Thermochemistry of imines: Experimental standard molar enthalpies of formation

Article abstract of DOI:10.1006/jcht.1997.0242

The standard (p^o = 0.1 MPa) molar enthalpies of formation Δ_fH^o_m(1 or cr) at the temperature T = 298.15 K were measured using combustion calorimetry for benzophenone-imine (A), N-methyl-benzaldehyde-imine (B), N-

Full text of DOI:10.1006/jcht.1997.0242

J. Chem. Thermodynamics 1997, 29, 1175–1183
Thermochemistry of imines: experimental standard
molar enthalpies of formation
Sergey P. Verevkin, a,b Jens Morgenthaler, and
Christoph Ruchardt a
Institute of Organic Chemistry and Biochemistry, University of Freiburg,
Albertstr. 21, D-79104 Freiburg i. Br., F.R.G.
The standard (p°
temperature
=
=
0.1 MPa) molar enthalpies of formation DfHm°(l or cr) at the
298.15 K were measured using combustion calorimetry for
T
benzophenone-imine (A), N-methyl-benzaldehyde-imine (B), N-benzyl-benzaldehyde-imine
(C), N-benzyl-pivalophenone-imine (D), N-cyclohexyl-(2,4,6-trimethyl)-benzaldehyde-imine
(E), N-phenyl-benzaldehyde-imine (F), N-phenyl-4-nitro-benzaldehyde-imine (G), and
N-phenyl-benzophenone-imine (H). The standard molar enthalpies of vaporization Dgl Hm°
g
or sublimation DcrHm° of compounds A to H were obtained from the temperature variation of
l
the vapour pressure measured in a flow system. Molar enthalpies of fusion DcrHm° of solid
compounds were measured by d.s.c.
g
g
l
Dl Hm° or DcrHm°
DfHm°(l or cr)
DcrHm°
DfHm°(g)
kJ·mol− 1
kJ·mol− 1
kJ·mol− 1
kJ·mol− 1
A(l)
B(l)
C(l)
D(cr)
E(cr)
F(cr)
G(cr)
H(cr)
172.69 2 0.85
105.85 2 0.83
183.78 2 0.70
46.74 2 0.98
−128.0 2 2.0
181.6 2 1.4
75.72 2 0.97
51.22 2 0.20
85.0 2 1.2
109.7 2 3.3
104.85 2 0.83
98.1 2 1.2
248.4 2 1.3
157.07 2 0.85
268.8 2 1.4
156.4 2 3.4
−23.2 2 2.2
279.7 2 1.8
263.5 2 1.5
372.2 2 2.3
27.86 2 0.21
25.61 2 0.21
20.42 2 0.21
24.56 2 0.21
29.14 2 0.21
137.50 2 0.74
252.5 2 1.4
126.0 2 1.3
119.7 2 1.8
7 1997 Academic Press Limited
KEYWORDS: enthalpy of vaporization; enthalpy of sublimation; enthalpy of formation; imine
1. Introduction
Only four imines were characterized with thermochemical data in the
recent literature: the standard molar enthalpies of formation DfHm° of two
methaneimines and ethaneimine were derived(1, 2) by mass spectrometry, with
uncertainties of about 2(8 to 16) kJ·mol−1; and the thermochemical quantities of
N-phenyl-benzaldehyde-imine were measured by combustion calorimetry.(3) These
a To whom correspondence should be addressed.
b Present address: Institute of Physical Chemistry, University of Rostock, Hermannstr. 14, 18051
Rostock, F.R.G. sergey.verevkin.chemie.uni-rostock.de
0021–9614/97/101175 + 09 $25.00/0/ct970242
7 1997 Academic Press Limited

1176
S. P. Verevkin, J. Morgenthaler, and C. Ruchardt
FIGURE 1. Structures of benzophenone-imine (A), N-methyl-benzaldehyde-imine (B),
N-benzyl-benzaldehyde-imine (C), N-benzyl-pivalophenone-imine (D), N-cyclohexyl-(2,4,6-trimethyl)-
benzaldehyde-imine (E), N-phenyl-benzaldehyde-imine (F), N-phenyl-4-nitro-benzaldehyde-imine (G),
and N-phenyl-benzophenone-imine (H).
results are too limited to provide any reasonable insight into the energetics of imines.
