The influence of hcl concentration on the rate of the hydrolysis–condensation reaction of phenyltrichlorosilane and the yield of (Tetrahydroxy)(tetraphenyl) cyclotetrasiloxanes, synthesis of all its geometrical isomers and thermal self-condensation of the

Article abstract of DOI:10.3390/molecules26144383

The rate of hydrolysis–condensation reaction of phenyltrichlorosilane in water-acetone solutions and the product yields were shown to significantly depend on the concentration of HCl (CHCl) in the solutions. The main product of the reaction was all-cis-(t

Full text of DOI:10.3390/molecules26144383

molecules
Article
The Influence of HCl Concentration on the Rate of the
Hydrolysis–Condensation Reaction of Phenyltrichlorosilane
and the Yield of (Tetrahydroxy)(Tetraphenyl)Cyclotetrasiloxanes,
Synthesis of All Its Geometrical Isomers and Thermal
Self-Condensation of Them under
“
Pseudo”-Equilibrium Conditions
Irina M. Petrova, Yury I. Lyakhovetsky, Nikolai S. Ikonnikov and Nataliya N. Makarova *
A.N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences, 28 Vavilov St.,
119991 Moscow, Russia; impetr2013@yandex.ru (I.M.P.); yulyakh@ineos.ac.ru (Y.I.L.); ikonns@ineos.ac.ru (N.S.I.)
*
Correspondence: nmakar@ineos.ac.ru; Tel.: +7-(499)700-5870 (ext. 1180)
ꢀ
ꢁꢂꢀꢃꢄꢅꢆꢇ
Abstract: The rate of hydrolysis–condensation reaction of phenyltrichlorosilane in water-acetone solu-
tions and the product yields were shown to significantly depend on the concentration of HCl (CHCl) in
the solutions. The main product of the reaction was all-cis-(tetrahydroxy)(tetraphenyl)cyclotetrasiloxane.
This was different from the earlier published results of analogous reactions of m-tolylSiCl3, m-ClPhSiCl3,
ꢀ
ꢁꢂꢃꢄꢅꢆ
Citation: Petrova, I.M.;
Lyakhovetsky, Y.I.; Ikonnikov, N.S.;
Makarova, N.N. The Influence of HCl
Concentration on the Rate of the
Hydrolysis–Condensation Reaction of
Phenyltrichlorosilane and the Yield of
and
α
-naphtylSiCl, in which some products of other types were formed. For example, trans-
-naphtyldisiloxane was obtained in the case of -naphtylSiCl . All-
1,1,3,3-tetrahydroxy-1,3-di-
α
α
3
cis-(tetrahydroxy)(tetraphenyl)cyclotetrasiloxane was treated in acetone with HCl to give the other
three geometric isomers (cis-cis-trans-, cis-trans-, and all-trans-). The thermal self-condensation of
these four isomers under “pseudo”-equilibrium conditions (under atmospheric pressure) was in-
vestigated in different solvents, in quartz or molybdenum glass flasks. The compositions of the
products were monitored by APCI-MS and 29Si NMR spectroscopy. It was shown that all-cis- and
cis-cis-trans-isomers in toluene or anisole mostly gave the cage-like Ph-T8,10,12,14 and uncompleted
cage-like Ph-T10,12OSi(HO)Ph compounds. In contrast to these two isomers, the cis-trans–isomer
in toluene mainly formed dimers with the loss of one or two molecules of water. However, in
acetonitrile, significant amounts of Ph-T10,12 and Ph-T10,12OSi(HO)Ph species were formed along
with the dimers. All-trans-isomer did not enter into the reaction at all.
(
Tetrahydroxy)(Tetraphenyl)
Cyclotetrasiloxanes, Synthesis of All
Its Geometrical Isomers and Thermal
Self-Condensation of Them under
“
Pseudo”-Equilibrium Conditions.
Molecules 2021, 26, 4383. https://
doi.org/10.3390/molecules26144383
Academic Editors: Masafumi Unno
and Krzysztof Pielichowski
Keywords: hydrolysis-condensation; self-condensation; “pseudo”-equilibrium conditions; phenyl-
trichlorosilane; isomers of (tetrahydroxy)(tetraphenyl)tetrasiloxane; cage-like compounds; NMR;
APCI-MS
Received: 9 June 2021
Accepted: 16 July 2021
Published: 20 July 2021
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
1
. Introduction
Polyorganosilsesquioxanes (POSSO), compounds with the formula (RSiO1.5
n
) , are the
object of comprehensive studies since they have unique thermal stability, low dielectric
constants and hygroscopicity, can serve as binders for ceramics, and form thin films and
microporous solid materials. POSSO formed as cyclolinear, cage-like species with different
degree of completion, and as branched polymers.
Data on hydrolysis-condensation and -polymerization of organotrichloro- and organ-
otrialkoxysilanes at different concentrations in solvents, different temperatures, and in the
Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
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presence of potassium hydroxide were summarized in a review [
1]. They included the
change in properties of POSSO in dependence on the molecular weights,
α
values in the
Mark-Houwink equation, solubility, and weight losses at high temperatures. In another
review, information was given on the synthesis, structure, and physical and chemical prop-
4
.0/).
erties of polyhedral organosilsesquioxanes [
2
]. Also, therein, the effects of initial functional
Molecules 2021, 26, 4383. https://doi.org/10.3390/molecules26144383
https://www.mdpi.com/journal/molecules

