A Study of the Influence of the HCl Concentration on the Composition and Structure of (Hydroxy)Arylsiloxanes from the Hydrolysis–Condensation Reaction of Aryltrichlorosilanes

The hydrolysis–condensation reactions of m-tolyl, m-chlorophenyl, and α-naphtyl-trichlorsilanes, (1, 2, and 3, respectively) in water-acetone solutions were examined for how they were influenced by the change in the concentration of HCl (CHCl). The composition of the products was monitored by 29Si NMR spectroscopy and atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The acidity of the medium was shown to affect the yields of the products, and so, what products were formed. For 3, e.g., APCI-MS showed peaks of α-naphtyl-T8 and α-naphtyl-T10 as the most abundant in the spectra taken after 48 and 240 h for the reaction conducted at CHCl = 0.037 mol L−1. Unlike this, at CHCl = 0.15 mol L−1, those peaks were of [α-naphtyl(HO)2SiO]2(α-naphtyl)(HO)Si and/or [α-naphtyl(HO)Si]3, [α-naphtyl(HO)Si]4,5, and α-naphtyl-T8 after 192 h. However, at both CHCl values, the main product (and an intermediate) after 24 h was trans-1,1,3,3-tetrahydroxy-1,3-di-α-naphtyldisiloxane. It was isolated and its structure established by 1H-, 29Si-NMR, and X-ray powder diffraction.


Introduction
Organosilicon chemistry is a developing area of chemistry. Organosilsesquioxanes are probably among the most important compounds within the whole family of organosilicon derivatives. Polyhedral oligomeric silsesquioxanes with mono and multifunctional groups or with organic groups of different structures are important building blocks for the obtainment of electroluminescent, electrochromic, organic optoelectronic materials, and molecules capable of tunable surface reactions. They are also used as building blocks for hybrid nanocomposites because of their nanometric size [1][2][3][4]. Polyorganosilsesquioxanes (POSSO) can be attributed to hybrid polymeric materials in which macromolecules with an inorganic siloxane backbone are framed by side organic groups R [5]. Depending on the order of the T-linking, polymer molecules with different stereoregularity of the cyclolinear chain, polyhedral framework molecules with different degrees of completeness, and The synthesis of isomers of organocyclosiloxanes by different methods is of interest not only because they can be initial blocks for the obtainment of stereoregular cyclolinear polyorganosilsesquioxanes [35], but these isomers can also be modified by the addition of side mesogenic groups to give isomeric liquid crystal (LC) compounds. This provides possibility to study the influence of the stereoisomeric structures of these species on the type of packing in the LC state [36].
All of this demonstrates that in spite of the fact that there have been publications on the hydrolysis of organotrichloro-, organotrialkoxysilanes and the condensation of their hydrolysates in the presence of acids and bases in different solvents or in aqueous solution, the mechanism of the process is not yet properly defined. It is especially because of the insufficient information on the structures of intermediates in these reactions. Our previous study of the polycondensation of (tetrahydroxy)(tetraaryl)cyclotetrasiloxanes showed that the polycondensation in the presence of montmorillonite produced polymers with a greater M w than in the case of its absence. It also showed mass spectrometry to be a good tool for detecting intermediates and for their identification [37]. It is clear and comes from the above that the results of the hydrolysis-condensation reactions of organotrichlorosilanes should depend on the reaction conditions, and in particular, on the acidity of the reaction mixture. Taking this in account we undertook a study of the hydrolysis-condensation reactions of three organotrichlorosilanes conducted at different acidities of the reaction mixtures, monitoring the processes with positive ion mode atmospheric pressure chemical ionization mass spectrometry (PI APCI-MS) and 29 Si-NMR spectroscopy.

