Protonation constants of hydroxybenzenes in hydrochloric acid

The absorption spectra of monohydroxybenzene (Fen), 1,3-dihydroxybenzene (Rez), 1,4-dihydroxybenzene (Hi), 1,2,3-trihydroxybenzene (Pg) and 1,3,5-trihydroxy-benzene (Fg) in aqueous solutions of hydrochloric acid with different values of the Hammett acidity function(H0) have two absorption bands in t...

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Bibliographic Details
Published in:Journal of the Serbian Chemical Society 1999, Vol.64 (9), p.533-538
Main Authors: Veselinovic, D.S., Obradovic, M.V., Tosic, S.B.
Format: Article
Language:English
Subjects:
hammett acidity function
hydrochloric acid
hydroxybenzenes
protonation
protonation constant
s-curve
uv spectra
Online Access:Get full text
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Summary:The absorption spectra of monohydroxybenzene (Fen), 1,3-dihydroxybenzene (Rez), 1,4-dihydroxybenzene (Hi), 1,2,3-trihydroxybenzene (Pg) and 1,3,5-trihydroxy-benzene (Fg) in aqueous solutions of hydrochloric acid with different values of the Hammett acidity function(H0) have two absorption bands in the region between 190-220 nm and 260-290 nm. This behavior is similar in another mineral acids (H2SO4, H3PO4, HClO4). The absorbance decreases with increasing of acidity (with decreasing of H0 values) because of O-protonation. The absorption maxima shift to longer wave-lengths, and the graphic dependence of the absorption of the second band as a function of H0 gives characteristic S-curves. These curves show the different effect of the acid on the form the protonation of the investigated hydroxybenzenes. The potonation constants of the hydroxybenzenes were calculated: pKFen=-1.95; pKRez=-2.40; pKHi= -1.93; pKPg=-2.95; pKFg=-1.83. nema
ISSN:0352-5139
1820-7421
DOI:10.2298/JSC9909533V