Determination of heat capacities and thermodynamic properties of 2-(chloromethylthio)benzothiazole by an adiabatic calorimeter

Article abstract of DOI:10.1021/je049678a

The molar heat capacities of 2-(chloromethylthio)benzothiazole (molecular formula C₈H₆ClNS₂, CA registry no. 28908-00-1) were measured with an adiabatic calorimeter in the temperature range between (80 and 350) K. The construction and procedures of the calorimeter were described in detail. The performance of the calorimetric apparatus was evaluated by heat capacity measurements on α-Al₂O₃. The deviation of experiment heat capacities from the corresponding smoothed values lies within ±0.3%, whereas the uncertainty is within ±0.5%, compared with that of the recommended reference data over the whole experimental temperature range. A fusion transition was found from the C _p-T curve of 2-(chloromethylthio)benzothiazole. The melting temperature and the molar enthalpy and entropy of fusion of the compound were determined to be T_m = (315.11 ± 0.04) K, Δ _fusH_m = (17.02 ± 0.03) kJ·mol^-1, and Δ_fuS_m = (54.04 ± 0.05) J·mol ^-1K^-1, respectively. The thermodynamic functions (H _T - H_298.15) and (S_T - S_298.15) were also derived from the heat capacity data. The molar fraction purity of the 2-(chloromethylthio)-benzothiazole sample used in the present calorimetric study was determined to be 99.21 by fraction melting.

Full text of DOI:10.1021/je049678a

270
J. Chem. Eng. Data 2005, 50, 270-273
Determination of Heat Capacities and Thermodynamic Properties of
2-(Chloromethylthio)benzothiazole by an Adiabatic Calorimeter
Mei-Han Wang,† Zhi-Cheng Tan,*,† Xiao-Hong Sun,‡ Hong-Tao Zhang,† Bei-Ping Liu,§
Li-Xian Sun,† and Tao Zhang†
Thermochemistry Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences,
Dalian 116023, China, College of Chemical Engineering, Northwest University, Xi’an 710069, China, and
Department of Chemistry, Hunan University of Arts and Science, Changde 415000, China
The molar heat capacities of 2-(chloromethylthio)benzothiazole (molecular formula C8H6ClNS2, CA registry
no. 28908-00-1) were measured with an adiabatic calorimeter in the temperature range between (80 and
350) K. The construction and procedures of the calorimeter were described in detail. The performance of
the calorimetric apparatus was evaluated by heat capacity measurements on R-Al2O3. The deviation of
experiment heat capacities from the corresponding smoothed values lies within (0.3%, whereas the
uncertainty is within (0.5%, compared with that of the recommended reference data over the whole
experimental temperature range. A fusion transition was found from the Cp-T curve of 2-(chlorometh-
ylthio)benzothiazole. The melting temperature and the molar enthalpy and entropy of fusion of the
compound were determined to be Tm ) (315.11 ( 0.04) K, ∆fusHm ) (17.02 ( 0.03) kJ‚mol-1, and ∆fusSm
) (54.04 ( 0.05) J‚mol-1‚K-1, respectively. The thermodynamic functions (HT - H298.15) and (ST - S298.15
)
were also derived from the heat capacity data. The molar fraction purity of the 2-(chloromethylthio)-
benzothiazole sample used in the present calorimetric study was determined to be 99.21 by fraction
melting.
1. Introduction
2. Experimental Section
Samples. 2-(Chloromethylthio)benzothiazole was pre-
pared according to the procedures given in the literature.4
The process is
Adiabatic calorimetry at low temperature is the classical
method for heat capacity measurement, from which many
other thermodynamic properties such as enthalpy, entropy,
and Gibbs free energy can be calculated. These data are of
significance in theoretical study, application development,
and industrial production of a compound. In the present
paper, a small-sample automated adiabatic calorimeter is
described in more detail on the basis of our previous
work.1,2 At the same time, the heat capacities of the
standard reference material R-Al2O3 were measured to
demonstrate the accuracy of this calorimeter.
2-(Thiocyanomethylthio)benzothiazole (TCMTB) is a
broad-spectrum fungicide that is used for soil and seed
treatment against various diseases of field crops, certain
vegetables, and ornamentals.3 It is synthesized from
2-mercaptobenzothiazole (MBT). 2-(Chloromethylthio)ben-
zothiazole is a very important intermediate in the synthesis
process of TCMTB. Understanding the thermodynamic
properties of this intermediate can improve the synthesis
process of TCMTB. However, previous research has focused
on the efficient synthesis of 2-(chloromethylthio)benzothia-
zole. The thermodynamic properties of this compound have
not been studied as far as we know. In the present study,
the low-temperature heat capacity has been measured in
the temperature range from (80 to 350) K with a small-
sample automated adiabatic calorimeter. The melting
temperature and the molar enthalpy and entropy of fusion
of the compound were determined.
