Heat capacity and enthalpy of formation of trimethyl phosphite, 2-chloromethylbenzonitrile, and 2-dimethylphosphonomethylbenzonitrile

Article abstract of DOI:10.1021/je060445o

The heat capacities, C_p, of trimethyl phosphite, 2-dimethylphosphonomethylbenzonitrile, and 2-chloromethylbenzonitrile are measured with an adiabatic calorimeter, and the standard enthalpies of formation, Δ_fH°(298.15 K) (l or cr), for the three substances are determined. For this purpose, C_p(T) values of trimethyl phosphite and 2-dimethylphosphonomethylbenzonitrile are measured in the temperature range from (298.15 to 350.32) K, and the C_p(T) curves of 2-chloromethylbenzonitrile are also obtained for the crystal (300.35 to 329.00 K) and the liquid (337.26 to 372.45 K), respectively. The deviation of experimental heat capacities from the corresponding smoothed values lies within ± 1.5%. A fusion transition phenomenon is found from the C_p(T) curves of 2-chloromethylbenzonitrile, and the enthalpy of fusion is measured with a differential scanning calorimeter (DSC). The gas-phase standard enthalpies of formation, Δ_fH°(g, 298.15 K), of the three compounds are evaluated by the Benson group additive method. The critical temperature T_c, critical pressure P_c, and enthalpy of vaporization Δ_vapH° of the compounds are also calculated by different group additive methods. On the basis of the above data, the values of Δ_fH°(1, 298.15 K) of trimethyl phosphate and 2-dimethylphosphonomethylbenzonitrile and of Δ_fH°-(cr, 298.15 K) of 2-chloromethylbenzonitrile are estimated. A thermochemical cycle including a chemical reaction is designed to examine the reliability of the values by measuring the heat of reaction. The result shows that the enthalpies of formation, Δ_fH°(298.15 K) (1 or cr), for the three substances are acceptable.

Full text of DOI:10.1021/je060445o

J. Chem. Eng. Data 2007, 52, 1189-1194
1189
Heat Capacity and Enthalpy of Formation of Trimethyl Phosphite,
2
-Chloromethylbenzonitrile, and 2-Dimethylphosphonomethylbenzonitrile
Xin-gang Xu, Zuo-xiang Zeng, Wei-lan Xue,* and Hai-ying Zhang
Institute of Chemical Engineering, East China University of Science and Technology, 200237 Shanghai, China
The heat capacities, Cp, of trimethyl phosphite, 2-dimethylphosphonomethylbenzonitrile, and 2-chloromethyl-
o
benzonitrile are measured with an adiabatic calorimeter, and the standard enthalpies of formation, ∆fH (298.15
K) (l or cr), for the three substances are determined. For this purpose, Cp(T) values of trimethyl phosphite and
2
-dimethylphosphonomethylbenzonitrile are measured in the temperature range from (298.15 to 350.32) K, and
the Cp(T) curves of 2-chloromethylbenzonitrile are also obtained for the crystal (300.35 to 329.00 K) and the
liquid (337.26 to 372.45 K), respectively. The deviation of experimental heat capacities from the corresponding
smoothed values lies within ( 1.5 %. A fusion transition phenomenon is found from the Cp(T) curves of
2
-chloromethylbenzonitrile, and the enthalpy of fusion is measured with a differential scanning calorimeter (DSC).
o
The gas-phase standard enthalpies of formation, ∆fH (g, 298.15 K), of the three compounds are evaluated by the
Benson group additive method. The critical temperature Tc, critical pressure Pc, and enthalpy of vaporization
o
∆
vapH of the compounds are also calculated by different group additive methods. On the basis of the above data,
o
o
the values of ∆fH (l, 298.15 K) of trimethyl phosphate and 2-dimethylphosphonomethylbenzonitrile and of ∆fH -
cr, 298.15 K) of 2-chloromethylbenzonitrile are estimated. A thermochemical cycle including a chemical reaction
(
is designed to examine the reliability of the values by measuring the heat of reaction. The result shows that the
o
enthalpies of formation, ∆fH (298.15 K) (l or cr), for the three substances are acceptable.
Introduction
Shanghai with the following purities, respectively: 99.5 % and
9 %. 2-Dimethylphosphonomethylbenzonitrile is prepared
according to the procedures given in the literature and purified
by reduced pressure distillation. Its mass fraction purity is better
than 98.5 % by gas chromatography.