The present paper describes a systematic investigation of the thermochemistry of
imines. The resulting standard molar enthalpies of formation in the gas state were
obtained from calorimetrically measured molar enthalpies of combustion and molar
enthalpies of sublimation or vaporization obtained by a transpiration method.
2. Experimental
Imines with hydrogen atoms or small alkyl groups attached to the carbon
or the nitrogen atom (methaneimine, ethaneimine) are known to be unstable
in the condensed phase.(1) This precludes the preparation of pure samples for
a thermochemical investigation. We chose, therefore, for this investigation, imine
molecules which were stabilized by attached phenyl substituents (figure 1).
The pure Aldrich products A, B, C, and F, each with a mass-fraction purity of
about 0.99, were purified by repeated distillation under reduced pressure (A to C).
To avoid traces of water in liquid samples for combustion experiments, the purified
samples were dried over molecular sieves and distilled once more before combustion.
Such a procedure produced a colourless material, and the absence of water was
shown by Karl Fischer titration. A synthetic pathway to the molecules D, E, G, and
H was successfully found following Padka et al.(4) A mixture with equal amounts of
aldehyde and amine and a catalytic amount of toluenesulfonic acid in toluene was
refluxed and stirred for 24 h. Then the ctalyst was removed by washing with NaOH.
The organic layer was dried over MgSO4, and the solvent was evaporated. The

Thermochemistry of imines
1177
TABLE 1. The structures of the investigated imines established by n.m.r. spectroscopy: 1H-n.m.r.
(frequency 250 Mhz, solvent CDCl3, and tetramethylsilane as internal standard)
Compound
n.m.r. peak assignments
N-benzyl-pivalophenone-imine
d = 1.21 ppm (s, 9H, -CH3), 4.23 (s, 2H, .N-CH2),
7.19–7.45 (m, 6H, ArH).
N-cyclohexyl-(2,4,6-trimethyl)-benzaldehyde-imine d = 1.20–1.51 ppm (m, 3H, qCH2), 1.54–1.92
(m, 7H, qCH2), 2.28 (s, 3H, -CH3), 2.36 (s, 6H,
-CH3), 3.12–3.27 (m, 1H, .N-CH) 6.85 (s, 2H,
Ar-H), 8.58 (s, 1H, -N.CH).
N-phenyl-benzaldehyde-imine
N-phenyl-4-nitro-benzaldehyde-imine
N-phenyl-benzophenone-imine
d = 7.13–7.28 ppm (m, 3H, Ar-H), 7.33–755 (m,
5H, Ar-H), 7.84–197 (m, 2H, Ar-H), 8.48 (s, 1H,
.N-CH).
d = 7.48–7.67 ppm (m, 5H, Ar-H), 7.88–8.00 (m,
2H, Ar-H), 8.03–8.17 (m, 2H, Ar-H), 8.52 (s, 1H,
-N.CH).
d = 6.67–6.80 ppm (m, 2H, Ar-H), 6.88–7.00 (m,
1H, Ar-H), 7.05–7.21 (m, 4H, Ar-H), 7.22–7.33
(m, 3H, Ar-H), 7.34–7.53 (m, 3H, Ar-H), 7.68–7.81
(m, 2H, Ar-H).
compounds D to H were purified by repeated crystallization from petroleum ether
(boiling temperature range 303 K to 323 K) and further sublimed under reduced
pressure to remove any traces of solvent.
The structures of the compounds D, E, G, and H were established by n.m.r.
spectroscopy: the n.m.r. peak assignments are shown in table 1. The degree of purity
was determined by g.l.c. and by d.s.c.(5) For all solid compounds, a purity greater
than mass fraction 0.9990 was established by d.s.c. studies of the melting process.(5)
No impurities (q1 mass fraction ·10−4) could be detected in B and D to H by g.l.c.
In the liquid samples A and C, mass fractions 15·10−4 and 17·15−4 of unidentified
impurities were found by g.l.c. (no corrections were applied in the calculation of the
molar enthalpies of combustion).