2-Mercaptobenzothiazole in acetone was mixed with
bromochloromethane in a round-bottomed flask, and the
reaction mixture was stirred for 10 min at room temper-
ature. Sodium hydroxide was added slowly, and the tem-
perature was kept at 0 °C for 2 h. The reaction mixture
was allowed to reach room temperature, when excess
acetone and bromochloromethane were removed. The
resulting mixture was extracted with chloroform and
washed with water. The organic layer was dried over
anhydrous sodium sulfate and concentrated under vacuum.
The residue was purified by column chromatography on
silica gel to yield the compound. Its melting point was
determined to be (314 to 315) K with a microscopic melting-
point device. The structure of the product was determined
1
by IR and H NMR. The IR (KBr) showed characteristic
absorption peaks at 3100 (ph-H), 2920 (C-H), 1693 (Cd
C), 1457 (CdN), and 995 (C-S) cm-1. The 1H-NMR (CDCl3)
absorption peaks were detected at δ (5.336-5.387) × 10-6
(2H, s, CH2) and (7.332-7.977) × 10-6 (4H, m, ph).
Automated Adiabatic Calorimeter. The adiabatic
calorimeter consisted of a sample cell, inner and outer
adiabatic shields, vacuum can, and Dewar vessel. The
cross-sectional diagram of the adiabatic calorimeter is
shown in Figure 1.
* Corresponding author. E-mail: tzc@dicp.ac.cn. Tel: +86-411-
84379199. Fax: +86-411-84691570.
† Dalian Institute of Chemical Physics.
‡ Northwest University.
The sample cell was made of thin-walled gold-plated
§ Hunan University of Arts and Science.
copper and had an inner volume of 6 cm3. Four L-shaped
10.1021/je049678a CCC: $30.25 © 2005 American Chemical Society
Published on Web 12/08/2004

Journal of Chemical and Engineering Data, Vol. 50, No. 1, 2005 271
Table 1. Experimental Molar Heat Capacity of
2-(Chloromethylthio)benzothiazole (M ) 215.72 g‚mol-1
)
C
p,m/J‚
C
p,m/J‚
Cp,m/J‚
T/K
K-1‚mol-1
T/K
K-1‚mol-1
T/K
K-1‚mol-1
80.927
84.537
102.3
106.6
110.9
114.0
118.9
122.4
124.9
127.4
129.9
132.3
135.0
137.0
140.1
141.4
144.0
146.3
148.7
150.4
152.4
154.1
155.6
157.4
159.2
161.3
163.4
165.2
167.1
168.8
170.2
172.2
174.3
176.9
179.2
180.3
182.0
184.3
186.0
187.3
189.0
191.1
204.068
207.197
210.320
213.413
216.476
219.498
222.480
225.406
228.251
231.007
233.737
236.448
239.123
241.718
244.352
247.031
249.689
252.315
254.916
257.491
260.864
265.095
269.256
273.680
278.043
282.062
286.072
290.054
293.901
297.722
301.512
305.286
308.964
312.217
314.078
314.600
314.772
193.3 314.911
196.3 314.938
198.5 316.595
200.5 320.288
202.5 323.952
203.4 327.473
205.3 330.940
206.9 334.437
208.2 337.976
210.1 341.562
213.4 345.165
215.3 348.805
217.0
30 686
10 748
328.2
330.2
331.6
334.4
335.8
337.4
340.2
342.7
345.4
348.3
88.029
91.402
94.665
97.853
100.970
104.023
107.005
109.957
112.836
115.690
118.496
121.273
124.012
126.719
129.395
132.041
134.665
137.259
139.831
142.374
145.381
148.830
152.246
155.625
158.969
162.291
165.584
168.862
172.121
175.363
178.588
181.801
185.005
188.201
191.385
194.562
197.730
200.904
218.9
221.0
222.4
224.2
225.6
227.4
228.6
230.5
232.4
234.1
236.1
Figure 1. Cross-sectional diagram of the adiabatic calorimeter:
1, sealing junction unit; 2, vacuum tube; 3, to high-vacuum system;
4, fuse gasket; 5, vacuum can; 6, outer adiabatic shield; 7, inner
adiabatic shield; 8, sample cell; 9, platinum resistance thermom-
eter.