9
The specific heat capacity and enthalpy of substances are not
only the most important thermodynamic properties but also the
characteristic data concerned with the structure of a substance.
They are widely used in physics and chemistry as well as in
chemical engineering, energy resources, and material engineer-
ing.
5
The process is
2-Dimethylphosphonomethylbenzonitrile (CASRN 78022-18-
1) is an important intermediate used in the synthesis of 1,4-
bis(cyanostyryl)benzene (CASRN 13001-93-3) which is the fluo-
rescent whitening agent ER (FWA ER), one of the fluorescent
1
dyes. It is synthesized from trimethyl phosphite (CASRN 121-
4
5-9) and 2-chloromethylbenzonitrile (CASRN 612-13-5). So,
2-Chloromethylbenzonitrile is heated to 423.15 K in a round-
bottomed flask by an oil bath. Then, trimethyl phosphite is added
slowly, and the temperature is kept at (423.15 to 433.15) K for
4 h. The product is purified by reduced pressure distillation. Its
boiling point at 0.1 MPa is determined to be (552 to 553) K
with a microscopic boiling point device.
it is necessary to understand the thermodynamic properties of
these compounds because it will be helpful to the engineering
design for producing 1,4-bis(cyanostyryl)benzene. Previous re-
search has focused on the efficient synthesis of 1,4-bis(cyano-
styryl)benzene.1 The thermodynamic properties of these com-
pounds have not been studied as far as we know. In this study,
-4
o
Apparatus and Procedures
Cp(T) and ∆fH (298.15 K) (l or cr) of trimethyl phosphite, 2-chlo-
romethylbenzonitrile, and 2-dimethylphosphonomethylbenzo-
nitrile are reported. An adiabatic calorimeter is used to measure
the heat capacities, and different group additive methods are
used to derive other thermodynamic properties such as enthalpy
Adiabatic Calorimeter. The apparatus and experimental
procedures used here are similar to those described in the
6
literature. Briefly, the automatic adiabatic calorimeter consisted
of a sample cell, a miniature platinum resistance thermometer,
an electric heater, inner and outer adiabatic shields, a Dewar
vessel, a high-vacuum can, and two sets of six-junction
chromel-constantan thermopiles which are installed between
the calorimetric cell and the inner shield and between the inner
and the outer shields. Prior to the heat capacity measurement
of the sample, the heat capacities of R-aluminum oxide, the
standard reference material, are measured from T ) (298 to
o
of formation ∆fH (g, 298.15 K), critical temperature Tc, critical
o
pressure Pc, and enthalpy of vaporization ∆vapH of the
compounds.
p
Measurement of C (T) for Trimethyl Phosphite,
2
2
-Dimethylphosphonomethylbenzonitrile, and
-Chloromethylbenzonitrile
Samples. Trimethyl phosphite and 2-chloromethylbenzonitrile
are purchased from Haohua Chemical Reagent Company of
3
80) K to verify the reliability of the adiabatic calorimeter. The
results show that the deviation of our calibration is within (
0.5 %.
*
Corresponding author. E-mail: wlxue@ecust.edu.cn.
1
0.1021/je060445o CCC: $37.00 © 2007 American Chemical Society
Published on Web 06/07/2007

1
190 Journal of Chemical and Engineering Data, Vol. 52, No. 4, 2007
Table 1. Heat Capacities of Trimethyl Phosphite Liquid
T
Cp
T
Cp
T
Cp
K
J‚g-1‚K-1
K
J‚g-1‚K-1
K
J‚g-1‚K-1
2
3
3
3
3
3
99.05
02.10
05.10
08.15
10.95
13.75
1.4237
1.4438
1.4562
1.4762
1.4818
1.5132
316.73
319.69
322.33
325.90
329.00
331.35
1.5206
1.5484
1.5652
1.5747
1.5870
1.6149
335.89
337.70
340.75
343.73
348.05
1.6310
1.6457
1.6719
1.7095
1.7290
Table 2. Heat Capacities of 2-Dimethylphosphonomethylbenzonitrile
Liquid
T
Cp
T
Cp
T
Cp
K
J‚g-1‚K-1
K
J‚g-1‚K-1
K
J‚g-1‚K-1
Figure 1. Heat capacities of trimethyl phosphite and 2-dimethyl phospho-
nomethylbenzonitrile: 9, trimethyl phosphite; 2, 2-dimethylphosphonom-
ethylbenzonitrile; s, values calculated by eq 1.