Results and Discussion
As aforesaid, the article deals with three substituted aryltrichlorosilanes, m-tolyl-, m-chlorophenyland α-naphthyltrichlorosilanes (1, 2, and 3, respectively), and their hydrolysis-condensation reactions in water-acetone media at different dilutions, and thus, different acidities of the medium. These organotrichlosilanes were chosen for the study since 1 and 2 had the substituents at the silicon atoms with close Van der Waals volumes, with different electronic properties. The substituent in compound 3 possesses the larger Van der Waals volume. From all of this, it could be anticipated that products of their reactions would be different. The reactions were conducted with the concentrations of HCl (C HCl ) between 0.032 and 0.40 mol L −1 at 4 • C, and the yields of the products were determined in the interval of 24-720 h (see Note 1 in the Supplementary Materials (SM)). Figure 1 shows these yields of the products from the reaction of 1 that precipitated from the solution depending on the reaction time (see Note 2 in the SM). As can be seen from Figure 1, the rate of the condensation of 1 and final yields of the products decreased with the decrease in acidity.
The synthesis of isomers of organocyclosiloxanes by different methods is of interest not only because they can be initial blocks for the obtainment of stereoregular cyclolinear polyorganosilsesquioxanes [35], but these isomers can also be modified by the addition of side mesogenic groups to give isomeric liquid crystal (LC) compounds. This provides possibility to study the influence of the stereoisomeric structures of these species on the type of packing in the LC state [36].
All of this demonstrates that in spite of the fact that there have been publications on the hydrolysis of organotrichloro-, organotrialkoxysilanes and the condensation of their hydrolysates in the presence of acids and bases in different solvents or in aqueous solution, the mechanism of the process is not yet properly defined. It is especially because of the insufficient information on the structures of intermediates in these reactions. Our previous study of the polycondensation of (tetrahydroxy)(tetraaryl)cyclotetrasiloxanes showed that the polycondensation in the presence of montmorillonite produced polymers with a greater Mw than in the case of its absence. It also showed mass spectrometry to be a good tool for detecting intermediates and for their identification [37]. It is clear and comes from the above that the results of the hydrolysis-condensation reactions of organotrichlorosilanes should depend on the reaction conditions, and in particular, on the acidity of the reaction mixture. Taking this in account we undertook a study of the hydrolysis-condensation reactions of three organotrichlorosilanes conducted at different acidities of the reaction mixtures, monitoring the processes with positive ion mode atmospheric pressure chemical ionization mass spectrometry (PI APCI-MS) and 29 Si-NMR spectroscopy.

Results and Discussion
As aforesaid, the article deals with three substituted aryltrichlorosilanes, m-tolyl-, mchlorophenyl-and α-naphthyltrichlorosilanes (1, 2, and 3, respectively), and their hydrolysiscondensation reactions in water-acetone media at different dilutions, and thus, different acidities of the medium. These organotrichlosilanes were chosen for the study since 1 and 2 had the substituents at the silicon atoms with close Van der Waals volumes, with different electronic properties. The substituent in compound 3 possesses the larger Van der Waals volume. From all of this, it could be anticipated that products of their reactions would be different. The reactions were conducted with the concentrations of HCl (CHCl) between 0.032 and 0.40 mol L −1 at 4 C, and the yields of the products were determined in the interval of 24-720 h (see Note 1 in the Supplementary Materials (SM)). Figure  1 shows these yields of the products from the reaction of 1 that precipitated from the solution depending on the reaction time (see Note 2 in the SM). As can be seen from Figure 1, the rate of the condensation of 1 and final yields of the products decreased with the decrease in acidity.
