Heat capacity and enthalpy of fusion of pyrimethanil laurate (C 24H37N3O2)

Article abstract of DOI:10.1016/j.jct.2004.06.002

Low-temperature heat capacities of pyrimethanil laurate (C ₂₄H₃₇N₃O₂) were precisely measured with an automated adiabatic calorimeter over the temperature range between T = 78 K and T = 340 K. The sample was obs

Full text of DOI:10.1016/j.jct.2004.06.002

J. Chem. Thermodynamics 36 (2004) 895–899
www.elsevier.com/locate/jct
Heat capacity and enthalpy of fusion of pyrimethanil
laurate (C24H37N3O2)
a,
a
b
b
Xiao-Hong Sun *, Yuan-Fa Liu , Zhi-Cheng Tan , You-Ying Di ,
a
Hui-Fang Wang , Mei-Han Wang
b
a
College of Chemical Engineering, Chemical Research Institute, Northwest University, Xi-an 710069, PR China
Thermochemistry Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, PR China
b
Received 5 May 2004; accepted 8 June 2004
Available online 17 August 2004
Abstract
Low-temperature heat capacities of pyrimethanil laurate (C24H37N3O2) were precisely measured with an automated adiabatic
calorimeter over the temperature range between T = 78 and T = 340 K. The sample was observed to melt at
K
(321.52 0.04) K. The molar enthalpy and entropy of fusion as well as the chemical purity of the compound were determined
to be (67244 11) J Æ molꢀ1, (209.28 0.02) J Æ molꢀ1 Æ Kꢀ1, (0.9943 0.0004) mass fraction, respectively. The extrapolated melting
temperature for the absolutely pure compound obtained from fractional melting experiments was (322.264 0.006) K.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Pyrimethanil laurate; Heat capacity; Adiabatic calorimetry; DSC
1. Introduction
showed it could be used for controlling many kinds of
fungi, such as Pythium solani, Gibberella nicotiancola,
Fusarium oxysporium f.sp. uasinfectum and Fusarium
oxysporium f.sp. cinerea [4] of plant, fruit, vegetable
and foodstuff. So, It can be used for a new high-effi-
ciency fungicide. The application and synthetic methods
of the compound have been reported [4], but no reports
on the thermodynamic properties of the new substance
have been reported. For the application of the com-
pound, the thermodynamic data for the pyrimethanil
laurate are urgently required. In the present work, it
was synthesized and its structure has been confirmed
Pyrimidinamine compounds are heterocyclic com-
pounds with novel biological activities [1]. They have
been applied to medicine and pesticide synthesis for
their important physiological-action [2,3]. Compared
with the free pyrimethanil, pyrimethanil salts have a re-
duced vapour pressure, which increases the persistence
of the compounds on the crop and they have increased
activities in many aspects. Pyrimethanil laurate (molec-
ular formula: C24H37N3O2) is an important new com-
pound. It was synthesized by pyrimidinamine and
lauric acid. The preliminary biological activities tests
1
by IR, H NMR and elemental analysis. The low-tem-
perature heat capacity measurements of the compound
were carried out with an adiabatic calorimeter. The ba-
sic thermodynamic parameters, such as the melting
point, molar enthalpy and entropy of melting have been
determined.
*
Corresponding author. Tel.: +86-29-88472411; fax: +86-29-
88483537.
E-mail address: xhsun888@sohu.com (X.-H. Sun).
0021-9614/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jct.2004.06.002

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X.-H. Sun et al. / J. Chem. Thermodynamics 36 (2004) 895–899
2. Experimental
in the temperature range of (78 to 364) K to eliminate
the heat loss owing to the gas convection, and a small
amount of helium gas was introduced through a length
of copper capillary at the centre of the upper cover into
the cell to improve the heat transfer of the whole sample
cell. The sample cell was sealed with the tin solder after
the copper capillary was pinched off from the tube end.
Two adiabatic shields surrounded the sample cell in turn
and a vacuum can was immersed in liquid nitrogen. The
two adiabatic shields were made of chromium-plated
copper and equipped with manganin heating wires.