2
3
3
3
3
3
98.15
03.16
08.11
11.36
14.55
17.75
1.8661
1.8781
1.8900
1.9188
1.9395
1.9521
320.36
322.75
326.25
329.25
332.55
336.54
1.9658
1.9884
2.0179
2.0547
2.0870
2.1249
339.02
342.19
345.14
347.69
350.32
2.1578
2.1923
2.2215
2.2495
2.2690
Table 3. Heat Capacities of 2-Chloromethylbenzonitrile
T
Cp
T
Cp
T
Cp
K
J‚g-1‚K-1
K
J‚g-1‚K-1
K
J‚g-1‚K-1
Crystal
3
3
3
3
00.35
03.10
05.10
08.15
1.1321
1.1438
1.1562
1.1662
310.95
313.75
316.73
319.69
1.1818
1.1832
1.1906
1.2084
322.33
325.90
329.00
1.2452
1.2547
1.2870
Liquid
3
3
3
3
3
37.26
40.28
44.05
46.70
49.55
2.2367
2.2405
2.2515
2.2678
2.2812
352.35
355.31
357.91
360.55
362.85
2.3193
2.3395
2.3512
2.3605
2.3789
365.85
367.00
370.10
371.20
372.45
2.3916
2.4156
2.4367
2.4518
2.4736
Figure 2. Heat capacities of 2-chloromethylbenzonitrile: 9, experimental
results; s , values calculated by eq 1.
The heat capacity measurements are conducted by the
Heat Capacity of 2-Chloromethylbenzonitrile. 2-Chloro-
methylbenzonitrile is a crystal at 298.15 K and 0.1 MPa. Heat
capacities of 2-chloromethylbenzonitrile are listed in Table 3
and plotted in Figure 2. The heat capacities of 2-chlorometh-
ylbenzonitrile increase with temperature in a smooth and
continuous manner, without any thermal anomaly in the range
from (300.35 to 329.35) K, which means that the compound is
stable in this range. However, a thermal anomaly is observed
in the temperature range from (329.35 to 335.15) K, which is
demonstrated by an increase curve. The thermal anomaly can
be ascribed to a solid-liquid-phase transition according to the
standard procedure of intermittently heating the sample and
alternately measuring the temperature. The heating rate and the
temperature increments of the experimental points were gener-
ally controlled from (0.1 to 0.4) K‚min-1 and (1 to 4) K. The
heating duration is 10 min, and the temperature drift rates of
the sample cell measured in an equilibrium period are always
-
3
-4
-1
kept within (10 to 10 ) K‚min during the acquisition of
all heat capacity data. Taking into account the above factors
and the effect of impurities in substances, the estimated uncer-
tainty of heat capacity measurements is better than ( 1 %.
Differential Scanning Calorimeter (DSC). The DSC experi-
ments are performed on a DSC 200F3 from Netzsch Instrument
Inc. Both the cell constant and the temperature calibrations are
obtained from the run in which a calibration material (e.g.,
indium) is heated through its melting point. The enthalpy of
fusion and the melting point of indium are used to determine
the cell constant and temperature calibrations. The samples are
7
melting point (334.15 K).
For each sample, a polynomial function of the type
-1
-1
2
C /J‚g ‚K ) a + a ‚T/K + a ‚(T/K)
(1)
p
0
1
2
was used to correlate the experimental values of Cp with
temperature by the method of least-squares. The coefficients ai
in eq 1, the deviations of experimental results from the smoothed
curve E, and the temperature range T of eq 1 are shown in Table
-1
cooled with an average rate of about 6 K‚min . The measure-
-
1
ments are made using a heating rate of 2.5 K‚min . The DSC
samples have a mass between (5 and 15) mg. The determination
of a melting temperature is estimated to be accurate to ( 0.1
K. The enthalpy of fusion can be determined with an accuracy
4
. The polynomial correlation functions are then valid in the
range of experimental temperatures.