All compounds were handled under an inert atmosphere (N2) using carefully dried
1
solvents. We used the following equipment: H-n.m.r., Bruker WM 250 (250 MHz),
CDCl3 solvent, and tetramethylsilane as an internal standard; G.l.c., Carlo Erba
Fraktometer Vega Series GC 6000, Hewlett Packard Integrator 3390A, N2-flow of
0.333 cm3·s−1, SE-30 capillary column length 25 m. The standard temperature
program of the g.l.c. was T = 363 K for 60 s, followed by a rate 0.167 K·s−1 up to
T = 523 K. Melting temperatures and enthalpies of fusion were determined with a
Perkin-Elmer DSC-2C coupled with an Olivetti PC M 28.
For measurements of the enthalpies of combustion of substances A to H, an
isoperibol macrocalorimeter with a static bomb and a stirred water bath was used.
The substances were pressed into pellets of mass 1400 mg or, if liquid, were placed
in polyethene capsules. All substances were burned in oxygen at p = 3.05 MPa. The
completeness of the combustion of the crystalline samples was ensured by the
addition of about 50 mg of oil to the pellet. The preparation of the samples for
combustion was carried out in a glove-box under an inert atmosphere (N2). The
detailed procedure has been described previously.(6, 7) The calorimetric bomb used in

1178
S. P. Verevkin, J. Morgenthaler, and C. Ruchardt
these experiments was lined with platinum. For complete dissolution of the product
gases after combustion, 0.78 g of water was added to the bomb. The energy of
ignition was determined to be 1.46 J. The energy equivalent of the calorimeter ocalor
was determined with a standard reference sample of benzoic acid (sample SRM 39i,
NIST). From eight experiments, ocalor was measured to be (25112.6 2 1.9) J·K−1. For
the reduction of the data to standard conditions, conventional procedures(8) were
used. The corrections made for nitric acid formation were based on titration with
0.1 mol·dm−3 NaOH(aq). The atomic weights used were those recommended by the
IUPAC Commission.(9) The densities of the solid substances were determined by
submerging pellets of the substances in water in a calibrated 10 cm3 pycnometer. The
densities of the liquid compounds were taken from the Aldrich catalog. The massic
heat capacities and enthalpies of fusion were measured with the d.s.c. A summary
of auxiliary quantities for the combustion experiments and information necessary for
reducing apparent mass to mass is given in table 2.
The enthalpies of vaporization of compounds A to C, and the enthalpies of
sublimation of compounds D to H, were determined from their equilibrium vapour
pressures, which were measured on the basis of the amount of the gaseous
compounds transported in a well-defined nitrogen stream.(10–12) The substances were
mixed with glass beads and placed in a thermostatted U-tube. At each of several
different temperatures, a nitrogen stream was passed through the U-tube, the
transported material was collected in a cold trap, and its amount was determined by
g.l.c. analysis using an internal standard. The vapour pressure p at the saturation
temperature was calculated from the amount of condensed product collected
within a definite time, and the residual vapour pressure at condensation temperature
was taken into account. The latter was calculated from a linear correlation
between ln[(m/m°)/{V(N2)/V°}] against T−1 obtained by iteration, where m is the
l
TABLE 2. Temperature Tfus and standard molar enthalpy of fusion DcrHm°, density r(293 K), massic heat capacity
cp (298.15 K), and expansion coefficients (dvm/dT)p of the materials used in present study
l
r(293 K) cp(298.15 K) a
10−6·(dvm/dT)p
a
c
Tfus
K
DcrHm° a
kJ·mol−1
g·cm−3
J·K−1 g−1
dm−3·K−1
benzophenone-imine
1.080
0.967
1.038
1.02
1.13
1.09
1.84
1.38
1.97
2.34
1.72
1.67
1.76
1.67
0.84(6)
1.67(6)
2.53
1.0
1.0
1.0
0.1
0.1
0.1
0.1
0.1
1.0
0.1
0.1
N-methyl-benzaldehyde-imine
N-benzyl-benzaldehyde-imine
N-benzyl-pivalophenone-imine
339.55
27.86
25.61
20.42
24.56
29.14
N-cyclohexyl-(2,4,6-trimethyl)-benzaldehyde-imine 339.35
N-phenyl-benzaldehyde-imine
N-phenyl-4-nitro-benzaldehyde-imine
N-phenyl-benzophenone-imine
oil d
329.65
347.15
392.25
1.15
1.12
0.880(6)
1.500(6)
0.920
cotton e
polyethene f
l
a From d.s.c. measurements; the usual error bars of DcrHm° measurements are 20.21 kJ·mol−1 b Measured with
.
