Thermochemistry of benzyl alcohol: Reaction equilibria involving benzyl alcohol and tert-alkyl ethers

Article abstract of DOI:10.1021/je049823k

Chemical equilibrium of the reactive systems of benzyl alcohol with tert-alkyl ethers was studied in the liquid phase in the temperature range (298 to 373) K and with a cation exchanger Amberlist 15 as a catalyst. Enthalpies of reactions involving benzyl alcohol were obtained from the temperature dependence of the equilibrium constants according to the Second Law and used to derive averaged standard enthalpies of formation of benzyl alcohol Δ_fH_m(1,298.15K) ^{= -(154-5 ± 1.7) kJ·mol-1} in the liquid state. Vapor pressures and enthalpy of vaporization, Δ_l^gH _{m(298.15 K)}, of benzyl alcohol were determined using transpiration method. The latter value, together with the reliable literature data, provided an averaged result Δ_l^gH_{m(298.15 K)} = (65.75 ± 0.51) kJ·mol^-1. Both averaged results for Δ_fH_m(1,298.15K)^o and Δ_fH_{m(298.15 K)} were used to calculate and to recommend the value of enthalpy of formation of benzyl alcohol in the gaseous state Δ_fH_m(298.15K)^o = -(88.8 ± 1.8) kJ·mol^-1. Auxiliary data for tert-butyl benzyl ether (energy of combustion, vapor pressures, and enthalpy of vaporization) were measured using calorimetry and transpiration method.

Full text of DOI:10.1021/je049823k

J. Chem. Eng. Data 2004, 49, 1717-1723
1717
Thermochemistry of Benzyl Alcohol: Reaction Equilibria Involving
Benzyl Alcohol and tert-Alkyl Ethers
Sergey P. Verevkin* and Tatiana V. Vasiltsova†
Department of Physical Chemistry, University of Rostock, Hermannstr. 14, 18051 Rostock, Germany
Chemical equilibrium of the reactive systems of benzyl alcohol with tert-alkyl ethers was studied in the
liquid phase in the temperature range (298 to 373) K and with a cation exchanger Amberlist 15 as a
catalyst. Enthalpies of reactions involving benzyl alcohol were obtained from the temperature dependence
of the equilibrium constants according to the Second Law and used to derive averaged standard enthalpies
-
1
of formation of benzyl alcohol ∆ H°
) -(154.5 ( 1.7) kJ‚mol in the liquid state. Vapor
f
m(l,298.15K)
g
pressures and enthalpy of vaporization, ∆ Hm(298.15 K), of benzyl alcohol were determined using transpi-
l
ration method. The latter value, together with the reliable literature data, provided an averaged result
g
-1
g
∆l
H
m(298.15 K) ) (65.75 ( 0.51) kJ‚mol . Both averaged results for ∆ H°
and ∆ Hm(298.15 K) were
f
m(l,298.15K)
l
used to calculate and to recommend the value of enthalpy of formation of benzyl alcohol in the gaseous
state ∆ H°
-
1
) -(88.8 ( 1.8) kJ‚mol . Auxiliary data for tert-butyl benzyl ether (energy of
f
m(g,298.15K)
combustion, vapor pressures, and enthalpy of vaporization) were measured using calorimetry and
transpiration method.
1. Introduction
The presence of two OH bands in the IR spectra of
aliphatic alcohols has been convincingly explained as due
1
to several conformers in the solution. In molecules con-
taining double-bond systems, such as benzyl alcohol, the
-1
low-frequency band is ca. 10 cm below the corresponding
band in the purely aliphatic alcohols. This has led several
authors to propose the existence of weak intramolecular
hydrogen bonds, the low-frequency band resulting from the
bonded conformer.2 Quantification of weak intramolecular
hydrogen bonds is difficult because their strength is usually
only several kJ per mol. For instance, according to ab initio
,3
4
calculations, the strength of intramolecular hydrogen
-
1
Figure 1. Structures of tert-alkyl ethers, involved in the inves-
tigation of chemical equilibrium: tert-butyl benzyl ether (BzOtBu);
tert-amyl benzyl ether (BzOtAm); tert-butyl butyl ethers (BuOtBu);
tert-amyl butyl ether (BuOtAm).
bonds in benzyl alcohol is only about 4 kJ‚mol . Thermo-
chemical properties of a molecule, such as enthalpy of
formation or enthalpy of vaporization, are very important
for the quantification of the hydrogen bond strength,5
provided that these thermodynamic properties are of high
accuracy. Unfortunately, it is not the case for benzyl
thermochemochemical quantities of benzyl alcohol. In our
previous works1
1-16
we developed a procedure to determine
alcohol. The determination of the ∆ H°m(l) of benzyl alcohol
f
enthalpies ∆ H° of etherification reactions from experi-
r
m
has long been a popular endeavor by using combustion
calorimetry. The impressive scatter of the experimental
mental equilibrium constants. The same procedure is
applied now in this work to obtain thermodynamic func-
tions of some tert-alkyl ethers (see Figure 1) synthesis reac-
tions (see Figure 2) in the liquid phase, which have been
used together with the results from vapor pressure mea-
surements to derive reliable enthalpies of formation of
benzyl alcohol in the liquid as well as in the gaseous state.
-
1
6
values: -(154.9 ( 3.0) kJ‚mol by Papina et al. from
-
1
7
1
995, -(161.0 ( 1.3) kJ‚mol by Parks et al. from 1954,
-1
8
-
174.0 kJ‚mol by Landrieu et al., from 1929, and -167.0
-
1
9
kJ‚mol by Schmidlin from 1906, could be explained by
hygroscopic nature of this compound. The more recent work
6
of Papina et al. has been done very carefully; however, its
experimental uncertainty is too large, and this fact makes
us reticent to involve this result into interpretation of the
hydrogen bond strength. Our recent work10 has confirmed
in general the magnitude of the enthalpy of formation of
2
. Experimental Section
2.1. Materials. Benzyl alcohol (BzOH) [100-51-6] and
butan-1-ol (BuOH) [71-36-3] were of commercial origin. A
technical fraction of isoamylenes (methylbutenes) with the
6
benzyl alcohol, measured by Papina et al. This paper
extends our previous studies on the systematic investiga-
tion of a series of equilibrium reactions involving branched
ethers and has been conducted in order to ascertain the
mass percentages of hydrocarbons C
ene (2MB1) [563-46-2] 39.6; 2-methylbut-2-ene (2MB2)
513-35-9] 56.0; and 3-methylbut-1-ene (3MB1) [563-45-
] 2.5 were used in the experiments. The structures of the
4
1.9; 2-methylbut-1-
[
1
*
To whom correspondence should be addressed. E-mail:
branched ethers studied in this work are presented in
sergey.verevkin@chemie.uni-rostock.de.