Two sets of six-junction chromel-contantan (Ni 55%,
Cu 45%) thermocouples were used to measure the tem-
perature differences between the sample cell and the in-
ner adiabatic shield and between the inner and the
outer adiabatic shields. The temperatures of the two
shields were controlled separately and automatically
with two units of auto-adiabatic controller. When the
2.1. Sample preparation and characterization
2.1.1. Equipment and reagents
Pyrimethanil laurate was made according to the
method reported in literature [5], pyrimethanil (purified
3 times, the purity was 0.9980 mole fraction, m.p. 96.3
ꢁC [6]), ethanol, lauric acid, were of analytical grade.
PE-2400 elemental analyzer, BRUKER EQUNINOX-
1
55 IR spectral meter, Varian Inova-400 H NMR spec-
trum, Agilent gas chromatograph/Hewlett Packard mass
spectrometry and SMP3 melting point apparatus were
applied to characterize the structure of the compound.
2.1.2. The scheme of the formation reaction of pyrimeth-
anil laurate
CH
CH3
N
3
N
N
EtOH
.
+
NH
CH (CH ) COOH
3 2 10
NH
CH (CH ) COOH
3
2 10
N
CH
CH3
3
2.1.3. Experimental procedures
temperature in the sample cell increases due to heating,
the thermocouples measure the temperature differences.
This signal is used to control the heaters distributed on
the walls of the inner and outer shields, respectively.
Both shields were heated under the control of the signal
and kept at the same temperature as that of the sample
cell. In this way, the heat loss caused by the radiation is
greatly reduced. The miniature platinum resistance ther-
mometer (IPRT No. 2, produced by Shanghai Institute
of Industrial Automatic Meters, 16 mm in length, 1.6
mm in diameter and a nominal resistance of 100 X)
was applied to measure the temperature of the sample.
The thermometer was calibrated on the basis of ITS-
90 by the Station of Low-temperature Metrology and
Measurements, Academia Sinica.
The sample was heated using the standard discrete
heating method and the temperature of the sample
was alternatively measured. The heating duration was
10 min, the equilibrium time of each temperature point
is 5 min, and the temperature drift rates of the sample
cell measured in an equilibrium period were usually
within (10ꢀ3 to 10ꢀ4) K Æ minꢀ1. During the heat-ca-
pacity measurements, the temperature difference be-
tween the inner adiabatic shield and the sample cell
was automatically kept within 10ꢀ3 K Æ minꢀ1 in order
to obtain a satisfactory adiabatic effect and corre-
sponding equilibrium temperature were corrected for
heat loss [7,8].
A solution of pyrimethanil and lauric acid in anhy-
drous alcohol was stirred for 1 h at room temperature.
The precipitate formed was filtered and recrystallized
from anhydrous alcohol to yield compound. The final
product pyrimethanil laurate was a colorless crystal.
Its mass fraction purity was 0.9957 (GC).
2.1.4. Analysis result of pyrimethanil laurate
The melting point of the final product was deter-
mined to be T = (321.55 to 322.35) K. The results of ele-
mental analysis were: N: 10.51 (10.52); C: 72.08 (72.16);
H: 9.26 (9.34). 1H MNR (CDCl3) absorption peaks were
detected at d = 0.88 (t, 3 H), 1.29 to 1.32 (m, 18 H), 1.63
to 1.71 (m, 3 H), 2.38 (s, 6 H), 6.46 (s, 1 H), 6.99 to 7.75
(m, 5 H), 8.92 (s, 1 H ) 1 · 10ꢀ6. IR (KBr disks) showed
characteristic absorption peaks at 3294 (NH), 2922
(CH), 2546 ðNHþ2 Þ, 1703 (C‚O), 1628 (Ph) cmꢀ1
.
2.1.5. Adiabatic calorimetry
The heat capacity measurements were made by an
adiabatic calorimetric system for small samples over
the temperature range between T = (78 and 340) K.