.   Three groups of signals were observed in these spectra of the products obtained at CHCl = 0.40 and 0.15 mol L −1 : at 61.0 to 62.0; 69.3 to 71.3; and 78.5 to 79.5 ppm. They coincided very closely with those from the 29 Si NMR spectra of phenylsiloxane products obtained by the hydrolysiscondensation of PhSiCl3 at CHCl = 0.35 mol L −1 [16]. Based on the results of this study, we attributed the above signals to compounds with two OH groups at the silicon atoms, one group, and no groups, respectively (see Note 3 in the SM). In the 29 Si NMR spectra of m-tolylcyclosiloxane products obtained at CHCl = 0.054 and 0.038 mol L −1 , two singlets at −70.05 and −70.43 ppm, and weak signals in the region of −78.5 to 79.5 ppm were present, while no signals in the region of 61.0 to 62.0 ppm were detected. In general, all spectra evidenced that the main products precipitated from the reaction mixtures up to 48 h were those, most, if not all of which, were of the second type; namely, containing one free OH group at each silicon atom. Figure 3 presents the dynamics of the 29 Si NMR spectra of m-tolylcyclosiloxane products separated from a water-acetone solution for the reaction of 1 conducted at CHCl = 0.054 mol L −1 . In the spectrum recorded after 48 h, as already mentioned, the singlets were registered at −70.05 and −70.43 ppm. According to [35][36][37], they had to belong to all cis-(tetrahydroxy)(tetra-mtolyl)tetracyclosiloxane (4, downfield signal) and the cis-trans-cis-isomer (upfield signal). In the course of the further reaction, the upfield signal decreased and almost completely vanished after 475 h. This indicated that the cis-trans-cis-isomer likely graded into the all cis-isomer 4 in the course of the reaction. However, an alternative yet exists: if the cis-trans-cis-isomer was less soluble than all cisisomer, it was probably deposited from the reaction mixture to a significantly greater extent than the latter to the point of its absence in the mixture, and thus, in the precipitate. The signals in the region of 78.5 to 79.5 ppm were virtually absent. All of this evidenced that the polycondensation did not take place to any significant extent and the final product was the abovementioned all-cis-isomer 4. Three groups of signals were observed in these spectra of the products obtained at C HCl = 0.40 and 0.15 mol L −1 : at −61.0 to −62.0; −69.3 to −71.3; and −78.5 to −79.5 ppm. They coincided very closely with those from the 29 Si NMR spectra of phenylsiloxane products obtained by the hydrolysis-condensation of PhSiCl 3 at C HCl = 0.35 mol L −1 [16]. Based on the results of this study, we attributed the above signals to compounds with two OH groups at the silicon atoms, one group, and no groups, respectively (see Note 3 in the SM). In the 29 Si NMR spectra of m-tolylcyclosiloxane products obtained at C HCl = 0.054 and 0.038 mol L −1 , two singlets at −70.05 and −70.43 ppm, and weak signals in the region of −78.5 to −79.5 ppm were present, while no signals in the region of −61.0 to −62.0 ppm were detected. In general, all spectra evidenced that the main products precipitated from the reaction mixtures up to 48 h were those, most, if not all of which, were of the second type; namely, containing one free OH group at each silicon atom. Figure 3 presents the dynamics of the 29 Si NMR spectra of m-tolylcyclosiloxane products separated from a water-acetone solution for the reaction of 1 conducted at C HCl = 0.054 mol L −1 . In the spectrum recorded after 48 h, as already mentioned, the singlets were registered at −70.05 and −70.43 ppm. According to [35][36][37], they had to belong to all cis-(tetrahydroxy)(tetra-m-tolyl)tetracyclosiloxane (4, downfield signal) and the cis-trans-cis-isomer (upfield signal). In the course of the further reaction, the upfield signal decreased and almost completely vanished after 475 h. This indicated that the cis-trans-cis-isomer likely graded into the all cis-isomer 4 in the course of the reaction. However, an alternative yet exists: if the cis-trans-cis-isomer was less soluble than all cis-isomer, it was probably deposited from the reaction mixture to a significantly greater extent than the latter to the point of its absence in the mixture, and thus, in the precipitate. The signals in the region of −78.5 to −79.5 ppm were virtually absent. All of this evidenced that the polycondensation did not take place to any significant extent and the final product was the abovementioned all-cis-isomer 4. Molecules 2019, 24, x FOR PEER REVIEW 5 of 18 The above results were in good accordance with those of TLC in a mixture of toluene:ether = 1.0:0.75 as an eluent. Two spots with Rf = 0.05 and 0.50 were observed for the 48 and 120 h products, while only a single spot with Rf = 0.05 was for the 475 h product.
