The influence of a medium on the rate of the reaction between N,N′-dioctylurea and n-octanol

Article abstract of DOI:10.1134/S0036024407010050

The kinetics and mechanism of alcoholysis of symmetrical dioctylurea in inert solvents were studied. The reaction was found to follow two parallel pathways, one involving the destruction of initial urea and the other, bimolecular interaction. For the reaction series under consideration, the influence of the nature of solvents on the rate of the reaction was studied. Nauka/Interperiodica 2007.

Full text of DOI:10.1134/S0036024407010050

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2007, Vol. 81, No. 1, pp. 18–22. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © A.A. Orlova, S.N. Mantrov, 2007, published in Zhurnal Fizicheskoi Khimii, 2007, Vol. 81, No. 1, pp. 24–28.
CHEMICAL KINETICS
AND CATALYSIS
The Influence of a Medium on the Rate of the Reaction
between N,N'-Dioctylurea and n-Octanol
A. A. Orlova and S. N. Mantrov
Mendeleev University of Chemical Technology, Miusskaya pl. 9, Moscow, 125190 Russia
E-mail: MantrovSN@yandex.ru
Received December 14, 2005
Abstract—The kinetics and mechanism of alcoholysis of symmetrical dioctylurea in inert solvents were stud-
ied. The reaction was found to follow two parallel pathways, one involving the destruction of initial urea and
the other, bimolecular interaction. For the reaction series under consideration, the influence of the nature of sol-
vents on the rate of the reaction was studied.
DOI: 10.1134/S0036024407010050
INTRODUCTION
increases expenditures for labor and environment pro-
tection. For this reason, industrial methods for synthe-
sizing carbamates without the use of chlorine-contain-
ing agents has been attracting much attention during the
past decades. One of such methods is the alcoholysis of
symmetrical dialkylureas prepared by the transamina-
tion of carbamide [11]. Although this method for the
preparation of carbamates is well known, it is virtually
not used in industry, and the literature data in this area
are limited to patents, in which the conditions of the
Thanks to the well-known biological properties,
carbamates, or urethanes (esters of N-substituted car-
bamic acids), are used as medicines [1–4] and chemical
plant-protective agents [5, 6]. In addition, carbamates
as thermally labile structures can be considered inter-
mediate products of phosgene-free synthesis of isocy-
anates [7–9].
The production of urethanes is a multistage process
involving the use of phosgene [10] or sodium cyanate
[10]. On the one hand, these methods are characterized process are not given and data on the kinetics of inter-
by high yields; on the other, they have several important
shortcomings. The search for alternative methods for
the preparation of carbamates on an industrial scale is
therefore necessary. The main problem related to the
preparation of urethanes with the participation of phos-
gene or cyanates is the production of inorganic wastes.
action are lacking [12].
In order to study the rules that govern the interaction
of aliphatic ureas with alcohols, we investigated the
kinetics and mechanism of the model reaction between
symmetrical dioctylurea and n-octanol in inert sol-
In addition, work with high-toxicity phosgene vents,
C8H17HN
NHC8H17
C8H17HN
OC8H17
+ C8H17OH
+ C8H17NH2.
O
O
EXPERIMENTAL
Initial N,N'-dioctylurea was prepared by the transamination of carbamide,
H2N
NH2
C8H17HN
NHC8H17
175–180°C
+ 2C8H17NH2
+ 2NH3.
O
O
Carbamide (40 g, 0.67 mol) and octylamine (242.4 ml, isopropanol (200 ml). The precipitate was washed three
189.6 g, 1.47 mol) were placed into a one-necked 500 ml or four times with isopropanol (30–40 ml) and dried in
flask with a reflux condenser. The mixture was refluxed air. The yield of N,N'-dioctylurea was 138.9 g (73.3%),
for 5 h. After cooling, it was twice recrystallized from melting point 94.5–95.5°ë. The structure and purity of
18