-
1
Enthalpy of Fusion for 2-Chloromethylbenzonitrile. The
of ( 0.05 kJ‚mol .
o
enthalpy of fusion ∆fusH of 2-chloromethylbenzonitrile was
-
1
8
Results and Discussion
determined to be 20.53 kJ‚mol , from the following equation
Heat Capacity of Trimethyl Phosphite and 2-Dimeth-
ylphosphonomethylbenzonitrile. The values for heat capacities
of trimethyl phosphite and 2-dimethylphosphonomethylben-
zonitrile are listed in Table 1 and Table 2 and plotted in Figure
o
∆fusH )
Tfus
Tf
Tf
Q - m
∫
C (cr)dT - m
∫
C (l)dT - m
∫
C (0)dT
p
Ti
p
p
Ti
Tfus
(2)
1
.
n

Journal of Chemical and Engineering Data, Vol. 52, No. 4, 2007 1191
Table 4. Parameters ai, Deviations E, and Temperature Range T of Equation 1
a2‚10-
5
E/%
T/K
sample
trimethyl phosphite
a0
a1
2.0396
8.8383
1.0505
9.6553
-0.00909
-0.05038
-0.00466
-0.00480
2.35345
9.04112
1.63299
7.60575
( 1.1
( 0.8
( 1.0
( 1.5
299 to 349
298 to 351
300 to 329
337 to 373
2
2
2
-dimethylphosphonomethylbenzonitrile
-chloromethylbenzonitrile(s)
-chloromethylbenzonitrile(l)
Table 5. Differences of Group Contributions When Br Is Replaced
by Cl
where Ti is a temperature slightly lower than the initial melting
temperature; Tf is a temperature slightly higher than the final
melting temperature; Q is the total energy introduced into the
sample cell from Ti to Tf; Cp(0) is the heat capacity of the sample
cell from Ti to Tf; Cp(cr) is the heat capacity of the sample in
the solid phase from Ti to Tfus; Cp(l) is the heat capacity of the
sample in the liquid phase from Tfus to Tf; m is the mass of the
sample; and n is the molar amount of the sample. The enthalpy
differences between
o
j
∆
fH (g, 298.15 K)
two groups
kJ‚mol-1
-51.83
group
kJ‚mol-
-53.5010
-1.671
1
C-(Cl)(C)3
C-(Br)(C)3 a
Cd-(Cl)(H)
Cd-(Br)(H)
CB-(Cl)b
0
10
-5.021
-51.00
-51.41
45.98 0
o
of fusion, ∆fusH , of 2-chloromethylbenzonitrile was measured
10
-15.88
-
1
to be (20.81 ( 0.05) kJ‚mol by a differential scanning
10
CB-(Br)
35.53
o
calorimeter (DSC). The difference of ∆fusH measured by the
a
two different kinds of methods is 1.3 %.
Cd represents a carbon atom that is joined to another carbon atom by
a double bond. b CB represents the aromatic C atoms.
o
Estimation of ∆fH (298.15 K) for 2-Chloromethylbenzoni-
trile, Trimethyl Phosphite, and 2-Dimethylphosphonomethyl-
benzonitrile. Because 2-chloromethylbenzonitrile is a crystal
under 298.15 K and 0.1 MPa, its solid standard enthalpy of
o
Table 6. Calculation of ∆fH (g, 298.15 K) for 2-Chloromethyl-
benzonitrile
o
j
∆
fH (g, 298.15 K)
o
formation ∆fH (cr, 298.15 K) can be expressed
kJ‚mol-
1
group
contribution number
o
o
o
10
∆fH (cr, 298.15 K) ) ∆ H (g, 298.15 K) - ∆ H (298.15 K)
CB-(C)
1
4
1
1
23.03
f
sub
1
0
CB-(H)
13.79
149.64
-72.73
(3)
10
CB-(CN)
o
C-(CB)(Cl)(H)2
Here ∆fH (g, 298.15 K) is the gas standard enthalpy of
formation and ∆subH (298.15 K) is the enthalpy of sublimation.
o
f
∆H
(g, 298.15 K)
155.12
o
Trimethyl phosphite and 2-dimethylphosphonomethylben-
zonitrile are liquids at 298.15 K and 0.1 MPa. The liquid
standard enthalpy of formation ∆fH (l, 298.15 K) can be
(
H)2 by comparing the group contribution differences of some
groups such as C-(Cl)(C)3, C-(Br)(C)3, Cd-(Cl)(H), Cd-(Br)-
H), CB-(Cl), and CBs(Br) in Table 5. It is clear that the
o
(
estimated by eq 4.
differences of group contributions tend to a value of -51.41
-
1
o
o
o
kJ‚mol when Br is replaced by Cl. So, the contribution value
∆fH (l, 298.15 K) ) ∆ H (g, 298.15 K) - ∆ H (298.15 K)
f
vap
-1
of C-(CB)(Cl)(H)2 is calculated to be -72.98 kJ‚mol .
