Organic solvents as catalysts of formation of phosphorus-containing thiosemicarbazides

Article abstract of DOI:10.1134/S107036320608010X

The kinetics of the reaction of O,O-diphenyl phosphorohydrazidothioate with phenyl isothiocyanate at 25°C in benzene in the presence of organic bases is studied. The dependences of the catalytic activity on the nature and structure of organic bases and on various parameters characterizing their basicity are analyzed. The catalytic activity exhibited in the formation of phosphorus-containing thiosemicarbazides by donor solvents added to benzene correlates well with both spectroscopic and thermodynamic parameters of basicity: Taft (pK _HB), Koppel-Palm (B), and Gutmann (DN) parameters. A common mechanism of the base catalysis of the thiosemicarbazide formation by organic bases of different classes is suggested and discussed. Nauka/Interperiodica 2006.

Full text of DOI:10.1134/S107036320608010X

ISSN 1070-3632, Russian Journal of General Chemistry, 2006, Vol. 76, No. 8, pp. 1236 1239.
Pleiades Publishing, Inc., 2006.
Original Russian Text N.I. Yanchuk, 2006, published in Zhurnal Obshchei Khimii, 2006, Vol. 76, No. 8, pp. 1286 1290.
Organic Solvents as Catalysts of Formation
of Phosphorus-Containing Thiosemicarbazides
N. I. Yanchuk
Gnatyuk National Pedagogical University,
ul. M. Krivonosa 2, Ternopol, 46004 Ukraine
Received May 31, 2005
Abstract The kinetics of the reaction of O,O-diphenyl phosphorohydrazidothioate with phenyl isothio-
cyanate at 25 C in benzene in the presence of organic bases is studied. The dependences of the catalytic ac-
tivity on the nature and structure of organic bases and on various parameters characterizing their basicity are
analyzed. The catalytic activity exhibited in the formation of phosphorus-containing thiosemicarbazides by
donor solvents added to benzene correlates well with both spectroscopic and thermodynamic parameters of
basicity: Taft (pKHB), Koppel Palm (B), and Gutmann (DN) parameters. A common mechanism of the base
catalysis of the thiosemicarbazide formation by organic bases of different classes is suggested and discussed.
DOI: 10.1134/S107036320608010X
The driving force of the base catalysis in reactions
S
of hydrazine derivatives with isocyanates is donor
acceptor interaction of a nucleophilic agent with a
catalyst [1]. Organic solvents can significantly affect
this process by interacting with the reaction partici-
pants [2].
C6H5O
C6H5O
P NHNH2 + S=C=N C6H5
XI
X
S
C6H5O
P NHNHC(S)NH C6H5
Therefore, we studied the kinetics of the reaction of
O,O-diphenyl phosphorohydrazidothioate with phenyl
isothiocyanate in a benzene solution in the presence
of various organic solvents at 25 C. As solvents we
chose nitrobenzene I, benzonitrile II, acetonitrile III,
ethyl acetate IV, diethyl ether V, tetrahydrofuran VI,
dimethylformamide VII, tributyl phosphate VIII, and
dimethyl sulfoxide IX. We chose donor solvents con-
taining different base centers and belonging to differ-
ent classes of organic compounds, capable of specific
interaction with the reactants. We proceeded from the
assumption that the specific solvation and catalysis
are similar in the mechanism. It was important to
elucidate the possibility of realization of this mechan-
ism in the reaction system under consideration and to
evaluate the catalytic properties of the bases in rela-
tion to their nature and structure.
C6H5O
XII
The reaction rate in a benzene solution in the pres-
ence of organic solvents as catalysts is desribed by
Eq. (1):
dx/dt = k0(a
x)(b
x) + kb(a
x)(b
x)m, (1)
where k0 and kb1are the rate constants of the noncata-
lytic (l mol 1 s ) and catalytic (l2 mol 2 s ) reac-
1
tions, respectively; a, b, and m, initial concentrations
of hydrazide, phenyl isothiocyanate, and catalyst, re-
spectively (M); x, product yield (M); and t, time (s).
It follows from Eq. (1) that the apparent rate constant
of the overall process is determined from Eq. (2):
k = k0 + kbm.
(2)
The reaction of O,O-diphenyl phosphorohydrazido-
thioate X with phenyl isothiocyanate XI in the pres-
ence of the above catalysts is irreversible and yields
phosphorus-containing thiosemicarbazide XII.
For the catalyzed reaction, the apparent rate con-
1
stants (k, l mol 1 s ) were found from the second-
order rate equation, because the reciprocal running
concentration at various concentrations of catalysts
was a linear function of time and the rate constants
did not change during the process. A linear relation-
ship was observed between the apparent rate constant
k and catalyst concentration (up to 0.05 M). The
We found that the reaction is quantitative, with no
side processes. At the same time, small additions of
organic bases appreciably accelerate the reaction
(Table 1).
1236