THE INFLUENCE OF A MEDIUM ON THE RATE OF THE REACTION
19
Table 1. Extinction coefficient (ε, l/(mmol cm)) for the
product of interaction between octylamine and chloranil at
540 nm (r is the correlation coefficient)
the product were proved by proton NMR spectroscopy.
The proton NMR spectra were recorded on Bruker
DRX500 instruments, the chemical shifts were mea-
sured with respect to tetramethylsilane, the solvent was
deuterated chloroform. The solvents used in this work
were purified as recommended in [13]. The physico-
chemical constants of the solvents and alcohols were
close to or coincided with those reported in the litera-
ture. The absorption of solutions was measured on a
Specord M-40 (Germany) spectrometer at a working
wavelength of 540 nm; the thickness of the optical cell
was 1 cm. Proton NMR spectrum (ppm): 0.86 (6H, tr,
CH3CH2, J = 9.1 Hz), 1.2–1.35 (20H, m, CH3CH2CH2),
1.45–1.5 (4H, m, CH3CH2CH2), 3.14 (4H, tr,
NHCH2CH2, J = 7.6 Hz), and 4.4 (2H, s, NH).
Solvent
Decane
ε
r
0.58 0.01
0.57 0.02
0.26 0.01
0.55 0.01
0.58 0.01
0.998
0.995
0.996
0.998
0.999
Phenetole
o-Dichlorobenzene
Nitrobenzene
Benzonitrile
Table 2. Specific initial rates of the reaction between
N,N'-dioctylurea and n-octanol at various octanol initial con-
centrations (c0, mol/l)
The reaction was performed in a three-necked reac-
tor (50 ml) under temperature-controlled conditions.
The reactor had a reflux condenser with a tube packed
with calcium chloride at the exit, a thermometer, and a
magnetic stirrer. Before attaining temperature-con-
trolled conditions, N,N''-dioctylurea (1.8–2.2 g)
weighed on an analytic balance and a solvent (30 ml)
were placed into the reactor. After the required temper-
ature was reached, n-octanol was introduced into the
reaction mixture. The weight of the alcohol was deter-
mined by the difference method. Time was counted
from the instant of its introduction. Samples (1 ml)
were taken in certain time intervals and analyzed by
photocolorimetry [14], which allowed us to monitor the
process as the accumulation of one of the reaction prod-
ucts, octylamine. The suggested method is based on the
formation of colored amine–chloranil compounds [14–
16]. For analytic purposes, we recorded the absorption
spectrum of a solution of the adduct of amine with chlo-
ranil over the wavelength range 300–700 nm. The
absorption maximum was observed at 540 nm in the
spectra of these compounds [15]. We also found that the
time necessary for the interaction between n-octy-
lamine and chloranil to be complete was 1.5–2 h. The
reaction products were stable for 5–6 h [15]. The
extinction coefficients of the octylamine–chloranil
adduct in various solvents were measured in calibration
experiments (see Table 1). We also determined the
boundaries within which the dependence of absorption
on the concentration of the substance analyzed obeyed
the Buger law.
t, °C
c0
W0 × 106, s–1
r
Decane
171.2
170.3
171.3
170.7
0.1267
0.2145
0.5268
0.8318
0.67 0.50
0.75 0.40
1.19 0.06
1.58 0.14
0.995
0.996
0.998
0.994
o-Dichlorobenzene
170.1
170.6
170.2
170.1
169.8
0.1095
0.3726
0.5188
0.8202
0.9417
1.13 0.11
0.996
0.995
0.999
0.992
0.995
2.37 0.39
2.69 0.11
4.25 0.13
4.71 0.51
Phenetole
169.5
169.3
169.9
169.4
0.3760
0.7109
0.8724
0.9759
3.12 0.10
5.30 0.70
6.57 0.19
7.47 0.51
0.999
0.999
0.999
0.998
Benzonitrile
169.5
170.1
169.9
169.2
0.1533
0.3677
0.7101
0.9873
0.80 0.03
1.22 0.06
2.15 0.17
2.90 0.14
0.999
0.998
0.994
0.999
Nitrobenzene
170.4
170.5
170.0
169.7
0.1879
0.3736
0.7096
0.8808
2.44 0.05
5.05 0.18
8.96 0.82
11.18 0.34
0.998
0.997
0.998
0.998
RESULTS AND DISCUSSION
Table 3. Rate constants for the reaction between N,N'-di-
octylurea and n-octanol in inert solvents
As has been mentioned above, data on the rules that
govern the alcoholysis of dialkylureas are lacking in the
literature. The earlier experiments with the interaction
of aromatic ureas and alcohols [17, 18] show that the
reaction predominantly proceeds as the dissociation of
diarylurea followed by the interaction of the dissocia-
tion product, isocyanate, with alcohol. Note that
another well-known pathway for the interaction of
ureas with nucleophiles, amines in particular, is the
direct attack of amines at the urea carbonyl group [19].
k1 × 106,
k3 × 105,
Solvent
t, °C
r
s–1
l/(mol s)
Decane
Phenetole
170.9 0.49 0.02 0.13 0.01 0.998
169.5 0.33 0.27 0.72 0.03 0.995
o-Dichlorobenzene 170.2 0.65 0.13 0.43 0.02 0.993
Benzonitrile
Nitrobenzene
169.7 0.35 0.07 0.26 0.01 0.997
170.2 0.22 0.18 1.24 0.03 0.999
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 81 No. 1 2007