238.1
240.7
242.2
244.5
246.6
249.5
252.5
255.1
287.7
473.7
2010
6220
9563
314.863 15 715
314.884 45 693
314.907 82 597
Meter, 16 mm long, 1.6 mm in diameter, nominal resistance
of 100 Ω) was calibrated on the basis of ITS-90 by the
Station of Low-Temperature Metrology and Measurements,
Academic Sinica. The resistance of the thermometer was
measured with a 71/2 digit nanovolt/micro ohm meter,
34420A Agilent. The temperature of the sample was
calculated by the computer according to the relationship
between resistance and temperature. A heater (Karma wire
of 0.12 mm diameter, 105 Ω) was wound bifilarly on the
surface of the cell and was covered with aluminum-plated
Dacron film. The electrical energy introduced into the
sample cell was supplied by a regulated dc power supply
(MATRIX-MPS-3002L-1) with a stability of 5 ppm and was
automatically picked up by the data acquisition/switch unit,
34970A Agilent.
Figure 2. Molar heat capacities of the standard reference
material R-Al2O3: inset O, deviation of the measured molar heat
capacities from the smoothed curves; inset b, plot of deviations
100∆Cp,m/Cp,m,ref of the measured values, where ∆Cp,m is the
difference between the measured values and the reference values;
Cp,m,ref is the molar heat capacity reported by Archer.5
0.10-mm-thick radial gold-plated copper vanes were placed
in the cell to shorten the thermal equilibrium time. A 5-m-
long copper capillary was welded at the center of the lid
for the introduction of helium gas into the sample cell. The
lid was sealed to the main body of the cell with special
epoxy adhesive (epoxy resine/curing agent ) 5/1). After 0.1
MPa helium exchanging gas was introduced into the cell,
the capillary was pinched off, and the resultant fracture
was soldered with a small amount of solder to ensure the
sealing of the cell.
The sample cell is surrounded by inner and outer
adiabatic shields, which are made of chromium-plated
copper. Each adiabatic shield consists of three parts: the
upper lid, the lower bottom, and the cylindrical main body.
Manganin heating wires are wound evenly on these three
parts so that the adiabatic shields have a uniform temper-
ature distribution. Two sets of chromel-copel (Ni-55%, Cu-
45%) thermocouples were mounted between the sample cell
and the inner shield and between the inner shield and the
outer shield, respectively. Each set of thermopiles consists
of six thermocouples so that the thermal emf is 171 µV‚K-1
at 80 K and 390 µV‚K-1 at 300 K. The thermal emf signal
was transferred to a temperature controller (Lake Shore
An Ω-shaped sheath was silver soldered at the bottom
of the cell so that a miniature platinum resistance ther-
mometer could be inserted. The thermometer (IPRT no. 2,
produced by the Shanghai Institute of Industrial Automatic

272 Journal of Chemical and Engineering Data, Vol. 50, No. 1, 2005
Table 2. Calculated Thermodynamic Functions of
2-(Chloromethylthio)benzothiazole
C
p,m/J‚
(HT - H298.15)/
kJ‚mol-1
(ST - S298.15)/
J‚K-1‚mol-1
T/K
K-1‚mol-1
Crystal
-40.07
-39.55
-39.00
-38.42
-37.82
-37.18
-36.53
-35.85
-35.15
-34.44
-33.70
-32.95
-32.19
-31.40
-30.60
-29.79
-28.96
-28.12
-27.26
-26.38
-25.49
-24.59
-23.67
-22.73
-21.78
-20.82
-19.83
-18.84
-17.82
-16.79
-15.75
-14.69
-13.61
-12.52
-11.41
-10.29
-9.148
-7.995
-6.828
-5.646
-4.451
-3.242
-2.020
-0.7845
0
80
100.1
107.0
113.2
118.8
124.1
128.9
133.3
137.4
141.3
145.0
148.5
151.8
155.1
158.2
161.3
164.3
167.3
170.3
173.3
176.4
179.4
182.4
185.5
188.6
191.7
194.8
198.0
201.2
204.3
207.5
210.7
213.8
217.0
220.1
223.1
226.2
229.1
232.1
234.9
237.7
240.5
243.1
245.7
248.3
249.8
250.8
253.2
-221.4
-215.1
-208.8
-202.6
-196.3
-190.2
-184.1
-178.1
-172.2
-166.3
-160.6
-154.9
-149.3
-143.8
-138.4
-133.0
-127.8
-122.6
-117.4
-112.4
-107.3
-102.4
-97.49
-92.64
-87.83
-83.06
-78.33
-73.64
-68.98
-64.36
-59.76
-55.20
-50.66
-46.15
-41.67
-37.22
-32.79
-28.40
-24.03
-19.69
-15.39
-11.11
-6.863
-2.644
0
85
90
95
100
105
110
115
120
125
130
135
140
145
150
155
160
165
170
175
180
185
190
195
200
205
210
215
220
225
230
235
240
245
250
255
260
265
270
275
280
285
290
295
298.15
300
305
Figure 3. Experimental molar heat capacity Cp,m of 2-(chloro-
methylthio)benzothiazole as a function of temperature (T).