ORGANIC SOLVENTS AS CATALYSTS OF FORMATION
1237
3
1
Table 1. Apparent (k) and catalytic (kb) rate constants of
the reaction of O,O-diphenyl phosphorohydrazidothioate
with phenyl isothiocyanate at various concentrations of
solvents-catalysts in benzene at 25 C (a = b = 0.00125 M)
data from Table 1 (k0 = 0.0958 10 l mol 1 s
[3]). The rate constants of the noncatalytic and cata-
lytic reactions calculated graphically and from Eq. (2)
are in good agreement.
Tables 1 and 2 show that bases belonging to differ-
ent classes strongly differ in the activity. The catalytic
activity of the solvents, evaluated as the ratio kb/k0,
is within 992 15344 (Table 2), i.e., the least and the
most active catalysts differ in the activity by a factor
of more than 15. The most active catalyst is dimethyl
sulfoxide IX; its nucleophilic solvating power is the
highest. The catalytic activity of the examined solv-
ents varies in parallel with their capability for specific
solvation. The most catalytically active solvents are
dimethyl sulfoxide, tributyl phosphate, and dimethyl-
formamide; their catalytic activity ranges from 11064
to 15344. Nitrobenzene, nitriles, ethers, and esters are
less active; their catalytic activity ranges from 992 to
6566. The catalytic activity of solvents increases in
the following order: aromatic nitro compounds < ni-
triles < carboxylic acid esters ethers < carboxylic
Solvent
concentration, M l mol 1 s
k 103,
kb,
Solvent
1
1
l2 mol 2 s
I
0.01
0.02
0.03
1.08 0.02
1.95 0.06
2.90 0.09
0.343 0.042
1.30 0.07
2.55 0.08
0.436 0.025
0.966 0.038
1.82 0.05
2.11 0.07
4.15 0.31
20.6 2.3
0.0984
0.0927
0.0939
0.247
0.241
0.245
0.340
0.348
0.346
0.402
0.405
0.410
0.458
0.457
0.452
0.632
0.627
0.628
1.08
1.06
1.04
1.12
1.10
1.11
1.48
1.48
1.45
II
0.001
0.005
0.01
0.001
0.0025
0.005
0.005
0.01
III
IV
V
0.05
0.005
0.0075
0.01
0.005
0.0075
0.01
0.0005
0.001
0.002
0.0005
0.00075
0.001
0.0005
0.00075
0.001
2.29 0.09
3.52 0.26
4.62 0.39
3.26 0.24
4.80 0.30
6.38 0.42
0.635 0.037
1.15 0.05
2.19 0.07
0.656 0.030
0.921 0.043
1.21 0.05
0.836 0.037
1.20 0.05
1.55 0.06
acid amides
phosphoric acid esters < sulfoxides.
Thus, the catalytic activity correlates with the capabil-
ity of the compounds to act as electron donors in the
interaction with proton donors, which increases in the
same order.
VI
VII
VIII
IX
To elucidate the mechanism of the catalytic effect
of various electron-donor solvents, it was appropriate
to construct a quantitative relationship between the
catalytic activity of the catalysts and parameters char-
acterizing their properties. An attempt to construct a
correlation between the logarithms of the catalytic rate
constants kb and the basicity of the solvents in water
+
(pKBH ) failed (Table 2). Therefore, we can conclude
tha the reaction does not involve complete dissocia-
tion into ions with the proton transfer from the hydra-
zide to the catalyst. At the same time, the catalytic
activity of the solvents varies in the same direction as
rate constants of the catalyzed reaction (kb) given in
Tables 1 and 2 were determined from Eq. (2) using
Table 2. Influence of the characteristics of organic solvents on the rate of the reaction of O,O-diphenyl phosphorohy-
drazidothioate with phenyl isothiocyanate in benzene at 25 C
1
1
kb, l2 mol 2 s
kb/k0, l mol
+
Solvent
pKBH [4]
pKHB [4]
DN [5, 6]
B [6, 7]
I
II
12.14
10.70
0.73
0.80
0.90
1.09
1.01
1.26
2.06
2.24
2.53
4.4
11.9
14.1
17.1
19.2
20.0
26.6
23.7
29.8
67
155
160
181
280
287
291
336
362
0.0950 0.0074
0.244 0.008
0.345 0.010
0.406 0.010
0.456 0.008
0.629 0.006
1.06 0.05
992
2547
3601
4238
4760
III
IV
V
VI
VII
VIII
IX
3.96
2.42
2.08
1.50
6566
11064
11587
15344
1.11 0.02
1.47 0.04
1.04
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 8 2006

