a few pieces of ice are added, and 100 cc. 1 N nitrite solution is added dropwise from a dropping funnel. The addition of the nitrite need not be made slowly provided the temperature does not rise above 0°C. and each drop is immediately stirred into the reaction mixture. If necessary, more ice is added to the mixture. There should be no formation of gas bubbles and the solution should not become cloudy or colored. The mixture is stirred for about 10 minutes after completing the addition of nitrite and is then tested to make sure that it gives a strong blue coloration with Congo red paper and a weak blue test with either starch-iodide paper or “sulfone-reagent.”* If the mixture does not give the weak test for nitrite, more nitrite solution is added dropwise until a positive test is obtained which persists for a few minutes. If, on the other hand, a strong test for nitrite is obtained, a few drops of a dilute solution of aniline hydrochloride is added until the nitrite test nearly disappears. If more than a few drops of nitrite or aniline hydrochloride solution is required for this final adjustment, a large error must have been made in weighing
* O. Stein, Ber., 27, 2806 (1894). This reagent is 4,4′ diaminodiphenylinethane-
2,2′-sulfone: .——
HSN—/
A few drops of a 10 per cent solution of the base in dilute hydrochloric acid is placed on a filter paper, and 1 drop of the solution under test is added. In the presence of nitrite, an unstable blue coloration is formed. The reagent is somewhat less sensitive than starch-iodide, but is usable even in strongly acid solutions.
or measuring, or the nitrite solution is incorrect. Under such circumstances, the experiment should be discarded and started over again. This applies also where the diazotization mixture becomes cloudy or strongly colored.
Instead of carrying out the reaction in a beaker with mechanical stirring, diazotization on a small scale can be done in an Erlenmeyer or round-bottomed flask using hand agitation. Under these conditions, external cooling is dispensed with and more ice is added to the reaction mixture (about 100 grams for the quantities of materials given above). The flask used must be sufficiently large to permit vigorous swirling without spilling. The flask is shaken continuously while the nitrite solution is added in a thin stream from a graduated cylinder. Any drops of nitrite adhering to the walls of the reaction flask are rinsed down with a wash bottle. The mixture is shaken for a few minutes more and then tested as described above.
When it is desired to make a concentrated diazo solution, 5 N nitrite solution, or even solid nitrite, is used instead of the 1 N solution. The solution must be especially well stirred if solid nitrite is added. Also, more concentrated acid can be used. Enough water must be present so that the hydrochloride of the amine is soluble at least in the warm solution, and an effort should be made to obtain as finely divided a precipitate as possible when the solution is cooled, e. g., by stirring or shaking during cooling. If this precaution is taken, the precipitated hydrochloride goes into solution easily when the nitrite is added. If the amine forms a very difficultly soluble hydrochloride, the base should be dissolved first in hot water containing only one equivalent of hydrochloric acid and the remainder of the acid (which has a salting out action) should be added later.
A similar procedure can be used in the diazotization of homologs and alkoxy derivatives of aniline, m-halogen derivatives of these, polynuclear bases such as benzidine, diaminodi — and -triphenylmethanes, di — aminodiphenylether, etc., and their derivatives, and, in general, for all amines of the benzene series whose hydrochlorides are not decomposed by water. Aminosulfonic and carboxylic acids can also be diazotized by the above procedure if they are sufficiently soluble in dilute hydrochloric acid.
2. p-Chloroaniline. A solution is made by warming 12.75 grams (0.1 mole) of p-chloroaniline with 100 cc. water and 30 cc. concentrated hydrochloric acid. The solution is cooled with stirring or shaking, ice is added, and diazotization is carried out as in example 1.
o-Chloroanffine, m-nitroaniline, and other amines having similar basicity, can be diazotized similarly, varying the amount of water used to suit the solubility of the particular amine.