340) to control the temperature of the two shields. When
the adiabatic circuits were operating, the temperature
difference between the sample cell and the inner shield was
e0.5 mK during the entire experimental process. The
temperature drift of the sample cell could be controlled
within 2 × 10-6 K‚s-1 under this shield control condition.
The sample cell and the adiabatic shields were housed
in the high-vacuum can to eliminate convection heat
transfer. During the heat capacity measurements, the
vacuum can was evacuated to (10-3 to 10-4) Pa by means
of a combined rotational mechanical pump and oil diffusion
pump (Edwards, model -NXK333000). A Dewar vessel filled
with liquid nitrogen was used to cool the sample cell down
to 78 K.
Prior to heat capacity measurements of the sample, the
reliability of the calorimetric apparatus was verified by
heat capacity measurements of the standard reference
material, synthetic sapphire (R-Al2O3, SRM 720).
3. Results and Discussion
Heat Capacity of r-Al2O3. The experimental molar
heat capacities of the reference standard material R-Al2O3
are plotted in Figure 2 in the sequence of the temperature
increment. The deviations of the measured values from the
smoothed curves lie within (0.3%, whereas the measuring
uncertainty, 100∆Cp,m/Cp,m,ref, is within (0.5% over the
whole temperature range, where ∆Cp,m is the difference
between the measured values and the reference values and
Cp,m,ref is the molar heat capacity reported by Archer.5
Heat Capacity of 2-(Chloromethylthio)benzothia-
zole. Heat capacity measurements are listed in Table 1 and
plotted in Figure 3. The heat capacities of the sample
increase with temperature in a smooth and continuous
manner without any thermal anomaly in the range from
(80 to 305) K, which means that the compound is stable in
this range. However, a thermal anomaly was observed in
the temperature range between (305 and 316) K. The
thermal anomaly can be ascribed to a solid-liquid-phase
transition according to the previous melting-point mea-
surement. The temperature of the phase transition (Tm)
was determined to be 315.11 K from the melting curve
obtained by observing the equilibrium temperatures and
the melted fractions of sample.
0.4631
1.723
1.548
5.715
Liquid
18.74
20.38
22.04
23.71
25.39
27.09
28.81
30.55
315
320
325
330
335
340
345
350
327.4
330.0
332.5
335.3
338.2
341.5
345.2
349.4
59.76
64.93
70.07
75.17
80.23
85.26
90.28
95.27
For the solid phase over the temperature range of (80 to
305) K, Cp,m/J‚K-1‚mol-1 ) 187.04 + 69.572X + 5.9225X2
- 1.5483X3 - 16.303X4 + 8.4965X5, where X ) {(T/K) -
192.5}/112.5 and T is the absolute temperature. The
correlation coefficient of the fitted curve is R2 ) 0.9996.
The deviations of experimental results from the smoothed
curve lie within (0.6%.
For the liquid phase over the temperature range of (316
to 349) K, Cp,m/J‚K-1‚mol-1 ) 336.7 + 9.7291X + 1.5184X2
+ 0.5627X3, where X ) {(T/K) - 332.5}/16.5 and R2
)
0.9981. The deviations of the experimental results from the
smoothed curve lie within (0.3%.
Thermodynamic Functions of 2-(Chloromethylthio)-
benzothiazole. The molar enthalpy and molar entropy of
The experimental molar heat capacities were fit to the
following polynomial equations in reduced temperature (X)
by a least-squares method.

Journal of Chemical and Engineering Data, Vol. 50, No. 1, 2005 273
thermodynamic functions above T ) 298.15 K. The results
are listed in Table 2.