(4)
o
∆
fH (g, 298.15 K) of 2-chloromethylbenzonitrile is estimated
o
-1
The ∆fH (l, 298.15 K) of trimethyl phosphite and 2-dimeth-
by the Benson method, and the value is 155.86 kJ‚mol . The
calculation process is presented in Table 6.
o
ylphosphonomethylbenzonitrile can be obtained, if ∆fH (g,
o
11
2
98.15 K) and ∆vapH (298.15 K) of these two compounds are
We also estimate the value by the Joback method, another
-
1
known.
Six group contribution methods on standard enthalpies of
broadly applicable method. The result is 159.38 kJ‚mol .The
deviation between these two methods is 2.3 %, so the ∆fH (g,
298.15 K) of 2-chloromethylbenzonitrile and the ∆fH (g,
o
o
j
9
formation in the gaseous state have been used in the literature.
Because the Benson method allows for effects of next-nearest
neighbors, it is the most useful method for complex, high
molecular weight species and yields the smallest errors with
only a few large deviations. In the present paper, the Benson
method is selected to estimate ∆fH (g, 298.15 K) of trimethyl
phosphite, 2-chloromethylbenzonitrile, and 2-dimethylphospho-
nomethylbenzonitrile using the expression
298.15 K) of group C-(CB)(Cl)(H)2 are acceptable and avail-
able. We select the value calculated by the Benson method as
the gas standard enthalpy of formation for 2-chloromethylben-
zonitrile.
o
o
Tc, Pc, and ∆fH (cr, 298.15 K) of 2-Chloromethylbenzoni-
o
trile. The calculation of ∆fH (cr, 298.15 K) for 2-chlorometh-
o
ylbenzonitrile is followed by eq 3 in which ∆subH can be
expressed as
o
o
j
∆fH (g, 298.15 K) )
n ∆ H (g, 298.15 K)
(5)
∑j
j
f
o
o
∆subH (298.15 K) ) ∆ H (T ) -
sub
fus
Tfus
o
j
where ∆fH (g, 298.15 K) is the group contribution value and nj
is the number of times the contribution is required. 2-Chlorom-
ethylbenzonitrile contains four kinds of groups shown in Table
. Three of them, ∆fH (g, 298.15 K), can be found from the
literature. The ∆fH (g, 298.15 K) of another one is deter-
mined as follows.
fH (298.15 K) and ∆fH (g, 298.15 K) of 2-Chloromethyl-
benzonitrile. The C-(CB)(Cl)(H)2 group contribution has not
been reported so far. Fortunately, the group contribution of
C-(CB)(Br)(H)2 can be found in the literature (-21.4 kJ‚mol ).
So, we can get a suitable contribution value of C-(CB)(Cl)-
∫
[C (g) - C (cr)]dT (6)
p p
298.15 K
In eq 6, the heat capacity difference [Cp(g) - Cp(cr)] is
approximately 3R for a nonplastic crystal, and the enthalpy of
sublimation at melting temperature ∆subH (Tfus) can be calculated
as follows
o
6
j
o
1
0
o
j
o
o
∆
o
o
o
∆subH (T ) ) ∆ H (T ) + ∆ H (T )
(7)
fus
vap
fus
fus
fus
-
1
10
o
o
where ∆vapH (Tfus) and ∆fusH are enthalpy of vaporization and
enthalpy of fusion at melting temperature, respectively.

1
192 Journal of Chemical and Engineering Data, Vol. 52, No. 4, 2007
Table 7. Structural Contributions to Calculate ∆T in Equation 11 and Φ in Equation 129
9
9
o
Table 8. Calculation of ∆ Ho(g, 298.15 K) for Trimethyl Phosphite
The Watson relation is used to estimate ∆vapH (T) at Tfus as
follows
f
o
∆
fH (g, 298.15 K)
j
1
n
group
contribution number
kJ‚mol-
1
- T/Tc
o
o
∆vapH (T) ) ∆ H (T )
(8)
10
vap
b
(
)
P-(O)3
1
3
3
-279.22
1
- T /T
b
c
10
O-(P)(C)
C-(P)(H)3
-98.23
1
0
-42.13
where Tc is critical temperature; Tb is boiling point; and
∆ Ho(g, 298.15 K)
-703.67
f
o
∆
vapH (Tb) is enthalpy of vaporization at Tb.
