SOLUBILITY OF WATER IN LIQUID PERFLUOROCARBONS M' G' Freire1, L' M' N' B' F' Santos2, I'M' Marrucho1

1
SOLUBILITY OF WATER IN LIQUID PERFLUOROCARBONSM
. G. Freire1, L. M. N. B. F. Santos2, I.M.
Marrucho1 and J.A.P. Coutinho11CICECO,
Departamento de Química, Universidade de Aveiro,
Aveiro, Portugal2Centro de Investigação em
Química, Departamento de Química, Faculdade de
Ciências, Universidade do Porto, Porto,
Portugal
Fluorinated molecules such as perfluorocarbons
(PFCs) and their derivates represent a very
interesting and stimulating class of chemicals in
the physical chemistry and polymer science due to
their specific and unusual properties. It is
however in the biomedical field where most of the
relevant applications of PFCs are found. They can
be used in tissue oxygenation as blood
substitutes, anti-tumural agents and perfusates
for isolated organs, gas-carriers in eye surgery,
diagnostic imaging agents, drug delivery and in
the aeration of biological reactors 1. The aim
of this work is the study of water solubility in
liquid perfluorocarbons at several temperatures
since data of this property are extremely scarce
in the literature.
From the Gibbs-Duhem equation, assuming that for
such a diluted solution both the activity
coefficient for water in the water phase and that
for the organic component in the organic phase
are equal to one, its possible to obtain the
following approximation 2
The linear dependence of ln(x) with temperature
for an individual case (C6F6) and for the linear
compounds studied is shown in Figures 1 and 2,
respectively.
A 737 model Karl Fisher titrator was used and it
has been adapted for measuring the low solubility
of water in the perfluorocarbons solvents. The
study of pure perfluorocarbons is based in
measurements of the solubility of water in
linear, cyclic and aromatic perfluorocarbons in
the temperature range between 295.7 and 309.6 K
and at atmospheric pressure. Since to our
knowledge there are no known data in literature
for the PFCs, the method was validated with the
determination of the n-heptane solubility in
water in the same temperature range comparing the
measures with literature data. Experimental
values of water solubility in PFCs, expressed in
mol fractions, are presented in Table 1. Table
1. Solubility of water in liquid PFCs
The determination of water solubility has a
particular significance since it may be a way to
access to thermodynamic properties of these
systems. Solubility measurements at different
temperatures allow the determination of
thermodynamic parameters of the solution that are
difficult to obtain using direct methods, such as
?Hº. The thermodynamic parameters are presented
in Table 2. Table 2. Thermodynamic parameters at
298.2 K for the water dissolution in PFCs
Experimental data is well described by the linear
representation of ln(x) with temperature for all
the studied cases. The solubility of water in the
linear PFCs is fairly insensitive to the carbon
number (CN), rising just slightly with increasing
CN because it seems to be primarily influenced by
the breaking of hydrogen bonds in water. The
water solubility in PFCs is strongly dependent on
the temperature.
The heat of solution for water in PFCs is always
positive and is nearly the same for all the PFC
compounds and slightly higher than the heat of
solution for the n-alkanes. This increase may be
due to the larger size of the PFC molecules
increasing the difficulty of the dissolution of
water. Typical values for the energy of a
normal hydrogen bond range between 20 and 40
KJ.mol-1 suggests that the dissolution of n water
molecules leads to the breaking of n hydrogen
bonds, which to a good approximation is
independent of both carbon number and
temperature. The lone pair electrons of oxygen
interaction with the ? system of the
hexafluorobenzene ring reduces the heat of
solution increasing the solubility of water on
this compound.