With nitrous acid

Usually prepared from the corresponding sulphonic acids by alkali fusion, methylation of phenol or from the aminotoluene by treatment with nitrous acid followed by boiling. Both o- and p-cresol are used as end components in azo dyes. 

With nitrous acid it gives l-nitroso-2-naph-thol. It can also be chlorinated and sulphonated. Oxidized ultimately to phthalic acid on prolonged oxidation. 

CH,),CHNO, -h HONO = (CH,),C(NO)NO, -h H,0 producing a blue solution. A tertiary nitro paraffin such as trimethylnitro-methane, (CH )jCNO, gives no reaction with nitrous acid. 

Aromatic primary amines differ markedly from aliphatic amines in their reaction with nitrous acid. Thus a cold aqueous solution of mono thylamine hydrochloride reacts with nitrous acid to give mainly the corresponding primary alcohol ... 

Secondary amines of both the aliphatic and the aromatic series react similarly with nitrous acid, giving nilrosamines ... 

If, however, a tertiary amine has two alkyl groups and also an aryl group having the para position unsubstituted, then the action of nitrous acid is to insert the nitroso group directly into this para position. Dimethylaniline, for example, when treated with nitrous acid readily gives p-nitrosodimethyl-... 

Tertiary amines containing one alkyl and two aryl groups, such as mono-I ncthyldiphenyhiniir.e, Cl l3(C, l l.diX , arc rarely encountered and arc unimportant. They usually react with nitrous acid with the insertion of a nitroso group into only one of the two available para positions monomethyl-diphenylamine thus gives monomethyl-mono - pnitroso-diphenylamine. Cl hj(C.ill .)N C l 1 jXO, or V-nicthyl-p-nitrosodiphcnylaniine. 

In addition to General Reactions i and 2, all amides react with nitrous acid evolving nitrogen ... 

Members of Class (ii) give bright green />-nitroso derivatives with nitrous acid (p. 204). 

React with nitrous acid to give nitrogen and the corresponding hydroxy-carboxylic acid. 

Another important method of following protein hydrolysis is that due to Van Slyke, and consists in estimating the free amino groups liberated by treatment with nitrous acid, whereby gaseous nitrogen is evolved and measured in a special apparatus. 

Secondary amines upon treatment with nitrous acid yield nitrosamiues, which are stable, neutral yellow liquids (or low melting point solids), for example ... 

They are readily hydrolysed by boiling dilute hydrochloric acid and the original amine can be recovered by neutralisation with alkali and steam distillation. Primary aliphatic amines liberate nitrogen with nitrous acid whilst tertiary amines are unaffected. 

Secondary and tertiary amines are not generally prepared in the laboratory. On the technical scale methylaniline is prepared by heating a mixture of aniline hydrochloride (55 parts) and methyl alcohol (16 parts) at 120° in an autoclave. For dimethylaniline, aniline and methyl alcohol are mixed in the proportion of 80 78, 8 parts of concentrated sulphuric acid are added and the mixture heated in an autoclave at 230-235° and a pressure of 25-30 atmospheres. Ethyl- and diethyl-anihne are prepared similarly. One method of isolating pure methyl- or ethyl-aniline from the commercial product consists in converting it into the Y-nitroso derivative with nitrous acid, followed by reduction of the nitroso compound with tin and hydrochloric acid ... 

Tertiary aliphatic - aromatic amines, unlike those of the aliphatic series, react with nitrous acid with the formation of G-nitroso compounds the nitroso group enters almost exclusively in the para position if available, otherwise in the ortho position. Thus dimethylaniline yields />-nitrosodiniethylaniline ... 

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 acetylmethylurea is converted by concentrated hydrochloric acid into methylurea the latter yields nitrosomethylurea with nitrous acid ... 

An alternative method of preparation involves the interaction of methylamine hydrochloride with urea to give methylurea, followed by interaction with nitrous acid as above ... 

Treatment of the sulphonylmethylamide with nitrous acid gives p-tolylsul-phonylmethylnitrosamide ... 

Butler recently reviewed the diazotization of heterocyclic amines (317). Reactions with nitrous acid yield in most cases N-exocyclic compounds. Since tertiary amines are usually regarded as inen to nitrosation, this... 

Nitrosation of amines is best illustrated by examining what happens when a sec ondary amine reacts with nitrous acid The amine acts as a nucleophile attacking the nitrogen of nitrosyl cation The intermediate that is formed m the first step loses a pro ton to give an N nitroso amine as the isolated product... 

Figure 22 5 shows what happens when a typical primary alkylamine reacts with nitrous acid Because nitrogen free products result from the formation and decomposition of diazonium ions these reactions are often referred to as deamination reactions Alkyl... 

FIGURE 22 5 The diazo mum ion generated by treatment of a primary al kylamine with nitrous acid loses nitrogen to give a car bocation The isolated prod ucts are derived from the carbocation and include in this example alkenes (by loss of a proton) and an al cohol (nucleophilic capture by water)... 

A Alkylarylammes resemble secondary alkylammes m that they form A nitroso compounds on reaction with nitrous acid... 

Treatment of adenosine with nitrous acid gives a nucleoside known as mosine Suggest a reasonable mechanism for this reaction... 

R—N=N Aryl diazonium 10ns are formed by treatment of primary aromatic amines with nitrous acid They are ex tremely useful in the preparation of aryl halides phenols and aryl cyanides... 

Nitrosation (Section 22 15) The reaction of a substance usu ally an amine with nitrous acid Pnmary amines yield dia zonium 10ns secondary amines yield N nitroso amines Tertiary aromatic amines undergo nitrosation of their aro matic ring... 

A photochemical partial synthesis of aldosterone (19) made the hormone available on an industrial scale for the first time (114). Corticosterone acetate (51 acetate) is treated with nitrosyl chloride in pyridine at 20°C to yield the 11-nitrite (115). Irradiation of (115) leads to rearrangement with formation of the C g-oxime (116). Removal of the oxime residue with nitrous acid furnishes aldosterone (19) in excellent yield. 

Sulfonic acid hydrazides, RSO2NHNH2, are prepared by the reaction of hydraziae and sulfonyl haUdes, generally the chloride RSO2CI. Some of these have commercial appHcations as blowiag agents. As is typical of hydrazides generally, these compounds react with nitrous acid to form azides (26), which decompose thermally to the very reactive, electron-deficient nitrenes (27). The chemistry of sulfonic acid hydrazides and their azides has been reviewed (87). 

Reaction with nitrous acid can be used to differentiate primary, secondary, and tertiary mononitroparaffins. Primary nitroparaffins give nitrolic acids, which dissolve in alkali to form bright red salts. 

Secondary nitroparaffins give alkali-insoluble nitroso derivatives known as pseudonitroles. As monomers in the hquid state, pseudonitroles have a characteristic blue color as sohds they exist as white crystalline dimers. Tertiary nitroparaffins do not react with nitrous acid and no color develops. 

Triaitrosophlorogluciaol is obtained by reaction of phlorogluciaol with nitrous acid in acetic acid (135). 

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