20
ORLOVA, MANTROV
–log k1expt
W0 × 106
6.1
6.3
6.5
6.7
4
12
3
2
10
1
4
8
6
4
2
6.7
6.5
6.3
6.1
–logk1calcd
2
Fig. 2. Correspondence between the experimental rate con-
stants k at 170°ë and the rate constants calculated by the
Palm–Koppel equation for various solvents: (1) phenetole,
(2) benzonitrile, (3) decane, and (4) o-dichlorobenzene.
1
–logk3expt
4.7
3
5
1
5.1
4
1
5.5
2
3
0
0.5
1.0
c0
5.9
5.9
5.5
5.1
4.7
–logk3calcd
Fig. 1. Dependences of the initial specific rate of the alco-
holysis of N,N'-dioctylurea with n-octanol at 170°ë on the
concentration of n-octanol in inert solvents: (1) decane,
(2) o-dichlorobenzene, (3) phenetole, (4) nitrobenzene, and
(5) benzonitrile.
Fig. 3. Correspondence between the experimental rate con-
stants k at 170°ë and the rate constants calculated by the
3
Palm–Koppel equation for various solvents: (1) phenetole,
(2) benzonitrile, (3) decane, and (4) o-dichlorobenzene.
The kinetic model of the reaction studied was therefore
selected taking into account the possibility of both urea
dissociation, the so-called dissociative route [17],
C8H17HN
OC8H17
k2
C8H17NCO + C8H17OH
,
k–2
O
C8H17HN
NHC8H17
k1
and the nucleophilic attack of the octanol molecule at
the urea carbonyl group, or “associative” route [17],
C8H17NCO + C8H17NH2,
k–1
O
C8H17HN
NHC8H17
C8H17HN
OC8H17
k3
+ C8H17OH
+ C8H17NH2.
k–3
O
O
The suggested scheme of chemical transformation
is described by the system of kinetic equations
dcC/dt = k2cIcA – k–2cC + k3cUcA – k–3cCcAm
,
where ki are the rate constants for the corresponding
reactions and cU, cA, cI, cAm, and cC are the concentra-
tions of urea, alcohol, isocyanate, amine, and carbam-
ate, respectively. This system of equations has no ana-
lytic solution. Kinetic data processing based on the ini-
tial specific rate of urea alcoholysis was therefore
dcU/dt = – k1cU + k–1cIcAm – k3cUcA + k–3cCcAm
,
dcA/dt = – k2cIcA + k–2cC – k3cUcA + k–3cCcAm
dcI/dt = k1cU – k–1cIcAm + k–2cC – k2cIcA,
,
(1)
dcAm/dt = k1cU – k–1cIcAm + k3cUcA – k–3cCcAm
,
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 81 No. 1 2007

