Synthesis of (chloromethyl)dimethylsilanol

Article abstract of DOI:10.1007/s00706-014-1366-7

Abstract (Chloromethyl)dimethylsilanol was synthesized by the hydrolysis of (chloromethyl)dimethylchlorosilane, N-[(chloromethyl)dimethylsilyl]amines, or N-(chloromethyl)dimethylsilyl-N-methylamide of diisopropylphosphoric acid. Graphical abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s00706-014-1366-7

Monatsh Chem
DOI 10.1007/s00706-014-1366-7
ORIGINAL PAPER
Synthesis of (chloromethyl)dimethylsilanol
•
Nataliya F. Lazareva Alexey Yu. Nikonov
Received: 28 April 2014 / Accepted: 24 November 2014
Ó Springer-Verlag Wien 2015
Abstract (Chloromethyl)dimethylsilanol was synthesized
by the hydrolysis of (chloromethyl)dimethylchlorosilane,
N-[(chloromethyl)dimethylsilyl]amines, or N-(chloromethyl)
dimethylsilyl-N-methylamide of diisopropylphosphoric acid.
silanols XCH2SiRR0OH (X = Hal, R2N, RO, RS) in syn-
thetic organic chemistry and chemistry of materials could
give rise to new polyfunctional synthons, catalysts and
polymers with unusual properties. A large number of pa-
pers are devoted to organosilicon compounds containing
silanol groups Si(OH)x (x = 1–3). However, the chemical
properties of a-carbofunctional silanols are poorly studied.
The reason is that a serious problem is the isolation of
pure silanols from the reaction mixtures. Intermolecular
condensation of compounds containing Si–OH motif re-
sults in the formation of stable siloxanes [2] and restricts
the lifetime of silanols. (Chloromethyl)dimethylsilanol
ClCH2SiMe2OH (1) as a simple bifunctional silanol is of
particular interest. It is a very good model for studying the
reactivity of the ClCH2Si and Si–OH groups in the same
molecule. We have found only a few publications about the
synthesis, chemical properties, and application of silanol 1
[22–28]. As in the case of other silanols, in the presence of
bases or acids, compound 1 undergoes condensation reac-
tion [22, 23].
Keywords (Chloromethyl)dimethylchlorosilane ꢀ
N-[(chloromethyl)dimethylsilyl]amines ꢀ
N-(chloromethyl)dimethylsilyl-N-methylamide of
diisopropylphosphoric acid ꢀ Hydrolysis
Introduction
The chemistry of silanols has attracted considerable inter-
est in recent decades (see reviews [1–5] and references
therein). Silanol groups Si–OH are widely distributed in
nature: many varieties of silica SiO2 have the surface
groups OH, the aqueous medium contains a quantity of
dissolved orthosilicic acid and its derivatives [6] and the
processes of biosilicification in living organisms proceed
with participation of the silanol groups [7–9]. Silanols are
nucleophilic coupling reagents in organic synthesis [10–14]
and versatile building blocks for the synthesis of silse-
quioxanes, metallasiloxanes and related silicon-based
polymeric materials [2–5, 15, 16]. They are considered as
bioisosteres of enzymes and pheromones [17–20]. Silanol
groups are also important structural fragments of zeolites
and silica, as they strongly modify the surface properties of
these materials [21]. A wide use of a-carbofunctional
(Chloromethyl)dimethylsilanol (1) was first synthesized
by the hydrolysis of 1,3-bis(chloromethyl)tetram-
ethyldisilazane [24, 25]. Note that in spite of the fact that
the authors of [26] used the earlier described protocol [25]
for the synthesis of 1, the IR spectra in the range of the Si–
OH absorption are substantially different [25, 26]. Oxida-
tion of (chloromethyl)dimethylsilane (among other silanes)
with hydrogen peroxide catalyzed by lacunary poly-
oxotungstate leads to (chloromethyl)dimethylsilanol in
83 % yield and high selectivity (silanol:siloxane = 96:4)
[27]. However, the yield and selectivity were determined
only by GC and NMR spectroscopy; a pure compound
was not isolated. This does not allow to consider the
proposed procedure as a convenient preparative method
for the synthesis of silanols. The hydrolysis of
N. F. Lazareva (&) ꢀ A. Y. Nikonov
Irkutsk Institute of Chemistry A. E. Favorsky,
Siberian Branch of the Russian Academy of Sciences,
Favorsky st., 1, 664033 Irkutsk, Russian Federation
e-mail: nataly_lazareva@irioch.irk.ru
123