Molecules 2021, 26, 4383
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monomer concentrations in the solutions, the nature of substituents and functional groups,
and the type of catalyst upon the reaction rates, the degree of oligomerization, and the
yields of cage-like compounds were reviewed. Cage-like species with carbofunctional
groups were synthesized by the hydrosilylation of the corresponding carbofunctional
olefins with octahydridsilsesquioxane as well as with sila-functional cubes [3]. Significant
progress was made in the synthesis of molecularly ordered nanoporous materials by the
controlled binding of cage siloxanes based on their self-assembly due to H-bondings and
their regioselective modification with silanol or alkoxy groups [4].
Completed and incomplete cage-like compounds were used as mono- and multifunc-
tional precursors for the synthesis of comb-like and branched copolymers [5]. Polyhedral
compounds appear to be among the most interesting precursors for use as building blocks
for constructing high-performance organic optoelectronic materials: electroluminescent
and electrochromic devices, and liquid crystals [6]. POSSO with organic groups such as
alkyl, aryl, alkoxy or hydride, those obtained via the hydrolysis and polycondensation of
trialkoxy- or trichlorosilane monomers, contain reactive or non-reactive organic groups.
Various organosilsesquioxane (OSSO)-based hybrid nanomaterials were examined with
regard to their application as polymer nanocomposites, catalysts, sensors, and for medical
purposes [7].
In recent years, new approaches to the synthesis of both POSSO and PPSSO (polyphenyl-
silsesquioxanes) have been tested, namely, the use of different building blocks such as
(
tetrahydroxy)(diphenyl)disiloxane [
droxy)(tetraphenyl)cyclotetrasiloxane in the hydrolysis-polycondensation reactions in or-
der to obtain stereoregular cyclolinear POSSO or PPSSO (See also [10 13]). The hydrolysis–
condensation reaction of phenyltrimetoxysilane in dilute solutions of various solvents
resulted in dodecaphenylsilsesquioxane (Ph-T ). An increase in concentration of the for-
8], tetrametoxydisiloxane [9], and isomers of (tetrahy-
–
12
mer led to cyclolinear PPSSO [14,15]. Octaphenylsilsesquioxane (Ph-T ) was obtained when
8
the condensation of all-cis-(tetrahydroxy)(tetraphanyl)cyclotetrasiloxane was implemented
at r.t. in the absence of a catalyst [16]. Octaarylsilsesquioxanes with reactive or non-reactive
organic groups were synthesized from cyclotetrasiloxanetetraols and their sodium salts in
the presence of ammonium catalysts [17]. Unsymmetrical silsesquioxane double-deckers
of new types [17–22], the basket [23] and butterfly types [24], or siloxane cages were re-
ported to be obtained by simple hydrolytic condensations of two cyclosiloxanes with an
organomonosilane. They can be building blocks for diverse applications since materials
based on them should have low dielectric constants and excellent thermal stability.
Hybrid cage-type organosiloxane oligomers can be formed by hydrolysis and poly-
condensation of bis(trialkoxy)silane [(EtO) Si-CH -Si(OEt) ] in the presence of a tetram-
3
2
3
ethylammonium salt [25].
Recently, we studied how the concentration of HCl in solutions, and characteris-
tics of substituents, affected the results of the hydrolysis–condensation reaction of three
aryltrichlorosilanes, m-tolylSiCl , m-ClPhSiCl , and α-naphtylSiCl . The alterations in
3
3
3
composition and structure of intermediates and final products occurred due to variation of
these factors were followed by atmospheric pressure chemical ionization mass spectrome-
29
try (APCI-MS) and Si NMR [26]. One of the purposes of the present study was to compare
the results of the above study with those of the analogous reaction of PhSiCl3.
2. Results and Discussion
We have now studied the hydrolysis–condensation reaction of phenyltrichlorosilane
1) at different concentrations of HCl (CHCl) in water-acetone solutions. Then, the thermal
(
self-condensations in “pseudo”-equilibrium conditions (under atmospheric pressure) of
four isomeric tetrahydroxy-(tetraphenyl)cyclotetrasiloxanes: all-cis- (2), cis-cis-trans- (3),
cis-trans-(4), and all-trans-(5) (Figure 1) have been performed.

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Figure 1. The geometric isomers of (tetrahydroxy)(tetraphenyl)cyclotetrasiloxane.
All reactions were monitored with APCI-MS and 29Si NMR spectroscopy. The re-
◦
actions of
0
1
were conducted at 4 C with the concentration of HCl between 0.032 and
−
1
.26 mol L . The yields of the products were determined in the interval of 24–570 h. The
reaction conditions were selected to be similar to those previously published for three
aryltrichlorosilanes [26], to compare the composition and structure of intermediates and
final products. Figure 2 shows these yields of the products that precipitated from the
solution depending on the reaction time. As can be seen from Figure 2, the rate of the
reaction and final yields of the products decreased with the decrease in acidity (See Note 1
in the Supplementary Materials (SM)).
Figure 2. Dependence of the yields of phenylcyclosiloxanes from the hydrolysis–condensation
reaction of
1
on time at different concentrations of C
in water-acetone solutions: CHCl = 0.26 (a);
HCl
−
1
0
.15 (b); 0.055 (c), and 0.032 mol L (d).
Figure 3 presents the 29Si NMR spectra of phenylcyclosiloxane compounds obtained
−
1
at CHCl = 0.15 and 0.26 mol L , separated from the reaction mixture after the 24 h reaction.
29
Samples of them were dissolved in acetone-d and subjected to Si NMR.
6
A number of signals at
dominant, were observed for the products obtained at C
−
69.0~
−
71.0 ppm, with one at
−
69.79 ppm being greatly pre-
= 0.15 and 0.26 mol L , while
−
1
HCl
any signals in the regions of
products had only one OH group at each silicon atom. All of this was valid for compounds
from the reaction conducted at CHCl = 0.055 mol L . The TLC tests of all the products with
−
50.0 and
−
80.0 ppm were absent. This evidenced that the
−
1
the toluene:diethyl ether = 4:1 eluent gave a value of R = 0.05 that was consistent with pre-
f
viously published data for all-cis-isomer of (tetrahydroxy)(tetraphenyl)cyclotetrasiloxane
(2) [27,28]. The small signals around the intensive one most likely belonged to other isomers
of (tetrahydroxy)(tetraphenyl)cyclotetrasiloxane. The calculation of the ratio of the integral
intensity of the main signal to the sum of it and the integral intensities of the small signals

