Oligomerization of organochlorosilanes in the acetylacetone-carbamide system

Article abstract of DOI:10.1007/s11172-013-0210-2

Condensation of acetylacetone with carbamide in nonpolar media (benzene, toluene) is initiated by organochlorosilanes. The reaction rapidly occurs under mild conditions to give oligosiloxanes and 4,6-dimethylpyrimidin-2(1H)-one hydrochloride. The conversi

Full text of DOI:10.1007/s11172-013-0210-2

Russian Chemical Bulletin, International Edition, Vol. 62, No. 6, pp. 1459—1461, June, 2013
1459
Oligomerization of organochlorosilanes in the acetylacetone—carbamide system
E. S. Trankina, B. G. Zavin, and A. M. Muzafarov
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
2
8 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 9354. Eꢀmail: zavin@ineos.ac.ru
Condensation of acetylacetone with carbamide in nonpolar media (benzene, toluene) is
initiated by organochlorosilanes. The reaction rapidly occurs under mild conditions to give
oligosiloxanes and 4,6ꢀdimethylpyrimidinꢀ2(1H)ꢀone hydrochloride. The conversion of chloroꢀ
silanes and the yields of oligosiloxanes are nearly ~100%.
Key words: organochlorosilanes, hydrolytic polycondensation, oligomerization in active
media, oligoꢀ and polydiorganosiloxanes, diorganocyclosiloxanes, cascade reactions, 1,3ꢀdiꢀ
ketones, acetylacetone, urea, condensation, pyrimidines.
Siloxane (Si—O—Si) bond formation reactions play
tem acetylacetone (AA)—carbamide (CA). These comꢀ
pounds undergo acidꢀcatalyzed condensation in alcoꢀ
hols with elimination of water (Scheme 1).
1
—3
20
a key role in the chemistry of polyorganosiloxanes.
The modern technology of industrial silicone producꢀ
tion largely involves hydrolytic polycondensation (HPC)
4
,5
reactions of organochloroꢀ and alkoxysilanes. For this
reason, investigations in this field have been of constant
Scheme 1
3
interest for many years.
Multiple methods of forming Si—O bonds and multiple
routes to oligoꢀ and polysiloxanes have been studied to date.
They involves reactions of Siꢀfunctionalized monomers
(
alkoxyꢀ or organochlorosilanes) with various compounds
such as water, alcohols, acid anhydrides, acid halides,
metal oxides, metal salts, etc.).6
—13
These compounds all
contain one or more O atoms used to form a siloxane
The reaction virtually does not occur in the absence of
an acid at t  20 C.
chain. HPC processes are usually described in terms of
parallelꢀserial reactions.1
4,15
It is known that the pattern
We found that even slight heating of AA with CA in the
presence of organylꢀcontaining dichlorosilanes (DCS) iniꢀ
tiates their reaction proceeding at an appreciable rate and
leading to oligoorganosiloxanes (hydrolysis products of
DCS) and 4,6ꢀdimethylpyrimidinꢀ2(1H)ꢀone hydrochloride.
According to available data, organochlorosilanes unꢀ
of HPC reactions in the heterogeneous system "water—
organic layer" is seriously complicated by diffusion conꢀ
trol at the interface.1
4,15
That is why HPC under homoꢀ
1
6,17
geneous conditions is of keen interest.
One of the HPC
types, viz., polycondensation in "active" media, has been
under extensive study in the last few years. In this case,
a homogeneous medium used for HPC of alkoxysilanes conꢀ
tains an anhydrous carboxylic acid as an "active" solvent
1
,3
dergo rapid hydrolysis even when cooled; the rate of the
hydrolysis approximates to the rates of ionic reactions. It
1
4,21
is known
that the hydrolysis rate constants khydr of
that reacts with a monomer to give the corresponding alꢀ
organochlorosilanes are much higher than the rate conꢀ
stants of heteroꢀ and homofunctional condensations; i.e.,
khydr >> kheterof > khomof. Therefore, one can suggest that
the condensation of AA with CA accompanied by water
elimination (see Scheme 1) is the rateꢀlimiting step of the
oligomerization of chlorosilanes in the system acetylꢀ
acetone—carbamide—chlorosilane.
We found that the rate of this condensation increases
noticeably in the presence of dichloro(dimethyl)silane. The
reaction occurs even in nonpolar organic solvents such as
benzene and toluene.
cohol.1
8,19
Subsequent alkylation of the acid produces waꢀ
ter as a secondary product, which is consumed in the hyꢀ
drolysis of the monomer to silanols bearing Si—OH groups.
In the next steps, these groups become involved in homoꢀ
and heterofunctional condensation reactions giving rise to
siloxane chains. Recently, the synthetic scope of polyconꢀ
densation in active medium has been successfully illusꢀ
1
8,19
trated with HPC of ethoxysilanes in anhydrous AcOH.
In searching for active media suitable to polycondenꢀ
sation of organosilicon monomers, we recurred to the sysꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1459—1461, June, 2013.
066ꢀ5285/13/6206ꢀ1459 © 2013 Springer Science+Business Media, Inc.
1

