Diazo tization

Equally, all the attempts of Haginiwa to diazotize 2-amino-4-methylselenazole led to complete decomposition. Later these investigations were taken up by Metzger and Bailly. They tried to prepare selenazoles unsubstituted in the 2-position by means of diazo-tization and a special Sandmeyer reaction. In spite of variations in the reaction conditions, they were not able to deaminate 2-amino-4-phenylselenazole by this method. 

An interesting rearrangement was found by Davies and Kirby (1967) in the diazo-tization of 7-amino-benzothiazole (6.68). As Scheme 6-45 shows, the diazonium ion formed initially rearranges under hydrolytic conditions into 7-amino-l,2,3-benzo-thiadiazole (6.69). 

Protoadamantanone has been prepared by the nitrous acid deamination of 2-amino-l-adamantanol (77%), by aprotic diazo-tization of endo-7-aminomethylbicyclo[3.3.1]nonan-3-one in benzene with an equivalent amount of acetic acid (67%), and by thermolysis of 1-adamantyl hypohalites followed by base-promoted cyclization of the resulting halo ketones (32-37%)." In spite of low and erratic yields, the last reaction sequence has provided the most convenient route to the protoadamantanes, since the other two approaches require lengthy syntheses of the starting materials. 

There are several methods for generation of benzyne in addition to base-catalyzed elimination of hydrogen halide from a halobenzene and some of these are more generally applicable for preparative work. Probably the most useful method is diazo-tization of o-aminobenzoic acids.127 Loss of nitrogen and carbon dioxide follows diazotization and generates benzyne. This method permits generation of benzyne in the presence of a number of molecules with which it can react. 

There are a number of important reactions in this category and all of them involve at least one heteroatom functioning as a nucleophile and another as an electrophile. Diazo-tization of a variety of ortho-substituted anilines for instance, followed by intramolecular nucleophilic trapping of the corresponding diazonium salts by either nitrogen or carbon nucleophiles, is the basis of a series of very important syntheses of 1,2,3-benzotriazine and cinnoline derivatives, and this general approach has been widely exploited for the preparation of polycyclic systems. Representative examples are given in equations (51)—(54). 

Guanyl azide is then isomerized to aminotetrazole (V) which undergoes diazo-tization and couples with aminoguanidine as stated above. 

Diazocompounds. A group of very reactive org compds, many of which are explosive, containing the bivalent radical -N N- or N N-. They are formed when nitrous acid acts at low temp on the salts of primary amines. The process of prepg diazocompds Is called diazo-tization and was discovered about I860 by P. Griess (Ref 4)... 

Iodo-3-nitrobenzoic acid has been prepared by the diazo-tization of 3-nitro-anthranilic acid.2... 

HO.C H,.N2) Cr207 N 12.2%, crysts, mp- expl ca 154° when dry and pure was prepd by diazo-tization of p-aminophenol followed by addn of a dichromate. It is fairly stable, but less so than the chromate obtd from p-phenylenediamine(Ref 2,pp 4-5). The same author prepd chromates of diazonium and nitrodiazonium derivatives of aniline, bromoaniline, chloroaniline, benzidine, p-phenylenediamine, etc and found them more or less expl when dry... 

In addition to conversion of existing amino groups to other amino groups, the amino groups also can be replaced by halogen or hydroxyl substituents by diazo-tization followed by the Sandmeyer reaction. 

Introduction of halogen yields dyes with especially valuable properties. A suitable diazo component is 4-amino-6-chlorobenzimidazole. The sequence of diazo-tization, coupling with aromatic amines, and quatemization gives colorants (e.g., 44) [36116-31-1] that confer fast orange and red shades to polyacrylonitrile [132],... 

Dibromo-4-chloroaniline 1,3-Dibromo-5-chlorobenzene HC1 should not be used in the diazo-tization. 168... 

Hydrogenation of the nitro derivative (134) (H, Pd/C) gave the amine (135), which after diazo-tization gave (136) and thermal decomposition followed by acid hydrolysis of (137) afforded the fluoro derivative (138) (Scheme 7) <87JHC55>. 

The driving force for this reaction is the formation of N2, an exceptionally stable molecule. The carbocations generated in this manner react like others we have seen by nucleophilic attack to give substitution, by proton loss to give elimination, and by rearrangement. Because of the many competing reaction pathways, alkanediazonium salts usually decompose to give complex mixtures of products. Therefore, the diazo-tization of primary alkylamines is not widely used for synthesis. 

The best general reagent for the reductive elimination of the diazonium group is hypophosphorus acid. Reduction proceeds readily at 0-5° with an aqueous solution of the reagent. The yields of hydrocarbons are in the range of 60-85%. Hydrochloric acid is recommended for the diazo-tization except in certain cases in which nuclear halogenation occurs as a side reaction when this acid is used. 

Problem 23.19 Suggest a reason for the use of excess mineral acid in the diazo-tization process. 

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