THE INFLUENCE OF A MEDIUM ON THE RATE OF THE REACTION
Table 4. Solvent parameters according to Palm–Koppel [20]
21
Solvent
Decane
–logk1
–logk3
Y
P
E
B
6.3098
6.4815
6.1871
6.4559
6.6576
5.8794
5.1427
5.3665
5.5935
4.9066
0.1989
0.3411
0.4286
0.4708
0.4788
0.3319
0.3888
0.4129
0.4004
0.4147
0
0
Phenetole
0.8
0
158
28
o-Dichlorobenzene
Benzonitrile
0
155
67
Nitrobenzene
0
suggested in [17]. For this purpose, the first equation
from system (1) is reduced to the initial conditions
It was found for the dissociative process constant
that only polarizability and basicity substantially influ-
enced the k1 value. This dependence was described by
the equation (r = 0.999)
W0 = –dcU/dt(t = 0) = k1cU + k3cU cA
0
0
0
or
logk1 = – 7.02 0.02
(3)
W0, sp = W0/cU = k1 + k3cA ,
(2)
+ (2.14 0.06)P – (0.0019 0.0001)B.
0
0
where k1 and k3 are the rate constants for the dissocia-
The correlation equation for the bimolecular reaction
characterized by the k3 constant had the form (r = 0.958)
tive and associative alcoholysis, respectively, and cU
0
and cA are the initial urea and alcohol concentrations.
0
logk3 = – 7.75 0.70
(4)
Based on these considerations, the unknown rate
constants for mono- and bimolecular alcoholysis were
determined in a series of experiments in inert solvents
at a fixed temperature with varying the initial alcohol
concentration. The kinetic curves were processed to
find the specific initial rates of the reaction (W0) at the
corresponding initial concentrations of n-octanol (see
Table 2).
The results obtained showed that the specific rate of
the alcoholysis of N,N'-dioctylurea linearly depended
on the initial concentration of octanol, which substanti-
ated the suggestion that the reaction followed parallel
mono- and bimolecular routes. Dependence (2)
remained valid for various solvents (see Fig. 1). A cor-
relation analysis of (2) was performed to find the sought
rate constants for the dissociative and associative pro-
cesses k1 and k3 (Table 3).
An analysis of the kinetic data shows that the rates
of the dissociative and associative processes character-
ized by the k1 and k3 constants are commensurate,
which is evidence of the occurrence of alcoholysis as
both the dissociation of initial urea and bimolecular
transformation. It follows than none of the mechanisms
predominates.
The observed alcoholysis constants were correlated
with solvent properties at 170°ë according to the
Palm–Koppel equation
+ (5.61 1.82)P + (0.54 0.16)E.
Note that we were able to construct these correlations
only after excluding the data on nitrobenzene.
REFERENCES
1. M. D. Mashkovskii, Pharmaceuticals (Meditsina, Mos-
cow, 1993), Vol. 1 [in Russian].
2. M. V. Rubtsov and A. G. Baichikov, Synthetic Chemical
Pharmaceuticals (Meditsina, Moscow, 1971), pp. 11–13
[in Russian].
3. Yu.Ya. Ivanov and N. M. Smirnova, Khim.-Farm. Zh. 29
(11), 19 (1995).
4. P. D. Senter and W. E. Pearce, J. Org. Chem. 55 (9), 2975
(1990).
5. N. N. Mel’nikov, Chemistry and Technology of Pesti-
cides (Khimiya, Moscow, 1974) [in Russian].
6. M. Nowak, U.S. Patent no. 5693849 (1997).
7. V. Valli and H. Alper, J. Org. Chem. 60, 257 (1995).
8. F. Sanda and F. Ogawa, J. Adhes. Soc. Jpn. 33 (5), 175
(1997).
9. R. Arnold, J. Nelson, and J. Verbanc, Chem. Rev. 57 (1),
47 (1957).
10. Review Information: Methods for Synthesis of Isocian-
ates, Carbamates, and Urea by Carbonylation of Nitro
Compounds, Research Institute of Technical and Eco-
nomic Studies, Moscow, 1984, p. 16 [in Russian].
logk = logk0 + yY + pP + eE + bB,
11. A. A. Orlova and S. N. Mantrov, in Proceeding of All-
Russia Scientific-Engineering Conference “Advances in
Special Chemistry and Chemical Engineering” (Mos-
cow, 2005), p. 96.
where Y, P, E, and B are the polarity, polarizability,
acidity, and basicity of the solvent (Table 4); y, p, e, and
b are the sensitivities of the reaction to changes in the
corresponding medium parameters; and k0 is the rate
constant in the gas phase.
12. A. J. Deutschman, U.S. Patent no. 2677698 (1954).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 81 No. 1 2007

22
ORLOVA, MANTROV
13. A. Weissberger, E. S. Proskauer, J. A. Riddick, and 17. S. N. Mantrov and A. L. Chimishkyan, Zh. Fiz. Khim.
E. E. Toops, Organic Solvents: Physical Properties and
Methods of Purification, Vol. 7 of Techniques in Modern
Chemistry (Interscience, New York, 1955; Inostrannaya
Literatura, Moscow, 1958).
76 (5), 834 (2002) [Russ. J. Phys. Chem. 76 (5), 738
(2002)].
18. S. N. Mantrov, K. V. Gorbunova, andA. L. Chimishkyan,
Zh. Fiz. Khim. 77 (12), 2165 (2003) [Russ. J. Phys.
Chem. 77 (12), 1949 (2003)].
14. R. E. Smith and W. R. Davis, Anal. Chem. 56, 2345
(1984).
19. N. D. Gulyaev, T. V. Leonova, and A. L. Chimishkyan,
15. S. U. Kreingol’d, V. N. Antonov, and E. M. Yutal’,
Zh. Org. Khim. 19 (10), 2194 (1983).
Zh. Anal. Khim. 32 (8), 1618 (1977).
20. V. A. Pal’m, Fundamentals of Quantitative Theory of
Organic Reactions (Khimiya, Leningrad, 1977) [in Rus-
sian].
16. P. C. Dwivedi and A. K. Banga, J. Phys. Chem. 85, 1768
(1981).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 81 No. 1 2007