Reduction of aryl diazonium salts

Reduction of aryl diazonium salts Aryl diazonium tetrafluoroborates are reduced to arenes by thiophenol in 85-100% yield. Replacement by deuterium can be effected with CsH SD. 

The versatility of the method is founded on the possibility of grafting a variety of functionalised aryl groups. This allows the attachment of a wide spectrum of substances[60]. In 1992, a study by Delamar and co-workers [61] demonstrated that reduction of diazonium salts at carbon surfaces resulted in a strongly attached surface layer. They attributed this to covalent bond formation between the aryl radical and the carbon surface [61,62], One electron reduction of aryl diazonium salts at carbon electrodes leads to grafting of aryl groups to the surface. Acetonitrile is often used as the modification medium. Reduction of the diazonium salt can be achieved by cyclic voltammetry or controlled potential electrolysis. The coupling reaction is favored both by the adsorption of the diazonium prior to its reduction and by the relatively positive potential of the diazonium prior to its reduction[62],... 

The Pschorr reaction is the intramolecular coupling of arenes involving aryl radicals generated by the reduction of aryl diazonium salts [68]. The reaction was extensively studied during the last 100 years [69]. This Cu(I)-catalysed reaction proceeds via an aryl diazenyl radical intermediate (Scheme 45) [70]. Non-protic solvents from which competitive hydrogen abstraction is impossible, are to be preferred [71]. 

Ethanediol. See Ethylene glycol Ethanoic acid. See Acetic acid Ethanol, 128, 130, 580-581 acidity of, 135, 740-741 and benzaldehyde, acetal from, 669 biological oxidation of, 600—602 chemical shifts, 606 conversion to diethyl ether, 592 dehydration of, 182 dipole moment of, 130, 863 by fermentation, 580-581 hydrogen bonding in, 130-131 industrial preparation of, 223, 581 physical properties of, 130, 132-133, 580 reduction of aryl diazonium salts by, 894, 907... 

Silyl and stannyl hydrides effect high yield reduction of aryl diazonium salts, and are compatible with a wider range of solvents than is HaP02. NaH prepared situ has been found to be much more active than the commercial product. Using the more active NaH, hydrogenolysis of benzylic halides is possible. Sodium borohydride has been reported to reduce nitriles to amines if Raney nickel is used as catalyst. 

When Pschorr reported more than a century ago on the first intramolecular homolytic aromatic substitution [25], he showed that biaryls could be readily prepared by intramolecular homolytic aromatic substitution using reactive aryl radicals and arenes as radical acceptors. The aryl radicals were generated by treatment of arene-diazonium salts with copper(l) ions. Today, this reaction and related processes are referred to as Pschorr reactions. It was later found that radical biaryl synthesis could be conducted without copper salts by photochemical or thermal generation of the aryl radical from the corresponding diazonium salt [26], Moreover, the reduction of aryl diazonium salts offers another route to generate reactive aryl radicals. Hence, electrochemistry [27], titanium(lll) ions [28], Fe(II)-salts [29], tet-rathiafulvalene [30] and iodide [31] have each been used successfully for the reduction of diazonium salts to generate the corresponding aryl radicals [32]. As an example, the iodide-induced cycUzation of diazonium salt 6 to phenanthrene derivative 7 is presented in Scheme 13.3 [31]. For further information on the... 

Bahr, J.L, Yang, J., Kosynik, D.V., Bronikowski, M.J., Smalley, R.E.,andTour, J.M. (2001) Fimctionalization of carbon nanotubes by electrochemical reduction of aryl diazonium salts a bucky paper electrode. J. Am. Chem. Soc., 123, 6536-6542. 

Electrochemically assisted modification of carbon electrodes has been accomplished by oxidation of amines (80, 81) and arylacetates (82), reduction of aryl diazonium salts (83), and anodization (oxidation) in a solution with alcohols (75). Of these schemes, reduction of diazonium salts, shown in Figure 8.11, provides a particularly convenient pathway for carbon electrode modification. 

Girard, A., F. Geneste, N. Coulon, C. Cardinaud, and T. Mohammed-Brahim. SiGe derivatization by spontaneous reduction of aryl diazonium salts. Appl. Surf. Sci. 282, 2013 146-155. 

Delamar, M., G. Desarmot, O. Fagehaume, R. Hitmi, J. Pinson, and J.-M. Saveant. Modification of carbon fiber surfaces by electrochemical reduction of aryl diazonium salts Application to carbon epoxy composites. Carbon 35,1997 801—807. 

We have found that SWNTs can be functionalized by electrochemical reduction of aryl diazonium salts in their presence. Using this method, about 1 in 20 carbon atoms of the nanotube framework are reacted. We have also found that the SWNTs can be functionalized by direct treatment with aryl diazonium tetrafluoroborate salts in solution, or by in situ generation of the diazonium moiety using an alkyl nitrite reagent. These functional groups give us handles with which we can direct further, more selective derivatization (Figure 5.2) and we recently reviewed the area of covalent sidewall derivatization of SWNTs. 

A first sign of the formation of an organic layer on metallic surfaces by electrochemical reduction of aryl diazonium salts is the disappearance of the expected characteristic broad and irreversible cathodic wave observed by cyclic voltammetry upon an initial scan towards negative potentials. Such blocking effect of the electrochemical response was firstly pointed out by Parker and coworkers.The different steps that take place along the electrografting process were established later on 17,371 been demonstrated that the electron transfer concerted with the loss of... 

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