Sandmeyer studies

The following mechanism of the Sandmeyer reaction has been proposed as a result of a kinetic study, and incidentally accounts for the formation of the azu compounds as by-products. The catalyst is the CuCl ion produced in the dissolution of cuprous chloride in the chloride solution ... 

Kochi (1956a, 1956b) and Dickerman et al. (1958, 1959) studied the kinetics of the Meerwein reaction of arenediazonium salts with acrylonitrile, styrene, and other alkenes, based on initial studies on the Sandmeyer reaction. The reactions were found to be first-order in diazonium ion and in cuprous ion. The relative rates of the addition to four alkenes (acrylonitrile, styrene, methyl acrylate, and methyl methacrylate) vary by a factor of only 1.55 (Dickerman et al., 1959). This result indicates that the aryl radical has a low selectivity. The kinetic data are consistent with the mechanism of Schemes 10-52 to 10-56, 10-58 and 10-59. This mechanism was strongly corroborated by Galli s work on the Sandmeyer reaction more than twenty years later (1981-89). 

With the ArH ArTlX2 Arl reaction sequence available as a rapid and reliable probe for aromatic thallation, a detailed study was undertaken of the various factors affecting orientation in this electrophilic metallation process (153). The results, which are summarized below, demonstrate that aromatic thallation is subject to an almost unprecedented degree of orientation control coupled with the ease with which thallium can then be displaced by other substitutent groups (this aspect of the synthetic exploitation of aromatic thallation is discussed in detail below), the sequential processes of thallation followed by displacement represent a new and versatile method for aromatic substitution which both rivals and complements the classic Sandmeyer reaction. 

Low-temperature chlorination of dibenzothiophene with elemental chlorine produces a chlorine adduct at the sulfur atom which is readily decomposed to dibenzothiophene 5-oxide. However, nuclear chlorination of dibenzothiophene has still not been studied. 2-Chlorodibenzo-thiophene has been prepared by the Sandmeyer reaction on 2-amino-dibenzothiophene and this route has now been extended to give... 

Of these methods, that of Sandmeyer 2 using aniline, chloral hydrate, and hydroxylamine salts, seemed most promising and has been studied in detail. The present method differs from that described by Sandmeyer in the use of hydroxylamine hydrochloride instead of a crude solution of hydroxylamine sulfate, and in the use of sodium sulfate to salt out the isonitroso compound. 

Electrophilic substitution reactions of substituted 2,1-benziso-thiazoles have already been discussed. The only other functionally substituted compound so far studied in any detail is the 3-amino derivative (87). This compound is readily diazotized and the dia-zonium salt formed (88) couples with tertiary aromatic amines yielding azo dyes.117,119-121 The salt (88) also undergoes the usual Sandmeyer reactions, and other 3-substituted derivatives, such as the cyano compound (89) may be prepared.111 Acylation of the amine (87) yields diacyl derivatives which appear to possess the 3-acylimino structure (90).111... 

Hanson, P., Jones, J. R., Gilbert, B. C., Timms, A. W. Sandmeyer reactions. Part 1. A comparative study of the transfer of halide and water ligands from complexes of copper(ll) to aryl radicals. J, Chem. Soc., Perkin Trans. 21991,1009-1017. 

Table I, which summarizes our preliminary survey of the reaction process, clearly shows the similarity of the Sandmeyer and Gattermann reactions to the hypophosphite and phosphite reductions studied by Kormblum and indicates that substituent groups facilitate these reactions in the sequence p-NOi > p-Cl > H > p-MeO, which is that for electron withdrawal from the nitrogen center, i.e., exactly what would be expected of an electron transfer to aryl ...

Table II gives results to date of a more detailed study of the Sandmeyer reaction which we propose to amplify by further quantitative work, including molecular weight examination of the polymers. Already the following features of this work can be seen ...

Copper is commonly used as a catalyst for a variety of organic reactions applying organometallic intermediates (114,115, 148-150). These processes include the Ullmann reaction, the Sandmeyer reaction, the Meerwein reaction, the Click reaction, a variety of atom transfer processes including pol5maerizations, etc. Many of these processes involve radicals and redox processes initiated by the copper species. All these processes are usually carried out in aprotic solvents and are therefore beyond the scope of this review. However, the mechanism of some of them was studied in aqueous solutions with the hope to perform them in this medium and in order of determining their detailed mechanisms. 

To study the conformational changes of tryptophan synthase by N-NMR, indole enriched in A-15 was required. Phillips used a Sandmeyer isatin synthesis starting with A-15-labeled aniline (45) to prepare 46 in good yield... 

A -oxide which is easily reduced to codeine with sulphur dioxide [303]. The 0-methylation of certain Erythrina alkaloids has been carried out in a similar manner [304]. A -Oxidation has also been used to protect tertiary ring nitrogen atoms in heteroaromatic compounds. Protonation of the ring nitrogen atom in 4- (and 2-) aminopyridines renders their diazonium salts very susceptible to hydrolysis, thus they cannot be converted into cyanides by the Sandmeyer reaction. The corresponding TV-oxides may, however, be used in the normal way and the oxide function removed at a later stage, as in the sequence (63) (64) used by Berson and Cohen in studies on ipecac... 

During an unsuccessful attempt to prepare phenylacetylene (5) from diazobenzene (4), Sandmeyer discovered that chlorobenzene (6) could be efficiently prepared from 4 under these reaction conditions. While investigating the formation of this unexpected product, he discovered that the active reagent was cuprous chloride, formed in hydrochloric acid solution. He further postulated that this particular reaction was unique to cuprous chloride, since cupric and ferrous chloride did not exhibit a similar behavior. It would be many years, however, before a more complete understanding of this process could be secured. Sandmeyer s subsequent studies demonstrated that, when reacted with diazobenzene (4), cuprous bromide produced bromobenzene (8) and cuprous cyanide produced cyanobenzene (7). Strictly... 

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