Another piece of support came from the PI APCI mass spectrum of the precipitate separated from the reaction mixture after 120 h that displayed the hydrates of the molecular ions of 4 and, apparently, its cis-trans-cis-isomer at m/z 626 ( Figure 4). Water obviously added in the mass spectrometer, as shown by the previously recorded mass spectra of similar compounds [37] and by the 29 Si NMR spectrum (Figure 3b), attesting to the lack of the second OH group at the silicon atoms (see Note 4 in the SM). The mass spectra of the precipitates separated from the 48 and 475 h reaction mixtures were similar. This method was also used to determine the composition of products of the hydrolysiscondensation reaction of silane 1 performed at CHCl = 0.40 mol L −1 (Note 5 in the SM). Figure 5 depicts the PI APCI mass spectrum of a mixture of hydrolysis-condensation products of compound 1 from the reaction conducted at CHCl = 0.40 mol L −1 for 24 h. A great number of peaks in the mass spectrum show that the products of the hydrolysis-condensation reaction of 1 included hydroxy(m-tolyl)cyclosiloxanes with a single tetracyclosiloxane ring, with double fused rings, and also polyhedral structures with different completeness. When the reaction was conducted for 48 h, the mass spectrum changed drastically. The main products turned out to be compound 4 and its cis- The above results were in good accordance with those of TLC in a mixture of toluene:ether = 1.0:0.75 as an eluent. Two spots with R f = 0.05 and 0.50 were observed for the 48 and 120 h products, while only a single spot with R f = 0.05 was for the 475 h product.
Another piece of support came from the PI APCI mass spectrum of the precipitate separated from the reaction mixture after 120 h that displayed the hydrates of the molecular ions of 4 and, apparently, its cis-trans-cis-isomer at m/z 626 ( Figure 4). Water obviously added in the mass spectrometer, as shown by the previously recorded mass spectra of similar compounds [37] and by the 29 Si NMR spectrum ( Figure 3b), attesting to the lack of the second OH group at the silicon atoms (see Note 4 in the SM). The mass spectra of the precipitates separated from the 48 and 475 h reaction mixtures were similar.  The above results were in good accordance with those of TLC in a mixture of toluene:ether = 1.0:0.75 as an eluent. Two spots with Rf = 0.05 and 0.50 were observed for the 48 and 120 h products, while only a single spot with Rf = 0.05 was for the 475 h product.
Another piece of support came from the PI APCI mass spectrum of the precipitate separated from the reaction mixture after 120 h that displayed the hydrates of the molecular ions of 4 and, apparently, its cis-trans-cis-isomer at m/z 626 ( Figure 4). Water obviously added in the mass spectrometer, as shown by the previously recorded mass spectra of similar compounds [37] and by the 29 Si NMR spectrum (Figure 3b), attesting to the lack of the second OH group at the silicon atoms (see Note 4 in the SM). The mass spectra of the precipitates separated from the 48 and 475 h reaction mixtures were similar. This method was also used to determine the composition of products of the hydrolysiscondensation reaction of silane 1 performed at CHCl = 0.40 mol L −1 (Note 5 in the SM). Figure 5 depicts the PI APCI mass spectrum of a mixture of hydrolysis-condensation products of compound 1 from the reaction conducted at CHCl = 0.40 mol L −1 for 24 h. A great number of peaks in the mass spectrum show that the products of the hydrolysis-condensation reaction of 1 included hydroxy(m-tolyl)cyclosiloxanes with a single tetracyclosiloxane ring, with double fused rings, and also polyhedral structures with different completeness. When the reaction was conducted for 48 h, the mass spectrum changed drastically. The main products turned out to be compound 4 and its cis- This method was also used to determine the composition of products of the hydrolysis-condensation reaction of silane 1 performed at C HCl = 0.40 mol L −1 (Note 5 in the SM). Figure 5 depicts the PI APCI mass spectrum of a mixture of hydrolysis-condensation products of compound 1 from the reaction conducted at C HCl = 0.40 mol L −1 for 24 h. A great number of peaks in the mass spectrum show that the products of the hydrolysis-condensation reaction of 1 included hydroxy(m-tolyl)cyclosiloxanes with a single tetracyclosiloxane ring, with double fused rings, and also polyhedral structures with different completeness. When the reaction was conducted for 48 h, the mass spectrum changed drastically. The main products turned out to be compound 4 and its cis-trans-cis-isomer registered as radical cations of their hydrates with the nominal mass of 626 Da, and [m-tolyl(OH)SiO] 8 (5a) and/or {[m-tolyl(OH)SiO] 3 -m-tolylSiO 1.5 } 2 (5b) were also detected as a hydrate and a dihydrate, respectively, both with the 1234 Da nominal mass. The peaks of all other products were of minor abundances ( Figure 6).  Figure 6).       A similar spectrum was recorded for the precipitate obtained after 120 h in which the relative abundance of the peaks of 5 increased pronouncedly, however ( Figure S1 in the SM).
