A calorimetric study of N,N-diethyl-N′-furoylthiourea and N,N-diisobutyl-N′-furoylthiourea

Article abstract of DOI:10.1006/jcht.2001.0853

The standard (p^o = 0.1 MPa) molar enthalpies of combustion in oxygen, at T = 298.15 K, were measured by rotative bomb calorimetry for crystalline N,N-diethyl-N′-furoylthiourea, (2-C₄H₃O)CONHCSN(C₂H₅) ₂, HFET, and N,N-diisobutyl-N′-furoylthiourea, (2-C₄H₃O)CONHCSN(iso-C₄H₉) ₂, HFIB. The standard molar enthalpies of sublimation of both HFET and HFIB were measured by high-temperature Calvet microcalorimetry. These values were used to derive the standard molar enthalpies of formation of the compounds, in their crystalline and gaseous phases.

Full text of DOI:10.1006/jcht.2001.0853

J. Chem. Thermodynamics 2002, 34, 155–161
doi:10.1006/jcht.2001.0853
Available online at http://www.idealibrary.com on
A calorimetric study of
N,N-diethyl-N0-furoylthiourea and
N,N-diisobutyl-N0-furoylthiourea
Manuel A. V. Ribeiro da Silva,a Maria D. M. C. Ribeiro da Silva,
Lu´ıs C. M. da Silva,b
Centro de Investigac¸a˜o em Qu´ımica, Departamento de Qu´ımica, Faculdade
de Cieˆncias, Universidade do Porto, Rua do Campo Alegre, 687,
P-4169-007 Porto, Portugal
and Frank Dietze
Institut fu¨r Anorganische Chemie, Fakulta¨t fu¨r Chemie und Mineralogie,
Universita¨t Leipzig, Johannisallee, 29, Leipzig 04103, F.R.G.
o
The standard (p = 0.1 MPa) molar enthalpies of combustion in oxygen, at
T
=
298.15 K, were measured by rotative bomb calorimetry for crystalline
N,N-diethyl-N0 -furoylthiourea, (2-C H O)CONHCSN(C H ) , HFET, and N,N-
4
3
2 5 2
diisobutyl-N0 -furoylthiourea, (2-C H O)CONHCSN(iso-C H ) , HFIB. The standard
4
3
4 9 2
molar enthalpies of sublimation of both HFET and HFIB were measured by high-
temperature Calvet microcalorimetry. These values were used to derive the standard molar
enthalpies of formation of the compounds, in their crystalline and gaseous phases.
g
cr
o
−1
o
−1
−1 u (cr)/J · g
1
H /kJ · mol
c
m
(2-C H O)CONHCSN(C H )
2 5 2
27505.0 ± 4.5
132.0 ± 3.5
4
3
(2-C H O)CONHCSN(iso-C H )
31218.8 ± 2.0
141.7 ± 5.6
4
3
4 9 2
c
ꢀ 2002 Published by Elsevier Science Ltd.
KEYWORDS:
N,N-diethyl-N0 -furoylthiourea;
N,N-diisobutyl-N0 -furoylthiourea;
enthalpy of combustion; enthalpy of sublimation; enthalpy of formation
a
b
To whom correspondence should be addressed (E-mail: risilva@fc.up.pt).
Present address: Departamento de Qu´ımica, Instituto Superior de Cieˆncias da Sau´de-Norte, Rua Central da
Gandra, 1317, P-4585-116 Gandra PRD, Portugal.
c
0021–9614/02
ꢀ 2002 Published by Elsevier Science Ltd.