N. F. Lazareva, A. Y. Nikonov
(chloromethyl)dimethylchlorosilane ClCH2SiMe2Cl in
two-phase system Et2O–H2O [28] seems to be more suit-
able for the preparation of (chloromethyl)dimethylsilanol.
According to [28], the compound was purified by distilla-
tion and the yield was as high as 95 %. As a matter of fact,
the authors provide the reader only with a general proce-
dure exemplified by the synthesis of 1,1,3,3,5,5,7,7,7-
nonamethyltrisiloxan-l-ol. When attempting to apply this
protocol to the synthesis of the target silanol 1, we failed to
achieve the reported high yield, possibly, because some
specific details, such as the temperature or time of the re-
action, were omitted in [28]. Therefore, the purpose of the
present study was to elaborate a simple and practical syn-
thetic approach to (chloromethyl)dimethylsilanol.
The use of the procedure given in [28] gave full con-
version of the starting silane 2, but a substantial amount of
the siloxane 3 was formed (the ratio 1:3 was 65/35) and the
product mixture could not be separated by distillation. The
structure of compounds 1 and 3 was confirmed by data of
NMR spectra, which agree closely with data [28, 29].
Therefore, we have studied the effect of the solvent, the
ratio of the reagents, temperature, and time of the reaction
on the yield of silanol 1; the results are presented in
Table 1. In all cases, the product was shown to be a mix-
ture of silanol 1 and siloxane 3. Lowering the temperature
of the reaction mixture and decrease of the amount of water
to 1 mol of silane 2 increase the selectivity of formation of
the target silanol 1. The hydrolysis under homogeneous
conditions (THF as a solvent) and the use of aniline as a
base further increase the contents of silanol 1 in the product
mixture. We failed to obtain pure silanol 1 using this
procedure, but the product containing *5 % of siloxane 3
can be successfully used in organic synthesis. The use of
trimethylamine as both a solvent and hydrogen chloride
scavenger also leads to a high selectivity of the reaction. In
spite of some experimental difficulties in handling liquid
trimethylamine, its use as a solvent has evident advantages:
the reaction proceeds in homogeneous solution, Me3N is
easily removed from the reaction mixture at low tem-
perature and can be trapped practically pure for reuse. No
products of the reaction of trimethylamine with silane 2
were detected under the conditions employed.
Results and discussion
The hydrolysis of the commercially available
(chloromethyl)dimethylchlorosilane ClCH2SiMe2Cl (2)
seems to be an attractive method for the synthesis of the
target (chloromethyl)dimethylsilanol ClCH2SiMe2OH
(Scheme 1).
Scheme 1
Table 1 Preparation of silanol
1 by hydrolysis of silane 2
Entry
Solvent
Base
H2O/equiv
T/°C
Time/h
1/3b
Conversion/%b
1a
2
H2O–Et2O
H2O–Et2O
H2O–Et2O
Et2O
(NH4)2CO3
(NH4)2CO3
(NH4)2CO3
(NH4)2CO3
Et3N
Excess
23
0
0.5
0.5
0.2
1
65/35
67/33
69/31
70/30
75/25
80/20
90/10
70/30
80/20
85/15
90/10
90/10
85/15
90/10
95/5
100
100
100
80
Excess
3
Excess
0
4
10
10
10
10
10
1
0
5
Et2O
25
0
0.5
0.5
1.5
0.5
0.5
0.1
0.1
0.5
0.5
0.5
0.1
0.2
0.1
0.5
75
6
Et2O
Et3N
75
7
Et2O
PhNH2
Et3N
0
100
100
100
100
95
8
THF
20
20
20
0
9
THF
Et3N
10
11
12
13
14
15
16
17
17
THF
Et3N
1
THF
Et3N
1
THF
Et3N
1
0
100
100
100
96
THF
PhNMe2
PhNMe2
PhNMe2
PhNMe2
Me3N
1
20
0
THF
1
THF
1
0
THF
1
0
95/5
100
90
a
The procedure was taken from
Me3N
Me3N
1
-5
-5
95/5
[28]
b
Me3N
1
95/5
100
1
From H NMR spectra
123