†
On leave from State Academy of Refrigeration, Odessa, Ukraine.
Figure 1. tert-Butyl benzyl ether (BzOtBu) [3459-80-1], tert-
1
0.1021/je049823k CCC: $27.50 © 2004 American Chemical Society
Published on Web 08/13/2004

1718 Journal of Chemical and Engineering Data, Vol. 49, No. 6, 2004
Figure 2. Equilibrium reactions of tert-alkyl ethers synthesis studied in this work.
Table 1. Results from the Liquid-Phase Investigation of
amyl benzyl ether (BzOtAm) [27674-74-4], tert-butyl butyl
ethers (BuOtBu) [1000-63-1], and tert-amyl butyl ether
Equilibrium of Reaction 1 and Experimentally
Determined Composition of Equilibrium Mixtures and Qx
(
BuOtAm) [3249-47-6] were synthesized via alkylation of
Values in the Liquid Phase, Calculated from Eq 5a
an appropriate alkanol with the olefins in the presence of
a catalytic amount of cation-exchange resin in the H form
T/K
n
xBzOH
xBuOH
xBuOtBu
XBzOtBu
Qx(1)
+
3
01.9
12.7
23.8
31.1
7
8
2
4
7
5
4
3
4
6
4
4
6
0.1711
0.2558
0.1762
0.1104
0.1605
0.1858
0.1082
0.1692
0.1169
0.1261
0.0999
0.1480
0.1884
0.3319
0.3416
0.5152
0.7245
0.5360
0.5061
0.6883
0.6320
0.7114
0.5505
0.5059
0.5814
0.6362
0.2450
0.1744
0.2053
0.1358
0.2116
0.2032
0.1695
0.1557
0.1434
0.2605
0.3247
0.2141
0.1345
0.2521
0.2282
0.1063
0.0293
0.0920
0.1049
0.0340
0.0491
0.0284
0.0629
0.0695
0.0565
0.0409
2.00
1.75
1.51
1.42
1.45
1.41
1.28
1.18
1.21
1.05
1.08
1.04
1.03
(
Amberlist 15, Aldrich) at 343 K. Prior to the experiments,
3
3
3
the catalyst was dried for 8 h at 383 K in a vacuum oven
at reduced pressure. Pure samples (99.9 mass % deter-
mined by gas chromatography (GC)) of branched ethers
(
Figure 1) were obtained by repeated distillations at
3
3
3
38.3
48.1
51.7
reduced pressure, and their structures were confirmed by
NMR analysis.
2
.2. Chemical Equilibrium Study in the Liquid
Phase. Glass vials with screwed caps were filled two-thirds
full with the initial liquid mixture of benzyl alcohol and
butyl tert-alkyl ether or benzyl alcohol and isoamylenes.
Cation-exchange resin Amberlist 15 was added as a solid
catalyst. The quantity of the catalyst was approximately
3
59.0
363.0
a
T is the temperature of investigation, n is number of deter-
minations of composition within the time of equilibrium study,
and xi is the mole fraction determined chromatographically.
1
0% of the mass of the mixture. The vial was thermostated
(
with uncertainty 0.1 K) and periodically shaken. After
definite time intervals, the vial was cooled rapidly in ice
and opened. A sample for the GC analysis was taken from
the liquid phase using a syringe. The thermostating of the
vial was then continued at the same temperature. The
samples were taken successively until no further change
of the compositions was observed, indicating that the
chemical equilibrium was established. The compositions of
the reaction mixtures were determined chromatographi-
cally with a Hewlett-Packard gas chromatograph 5890
Series II equipped with a flame ionization detector. A
capillary column HP-5 (stationary phase cross linked 5%
PH ME silicone) was used with a column length of 30 m,
an inside diameter of 0.32 mm, and a film thickness of 0.25
µm. Response factors of all reagents were determined using
calibration mixtures of the corresponding components
prepared gravimetrically. Accuracy of the GC analysis of
the liquid-phase composition was estimated to be within
x
The equilibrium ratios Q of reactions 3 and 4 were
calculated with the help of mole fractions x
i
of the reaction
participants
Q ) x(ether)/x(ROH)x(2MB2)
(6)
x
i
Mole fractions at equilibrium x and the equilibrium ratios
Q
x
in the liquid phase are listed in Tables 1 and 2. Response
factors of all reagents were determined using calibration
mixtures of the corresponding components prepared gravi-
metrically.
