Aryldiazonium salt nucleophilic substitution reaction

Fig. 5.56. Nucleophilic substitution reactions on a masked aryldiazonium salt. The introduction of fluorine takes place by the SN1 mechanism in Figure 5.50, the introduction of iodine occurs by the radical mechanism of Figure 5.56.

Fig. 5.46. Nucleophilic substitution reactions on a masked aryldiazonium salt.

Fig. 5.53. Mechanistic aspects I of nucleophilic aromatic substitution reactions of aryldiazonium salts via radicals introduction of Nu=Cl, Br, CN or N02 according to Figure 5.52. Following step 2 there are two alternatives either the copper(II) salt is bound to the aryl radical (step 3) and the compound Ar-Cu(III)NuX decomposes to Cu(I)X and the substitution product Ar-Nu (step 4), or the aryl radical reacts with the cop-per(II) salt in a one-step radical substitution reaction yielding Cu(I)X and the substitution product Ar-Nu.

Fig. 5.55. Mechanistic aspects III of nucleophilic aromatic substitution reactions of aryldiazonium salts via radicals introduction of Nu = I through reaction of aryldiazonium salts with KI. In this (chain) reaction the radical I2 —apart from its role as chain-carrying radical—plays the important role of initiating radical. The scheme shows how this radical is regenerated the initial reaction by which it presumably forms remains to be provided, namely (1) Ar-N =N + I -> Ar- N=N + h ...

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. 

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