Full text of DOI:10.1134/S1070363211090179

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 9, pp. 1839–1844. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © L. Shteinberg, V.V. Marshalova, V.M. Dibrova, S.M. Shein, 2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81, No. 9,
pp. 1501–1506.
Effect of the Benzoic Acid Additives
on the Catalytic Activity of Tetrabuthoxytitanium
in the Synthesis of Benzanilide
L. Shteinberga, V. V. Marshalovab, V. M. Dibrovaa, and S. M. Sheina
a Institute of Chemical Technology and Industrial Ecology,
pl. Khimikov 3, Rubezhnoe, Luganskaya oblast, 93000 Ukraine
e-mail: alex12-01@yandex.ru
b Institute of Chemical Technology, East Ukrainian National University, Rubezhnoe, Luganskaya oblast, Ukraine
Received August 3, 2010
Abstract—Catalytic activity of tetrabutoxytitanium in the synthesis of benzanilide is changed at its pre-
coordination with benzoic acid in boiling ortho-xylene. Upon increase in the amount of added benzoic acid the
catalyst activity increases and then decreases. In the presence of aniline, benzoic acid does not activate
tetrabutoxytitanium that may result from its binding to the H-complex with aniline. The formation of such
1
complexes was confirmed indirectly by H NMR spectroscopy. Under comparable conditions, the effective
catalysts for the benzanilide synthesis are polytitanates obtained from tetrabutoxytitanium at its interaction with
water and benzoic acid, and the still bottoms after their vacuum distillation.
DOI: 10.1134/S1070363211090179
It was found previously that tetrabutoxytitanium,
being an effective catalyst for the synthesis of
benzanilide by aniline acylation with benzoic acid,
alters its activity under the action of water: irreversibly
at the preliminary hydrolysis [1, 2] and reversibly at
the contact with water released in the reaction process
[3]. Both initial compounds and benzanilide can form
with tetrabutoxytitanium complexes of different
hydrolytic stability [4]. The tetrabutoxytitanium com-
plexes with benzoic acid and benzanilide are less prone
to hydrolysis. It is presumable that they would differ
by effeiciency in the catalysis.
The aim of this work is to study the effect of
benzoic acid additives on the catalytic activity of
tetrabutoxytitanium in the synthesis of benzanilide.
CONH
COOH
NH2
Ti(OBu)4
(1)
+
+
H2O
The reaction of tetrabutoxytitanium (two samples
activated by pre-hydrolysis at the storage [1]) with
benzoic acid was carried out in boiling ortho-xylene.
We found that pretreatment of the catalyst with
benzoic acid leads to a change in its activity (as judged
from the yield of benzanilide within 1 h under
comparable conditions). The increase in the amount of
benzoic acid additive initially increases and then
decreases the benzanilide yield (Fig. 1).
3.35 times (Fig. 1, curve 1) and 96/58 = 1.65 times
(Fig. 1, curve 2). With the less active sample of tetra-
butoxytitanium (Fig. 1, curve 1) the relative increase in
the catalysis efficiency is higher. At the same time the
initially more active sample of tetrabutoxytitanium
showed higher absolute activity at the treatrment with
benzoic acid.
In general, in both series of experiments, the
maximum catalytic activity was higher than that of
unhydrolyzed tetrabutoxytitanium: 96/12 = 8 times and
in 67/12 = 5.5 times, respectively (the figure in the
The maximum relative increase in the catalytic
activity in two series of experiments was 67/20 =
1839

1840
SHTEINBERG et al.
tetrabutoxytitanium can originate from the variations
in the composition and structure of the formed poly-
titanate. It is known [5] that at the interaction of
titanium tetraalkoxides with carboxylic acids various
polytitanates are formed depending on the ratio of the
initial components [Eqs. (2)–(4)]:
n (RO)4Ti + 2n R'COOH → [–O–Ti(–OCOR')(OR)–]n +
+ n R'CO2R + 2nROH,
(2)
2n (RO)4Ti + 5n R'COOH
→ [–(OR)(R'OCO–)Ti–O–Ti(–OCOR')2–]n
+ 2n R'CO2R + 5n ROH,
Benzoic acid additive, %
(3)
(4)
Fig. 1. Dependence of the benzanilide yield on the amount
of benzoic acid additive (mol % relative to the total charge
of benzoic acid).
n (RO)4Ti + 3n R'COOH → [–(R'OCO–)2Ti–O–]n
+ n R'CO2R + 3n ROH.
