Determination of the Dissociation Constant of Some Substituted Phenols by Potentiometric Method in Acetonitrile-Water Mixtures

Abstract

 The dissociation constants of phenol, 2−methylphenol, 3−methylphenol, 4−methylphenol, and 4−ethylphenol have been determined by potentiometric titration in a electrochemical cell with glass electrode at 25 o C in water and in the mixtures of acetonitrile and water where the following volume fractions (before mixing) of acetonitrile were used: 0.10, 0.20, and 0.30. The ionic strength of the solutions was adjusted to be 0.1 mol dm−3 using KCl. The dissociation constants were calculated by using the commercial Hyperquad 2008 program. The obtained results are in good concordance withliterature values.

Keywords

• Phenols,acid dissociation constant,potentiometric method

Bazı Substitue Fenollerin Ayrışma Sabitlerinin Asetonitril-Su Karışımlarında Potansiyometrik Metotla Tayini

Abstract

Fenol, 2-metilfenol, 3-metilfenol, 4-metilfenol ve 4-etilfenol’ün ayrışma sabitleri %10-20-30 oranlarında hazırlanan asetonitril –su karışımında 25 o C potansiyometrik olarak elektrokimyasal hücrede elektrot ile tayin edilmiştir.Titrasyon çözeltilerinde iyonik şiddet KCl kullanılarak 0.1 mol dm−3 olarak ayarlanmıştır. Ayrışma sabitleri ticari bir program olan Hyperquad 2008 ile hesaplanmıştır. Elde edilen sonuçlar literatürdeki değerlerle uyumluluk göstermektedir.

Keywords

• Fenol, asidik ayrışma sabiti, potansiyometrik yöntem

References

1. Pekcan G., Aktaş A.H., 2006. Spectrophotometric determination of pK(a) values for some benzoic acid compounds in acetonitrile-water mixtures. Asian Journal of Chemistry, 18: 2168-2178.
2. Ertokuş Pekcan G., Aktaş A.H., 2009. Potentiometric Determination of pK(a) Values of Benzoic Acid and Substituted Benzoic Acid Compounds in Acetonitrile-Water Mixtures. Asian Journal of Chemistry, 21: 3825-3835.
3. Wrobel R., Chmurzynski L., 2000. Potentiometric pK(a) determination of standard substances in binary solvent systems. Analytica Chimica Acta, , 405: 303-308.
4. Ràfols C., Rosés M., Bosch E., 1997. Dissociation constants of several non-steroidal anti- inflammatory drugs in isopropyl alcohol/water mixtures, Analytica Chimica Acta, 350: 249- 255.
5. Ertokuş Pekcan G., Aktaş A.H., 2008. Ionization constants and partition coefficient of some antiinflammatory agents in non-aqueous media. Asian Journal of Chemistry, 20: 3042-3048.
6. Aktaş A.H., Şanli N., Pekcan G., 2006. Spectrometric determination of pK(a) values for some phenolic compounds in acetonitrile-water mixture. Acta Chimica Slovenica, 53: 214-218.
7. Rondinini S., Mussini P.R. , Mussini T.,1987. Reference value standards and primary standards for pH measurements in organic solvents and water + organic solvent mixtures of moderate to high permittivities, Pure Applied Chemistry, 59: 1549.
8. Mussini P.R., Mussini T., Rondinini S., 1997. Reference value standards and primary standards for pH measurements in D2O and aqueous organic solvent mixtures: New accessions and assessments, Pure Applied Chemistry , 69: 1007.

9. Gran G., 1952. Determination of the equivalence point in potentiometric titrations-- Part II. Analyst, 77: 661-671.
10. Gans P., Sabatini A., Vacca A., 1996. Investigation of equilibria in solution. Determination of equilibrium constants with the HYPERQUAD suite of program. Talanta, 43: 1739-1753.
11. Diamond D., Hanratty V.C.A., 1997. Spreadsheet application in chemistry using microsoft excel, Chapter 5, New York, NY:Wiley, pp. 130-145.
12. Espinosa S., Bosch E., Rosés M., 2002. Retention of ionizable compounds in high-performance liquid chromatography: IX. Modelling retention in reversed-phase liquid chromatography as a function of pH and solvent composition with acetonitrile–water mobile phases.. Journal of Chromotography, 964: 55-66.
13. Hakan Aktaş email: [e-mail]