9
Viswanath and Kuloor recommend that n can be obtained
Taking Φ from eq 12, Pc is calculated to be 3.21 MPa. The
value estimated by Riedel’s method is 3.15 MPa. The
by the expression
10
difference between these two methods is small, so the values
are reliable and available to use. We choose 3.21 MPa for the
critical pressure of 2-chloromethylbenzonitrile.
o
10
∆vapH (T )
b
n ) 0.00264
+ 0.8794
(9)
(
)
RTb
o
Taking Tc and Pc from eq 10, the value of ∆vapH (Tb) is 52.63
o
-1
The value of ∆vapH (Tb) can be estimated by Riedel’s
kJ‚mol . With the same T and P , we can get the value of
c
c
9
∆vapH (T ) ) 51.54 kJ‚mol by Giacalone’s method.9
The value 52.63 kJ‚mol is selected as the ∆vapH (Tb) of
2-chloromethylbenzonitrile. Using eqs (9 to 6) and eq 3
o
-1
equation
b
-
1
o
2
4
.18T T /K (5 log P /MPa + 2.83)
o
-1
c
b
c
∆vapH (T )/kJ‚mol
)
b
o
-1
successively, we can get ∆vapH (Tfus) ) 66.00 kJ‚mol ,
(
0.930T - T )/K
c
b
o
-1
o
(
10)
∆subH (Tfus) ) 86.53 kJ‚mol , and ∆fH (cr, 298.15 K) ) 70.23
-
1
kJ‚mol , respectively.
where Pc is critical pressure and Tc is critical temperature.
o
o
∆
fH (g, 298.15 K) and ∆fH (298.15 K) for Trimethyl
To estimate the enthalpy of vaporization of 2-chloromethyl-
benzonitrile at any temperature, we must know the critical
temperature and critical pressure of 2-chloromethylbenzonitrile.
However, there are no data on this compound. Tc can be
calculated by the equation proposed by Riedel et al.: Tc ) Tb/
θ. In this study, the Lydersen method12 is used to estimate θ
Phosphite. The calculation process by the Benson method is
shown in Table 8, and the result is compared with the literature
value.
-
1
The calculation value is -703.67 kJ‚mol . The value
1
3
-1
reported in the literature is -704.1 kJ‚mol , and the deviation
is only 0.09 %. The calculation value of trimethyl phosphite
2
with the Benson method is accurate.
θ ) 0.567 +
∆ - ( ∆ )
(11)
∑
T
∑
T
o
∆
fH (l, 298.15 K) of trimethyl phosphite is estimated by eq
4
. The calculation procedure is similar to that of 2-chlorom-
where ∑ ∆T is obtained by adding the contributions listed in
ethylbenzonitrile. The boiling point of trimethyl phosphite is
Table 7.
7
The boiling point of 2-chloromethylbenzonitrile is 525.15 K.7
Taking ∑ ∆T from eq 11, θ can be estimated as 0.703. Finally,
Tc is calculated to be 746.6 K. We also estimate the value by
Vowle’s method, another broadly applicable method. The result
is 745.1 K. So 746.6 K can be selected as the critical temperature
384.15 K. The critical temperature could be approximated by
9
14
the Guldberg rule: Tc ) 1.5Tb ) 576.23 K. In the literature,
Tc is found to be 576.2 K. The critical pressure is calculated to
9
9
be 3.39 MPa by Herzog’s method, which is close to the
1
4
literature value (3.45 MPa). Taking Tc and Pc to eq 10, the
o
-1
value of ∆vapH (Tb) is 33.69 kJ‚mol . With the same Tc and
of 2-chloromethylbenzonitrile in this paper.
o
-1
The Lydersen method12 is used to calculate Pc of 2-chloro-
Pc, we can get the value of ∆vapH (Tb) ) 33.40 kJ‚mol by
-
1
Giacalone’s method. The value 33.69 kJ‚mol is selected as
methylbenzonitrile by the expression
o
o
the ∆vapH (Tb). ∆vapH (298.15 K) is calculated to be 38.65
-
1
o
0
.1M
kJ‚mol by eqs 8 and 9. Finally, we get the ∆fH (l, 298.15 K)
Pc )
(12)
-1
2
of trimethyl phosphite of -742.34 kJ‚mol , which is close to
(
Φ + 0.34)
-
1 13
the literature value (-741.0 kJ‚mol ).
o
o
where M is the molecular weight and Φ is an additive constant
which is determined from the molecular structure.
Φ can be calculated by adding structural constants listed in
Table 7.