As the amount of benzoic acid per 1 mol of the
tetrabutoxytitanium grows, along with the formation of
polytitanates, more and more labile alcohol groups in
their composition will be replaced by benzoate
residues. In addition, benzoate ligands can form stable
chelate complexes due to additional coordination of
the carbonyl groups with the central ion of the catalyst.
For example, there is information on the stability of
benzoate tin complexes I, catalysts for the synthesis of
carboxylic acid amides [8]:
denominator, 12%/h of benzanilide, is the activity of
unhydrolyzed tetrabutoxytitanium [2]).
The shape of the curves (Fig. 1) resembles that of
the change in the catalytic activity of tetrabutoxy-
titanium due to prior interactions with water [1, 2]: the
growth of benzanilide yield upon increase in the
amount of water added to the catalyst, reaching a
maximum and then the decrease in the catalytic
activity.
It was shown previously [2] that the effect of water
on the efficiency of catalysis of the benzanilide
synthesis catalyzed by tetrabutoxytitanium is as-
sociated with the formation of polytitanates of various
structures. It was suggested that polyfunctional
catalysis occurred because of the close and simulta-
neous interaction of benzoic acid and aniline with
several few atoms of titanium and the ligands that
serve as the nucleophilic centers of catalysis located in
the polytitanate chain.
O
C
O
O
C
Sn
O
I
Benzoate ligands prevent access of the initial
materials (amine and carboxylic acid esters) to the
central tin ion, therewith, the ligands thmselves do not
react with amines to form benzoic acid amides.
It is known [5, 6] that carboxylic acids, including
benzoic acid, like water, contribute to the formation of
polytitanates in the process of reaction with titanium
alkoxides, which occurs with the substitution of a part
of alcohol groups by the carboxylate ligands. In some
cases these polytitanates are more active catalysts of
esterification (polyesterification) reaction than the
titanium alkoxides [6, 7].
It is not excluded that at the interaction of
tetrabutoxytitanium with benzoic acid such stable
complexes also can be formed. Upon increase in the
amount of benzoic acid additive, the size of poly-
titanate and the number of titanium ions inaccessible
for the catalysis increase. By the example of a
fragment of such complex II it can be seen that all six
coordination sites of the central titanium atom are
occupied, and it becomes coordinatively saturated.
In the benzanilide synthesis the mechanism of
activation by tetrabutoxytitanium at the treatment with
benzoic acid is possible through the formation of
polytitanate and implementation of multifunctional
catalysis (by analogy with [2]).
The benzoate ligands and the oxygen bridges
prevent access of reacting substances (benzoic acid
and aniline) to the titanium atom, which is equivalent
The reduction of the catalyst activity at the increase
in amount of benzoic acid added for the treatment of
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EFFECT OF THE BENZOIC ACID ADDITIVES
1841
Such a mechanism is suggested in [10, 11] for the
esterification of carboxylic acids.
O
C
Ti
However, in the studied catalytic benzanilide
synthesis the benzoic acid in a non-polar ortho-xylene
can bind aniline to form salt or H-complex IV [12]:
O
O
O
O
Ti
Ti
PhCOOH + H2NPh → [PhCOOH···NH2Ph].
(6)
C
O
IV
n
II
Given that in the reaction mixture the aniline is in
excess relative to benzoic acid, and especially to the
tetrabutoxytitanium, we can assume the existence of
significant competition for the benzoic acid hydrogen
between aniline and butoxy ligand of the tetra-
butoxytitanium. Such a competition can result in the
formation of complex V in which the benzoate ligand
does not enter the titanium coordination sphere:
to reducing the concentration of active catalyst. This
inhibition of catalysis can occur when the benzoate
associated with titanium does not react with aniline
with the formation of benzanilide.
Note that as a key stage in the catalysis of the
synthesis of carboxylic acid esters and amides by tetra-
butoxytitanium the polarization is considered of car-
bonyl bond at the coordination of carboxylic acid or
ester with titanium ion [6, 7]. At the same time, the
carboxylate ligands form mostly a ionic bond with tita-
nium [6, 9], and it can be assumed that the activation
of a carboxylic acid in the reactions of nucleophilic
substitution in such a complex does not occur.