Molecules 2021, 26, 4383
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around it made for spectrum “c” in Figure 3 showed that the content of isomer
mixture of isomers ought to be higher than 95%.
2
in the
Figure 3. 29Si NMR spectra of phenylcyclosiloxane compounds from the reaction of
1
carried out for
−
1
−1
−1
2
4 h at CHCl = 0.15 mol L
(a); 120 h at CHCl = 0.15 mol L
(b), and 24 h at CHCl = 0.26 mol L
(c).
It was of interest to compare the results of the hydrolysis-condensation reaction
of PhSiCl with those of hydrolysis-condensations of m-tolylSiCl , m-ClPhSiCL , and
3
3
3
α-naphtylSiCl reported in [26].
3
For all these compounds, the rates of the reactions and the yields of products increased
with the increase in the acidity of the reaction mixtures.
However, there were differences in the types of the products.
Thus, the 29Si NMR spectra of the products (Figure 3) showed that, in the hydrolysis–
condensation reaction of
other isomers formed in negligible amounts or isomerization of
1
, at different CHCl in the solutions, isomer
to them occurred to a
was obtained
2 formed mostly, and
2
very small extent, even if the reaction was conducted for 120 h. Compound
in the 73.6% yield (See Section 3.3.1).
2
The 29Si NMR spectra in Figure 3 (the spectra of the precipitates when the reaction
−
1
was performed at the CHCl = 0.055 mol L were similar) were compared with those
for the hydrolysis–condensation of m-tolylSiCl implemented at the CHCl = 0.054 mol L
−
1
3
and reported in [26]. In the former case, as was told above, the intensive singlet of
at −69.79 ppm was present in the spectra. At the same time, in the latter case, two
singlets at 69.98 and 70.49 ppm (these values were more accurately measured than
2
−
−
29
those given in [26]) were first present in the Si NMR spectrum, the upfield singlet being
of an even greater intensity than the downfield one. Then the intensity of the upfield
signal decreased in time until it completely disappeared, and only the downfield singlet
remained in the spectrum. The upfield signal was ascribed to the cis-trans-isomer of
(tetrahydroxy)(tetra-m-tolyl)cyclotetrasiloxane (In [26], the cis-trans-isomer was mistakenly
named as the cis-trans-cis-isomer) which graded into all cis-isomer, that gave the downfield
signal at −69.98 ppm.
Two singlets in the region of
−
71.3 to
−
72.3 ppm (the more accurate measurements
29
gave values
−
71.55 and
−
71.78 ppm) were found in the Si NMR spectrum of the precipi-
tate from the reaction mixture of the hydrolysis–condensation of m-ClPhSiCl carried out
3
−
1
at CHCl = 0.032 mol L for 48 h. They were ascribed to the all cis- and cis-trans-isomers of
tetrahydroxy)(tetra-m-chlorophenyl)cyclotetrasiloxanes, respectively [26].
Two singlets at 60.68 and
61.64 ppm were present in the 29Si NMR spectrum of the
precipitate from the reaction of the hydrolysis–condensation of -naphtylSiCl conducted
(
−
−
α
3
−
1
at CHCl = 0.15 mol L . Most likely, they belonged to isomers of 1,1,3,3-tetrahydroxy(1,3-
di-α-naphtyl)disiloxane.
What is the reason for such different steric results for the reactions of
1 and its
aryl analogs? Probably, in the last three cases, trans-isomers of 1,1,3,3-tetrahydroxy(1,3-

Molecules 2021, 26, 4383
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diaryl)disiloxanes formed as intermediates along with the cis-isomers. They seem to be
more stable than the cis-ones since the m-tolyl, m-ClPh, and
more bulky than the Ph one, and the reaction partly occurred through them. The con-
densation in the case of occurred completely via the formation of the cis-isomer as an
α-naphtyl substituents are
1
intermediate (Scheme 1).
Ar
Si
Ar
Si
Ar
OH
HO
O
HO
HO
Si
O
Si
O
condensation
condensation
O
OH
O
OH
HO
OH
Si
Si
Ar
Ar
Cis-trans isomer
Ar
trans-isomer
a)
+
H O, (CH ) CO
2
3 2
Ar
ArSiCl3
Ar
Ar
Ar
Si
Si
Si
O
Si
HO OH
Ar
Si
Ar
O
O
O
HO
OH
OH
Si
HO
cis-isomer
O
HO
OH
All-cis-isomer
Ar = m-tolyl, m-chlorophenyl, a-naphtyl
Ph
Si
Ph
Si
condensation
O
b)
compound 2
All-cis-isomer
H O, (CH ) CO
PhSiCl3
2
3 2
HO OH
OH
HO
cis-isomer
Scheme 1. The ways of formation of stereoisomers of (tetrahydroxy)(tetraaryl)cyclotetrasiloxanes in the hydrolysis–
condensation of m-tolyl-, m-chlorophenyl-, or α-naphtyltrichlorosilane (a) and phenyltrichlosilane (b).
As an indirect evidence in support of Scheme 1, it is necessary to mention that the trans-
isomer of 1,1,3,3-tetrahydroxy-1,3-di- -naphthyldisiloxane was obtained in 48% yield by
the hydrolysis–condensation reaction of
for 190 h. It was characterized by the XRPD method [26].
α
−
-naphtylSiCl carried out at CHCl = 0.15 mol L
3
1
α
Thus, in the case of m-tolylSiCl , though the analog of 2, all cis-(tetrahydroxy)(tetra-
3
m-tolyl)cyclotetrasiloxane was obtained in the 30.8% yield, the cis-trans-isomer formed in
significant amounts in the course of the reaction. It was then graded into all cis-isomer.
This was not characteristic of the reactions of 1.
Besides, at a greater acidity, a mixture containing many m-tolylcyclosiloxanes was
obtained in the course of the 24 h reaction of m-tolylSiCl , as was shown by PI APCI-MS.
3
In the case of m-ClPhSiCL , two isomers of (tetrahydroxy)(tetra-m-chlorophenyl)
3
cyclotetrasiloxane were obtained by the hydrolysis-codensation reaction of it: the all-cis
one in the yield of 19% and the cis-trans-isomer in the yield of 24.9%. Apart from this,
the formation of poly-m-chlorophenylsilsesquioxanes in the course of the reaction was
displayed by 29Si NMR.
The trans-isomer of 1,1,3,3-tetrahydroxy-1,3-di-
the 48% yield by the hydrolysis–condensation reaction of
α
-naphtyldisiloxane was obtained in
-naphtylSiCl . Besides, PI APCI-
α
3

