Additions nitrosylsulfuric acid

Amines which are considerably or entirely insoluble in water are dissolved in glacial acetic acid or in other organic media, possibly mixed with water e.g., alcohols or aprotic solvents. Addition of acid is followed by a typical diazotization reaction in an aqueous sodium nitrite solution. Other possible sources of the nitrosating species NO include nitrosylsulfuric acid, nitrosylchloride, alkylnitrite, and nitrous gases. 

The rates of diazotizations in nitrosylsulfuric acid can be increased favorably by the addition of acetic or propionic acid. A mixture of the two acids is frequently used as an additive in diazotizations of heteroaromatic amines, as it has a lower melting point than acetic acid (0 °C or lower), but little is mentioned about it in the scientific literature... 

In making disperse azo dyes, nitrosylsulfuric acid is produced by the addition of sodium nitrite, NaN02, to concentrated sulfuric acid (Ig NaN02 per 13 g H2SO4)... 

It is necessary to carry out the preparation under a hood. About 200 ml. of fuming nitric acidt (sp. gr. 1.60) contained in a 350-ml. tube (test-tube shape) is cooled with ice and salt, and sulfur dioxide is passed into it fairly rapidly. The reaction is exothermic, and the rate of addition should be such that the temperature of the solution does not rise above 5°C. In 6 or 8 hours, the crystals of nitrosylsulfuric acid fill the space of the original liquid, forming a compact mass with a layer of dark fuming liquid 2 to 3 cm. 

This is prepared on an enormous scale by the lead chamber and contact processes. In the former, S02 oxidation is catalyzed by oxides of nitrogen (by intermediate formation of nitrosylsulfuric acid, H0S020N0) in the latter, heterogeneous catalysts such as Pt are used for the oxidation. Pure H2S04 is a colorless liquid that is obtained from the commercial 98% acid by addition first of S03 or oleum and then titration with water until the correct specific conductance or melting point is achieved. 

Dicyanoaniline (31.4 g) was treated with nitrosylsulfuric acid (72 g) at 0°C to 5°C in 300 ml of 50% aqueous sulfuric acid, and the batch was stirred for 1 hour. This mixture was then slowly poured into a solution of aniline (20.4 g) and urea (4.5 g) dissolved in 300 ml of 50% aqueous sulfuric acid and then stirred for an additional hour at 0°C to 5°C. Thereafter the reaction mixture pH was raised to 5.5 with sodium carbonate. A precipitate formed that was filtered off under suction, washed with water, and dried 34 g of product were isolated. This material was used in the next step without further purification. 

The synthesis of diazonium salts of less basic amines does not proceed satisfactorily under the above conditions because of the reduced nucleophilic nature of the amino group and the reaction is usually carried out in concentrated sulfuric acid. The addition of sodium nitrite to concentrated sulfuric acid produces the stable nitrosylsulfuric acid, (NOHSO ). Diazotization of the most weakly basic amines is carried out using nitrosylsulfuric acid in a mixture of one part of propionic acid in five parts of acetic acid at 0-5 °C. The propionic acid prevents the mixture from freezing. 

Picramide is diazotized by treating a solution of the amine in (glacial acetic acid with nitrosylsulfuric add (prepared by dissolving sodium nitrite in concentrated sulfuric add).61 Addition of ice-cold water to the diazonium solution results in immediate decomposition of the diazonium salt.61-62- /... 

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