Replacement of diazonium

Aryl Halides from Diazonium Ion Intermediates. Replacement of diazonium groups by halides is a valuable alternative to direct halogenation for the preparation of aryl halides. Aryl bromides and chlorides are usually prepared by a reaction using the appropriate Cu(I) salt, which is known as the Sandmeyer reaction. Under the classic conditions, the diazonium salt is added to a hot acidic solution of the cuprous halide.99 The Sandmeyer reaction occurs by an oxidative addition reaction of the diazonium ion with Cu(I) and halide transfer from a Cu(III) intermediate. 

A useful addition to the roster of reducing agents capable of replacement of diazonium groups by hydrogen in good yields is sodium borohydride. It is applied to dry diazonium fluoroborates in suspension in methanol or in solution in dimethylformamide (equation 95). ... 

Examples of replacement of diazonium groups by hydrogen by means of various reducing agents are shown in Table 9. 

Table 9 Comparison of Various Methods of Replacement of Diazonium Group by Hydrogen...

I formula, but following a radical mechanism, is the Sand-ch replacement of diazonium groups by CN , Cl , Br or... 

Preparation by diazotization of 3-amino-4-hydroxy-acetophe-none and replacement of diazonium group by chlorine (Sandmeyer reaction) [1953,1999], (84%) [1953]. 

Replacement of diazonium groups by halide is a very valuable synthetic alternative to direct halogenation for preparation of aryl halides. There are three broad types of procedures decomposition of aryl diazonium-halide adducts with expulsion of nitrogen, copper-mediated redox processes, and thermal processes proceeding via aryl radicals. The first type of process is probably involved in the reaction of aryl diazonium salts with iodide ion. Smooth high-yield transformation takes place in the absence of any metal catalyst. The mechanism of the reaction... 

Among the indirect methods of preparing aromatic nitro compounds are the displacement of sulfonic acid groups with nitro groups and the replacement of diazonium groups. 

The direct replacement of the diazonium group by hydrogen. These methods are discussed further in Chapter VI. 

The name Sandmeyer reaction - is used for the replacement of the diazonium group in an arenediazonium compound by halide or pseudohalide, taking place in the presence of a metal salt. However this is not a strict definition, since the replacement of the diazonium group by iodide, which is possible without a metal catalyst, is also called a Sandmeyer reaction. 

Ciprofibrate (48), a more potent lipid-lowering agent clofibrate, is prepared from Simmons-Smith product by Sandmeyer replacement of the amino group by a hydroxyl via the diazonium salt. Phenol undergoes the Reimer-Thiemann like process common to these agents upon alkaline treatment with acetone and chloroform to complete the synthesis of ci profib-rate (48). 

Replacement of chlorine on the pendant benzoyl group by azide is apparently consistent with antiinflammatory activity. Acylation of indomethacin intermediate with p-nitrobenzoyl chloride leads to the corresponding amide (7). Saponification ( ) followed by reduction of the nitro group gives the amine 9. The diazonium salt (10) obtained on treatment with nitrous acid is then reacted with sodium azide there is thus obtained zidomethacin (11). 

H5C20 —C-S K+) to the diazonium salt solution. This leads to replacement of... 

The replacement of an electrofugic atom or group at a nucleophilic carbon atom by a diazonium ion is called an azo coupling reaction. By far the most important type of such reactions is that with aromatic coupling components, which was discovered by Griess in 1861 (see Sec. 1.1). It is a typical electrophilic aromatic substitution, called an arylazo-de-hydrogenation in the systematic IUPAC nomenclature (IUPAC 1989c, see Sec. 1.2). 

A novel result of azo coupling was observed by Bagal et al. (1992 a) when they reacted 4-phenylazophenol and its 2-methyl derivative with an excess of 4-nitroben-zenediazonium salt. They obtained a compound whose elemental analysis and H NMR, UV, and IR spectra are consistent with 4,4-bis(4 -nitrophenylazo)-cyclohexa-2,5-dienone (12.14). The replacement of an arylazo group by a more electrophilic diazonium ion had occasionally been observed before this, but the double azo coupling in the 4-position is new. 

Replacement of the Diazonium Group by Sulfur-Containing Groups... 

CINNOLINES AND QUINOXALINES Replacement of a methine in oxolinic acid (46) by nitrogen is apparently consistent with retention of antibacterial activity. One approach begins with reduction of nitroacetophenone 144 to afford the corresponding aminoketone (145). Treatment of this intermediate with nitrous acid leads to the diazonium salt the diazonium group condenses with the ketone methylene group (as its enol form) to lead to the cyclized product, cinnoline 147. Bromination proceeds at the position adjacent the enol grouping (148) ... 

Chlorobromobenzene has been prepared by the diazotiza-tion of o-bromoaniline followed by replacement of the diazonium group by chlorine 1 by the elimination of the amino group from 3-chloro-4-bromoaniline 2 by the chlorination of bromobenzene in the presence of thallous chloride,3 aluminum chloride,4 or ferric chloride 4 by the bromination of chlorobenzene without a catalyst6 or in the presence of aluminum,4 iron,4 or ferric bromide 6 by the diazotization of o-chloroaniline followed by replacement of the diazonium group with bromine 4,6 and from o-chlorophenylmercurie chloride by the action of bromine.7... 

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. 

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