2
.3. Combustion Calorimetry. The pure sample of tert-
butyl benzyl ether was obtained by repeated distillation
under N using a spinning-band column at reduced pres-
2
sure. No impurities (e0.01 mass %) could be detected in
BzOtBu by GC. For combustion experiments, the purified
liquid samples were dried over molecular sieves and
distilled once more before combustion. This procedure
provided a colorless material, and the absence of water was
shown by the Karl Fischer titration. For measurements of
the energies of combustion of the BzOtBu, a rotating-bomb
(
x
0.0005 mass %. The equilibrium ratios Q of reactions 1
and 2 were calculated with help of mole fractions x
i
of
reaction participants
Q ) x(BzOtAlk)x(BuOH)/x(BzOH)x
(BuOtAlk)
(5)
17
x
calorimeter described elsewhere was used. The combus-

Journal of Chemical and Engineering Data, Vol. 49, No. 6, 2004 1719
Table 2. Results from the Liquid-Phase Investigation of Equilibrium of Reactions 2-4 and Experimentally Determined
Composition of Equilibrium Mixtures and Qx-Values in the Liquid Phase, Calculated from Eqs 5 and 6a
T/K
n
xBzOH
xBuOH
xMB
x2MB2
xBuOtAm
xBzOtAm
Qx(2)
Qx(3)
Qx(4)
2
98.2
6
8
8
4
5
8
5
3
5
6
4
4
6
6
4
5
6
6
3
4
4
4
3
5
6
6
3
4
3
6
5
3
2
6
0.1678
0.4987
0.8065
0.2739
0.3197
0.7662
0.1964
0.2701
0.0923
0.3114
0.5777
0.8367
0.2092
0.1803
0.6950
0.8086
0.1380
0.3902
0.6103
0.8447
0.7246
0.8372
0.2252
0.3012
0.3051
0.4272
0.6112
0.8536
0.2164
0.1184
0.2097
0.6884
0.8469
0.4586
0.0687
0.0491
0.0659
0.0091
0.0204
0.0327
0.0054
0.0075
0.1026
0.0762
0.0077
0.0038
0.0066
0.0060
0.0069
0.0076
0.1520
0.1020
0.0127
0.0057
0.0112
0.0103
0.0075
0.0296
0.0988
0.0702
0.0289
0.0056
0.0067
0.0350
0.0309
0.0221
0.0121
0.0832
0.0550
0.0321
0.0060
0.0493
0.0542
0.0136
0.0238
0.0789
0.2565
0.1525
0.0571
0.0177
0.0442
0.0311
0.0528
0.0342
0.3800
0.2040
0.1058
0.0360
0.0905
0.0509
0.0505
0.1600
0.2824
0.2340
0.1831
0.0616
0.0584
0.2699
0.2396
0.184
0.7084
0.4200
0.1216
0.2448
0.2704
0.1875
0.0460
0.2175
0.5486
0.4599
0.3575
0.1419
0.0646
0.0381
0.2452
0.1495
0.3299
0.3038
0.2712
0.1136
0.1737
0.1016
0.0304
0.1181
0.3136
0.2681
0.1768
0.0792
0.0181
0.0318
0.0490
0.1055
0.0549
0.1982
76.8b
26.2
25.1
18.2
15.6
18.0
9.80
10.2
3
03.4
0.2144
0.2264
0.2084
0.1087
0.917b
1.76
19.7b
8.86
3
12.7
13.2
0.6293
0.2193
0.0991
0.2067
1.49
0.854
6.62
b
b
11.9
b
3
23.2
9.68
10.9
9.80
6.99
6.80
6.68
5.41
6.29
3.81
4.20
3.74
2.65
2.38
2.67
2.45
3.63
2.68
1.59
1.51
1.43
322.4
323.2
333.2
0.5095
0.6502
0.1658
0.1043
0.952b
1.31
5.18
5.16
b
3
43.2
0.5955
0.2891
0.0908
0.1020
0.882
1.11
3.02
2.21
b
b
3
53.2
3
3
54.2
68.2
0.6372
0.4074
0.3584
0.0632
0.1374
0.1123
0.840
0.796
0.746
1.70
1.25
1.32
0.995
0.975
0.833
0.754
3
71.2
73.2
0.0860
0.2600
b
3
1.66
a
T is the temperature of investigation, n is number of determinations of composition within the time of equilibrium study, and xi is the
b
mole fraction determined chromatographically. The value was not taken into account by calculation of the thermodynamic functions of
reactions 2-4 because it did not meet the requirement (xROH > 0.5).
Table 3. Results for Typical Combustion Experiment at
Table 4. Summary of Experimental Energies of
Combustion of Benzyl tert-Butyl Ether and Standard
Molar Thermodynamic Functions at T ) 298.15 K (p° )
T ) 298.15 K (p° ) 0.1 MPa) for Benzyl tert-Butyl Ethera
b
m (substance)/g
m′ (cotton)/gb
0.366423
0.001003
0.558724
1.30070
-32654.11
-23.69
0
.1 MPa)
[(∆cu°)(benzyl tert-butyl ether, liquid, 298.15 K )]/(J‚g-1
38753.9 -38761.2 -38762.0 -38747.9 -38755.1 -38743.6
b
m′′ (polythen)/g
)
∆
Tc/Kc
-
(
ꢀcalor)(-∆Tc)/J
ꢀcont)(-∆Tc)/J
〈-∆cu°〉/(J‚g-
1
)
-38754.04 ( 3.0
-6374.0 ( 1.6
-241.3 ( 2.2
(
∆
Ucorr/Jd
16.30
∆ H° (l)/(kJ‚mol
-1
)
)
c
m
-
1
-
-
m′∆cu′/J
m′′∆cu′′/J
17.00
25903.0
-38753.9
∆ H° (l)/(kJ‚mol
f m
∆
cu° (substance)/(J‚g-1)
procedure18 using the molar enthalpies of formation for
1
9
a
2 2
H O(l) and CO (g) as recommended by the IUPAC. The
For the definition of the symbols, see ref 18: Th ) 298.15 K;
3
i
i
assigned standard deviations of the mean values of ∆ H°
V(bomb) ) 0.2664 dm ; p (gas) ) 3.04 MPa; m (H2O) ) 0.78 g;
f
m
b
∆
U(ign) ) 1.46 J; m(Pt) ) 12.18 g. Masses obtained from
include the uncertainties from calibration, from the com-
bustion energies of the auxiliary materials, and the un-
certainties of the enthalpies of formation of the reaction
c
f
i
i
i
apparent masses. ∆Tc ) T - T + ∆Tcorr; (ꢀcont)(-∆Tc) ) (ꢀ cont)(T
f
f
-
1
298.15 K) + (ꢀ cont)(298.15 K - T + ∆Tcorr.). ꢀcalor ) (25088.1 (
-
1 d
.2) J‚K
.
∆Ucorr, the correction to standard state, is the sum of
2 2
products H O and CO .
1
8
items 81-85, 87-90, 93, and 94 in reference Hubbard et al.