Molecules 2021, 26, 4383
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MS showed some other condensation products (e.g.,
present in the reaction mixtures.
α
-naphtyl-T and α-naphtyl-T ) to be
8 10
As it was told above, other isomers apart from
2
were formed in negligible amounts
in the course of the hydrolysis-condensation reaction of 1. However, it was earlier re-
ported that underwent isomerization to the other isomers in a dilute acetone solution if
2
hydrochloric acid or methylchlorosilanes were added to the solution [27–29].
Recently, the stereoisomerization of all cis-[iso-C H Si(OH)O] in an acetone solution
4
9
4
under the action of HCl taken in concentrations from 0.01 M to 5 M was studied. It was
found that after 10 min, regardless of the CHCl, three isomers were formed and the ratio
between the four isomers changed insignificantly with the change in CHCl [30].
We prepared these other isomers of 2 with the protocol reported in [28].
The isomers were separated by fractional crystallization and their identification was
first made by the R values and IR spectra [27]. According to the 29Si NMR spectral data,
f
the presence of 5% of any isomer
we used 29Si NMR for the additional identification of the isomers. With that, it was taken
into account that the chemical shifts ( ) for stereoisomers changed depending on the
concentration and composition of the mixture, however the differences (∆δ) between three
singlets of isomer , and were constant, whereas isomer gave three singlets with the
ratio of 1:2:1. APCI-MS was also employed for this purpose in the cases of and (see
below). Previously, structures of and were confirmed by X-ray powder diffraction and
single crystal analysis [31] and [10], respectively
Stereoisomers were used as the starting compounds for the condensations carried
2–5 in solution could easily be determined [28]. Thus,
δ
2–5
2,
4
5
3
2
3
2
5
2–5
out under “pseudo”-equilibrium conditions (under atmospheric pressure). As it was told
above, APCI-MS and 29Si NMR were employed for monitoring the reactions.
As mentioned above, the APCI-MS was also used in the identification of isomers
2
and 3. However, these compounds, as well as
reaction under conditions of APCI–MS. Because of this, the PI (positive ion mode) and
NI (negative ion mode) APCI mass spectra of and were thoroughly analyzed and
4 and 5, could enter into the self-condensation
2
3
additional spectra were recorded. It was believed that this would allow us to understand
what results corresponded to the reactions in flasks rather than in the mass spectrometer.
Samples of
priori, the results could depend on the concentration of
the spectra of 2 were recorded at different dilutions. Figure 4 shows these mass spectra.
When the concentration of was relatively high, the PI APCI mass spectrum dis-
played a peak at m/z 570 due to ion [M + H O] (See Note 2 in the SM), whereas
2
and
3
were dissolved in acetonitrile before introduction in the instrument. A
2
or in this solvent. That is why
3
2
2
+•
2
2
+•
2
+
peaks of [M ] and [M + H] were virtually absent (Figure 4a). In the spectrum, the
maximal ion peak proved to be that of a compound formed owing to the uncompleted
condensation of two molecules of
2 with a water molecule added in the mass spectrometer
2
+•
2
+•
H O) + H O] at m/z 1104 and ions
2 2
(
[(M ) − 2H O) + H O] at m/z 1086). Ion [(M )2
−
2
2
2
from a dimer formed due to the loss of three water molecules in the course of the condensation
(
also with the addition of H O during the analysis) were also present (See Note 3 in the SM).
2
However, when the analyte was significantly diluted with acetonitrile, the self-
2
+•
condensation of 2 was almost suppressed, and the mass spectrumdisplayed the [M + H O]
2
ion peak being predominant (Figure 4b).
In the NI APCI mass spectrum of the former variant of analyte, ion peaks of anions
M2
−
H] at m/z 551 and [(M
−
2
−
H)M ] or [((M )
2 −
2
−
H O)
2
−
−
H + H O] at m/z 1103
2
[
2
were present. For the latter (diluted) analyte, the peak of the dimer was absent (Figure 4c,d,
respectively; also see Note 4 in the SM).
For compound
3, the most abundant ion peak in PI APCI mass spectra turned out
3
+•
to be one of radical cation [M + H O] , and ion peaks due to higher molecular mass
2
compounds were more abundant than in the case of
recorded by APCI-MS are specified).
2 (See Figure S1 in the SM where ions

Molecules 2021, 26, 4383
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Figure 4. APCI mass spectra of isomer
2: (a,b)—recorded in the PI mode when the concentration of 2 in analyte was greater
and less, respectively; (c,d)—in the NI mode, analogously.
The results obtained showed that, when analyzing the reaction mixtures of the self-
condensation of species by APCI-MS, if the starting isomer still remained in the
2–5
mixture, the samples for analysis should sufficiently be diluted to avoid additional reactions
occurring immediately inside the mass spectrometer.
Moreover, polyhedral compounds: octaphenylsilsesquioxane (Ph-T ) and dodecaphenyl-
8
silsesquioxane (Ph-T ), (
condensations of species
6
2
and
7, respectively) were awaited to be formed as products of
12
–5. Though APCI-MS is considered as a rather mild method of
ionization, fragmentations of ions could occur, especially as “in source collision induced
dissociations”, owing to the construction peculiarity of the instrument [32 33]. Thus, it
was also interesting to obtain the APCI mass spectra of and and estimate how the
fragmentations of ions of these compounds could hinder understanding what products
and intermediates formed in the course of the reactions in flasks. Compounds and were
,
6
7
6
7
obtained by the corresponding protocols described in [34] and [14], respectively. Their
APCI mass spectra are presented in Figures 5 and 6.