The construction of the calorimeter has been described
previously [5,6] in detail. It consists of a sample cell, a
platinum resistance thermometer, a heater, two (inner
and outer) adiabatic shields, two sets of differential ther-
mocouples, a vacuum can and a Dewar vessel. Liquid
nitrogen was used as the cooling medium. The evacu-
ated can or chamber was kept within 10ꢀ3 Pa vacuum
The mass of the sample loaded in the sample cell
amounted to 2.1856 g, which was equivalent to
0.00547 mol based on its molar mass of 399.57 g Æ molꢀ1
.

X.-H. Sun et al. / J. Chem. Thermodynamics 36 (2004) 895–899
897
TABLE 1
Experimental molar heat capacities of pyrimethanil laurate of molar mass
The molar heat capacities of a-Al2O3 used as the stand-
ard substance were measured in the same temperature
range as that of the sample measurement in order to verify
the reliability of the calorimeter. The sample mass used
for the measurements was 1.6382 g, which was equivalent
to 0.0161 mol based on its molar mass, M(Al2O3)
= 101.9613 g Æ molꢀ1. Deviations of the experimental re-
sults from those of the smoothed curve lie within
0.2%, while the inaccuracy is within 0.5%, as com-
pared with those of the former National Bureau of Stand-
ard [9] over the whole experimental temperature range.
M = 399.57 g Æ molꢀ1 where the gas constant R = 8.314472 J Æ molꢀ1 Æ Kꢀ1a
T/K
Cp.m/R
T/K
Cp.m/R
T/K
Cp.m/R
78.402
25.806
26.342
26.946
27.546
27.791
28.310
28.694
29.016
29.400
29.956
30.746
31.088
31.614
32.031
32.338
32.768
33.320
33.724
34.116
34.421
34.859
35.093
35.511
35.970
36.366
36.716
37.201
37.702
38.090
38.589
39.140
39.491
40.014
40.285
40.479
40.670
40.961
41.228
41.405
41.678
41.845
42.261
42.710
42.901
43.317
43.738
44.006
44.290
44.530
45.092
45.556
45.856
46.288
46.597
47.132
47.352
47.677
48.154
48.571
48.924
49.406
49.881
50.034
205.489
207.387
209.269
213.631
215.481
217.331
219.163
220.991
222.806
224.609
226.397
228.168
229.915
231.659
233.448
235.258
237.065
238.858
240.619
242.331
244.029
245.761
248.096
250.994
253.795
256.525
259.211
261.873
264.512
267.132
269.725
272.295
274.788
277.250
279.668
282.044
284.355
286.643
288.902
291.095
293.226
295.400
297.595
299.782
301.949
304.046
306.132
308.199
310.218
312.144
313.960
315.689
317.308
318.738
319.810
320.446
320.780
320.932
321.029
321.100
321.151
321.190
321.219
50.354
321.244
321.266
321.284
321.299
321.318
321.337
321.354
321.390
321.995
323.462
325.282
327.089
328.879
330.652
332.412
334.150
335.872
337.574
339.257
6081.8
6448.8
7395.2
7745.4
8035.7
7398.2
7007.2
4292.2
216.58
99.893
100.64
101.29
101.98
102.39
102.91
103.46
104.24
104.55
104.98
80.594
82.774
50.971
51.390
51.829
52.161
52.578
52.959
53.470
53.776
54.208
54.623
55.016
55.523
55.837
56.407
56.800
57.247
57.650
58.443
58.872
59.460
60.049
60.377
60.769
61.335
61.872
62.252
62.705
63.041
63.697
64.193
64.674
65.119
65.554
66.144
66.630
66.994
67.361
67.932
68.380
68.949
69.483
70.073
70.546
71.003
71.655
72.001
72.655
82.834
91.243
100.52
113.50
139.92
211.91
408.75
788.02
1332.7
1960.5
2629.8
3383.6
4107.6
4945.8
5681.4
84.912
87.020
89.126
91.210
93.268
95.351
97.443
99.517
101.557
103.546
105.483
107.373
109.228
111.051
112.844
114.617
116.367
118.099
119.809
121.504
123.181
124.846
126.497
128.130
129.753
131.360
133.506
136.037
138.469
140.851
143.199
145.519
147.817
150.087
152.338
154.568
156.779
158.978
161.158
163.312
165.460
167.591
169.710
171.815
173.908
175.989
178.061
180.105
182.135
184.155
186.153
188.138
190.109
192.064
194.009
195.939
197.862
199.773
201.683
203.584
a
2.1.6. Differential scanning calorimetry
A TA 2100 Thermal Analysis System coupled with a
personal computer loaded with the program for data
processing was used for the differential scanning calori-
metry (DSC) measurements, the DSC with aluminum
sample tray and sapphire reference was operated at a
heating rate of 10 K Æ minꢀ1 under nitrogen atmosphere
with a flow rate of 40 ml Æ minꢀ1. The mass of the sample
used for experiment was 3.8430 mg.