2.4. Measurements of the Enthalpies of Vaporiza-
tion Using the Transpiration Method. Vapor pressures
and enthalpies of vaporization of BzOH and BzOtBu were
determined using the method of transpiration in a satu-
tion products were examined for carbon monoxide (Dr a¨ ger
tube) and unburned carbon, but none was detected. The
results are based upon the mass of sample burned. For
converting the energy of the actual bomb process to that
of an isothermal process and reducing to standard states,
the conventional procedure18 was applied. Results of a
typical combustion experiment for BzOtBu and the mean
rated N
2
stream20 and applying the Clausius-Clapeyron
equation. About 0.5 g of the sample was mixed with glass
beads and placed in a thermostated U-shaped tube having
a length of 20 cm and a diameter of 0.5 cm. Glass beads
with a diameter of 1 mm provide a surface that is sufficient
enough for the vapor-liquid equilibration. At constant
temperature ((0.1 K), a nitrogen stream was passed
through the U-tube and the transported amount of gaseous
material was collected in a cooling trap. The flow rate of
the nitrogen stream was measured using a soap bubble flow
c
values of the standard specific energies of combustion ∆ u°,
together with their standard deviations, are listed in the
Tables 3 and 4. Standard enthalpy of combustion ∆ H°
c
m
and standard enthalpy of formation ∆ H° of BzOtBu (see
f
m
Table 4) were calculated according to the established

1720 Journal of Chemical and Engineering Data, Vol. 49, No. 6, 2004
meter and optimized in order to reach the saturation
equilibrium of the transporting gas at each temperature
under study. On one hand, the flow rate of the nitrogen
stream in the saturation tube should not be too slow in
order to avoid the transport of material from the U-tube
due to diffusion. On the other hand, the flow rate should
not be too fast in order to reach the saturation of the
nitrogen stream with a compound. We tested our apparatus
at different flow rates of the carrier gas in order to check
the lower boundary of the flow below which the contribu-
tion of the vapor condensed in the trap by diffusion becomes
comparable to the transpired one. In our apparatus, the
contribution due to diffusion was negligible at a flow rate
Table 5. Vapor Pressures p and Vaporization Enthalpy,
g
∆
Hm, Obtained by the Transpiration Method
l
g
T
m
V(N2)
p
N2 flow (pexp - pcalc)
∆ Hm
l
Ka
mgb
dm3 c
Pad
3
-1
kJ‚mol-1
cm ‚s
Pa
Benzyl Alcohol
309.1 85822.6 66.7
T/K
298.15
ln(p/Pa) )
82.9 0.664 5.00
285.9 0.698 3.94
288.9 0.726 3.13
92.1 0.753 2.34
95.3 0.822 1.91
98.2 0.801 1.46
01.2 0.746 1.04
02.8 0.917 1.09
-
-
ln
(
)
R
R(T/K)
R
2
3.06
4.07
5.32
7.38
9.83
12.51
16.45
19.23
1.11
0.82
0.33
1.11
0.82
1.11
0.82
0.82
0.33
0.82
0.33
0.15
0.33
0.15
0.06
0.02
-0.10
0.04
-0.03
-0.30
-0.24
0.06
66.96
66.76
66.56
66.34
66.13
65.94
65.74
65.63
65.43
65.23
65.04
64.82
64.61
64.41
2
2
2
3
3
3
-1
up to 0.11 cm ‚s . The upper limit for our apparatus where
the speed of nitrogen could already disturb the equilibra-
3
-1
tion was at a flow rate of 1.5 cm ‚s . Thus, we carried out
the experiments in the flow rate interval of (0.28-0.52)
305.8 0.746 0.671 25.41
308.8 0.733 0.524 31.92
311.7 0.808 0.461 39.99
14.9 0.760 0.335 51.72
18.1 0.801 0.272 67.09
21.1 0.767 0.210 83.48
0.66
0.15
3
-1
-0.24
-0.18
0.53
cm ‚s , which has ensured that the transporting gas was
in saturated equilibrium with the coexisting liquid phase
in the saturation tube. The mass of compound collected
within a certain time interval is determined by dissolving
it in a suitable solvent with a certain amount of internal
standard (hydrocarbon). This solution is analyzed using a
gas chromatograph equipped with an autosampler. Uncer-
tainty of the sample amount determined by GC analysis
was assessed to be within 1-3%. The peak area of the
compound related to the peak of the external standard
3
3
3
-0.11
Benzyl tert-Butyl Ether
3
27.9 89455.8 108.0
T/K
298.15
ln(p/Pa) )
277.8 0.430 1.29
-
-
ln
(
)
R
R(T/K)
0.22
R
5.12
5.28
0.01
0.05
0.03
59.45
59.43
59.32
59.08
58.90
58.76
58.55
58.43
58.37
58.34
58.14
57.90
57.81
57.80
57.58
57.47
57.36
57.27
57.26
57.15
57.03
56.82
56.72
56.72
56.19
2
2
2
2
2
78.1 1.232 3.56
79.1 1.102 2.90
81.3 1.507 3.27
0.82
0.82
0.82
0.22
0.82
0.82
0.82
0.22
0.82
0.82
0.82
0.22
0.82
0.82
0.82
0.82
0.22
0.82
0.82
0.82
0.82
0.22
0.82
0.22
5.77
6.98
-0.03
-0.15
-0.21
0.17
-0.07
-0.32
0.32
-0.02
0.38
-0.21
-0.25
0.44
(
n
hydrocarbon n-C H2n+2) is a direct measure of the mass
82.9 0.440 0.830
84.3 1.428 2.41
7.97
8.93
10.95
11.77
of the compound condensed into the cooling trap provided
a calibration run has been made. From this information,
the vapor pressure of the compound under study can be
determined, i.e., the ideal gas law can be applied provided
that the vapor pressure of the substance is low enough.
Real gas corrections arising from interactions of the vapor
286.2 1.428 1.96
287.3 1.473 1.88
2
2
2
2
87.8 0.700 0.870 12.09
88.2 1.552 1.78
90.0 1.417 1.43
92.2 1.417 1.17
13.10
14.85
18.20
with the carrier gas turned out to be negligible. The
293.0 0.980 0.780 18.88
293.2 1.642 1.29 19.08
95.2 1.518 0.982 23.12
96.2 1.338 0.818 24.45
97.2 1.271 0.716 26.52
98.0 0.810 0.430 28.43
sat
saturation vapor pressure p
i
i
at each temperature T was
2
2
2
2
2
calculated from the amount of product collected within a
definite period of time. Assuming that Dalton’s law of
-0.11
-0.04
0.05
partial pressures applied to the nitrogen stream saturated
sat
with the substance i of interest is valid, values of p
i
were
98.2 2.002 1.02
29.24
0.53
calculated
299.2 1.394 0.675 30.85
00.3 1.406 0.614 34.19
02.2 1.541 0.593 38.75
303.1 0.830 0.300 41.77
03.2 1.653 0.573 43.05
08.0 1.000 0.260 57.54
-0.16
0.46
3
3
-0.18
-0.02
1.10
sat
pi ) m RT /VM
i
a
i
3
3
-2.15
V ) VN2 + Vi
a
b
Temperature of saturation. Mass of transferred sample,
c
condensed at T ) 243 K. Volume of nitrogen, used to transfer
(
VN2 . Vi)
(7)
d
mass m of sample. Vapor pressure at temperature T, calculated
from m and the residual vapor pressure at T ) 243 K.
