Diazonium salt hydrolysis

Nitriles of the aromatic acids may be obtained fiom the sulfonic acids or from diazonium salts. Hydrolysis of the nitrile produces the carboxylic acid ... 

The amines are comparatively weak bases, so that a certain amount of free amine will be produced by salt hydrolysis unless an excess of acid is present. The reaction mixture must be kept very cold during the process (which is exothermic in character), otherwise the diazonium salt may be partially converted into the corresponding hydroxy compound ... 

Decomposition of diazonium salts obtained from 2-aminothiazole (4) (29, 34. 35) could be an interesting reaction to introduce O in A-4-thiazoline-2-one. Acidic hydrolvsis of ethers (36. 37). oxidative hydrolysis... 

By the alkaline hydrolysis of the sultone formed on boiling an aqueous solution of the diazonium salt of S-amino-l-naphthalenesulfonic acid or its appropriate derivatives. 

An increased hydrogen ion concentration, that is a considerably greater amount of acid than the theoretical two equivalents of Scheme 2-1, is necessary in the diazotization of weakly basic amines. The classic example of this is the preparation of 4-nitrobenzenediazonium ions 4-nitroaniline is dissolved in hot 5-10 m HC1 to convert it into the anilinium ion and the solution is either cooled quickly or poured onto ice. In this way the anilinium chloride is precipitated before hydrolysis to the base can occur. On immediate addition of nitrite, smooth diazotization can be obtained. The diazonium salt solution formed should be practically clear and should not become cloudy on standing in the dark. Some practice is necessary, and details can be found in the books emphasizing preparative aspects (Fierz-David and Blangey, 1952 Saunders and Allen, 1985 in Houben-Weyl, Vol. E 16a, Part II, the chapter written by Engel, 1990). These books give a series of detailed prescriptions for specific examples and a useful review of the principal variations of the methods of diazotization. Such reviews have also been written by Putter (1965) and Schank (1975). 

P-coupling occurs in the formation of azophosphonic esters [ArN2PO(OCH3)2] from diazonium salts and dimethyl phosphite [HPO(OCH3)2] (Suckfull and Hau-brich, 1958). P-coupled intermediates are formed in the reaction between diazonium salts and tertiary phosphines, studied by Horner and Stohr (1953), and by Horner and Hoffmann (1956). The P-azo compound is hydrolyzed to triphenylphosphine oxide, but if a second equivalent of the tertiary phosphine is available, phenyl-hydrazine is finally obtained along with the phosphine oxide (Scheme 6-26 Horner and Hoffmann, 1958). It is likely that an aryldiazene (ArN = NH) is an intermediate in the hydrolysis step of the P-azo compounds. 

The initial product is a salt of hydrazinesulfonic acid, which is converted to the hydrazine by acid treatment. Diazonium salts can also be reduced to arenes (14-24). N-Nitrosoamines can be denitrosated to secondary amines by a number of reducing agents, including H2 and a catalyst, BF3—THF—NaHC03, and NaBH4— TiCU, as well as by hydrolysis. ... 

Reaction of diazonium salts with oximes, followed by hydrolysis... 

Examples of the three mechanistic types are, respectively (a) hydrolysis of diazonium salts to phenols89 (b) reaction with azide ion to form aryl azides90 and (c) reaction with cuprous halides to form aryl chlorides or bromides.91 In the paragraphs that follow, these and other synthetically useful reactions of diazonium intermediates are considered. The reactions are organized on the basis of the group that is introduced, rather than on the mechanism involved. It will be seen that the reactions that are discussed fall into one of the three general mechanistic types. 

The phthalide 25, obtainable by condensation of 4,4 -bisdimethyl-aminobenzophenone-2-carboxylic acid with 3-dimethylaminoacetanilide and subsequent hydrolysis, was diazotized in sulfuric acid and the resultant diazonium salt treated with copper powder to yield 26. However, better yields are reportedly obtained by carrying out ring closure of the diazonium salt in phosphoric acid.103 A further synthetic route has also been described in which phthalides undergo intramolecular cyclization in the presence of aluminum chloride and urea.104,105 Thus, Crystal Violet lactone (2) has been directly converted into phthalide 26.106... 

Diazonium salts react with bis(methylsulfonyl) methane (107) (X = S02CH3) to yield a 1,3-diaryl tetrazolinone (111). The reaction proceeds through an azo (108) and a tetrazene (109) intermediate, followed by hydrolysis under the alkaline conditions of the reaction to the carbonyl compound (110). An unexplained oxidation leads to the 1,3-diaryl tetrazolinone (111) either directly or through the intermediate 110a (Scheme 15).18,35 A similar reaction occurs between a diazonium salt and the potassium salt of phenyl hydrazonomethane disulfonic acid (Scheme 15).175... 

It is synthesized by reaction of the diazonium salt from amine 1 with potassium ethyl xanthate, followed by alkaline hydrolysis to afford thiophenol 2. 

The triazinedione, triazuril (163) is active as a poultry coccidiostat. Diazonium salt 160, prepared from the appropriate aniline, is coupled with the active methylene group of N-carbethoxycyanoacetamide to give 161. Hydrolysis of the cyano group is accompanied by cyclization, and the resulting acid (162) is decarboxylated to triazuril (163) on heating.50... 

DTA examination of a 35% solution of the diazonium salt in sulfuric acid showed 3 exotherms, corresponding to hydrolysis of the nitrile group (peak at 95°), decomposition of the diazonium salt (peak at 160°) and loss of the nitro group (large peak at 240°C). Adiabatic decomposition of the solution from 50°C also showed 3 steps, with induction periods of around 30, 340 and 380 min, respectively. 

The synthetic route to tetrachlorothioindigo may serve as an example for an industrial scale synthesis. Starting material is 2,5-dichlorothiophenol, which is obtained by reduction of 2,5-dichlorobenzene sulfochloride or by reaction of the 2,5-dichlorobenzene diazonium salt with potassium-o-ethyldithiocarbonate and hydrolysis or with disodium sulfide and subsequent reduction ... 

The esters of nitrous acid are characterised by their high velocities of formation and hydrolysis. They are almost instantaneously decomposed by mineral acids and in the method of preparation given this has been taken into account. The slightest excess of hydrochloric acid must be avoided. Advantage is taken of this property of the alkyl nitrites in all cases where it is desired to liberate nitrous acid in organic solvents (in which metallic nitrites are insoluble). Examples addition of N203 to olefines, preparation of solid diazonium salts (p. 286), production of isonitroso-derivatives from ketones by the action of HN02. This synthesis is often also carried out in the manner of the acetoacetic ester synthesis, with ketone, alkyl nitrite, and sodium ethylate the sodium salt of the isonitrosoketone is formed (cf. in this connexion p. 259) ... 

It cannot be decided with certainty whether in this case the diazonium salt itself couples or whether, more probably, we must assume a partial hydrolysis to diazohydroxide and acid in the feebly acid solution. Our deductions will be based on the second explanation. 

Phthalylsulphathiazole undergoes hydrolysis to give phthalic acid and sulphathizole. The latter reacts with nitrous acid to yield the corresponding diazonium salt quantitatively. 

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