1238
YANCHUK
their capability for hydrogen bonding, described by
the quantity pKHB [2, 4, 8, 9]. The catalytic effect of
donor solvents on the rate of the reaction of O,O-di-
phenyl phosphorohydrazidothioate with phenyl iso-
thiocyanate is described by the following correlation
S
C6H5O
C6H5O
P NHNH2 + B
X
I IX
S
C6H5O
of kb with pKHB
:
(6)
P NHHN H B
C6H5O
logkb = ( 1.02 0.11) + (0.507 0.080)pKHB
,
(3)
XIII
n 9, r 0.933, s 0.142.
and involves the reaction of associate XIII with phen-
yl isothiocyanate XI. The increased nucleophilicity of
the hydrazide in the associate facilitates formation of
a new bond with the carbon atom of the isothiocya-
nate in the cyclic transition state XIV; this is followed
by the transformation into the reaction product, thio-
semicarbazide derivative XII, with the regeneration of
the catalyst I IX.
The existence of this correlation indicates that the
catalytic effect of solvents is due to only partial with-
drawal of a proton from the hydrazide via hydrogen
bonding. Therefore, it can be suggested that catalysts
of diverse nature act by the same mechanism, presum-
ably by the mechanism of general base catalysis, in-
volving formation of an H bond (structure XIII). The
fact that correlation (3) covers both weak and strong
bases also counts in favor of the suggested mechan-
ism. It should be noted that isocyanate molecules have
very weakly pronounced coordination properties and
do not form complexes even with very strong electron
donors [10 12].
S
C6H5O
P
N
C6H5O
XIII + S=C=N C6H5
HN
H B
H
XI
<
+
/
C6H5
S===C===N
An important quantitative parameter of donor solv-
ents is their donor number [5, 13]. The donor number
characterizes the overall intensity of the interaction of
an electron donor with an acceptor molecule. As seen
from Table 2, the catalytic activity of the solvents
increases with an increase in their donor number. This
trend is quantitatively described by linear relation-
ship (4):
XIV
S
C6H5O
C6H5O
(7)
P NHNHC(S)NH C6H5 + B
XII
Thus, the formation of phosphorus-containing thio-
semicarbazides in a benzene solution, catalyzed by
electron-donor solvents, follows a common mechan-
ism of general base catalysis involving fast equilibri-
um formation of a hydrogen-bonded (N H B) prere-
action complex followed by its reaction with the sub-
strate.
logkb = ( 1.18 0.06) + (0.0470 0.0029)DN, (4)
n 9, r 0.987, s 0.064.
The nucleophilic solvating power of solvents is
quantitatively characterized by their Koppel Palm
basicity (parameter B) [7, 14]. As expected, this quan-
tity also lienarly correlates with the logarithms of the
catalytic rate constants:
EXPERIMENTAL
Benzene was purified as described in [15]. Nitro-
benzene (analytically pure grade) was dried over cal-
cium chloride and distilled twice in a vacuum. Benzo-
nitrile (chemically pure grade) was refluxed for 5 h
over phosphorus pentoxide and then distilled twice
without the desiccant at a reduced pressure. Acetoni-
trile (analytically pure grade) was refluxed for 3 h
over phosphorus pentoxide and then distilled two
times from fresh portions of P2O5 and the third time
without the desiccant. Ethyl acetate (pure grade) was
washed with a saturated aqueous solution of NaCl,
dried for a week over magnesium sulfate, and then
distilled two times from fresh portions of P2O5 and
the third time without the desiccant. Diethyl ether and
tetrahydrofuran (pure grade) were refluxed over KOH
and distilled on a column from sodium. Dimethyl-
logkb = ( 1.16 0.11) + (0.00361 0.00043)B, (5)
n 9, r 0.954, s 0.120.
These facts allow us to consider the catalysis mech-
anism as preassociative (a particular case of general
base catalysis) and common for all the examined solv-
ents belonging to different classes of organic com-
pounds. The first step [scheme (6)] involves associa-
tion of hydrazide X with a solvent molecule B (B is
I IX) with the formation of hydrogen-bonded com-
plex XIII. The association is a fast and reversible
process.
The second step [scheme (7)] is rate-determining
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 8 2006