the pycnometer only for solids; for liquids, densities from the Aldrich catalog were used. c Estimated. d From nine
combustion experiments, Dcu°(CH1.940) = −(46003.624.0) J·g−1. e From 10 combustion experiments, Dcu°(CH1.774O0.887) =
−(16945 2 4.2) J·g−1) J·g−1 f From 11 combustion experiments, Dcu°(CH1.930) = −(46361.0 2 3.1) J·g−1
. .

Thermochemistry of imines
1179
mass of transported compound; m° = 1 mg; V(N2) is the volume of transporting gas;
and V° = 1 dm3. The molar enthalpies of vaporization or sublimation were
calculated from the slope of the linear correlation:
Dgl Hm° = −R(dln[(m/m°)/{V(N2)/V°}]/dT−1),
(1)
with R = 8.31451 J·K−1·mol−1. The observed enthalpies of vaporization DlgHm°(T) or
g
sublimation DcrHm°(T) obtained by this procedure are listed in table 3.
3. Results and discussion
The results for a typical combustion experiment on each compound are given in
table 4. The individual values of the standard massic energy of combustion Dcu°,
together with the mean and its standard deviation, are given in table 5. To derive
DfHm° from DcHm° the following molar enthalpies of formation were used:(9) for H2O(l),
−(285.83 2 0.04) kJ·mol−1; and for CO2(g), −(393.51 2 0.13) kJ·mol−1
.
TABLE 3. Results from measurements of the vapour pressure p by the transpiration method(11, 12)
c
c
T/K a
m/mg b
V(N2)/dm3
p/Pa d
T/K a
m/mg b
V(N2)/dm3
p/Pa d
benzophenone-imine
308.5
314.3
318.5
323.6
1.04
1.54
0.987
0.987
30.52
28.05
11.62
7.81
g
0.486
0.752
1.161
1.726
328.5
333.2
338.3
1.15
1.22
1.35
5.80
4.15
3.20
2.712
4.025
5.769
Dl Hm°(323.4 K) = (74.21 2 0.97) kJ·mol−1
g
Dl Hm°(298.15 K) = (75.72 2 0.97) kJ·mol−1
N-methyl-benzaldehyde-imine
283.4
288.5
293.6
298.4
4.95
6.00
5.68
7.67
4.22
3.43
2.22
2.12
25.84
37.84
54.65
76.69
303.6
308.4
313.3
318.3
7.75
5.26
3.38
2.43
1.52
107.5
0.747
0.343
0.182
147.9
206.4
278.6
g
Dl Hm°(300.9 K) = (51.06 2 0.20) kJ·mol−1
g
Dl Hm°(298.15 K) = (51.22 2 0.20) kJ·mol−1
N-benzyl-benzaldehyde-imine
308.5
313.5
314.3
318.5
323.6
0.397
0.602
0.748
0.436
0.517
34.03
30.40
32.59
12.95
8.88
0.1482
0.2511
0.2910
0.4274
0.7385
326.5
328.5
333.2
338.3
339.5
0.504
0.602
0.660
0.748
0.534
6.80
6.47
4.63
3.57
2.41
0.9408
1.180
1.808
2.656
2.808
g
Dl Hm°(324.0 K) = (83.4 2 1.2) kJ·mol−1
g
Dl Hm°(2983.15 K) = (85.0 2 1.2) kJ·mol−1
N-benzyl-pivalophenone-imine
318.4
323.2
328.2
2.39
4.17
6.53
117.6