1
460
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 6, June, 2013
Trankina et al.
The general pattern of the oligomerization of orgaꢀ
Table 1. Oligomerization conditions, the reaction products, and
their yields according to H and Si (in parentheses) NMR data
1
29
nochlorosilanes in the AA—CA system can be represented
as follows. First the condensation of AA with CA (see
Scheme 1) is initiated by small amounts of hydrogen chloꢀ
ride almost always present in organochlorosilanes. The
resulting water molecules cause the hydrolysis of organoꢀ
chlorosilane that generates reactive silanol groups (Si—OH)
and new portions of HCl required to sustain the reaction.
Finally, the reactive silanols undergo condensation yieldꢀ
ing oligoorganosiloxanes (Scheme 2).
1
2
R R SiCl
Ratio of
the reagents
DCS : АА : CA
Yields of the products
(%)
X
2
(
DCS)
R1
R2
1
2
3, 4*
Me
Me
Me
Me
Me
Me
Vin
Ph
0.5 : 1 : 1
0.1 : 1 : 1
0.5 : 1 : 1
0.5 : 1 : 1
38 (47) 31 (38) 31 (15) OH
49 (53) 51 (47) Сl
35 (40) 25 (33) 40 (27) OH
50 (58) 14 (15) 28 (35) ОН
—
1
2
1 2
*
X—[R R SiO] SiR R —X (3, 4), X = OH (3), Cl (4).
n
Scheme 2
some experiments, the cyclosiloxane content of the reacꢀ
tion products is ~70% of the weight of the oligosiloxanes
2
9
(
Si NMR data).
The set of cyclosiloxane products and their yields deꢀ
pend on the ratio of the reagents (see Table 1). For inꢀ
stance, when the DCS : AA : CA ratio is 0.5 : 1 : 1 and
hence HCl can fully be bound by pyrimidine, the reaction
gives a mixture of cyclic and linear oligoorganosiloxanes
with terminal OH groups (see Scheme 2). When the conꢀ
tent of DCS is higher (DCS : AA : CA = 1 : 1 : 1), the
amount of water formed is sufficient for the hydrolysis of
dichlorosilane. However, the latter produces two moles of
HCl, and they cannot be bound completely by available
pyrimidine in the system because it can form only monoꢀ
n = 3 (1), 4 (2); m = 3—6
2
0
hydrochloride. In this case, the reaction yields octameꢀ
thylcyclotetrasiloxane and oligoorganosiloxanes with terꢀ
minal Cl groups (Scheme 3).
Thus, the reactions in the DCS—AA—CA system are
"
coupled": the hydrolysis of DCS enables the condensaꢀ
tion of AA with CA and the water eliminated in the conꢀ
densation in turn enables the hydrolysis of DCS.
It is significant that the hydrolysis of chlorosilane
occurs under homogeneous conditions (in an organic solꢀ
vent). The hydrolysis products (oligosiloxanes) remain in
solution, while 4,6ꢀdimethylpyrimidinꢀ2(1H)ꢀone binds
HCl formed upon the hydrolysis of chlorosilane and preꢀ
cipitates as a monohydrochloride salt. Because of this, the
oligoorganosiloxanes obtained can easily be separated from
the product of the "coupled" reaction simply by filtration.
An attractive feature of the system under study is that
both the "coupled" reactions (condensation of 1,3ꢀdiketone
with carbamide and hydrolysis of organochlorosilane) proꢀ
ceed quantitatively: the yield of 4,6ꢀdimethylpyrimidinꢀ
Scheme 3
2
(1H)ꢀone hydrochloride as well as the conversion of chloꢀ
rosilanes are nearly 100%.
n = 4, m = 3—6
The structures of organosiloxanes present in the reacꢀ
1
29
tion mixture were analyzed by H and Si NMR spectroꢀ
scopy. The results obtained are given in Table 1. The prodꢀ
ucts of the reactions are oligosiloxanes and 4,6ꢀdimethylꢀ
pyrimidinꢀ2(1H)ꢀone hydrochloride. Organosilicon
products (oligoorganosiloxanes) are mainly cyclic comꢀ
Note that this approach provides not only a conveꢀ
nient method for the synthesis of cyclosiloxanes but it is
also of interest as a promising route to 4,6ꢀdimethylpyriꢀ
midinꢀ2(1H)ꢀone and its derivatives. 4,6ꢀDimethylpyriꢀ
midinꢀ2(1H)ꢀone is a starting material for the preparation
29
pounds. The Si NMR spectra show intense signals at  –9
and –19 characteristic of hexamethylcyclotrisiloxane (1)
and octamethylcyclotetrasiloxane (2), respectively. In
2
2,23
24,25
of drugs,
ligands.
convenient phosphorylating agents,
and
2
6,27
By varying 1,3ꢀdiketones and carbamide deꢀ