156
Manuel A. V. Ribeiro da Silva et al.
1. Introduction
Acylchalcogenoureas are good chelating ligands due to there ability to act as selective
complexing agents and so are widely used in analytical applications,(1) in heavy-metal
hydrometallurgy,(2) in trace enrichment and in chromatographic separation of metals.(3)
Its complexes are easily extracted by apolar solvents and separated by chromatographic
techniques, allowing efficient yield even in low residual metal concentrations. Moreover,
it is known that the nature of the acyl group and terminal nitrogen atom substituents
are important to the coordination ability of the ligands.(4) Therefore, a systematic study
of these type of molecules with different substituents has been carried and although a
large number of papers(1–6) have been devoted to the synthesis and physical properties of
these kinds of ligands and their complexes, very few studies were published(7) on their
thermochemical properties, either in the gaseous or condensed phases.
This paper, which is a part of a broader research programme on the energetic properties
of acylchalcogenoureas and their metal complexes, presents a thermochemical study of
N,N-diethyl-N0 -furoylthiourea (HFET) and N,N-diisobutyl-N0 -furoylthiourea (HFIB),
both in the condensed and gaseous phases.
2. Experimental
Although the synthesis of monoalkylfuroylthioureas, RCO NH CS NHR0, was already
described by Douglass et al.,(8) the preparation of dialkyl derivatives, RCO NH CS NR02,
has not been reported before.
The N,N-diethyl-N0 -furoylthiourea, (2-C4H3O)CONHCSN(Et)2 (HFET), was pre-
pared according to the method previously reported for other acylthioureas(8) by adding
an acetone solution of 0.10 mol (9.8 g) of potassium thiocianate to an acetone solution of
0.11 mol (13.9 g) of 2-furoyl chloride. After mixture, a cold acetone solution of 0.14 mol
(10.3 g) of diethylamine was added and stirred for another 0.5 h, after which time it was
poured into a water/ice mixture. The filtrate was recrystallized from an ethanol/water
mixture, yielding white crystals with a melting temperature of Tfus = 373 K–375 K.
The N,N-diisobutyl-N0 -furoylthiourea, (2-C4H3O)CONHCSN(iBut)2 (HFIB), was
prepared by the same procedure: an acetone solution of 0.10 mol (9.9 g) of potassium
thiocianate was added to an acetone solution of 0.11 mol (13.9 g) of 2-furoyl chloride.
After mixture, a cold acetone solution of 0.12 mol (15.2 g) of diisobutylamine was added
and stirred for another 0.5 h, after which it was poured into a water/ice mixture. The filtrate
was washed with n-pentane and recrystallized from an ethanol/water mixture, yielding
white crystals with a melting temperature of Tfus = 360 K–361 K.
The enthalpies of combustion for both compounds were measured using a rotating bomb
calorimeter previously described.(9) The experiments were performed in a platinum-lined
bomb of internal volume 0.337 dm3. Water was added to the calorimeter from a weighed
perspex vessel and a correction to the energy equivalent was made to account for the
deviation in the mass of water from 4059.0 g. The ignition temperatures were chosen
in such a way to have a final temperature as close as possible to 298.15 K. In each
experiment, rotation started at a time from the main period when the temperature rise was

Thermochemical study of Furoyldialkylthioureas
157
about 63 per cent of the total expected, so the frictional work due to bomb rotation could
be included in the corrections for the heat leakage and work of stirring, in accordance with
the procedures of Good et al.(10)
The system described above was calibrated by burning benzoic acid pellets (Bureau of
Analyzed Samples, Thermochemical Standard, BCS-CRM-190r) with a specific heat of
combustion under certificate conditions of −(26432.3 ± 3.8) J · g−1. This procedure led,
from eight experiments, to an energy equivalent of ε(calor) = (20690.2 ± 3.3) J · K−1
referred to a 4059.0 g mass of water. The uncertainty given corresponds to the standard
deviation of the mean. The electrical energy for ignition was determined from the change
in potential difference across a capacitor when discharged through the platinum ignition
wire. The massic energy of combustion of the cotton thread used, of empirical formula
CH1.686O0.843, was 1cuo = −16250 J · g−1 (11)
.
The corrections for nitric acid formation
were based on −59.7 kJ · mol−1 (12)
,
for the molar energy of formation of 0.1 mol · dm−3
HNO3(aq) from gaseous N2 and O2, and liquid H2O. The relative atomic masses used
were those recommended by the IUPAC Commission in 1995.(13) The calorimetric system
was tested by burning thiantrene pellets, (C12H8S2), giving a massic energy of combustion
after eight experiments of 1cuo = −(33479.9 ± 1.2) J · g−1
.
The procedure described by Waddington et al.(14) for combustion calorimetry of
organosulphur compounds was followed. The RCONHCSNR0 2 compounds were burned
in pellet form under a p = 3.04 MPa oxygen atmosphere, and in the presence of 10.0 cm3
(HFET) or 5.0 cm3 (HFIB) of water. The amount of nitric acid was determined using
Devarda’s method. At T = 298.15 K, (∂u/∂p)T for these compounds was assumed to be
−0.2 J · g−1 · Pa−1, which is a typical value for organic solids.(15) The procedure given by
Hubbard et al.(16) was used for the calculation of 1cuo.
The standard molar enthalpies of sublimation of both HFET and HFIB were measured
using the vacuum sublimation drop microcalorimetric method,(17) in which samples
(about 3 mg) of each crystalline compound, contained in a thin one-end sealed glass
capillary tube are dropped from room temperature to the hot zone of the calorimetric cell
and then evacuated. The Calvet microcalorimeter apparatus (SETARAM HT 1000) hot
zone was held at T = 385 K in both studies. The observed enthalpies of sublimation
{Hmo (g, 385 K) − Hmo (cr, 298 K)} were corrected to T = 298.15 K, by estimating
1328958 KK Hmo (g) using a group contribution method based on the Stull et al.(18) values.
The calibration of this calorimetric system was carried by the sublimation of naphthalene
samples, C10H8, 1cgr Hmo (C10H8) = (72.51±0.01) kJ · mol
.
−1 (19) The calibration constant
was set as k385 K = (18.42 ± 0.28) mJ · V−1 · s−1 from six independent experiments.
3. Results
Table 1 lists typical combustion experimental results for each compound. In this table,
1m (H2O) represents the departure from the 4059.0 g of the water added to the calorimeter,
the mass of water assigned to ε(calor), 1U6 is the correction to the standard state, and
the remaining terms are as previously described.(16) As the final temperature of the main
period is T = 298.15 K,