107.0
99.11
0.2006
0.3848
0.6493
333.2
336.5
6.36
5.06
47.47
28.18
1.320
1.769

1180
S. P. Verevkin, J. Morgenthaler, and C. Ruchardt
TABLE 3—continued
c
c
T/K a
m/mg b
V(N2)/dm3
p/Pa d
T/K a
m/mg b
V(N2)/dm3
p/Pa d
g
DcrHm°(327.5 K) = (107.9 2 3.3) kJ·mol−1
g
DcrHm°(327.5 K) = (109.7 2 3.3) kJ·mol−1
N-benzyl-pivalophenone-imine
341.3
346.3
352.6
4.95
4.95
3.08
17.91
12.44
4.58
2.728
3.926
6.637
357.1
361.5
366.1
1.78
2.16
2.45
1.91
1.71
1.37
9.192
12.45
17.65
g
Dl Hm°(353.7 K) = (78.31 2 0.85) kJ·mol−1
g
Dl Hm°(298.15 K) = (81.64 2 0.85) kJ·mol−1
N-cyclohexyl-(2,4,6-trimethyl)-benzaldehyde-imine
318.2
323.6
328.4
0.982
1.46
2.44
52.59
41.82
38.98
g
0.2019
0.3766
0.6759
331.3
336.1
1.36
0.516
15.59
3.50
0.9414
1.592
DcrHm°(327.2 K) = (103.11 2 0.83) kJ·mol−1
g
DcrHm°(298.15 K) = (104.85 2 0.83) kJ·mol−1
N-cyclohexyl-(2,4,6-trimethyl)-benzaldehyde-imine
341.4
348.2
353.5
0.505
0.788
0.699
2.27
2.02
1.26
2.404
4.215
5.998
358.2
363.4
368.5
0.835
0.680
0.779
1.09
0.600
0.490
8.283
12.25
17.19
g
Dl Hm°(355.0 K) = (75.30 2 0.95) kJ·mol−1
g
Dl Hm°(298.15 K) = (78.71 2 0.95) kJ·mol−1
N-phenyl-benzaldehyde-imine
293.5
298.6
302.4
307.5
312.6
1.36
1.32
1.71
2.79
2.73
442.9
205.8
151.7
139.3
69.35
0.04183
0.08763
0.1543
0.2740
0.5384
316.7
318.4
321.2
321.8
326.2
2.22
4.76
1.23
5.31
5.02
34.87
60.98
12.42
48.73
30.03
0.8686
1.066
1.349
1.490
2.282
g
DcrHm°(309.9 K) = (97.4 2 1.2) kJ·mol−1
g
DcrHm°(298.15 K) = (98.1 2 1.2) kJ·mol−1
N-phenyl-4-nitro-benzaldehyde-imine
359.2
363.6
368.3
372.8
1.19
1.96
1.52
1.80
41.10
46.32
24.45
18.15
0.3178
0.4647
0.6823
1.086
377.7
382.7
386.9
1.30
1.61
1.69
9.32
7.51
5.79
1.530
2.342
3.194
g
Dl Hm°(373.1 K) = (96.9 2 1.3) kJ·mol−1
g
Dl Hm°(298.15 K) = (101.4 2 1.3) kJ·mol−1
N-phenyl-benzophenone-imine
348.1
352.9
359.2
363.6
368.3
1.02
1.98
1.77
3.01
2.61
81.67
83.50
42.18
47.53
25.09
0.1205
0.2286
0.4031
0.6106
1.000
372.8
377.7
382.7
386.9
3.23
2.77
3.76
4.12
18.62
9.57
7.70
5.94
1.670
2.791
4.699
6.675
g
DcrHm°(367.5 K) = (115.5 2 1.8) kJ·mol−1
g
DcrHm°(298.15 K) = (119.7 2 1.8) kJ·mol−1
a Temperature of saturation, N2 gas flow (0.26 to 0.52) cm3·s−1 by each run of saturation. b Mass of
transferred sample condensed at T = 243 K. c Volume of nitrogen used to transfer sample. d Vapour
pressure at temperature T of experiment; corrections for residual vapour pressure at T = 243 K were
made.

