186
S. Mallakpour et al. / Chinese Chemical Letters 22 (2011) 185–188
Scheme 1. Structure of 3,5-diamino-N-(3,4-dihydroxyphenethyl)benzamide (3,5-DAB).
3,5-DAB was prepared from the reaction of 3,5-dinitrobenzoylchloride and 3-hydroxytryaminum chloride in N,N-
dimethylacetamide (DMAc) as a solvent in the presence of propylene oxide as an acid scavenger and then reduction in
hydrazine hydrate in the presence of palladium activated carbon.
The FT-IR spectrum of 3,5-DAB is shown in Fig. 1. This data showed peaks at 3410, 3326 and 3306 cmꢀ1 due to the
OH and NH stretching bonds. Peak at 3056 was assigned for aromatic C–H bonds and at 2933 related to the aliphatic
C–H stretching bond. Absorption band at 1643 cmꢀ1 was due to the carbonyl of amide group. The 1H NMR spectrum
of this compound demonstrated 10 peaks at about d 8.60 (s, 2H, –OH), 7.97(t, 1H, –NH–), 6.64 (d, 1H, Ar–H), 6.62 (d,
1H, Ar–H), 6.60 (d, 1H, Ar–H), 6.19 (d, 2H–Ar–H), 5.93 (d, 1H–Ar–H), 4.81 (s, 4H, –NH2), 3.30 (q, 2H–CH2), 2.59 (t,
2H–CH2). Therefore, the catechol-derivative with amide linkage and amine groups was successfully synthesized. This
compound was obtained in high yield (82%).
As the 3,5-DAB as a catechol-derivative is electrochemical active and insoluble in aqueous solutions, it can be
easily incorporated into the carbon paste without concern regarding its leaching from the electrode surface. For the
electrochemical investigation of 3,5-DAB we prepared a mixture of 4 mg of 3,5-DAB with 86 mg of graphite powder
and 10 mg of carbon nanotubes in a mortar and pestle. Then using a syringe, 0.88 g paraffin was added to the mixture
and was mixed well for 40 min until a uniformly wetted paste was obtained. The paste was then packed into a glass
tube. Electrical contact was made by pushing a copper wire down the glass tube into the back of the mixture. When
necessary, a new surface was obtained by pushing an excess of the paste out of the tube and polishing it on a weighing
paper. The unmodified carbon nanotubes paste electrode (CNPE) was prepared in the same way without adding 3,5-
DAB to the mixture to be used for comparison purposes.
The cyclic voltammogram of bare carbon nanotubes paste electrode in pure supporting electrolyte shows no anodic or
cathodic peaks (Fig. 2, curve a). But cyclic voltammogram of 3,5-DAB exhibits two anodic (Epa = 0.30 and 0.870 V)
peaks and a cathodic peak with Epc = ꢀ0.20 V vs. AgjAgClj KClsat (Fig. 2 curve b) related to hydroquinone/quinone
redox couple (Epa = 0.30, Epc = ꢀ0.20 V) with quasi-reversible behavior at a surface of carbon paste electrode. The
second oxidation peak is related to amine groups present in this compound that is irreversible. Also, the obtained result
shows that the redox process of 3,5-DAB to benzoquinone-derivative is dependent on the pH of aqueous solution.
Similarly, when we compared the oxidation of 3,5-DAB at the surface of carbon nanotubes paste electrode
(Fig. 2c), an enhancement of the anodic peak current was found to occur at 3,5-DAB-carbon nanotubes paste electrode
versus AgjAgCljKClsat. In other words, the data obtained clearly showed that the combination of carbon nanotubes and
the 3,5-DAB definitely improve the characteristics of the electrode for the oxidation of this matter.
Fig. 1. FT-IR spectrum of 3,5-DAB.