Journal of Chemical & Engineering Data
boiling points of substances at 101.3 kPa (±1 kPa) were
determined by ebulliometer with an accuracy of ±0.05 K. All
suppliers, CAS Registry number, and the mole fraction purity
of substances used in the experiments are listed in Table 1.
2
.2. CE Determination. The compositions of reacting
mixtures corresponding to CE in the system formic acid−
ethanol−ethyl formate−water were determined by GC
analysis. The experimental procedure was similar to the studies
described in refs 8 and 9. Original quaternary solutions with
known mole fractions of each component were prepared in
vials (5 mL) by a gravimetric method with an accuracy of
0
.001 g. Then sealed vials were held in liquid thermostat at a
given temperature (298.15 K) for at least 72 h. Because of the
presence of formic acid in all solutions, it was not necessary to
use additional catalyst in this case: the catalytic properties of
formic acid were sufficient for the run of the reaction. It was
considered that chemical equilibrium was reached when the
concentration of each component was constant for several
hours. It should be noted that during the experiment all
samples remained homogeneous at 298.15 K.
Figure 1. Comparison of mutual position of the binodal and the
surface of chemical equilibrium in the system formic acid−ethanol−
ethyl formate−water at 298.15 K. Red color, surface of CE and
compositions belonging to this surface (experimental results of this
work); blue color, binodal surface, according to ref 6.
The samples of equilibrium and nonequilibrium (also during
reaction) solutions were analyzed by the GC method. The
chromatographic syringe (“Hamilton”, USA, 10 μL) was
preliminary heated to avoid the splitting of samples. A gas
chromatograph “Chromatec Crystal 5000.2” (Russia) with
thermal conductivity detector (TCD) and packed column
Porapak QS (1 m × 3 mm i.d.) was used. The choice of the
TCD is connected with the presence of water in the system
and, accordingly, in samples. The carrier gas was helium with
the flow rate of 60 mL/min. Operating temperatures of the
vaporizing injector and TCD were 513 K. For the chromato-
graphic column, a variable temperature regime was applied: 2
min at 453 K, then heating to 483 K at a rate of 20 K/min. The
method of external standard and relative calibration were used
to determine CE compositions. Propyl acetate was accepted as
a linking component. The average uncertainty of GC analysis
was ±0.005 mole fraction.
contains a binodal surfacethat was presented in our previous
6
work at 298.15 K.
As it was noted before, during the experimental investigation
of chemical equilibrium in the system formic acid−ethanol−
ethyl formate−water, the splitting of samples was not detected,
that is, all chemically equilibrium samples remained homoge-
neous. To verify the fact that in the system formic acid−
ethanol−ethyl formate−water only homogeneous solutions
correspond to chemical equilibrium, the obtained data were
6
compared with solubility data of work. Surfaces of CE and
solubility are presented in Figure 1.
It is evident that the surface of chemical equilibrium and the
surface of solubility do not intersect, which confirms the
experimentally observed fact: the CE of the ethyl formate
synthesis reaction at 298.15 K is achieved only in the
homogeneous region of compositions. It should be noted
that some systems carboxylic acid−monohydric alcohol−
ester−water show similar phase behavior (for example, acetic
acid−ethanol−ethyl acetate−water, refs 8 and 10), while in
others there are both areas of homogeneous and splitting
chemically equilibrium solutions (for example, acetic acid−n-
propanol−n-propyl acetate−water and propionic acid−etha-
nol−ethyl propionate−water, refs 9 and 11).
3
. RESULTS AND DISCUSSION
.1. Experimental Data. Experimentally obtained compo-
3
sitions of chemically equilibrium solutions for the system with
ethyl formate synthesis reaction (formic acid−ethanol−ethyl
formate−water)
The obtained data gave opportunity for the calculation of
the so-called “concentration constant” of CE (K ). Opposite to
c
the thermodynamic constant of CE that is constant at given
temperature and pressure, the values Kc depend on
composition. Nevertheless this parameter reflects the shifting
of compositions corresponding to chemical equilibrium and is
at 298.15 and 308.15 K and atmospheric pressure are tabulated
in Table 2. The surface of chemical equilibrium at 298.15 K
constructed on the basis of obtained experimental data is
presented in Figure 1. This surface is located inside the
concentration 3D space (composition tetrahedron) in a certain
way: its lean on four edges corresponding to the binary
subsystems without chemical interaction (ethanol−water,
ethanol−ethyl formate, formic acid−water, and formic acid−
ethyl formate) and passes near the edge corresponding to the
only binary subsystem with limited solubility (ethyl formate−
water) and homogeneous binary system formic acid−ethanol.
The appearance of the chemical equilibrium surface coincides
with the overall view of chemical equilibrium surfaces of other
systems of carboxylic acid−monohydric alcohol−ester−water
useful for the presentation of the data. The K values are also
c
presented in Table 2. According to these data we calculated
and plotted isolines of K using transformed composition
c
12,13
variables, αi.
variables are
In the case of the considered reaction these
α = x + x
1
1
3
α = x + x
2
2
3
α = x − x
(
e.g., presented in refs 8 and 9). The diagram in Figure 1 also
4
4
3
C
J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Samarov, Artemiy