When the concentration of HCl was reduced to 0.15 mol L −1 , the mass spectrum recorded after 48 h from the beginning of the reaction showed an abundant peak of compound 4 and its isomer, the peaks of other products being significantly less abundant or even of minor abundances ( Figure S2 in the SM).
On the basis of the PI APCI mass and 29 Si NMR spectra of m-tolylcyclosiloxane products, it is possible to present Scheme 1 of the hydrolysis-condensation reaction of m-tolylSiCl 3 (1) in water-acetone media. The scheme displays the formation of the main products and intermediates. For other products and intermediates and the mass numbers of all species detected, see Figure 5, Figure 6, Figures S1 and S2.   The precipitate obtained from the reaction at C HCl = 0.054 mol L −1 up to and including the 475 h time point was recrystallized from diethyl ether to furnish compound 4 in 30.8% yield.
The hydrolysis-condensation reaction of m-chlorophenyltrichlorosilane (2) was carried out at 4 • C in water-acetone solutions at C HCl = 0.032-0.056 mol L −1 . Figure 7 presents the yields of reaction products as a function of time. It shows that the final yield of the products increased with the increase in C HCl .
48 h from the beginning of the reaction showed an abundant peak of compound 4 and its isomer, the peaks of other products being significantly less abundant or even of minor abundances ( Figure S2 in the SM).
On the basis of the PI APCI mass and 29 Si NMR spectra of m-tolylcyclosiloxane products, it is possible to present Scheme I of the hydrolysis-condensation reaction of m-tolylSiCl3 (1) in wateracetone media. The scheme displays the formation of the main products and intermediates. For other products and intermediates and the mass numbers of all species detected, see Figures 5,6, S1, and S2.
The precipitate obtained from the reaction at CHCl = 0.054 mol L −1 up to and including the 475 h time point was recrystallized from diethyl ether to furnish compound 4 in 30.8% yield.
The hydrolysis-condensation reaction of m-chlorophenyltrichlorosilane (2) was carried out at 4 °C in water-acetone solutions at CHCl = 0.032-0.056 mol L −1 . Figure 7 presents the yields of reaction products as a function of time. It shows that the final yield of the products increased with the increase in CHCl.    (Figure 2, traces a and b). It should also be highlighted here, that in the case of CHCl = 0.032 mol L −1 , the spectrum of m-chlorophenylcyclosiloxane products displayed two singlets (on the background of a very small broad signal) at −71,3 to −72.3 ppm and an insignificant broad signal at −80.0 to −82.2 ppm Thus, the increase of CHCl to 0.056 mol L −1 led to further condensation of mchlorophenylsiloxane products with the formation of poly-m-chlorophenylsilsesquioxanes, as inferred from the appearance of the noticeable broad signal in the region −80.0 to −82.2 ppm. The signal was attributed to poly-m-chlorophenylsilsesquioxane with different conformational and configuration sequences of units that were inherited from the isomers of (tetrahydroxy)(tetra-mchlorophenyl)cyclotetrasiloxane that manifested themselves in the 29 Si NMR spectrum in the region of −71.3 to −72.3 ppm (Figure 8).