Synthesis of (chloromethyl)dimethylsilanol
An alternative route to silanol 1 is the hydrolysis of
[(chloromethyl)dimethylsilyl]amines 4. We have studied
the hydrolysis of N-[(chloromethyl)dimethylsilyl]dimethy-
lamine (4a) and N-[(chloromethyl)dimethylsilyl]-N-
methylaniline (4b) in THF and MeCN; the results are
presented in Table 2 (Scheme 2).
Scheme 2
Lowering the temperature of the reaction mixture and
decrease of the reaction time increase the contents of si-
lanol 1 in the reaction products. The hydrolysis of
compound 4b in THF or acetonitrile at 5 °C in the course
of 1 h results in full conversion of the starting aminosi-
lane and formation of silanol 1 having *5 % of siloxane
3. Under the same conditions, the hydrolysis of compound
4a gives rise to the formation of the mixture silanol/
siloxane in the ratio of *90/10. Amines are known to
catalyze the formation of the siloxane bonds [30, 31]. In
the hydrolysis of compound 4b, N-methylaniline is
eliminated, whose basicity is much lower than that of
dimethylamine (pK 4.85 and 10.77, respectively [32]).
Apparently, a higher percentage of the siloxane in the
products of the hydrolysis of compound 4a is due to a
higher rate of condensation of silanol 1 in the presence of
a more basic amine. Still, the use of compound 4a is
preferable since the released dimethylamine is easily re-
moved under vacuum. The reduction of the reaction time
of the hydrolysis of compound 4a to half an hour leads to
silanol 1 of 95 % purity. THF is preferable as a solvent in
the reactions of hydrolysis since it has a lower boiling
point as compared to acetonitrile and is more readily re-
moved from the reaction mixture.
Scheme 3
slight heating of the solution of 5 in HMPT with equimolar
amount of water and condensed from the reaction mixture
to a cooled trap under vacuum (*1 mbar).
Conclusion
The hydrolysis of N-(chloromethyl)dimethylsilyl-N-methyl-
amide of diisopropylphosphoric acid results in practically
pure (chloromethyl)dimethylsilanol. However, this method is
rather expensive and its use is limited (and can be recom-
mended only if pure compound is needed). Note that the
commercially available diphenylsilanediol from Aldrich has
purity of 95 %. Therefore, (chloromethyl)dimethylsilanol
prepared by the hydrolysis of (chloromethyl)dimethylchlo-
rosilane or [(chloromethyl)dimethylsilyl]amines and
containing *5 % of the siloxane is quite suitable for the use
in synthetic organic chemistry.
Finally, the hydrolysis of N-(chloromethyl)dimethylsi-
lyl-N-methylamide of diisopropylphosphoric acid (5) in
HMPT was examined (Scheme 3). We have found that
practically pure silanol 1 can be prepared in good yield by
Experimental
Table 2 Preparation of silanol 1 by hydrolysis of ClCH2SiMe2NRR0
Silane Solvent H2O/equiv T/°C Time/h 1/3a
Conversion/%a
NMR spectra were recorded on a Bruker 400 MHz in-
strument for 20 % solutions in CDCl3 with cyclohexane as
an internal standard. The IR spectrum was taken on a
Bruker Vertex spectrometer. Mass spectrum of electron
impact (70 eV) was obtained on a GCMS-QP5050A Shi-
madzu spectrometer (capillary column). Commercial
(chloromethyl)dimethylchlorosilane (2) was distilled in the
presence of Bu3N directly before use. N-[(chloro-
methyl)dimethylsilyl]amines 4a and 4b were synthesized
according to [33, 34]. N-(chloromethyl)dimethylsilyl-N-
methylamide of diisopropylphosphoric acid (5) was pre-
pared by the earlier described procedure [35].
Trimethylamine was dried by double recondensation over
CaH2. Diethyl ether and HMPT were dried by standard
protocol [36]. Distilled water was used.
4a
4a
4a
4a
4a
4a
4a
4a
4b
4b
4b
4b
a
THF
THF
10
1
1
1
1
1
1
1
1
1
1
1
25
25
0
2
68/32 100
2
75/25 100
85/15 100
90/10 100
95/10 100
THF
2
THF
0
1
THF
5
0.5
1
MeCN
MeCN
MeCN
THF
0
91/9
92
0
2
87/13 100
90/10 100
5
1
0
1.5
1
95/5
95/5 100
95/5 94
95/5 100
93
THF
5
MeCN
MeCN
1
0
1.5
1
5
From H NMR spectra
123

N. F. Lazareva, A. Y. Nikonov
Hydrolysis of (chloromethyl)dimethylchlorosilane (2)
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reaction mixture was kept at room temperature for 1 h, then
evacuated to 1 mbar and heated on water bath (40–45 °C).
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1
trap. H NMR: d = 0.25 (SiMe, 6H), 2.79 (CH2, 2H), 3.45
(OH, 1H) ppm; 13C NMR: d = -1.83 (SiMe), 30.94 (CH2)
ppm; 29Si NMR: d = 10.70 ppm; IR (CCl4): vꢀ = 3,685 (Si–
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123