3. Results and discussion
3.1. Heat capacity
All heat capacity measurements are listed in table 1
and plotted in figure 1. The structure of the compound
is stable; no phase change occurred in the solid phase
from T = (78 to 308) K, nor did association or decompo-
sition occur in the liquid phase from T = (323 to 340) K.
The experimental values of the heat capacities have
been fitted to polynomial equations by the least square
fitting.
For the solid phase:
C
p:m=J ꢁ Kꢀ1 ꢁ molꢀ1 ¼ 113:8876 þ 1:3694Xþ
6:7794 ꢂ 10ꢀ4X2:
ð1Þ
In which X = {(T/K) ꢀ 193}/115. The above equation is
valid from T = (78 to 308) K, with an uncertainty of
0.3%.
For the liquid phase:
C
p:m=J ꢁ Kꢀ1 ꢁ molꢀ1 ¼ 824:7170 þ 6:3316Xꢀ
0:2082X2 þ 0:0061X3:
ð2Þ
In which X = {(T/K) ꢀ 331.5}/8.5. This equation applies
to the range from T = (323 to 340) K, with an uncer-
tainty of 0.25%.
3.2. Melting point, molar enthalpy and entropy of fusion
Obtained from [13].
Pre-melting occurred owing to the presence of impu-
rities in the sample. The measurement of the melting
point and molar enthalpy of fusion of the sample was
done as follows: first, the temperatures for the start of
the pre-melting and for compete melting were deter-
mined. Between these two temperatures, the melting

898
X.-H. Sun et al. / J. Chem. Thermodynamics 36 (2004) 895–899
323
322
321
320
319
318
8000
6000
4000
2000
0
8000
6000
4000
2000
0
T0 = 322.264K
T1 = 321.587K
T
C
317
290
300
310
320
330
340
316
315
314
313
T / K
100% 99.43%
50
100
150
200
250
300
350
0
2
4
6
8
10
12
14
T / K
1 / F
FIGURE 1. The experimental molar heat-capacities (Cp,m/R) of
pyrimethanil laurate (C24H37N3O2) plotted against the temperature (T).
FIGURE 2. The equilibrium temperature (T) plotted against the
reciprocal of the melting fractions (1/F) for pyrimethanil laurate
(C24H37N3O2) during fusion.
3.3. Purity determination of the sample
point was determined by successive approximation
through stepwise heating. Then, by heating the sample
from a temperature slightly lower than the initial melt-
ing temperature to a temperature slightly higher than
the final melting temperature, the enthalpy of fusion
of the sample was evaluated. The heat used for heating
the empty container and the sample was subtracted from
the total amount of heat introduced to the sample and
container during the whole melting process [8].
The melting temperature, Tfus of the sample was cal-
culated from an equation based on the heat capacity
measurements in the fusion region, as described in liter-
ature [8,10]. The molar enthalpy of fusion, DfusHm, was
determined in accordance with the method reported in
the literature [8–10]. The molar entropy of fusion,
The purity of the sample is evaluated from a set of
equilibrium melting temperature (T) and melting frac-
tions (F) corresponding to these temperatures [10,11].