Ti
BuO
O
H
C
NH
O
A separate question is, why just after pouring
together all the components of the reaction mixture
(benzoic acid, aniline, tetrabutoxytitanium, and ortho-
xylene) and carrying out the reaction of acylation the
above mentioned activation of the catalyst does not
occur. Such an order of mixing may be formally
regarded as the maximal addition of benzoic acid with
respect to tetrabutoxytitanium,.
H
V
To check the possible existence of complex IV, we
studied the interaction of benzoic acid with aniline in
ortho-xylene using 1H NMR spectroscopy. This
method allowed us to fix the presence of salts and H-
complexes formed by amines and carboxylic acids [12,
13].
It is known [5, 6] that the first stage in the reaction
of benzoic acid with tetrabutoxytitanium is the
entrance of the benzoate ligand in the coordination
sphere of titanium [Eq. (5)].
In the spectrum of aniline (0.35 M) in ortho-xylene
there is a broadened peak at 2.4–3.0 ppm correspond-
ing to the protons of the amino group, and a group of
signals of aromatic protons in the region of 6.06–
6.18 ppm [13] (Fig. 2, curve 1).
OCOC6H5
+ C4H9OH
OC4H9
+ C6H5COOH
(5)
Ti
Ti
In the spectrum of benzoic acid (0.35 M) in ortho-
xylene a group of signals of aromatic protons is
observed in the region of 7.80–7.96 ppm, the signal of
hydroxy group is located in a weak field [13] (Fig. 2,
curve 2).
This reaction occurs initially at the coordination of
benzoic acid at the titanium and butoxy group,
followed by simultaneous rupture and formation of
bonds in the complex III:
In the spectrum of a mixture of benzoic acid with
aniline a peak appears at 5.1 ppm, which corresponds
to a new common signal of hydroxy and amino groups
(Fig. 2, curve 3) indicating the interaction between
these groups. The previously observed peak of the
individual amino group disappears. Signals of aromatic
protons of aniline undergo an upfield shift by 0.11 ppm,
and signals of the aromatic protons of benzoic acid are
Ti
BuO
O
H
C
O
III
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1842
SHTEINBERG et al.
heteroassociate, which could prevent the entry of the
benzoate ligand in the titanium coordination sphere
and creating a structure of the active catalyst.
In general, we can note that the two substances,
benzoic acid and water, act in a similar manner on the
tetrabutoxytitanium, contributing to the formation of
the polymer structure of a more efficient catalyst. It
can be assumed that other methods of obtaining poly-
titanate from tetrabutoxytitanium can lead to the same
result (increase of the catalytic activity).
The table contains the results of testing several
versions of such activation. For comparison, the table
contains also the results the activation of tetrabutoxy-
titanium obtained previously.
As seen from the table, the least active is freshly
distilled tetrabutoxytitanium (run no. 1). Its efficiency
varies in some series of experiments, due, apparently,
to the uncontrolled hydrolysis of the catalyst during
vacuum distillation, storage and conducting experi-
ments on the synthesis of benzanilide. Note that in the
works of other researchers on the esterification and
transesterification also a difference was observed in
the catalytic activity and other properties even at the
use of freshly distilled tetrabutoxytitanium. Therefore,
as a base of comparison in such cases the least hyd-
rolyzed catalyst is taken, assuming that it corresponds
to the maximally pure tetrabutoxytitanium [14].
δ, ppm
Fig. 2. 1H NMR spectra (in ortho-xylene): (1) aniline
(0.35 M), (2) benzoic acid (0.35 M), (3) aniline (0.35 M) +
benzoic acid (0.35 M).
shifted downfield by 0.06 ppm. These shifts of the
signals also indicate a change in the charges on the
hydroxy and amino groups and the effect of such changes
on the shift of the signals of aromatic protons.
In general, the activity of the tetrabutoxytitanium is
so low that such pure catalyst hardly ever can be of
practical interest.
Signals of aromatic protons at 6.83 ppm and aliphatic
protons at 1.91 ppm correspond to ortho-xylene, as
shown previously [2].
Prolonged storage of tetrabutoxytitanium in a
xylene solution or forced hydrolysis in a moist chamber
increases the catalytic activity more than 10 times
relative to the least active fresh catalyst (the table, run
nos. 2, 3). Almost the same effect can be achieved at
Thus, at mixing in ortho-xylene benzoic acid with
aniline they interact with each other forming a
Activation techniques in the synthesis of tetrabutoxytitanium benzanilide
Run no.