158
Manuel A. V. Ribeiro da Silva et al.
TABLE 1. Typical combustion experi-
mental results for N,N-diethyl-N0 -
furoylthiourea, HFET, and N,N-diisobutyl-
N0 -furoylthiourea, HFIB, at T = 298.15 K
HFET
HFIB
m(cpd)/g
m(fuse)/g
0.80350
0.00408
23.8947
24.9998
1.07214
74.70
0.68656
0.00470
23.9122
24.9853
1.04056
33.21
(T /K) − 273.15
i
(T /K) − 273.15
f
1T /K
ad
−1
−1
ε /(J · K
f
)
)
i
ε /(J · K
74.34
33.11
1m(H O)/g
+0.4
22263.49
+2.4
21573.19
2
a
−1U(IBP)/J
1U(HNO )/J
66.86
47.16
3
1U(ign)/J
1.18
1.19
1U /J
33.89
14.80
6
o
−m1 u (fuse)/J
66.26
76.33
c
o
−1
)
−1 u (cpd)/(J · g
27500.2
31220.9
c
a
1U(IBP) includes 1U(ign); m(cpd) mass of
compound burnt in each experiment; m(fuse) mass
of fuse (cotton) used in each experiment; 1T cor-
ad
rected temperature rise/variation of adiabatic tem-
perature; T and T initial and final temperatures of
i
f
main period; ε , ε energy equivalent of contents
i
f
in the initial and final states; 1m(H O) deviation
2
of the mass of water added to the calorimeter from
4059.0 g; 1U(IBP) energy change for the isother-
mal combustion reaction under actual bomb con-
ditions; 1U(HNO ) energy correction for the ni-
3
tric acid formation; 1U standard state correction;
6
o
m1 u (fuse) energy of combustion of the cotton
fuse; 1 u (cpd) compound massic energy of com-
c
o
c
bustion.
1U(IBP) = −{ε(calor) + cp(H2O, l)1m(H2O)}1Tad + εi(Ti − 298.15) + εf(298.15 −
Ti − 1Tad) + 1U(ign),
where 1Tad is the calorimeter temperature change corrected for heat exchange and work
done due to stirring. Table 2 lists the individual values of −1cuo together with its mean
and standard deviation. In table 3, the derived standard molar enthalpies of combustion and
formation in the crystalline and gaseous states at T = 298.15 K are listed. The uncertainties
assigned to the standard molar enthalpies of combustion and formation, in accordance with
normal thermochemical practice, are taken as twice the overall standard deviation of the