3. 2,5-Dichloroaniline. A mixture of 16.2 grams (0.1 mole) of 2,5- dichloroaniline, 50 cc. concentrated hydrochloric acid, and 200 cc. water is boiled in a 1-liter round-bottomed flask until solution is complete (except for possible impurities in the amine). The solution is cooled under a water tap with vigorous shaking to obtain a finely divided precipitate of the amine hydrochloride. 100 grams of ice is added and then 100 cc. 1 N nitrite solution is added slowly with continuous shaking. Shaking is continued until all of the precipitate has gone into solution, and the usual tests with Congo red and starch-iodide are made. The solution is filtered if necessary.
Other dihalogenated bases are diazotized in the same manner.
4. Aceto-p-phenylenediamine. The hydrochloride of this base is quite insoluble, and heating with acids must be avoided because of the danger of hydrolysis. An attempt is not made, therefore, to obtain complete solution of the base, but the diazotization is carried out with a suspension of the finely divided hydrochloride.
15 grams (0.1 mole) of monoaceto-p-phenylenediamine is ground to a fine powder in a mortar, and 50 cc. 2 N hydrochloric acid is added gradually along with pieces of ice to prevent the mixture from becoming too warm. The mixture is ground to a uniform paste, then transferred to a filter flask, rinsing out the mortar with cold water. The filter flask is placed in an ice bath and more ice is added directly to the mixture, and then are added, successively, 75 cc. 2 N hydrochloric acid and 100 cc. 1 N nitrite solution, the latter addition being made dropwise with constant stirring. Stirring is continued until all of the material has gone into solution. A few larger lumps, which may remain undissolved, are removed by filtration.
5. Aminoazobenzene. Aminoazobenzene and many other amino — azo compounds are only slightly soluble even in hot, dilute hydrochloric acid. Again, no attempt is made to dissolve the base completely, and a procedure similar to example 4 is used except that it is not necessary to cool the mixture while the base is being ground with hydrochloric acid.
6. «-Naphthylamine. A mixture of 14.3 grams (0.1 mole) of a-naph — thylamine, 120 cc. water, and 10 cc. concentrated hydrochloric acid (preferably free from sulfuric acid) is placed in a 1-liter round-bottomed flask and heated until solution is complete. An additional 12 cc. concentrated hydrochloric acid is then added, and the solution is cooled to room temperature under the tap with vigorous stirring. The resulting thick paste is mixed with 200 grams of ice, and an amount of dry, powdered sodium nitrite, equivalent to 6.9 grams of pure NaN02, is added in one portion with stirring. The flask is then immediately closed with a rubber stopper and shaken vigorously until a nearly clear solution is formed. Any remaining lumps of a-naphthylamine hydrochloride are broken up with a glass rod and shaking is resumed until solution is complete. The diazotization should be complete in 10 to 15 minutes, giving a diazo solution reacting strongly acid to Congo red and giving a weak test with starch-iodide paper. The success of the reaction depends on quick addition of the nitrite and on obtaining rapid mixing. Under these conditions, the formation of aminoazonaphthalene is greatly reduced, but is not prevented entirely. The few dark colored flocks can be removed by filtration. The material filtered off should be in very small amount, and the filtrate should be light yellow in color and completely clear. Reappearance of cloudiness in the filtrate indicates that an insufficient amount of acid or of nitrite was used. If a considerable amount of a violet brown precipitate is formed in the diazotization, the experiment has failed and cannot be corrected.
The diazotization can be effected more easily and smoothly by using a larger amount of hydrochloric acid and also a small excess of nitrite, provided that these changes do not interfere in subsequent reactions of the diazo compound.
/J-Naphthylamine is diazotized in the same manner.