Oligomerization of organochlorosilanes
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 6, June, 2013
1461
rivatives in this process, one can obtain other compounds
of the pyrimidine series.
10. M. G. Voronkov, N. P. Ivanova, Zh. Obshch. Khim., 1998,
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2. M. Ando, M. Ikeno, Chem. Lett., 1980, 1255.
6
1
1
(
1
Experimental
Reagentꢀgrade acetylacetone, urea, and organodichloroꢀ
silanes and reagentꢀgrade solvents (benzene and toluene) were
used. Commercial dichlorosilanes were purified by distillation at
atmospheric pressure. H and Si NMR spectra were recorded
on a Bruker Avance 400 spectrometer (400.13 and 79.49 MHz,
13. M. G. Voronkov, S. V. Basenko, J. Organomet. Chem., 1995,
500, 325.
14. E. A. Chernyshev, P. V. Ivanov, D. N. Golubykh, Russ.
Chem. Bull. (Int. Ed.), 2001, 50, 1998 [Izv. Akad. Nauk, Ser.
Khim., 2001, 1909].
1
29
respectively) in CDCl at 298 K. Chemical shifts  are referꢀ
15. P. V. Ivanov, Vestnik MITKhT [Bulletin of the Moscow State
University of Fine Chemical Technologies], 2011, 6, No. 3, 3
(in Russian).
16. N. S. Leznov, L. A. Sabun, K. A. Andrianov, Zh. Obshch.
Khim., 1959, 29, 1508 [J. Gen. Chem. USSR (Engl. Transl.),
1959, 29].
17. N. S. Leznov, L. A. Sabun, K. A. Andrianov, Zh. Obshch.
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18. E. V. Egorova, N. G. Vasilenko, N. V. Demchenko, E. A.
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200 [Dokl. Chem. (Engl. Transl.), 2009].
3
enced to SiMe . For quantitative measurements of signal intenꢀ
4
sities, 29Si NMR spectra were recorded by applying delayed (25 s)
pulses to suppress the nuclear Overhauser effect.
Oligomerization of DCS in the acetylacetone—carbamide sysꢀ
tem (general procedure). A mixture of DCS, acetylacetone, and
urea was heated in an organic solvent (benzene or toluene) to
boiling and refluxed with vigorous stirring for 2 h. Then the
reaction mixture was filtered to remove pyrimidine hydrochloride
and analyzed using NMR spectroscopy without isolation of orꢀ
ganosiloxanes. The yields and structures of the organosiloxanes
obtained were determined from the chemical shifts and signal
1
29
intensities in the H and Si NMR spectra.
19. A. A. Bychkova, F. V. Soskov, A. I. Demchenko, P. A. Storoꢀ
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6
0, 2384 [Izv. Akad. Nauk, Ser. Khim., 2011, 2337].
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