Replacement of the diazonium group

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. 

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

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. 

When a primary aromatic amine, dissolved or suspended in cold aqueous mineral acid, is treated with sodium nitrite, a dlazonlum salt is formed (Unit 13, Class XII). Mixing the solution of freshly prepared diazonium salt with cuprous chloride or cuprous bromide results in the replacement of the diazonium group by -Cl or -Br. 

Replacement of the diazonium group by iodine does not require the presence of cuprous halide and is done simply by shaking the diazonium salt with potassium iodide. 

Aryldiazonium salts, usually obtained from arylamines, undergo replacement of the diazonium group with a variety of nucleophiles to provide advantageous methods for producing aryl halides, cyanides, phenols and arenes by reductive removal of the diazo group. Coupling reaction of aryldiazonium salts with phenols or arylamines give rise to the formation of azo dyes. 

Aromatic diazonium compounds which are prepared readily by diazotization of primary amines can be converted either to their parent compounds by replacement of the diazonium group with hydrogen, or to hydrazines by reduction of the diazonium group. Both reactions are carried out at room temperature or below using reagents soluble in aqueous solutions, and usually give high yields. 

Bromotoluene has been obtained by the bromination of toluene with bromine in the presence of various catalysts 1 and with hypobromous acid.2 The best method for its preparation, however, is the diazotization of -toluidine followed by replacement of the diazonium group by bromine.3... 

Although sodium sulfite and stannous chloride are used with about equal frequency in this process, a preference for sodium sulfite is sometimes expressed.11 ul m Stannous chloride occasionally brings about dij-ect replacement of the diazonium group by hydrogen, but this is not a reliable reaction.113 7-461114... 

Iodophenol was first obtained as a by-product of the action of iodine on salicylic acid in alkaline solution or by heating iodo-salicylic acid.1 It has also been obtained by the action of iodine on phenol in alkaline solution2 or in the presence of mercuric oxide,3 or by the action of iodine monochloride.4 It is best prepared by the diazotization of -aminophenol and replacement of the diazonium group by iodine 5 although it has also been obtained from />-iodoaniline by diazotization and replacement of the diazonium group by hydroxyl.6... 

Replacement of the Diazonium Group by Hydroxide Hydrolysis Hydrolysis takes place when the acidic solution of an arenediazonium salt is warmed. The hydroxyl group of water replaces N2, forming a phenol. This is a useful laboratory synthesis of phenols because (unlike nucleophilic aromatic substitution) it does not require strong electron-withdrawing substituents or powerful bases and nucleophiles. 

Replacement of the Diazonium Group by Chloride, Bromide, and Cyanide The Sandmeyer Reaction Copper salts (cuprous salts) have a special affinity for diazonium salts. Cuprous chloride, cuprous bromide, and cuprous cyanide react with arenediazonium salts to give aryl chlorides, aryl bromides, and aryl cyanides. The use of cuprous salts to replace arenediazonium groups is called the Sandmeyer reaction. The Sandmeyer reaction (using cuprous cyanide) is also an excellent method for attaching another carbon substituent to an aromatic ring. 

Replacement of the Diazonium Group by Fluoride and Iodide When an arenediazonium salt is treated with fluoroboric acid (HBF4), the diazonium fluoroborate precipitates out of solution. If this precipitated salt is filtered and then heated, it decomposes to give the aryl fluoride. Although this reaction requires the isolation and heating of a potentially explosive diazonium salt, it may be carried out safely if it is done carefully with the proper equipment. There are few other methods for making aryl fluorides. 

Replacement of the diazonium group by a variety of other functional groups is facilitated by the presence of one of chemistry s best leaving groups, the nitrogen molecule. 

The replacement of the diazonium group by chlorine or bromine is accomplished using the Sandmeyer reaction Replacement with fluorine and iodine can be achieved by variations of this reaction. 

The replacement of the diazonium group by halogen constitutes an Important method for the preparation of aromatic halides, particularly when the assignment of the halogen to a definite position is desired. 

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