Halides Sandmeyer reaction

One cannot distinguish between the analogous copper intermediates involved in oxidative electron-transfer and ligand-transfer reactions. In each the ionization of the ligand to copper(II) has an important role in the formation of carbonium ion intermediates. A reaction analogous to the copper-catalyzed decomposition of peroxides is the copper-promoted decomposition of diazonium salts (178). The diazonium ion and copper(I) afford aryl radicals which can undergo ligand-transfer oxidation with copper(II) halides (Sandmeyer reaction) or add to olefins (Meerwein reaction). 

Introduction. The diazo group, N2X, is easily replaced by a number of other functional groups, such as OH, Cl, Br, I and CN. This affords a convenient method for the preparation of such derivatives as cannot be obtained by other methods except with great difficulty. The replacement of N2X by a halogen group is accomplished by heating the solution of diazonium salt with cuprous halide (Sandmeyer reaction) or with finely divided copper (Gatterman reaction). In the preparation of iodides the catalytic effect of copper is not required it is necessary only to pour the diazonium salt into a solution of potassium iodide and then to acidify the solution ... 

It is thought that the decomposition of aryldiazonium halides by copper salts, which gives aromatic halides (Sandmeyer reaction), proceeds via a free radical mechanism and that Cu—Ar intermediates arc probably not important. It is however proposed that copper-diazo intomediates such as Ar—N=N—Cu are formed [121]. These may be compared with the aryl-diazomolybdenum and tungsten complexes jr-C5H5M(CO)2N2Ar [122]. 

Gattermann s reaction A variation of the Sandmeyer reaction copper powder and hydrogen halide are allowed to react with the diazonium salt solution and halogen is introduced into the aromatic nucleus in place of an amino group. 

By the hydrolysis of nitriles. The nitriles may be easily prepared either from amines by the Sandmeyer reaction (Section IV,66) or by the action of cuprous cyanide upon aryl halides (compare Section IV,163). Benzyl cyanide... 

Chlorination of OCT with chlorine at 90°C in the presence of L-type 2eohtes as catalyst reportedly gives a 56% yield of 2,5-dichlorotoluene (79). Pure 2,5-dichlorotoluene is also available from the Sandmeyer reaction on 2-amino-5-chlorotoluene. 3,4-Dichlorotoluene (l,2-dichloro-4-methylben2ene) is formed in up to 40% yield in the chlorination of PCT cataly2ed by metal sulfides or metal halide—sulfur compound cocatalyst systems (80). 

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 similar vein, the amino group in sulfide 14 (obtained presumably by an aromatic displacement reaction) is first converted to the bromide by Sandmeyer reaction to give 25. Reduction of the nitro group (16) followed by cyclization gives the substituted phenothiazine. Alkylation with the familiar halide (3) affords dimethothiazine (18). ... 

Aryl chlorides and bromides are prepared by reaction of an arenediazonium salt with the corresponding copper(I) halide, CuX, a process called the Sandmeyer reaction. Aryl iodides can be prepared by direct reaction with Nal without using a copper(T) salt. Yields generally fall between 60 and 80%. 

Sandmeyer reaction (Section 24.8) The nucleophilic substitution reaction of an arenediazonium salt with a cuprous halide to yield an aryl halide. 

On the basis of these redox potentials it seems likely that direct electron release to the benzenediazonium ion takes place only with iodide. This corresponds well with experience in organic synthesis iodo-de-diazoniations are possible without catalysts, light, or other special procedures (Sec. 10.6). For bromo- and chloro-de-di-azoniations, catalysis by cuprous salts (Sandmeyer reaction, Sec. 10.5) is necessary. For fluorination the Balz-Schiemann reaction of arenediazonium tetrafluoroborates in the solid state (thermolysis) or in special solvents must be chosen (see Sec. 10.4). With astatide (211At-), the heaviest of the halide ions, Meyer et al. (1979) found higher yields for astato-de-diazoniation than for iodo-de-diazoniation, a result consistent with the position of At in the Periodic System. It has to be emphasized, however, that in investigations based on measuring yields of final products (Ar-Hal), the possibility that part of the yield may be due to heterolytic dediazoniation is very difficult to quantify. 

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. 

An alternative approach to developing new reagents for DNA cleavage was founded in the conversion of aryl diazonium salts to aryl halides by the well-known Sandmeyer reaction. The reaction (Eq. 1) is thought to proceed via aryl radicals [7]. These reactions are high yielding and catalytic with respect... 

