Synthesis Of Organic Electrocatalyst And Their Electrocatalytic Oxidation Of C-H Bonds And Alcohols

The electro-catalytic oxidation of small organic molecules is an important research area in the field of catalysis.Selective oxidation of C-H bonds and alcohols to the corresponding aldehydes and ketones is of great significance in the synthesis of fine chemicals and organic intermediates.Organic electro-catalysis is recognized as an environmentally compatible methodology because it avoids using toxic and dangerous redox,and most of the reactions can be carried out under mild conditions.However,in direct electro-oxidation synthesis,the working electrode is easily passivated by the formation of a polymer film on the electrode surface,which can sharply decrease the current efficiency.Indirect electro-oxidation with an electron transfer mediator is a good way to avoid the passivation of the electrode and also can control the over oxidation of the target product.Triarylamines have received extensive attention from researchers as a new type of electro-redox mediator because of their broad range of redox potentials.The oxidation potential of triarylamines can become positive after introducing an electron-withdrawing group.Therefore,in this paper,a series of nitro-containing organic electro-catalysts were synthesized by introducing the nitro group with strong electron-withdrawing properties,and their electro-catalytic activity on the electro-oxidation of C-H bonds were studied.First,the imidazole,triphenylamines and carbazoles framework compounds with different substituents were synthesized and characterized through H¹ NMR.Their electrochemical performance as organic electro-catalysts were studied by cyclic voltammetry.The electrochemical reversibility and redox potential of the compounds were greatly affected by their substituents.The redox potential of the compound with electron-donating group was negative,while the redox potential of the compound with electron-withdrawing group was positive.The electro-catalytic activity of triphenylamines and carbazoles framework compounds for the electrochemical oxidation of C-H bonds and alcohols were studied at room temperature by constant potential electrolysis.The electrolysis results showed that the appropriate amount of water could greatly promote the transformation of the C-H bond to carbonyl group.When the triphenylamines(T_3b)was used as electro-catalyst,the yield of p-methoxybenzaldehyde?p-MBA?was up to 83%on the electro-oxidation of p-methoxy toluene?p-MT?under the condition of 10%water added at 1.2 V;the yield of p-MBA was 90%on the on the electro-oxidation of p-methoxybenzyl alcohol?p-MBzOH?under anhydrous conditions at 1.3V.When the carbazoles(C_3c)was used as electro-catalyst,the yield of p-MBA was 69%on the electro-oxidation of p-MT under the condition of 10%water added at 1.28V;and the p-MBzOH could be totally transformed to the corresponding aldehyde under anhydrous conditions.