Thermochemical study of Furoyldialkylthioureas
159
TABLE 2. Individual values of
the massic energies of combustion
of N,N-diethyl-N0 -fu-
o
−1 u
c
roylthiourea,0 HFET, and N,N-
diisobutyl-N -furoylthiourea,
HFIB, at T = 298.15 K
HFET
HFIB
o
−1
)
−1 u /(J · g
c
27513.8
27487.9
27500.2
27515.2
27494.4
27520.8
27502.4
31214.4
31226.9
31218.1
31213.2
31219.6
31220.9
o
−1
)
h−1 u i/(J · g
c
27505.0 ± 4.5
31218.8 ± 2.0
o
h−1 u i represents the mean values.
c
o
TABLE 3. Derived standard (p = 0.1 MPa) molar energies of combus-
o
o
tion, 1 U , standard molar enthalpies of combustion, 1 H , standard molar
c
c
m
m
o
enthalpies of formation, 1 H and standard0 molar enthalpies of sublimation,
f
m
g
cr
o
1
H , at T = 298.15 K, for N,N-diethyl-N -furoylthiourea, HFET, and N,N-
m
diisobutyl-N0 -furoylthiourea, HFIB
g
o
o
o
o
o
−1 U (cr)
−1 H (cr)
1 H (cr)
1
H
1 H (g)
f
m
c
c
f
cr
m
m
m
m
−1
−1
−1
−1
−1
kJ · mol
kJ · mol
kJ · mol
kJ · mol
kJ · mol
HFET
HFIB
6224.4 ± 3.0
8816.4 ± 3.3
6231.8 ± 3.0
8828.8 ± 3.3
−306.1 ± 3.3
−426.4 ± 3.8
132.0 ± 3.5
141.7 ± 5.6
−174.1 ± 4.8
−284.7 ± 6.8
mean and include the errors from the calibration and use of auxiliary data. To derive 1f Hmo
from 1c Hmo , the following standard enthalpies of formation, at T = 298.15 K, of H2O(I),
−(285.83 ± 0.04) kJ · mol−1 (20) and CO2(g), −(393.51 ± 0.13) kJ · mol−1 (20) were used.
The individual results of the enthalpies of sublimation of HFET and HFIB are given at
table 4, where once again the quoted uncertainties are equal to twice the standard deviation
of the mean.

160
Manuel A. V. Ribeiro da Silva et al.
TABLE 4. Individual microcalorime-
o
tric standard (p
lar enthalpies of sublimation 1 H ,
=
0.1 MPa) mo-
g
o
cr
m
at0 T = 298.15 K, for N,N-diethyl-
N -furoylthiourea, HFET, and N,N-
diisobutyl-N0 -furoylthiourea, HFIB
HFET
g
HFIB
o
−1
)
1
H
(T = 298.15 K)/(kJ · mol
cr
m
125.5
127.6
129.4
131.7
135.5
136.7
137.5
g
132.8
135.6
140.6
142.8
147.1
151.1
o
a
−1
)
h1
H
i (T = 298.15 K)/(kJ · mol
cr
m
132.0 ± 3.5
141.7 ± 5.6
g
cr
a
o
h1
H
i represents the mean values.
m
4. Discussion
Since the compounds in this study are reported for the first time, there are no previous
results regarding their thermochemistry or any other physical properties. However, there
are a few papers about the thermochemistry of related compounds as benzoylureas(7) and
on the additivity of thermodynamic properties of alkylureas.(21, 22) As it was previously
done for other compounds of the same acylchalcogenoureas family,(7) the self-consistency
of the results can be tested from the difference of the enthalpies of formation of the two
compounds, which corresponds to the substitution of an ethyl by an iso-butyl group.
As estimated previously(7) from group energy contributions, this enthalpic difference
should correspond to 99.3 kJ · mol−1. On the other hand, a simple difference between
the corresponding standard molar enthalpies of formation in the gaseous phase(23) yields
a difference of (108 ± 3) kJ · mol−1, well in accordance with the experimental difference
found for the pair of thioureas reported in this paper, (110 ± 8) kJ · mol−1
.
This work is part of a joint research project between the University of Porto, Portugal, and
the University of Leipzig, F. R. G., under the auspices of the INIDA program, between
JNICT (Junta Nacional de Investigac¸a˜o Cient´ıfica e Tecnolo´gica), Lisboa, Portugal, and
DAAD (Deutscher Akademischer Austauschdienst), Bonn, Germany, for which we express
our greatest thanks. Thanks are also due to FCT, Fundac¸a˜o para a Cieˆncia e Tecnologia,
Lisboa, Portugal for financial support granted through Centro de Investigac¸a˜o em Qu´ımica
da Universidade do Porto (research unit number 81) and for the research project PRAXIS