Molecules 2021, 26, 4383
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Figure 5. PI APCI mass spectrum of compound 6.
Figure 6. APCI mass spectra of compound 7 recorded in (a) the PI mode and (b) in the NI mode.
Figures 5 and 6 displayed fragment ions that exist in the PI APCI mass spectra for
and in the NI mode for compound . As underlined above, this should be taken into
6
7
account when analyzing the reaction mixtures with these methods.
The spectra also demonstrated both these compounds to be registered in the PI mode
(
analogously to 2 and 3) as hydrates of their ions (see the last sentence of Note 2 in the SM)
with the molecular ions being absent. Spectrum 6b showed that all of this was valid for
compound 7, even in the NI mode.
The reaction of condensation of compound 2 was first performed in toluene solution
◦
in a quartz flask at 110 C for 120 min (Note 5 in the SM). The PI APCI mass spectra of the

Molecules 2021, 26, 4383
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precipitates from the reaction mixture were taken after 30, 45, and 120 min periods. The
spectra of the precipitates obtained after the 45 and 120 min periods are given in Figure S2
in the SM and Figure 7a, respectively. They do not contain peaks at m/z 570, characteristic
of the starting compound. This means that they show products of the solution reaction
rather than those of the reaction that occurred in the mass spectrometer.
Figure 7.
(
a
) PI APCI mass spectrum of the precipitate from the reaction mixture of the self-condensation of compound
2
◦
carried out in a quartz flask in toluene at 110 C for 120 min, (
b,
c)—The m/z 1555–1615 segments of the spectra recorded
when H O and D O were simultaneously syringed into the mass spectrometer, respectively.
2
2
Of interest are groups of the most intensive peaks at m/z 1566, 1446, 1308, 1291, 1254,
and 996 (the peaks of the nominal mass ions) in Figure 7a. The 1566 group obviously
belongs to the hydrate of compound
7 (Ph-T ), and the lower mass ions are not its
12

Molecules 2021, 26, 4383
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fragment ions. This comes from the fact that the fragmentations were not observed in
2
the PI APCI mass spectrum of pure
7
(See Figure 6a). Moreover, the ms spectrum of the
1
568 Da ion supported this. Also, the ions of the 1308 ion group are not the fragment
2
ions of the 1446 one, since the ms spectrum of the 1446 Da ion showed it. Thus, the 1446
and 1308 ion groups correspond to the hydrates of products of the reaction in the flask.
The latter is obviously present due to the hydrate of compound
8 (Ph-T , see Figure 7a).
10
The former group can be attributed to the hydrates of species , (Ph-T OSi(OH)Ph, also
9
10
see Figure 7a) and/or the isomeric one where the OSi(OH)Ph group is connected to the
polyhedral cage with breakage of a vertical edge rather than one in a pentagon. The ion
with the nominal mass 1291 Da could be the protonated molecule of
8
, and/or a fragment
8
+•
•
2
ion of [M + H O] formed via the loss of OH from it. However, the ms spectrum of the
2
1
308 Da ion showed the fragmentation producing the 1290 Da ion (the loss of a molecule
of water). Thus, the 1291 Da ion appears to be the protonated molecule of the reaction
product 8.
One more product was found, compound 6 (Ph-T ) registered as the molecular radical
8
6
+•
cation of its hydrate, [M + H O] . The 996 Da ion appeared to be its fragment ion formed
2
due to the loss of three water molecules from this radical cation. This found support from
the finding that this ion was present in the PI APCI mass spectrum of pure
similar process was observed for the 1308 Da ion to give the 1254 Da ion.
6 (Figure 5). A
Two other products were detected. Their possible structures are depicted in Figure 7
under numbers 10 (Ph-T OSi(OH)Ph) and 11 (Ph-T )).
12
14
Two comparative experiments were made with the precipitate from the 120 min
reaction mixture. Samples of it in acetonitrile were introduced in the mass spectrometer,
either water or heavy water (D O) being introduced simultaneously. Figure 7b,c give the
2
PI APCI mass spectra in the region of the molecular ions of the compound
7 hydrates for
the H O and D O cases, respectively. As expected, in the second spectrum, the peak of the
2
2
ion with the nominal mass of 1566 Da shifted by two units to that of 1568 Da, indicating the
addition of a D O molecule. An interesting fact was also observed: a peak at m/z 1584 of
2
the dihydrate was registered at m/z 1588. This indicated the addition of two water or heavy
7
+•
water molecules to the molecular ion of
7 ([M ] ) in the mass spectrometer (see Note 6
in the SM). A group of peaks beginning with that at m/z 1602, belonging to the trihydrate,
7
+•
were found in spectrum 7a. Most likely, the third water molecule added to [M ] in the
mass spectrometer; the abundances of the corresponding peaks in spectrum 7b, however,
were too small to make the correct conclusion.
The mass spectra of the solution and the precipitate from the same time reaction
mixture were virtually similar. This proved to be so for the reactions of
under any other conditions employed.
2–4 carried out
As mentioned before, Figure S2 in the SM and Figure 7a present the PI-APCI mass
◦
spectra recorded after 45 and 120 min of heating of compound
2
at 110 C in toluene,
respectively. They reflected changes in the reaction mixture in time: a decrease in products
of the condensation of two molecules of (peaks of the nominal mass ions at m/z 996 and
050) and an increase in those of three and four molecules (peaks at m/z 1254, 1291, 1308,
2
1
1
446, 1566, 1584, and 1704, 1824, respectively).
It was previously reported that, when implementing the zone melting of a mixture of
isomeric cyclosiloxanes in a molybdenum glass ampoule, a polymerization process was
observed. The authors believed this to occur owing to the breakage of the cyclosiloxane
rings catalyzed by metal ions present in the glass [35]. Bearing this in mind, we carried
◦
out the reaction of
2
in a molybdenum glass flask in toluene at 110 C for 120 min. In the
PI-APCI mass spectrum of the precipitate (Figure S3 in the SI), all ion peaks that were
found in the corresponding spectrum of the precipitate from the reaction in the quartz
flask were present. However, the ion peaks due to product
9 turned out to be significantly
greater in abundances. As mentioned above, it probably could be owing to the catalysis
by metal ions present in molybdenum glass, however, further thorough experiments are
required to prove this.