7. p-Nitroaniline. A mixture of 13.8 grams (0.1 mole) of p-nitro — aniline, 30 cc. water, and 30 cc. concentrated hydrochloric acid, is heated until solution is complete. The solution is cooled to room temperature with shaking under the tap, 80 grams of ice is added, and then an amount of dry, powdered sodium nitrite equivalent to 6.9 grams of pure NaNOL. is added in one portion with constant shaking. Shaking is continued until most of the precipitated material has redissolved, and the mixture is allowed to stand for about 10 minutes in ice and is then tested with Congo red paper and sulfone reagent. Any residual undissolved material is removed by filtration. The residue should be very small; the filtrate should be clear and almost colorless and no cloudiness should reappear. The final diazo solution is relatively stable in the dark but is very sensitive to light.
8. o-Nitroaniline. A solution is made by heating 13.8 grams (0.1 mole) of o-nitroaniline with 50 cc. concentrated hydrochloric acid. The hot solution is cooled to 30°C. with stirring, resulting in a thick, almost colorless paste of the hydrochloride. The paste is diluted with 100 cc. water, 100 grams of ice is added, and 20 cc. 5 N nitrite is dropped in with vigorous stirring. Stirring is continued, and more ice is added if necessary, until most of the material is in solution and all but a trace of the nitrite has been used. After filtration, the diazo solution is clear and almost colorless, and remains clear on standing.
9. 3-Nitro-4-toluidine. A mixture of 15.2 grams (0.1 mole) of 3- nitro-4-toluidine and 50 cc. concentrated hydrochloric acid is ground in a mortar and then allowed to stand until the orange yellow base is completely converted to the colorless hydrochloride — as shown by the absence of yellow specks on further grinding. Ice (100 grains) is added, and then 20 cc. 5 N nitrite solution is added slowly while stirring with the pestle. Most of the precipitate dissolves and any remaining lumps are broken up by continued grinding. The solution is finally filtered to remove residual undissolved material, yielding an almost colorless filtrate.
Alternatively, the procedure of example 10 may be followed after the nitro — toluidine is in the paste form.
10. 2-Nitro-4-chloroaniline. To a well-stirred mixture of 172.5 grams of a 10 per cent paste of 2-nitro-4-chloraniline, 30 cc. concentrated hydrochloric acid, and 100 grams of ice in a beaker, is added slowly 100 cc. 1 N nitrite solution. Stirring is continued and the mixture is kept cold until most all of the solid material has gone into solution and only traces of nitrite remain in the mixture. The diazo solution is then filtered to remove traces of undissolved material.
The isomeric nitrochloroanilines can also be diazotized in this way when they are available in paste form. If the bases are to be used in the dry state, the procedure of example 11 can be used. Alternatively, the base can be made into a paste by dissolving in about 10 parts of concentrated sulfuric acid, pouring the resulting solution, with stirring, onto ice, filtering off the precipitate, and washing it with cold water until it is free from sulfuric acid.
11. 2,4-Dinitroaniline. 80 grams of concentrated sulfuric acid in a small round-bottomed flask is cooled in ice, or better in a freezing mixture, and to it is added, slowly and with stirring, an amount of dry powdered sodium nitrite equivalent to 6.9 grams of pure NaN02. The temperature of the mixture is kept below 10°C. and precautions are taken that each portion of nitrite is immediately mixed into the acid and that no water gets into the mixture. No red fumes should be formed, and the solution should not become colored. Stirring is continued for about 10 minutes after all of the nitrite has been added, and then the flask is transferred to a water bath. When the temperature of the mixture has reached that of the water bath, very gradual heating is started and continued until the temperature has reached 70°. The mixture is then stirred at this temperature until all of the nitrite has dissolved. During these operations, care must be taken that the mixture never becomes appreciably hotter than the surrounding water bath, and at no time should fumes be generated or the solution become colored. When a clear solution is finally obtained, it is cooled in water or ice to about 20° (bisulfate separates), and 18.3 grams (0.1 mole) of pulverized 2,4- dinitroaniline is added in small portions. The mixture is stirred at room temperature until a test sample, diluted with ice, gives only a faint test
for nitrite. The reaction mixture is then poured onto 240 grams of ice (not morel), and the resulting solution is filtered to remove small amounts of undissolved material. The diazo solution should be used without delay.