Thermochemical study of Furoyldialkylthioureas
161
XXI/PCEX/QUI/62/96. One of us (L.C.M.S.) is grateful to FCT for the award of a
scholarship BD/5591/95.
We also thank Dr P. A. G. O’Hare for his highly valuable contributions to the field of
thermochemistry during his scientific life, not only producing excellent thermodynamic
data using different calorimetric techniques, but also for the work he has done on the
IUPAC Commission 1.2 and continues to do editing the Journal of Chemical Thermo-
dynamics.
REFERENCES
1. Vest, P.; Schuster, M.; Ko¨nig, K.-H. Fresenius’ Z. Anal. Chem. 1991, 339, 142–144.
2. Koch, K. R.; Sacht, C.; Grimmbacher, T.; Bourne, S. S. Afr. Chem. 1995, 48, 71–77.
3. Schuster, M.; Kugler, B.; Ko¨nig, K.-H. Fresenius’ Z. Anal. Chem. 1990, 338, 710–720.
4. Beyer, L.; Hoyer, E.; Liebscher, J.; Hartmann, H. Z. Chem. 1981, 21, 81–91.
5. Sosa, M.; Esteva, A. M.; Rodr´ıguez, Y.; Morales, M.; Plutin, A. M.; Alp´ızar, J.; Cerda´, V. An.
de Qu´ımica Int. Ed. 1997, 93, 337–340.
6. Rodriguez Esteva, A. M.; Cardena Vasaquez, M. C.; Plutin Stevens, A. M.; Macias Cabrera, A.;
Bosque Arin, J. R. An. de Qu´ımica 1995, 91, 696–701.
7. Ribeiro da Silva, M. A. V.; Ribeiro da Silva, M. D. M. C.; da Silva, L. C. M.; Dietze, F.; Hoyer,
E. J. Chem. Thermodynamics 2000, 32, 1113–1119; doi: 10.1006/jcht.1999.0527.
8. Douglass, I. B.; Dains, F. B. J. Am. Chem. Soc. 1934, 56, 719–721.
9. Ribeiro da Silva, M. A. V.; Gonc¸alves, J. M.; Pilcher, G. J. Chem. Thermodynamics 1997, 29,
253–260; doi: 10.1006/jcht.1996.0143.
10. Good, W. D.; Scott, D. W.; Waddington, G. J. Phys. Chem. 1960, 60, 1080–1089.
11. Coops, J.; Jessup, R. S.; Van Nes, K. Experimental Thermochemistry, Vol. 1, Chap. 3. Rossini,
F. D.: editor. Interscience: New York. 1956.
12. The NBS Tables of Chemical Thermodynamics Properties. J. Phys. Chem. Ref. Data 1982, II
(Suppl. 2).
13. J. Phys. Chem. Ref. Data 1997, 26, 1239–1253.
14. Waddington, G.; Sunner, S.; Hubbard, W. N. Experimental Thermochemistry, Vol. 1, Chap. 7.
Rossini, F. D.: editor. Interscience: New York. 1956.
15. Washburn, E. W. J. Res. Natl. Bur. Stand. (U.S.) 1933, 10, 525–588.
16. Hubbard, W. N.; Scott, D. W.; Waddington, G. Experimental Thermochemistry, Vol. 1, Chap. 5.
Rossini, F. D.: editor. Interscience: New York. 1956.
17. Adedeji, F. A.; Brown, D. L. S.; Connor, J. A.; Leung, M.; Paz Andrade, M. I.; Skinner, H. A.
J. Organometallic Chem. 1975, 97, 221–228.
18. Stull, D. R.; Westrum, E. F.; Sinke, G. C. The Chemical Thermodynamics of Organic Com-
pounds. Wiley: New York. 1969.
19. Kruif, C. G. de; Kuipers, T.; Mittenburg, J. C. van; Schnake, R. C. F.; Stevens, G. J. Chem.
Thermodynamics 1981, 13, 1081–1086.
20. Cox, J. D.; Wagman, D. D.; Medvedev, D. A. CODATA Key Values for Thermodynamics.
Hemisphere: New York. 1989.
21. Simirsky, V. V.; Kabo, G. J.; Frenkel, M. L. J. Chem. Thermodynamics 1987, 19, 1121–1127.
22. Kabo, G. J.; Kozyrio, A. A.; Diky, V. V.; Simirsky, V. V. J. Chem. Eng. Data 1995, 40, 371–393.
23. Ribeiro da Silva, M. A. V.; Ribeiro da Silva, M. D. M. C.; Gomes, M. L. A. C. N.; Johnson, M.;
Pilcher, G. J. Chem. Thermodynamics 1997, 29, 1025–1030.
(Received 7 March 2001; in final form 9 April 2001)
WE-295