∆fH (g, 298.15 K) and ∆fH (298.15 K) for 2-Dimeth-
o
ylphosphonomethylbenzonitrile. In the estimation of ∆fH (g,
298.15 K) for 2-dimethylphosphonomethylbenzonitrile, the
C-(PO)(CB)(H)2 group contribution is determined by a proce-

Journal of Chemical and Engineering Data, Vol. 52, No. 4, 2007 1193
Table 9. Differences of Group Contributions When C Is Replaced
by CB
o
o
∆rH (298.15 K) )
V ∆ H (B, 298.15 K)
(13)
∑
B
B
f
o
differences between
According to the Kirchhoff equation, ∆rH (298.15 K) can
o
j
∆
fH (g, 298.15 K)
two groups
kJ‚mol-1
1.97
be obtained
group
kJ‚mol-
1
o
10
10
10
10
10
10
∆ H (298.15 K) )
C-(Cd)(CB)(H)2
C-(Cd)(C)(H)2
C-(CB)(Br)(H)2
C-(C)(Br)(H)2
C-(CB)(I)(H)2
C-(C)(I)(H)2
-17.93
-19.90
-21.32
-22.57
35.11
r
o
∆rH (353.15 K) + ∆H + ∆H + ∆H + ∆H (14)
1
2
3
4
1.25
1.67
In eq 14, ∆H1, ∆H2, ∆H3, and ∆H4 are enthalpy changes of
2-chloromethylbenzonitrile, trimethyl phosphite, 2-dimethyl-
phosphonomethylbenzonitrile and methane chloride, and can be
calculated as follows, respectively.
33.44
Table 10. Calculation of Gas Standard Enthalpy of Formation for
-Dimethylphosphonomethylbenzonitrile
2
o
j
334.15 K
o
∆
fH (g, 298.15 K)
∆H ) 151.5 ×
∫
C (cr)dT + ∆ H (334.15 K) +
1
p
fus
298.15 K
1
group
contribution number
kJ‚mol-
3
53.15 K
-1
1
51.5 ×
∫
C (l)dT ) 33.65 kJ‚mol (15)
p
CB-(C)
CB-(H)
CB-(CN)
PO-(C)(O)2
O-(C)(PO)
C(H3)O
1
4
1
1
2
2
1
23.037
334.15 K
7
13.79
149.647
353.15 K
-1
-415.917
-170.13
∆H
2
) 124 ×
∫
C
p
(l)dT ) 10.78 kJ‚mol
(16)
298.15 K
7
-42.137
-12.54
298.15 K
-1
∆
H ) 225 ×
∫
C (l)dT ) -24.89 kJ‚mol (17)
p
C-(PO)(CB)(H)2
fH (g, 298.15 K)
3
353.15 K
o
∆
-625.12
2
98.15 K
-1
∆
H ) 50.5 ×
∫
C (g)dT ) -2.36 kJ‚mol (18)
p
4
dure similar to C-(CB)(Cl)(H)2. As shown in Table 9, contribu-
tion values of three pairs of groups are listed and compared. It
can be seen that the differences of group contributions tend to
a value (1.67 kJ‚mol ) when C is replaced by CB. The
contribution value of C-(PO)(C)(H)2 is -14.21 kJ‚mol , so
the value of C-(PO)(CB)(H)2 is calculated to be -12.54
kJ‚mol .
The calculation for the gas standard enthalpy of formation is
the same as that mentioned above for 2-dimethylphosphono-
methylbenzonitrile, and the corresponding data are shown in
Table 10. The gas standard enthalpy of formation is -625.12
353.15 K
-
1
-1
where Cp(g)/J‚g ‚K ) 0.2729 + 0.002025T/K - 8.04‚
-
7
2
-11
3
-
1
10 (T/K) + 6.8159‚10 (T/K) is the heat capacity of gas
1
5
-
1
methane chloride.
o
∆
rH (353.15 K) is measured by a heat conduction micro-
-
1
calorimeter which consists of a sample cell and a reference cell.
This method has been described in more detail in the literature.16
The temperature of this calorimetric experiment is (353.15 (
0
.01) K. The sample cell has the same volume as the reference
3
cell (16 cm ). To prevent corrosion of the stainless steel cells,
two double-layer glass tubes are put in the cells, respectively.
In the sample cell, 1.0 g (( 0.0001 g) of trimethyl phosphate
and 1.22 g (( 0.0001 g) of 2-chloromethylbenzonitrile are added
into the inner tube and the outer tube, respectively. Then the
system is heated to the required temperature. After 1 h, the inner
tube is broken by a rod, and a chemical reaction between
trimethyl phosphate and 2-chloromethylbenzonitrile takes place.