Molecules 2021, 26, 4383
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The 29Si NMR spectrum of this precipitate showed two groups of signals, at
76.0~ 79.5 ppm. The former contained signals of low intensities belonging to the
OSi(OH)Ph groups. The latter consisted of narrow well-resolved signals at −78.5~−79.5 ppm
related to PhSiO1.5 fragments and also narrow signals at 76.8~ 77.9 ppm attributed to the
PhSiO1.5 group in the PhSiO1.5-PhSi(OH)O-PhSiO1.5 fragments. Earlier, we observed simi-
lar upfield signals at 76.0~ 77.5 ppm in the spectra of PPSSO with Mw = 1300–16000 12].
These results were in good accord with those of APCI-MS (See Figure S3 in the SM).
−
68.0~
−
71.0
and
–
−
−
−
−
−
−
[
To increase the temperature at which the reaction of
out in anisole as a solvent in a molybdenum glass flask at the temperature of 130 C. The
mass spectra of the precipitates were obtained after 5 and 15 min from the beginning
2
was conducted, it was carried
◦
of the reaction. The ion peak due to the starting compound
2 was absent even in the
former spectrum. The latter one is given as Figure S4 in the SM. In this spectrum, all
ions of products being in the spectrum of the precipitate from the mixture obtained after
◦
the reaction was implemented in toluene, also in a molybdenum glass flask, at 110 C for
120 min (Figure S3 in the SM) are present. However, in the spectrum S3, the ion peaks of the
monohydrate of compound with the 1446 Da nominal mass were maximal in abundance,
9
while all other peaks, except those at m/z 996 and 997, were of minor ones. On the contrary,
Figure S4 shows several peaks to be abundant (of ions with the 996, 1254, 1291, 1308, 1326,
1
446, 1464, 1566, 1584, and 1704 Da nominal masses) (see Figure S4 for the structures of
these products and ions.) Two facts are of interest here. The first is the great abundance of
peaks of dihydrates in products , and . Earlier, we showed that two water molecules
7,
8
9
really added to molecular ions in the mass spectrometer (see Note 6 in the SM). However,
the abundances of the corresponding peaks are rather great, and the reaction time was
rather short in this case. Hence, the contribution of ions of the incompletely closed
and formed during the reaction in the flask in the abundances of the corresponding ion
peaks cannot be excluded.
7, 8,
9
The second finding here is that the abundances of ion peaks in this spectrum (and
hence the amounts of the corresponding products in the precipitate) of the higher molecular
mass products 10 and 11 are greater than in the spectrum of Figure S3. Moreover, ion peaks
of the product 12 hydrate and/or its isomer (See Figure S4 in the SM for the structure of 12
)
are present in this spectrum, whereas they are absent in Figure 7 and Figure S3. Thus, the
reaction of 2 went deeper in this case.
Of interest also is a group of peaks at m/z 996, 997, 998, and 999. Earlier, we attributed
6
+•
this ion to the fragmentation of the [M + H O] radical cation with the elimination of
2
three water molecules. However, another fragmentation seems to be possible. All of this is
discussed in Note 7 in the SM.
The 29Si NMR spectrum of the products of this reaction precipitated for 15 min showed
two broad signals at
−
67.0~
−
71.0 and
−
76.5~ 80.5 ppm, characteristic of the Ph(HO)SiO
−
and PhSiO1.5 fragments, respectively, with the integral intensity ratio of 1:5. This agreed
well with the results of the PI APCI mass spectrum.
The thermal self-condensation of compound 3 was performed in “pseudo”-equilibrium
conditions (under atmospheric pressure) in a quartz flask with toluene as a solvent. The
◦
reaction was carried out at 110 C, and samples of the precipitates were taken for the
PI APCI analyses after 10, 20, 40, 60, and 120 min from the beginning of the reaction.
The 120 min spectrum is given in Figure 8a. Though the products turned out to be the
same, as in the case of compound 2, the abundances of their peaks and thus their contents
in the precipitates were rather different from those in the case of
2. All spectra did not
virtually contain peaks of initial compound (peaks at m/z 532 and 570 were present on the
3
background level only). However, peak groups beginning with the peak of the ion with
the nominal mass of 996 Da was strongly prevailing in abundance in all the spectra, while
the abundances of the other peaks in the spectra were significantly less. This indicated
that, in contrast to the case of species 2, the main product ought to be of a relatively lower
molecular mass. With that, in moving from the 10 min spectrum to the 20 min one, the rela-
tive abundances of the peaks due to the higher molecular mass products slightly increased

Molecules 2021, 26, 4383
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while, further, these abundances changed insignificantly (compare the spectra in Figure 8a
and Figure S5 in the SM).
Figure 8. PI APCI mass spectra of precipitates from the reaction mixtures of condensation: (
a
) of compound
3
conducted
◦
◦
in a quartz flask in toluene at 110 C for 120 min and (
20 min (See Note 8 in the SI).
b) of species
4
carried out in a quartz flask in anisole at 150 C for
1
Since compound
4 was poorly soluble in toluene, its condensation was performed in
other solvents. Figure 8b shows the PI APCI mass spectrum of the precipitate from the
◦
reaction mixture of the condensation of
4
in anisole at 150 C for 120 min. The picture
here was rather different from that of Figure 8a. Very small abundance peaks of the initial
hydrate at m/z 570 were detected. The main ions proved to be those of two dimers
of ; formed with the loss of 2H O and H O, both registered as their hydrates with the
4
4
2
2
nominal masses of 1086 and 1104 Da, respectively. Also present in the spectrum were ions
of species 13 and 14 (See Scheme 2), again detected as the hydrates with the nominal masses
1206 and 1224 Da.
The reaction of
4
in acetonitrile went even deeper at a lower temperature. Figure S6a
in the SM gives the PI-APCI mass spectrum of the precipitate obtained after the heating
◦
of the reaction mixture in a quartz flask at 75 C for 120 min. The main peaks turned
out to be of [M13 + H O] , [M + 2H O] , and [M + 2H O] radical cations with the
+•
8
+•
9
+•
2
2
2
nominal masses 1206, 1326, and 1464 Da, respectively. At that, as it was discussed above,
the last two ions, along with contributions from the dihydrates of species and formed
during the MS analysis, could contain contributions from the incompletely condensed
and from the reaction that occurred in the flask. When the reaction was prolonged up to
40 min, it again went slightly deeper, with peaks of [M + H O] radical cation increasing
8
9
8
9
7
+•
2
2
10
+•
11
+•
significantly in abundance. Also, noticeable peaks of [M + H O] and [M + H O]
2
2
were registered (Figure S6b).
Attempts to carry out the self-condensation of isomer
5 under “pseudo”-equilibrium
conditions using different solvents (toluene, anisole, or ditolylmethane) in molybdenum
◦
glass in the temperature range of 80–155 C for 30 h failed. No OSSO were detected by MS.
An abundant peak of starting isomer 5 was present only.