-
1
-1
where R ) 8.31451 J‚K ‚mol , m
ported compound, M is the molar mass of the compound,
and V is its volume contribution to the gaseous phase. V 2
is the volume of transporting gas, and T is the temperature
of the soap bubble meter. The volume of transporting gas
i
is the mass of trans-
expression for the vaporization enthalpy at temperature
T is derived
i
i
N
a
g
g
l
∆l H (T) ) -b + ∆ C T
(9)
m
p
V 2
N
was determined from the flow rate and time measure-
sat
ments. Data of p
temperature and were fitted using following equation
i
have been obtained as a function of
g
Values of ∆ C
p
have been calculated according to a proce-
20
l
21-22
dure developed by Chickos.
Experimental results and
parameters a and b are listed in Table 5. The errors in the
enthalpies of vaporization are calculated from eq 8 by using
sat
b
T
g
T
T0
R ln pi ) a + + ∆ C ln
(8)
l
p
(
)
the method of least squares, and uncertainties in values
g
of ∆ C
p
are not taken into account. We have checked
l
g
l
where a and b are adjustable parameters and ∆ C
difference of the molar heat capacities of the gaseous and
the liquid phase, respectively. T appearing in eq 8 is an
arbitrarily chosen reference temperature (which has been
chosen to be 298.15 K). Consequently, from eq 8 the
p
is the
experimental and calculation procedure with measure-
ments of vapor pressures of n-alcohols.20 It turned out that
vapor pressures derived from the transpiration method
were reliable within 1-3% and their accuracy was gov-
erned by reproducibility of the GC analysis.
0

Journal of Chemical and Engineering Data, Vol. 49, No. 6, 2004 1721
Table 6. Enthalpies ∆ H° of Reactions 1-4 in the Liquid Phase at T ) 298.15 K, Coefficients A and B of the Temperature
r
m
-
1
Dependence of the Equilibrium Ratios ln Qx ) A + B(T/K) , and Standard Enthalpy of Formation of Benzyl Alcohol in
the Liquid State at 298.15 K Derived from Enthalpies of Reactions 1, 2, and 3, Respectively (See Text)
T〉a
∆ H°
b
ln Qx ) A + B‚(T/K)-1
∆ H°
〈
r
m
r
m(l,BzOH)
kJ‚mol-
1
A
B
kJ‚mol-1
reaction
K
1
2
3
332.5
335.8
335.7
-9.9 ( 0.4
-12.1 ( 0.9
-42.7 ( 1.1
-42.7 ( 1.4
-28.5 ( 2.0
-28.1 ( 0.8
-3.2
-4.2
1187.0
1453.7
5138.2
5130.7
3422.6
3384.5
-155.1 ( 2.9
-154.7 ( 3.9
-153.0 ( 3.5
-14.1
-14.0
-9.1
c
c
c
c
c
c
3
37.3
335.8
45.7d
4
c
3
-8.9
a
The average temperature of the equilibrium study. Derived from the temperature dependence of Qx for xROH > 0.5. c Results from
b
1
0
d
11
our previous work.
Results from our previous work.
3
. Results and Discussion
mixtures of BzOH with 2MB2. Thus, in this case, the
reacting mixture consisted from BzOH, BzOtAm, and
3.1. Equilibrium Constants and Reaction Enthal-
methyl-butenes. However, Q
in this system for the mole fraction of alcohol xROH > 0.5
see Table 2) were indistinguishable with those measured
in the presence of BuOH and BuOtAm and were treated
together. The experimental values of Q of the reaction 4
x
values of reaction 3 measured
pies. The experimental results of chemical equilibrium
study of the reactions 1-4 are listed in Tables 1 and 2. It
is well established that reactive mixtures of the tert-alkyl
(
ethers synthesis behave strongly nonideally, especially
when the mole fractions of alkanol are low.1
1-16
x
On this
measured in this work (in the presence of BzOH and
BzOtAm), as well as the enthalpy of this reaction, are also
in very close agreement (see Table 6) with those obtained
i
basis, the activity coefficients γ should be used to calculate
a
the true thermodynamic equilibrium constant K . However,
in our previous works,1
1-16
we developed a procedure to
1
1
by direct alkylation of BuOH with methyl-butenes.
determine ∆ H° for etherification reactions from experi-
r
m
The chemical equilibrium of the reactive systems 1-4
was studied in the liquid phase in the temperature range
mental data of Q
measuring activity coefficients γ
we observed that Q values are almost independent of the
mole fraction of alcohol if xROH > 0.5, it was suggested that
values in this concentration range are close to the true
thermodynamic equilibrium constant K . Under this as-
sumption, experimental values of Q could be approximated
as a function of temperature by the linear equation ln Q
x
(according to eqs 5 and 6) without
i
of the reactants. Because
(
298 to 373) K. Although equilibrium studies have been
x
performed at elevated temperatures, the corrections of the
enthalpies of reactions 1-4 are assessed to be less than
Q
x
-
1
(
0.3-0.5) kJ‚mol according to our estimations with help
a
of heat capacities of the reaction participants collected in
the database.22 In further calculations, it was assumed that
the enthalpies of reactions 1-4 hardly change on passing
from the average temperature of the experimental range
to T ) 298.15 K.
x
x
-
-
1
(xROH > 0.5) ) A + B(T/K) using the method of least
squares. The slope of this line when multiplied by the gas
constant yields the enthalpy of reaction, ∆ H° . We tested
r
m
11-16
3.2. Enthalpy of Formation of Benzyl Alcohol in the
Liquid Phase. We investigated the chemical equilibrium
of reactions 1-3 and derived the enthalpy of this reaction
in the liquid phase. The enthalpy of formation ∆ H° of
this procedure for numerous etherification reactions.
