1070-4272/03/7603-0500$25.00C2003 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 76, No. 3, 2003, pp. 500!502. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 3,
2003, pp. 515!517.
Original Russian Text Copyright + 2003 by Korenman, Konstantinova, Niftaliev.
Turbidimetric Titration of Ethyl Acetate Extracts
of Halo- and Aminobenzoic Acids
Ya. I. Korenman, N. A. Konstantinova, and S. I. Niftaliev
Voronezh State Technological Academy, Voronezh, Russia
Received September 10, 2002
Abstract-The extraction of halo- and aminobenzoic acids from aqueous solutions with a hydrophilic solvent
(ethyl acetate) was studied. Conditions for turbidimetric titration of these acids in the organic extract were
optimized. Procedures for reliable nonaqueous titration of acids were developed.
Wastewaters from paint-and-varnish industry and
production of chemical agents for plant protection,
polymeric materials, drugs, and vitamins are contami-
nated with halo- and aminobenzoic acids [1, 2]. Sup-
ply of these acids into water of storage basins and
sewage treatment plants affects pH, destroys micro-
flora, and prevents biological treatment of water.
We found that these acids can be extracted from
aqueous solutions with a hydrophilic solvent (ethyl
acetate) and then determined in nonaqueous extract
The aim of this work was to develop an extraction-
titrimetric method for determination of monoamino-
and also mono- and polyhalo-substituted benzoic
acids in aqueous solutions.
The acids under consideration were extracted at
pH ~ 2 and 20+2oC. In order to prevent mutual dis-
solution of the organic and aqueous phases in extrac-
tion, ethyl acetate and water were preliminarily satu-
rated with water and ethyl acetate, respectively.
Before extraction, an aqueous solution of an organic
acid to be determined was acidified with H
then a prescribed amount of ethyl acetate was added.
Extraction was performed at the organic to aqueous
phase ratio of 1 : 10 (by volume) for 10315 min.
Under these conditions, the extraction equilibrium was
attained. The equilibrium extract was quantitatively
separated from the aqueous phase, transferred to titra-
tion cell, and titrated potentiometrically with 0.01 M
KOH in ethanol using a glass indicator electrode and
an electrochemical circuit with charge transfer
where GE is a glass electrode; BA, substituted benzo-
ic acid; and AgCl/KCl, silver chloride electrode filled
with saturated ethanolic solution of KCl.
The distribution factor D and degree of recovery
of acids in single extraction step were calculated by
known equations .
The concentration of substituted benzoic acid in
the nonaqueous concentrate obtained by extraction of
this acid with ethyl acetate was determined as follows.
The concentrate, preliminarily diluted with ethyl ace-
tate if necessary, was poured into a photometric cell
and then titrated with 0.01 M KOH in ethanol. In
titration, 0.02-ml portions of the titrant were added
from a microburet to the titrated solution at its con-
tinuous stirring with a mechanical stirrer. The changes
in the optical density of the solution in the course
of titration was registered in 20 s after addition of
each portion of the titrant on a KFK-2MP photo-
The amount of acid in the solution analyzed m
(mg) was calculated by the equation
m = 0.01cVMR,
where c is the titrant concentration (M); V, titrant
volume (ml) consumed in titration; M, equivalent
weight of acid (g mol
); and R, degree of extractive
recovery of the acid (%).
It is known that the degree of extractive recovery
of weak acids from aqueous solution is dependent
on pH of the aqueous phase . With lowering pH,
ionization of weak acids in the aqueous phase is sup-
pressed, and, as a result, the degree of their transfer
into the organic solvent (i.e., the extraction efficiency)
increases. To ensure favorable conditions for extrac-