When working with small amounts of material, it is convenient to use more sulfuric acid than specified above if it does not interfere with subsequent operations. When the diazotization mixture is diluted, sufficient ice is used to make the diluted mixture 25 per cent with respect to sulfuric acid. The more dilute the acid, the more rapid is the reaction in which the nitro group is replaced by hydroxyl.
The procedure given can be used for diazotizing all primary amines whose basicity is so low that they do dissolve in aqueous acids, such as the tri — and tetrahalogenanilines, dihalogennitroanilines, dinitroaniline, aminoanthraquinone, etc. If necessary, the amount of sulfuric acid can be increased in order to obtain complete solution. The sulfates of diazo- anthraquinones are very difficultly soluble in dilute sulfuric acid. Hence, they can be filtered off after pouring the concentrated sulfuric acid solution onto ice, and thus freed from most of the excess acid.
12. Sulfanilic Acid. A solution of 17.3 grams (0.1 mole) of sulfanilic acid in 50 cc. 2 N soda solution and 50 cc. water is mixed with 100 cc. 1N nitrite solution, and the resulting solution is added slowly with stirring to a mixture of 125 cc. 2 N hydrochloric acid and 100 grams of ice. A large part of the difficultly soluble diazo compound separates. If purity is a more important consideration than good yield, the diazo compound can be filtered off and mixed with a small amount of water for the coupling reaction.
The method given above is suitable for all aminosulfonic and carboxylic acids which are difficultly soluble in dilute hydrochloric acid. If the amino acid is very insoluble, the addition of its solution to the acid should be made very slowly ana with vigorous stirring. With some of the naphthylaminesulfonic acids which have a tendency to couple with themselves, it is desirable to add some of the nitrite to the hydrochloric acid before the amine is added. It is also advantageous to use an excess of nitrite in these cases, if it does not interfere in later steps or if it can be removed by filtering off the diazo compound.
13. l-Amino-2-naphthol-4-sulfonic Acid.81 To a mixture of 24 grams (0.1 mole) of finely powdered l-amino-2-naphthol-4 sulfonic acid in 100 cc. water and some ice, is added a concentrated aqueous solution of 2 grams of copper sulfate. The mixture is cooled in ice, and 20 cc. 5 N nitrite solution is added slowly with stirring. The amino — naphtholsulfonic acid goes into solution slowly to form a yellow colored solution from which a few coarse particles are removed by filtration.
si Geigy, Ger. Pat. 171,024 (1906) and 172,446 (1906) [Frdl, 8, 640, 646 (1905- 1907)1.
The filtrate is treated with 30 cc. concentrated hydrochloric acid which precipitates the diazo compound almost completely. The diazo compound is filtered off and washed with dilute hydrochloric acid. It is very stable and can be dried, without danger, to remove retained hydrochloric acid.
All other sulfonic acid derivatives of 1,2- and 2,1-aminonaphthols, as well as the unsubstituted 1,2- and 2,1-aminonaphthols (the latter in the form of their hydrochlorides), can be diazotized in this way. It is necessary to modify the conditions used in isolating the various diazo compounds because of their differing solubility properties. In cases where the free acid is too soluble, it can frequently be isolated satisfactorily as the barium salt.
The separation of the diazo compound can usually be eliminated altogether if the diazotization is carried out in the presence of zinc sulfate[50] instead of copper sulfate.
14. p-Aminodiphenylamine. [51] A mixture of 23.3 grams (0.1 mole) of p-aminodiphenylamine sulfate and 30 cc. concentrated hydrochloric acid is ground in a mortar and rinsed with cold water into a beaker. Ice is added and 40 cc. 5 N nitrite solution is run in with thorough stirring. The mixture is stirred and kept cold until all of the nitrite has been consumed. In the reaction, the primary amino group is diazotized and the secondary amino group is nitrosated. After coupling, the nitroso group must be split off from the dye, usually by treatment with a mild reducing agent such as sodium bisulfite.
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