ORGANIC SOLVENTS AS CATALYSTS OF FORMATION
1239
formamide (pure grade) was kept for 3 4 h under
reduced pressure of nitrogen to remove low-boiling
amines, the low-boiling fraction was distilled off, and
the residue was refluxed for 2 h with hexamethylene
katalizatory i gomogennyi kataliz (Organic Catalysts
and Homogeneous Catalysis), Kiev: Naukova Dumka,
1981.
5. Gutmann, V., Coordination Chemistry in Non-
Aqueous Solutions, Wien: Springer, 1968.
1
diisocyanate (10 ml l ) and distilled three times on
a column, with the collection of the fraction boiling
at 55 C (20 mm Hg). Tributyl phosphate (pure grade)
was vacuum-distilled. Dimethyl sulfoxide (pure grade)
was distilled at a reduced pressure from barium oxide
and then two times without the desiccant; the first and
the last fractions were discarded. O,O-Diphenyl phos-
phorohydrazidothioate was prepared from the corre-
sponding acid chloride and hydrazine hydrate and was
purified as described in [16, 17]. Phenyl isothiocya-
nate was vacuum-distilled just before use. The physi-
cochemical constants of all the chemicals used agreed
with the published data.
6. Makitra, R.G. and Pirig, Ya.N., Ukr. Khim. Zh., 1980,
vol. 46, no. 1, p. 83.
7. Koppel, I.A. and Paju, A.I., Reakts. Sposobn. Org.
Soedin., 1974, vol. 11, no. 1, p. 121.
8. Taft, R.W., Gurka, D., Joris, L., Schleyer, P. von R.,
and Rakshys, J.W., J. Am. Chem. Soc., 1969, vol. 91,
no. 17, p. 4801.
9. Joris, L., Mitsky, J., and Taft, R.W., J. Am. Chem.
Soc., 1972, vol. 94, no. 10, p. 3438.
10. Varentsova, N.V., Gol’dshtein, I.P., Paleeva, I.E.,
Tarakanov, O.G., and Gur’yanova, E.N., Zh. Obshch.
Khim., 1982, vol. 52, no. 7, p. 1612.
The reaction progress in benzene in the presence of
organic catalysts was monitored as described previ-
ously [18]. The kinetic experiments were performed in
benzene at 25 0.05 C. The initial concentration of
11. Varentsova, N.V., Gol’dshtein, I.P., Paleeva, I.E.,
Tarakanov, O.G., and Gur’yanova, E.N., Zh. Obshch.
Khim., 1980, vol. 50, no. 9, p. 2085.
3
the reactants was 1.25 10 M; the catalyst concen-
12. Varentsova, N.V., Gol’dshtein, I.P., Shifrina, R.R.,
Shcherbakova, E.S., Tarakanov, O.G., and Gur’yano-
va, E.N., Zh. Obshch. Khim., 1979, vol. 49, no. 9,
p. 2082.
tration was varied from 0.0005 to 0.05 M.
The accuracy of the results was evaluaed by meth-
ods of mathematical statistics [19] at a confidence
level of 0.95.
13. Gutmann, V. and Wychera, E., Inorg. Nucl. Chem.
Lett., 1966, vol. 2, no. 2, p. 257.
REFERENCES
14. Koppel, I.A. and Palm, V.A., in Advances in Linear
Free Energy Relationships, London: Plenum, 1972,
p. 203.
1. Grekov, A.P., Shandruk, M.I., and Yanchuk, N.I.,
Dokl. Akad. Nauk SSSR, 1974, vol. 214, no. 5,
p. 1077.
15. Litvinenko, L.M. and Grekov, A.P., Ukr. Khim. Zh.,
1954, vol. 20, no. 2, p. 194.
2. Litvinenko, L.M. and Oleinik, N.M., Mekhanizmy
deistviya organicheskikh katalizatorov. Osnovnyi i
nukleofil’nyi kataliz (Mechanisms of the Effect of
Organic Catalysts. General and Nucleophilic Catal-
ysis), Kiev: Naukova Dumka, 1984.
16. Shandruk, M.I., Yanchuk, N.I., and Grekov, A.P., Zh.
Obshch. Khim., 1973, vol. 43, no. 10, p. 2194.
17. Klement, R. and Knollmuller, K.O., Chem. Ber.,
1960, vol. 93, no. 4, p. 1088.
18. Yanchuk, N.I. and Balukh, V.M., Zh. Obshch. Khim.,
1984, vol. 54, no. 12, p. 2663.
3. Yanchuk, N.I. and Ivanets, L.N., Zh. Obshch. Khim.,
2005, vol. 75, no. 6, p. 893.
19. Doerffel, K., Statistik in der analytischen Chemie,
Leipzig: Inst. fur Analytische Chemie, 1966.
4. Litvinenko, L.M. and Oleinik, N.M., Organicheskie
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 8 2006