The electrochemical reduction of N-haloamides (ZCONRX) in acetonitrile involves two consecutive one-electron transfers and generates the amide anion. Attempts to trap the intermediate amidyl radical resulting from the first electron transfer were unsuccessful. In the case of the N-halo-N-hydroamides (R = H), the amide anion formed at the electrode abstracts a proton from an incoming N-halo-N-hydroamide molecule to give the parent amide and the conjugate base of the N-haloamide (father–son protonation). Thus, half of the N-halo-N-hydroamide reaching the electrode is reduced, the other half being converted to its conjugate base. In acetonitrile-LiClO4 (0.2 M) containing 0.2% water, the conjugate base is reducible and the polarograms therefore show two waves (irreversible and diffusion controlled) of equivalentintensities due respectively to the reduction of the N-halo-N-hydroamide and to the reduction of its conjugate base. In the case of the N-chloro-N-alkyl(aryl)amides (X = Cl, R = alkyl or aryl), the amide anion abstracts a proton from the medium to give the parent amide and anionic species that react with the starting N-chloroamide regenerating the amide anion. Hence, the coulometric results are low [Formula: see text] However, in the presence of acetic acid, the reduction consumes 2 F/mol as expected. The N-alkylamide anion has been trapped by N-alkylation and N-acylation. The voltammograms of N-chloro-N-alkyl(aryl)amides show multiple waves on mercury and platinum due to passivation–adsorption phenomena but a single wave on vitreous carbon.
在乙腈中,N-卤代酰胺(ZCONRX)的电化学还原包括两个连续的单电子转移,并生成酰胺负离子。试图捕获由第一个电子转移产生的中间酰基自由基的尝试未成功。在N-卤代-N-羟酰胺(R = H)的情况下,电极上形成的酰胺负离子从进入的N-卤代-N-羟酰胺分子中提取一个质子,从而形成母酰胺和N-卤代酰胺的共轭碱(父子质子化)。因此,达到电极的N-卤代-N-羟酰胺的一半被还原,另一半被转化为其共轭碱。在含0.2%水的乙腈-LiClO4(0.2 M)中,共轭碱可被还原,因此极谱图显示了两个波(不可逆和扩散控制),分别由于N-卤代-N-羟酰胺的还原和其共轭碱的还原而产生等强度。在N-氯代-N-烷基(芳基)酰胺(X = Cl,R = 烷基或芳基)的情况下,酰胺负离子从介质中提取一个质子,形成母酰胺和与起始N-氯代酰胺反应的阴离子物种,再生酰胺负离子。因此,库仑计量结果较低。然而,在存在乙酸的情况下,还原消耗2 F/mol,符合预期。N-烷基酰胺负离子已通过N-烷基化和N-酰化进行捕获。N-氯代-N-烷基(芳基)酰胺的伏安图在汞和铂上显示多个波,由于钝化-吸附现象,但在玻璃碳上只显示单个波。