Thermochemistry of imines
1181
TABLE 4. Results from typical combustion experiments at T = 298.15 K (p° = 0.1 MPa), where
benzophenone-imine, N-methyl-benzaldehyde-imine, N-benzyl-benzaldehyde-
A
imine,
imine,
=
B
=
C =
D
F
=
=
N-benzyl-pivalophenone-imine,
N-phenyl-benzaldehyde-imine,
E
G
=
=
N-cyclohexyl-(2,4,6-trimethyl)-benzaldehyde-
N-phenyl-4-nitro-benzaldehyde-imine, and
H = N-phenyl-benzophenone-imine a
A
B
C
D
m(substance)/g b
m'(cotton)/g b
m0(oil)/g b
0.684844
0.001057
0.392126
0.001070
0.744186
0.001033
0.600494
0.000894
0.045788
m1(polyethene)/g b
0.266933
1.52642
−38332.39
0.273294
1.10077
−27643.24
0.271073
1.64770
−41377.98
DTc/K c
1.04807
−26319.86
ocalor·(−DTc)/J
ocont·(−DTc)/J
DUcorr/J
−21.59
20.36
17.91
−15.34
11.65
18.13
−23.66
21.74
17.50
−14.32
12.77
15.14
−m'Dcu'/J d
−m0Dcu0/J d
−m'0Dcu1/J d
DU(HNO3)/J
2106.43
12375.29
38.51
−37819.5
12670.16
31.35
−38063.9
12567.21
40.00
−38637.8
26.27
−40253.7
Dcu°(sub)/(J·g−1
)
E
F
G
H
m(substance)/g b
m'(cotton)/g b
m0(oil)/g b
0.368441
0.000841
0.059312
0.481974
0.001023
0.065000
0.435449
0.000906
0.047526
0.547545
0.000881
0.062338
m1(polyethene)/g b
DTc/K c
0.71361
−17920.48
0.84800
−21295.48
0.60095
−15091.28
0.95164
−23898.08
ocalor·(−DTc)/J
ocont·(−DTc)/J
DUcorr/J
−9.21
7.03
14.24
−11.08
11.42
17.33
−7.86
9.29
15.35
−13.02
13.42
14.92
−m'Dcu'/J d
−m0Dcu0/J d
−m'0Dcu1/J d
DU(HNO3)/J
2728.56
2990.23
2186.39
2867.76
18.51
−41146.1
25.08
−37888.0
29.55
−29526.1
22.09
−38337.4
Dcu°(sub)/(J·g−1
)
a For the definition of the symbols see reference 8: Th = 298.15 K; V(bomb) = 0.2664 dm3;
pi(gas) = 3.05 MPa; mi(H2O) = 0.78 g; DU(ign) = 1.5 J; m(Pt) = 12.18 g. b Masses obtained from apparent
masses. DTc = (Tf − Ti + DTcorr); ocalor = (25112.6 2 1.9) J·K−1; ocont·(−DTc) = (ociont)·(Ti − 298.15 K) +
c
f
d
(ocont)·(298.15 K − Tf + DTcorr). DUcorr, the correction to standard states, is the sum of items 81 to 85, 87
to 90, 93, and 94 in reference 8.
g
g
The enthalpies of vaporization Dl Hm° or sublimation DcrHm° at T = 298.15 K
are recorded in table 6. Because the temperature range of the vapour pressure
measurements was usually above T = 298.15 K the enthalpies of vaporization
or sublimation had to be corrected to this reference temperature. The
corrections were estimated with the help of the ‘‘Sidgwick correction’’:
g
g
{DcrHm°(ꢀTꢁ) − DcrHm°(298.15 K)}/(kJ·mol−1) = −6·10−2·{(ꢀTꢁ/K) − 298.15},
following the recommendation of Chickos et al.(13) With these corrections, and
the measured values of Dl Hm°(T) and DcrHm°(T) from table 3, the standard molar
enthalpies of vaporization or sublimation at T = 298.15 K wre calculated (tables 3
and 6). Table 6 also lists the standard molar enthalpies of combustion, and standard
g
g

1182
S. P. Verevkin, J. Morgenthaler, and C. Ruchardt
TABLE 5. Values of massic energies of combustion Dcu° at T = 298.15 K (p° = 0.1 MPa) for
imines: A = benzophenone-imine; B = N-methyl-benzaldehyde-imine; C = N-benzyl-benzaldehyde-
imine;
imine;
D
F
=
=
N-benzyl-pivalophenone-imine;
N-phenyl-benzaldehyde-imine;
E
G
=
=
N-cyclohexyl-(2,4,6-trimethyl)-benzaldehyde-
N-phenyl-4-nitro-benzaldehyde-imine; and
H = N-phenyl-benzophenone-imine
A
B
C
D
E
F
G
H
−Dcu°/(J·g−1
)
37819.5
37829.8
37812.8
37824.9
38051.2
38063.9
38055.8
38079.2
38637.2
38637.8
38631.5
38630.7
40258.6
40253.7
40250.6
40261.0
41146.1
41181.9
41160.2
41175.5
37888.0
37860.2
37861.9
37856.1
37888.4
29526.1
29536.2
29528.3
29533.8
38337.4
38322.0
38334.8
38342.0
a
ꢀ−Dcu°ꢁ/(J·g−1
)
37821.8
23.7
38062.5
26.2
38634.3
21.9
40256.0
22.4
41165.9
28.0
37870.9
27.1
29531.0
22.4
38334.1
24.3
a Mean value and uncertainty interval of Dcu°.