The thermal effect is recorded automatically on a computer.
According to the mass and the composition of the residue, the
heat of reaction at this temperature can be calculated. The
experiment is performed five times, and the results are listed in
Table 11 in which m is the mass of 2-dimethylphosphono-
methylbenzonitrile. The estimated uncertainty of measure is (
-
1
kJ‚mol
for 2-dimethylphosphonomethylbenzonitrile. This
value will be manifested by experimental data in the back of
this article.
In this work, the boiling point of 2-dimethylphosphono-
methylbenzonitrile is measured to be (552 to 553) K with a
microscopic boiling point device. With the same method as that
used for trimethyl phosphite, we can get Tc ) 829.5 K, Pc )
o
-1
o
2
.30 MPa, ∆vapH (Tb) ) 43.64 kJ‚mol , and ∆vapH (298.15
-
1
K) ) 54.69 kJ‚mol , respectively. Finally, we get the value of
o
-1
∆
fH (l, 298.15 K) (-679.80 kJ‚mol ). This value cannot be
checked by another prediction method as 2-chloromethylben-
zonitrile and cannot be manifested by the literature value as
trimethyl phosphite. So we design a thermochemical cycle to
verify it.
0
.5 %.
o
-1
o
Finally, ∆rH (298.15 K) ) -89.86 kJ‚mol is obtained from
Verification of the ∆fH (l, 298.15 K) for 2-Dimethylphospho-
nomethylbenzonitrile by Experiment. The thermochemical cycle
designed for the derivation of ∆fH (l, 298.15 K) of 2-dimethyl-
phosphonomethylbenzonitrile is shown as follows.
o
-1 9
eq 14. ∆fH (298.15 K) of methane chloride is -81.96 kJ‚mol .
o
o
According to eq 13, ∆fH (298.15 K) of 2-dimethylphospho-
-1
nomethylbenzonitrile is calculated to be -680.01 kJ‚mol . The
deviation between experiment and calculation is 0.03 %. The
result shows that the calculated values of ∆fH (l, 298.15 K) of
o
trimethyl phosphate and 2-dimethylphosphonomethylbenzo-
o
nitrile and of ∆fH (cr, 298.15 K) of 2-chloromethylbenzonitrile
are reliable and available.
Summary
The heat capacities of trimethyl phosphite, 2-chloromethyl-
benzonitrile, and 2-dimethylphosphonomethylbenzonitrile have
o
been measured. To calculate ∆fH (g, 298.15 K) of 2-chloro-
methylbenzonitrile and 2-dimethylphosphonomethylbenzonitrile,
o
We can derive ∆fH (l, 298.15 K) of 2-dimethylphosphono-
the enthalpy group values of C-(CB)(Cl)(H)2 and C-(PO)(CB)-
-
1
methylbenzonitrile from eq 13.
(H)2 for the Benson method are derived to be -72.73 kJ‚mol

1
194 Journal of Chemical and Engineering Data, Vol. 52, No. 4, 2007
Table 11. Enthalpy of Reaction at 353.15 K
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o
o
m
∆rH (353.15 K)
∆rH (353.15 K)
kJ‚mol-1
no.
mg
mJ
(7) Weast, R. C. CRC Handbook of Chemistry and Physics, 70th ed; CRC
1
2
3
4
10.34
10.92
9.85
10.00
11.76
-4917.71
-5185.79
-4674.15
-4762.67
-5591.49
-107.01
-106.85
-106.77
-107.16
-106.98
-106.95
Press: Boca Raton, FL, 1989.
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10) Benson, S. W. Thermochemical Kinetics, 2nd ed; Wiley-Inter-
science: New York, 1976.
(11) Joback, K. G. S. M. Thesis in Chemical Engineering, Massachusetts
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5
mean
(
-
1
and -12.54 kJ‚mol , respectively. After determining Tc and
o
Pc of the compounds, ∆fH (cr, 298.15K) of 2-chloromethyl-
o
benzonitrile and ∆fH (l, 298.15 K) for trimethyl phosphite and
(
2
7
-dimethylphosphonomethylbenzonitrile were calculated to be
0.23 kJ‚mol , -742.34 kJ‚mol , and -679.80 kJ‚mol ,
-
1
-1
-1
respectively.
(
14) Dutt, N. V. K.; Kahol, A. P.; Jyothiraju, P. Vapor Pressure of Trimethyl
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