PENENTUAN NILAI pKa INDIKATOR TITRASI ASAM-BASA 4-((2-(2,4-DINITROFENIL)HIDRAZON)METIL)-2-METOKSIFENOL DARI VANILIN DENGAN METODE SPEKTROFOTOMETRI UV-VIS; DETERMINATION OF pKa VALUE OF 4-((2-(2,4-DINITROPHENYL) HYDRAZONE)METHYL)-2-METHOXYPHENOL FROM VANILLIN AS INDICATOR FOR ACID-BASE TITRATION USING UV-VIS SPECTROPHOTOMETRY METHOD

Aryawan, I Nyoman Agus, Bambang Purwono

2015 | Skripsi | FMIPA

Synthesis and determination of pKa value of 4-((2-(2,4-dinitrophenyl)hydrazone)methyl)-2-methoxyphenol from vanillin by using UV-Vis spectrophotometry method have been conducted. Synthesis was done by reacting vanillin and 2,4-dinitrophenylhydrazine through the addition-elimination reaction with an acid catalyst. The functional group of the product was identified by using Infrared Spectrophotometer while its purity was determined by knowing the melting point. The pKa value of 4-((2-(2,4-dinitrophenyl)hydrazone)methyl)-2-methoxyphenol compound was determined by measuring the absorbance using validated UV-Vis spectrophotometry method from phenolphthalein indicator. Then, hydrazone was dissolved in water-ethanol mixture (20:80), then converted into acid and base conditions. The results of the absorbance measurement were plugged into Henderson-Hasselbalch’s equation. Synthesis of 4-((2-(2,4-dinitrophenyl)hydrazone)methyl)-2-methoxyphenol yielded 33.4% with melting point at 269.9-271.6 °C. pKa value of 4-((2-(2,4-dinitrophenyl)hydrazone)methyl)-2-methoxyphenol was 12.908 ± 0.287.

Kata Kunci : vanillin; hydrazone; indicator; pKa; UV-Vis spectrophotometry