PENENTUAN NILAI pKa SENYAWA INDIKATOR TITRASI ASAM-BASA TURUNAN AZO DARI VANILIN DENGAN METODE SPEKTROFOTOMETRI UV-VIS; DETERMINATION pKa VALUE OF AZO COMPOUND DERIVATIVE FROM VANILLIN AS INDICATOR FOR ACID-BASE TITRATION USING UV-VIS SPECTROPHOTOMETRY METHOD

Hidayah, Nurul, Bambang Purwono

2015 | Skripsi | FMIPA

Synthesis and determination of pKa value of azo derivative compound of 4-hydroxy-3-methoxy-5-(o-nitrophenyldiazenil)benzaldehyde from vanillin by using UV-Vis spectrophotometry. Research was started from synthesis of 4-hydroxy-3-methoxy-5-(o-nitrophenyl-diazenil)benzaldehyde compound by diazo coupling reaction between o-nitrobenzenadiazonium chloride salt and sodium vanillat at 0-5 ?C. The result of synthesized compound was then characterized using FT-IR spectrophotometer, DI-MS, and 1H-NMR. The pKa value of 4-hydroxy-3-methoxy-5-(o-nitrophenyldiazenil)benzaldehyde compound was determined by measuring the absorbance using validated UV-Vis spectrophotometry method from phenolphthalein. Then, synthesized product was dissolved in ethanol and water:ethanol (70:30), then into acid and base conditions. The results of the absorbance measurement were plugged into Henderson-Hasselbalch’s equation. Synthesis of 4-hydroxy-3-methoxy-5-(o-nitrophenyldiazenil)benzal-dehyde was yielded 49.79%. pKa value of 4-hydroxy-3-methoxy-5-(o-nitrophenyldiazenil)benzaldehyde in 30% ethanol was 8.781 ± 0.2 and pKa value of 4-hydroxy-3-methoxy-5-(o-nitrophenyldiazenil)benzaldehyde in 100% ethanol was 11.510 ± 0.2.

Kata Kunci : Azo compound; Henderson-Hasselbalch; Phenolphthalein; pKa, UV-Vis spectrophotometry