In all cases, the enthalpy of reaction calculated from Q
values measured for the mole fraction of alcohol xROH
.5 (according to the Second Law) was in excellent agree-
ment with those ∆ H° calculated using enthalpies of
x
>
f
m(l)
0
tert-butyl benzyl ether at 298.15 K was measured by means
of combustion calorimetry in this work (see Table 4). The
latter value, as well as enthalpies of reactions 1-3 (see
Table 6), was involved in the calculation of the standard
enthalpies of formation of the benzyl alcohol. For this
purpose, standard molar enthalpies of formation,
∆fH°m(l,298.15K), of 2-methylbutene-2, tert-alkyl ethers, and
butan-1-ol are required. Enthalpy of formation in the liquid
r
m
formation derived from combustion calorimetry (according
to the First Law). In this work, we applied this simplified
procedure to the reactions 1-4 and derived their ∆ H°
r
m
from Q
x
values determined for the mole fraction of alcohol
xROH > 0.5 according to the Second Law. Numerical results
are presented in Table 6. The errors in the thermodynamic
functions from equilibrium study are given by the standard
phase of 2-methylbut-2-ene, ∆ H°
) -(68.1 ( 1.3)
f
m(l)
x
deviations from the linear equation ln Q (xROH > 0.5) ) A
+
-
1
23
-
1
kJ‚mol , was taken from combustion experiments. Ex-
perimental data for tert-alkyl ethers have been reviewed
recently,24 and values for BuOtBu, ∆ H° ) -(403.3 (
B(T/K) for the level of confidence of 95%.
Equilibrium of reaction 1 (see Table 1) was investigated
f
m(l)
from both sides - using initial liquid mixtures of BzOH
with BuOtBu, as well as with initial mixtures of BzOtBu
and BuOH. Small amounts of iso-butene as a byproduct
were detected in the reacting mixture. It was not possible
to measure this amount reproducibly, because it escaped
during analytical procedure very rapidly.
Equilibrium of reaction 2 (see Table 2) was investigated
using initial liquid mixtures of BzOH with BuOtAm.
Certain amounts of methyl-butenes were detected in the
reacting mixture. These olefins alkylated BzOH and BuOH,
and due to this reason, reactions 3 and 4 reached equilib-
rium parallel to the reaction 2 (by using initial liquid
mixtures of BzOH with BuOtAm). Equilibrium constants
for all three reactions are listed in Table 2. To prove
-
1
1
.9) kJ‚mol , for BuOtAm ∆ H°
) -(424.0 ( 2.4)
f
m(l)
-
1
-1
kJ‚mol , andforBzOtAm∆ H° )-(263.8(3.0)kJ‚mol
were taken from this source. Data for butan-1-ol ∆ H°
(327.0 ( 0.2) kJ‚mol were taken from Mosselman and
Dekker. These data were used to calculate the enthalpy
of formation of benzyl alcohol in the liquid phase (e.g., for
the reaction 1)
f
m(l)
)
f
m(l)
-
1
-
25
∆fH°m(l,BzOH) ) -∆ H° + ∆ H°
+ ∆ H°
-
r
m(1)
f
m(l,BzOtBu)
f
m(l,BuOH)
-1
∆ H°
) -(155.1 ( 2.9) kJ mol
f
m(l,BuOtBu)
In a similar way, ∆ H°
was calculated from data for
f
m(l,BzOH)
reactions 2 and 3 (see Table 6). All three values are in very
6
whether Q
x
of reaction 3 depends on reacting mixture
close agreement to the recent result from Papina et al.
-
1
content, the latter reaction was studied using initial liquid
∆ H°
) -(154.9 ( 3.0) kJ mol
measured by
f
m(l,BzOH)

1722 Journal of Chemical and Engineering Data, Vol. 49, No. 6, 2004
Table 7. Comparison of Data for the Enthalpy of Vaporizationa of Benzyl Alcohol at 298.15 K
g
l
-1
technique
T/K
∆ Hm at T ) 298.15 K/kJ‚mol
ref
2
8,27
ebulliometr
ebulliometr
ebulliometr
ebulliometr
transpiration
not specified
not specified
ebulliometr
transpiration
transpiration
transpiration
average
not specified
312.0-424.8
395.7-478.6
312-397
60.29 ( 0.42
63.0 ( 2.2
Mathews, 1926
3
5
Gardner, 1937
3
4
62.08 ( 0.27
Dreisbach, 1949
b
32
65.4 ( 2.0
Belina, 1974
b
33
302.6-333.2
385-573
66.8 ( 1.4
Grayson, 1982
3
3
7
7
62.7
61.8
Stephenson, 1987
Stephenson, 1987
293-313
b
29
404.1-507.4
277.4-318.2
282.2-323.0
282.9-321.1
62.46 ( 0.30
Ambrose, 1990
Verevkin, 1999
b
30
64.82 ( 0.64
b
31
65.46 ( 0.38
Vasiltsova, 2004
this work
b
65.94 ( 0.24
c
65.75 ( 0.51
this work
a
Vapor pressure available in the literature were treated using eqs 8 and 9 in order to calculate enthalpy of vaouorization at 298.15 K
in the same way as our own results from Table 5. b Values selected to calculate average enthalpy of vaporization. Average value (was
calculated taking into consideration the uncertainty as a statistical weighting factor ) recommended for calculation of gaseous enthalpy
of formation of benzyl alcohol.
c
2
6
-
1
combustion calorimetry. Taking into account such close
agreement, we calculated the average from 4 values taking
into consideration the uncertainty as a statistical weighting
∆ H° (298.15 K) ) 53.93 kJ‚mol , measured by Cub-
r m
36
berley and Mueller in the gaseous phase using equilib-
rium technique. With the help of the ∆ H° ) -(36.7 (
2.9) kJ‚mol of benzaldehyde (Pedley et al.), we esti-
mated the gaseous enthalpy of formation ∆ H° ) -90.6
kJ‚mol of benzyl alcohol. This value is in close agreement
with those from our recommendations. Concordance of the
data obtained from different sources supports the correct-
f
m(g)
2
6
-1
27
factor, and the average value ∆ H°
) -(154.5 (
f
m(l,BzOH)
-
1
1
.7) kJ‚mol at 298.15 K could be recommended.
