J. Chem. Sci.
(2019) 131:68
Page 3 of 9
68
fresh ABTS solution for each assay. 100 μL of the solutions (C–OH), 122.21 (Aromatic C–N); GCMS(m/z):
316.1(M·+)
(prepared in methanol) of each compound, as well as trolox
(used as a standard) at four different concentrations (2, 4, 6, 8
10 mmol/L of methanol), were allowed to react with 2.5 mL of
the ABTS solution. The absorbance was observed at 734 nm
Schiff Base 2:
FT-IR (KBr, cm−1): 3209.69 (Phenolic OH), 3039.94
(Aromatic C–H), 1607.74 (Aromatic C=N), 1514.19–
1457.28 (Aromatic C=C); 1H NMR DMSO-d6; δ, ppm):
8.18 (singlet, N=C–H), 5.42 (singlet, O–H), 7.66–6.61
(multiplet, Aromatic protons); 13CNMR (DMSO-d6; δ,
ppm): 161.02 (C=N), 160.19 (C–OH), 153.87 (aromatic
C–N); GCMS(m/z): 316.1(M·+)
after 6 min for each sample for each concentration.
The percentage inhibitions of the synthesized products
for both the methods were calculated using the following
formula-
% Inhibition = (AB − AS)/AB × 100
Where, AB is the absorbance of the ABTS/DPPH solution
without sample and AS is the absorbance of ABTS/ DPPH
solution with the sample. The percentage inhibition was plot-
ted against concentration and a straight line is obtained. From
this graph we have calculated the IC50 values of the Schiff
bases; that is, the amount of antioxidant Schiff bases neces-
sary to decrease the 50% of the initial ABTS or DPPH radical
concentration.
Schiff Base 3:
FT-IR (KBr, cm−1): 3229.04 (Phenolic OH), 3062.96
(Aromatic C–H), 1602.85 (Aromatic C=N), 1498.69–
1
1458.18 (Aromatic C=C); H NMR (DMSO-d6; δ,
ppm): 8.24 (singlet, N=C–H), 5.35(singlet, O–H), 7.76–
6.92 (multiplet, Aromatic protons); 13C NMR
(DMSO-d6; δ, ppm): 163.61 (C=N), 160.01 (C–OH),
142.59 (aromatic C–N); GCMS(m/z): 316.1(M·+)
Schiff Base 4:
FT-IR (KBr, cm−1): 3327.21 (Phenolic OH), 3024.38
(Aromatic C–H), 1603.05 (Aromatic C=N), 1504.48–
1435.04 (Aromatic C=C); 1HNMR (DMSO-d6; δ, ppm):
8.42 (singlet, N=C–H), 5.44 (singlet, O–H), 7.68–6.33
(multiplet, Aromatic protons); 13CNMR (DMSO-d6; δ,
ppm): 161.80(C=N), 158.19 (C–OH), 122.95 (Aromatic
C–N); GCMS(m/z): 316.1(M·+)
3. Results and Discussion
All the synthesized compounds were crystalline solids
and found to be soluble in methanol and insoluble in
dichloromethane. The reaction scheme, the time period
of reactions, their percentage yields and the name of the
synthesized products are mentioned in Table 1.
Schiff Base 5:
3.1 Characterization
FT-IR (KBr, cm−1): 3354.21 (Phenolic OH), 3076.48
(Aromatic C–H) 1600.92 (Aromatic C=N), 1500.62–
1486.38 (Aromatic C=C); 1HNMR (DMSO-d6; δ, ppm):
8.36 (singlet, N=C–H), 5.21(singlet, O–H), 7.58–6.69
(multiplet, Aromatic protons); 13CNMR (DMSO-d6; δ,
ppm):163.97(C=N), 157.66(C–OH), 153.97(Aromatic
C–N); GCMS(m/z): 316.1(M·+)
The FT-IR Spectra of all the compounds gave character-
istic bands for C=N stretching whereas the characteristic
bands for carbonyl group of the aldehydes and the pri-
mary amino groups present in the starting materials did
not occur in the IR spectra of each of the nine com-
pounds, giving rise to the inference that the substrates
were successfully converted into the desired di-Schiff
bases. No characteristic peaks were observed for pro-
tons of the aldehyde or the amino group in the 1H-NMR
spectra, which affirms the formation of the desired di-
schiff base products and also by the 13C-NMR spectra
of the compounds, the formation of imine bonds were
confirmed. In the GCMS analysis of the compounds, the
existence of molecular ion peak (M·+) with m/z value of
316.1 confirmed the formation of the desired products.
Schiff Base 6:
FT-IR (KBr, cm−1): 3215.37 (Phenolic OH), 3018.04
(Aromatic C–H), 1660.00 (Aromatic C=N), 1593.20–
1443.17 (Aromatic C=C); 1HNMR (DMSO-d6; δ, ppm):
8.51 (singlet, N=C–H), 5.20 (singlet, O–H), 7.79–6.88
(multiplet, Aromatic protons); 13CNMR (DMSO-d6; δ,
ppm): 163.15 (C=N), 158.88 (C–OH), 142.13 (aromatic
C–N); GCMS(m/z): 316.1(M·+)
Schiff Base 7:
Schiff Base 1:
FT-IR (KBr, cm−1): 3500.80 (Phenolic OH), 3058.57
FT-IR (KBr, cm−1): 3571.36 (Phenolic OH), 3108.42 (Aromatic C–H), 1610.56 (Aromatic C=N), 1496.78–
(Aromatic C–H), 1612.56 (aromatic C=N), 1572.05– 1462.04 (Aromatic C=C); 1H NMR (DMSO d6; δ, ppm):
1
1465.96 (Aromatic C=C); H NMR (DMSO-d6; δ, 8.03 (singlet, N=C–H), 5.40 (singlet,O–H), 7.65–6.58
ppm):8.55 (singlet, N=C–H), 5.21 (singlet,O–H), 7.30– (multiplet. Aromatic protons); 13C NMR (DMSO-d6; δ,
6.56 (multiplet, Aromatic protons); 13C NMR ppm): 163.07 (C=N), 158.98(C–OH), 120.96 (aromatic
(DMSO-d6; δ, ppm): 162.41 (Aromatic C=N), 161.01 C–N); GCMS(m/z): 316.1(M·+)