Adiabatic calorimetry provides an accurate way of de-
termining the purity of a substance. The purity of a sample
can be evaluated from the observed melting curve.8 If the
liquid solution formed in the premelting region is ideal and
thus obeys Raoult’s law, then the following expressions can
be used to calculate the purity of the sample:
∆Hm(T0 - T1)
T0 - T1
q
Q
x2 )
F )
T0 - T )
RT20
F
where F is the fraction of sample melted, ∆Hm is the molar
enthalpy of fusion, T0 is the triple-point temperature of the
pure substance, T1 is the triple-point temperature of the
given sample, and x2 is the mole fraction of impurity in
the liquid solution. The plots of T against 1/F in the melting
process are shown in Figure 4. T0 is the temperature when
1/F equals 0, and T1 is equivalent to the temperature when
1/F is 1. From Figure 4, T0 and T1 are found to be 315.49 K
and 315.11 K, respectively. Thus x2 ) 0.79 mol % can be
calculated, and the purity of the 2-(chloromethylthio)-
benzothiazole sample studied in the present calorimetric
experiment amounts to 1 - x2 ) 99.21 mol % (Table 3).
Figure 4. Plot of temperature versus reciprocal of the fraction
melted during the melting process of 2-(chloromethylthio)ben-
zothiazole.
Table 3. Observed Equilibrium Temperature (T) and
Fraction Melted (F) during the Melting Process
F ) q/Q
1/F
T/K
0.1179
0.2727
0.3925
0.5151
0.6399
0.7122
8.478
3.667
2.548
1.941
1.563
1.404
312.22
314.08
314.60
314.77
314.86
314.88
Literature Cited
(1) Tan, Z. C.; Sun, G. Y.; Yin, A. X.; Wang, W. B.; Ye, J. C.; Zhou, L.
X. An Adiabatic Low-Temperature Calorimeter for Heat Capacity
Measurement of Small Samples. J. Therm. Anal. 1995, 45, 59-
67.
(2) Tan, Z. C.; Sun, L. X.; Meng, S. H.; Li, L.; Xu, F.; Yu, P.; Liu, B.
P.; Zhang, J. B. Heat Capacities and Thermodynamic Functions
of P-Chlorobenzoic Acid. J. Chem. Thermodyn. 2002, 34, 1417-
1429.
fusion of the compound were determined to be (17.02 (
0.03) kJ‚mol-1 and (54.04 ( 0.05) J‚K-1‚mol-1, respectively,
from the following equations.6,7
(3) Meister, R. T.; Berg, G. L.; Sine, C.; Poplyk, J. Farm Chemicals
Handbook, 70th ed.; Meister Publishing Co.; Willoughby, OH,
1984.
(4) Muthusubramanian, L.; Sundara Rao, V. S.; Mitra Rajat, B.
Efficient synthesis of 2-(thiocyanomethylthio)benzothiazole J.
Cleaner Production 2001, 9, 65-67.
(5) Archer, D. G. Thermodynamic Properties of Synthetic Sapphire
(R-Al2O3), Standard Reference Material 720 and the Effect of
Temperature-Scale Difference on Thermodynamic Properties. J.
Phys. Chem. Ref. Data 1993, 22, 1441-1453
(6) Tan, Z. C.; Sun, G. Y.; Song, Y. J.; Wang, L. An Adiabatic
Calorimeter for Heat Capacity Measurements of Small Samples:
The Heat Capacity of Nonlinear Optical Materials KTiOPO4 and
RbTiOAsO4 Crystals. Thermochim. Acta 2000, 352-353, 247-
253.
(7) Xue, B.; Tan, Z. C.; Lu, S. W.; Meng, S. H.; Yuan, X. H. Study of
Heat Capacity and Thermodynamic Properties of Fenpropathrin.
Acta Chim. Sin. 1999, 57, 881-886.
(8) Todd, S. S.; Oliver, G. D.; Huffman, H. M. The Heat Capacities,
Heats of Fusion and Entropies of the Six Pentenes. J. Am. Chem.
Soc. 1947, 69, 1519-1525.
∆Hm
)
Tm
Tf
Tf
Q - n
Cp,m(s) dT - n
Cp,m(l) dT - n
Cp(0) dT
∫
∫
∫
Ti
Tm
Ti
n
∆Hm
∆Sm
)
T
where Ti is a temperature slightly lower than the initial
melting temperature, Tf a temperature slightly higher than
the final melting temperature, Q the total energy intro-
duced into the sample cell from Ti to Tf, Cp(0) is the heat
capacity of the sample cell from Ti to Tf, Cp,m(s) is the heat
capacity of the sample in the solid phase from Ti to Tm,
Cp,m(l) is the heat capacity of the sample in the liquid phase
from Tm to Tf, and n is the molar amount of the sample.
The heat capacity polynomials mentioned above were used
to calculate the smoothed heat capacities and were nu-
merically integrated to obtain the values of the standard
Received for review September 7, 2004. Accepted October 25, 2004.
This work was financially supported by the National Natural
Science Foundation of China under the grant NSFC no. 20373072.
JE049678A