For more than a century, stoichiometric methods were presumed in the preparation of benzonitriles in laboratory and industry. These particularly include the Rosenmund-von Braun reaction of aryl halides, the diazotization of anilines and subsequent Sandmeyer reaction, and the ammoxidation. Because of (over)stoichiometric amounts of metal waste, lack of functional group tolerance, and harsh reaction conditions, these methods do not meet the criteria of modern sustainable synthesis. 

While halogenation and Sandmeyer reactions are suitable for preparation of oxazolyl halides, benzoxazolyl halides with halogen on the benzene ring moiety may be synthesized via other approaches. For instance, 5-halobenzoxazoles were prepared by treating 4-halo-2-aminophenols with trimethyl orthoformate and concentrated aqueous HC1 [6]. 

Replacement by halide or cyanide ion The Cl , Br and CN nucleophiles can easily be Introduced in the benzene ring in the presence of Cu(I) ion. This reaction is called Sandmeyer reaction. 

The Sandmeyer reaction utilizes a diazonium salt to produce an aryl halide. The process begins by converting an amine to a diazonium salt. Decomposition of the diazonium salt in the presence of a copper halide places the halide ion into the position originally occupied by the amine. The most useful copper halides are CuCl and CuBr in addition, the copper pseudohalides, such as CuCN, also works by placing a nitrile in the position originally occupied by the amine. Figure 13-27 shows an example of the Sandmeyer reaction. 

This reaction is similar to the Sandmeyer reaction, but the halide source is potassium iodide (Kl). Figure 13-28 illustrates this reaction. 

Sandmeyer Reaction A reaction utilizing a diazonium salt to produce an ciryl halide. The process begins by converting an amine to a diazonium salt. 

Chloro- and bromo-l,3,4-thiadiazoles are usually prepared by nucleophilic processes, e.g., Sandmeyer reactions of diazonium salts [56CB1534 68AHC(9)165 86CHE1148], and reactions of thiadiazolinones with phosphorus halides [68AHC(9)165]. The halogeno derivatives are important... 

When citing the Sandmeyer reaction, organic chemistry textbooks frequently write the needed copperfl) halide as Cu CL, Cu.Br , etc Comment. 

Displacement reactions with nitrite ion do not work well with aryl halides. However, displacement of the diazonium group is a practical route to nitroarenes (the Sandmeyer reaction), as described in Section 23-10B ... 

One of the drawbacks of the Sandmeyer reaction is the number of competing side reactions leading to the formation of biaryls, azo compounds and phenols. A recent procedure to maximise the yield of aryl halide involves treatment of the arylamine with t-butyl nitrite and anhydrous copper(n) halide (the chloride or the bromide) in acetonitrile at 65 °C.28 The method is illustrated by the preparation of p-chloronitrobenzene (Expt 6.73) the overall reaction may be represented as ... 

A second method for preparing aryl halides is the Sandmeyer reaction. During a Sandmeyer reaction, a diazonium salt reacts with copper (I) bromide, copper (I) chloride, or potassium iodide to form the respective aryl halide. The diazonium salt is prepared from aniline by reaction with nitrous acid at cold temperatures. 

The Sandmeyer reaction requires the aromatic diazonium salt and cuprous halide (CuX). ... 

Although nitriles lack an acyl group, they are considered acid derivatives because they hydrolyze to carboxylic acids. Nitriles are frequently made from carboxylic acids (with the same number of carbons) by conversion to primary amides followed by dehydration. They are also made from primary alkyl halides and tosylates (adding one carbon) by nucleophilic substitution with cyanide ion. Aryl cyanides can be made by the Sandmeyer reaction of an aryldiazonium salt with cuprous cyanide. a-Hydroxynitriles (cyanohydrins) are made by the reaction of ketones and aldehydes with HCN. 

Sec. 16.1, 16.2) from anenes by electrophilic aromatic substitution with halogen (Sec. 24.8) from arenediazonium salts by reaction with cuprous halides (Sandmeyer... 

The mechanism of the Sandmeyer reaction involves the transfer of electron from Cu" " to diazonium salt. Elimination of nitrogen generates aryl free radical, which reacts with CuXCl to give aryl halide via either path a or path b (Scheme 2.33). 

In the Sandmeyer reaction, the cold diazonium salt solution is run into a solution of the copper(I) halide dissolved in the halogen acid. The complex, which usually separates, is decomposed to the aryl halide by heating the reaction mixture. The mechanism (Scheme 8.16) involves generation of an aryl radical by electron transfer from Cu(I), which then reacts with the halide ion. 

---