Diazonium group

This elimination of the diazonium group is therefore a very valuable reaction, as it affords almost the only method by which nitro and primary amino groups directly attached to the benzene ring can be eliminated. 

The diazonium group may be replaced by hydrogen, thus effecting the removal of the primary amino group, deamination, by the following methods ... 

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

Amino groups in pyridazine A-oxides can be diazotized and the diazonium group further replaced by halogens, hydroxy group or hydrogen. So, 3-, 4-, 5- and 6-bromopyridazine 1-oxides can be prepared from the corresponding amino A-oxides. 

The substitution of fairly labile nucleophilic groups (halogen, methoxy group) in the 3- and 5-positions, and the noncatalytic substitution of the diazonium group at C-4, are to be considered as nucleophilic substitution reactions. As in the benzenoid series, these reactions are believed to proceed in the former case by the Sx2 mechanism and in the latter by the SnI mechanism. 

The noncatalytic substitution of a 4-diazonium group by nucleophiles, which has proved widely useful in this series, is probably an example of a unimolecular nucleophilic substitution. The first example... 

Most functional groups do not interfere with the diazotization reaction. Since aliphatic amines are stronger bases and therefore completely protonated at a pH < 3, it is possible that an aromatic amino group is converted into a diazonium group, while an aliphatic amino group present in the same substrate molecule is protected as ammonium ion and does not react. ... 

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. 

In a synthesis of minocycline, interesting use was made of a reductive alkylation of a nitro function, accompanied by loss of a diazonium group. The sequence provides a clever way of utilizing the unwanted 9-nitro isomer that arises from nitration of 6-demethyl-6-deoxytetracycline (//). When di-azotization was complete, urea and 40% aqueous formaldehyde were added, and the entire solution was mixed with 10% palladium-on-carbon and reduced under hydrogen. No further use of this combined reaction seems to have been made. 

The NH2 groups can be diazotized and reduced in the presence of thiosulphates and different metal ions. The effect of some metal ions, namely Fe ", Sn, Cu +, and Co on the graft yield of cotton modified with aryl diazonium groups via its reaction with 2,4-dichloro-6-(p-nitroaniline)-5-triazine in the presence of alkali and followed by reduction of nitro group was studied [4]. 

Some time ago Tedder (1957) recommended a process which he called direct introduction of the diazonium group , because it replaces the steps of nitration, reduction, and diazotization of an aromatic compound by a one-pot operation with three equivalents of a nitrosating reagent in acidic solution. The first step (Scheme 2-35) is a C-nitrosation and the following steps (Scheme 2-36) are the reduction of the nitroso-arene. 

The diazonium group can be replaced by a number of groups. Some of these are nucleophilic substitutions, with SnI mechanisms (p. 853), but others are free-radical reactions and are treated in Chapter 14. The solvent in all these reactions is usually... 

Reduction of the diazonium group (dediazoniation) provides an indirect method for... 

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

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. 

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) ... 

As noted above, a convenient pathway to cinno-lines consists of intramolecular condensation of a diazonium group with a ketonic methyl group, or alternately with a double bond. The analogous reaction with an amide nitrogen leads to 1,2,3-benzotriazines, such as 198. Reaction of isatoic anhydride with N-aminomorpholine affords the hydrazide 196 then, treatment with nitrous acid yields initially the diazonium salt (197). Under the reaction conditions... 

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... 

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