Diazonium salts, aryl 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. 

Section 24.6 Table 24.3 listed the main industrial methods for the preparation of phenol. Laboratory syntheses of phenols are usually carried out by hydrolysis of aryl diazonium salts. 

The Leuckart Thiophenol Reaction allows the preparation of thiophenols and corresponding thioethers from anilines or their corresponding diazonium salts. The first step is the reaction of an aryl diazonium salt with a potassium alkyl xanthate to give an aryl xanthate, which affords an aryl mercaptan upon basic hydrolysis or an aryl thioether upon warming. 

Among the early synthetic works, we wish to mention here the synthesis of polyporic acid (3) [115] and thelephoric acid (82) [78]. As summarised in Scheme 3a, several terphenylquinones have been synthesized with moderate yields starting from 2,5-dichlorobenzoquinone by arylation with V-nitrosoacetanilides or diazonium salts and subsequent alkaline hydrolysis. This method allowed preparation of symmetrical and unsymmetrical terphenylquinones, this latters with low yields. 

A modification of this reaction involves conversion of the diazonium salt to the diazonium fluoroboride with fluoroboric acid. Treatment with glacial acetic acid then gives the aryl acetate, from which the free phenol is obtained by hydrolysis. ... 

Elimination of carbon dioxide from a carboxylic acid in the presence of a diazonium salt leads to an aryl hydrazone (Japp-Klingemann). Subsequent hydrolysis in the presence of pyruvic acid furnishes the carbonyl Compound, as illustrated by the preparation of 2- -butyrylpyridine (81%). ... 

The esters also react readily with aryl hydrazines to give aryl hydrazone derivatives. Examples of the latter were first synthesized (prior to the availability of tetraalkyl carbonylphosphonates) from tetraalkyl methylenebisphosphonates and aryl diazonium salts, analogously to the phosphonoglyoxylate hydrazone synthesis described in a previous section. First made as possible precursors in a ketone synthesis, several of these compounds, converted to free acid salts by treatment with BTMS followed by dicyclohexylamine in methanol, proved to have unexpected inhibitory activity vs the pyrophosphate-dependent phospho-fructokinase of the parasite T. gondii, which causes a potentially lethal opportunistic infection in immunocompromised persons such as AIDS patients [94]. In fact, the 2,4-dinitrophenylhydrazone of carbonylbisphosphonic acid (as the tetrasodium salt) dramatically abated toxoplasmosis lesions in infected human foreskin fibroblasts [94]. Animal toxicity in this compound, probably arising from in vivo hydrolysis to the highly toxic hydrazine, precluded its future development, but the result remains an interesting lead. 

The reagent reacts with a diazonium salt to form an oxime which on acid hydrolysis affords an aryl methyl ketone. ... 

Dutt-Wormall reaction. Preparation of dia-zoaminosulfinates by reaction of diazonium salts with aryl- or alkylsulfonamides followed by alkaline hydrolysis to the corresponding sulfinic acid of the sulfonamide and the azide. 

Only half-a-dozen of these compounds are known (Table XLI) and at least this number of methods of preparing them have been reported. Borsche and Manteuffel125 have found that 2-pyrazolin-4,5-diones are formed as the by-products when oc-ketoesters are treated with aryl-diazonium salts. The principal products are 4-arylazo-2-pyrazolin-5-ones. Nitric acid oxidation of 3-methyl-l-phenyl-2-pyrazolin-5-one forms the corresponding 4,5-dione.809 Wislicenus and Gtiz1842 heated 4 -bromo - 4 - nitro -1 - (4 - bromophenyl) - 3 - methyl - 2 -pyrazolin - 5 - one in water and obtained the analogous 4-oxo compound. Acid hydrolysis of rubazonic acids, which are 4-imino-2-pyrazolin-5-ones, leads to 2-pyrazolin-4,5-diones.424 809 Oxidation of 4,4 -bis(2-pyrazolin-5-ones) or of rubazonic acids with nitric acid809 forms the 4,5-diones. 

Diazonium compounds can be converted to phenols by hydrolysis, under conditions where formation of the aryl cation takes place (equation 20) . This reaction is usually accomplished synthetically by heating an aqueous solution of the diazonium salt . Some examples of this type of reaction are given in equations 21-26. 

Laboratory syntheses of phenols are usually carried out by hydrolysis of aryl diazonium salts. 

Examples of the three mechansims are, respectively (a) hydrolysis of aryl diazonium salts to phenols (b) reaction of aryl diazonium ions with Ns to give the aryl azides " and (c) the Sandmeyer reaction, involving cuprous chloride or bromide for synthesis of aryl halides. Specific synthetically important substitution processes are considered in the succeeding sections. 

Grignard reagents (aryl, vinyl, or alkyl) can be electrograted by oxidation on Si-H to give 5f-alkyl, vinyl, or aryl mnltilayers through the formation of radicals [420-421]. The films are therefore quite similar to those obtained from diazonium salts. The drawback of the method lies in the necessity to work under oxygen- and water-free conditions to prevent the oxidation of Si and the hydrolysis of the reagent. 

Ruff degnulation a method used to shorten an aldose by one carbon. Sandmeyer reaction the reaction of an aryl diazonium salt with a cuprous salt, saponification hydrolysis of an ester (such as a fat) under basic conditions, saturated hydrocarbon a hydrocarbon that is completely saturated (i.e., contains no double or triple bonds) with hydrogen. 

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