1
Method of activation
Freshly distilled tetrabutoxytitanium
Yield of benzanilide, % per h
7–12
2
3
Long-term storage and the use of tetrabutoxytitanium in ortho-xylene for 1 year
58–78
44
Hydrolysis of tetrabutoxytitanium in ortho-xylene with the water vapor in a moist
chamber for 1–6 h
4
5
6
Pre-boiling of tetrabutoxytitanium in ortho-xylene with benzoic acid
55–76
23–29
60
Still bottoms after vacuum distillation of tetrabutoxytitanium at 170–250°C
Polytitanate VI
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EFFECT OF THE BENZOIC ACID ADDITIVES
1843
ν, cm–1
Fig. 3. IR absorption spectra (thin layer): (1) still bottoms after vacuum distillation of tetrabutoxytitanium and (2) tetrabutoxy-
titanium.
(BuO)4Ti + HOC(CH3)2 – C≡C–CH=CH2
→ (BuO)3TiOC(CH3)2 – C≡C–CH=CH2.
treatment with benzoic acid of the tetrabutoxytitanium
partially activated during the storage in ortho-xylene
(the table, run no. 4).
(7)
Thus, different methods of treatment of tetra-
butoxytitanium, the catalyst for the synthesis of
benzanilide, resulting in the formation of polytitanate
oligomers showed a similar effect of the tetra-
butoxytitanium activation. These methods include the
addition of benzoic acid and water, the reagent and the
final product involved in the formation of active
catalyst, that allows controlling the catalytic reaction
without the use of special additives and ligands.
After vacuum distillation of tetrabutoxytitanium
remain still bottoms that possess a high catalytic
activity (see the table, run no. 5), apparently also
polytitanates. It was shown in [6] that the thermolysis
of titanium alkoxides, including tetrabutoxytitanium, at
high temperature, under the conditions close to
distilling the tetrabutoxytitanium and the formation of
still bottoms, results in decomposition of the ethers
leading to the formation of polytitanates containing
hydroxy and alkoxy groups.
The role of benzoic acid is rather contradictory: On
the one hand, it promotes the formation of active
polytitanate chain, but on the other hand, it forms a
stable complex with tetrabutoxytitanium [4] and
thereby prevents its hydrolysis and activation by water.
In the presence of aniline, benzoic acid does not
activate tetrabutoxytitanium, that is, both the initial
materials involved in the formation of effective
catalyst serve as regulators of the catalytic activity,
which can vary, depending on the order of their charging.
For qualitative estimation of the structure of the
still bottoms we recorded its IR spectrum to compare
with the spectrum of partially hydrolyzed tetra-
butoxytitanium (Fig. 3). The IR spectrum of the still
bottoms contains the same absorption bands as that of
tetrabutoxytitanium (Fig. 3, curve 2): 600–900 cm–1
(Ti–O), 1375–1450 and 2850–2050 cm–1 (butyl
groups), 3100–3500 cm–1 (diffuse hydroxyl peaks)
[15]. These data indicate that the still bottoms have the
same functional groups as tetrabutoxytitanium.
EXPERIMENTAL
Polytitanate VI, the cured product of the reaction of
tetrabutoxytitanium with dimethylvinylethynylcarbinol
[Eq. (7)] applied on silica gel [9], was also tested as
catalyst. It also showed a high activity (the table, run
no. 6).
Benzoic acid, aniline, ortho–xylene, and tetra-
butoxytitanium were purified and used as in [1–3, 16].
The samples of hydrolyzed tetrabutoxytitanium with
different degree of catalytic activity were prepared as
in [1, 2]. Tetrabutoxytitanium was distilled in a
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SHTEINBERG et al.
2. Shteinberg, L.Ya., Kondratov, S.A., Shein, S.M.,
Mishchenko, S.E., Dolmat, V.M., and Dibrova, V.M.,
Kinetika i Kataliz, 1999, vol. 40, no. 4, p. 566.
vacuum at 150–200°C and residual pressure 10–
12 mm Hg, collecting the main fraction at 173–175°C.