Molecules 2021, 26, 4383
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Scheme 2. The ways of formation of species 13 and 14 in the course of condensation of 4.
3. Materials and Methods
3.1. Materials
Phenyltrichlorosilane (1) was bought from a firm, abcr, Karlsruhe, Germany. Commercial
grade organic solvents (acetone, acetonitrile, toluene, ethanol, methylene chloride, anisole,
ditolylmethane, and tetrahydrofuran) were purified and dried (if necessary) according to
conventional procedures. Acetone-d and CD Cl were used without additional purification.
6
2
2
cis-cis-trans-(Tetrahydroxy)(tetraphenyl)cyclotetrasiloxane (compound
3) was synthe-
sized by a previously described procedure [28]. The fractional crystallization of a mixture

Molecules 2021, 26, 4383
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◦
of compounds
3
–
5
from a toluene:diethyl ether solution (1.0:1.0) gave
3
. M.p. 186~188 C,
29
R = 0.29 (TLC, eluent, diethyl ether:toluene = 1.0:1.0). Si NMR (acetone-d ,
δ
+•
/ppm):
f
6
3
−
70.05,
−
70.20, and
−
70.35 (all s, ratio 1:1:2). PI APCI-MS, m/z: 570 ([M + H O] ) and
2
3
−
NI APCI-MS, m/z: 551 ([M − H ]).
cis-trans-(Tetrahydroxy)(tetraphenyl)cyclotetrasiloxane (compound 4) was also syn-
thesized according to the previously described procedure [28]. The fractional crystalliza-
tion of a mixture of compounds
3
–
5
in a ratio of 0.15:0.50:0.35 from a toluene:diethyl
◦
ether solution (1.0:0.25) gave
4
with m.p. 219~222 C. R = 0.53 (TLC, eluent, diethyl
f
ether:toluene = 1.0:1.0). 29Si NMR (acetone-d , δ/ppm): −69.95 (s).
6
All trans-(tetrahydroxy)(tetraphenyl)cyclotetrasiloxane (compound 5) was obtained
according to the procedure reported in [28], including the fractional crystallization of a
mixture of compounds
solution. M.p. 248~250 C. R = 0.64 (TLC, eluent, diethyl ether:toluene = 1.0:1.0). Si NMR
3
–
5
in a ratio of 0.40:0.15:0.45 from a toluene:diethyl ether = 1.0:1.0
◦
29
f
(
acetone-d6,
δ
/ppm):
−
70.51 (s). Its structure was earlier confirmed by X-ray diffraction
analysis of a single crystal [10].
◦
Compound
6 was obtained by method [34]. M.p. 498 C, PI APCI-MS, m/z: 1050
6
+•
6
+•
[
M + H O] , 996 [(M + H O) − 3H O] (see Note 7 in the SM).
2
2
2
◦
Compound
7 was obtained by a protocol reported in [14]. M.p. 384–386 C, PI
7
+• 29
APCI-MS, m/z: 1566 [M + H O] . Si NMR (CD Cl , δ/ppm): −81.31(s), −84.79 (s).
2
2
2
3
.2. Measurements
29
Si NMR spectra were taken on Bruker AV-400 and AV-600 spectrometers (Bruker
◦
Corporation, Karlsruhe, Germany) in aceton-d or CD Cl solutions at 20 C.
6
2
2
The PI and NI APCI mass spectra were obtained on a Thermo Finnigan LCQ Ad-
vantage tandem dynamic mass spectrometer (Thermo Finnigun, San Jose, CA, USA). The
instrument was equipped with an octapole ion trap mass analyzer, a Surveyor MS pump,
and a nitrogen generator Schmidlin-Lab., model N2-Mistral-4 (Shmidlin-Lab, Neuheim,
Switzerland). Nitrogen was employed as the sheath and auxiliary gases. The temperature
◦
−1
of the vaporizer was 400 C, and the flow rate of acetonitrile was 350
µ
L min . The heated
µ
◦
capillary temperature was 150 C; the corona discharge current was 5
A. Samples were
dissolved in acetonitrile and introduced into the ion source through a Reodyne injector
with a 5 L loop. The program Xcalibur, version 1.3 was used for the data collection
and treatment.
µ
3.3. Methods
3
.3.1. The Hydrolysis–Condensation of Phenyltrichlorosilane (1)
◦
A solution of compound
under stirring to a mixture of water and ice (1:1), 270 g (taken in an amount that was
necessary to obtain the required CHCl = 0.26 mol L after the complete hydrolysis of 1).
1, 5.2 g (0.025 mol) in 15 mL of acetone, was added at 2~4 C
−
1
◦
The mixture was then placed into a fridge operated at 4 C. Products precipitated from
the solution in time. The precipitates were isolated after several time periods and their
PI APCI mass spectra obtained. Each precipitate was dissolved in diethyl ether; the
ether layer was separated, washed with water until the neutral reaction of washing water,
29
and dried over Na SO that was then removed. The Si NMR spectrum was recorded.
2
4,
Ether was evaporated, the precipitate was washed with benzene to remove the impurities
including other isomers of (tetrahydroxy)(tetraphenyl)cyclotetrasiloxane which could
be present in negligible amounts only according to the 2 Si NMR spectrum. All the
9
precipitates collected up to 240 h were combined to give 2.52 g of compound
2
(73.6%).
◦
29
+•
M.p. 178~180 C, R = 0.05 (TLC, eluent, diethyl ether:toluene = 1:1). Si NMR spectrum
f
2
(acetone-d6,
δ
/ppm): −69.79 (s). PI APCI-MS, m/z: 570 ([M + H O] ). The molecular
2
structure of compound 2 was earlier confirmed by X-ray powder diffraction [31].
The reactions at the other values of CHCl were implemented in a similar fashion.

