Diazonium salt, to phenol

Entries 7 and 8 illustrate conversion of diazonium salts to phenols. Entries 9 and 10 use the traditional conditions for the Sandmeyer reaction. Entry 11 is a Sandmeyer reaction under in situ diazotization conditions, whereas Entry 12 involves halogen atom transfer from solvent. Entry 13 is an example of formation of an aryl iodide. Entries 14 and 15 are Schiemann reactions. The reaction in Entry 16 was used to introduce a chlorine substituent on vancomycin. Of several procedures investigated, the CuCl-CuCl2 catalysis of chlorine atom transfer form CC14 proved to be the best. The diazonium salt was isolated as the tetrafluoroborate after in situ diazotization. Entries 17 and 18 show procedures for introducing cyano and azido groups, respectively. 

A secondary reaction yields at the same time phenol ether by the replacement of the diazonium group by alkoxyl. This is clearly analogous to the conversion of diazonium salts to phenols. 

Examples of the three mechanistic types are, respectively (a) hydrolysis of diazonium salts to phenols 82 (b) reaction with azide ion to form aryl azides 83 and (c) reaction with cuprous halides to form aryl chlorides or bromides.84 In the paragraphs which follow, these and other synthetically useful reactions of diazonium intermediates are considered. The reactions are organized on the basis of the group which 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 main uses for steam distillation are to separate a reaction product from a tarry reaction mixture and to separate compounds which for some special reason have a markedly different volatility with steam. For example, the conversion of diazonium salts to phenols and certain Friedel-Crafts reactions lead to tarry by-products which cannot be conveniently removed by distillation or recrystallization. In this case, steam distillation effects a separation of volatile from essentially nonvolatile material. 

Phenols. Cohen and co-workers have described complete details for conversion of diazonium salts to phenols by a redox procedure first published in 1967. The classical method involves thermal decomposition in a strongly acidic medium and involves a cationic intermediate. In the newer method the diazonium... 

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. 

Preparation of phenols Heating its aqueous acidic solution converts a diazonium salt to a phenol This IS the most general method for the synthesis of phenols... 

Coupling reactions with diazonium salts to yield intensely colored azo derivatives have often been used for the detection of phenols, primary aromatic amines and electron-rich heterocyclics. 

The hydrolytic action of alkalis on the thiophosphate insecticides, such as parathion, yields free phenols that then couple with the diazonium salt to yield azo dyes. 

The synthesized CPMV-alkyne 42 was subjected to the CuAAC reaction with 38. Due to the strong fluorescence of the cycloaddition product 43 as low as 0.5 nM, it could be detected without the interference of starting materials. TMV was initially subjected to an electrophilic substitution reaction at the ortho-position of the phenol ring of tyrosine-139 residues with diazonium salts to insert the alkyne functionality, giving derivative 44 [100]. The sequential CuAAC reaction was achieved with greatest efficiency yielding compound 45, and it was found that the TMV remained intact and stable throughout the reaction. 

A general method leads from the primary aromatic amines by way of the diazonium salts to the phenols (p. 282). 

The azo produets obtained have an extended conjugate system having both the aromatie rings joined through the -N=N- bond. These compormds are often coloured and are used as dyes. Benzene diazonium chloride reacts with phenol in which the phenol molecule at its para position is coupled with the diazonium salt to formp-hydroxyazobenzene. This type of reaction is known as coupling reaction. Similarly the reaction of diazonium salt with anUtne yields p-aminoazobenzene. This is an example of electrophilic substitution reaction. 

Using a diazonium salt to produce an ether and a phenol. 

Hydrazine reacts with phenol diazonium salts to give products presumed to be the hydrazine salts of a Tetrazenepbenol. Hydrazine dissolved in water is added to an alc-water... 

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. ... 

As we shall see, phenols can cou) with diazonium salts to form azo compounds (Sec. 23.17) the more acidic the solution, however, the more slowly this coupling occurs. To minimize coupling during the synthesis of a phenol, therefore —coupling, that is, between phenol that has been formed and diazonium ion that has not yet reacted—the diazoiuum sdukiM is added slowly to a large volume of boiling dilute sulfuric add. 

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