1H NMR spectra were recorded on a Tesla BS-
487C spectrometer (80 MHz) at 20°C with internal
reference hexamethyldisiloxane. IR spectra were
recorded on a Specord UR-75 instrument from thin
films.
3. Shteinberg, L.Ya., Kondratov, S.A., Shein, S.M., and
Marshalova, V.V., Kinetika i Kataliz, 2007, vol. 48,
no. 5, p. 1.
4. Shteinberg, L.Ya., Marshalova, V.V., Dibrova, V.M.,
and Shein, S.M., Zh. Obshch. Khim., 2008, vol. 78,
no. 9, p.1463.
The concentration of unreacted benzoic acid was
determined by potentiometric titration on an EV-74
ionomer [16]. As the working electrode a glass elec-
trode ESL-43-07 was used, as the reference, a silver
chloride electrode.
5. Field, R. and Couth, P., Organic Chemistry of Titanium,
Moscow: Mir, 1969.
6. Yatluk, Yu.G., Khrustaleva, E.A., Sorokina, I.A., and
Barshtein, R.S., Titansoderzhashchie soedineniya–
katalizatory
polikondensatsionnykh
protsessov
The synthesis of benzanilide was performed as
described in [1] using a catalyst activated during
storage, freshly distilled tetrabutoxytitanium, the still
bottoms after vacuum distillation of tetrabutoxy-
titanium, and polytitanate VI.
(Titanium-Contaning Compounds, the Catalysts of the
Polycondensation Processes), Moscow: NIITEKhIM,
1990.
7. Laricheva, T.N., Raskina, I.G., and Siling, M.I.,
Katalizatory sinteza polialkilentereftalatov (Catalysts
for the Synthesis of Polyalkyleneterephthalates),
Moscow: NIITEKhIM, 1989.
In all experiments on testing the catalytic activity
the amount of catalyst was 2 mol % calculated on
titanium. The tetrabutoxytitanium still bottoms ob-
tained after vacuum distillation was used as the
catalyst, taking its average molecular weight equal to
that of tetrabutoxytitanium.
8. Garkusha-Bozhko, I.P., Oleinik, N.M., and Litvinen-
ko, L.M., Zh. Org. Khim., 1982, vol. 18, no. 11, p. 2340.
9. Pomogailo, A.D. and Savost’yanov, V.S., Metall-
soderzhashchie monomery i polimery na ikh osnove
(Metal-Containing Monomers and the Polymers Based
on Them), Moscow: Khimiya, 1988.
The catalyst VI contained 0.5% of polytitanate on
silica gel and was applied proceeding from the
percentage of the titanium content.
10. Pilati, F., Manaresi, P., Fortunato, B., Monari, A.,
Monari, P., Polymer, 1983, vol. 24, no. 11, p. 1479.
Studies on the effect of benzoic acid additives on
the catalytic activity of tetrabutoxytitanium. A flask
equipped with a Dean–Stark trap and reflux condenser
was charged with a varied amount of benzoic acid and
40 cm3 of ortho-xylene, heated to 140°C. Tetra-
butoxytitanium, 0.05 g (0.16 mmol), was charged, and
the mixture was quickly heated to boiling, kept for
30 min, then cooled by 1–2°C to stop the boiling, and
to the flask was added 1.53 g (16.4 mmol) of aniline
and then benzoic acid to the desired molar ratio (tetra-
butoxytitanium : benzoic acid : aniline = 1 : 50 : 100),
the mixture was heated to boiling and thus maintained
for 1 h.
11. Siling, M., I., Kuznetsov, V.V., Nosovskii, Yu.E.,
Osintseva, S.A., and Kharrasova, A.N., Kinetika i
Kataliz, 1986, vol. 27, no. 1, p. 98.
12. Litvinenko, L.M. and Oleinik, N.M., Organicheskie
katalizatory i gomogennyi kataliz (Organic Catalysts
and Homogenous Catalysis), Kiev: Naukova Dumka,
1981.
13. Ionin, B.I., Ershov, B.A., and Kol’tsov, A.I., YaMR-
spektroskopiya v organicheskoi khimii (NMR Spec-
troscopy in Organic Chemistry), Leningrad: Khimiya,
1988.
14. Bulai, A.Kh., Slonim, I.Ya., Barshtein, R.S., Soroki-
na, I.A., and Gorbunova, V.G., Kinetika i Kataliz, 1990,
vol. 31, no. 3, p. 598.
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