The experimental results obtained from the heat
capacity measurements in the fusion region are listed
in the table 3. The equilibrium melting temperature
(T) versus the reciprocal of the melting fractions (1/
F) is a straight line, as shown in figure 3. Extrapola-
tion of the straight line to 1/F = 0 and 1/F = 1 gives
T0 and T1 for the experiment, as indicated in table
3. Here, T1 is the melting temperature of the impure
compound obtained form fraction fusion experiment
and T0 is the melting temperature of a theoretically
or absolutely pure sample. The melting point
(T1 = 321.587 K) obtained from the fractional melting
agrees well with that (Tfus = 321.52 0.04 K) obtained
from the heat capacity measurements as described
from the Vanꢀt Hoff equation [12]. The purity of
the sample (1 ꢀ N) is 0.9943 mole fraction, in agree-
ment with the result of gas chromatograph analysis
(0.9957).
D
fusSm, was derived from the molar enthalpy of fusion,
using DfusSm = DfusHm/Tfus [10,11].
The results of Tfus, DfusHm and DfusSm obtained from
the heat capacity measurements are listed in table 2.
The purity of the sample was determined from the
fractional melting in accordance with the method given
in the literature [8,10,11] to be higher than 0.9957 mole
fraction (see figure 2).
TABLE 2
The results of phase transition obtained from three series of repeated experiments of pyrimethanil laurate (M = 399.57 g Æ molꢀ1
)
Thermodynamic properties
Series 1, xi
Series 2, xi
Series 3, xi
Mean value, ꢀx
Standard deviation, ra
Tfus/K
321.42
67,247
209.23
322.264
321.587
0.9943
321.61
67,260
209.31
322.332
321.665
0.9950
321.53
67,228
209.29
322.148
321.523
0.9936
321.52
67,245
209.28
322.248
321.592
0.9943
0.04
9.29
D
D
fusHm/(J Æ molꢀ1
)
fusSm/(J Æ Kꢀ1 Æ molꢀ1
)
0.02
T0/K
T1/K
0.054
0.041
0.0004
(1 ꢀ N)
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
P
n
2
ra ¼
i¼1ðxi ꢀ ꢀxÞ =nðn ꢀ 1Þ, in which n is experimental number (n = 3); xi, experimental value of each series of repeated measurement; ꢀx, mean
value.

X.-H. Sun et al. / J. Chem. Thermodynamics 36 (2004) 895–899
899
TABLE 3
Experimental results of melting fractions (F) and equilibrium temper-
ature (T) of pyrimethanil laurate (C24H37N3O2)
0
-2
-4
T/K
F
1/F
Series 1
314.344
317.770
319.994
320.595
320.988
321.167
321.318
C24H37N3O2
-6
0.0801
0.1457
0.2905
0.3933
0.5305
0.6496
0.7963
12.3636
6.8636
3.4424
2.5424
1.8849
1.5394
1.2558
Tm = 322.05K
∆ Hm = 67.24KJmol-1
-8
-10
-12
-14
-16
-18
Series 2
317.658
320.136
320.702
321.042
321.267
321.418
0.1439
0.2872
0.4005
0.9570
0.5196
0.7931
6.9179
3.4823
2.4969
1.9246
1.5487
1.2609
300
320
340
360
380
400
420
440
460
Temperature/ K
FIGURE 3. The DSC curve of pyrimethanil laurate (C24H37N3O2)
with heat flow plotted against the temperature.
Series 3
317.885
320.014
320.568
320.965
321.149
Financial support to this work under NSFC Grant
No. 20073047 and NSFSP Grant No. 2001H11,
respectively.
0.1470
0.2900
0.3874
0.5333
0.6434
6.8036
3.4481
2.5814
1.8751
1.5543
F = q/(DfusHmn), in which q is the amount of the heat introduced to
melt the sample for the melting fraction F and n is the mole number of
the sample.
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It can be seen from the DSC curve (figure 3) that
there is a melting endothermic peak in the temperature
range from (300 to 450) K. It begins from 321.3 K
and ends at 337.4 K. This peak is in agreement with that
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The authors gratefully acknowledge The National
Nature Science Foundation of China and The Nature
Science Foundation of of Shannxi Province, China for
JCT 04/101