f
m(g)
-1
3
.3. Enthalpy of Vaporization of Benzyl Alcohol and
Benzyl tert-Butyl Ether at 298.15 K. Vapor pressure and
g
-1
enthalpy of vaporization ∆ H
m
) (57.26 ( 0.28) kJ‚mol
l
-
1
of BzOtBu have been measured for the first time. Enthal-
pies of vaporization of benzyl alcohol derived from the vapor
pressure measurements using eqs 7 and 8 are collected in
ness of the values of ∆fH°m(g) ) -(88.8 ( 1.8) kJ‚mol ,
g
-1
∆ H
m
) (65.75 ( 0.51) kJ‚mol , and ∆ H° ) -(154.5 (
l
f
m(l)
-
1
1.7) kJ‚mol for benzyl alcohol at 298.15 K recommended
for the further thermochemical calculations. Quantification
of the hydrogen bond strength in benzyl alcohol, with help
of gaseous enthalpy of formation obtained in this work, will
be reported in our next paper.
27
Table 7. Pedley et al. reanalyzed the earliest value of
g
-1
∆l
m
H ) (50.50 ( 0.04) kJ‚mol reported in the litera-
2
8
g
-1
ture and calculated ∆ H
m
) (60.29 ( 0.42) kJ‚mol .
l
The most reliable measurements of the p-T data for benzyl
alcohol were performed by Ambrose and Ghiasse,29 using
ebulliometry in the temperature range 404.1-507.4 K.
However, a long way of extrapolation of their vaporization
enthalpy over 150 K to the reference temperature 298.15
K is accompanied with the large uncertainty. Our first
Acknowledgment
S.V. expresses his gratitude to Professor Dr. C. R u¨ chardt
and Dr. H.-D. Beckhaus for supporting the combustion
experiments and for the exceedingly creative atmosphere
in their laboratory.
3
0
g
l
-1
result ∆ H
m
) (64.8 ( 0.6) kJ‚mol was essentially
different from most of the earlier investigations (see Table
). This fact has prompted us to ascertain vapor pressure
Literature Cited
7
measurements on BzOH by the transpiration method.
(1) Joris, L.; Schleyer, P. v. R.; Osawa, E. Infrared Spectral Conse-
quences of Conformational Heterogeneity in Saturated Alcohols.
Tetrahedron 1968, 24, 4759-4777.
However, our recent result31 ∆ H
g
-1
m
) (65.5 ( 0.4) kJ‚mol
l
was in agreement to previous determination within the
boundaries of experimental uncertainties. In this work, the
most attention has been played to a proof of saturation
conditions during the transpiration experiment (by varia-
tion of nitrogen stream speed) in a broad range (see Table
(
2) Bellamy, L. J. Advances in Infrared Group Frequences; London:
Methuen, 1968.
(3) Joesten, M. D.; Schaad, L. J. Hydrogen Bonding; Marcel Dekker:
New York, 1974.
(
4) Mons, M.; Robertson, E. G.; Simons, J. P. Intra- and Intermo-
lecular p-Type Hydrogen Bonding in Aryl Alcohols: UV and IR-
UV Ion Dip Spectroscopy. J. Phys. Chem. A 2000, 104, 1430-
1437.
7
). Nevertheless, this latest and somewhat more precise
-
1
result (65.94 ( 0.24) kJ‚mol (Table 7) was again in close
agreement with our previous determinations as well as
with the results from refs 32 and 33, which were obtained
(
5) Pimentel, G. C.; McClellan, A. L. The Hydrogen Bond. San
Francisco and London: W. H. Freeman and Co., 1960.
(6) Papina, T. S.; Pimenova, S. M.; Luk’yanova, V. A.; Kolesov, V. P.
Standard Enthalpies of Formation of Benzyl Alcohol and R,R,R-
Trichlorotoluene. Russ. J. Phys. Chem. 1995, 69, 1951-1953.
in the similar to ours temperature ranges. We selected
these two results3
2,33
and together with three of our own
(
7) Parks, G. S.; Manchester, K. E.; Vaughan, L. M. Heats of
Combustion and Formation of Some Alcohols, Phenols, and
Ketones. J. Chem. Phys. 1954, 22, 2089-2090.
values used them to calculate average value of enthalpy
g
of vaporization of benzyl alcohol ∆ H
m
(298.15 K) ) (65.75
l
(
8) Landrieu, P.; Baylocq, F.; Johnson, J. R. Etude Thermochimique
Dans la Serie Furanique. Bull. Soc. Chim. Fr. 1929, 45, 36-49.
-1
(
0.51) kJ‚mol taking into consideration the uncertainty
26
as a statistical weighting factor.
(9) Schmidlin, M. J. Recherches Chimiques et Thermochimiques sur
la Constitution des Rosanilines. Ann. Chim. Phys. 1906, 1, 195-
3
.4. Enthalpy of Formation of Benzyl Alcohol in the
2
56.
Gaseous Phase at 298.15 K. Average values of enthalpy
(
(
(
10) Verevkin, S. P.; Krasnykh, E. L. Wright, J. S. Thermodynamic
Properties of Benzyl Halides: Enthalpies of Formation, Strain
Enthalpies, and Carbon-Halogen Bond Dissociation Enthalpies.
PCCP 2003, 5, 2605-2611.
g
l
m
f m(l)
of vaporization ∆ H and enthalpy of formation ∆ H° of
benzyl alcohol have allowed us to derive ∆ H° ) -(88.8
f
m(g)
-
1
(
1.8) kJ‚mol for this compound. An independent way
11) Verevkin, S. P. Thermochemistry of Branched Ethers. Experi-
mental Study of Chemical Equilibrium in the Reacting System
of tert-Amyl Alkyl Ether Synthesis. J. Chem. Eng. Data 2004,
to obtain support for this result serves the enthalpy of
reaction of dehydrogenation of benzyl alcohol
4
9, 576-581.
12) Verevkin, S. P.; Kapteina, S.; Heintz, A. Comprehensive Experi-
mental and Theoretical Study of Chemical Equilibrium in the
benzyl alcohol T benzaldehyde + H2

Journal of Chemical and Engineering Data, Vol. 49, No. 6, 2004 1723
Reacting System of tert-Amyl Methyl Ether Synthesis. PCCP
004, 6, submitted
(25) Mosselman, C.; Dekker: H. Enthalpies of Formation of n-Alkan-
1-ols. J. Chem. Soc. Faraday Trans. 1 1975, 417-424.
