Evidence of two-step deprotonation of D-mannitol in aqueous solution.
Deprotonation of D-mannitol was studied in aqueous basic solutions by means of potentiometry and (13)C NMR spectroscopy. Two-step dissociation in the pH range from 12 to 13.8 was shown, and successive dissociation constants K(a1) and K(a2) were determined. In a solution with ionic strength I = 1.0 M (NaOH + NaNO(3)) pK(a1) = 13.1 +/- 0.1 and pK(a2) = 13.8 +/- 0.2. With increasing ionic strength from 0.75 to 3.0 M, both pK(a1) and pK(a2) values decrease. Deprotonation-induced chemical shifts in pH-variable (13)C NMR spectra show that the OH-groups next to internal carbon atoms C-3 and C-4 dissociate to a greater extent compared to OH-groups next to external carbon atoms C-1 and C-6.
Gaidamauskas
Ernestas
E
Vilnius University, Faculty of Chemistry, Vilnius, Lithuania. ernestas.gaidamauskas@chf.vu.lt
Norkus
Eugenijus
E
Vaiciūniene
Jūrate
J
Crans
Debbie C
DC
Vuorinen
Tapani
T
Jaciauskiene
Jane
J
Baltrūnas
Gintaras
G
D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008353:Mannitol / Q000737:chemistry*; D015394:Molecular Structure; D011522:Protons; D012996:Solutions / Q000737:chemistry; D014867:Water / Q000737:chemistry*
D011522:Protons; D012996:Solutions; D014867:Water; D008353:Mannitol