Entry Catalyst Amax [I]s % [IH+]s % H0
1 - 2.9839 100 0 -
2 NSPVPC 1.4387 48.2 51.8 0.96
3 PVPHS 1.0942 36.7 63.3 0.75
4 NSPVPHS 0.6831 22.9 77.1 0.46
Conditions for UV–visible spectrum measurement: solvent: CH2Cl2, indicator: 4-nitroaniline (pK(I)aq = 0.99), 1.44x 10-4 mol/L; Catalyst: PVPHS or NSPVPHS, 2 mg, 20.9 °C. The calibration curves with the linearity higher than 0.999 for indicator in the unprotonated form were constructed using its CH2Cl2 solution
Table 2: Calculation of Hammett acidity function (H0) of NSPVPC, PVPHS and NSPVPHS.