(26) Oleynik, B. N. Precise Calorimetry; Izd. Standartov: Moscow,
1973.
2
(
13) Heintz, A.; Verevkin, S. P. Simultaneous Study of Chemical and
Vapor-Liquid Equilibria in the Reacting System of the Methyl
Cumyl Ether Synthesis from Methanol and R-Methyl-Styrene.
Fluid Phase Equilib. 2001, 179, 85-100.
(27) Pedley, J. P.; Naylor, R. D.; Kirby, S. P. Thermochemical Data of
Organic Compounds, 2nd ed.; Chapman and Hall: London, 1986.
28) Mathews, J. H. The Accurate Measurement of Heats of Vaporiza-
tion of Liquids. J. Am. Chem. Soc. 1926, 48, 562-576.
(
14) Verevkin, S. P.; Heintz, A. Chemical Equilibria Study in the
Reacting System of the Alkyl Cumyl Ether Synthesis from
n-Alkanols and R-Methyl-styrene. J. Chem. Eng. Data 2001, 46,
(
(
29) Ambrose, D.; Ghiassee, N. B. Vapor Pressures, Critical Temper-
atures, and Critical Pressures of Benzyl Alcohol, Octan-2-ol, and
41-46.
(
15) Verevkin, S. P.; Heintz, A. Chemical Equilibria Study in the
Reacting System of the (1-Alkoxy-ethyl)benzene Synthesis from
Alkanols and Styrene. J. Chem. Eng. Data 2001, 46, 984-990.
16) Verevkin, S. P.; Heintz, A. Chemical Equilibria Study in the
Reacting System of the (1-Alkoxy-ethyl)benzene Synthesis from
iso-Alkanols and Styrene. J. Chem. Soc., Perkin Trans. 2 2002,
2
-Ethylhexan-1-ol. J. Chem. Thermodyn. 1990, 22, 307-311.
(
30) Verevkin, S. P. Strain Effects in Phenyl Substituted Methanes.
Geminal Interaction between Phenyl and Electron Releasing
Substituent in Benzylamines and Benzyl Alcohols J. Chem. Eng.
Data 1999, 44, 1245-1251.
(
(
31) Verevkin, S. P.; Vasiltsova, T. V.; Bich, E.; Heintz, A. Thermo-
dynamic Properties of Mixtures Containing Ionic Liquids. Activity
Coefficients of Aldehydes and Ketones in 1-Methyl-3-Ethyl-
Imidazolium Bis(trifluoromethyl-sulfonyl) Imide Using the Tran-
spiration Methodol. Fluid Phase Equilib. 2004, 218, 165-175.
32) Belina-Freundlich, D.; Respondek, J.; Szust, J. Liquid-Vapor
Equilibriums under Reduced Pressure. Przem. Chem. 1974, 53,
728-733.
(
17) Beckhaus, H.-D.; Kratt, G.; Lay, K.; Geiselmann, J.; R u¨ chardt,
C.; Kitschke, B.; Lindner, H. J. 3,4-Dicyclohexyl-3,4-dimethyl-
hexane - Enthalpy of Formation, Thermal Stability and Structure.
Chem. Ber. 1980, 113, 3441-3455.
(
(
18) Hubbard, W. N.; Scott, D. W.; Waddington, G. Experimental
Thermochemistry; Rossini, F. D., Ed.; Interscience: New York,
5
64-566.
1956; pp 75-127.
(
(
33) Grayson, B. T.; Fosbraey, L. A. Determination of the Vapor
Pressure of Pesticides. Pestic. Sci. 1982, 13, 269-278.
(
19) CODATA Key Values for Thermodynamics; Cox, J. D., Wagman,
D. D., Medvedev, V. A., Eds.; Hemisphere: New York, 1989.
20) Kulikov, D. V.; Verevkin S. P.; Heintz, A. Enthalpies of Vaporiza-
tion of a Series of Linear Aliphatic Alcohols. Experimental
Measurements and Application of the ERAS-Model for Their
Prediction. Fluid Phase Equilib. 2001, 192, 187-202.
34) Dreisbach, R. R.; Shrader, S. A. Vapor Pressure-Temperature
Data on Some Organic Compounds. Ind. Eng. Chem. 1949, 41,
(
2
879-2880.
(
35) Gardner, G. S.; Brewer, J. E. Vapor Pressure of Commercial High-
Boiling Organic Solvents. J. Ind. Eng. Chem. 1937, 29, 179-181.
36) Cubberley, A. H.; Mueller, M. B. Equilibrium Studies on the
Dehydrogenation of Primary and Secondary Alcohols. I. 2-Bu-
tanol, 2-Octanol, Cyclopentanol and Benzyl alcohol. J. Am. Chem.
Soc. 1946, 68, 1149-1151.
(
(
(
21) Chickos, J. S.; Hesse, D. G.; Liebman, J. F. A Group Additivity
Approach for the Estimation of Heat Capacities of Organic Liquids
and Solids. Struct. Chem. 1993, 4, 261-269.
(
22) Domalski, E. S.; Hearing, E. D. Estimation of the Thermodynamic
Properties of C-H-N-O-S-Halogen Compounds at 298.15 K.
J. Phys. Chem. Ref. Data 1993, 22, 805-1159.
(37) Stephenson, R. M.; Malanowski, S. Handbook of the Thermody-
namics of Organic Compounds; New York: Elsevier: 1987.
23) Good, W. D.; Smith, N. K. The Enthalpies of Combustion of the
Isomeric Pentenes in the Liquid State. A Warning to Combustion
Calorimetrists about Sample Drying. J. Chem. Thermodyn. 1979,
11, 111-118.
Received for review May 10, 2004. Accepted July 1, 2004. T.V.
gratefully acknowledges a research scholarship from the DAAD
(Deutscher Akademischer Austauschdienst).
(
24) Verevkin, S. P. Improved Benson’s Increments for the Estimation
of the Standard Enthalpies of Formation and Enthalpies of
Vaporization of Alkyl Ethers, Acetals, Ketals, and Ortho Esters.
J. Chem. Eng. Data 2002, 47, 1071-1097.
JE049823K