Molecules 2021, 26, 4383
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3
.3.2. General Procedure of the Self-Condensation of Isomers 2–4 under
“
Pseudo”-Equilibrium Conditions (under Atmospheric Pressure)
The corresponding compound ( , or ), 55~75 mg, was dissolved in one of the
2
,
3
4
solvents (toluene, anisole, or acetonitrile) taken in the amounts to obtain a 30% solution.
A quartz or molybdenum glass flask equipped with a Dean–Stark trap was vacuumized
and filled with argon by a triple procedure. The above solution was transferred into it and
◦
heated with stirring with a magnetic stirrer at 75, 110, 130, or 150 C for several h. Samples
of the precipitates formed and of the solutions were analyzed at several time points of
the reaction by PI APCI-MS and 29Si NMR spectroscopy. If there were no changes in the
composition of the products, the reaction was stopped, the solvent was removed, and the
products were washed with benzene, analyzed, recrystallized, and analyzed again.
4
. Conclusions
The results obtained showed that the acidity of the water-acetone solutions affected
the rate of the hydrolysis–condensation reaction of phenyltrichlorosilane ( ) and the yields
was obtained as
the main product of reaction whose yield increased with the increase in CHCl
This result differed from the results of the analogous reactions of m-tolylSiCl m-ClPhSiCl ,
1
, 2
−
1
of the products. In the concentration range of CHCl = 0.032~0.26mol L
.
,
3
3
and
α-naphtylSiCl published earlier [26] since some products of other types were obtained
3
by these reactions, e.g., cis-trans-(tetrahydroxy)(tetra-m-chlorophenyl)cyclotetrasiloxane in the
case of m-ClPhSiCl , and trans-1,1,3,3-tetrahydroxy-1,3-di-
α
-naphtyldisiloxane in the case
3
of α-naphtylSiCl3.
For further study, isomers
3, 4, and 5 were obtained by rearrangement of isomer 2
when HCl was added to its solution in acetone.
It was shown that, in “pseudo”-equilibrium conditions (under atmospheric pressure),
◦
the self-condensations of isomer
2
in toluene in quartz or molybdenum glass flasks at 110 C
◦
or in anisole in a molybdenum glass flask at 130 C, and of isomer
3 in toluene in a quartz
and uncompleted cage-like compounds
◦
flask at 110 C, led to completed Ph-T8
,10,12,14
Ph-T10,12OSi(HO)Ph. The starting reagents
2 and 3 were already absent after 5 min. In the
case of compound in toluene and in a quartz flask, peaks corresponding to compound
2
Ph-T proved to be prevailing in the PI APCI mass spectra taken at the beginning stages of
8
the reaction, whereas those of Ph-T10,12,14 were less abundant. The situation changed in
time and the last-mentioned ones became more abundant, with those of Ph-T12 becoming
predominant. With isomer
remained the major one during the entire reaction. The reaction of
glass flask was characterized by greater amounts of Ph-T12 in the mixture and the presence
of small amounts of Ph-T . As was underlined above, this might be caused by the catalysis
3, the products turned out to be the same, however, Ph-T8
2
in a molybdenum
14
by metal ions present in the molybdenum glass. The move to anisole as a solvent seemed
to result in a shift in the equilibrium towards uncompleted cage-like species, their peaks
in the PI APCI mass spectrum being more abundant. This appears to be due to a higher
temperature of the reaction.
The reactions of isomer 4 were performed in anisole or acetonitrile, since it was poorly
soluble in toluene. The main characteristic of the process in anisole was the formation of
dimers owing to the loss of one or two molecules of water. They and their derivatives,
compounds 13 and 14, proved to be the main products. In acetonitrile, the reaction went
deeper and, along with the dimeric species, compounds Ph-T10,12 and incomplete cage-like
species formed in significant amounts in spite of the lower reaction temperature.
Isomer
5 did not enter into the self-condensation reaction. The reason for this appears
to be that it dissolved significantly less in the above solvents than
another type of hydrogen bonds in it [10].
4, maybe owing to
Supplementary Materials: The following are available online. Notes 1–8. Figure S1: APCI mass
spectra of compound : (a) recorded in the PI mode, (b) recorded in the NI mode when the analyte
was essentially diluted by acetonitrile. Figure S2: PI APCI mass spectrum of the precipitate from the
reaction mixture of the self-condensation of compound carried out in a quartz flask in toluene at
3
2

Molecules 2021, 26, 4383
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◦
10 C for 45 min. Figure S3: PI-APCI mass spectrum of the precipitate from the reaction mixture
1
of self-condensation of compound
2
carried out in a molybdenum glass flask in toluene solution at
◦
1
10 C for 120 min. Figure S4: PI APCI mass spectrum of a mixture of compounds precipitated from
the reaction mixture after the condensation of species
glass flask at 130 C for 15 min. Figure S5: PI APCI mass spectrum of the precipitate from the
2 was carried out in anisole in a molybdenum
◦
◦
reaction mixture of the compound
3
condensation conducted in a quartz flask in toluene at 110 C for
1
0 min. Figure S6: PI APCI mass spectra of samples of the precipitates from the reaction mixture of
◦
compound
4 condensation conducted in acetonitrile in a quartz flask at 75 C: (a) taken after 120 min
and (b) taken after 240 min.
Author Contributions: N.N.M. and I.M.P. conceived, designed, and carried out experiments; N.S.I.
monitored the hydrolysis–condensation reactions of phenyltrichlorosilanes and the thermal con-
densation of (tetrahydroxy)(tetraphenyl)cyclotetrasiloxanes by APCI-MS; Y.I.L. analyzed the APCI
mass spectra; N.N.M. and Y.I.L. wrote the article. All authors have read and agreed to the published
version of the manuscript.
Funding: This research was funded by the RFBR (Grant No. 16-03-00389). The 29Si NMR studies
were performed with the financial support from the Ministry of Science and Higher Education of
the Russian Federation using the equipment of the Center for molecular composition studies of
INEOS RAS.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: All necessary data are given in the article.
Conflicts of Interest: The authors declare no conflict of interest.
Sample Availability: Samples of the compounds are not available from the authors.
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