molar enthalpies of formation in the condensed and gaseous states. The given
standard deviations of the mean include the uncertainties from calibration and
the combustion energies of the auxiliary materials.
The thermochemical properties of substances A to E and G to H were determined
for the first time. Only the enthalpy of formation DfHm°(cr) = (167.8 2 7.1) kJ·mol−1
of N-phenyl-benzaldehyde-imine (F) had been measured earlier by Coates and
Sutton,(3) using combustion calorimetry. The reported value is 13.8 kJ·mol−1 more
negative than that determined in this work, but due to the error limit of
27.1 kJ·mol−1, both measurements are in acceptable agreement. The enthalpy of
sublimation of F, (98.1 2 1.2) kJ·mol−1, however, is significantly different from
the value (85.8 2 2.1) kJ·mol−1 of Coates and Sutton.(3)
The investigation of the compounds A to H covered a broad range of structures
of imines. The resulting standard enthalpies of formation fill the gap of available
thermochemical data for imines and provide data to use in the calculation of the
thermochemical properties of compounds with similar structures.
TABLE 6. Thermochemical results at T = 298.15 K (p° = 0.1 MPa)
g
b
a
g
b
Dl Hm°
−DcHm°(l or cr)
DfHm°(l or cr)
DcrHm°
DfHm°(g)
−1
State
−1
−1
−1
−1
kJ·mol
kJ·mol
kJ·mol
kJ·mol
kJ·mol
benzophenone-imine
l
l
l
cr
cr
cr
cr
cr
6860.37 2 0.85
4540.16 2 0.83
7550.80 2 0.70
10131.20 2 0.98
9455.2 2 2.0
6869.3 2 1.4
6682.26 2 0.74
9872.9 2 1.4
172.69 2 0.85 75.72 2 0.97
105.85 2 0.83 51.22 2 0.20
248.4 2 1.3
157.07 2 0.85
268.8 2 1.4
156.4 2 3.4
−23.2 2 2.2
279.7 2 1.8
263.5 2 1.5
372.2 2 2.3
N-methyl-benzaldehyde-imine
N-benzyl-benzaldehyde-imine
N-benzyl-pivalophenone-imine
N-cyclohexyl-(2,4,6-trimethyl)-benzaldehyde-imine
N-phenyl-benzaldehyde-imine
N-phenyl-4-nitro-benzaldehyde-imine
N-phenyl-benzophenone-imine
183.78 2 0.70
85.0 2 1.2
c
c
d
46.74 2 0.98 81.64 2 0.85
109.7 2 3.3
d
−128.0 2 2.0
181.6 2 1.4
137.50 2 0.74 101.4 2 1.3
252.5 2 1.4
78.71 2 0.95
104.85 2 0.83
98.1 2 1.2
c
e
126.0 2 1.3
119.7 2 1.8
a
b
Calculated from the massic energies of combustion in table 5. From the measurements of vapour pressures at different temperatures (table 3)
c
d
e
using the Clausius–Clapeyron equation. Measured above the melting temperature. Taken into account in the estimation of DfHm° (g). Enthalpy
of sublimation DcrHm° calculated as the sum of Dl Hm° (this table) and DcrHm° (table 2).
g
g
l

Thermochemistry of imines
1183
Thanks are due to the Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie for financial support. Thanks are also due to F. Schillinger and
E. Hickl for technical assistance and to Dr H.-D. Beckhaus for his advice.
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(Received 31 January 1997, in final form 15 April 1997)
O-663