The 29 Si NMR spectrum of a mixture of products obtained after the 90 h reaction at CHCl = 0.032 −1  (Figure 2, traces a and b). It should also be highlighted here, that in the case of C HCl = 0.032 mol L −1 , the spectrum of m-chlorophenylcyclosiloxane products displayed two singlets (on the background of a very small broad signal) at −71,3 to −72.3 ppm and an insignificant broad signal at −80.0 to −82.2 ppm Thus, the increase of C HCl to 0.056 mol L −1 led to further condensation of m-chlorophenylsiloxane products with the formation of poly-m-chlorophenylsilsesquioxanes, as inferred from the appearance of the noticeable broad signal in the region −80.0 to −82.2 ppm. The signal was attributed to poly-m-chlorophenylsilsesquioxane with different conformational and configuration sequences of units that were inherited from the isomers of (tetrahydroxy)(tetra-m-chlorophenyl)cyclotetrasiloxane that manifested themselves in the 29 Si NMR spectrum in the region of −71.3 to −72.3 ppm (Figure 8).
The 29 Si NMR spectrum of a mixture of products obtained after the 90 h reaction at C HCl = 0.032 mol L −1 proved to be similar to that of the products from the 48 h reaction with the singlets retained in the original ratio. A similar 29 Si NMR spectrum was obtained for the precipitate taken after 48 h for the reaction carried out at C HCl = 0.047 mol L −1 . However, the spectrum for the 72 h reaction at C HCl = 0.056 mol L −1 displayed only the broad signal in the region of −78.5 to −81.8 ppm ( Figure S3 in the SM). The comparison of the data of the 29 Si NMR spectra in Figure 3 with the above results showed that at close values of the Van der Waals volumes of the m-tolyland m-chlorophenyl groups but with the different inductive effects of these substituents, the reactivities of the OH-groups of the corresponding intermediates, including hydroxyorganocyclotetrasiloxanes, in the presence of HCl, were different. It led to the formation of poly-m-chlorophenylsilsesquioxanes at a concentration of C HCl = 0.056 mol L −1 in the case of the m-chlorophenyl derivative, while the polycondensation did not occur for m-tolyl-one at virtually the same concentration of the acid (C HCl = 0.054 mol L −1 ).
The following should be mentioned about two singlets registered in the 29 Si NMR spectra in the region of −71.3 to −72.3 ppm. They can be ascribed to cis-trans-cis-(tetrahydroxy) (tetra-m-chlorophenyl)cyclotetrasiloxane (6a) (upfield signal) and its all cis-isomer (6b) (downfield signal) according to [31][32][33]. All of this found support in the TLC data. Earlier, we made the assignments of the R f values for four isomers of [Ph(OH)SiO] 4 based on the X-ray study of their synthesized liquid crystal derivatives [36]. These TLC values were later confirmed in another publication where X-ray single crystal determination of the all trans-isomer was performed and three singlets characteristic of the cis-cis-trans-isomer were registered in the 29 Si NMR spectrum [22]. The R f of 6a and 6b were close to those of the corresponding phenyl analogs.
A study of the hydrolysis-condensation reaction of α-naphtyltrichlorosilane (3) was carried out at C HCl = 0.37-0.037 mol L −1 in water-acetone solutions at 4 • C. Figure 9 shows the yields of α-naphthylsiloxane products depending on C HCl and the reaction time.
Molecules 2019, 24, x FOR PEER REVIEW 10 of 18 chlorophenyl)cyclotetrasilloxane (6a (24.9%) and 6b (19.0%)) that were characterized by 1 H and 29 Si-NMR spectra (see Section 3.2). A study of the hydrolysis-condensation reaction of α-naphtyltrichlorosilane (3) was carried out at CHCl = 0.37-0.037 mol L −1 in water-acetone solutions at 4 °C. Figure 9 shows the yields of αnaphthylsiloxane products depending on CHCl and the reaction time. The maximum yields of the products proved to be at CHCl = 0.37 mol L −1 . With the decrease of CHCl to a value of 0.037 mol L −1 , the yields decreased drastically. Figure 10 gives the 29 Si NMR spectra of α-naphtylsiloxane products obtained at CHCl = 0.37 and 0.15 mol L −1 ; for CHCl = 0.37 mol L −1 , two broad signals were observed in the regions of −59.0 to −59.3 and −66.4 to −69.1 ppm (Figure 10a). This means that a great number of siloxane products with one and two hydroxyl groups at the silicon atoms were present in this time precipitate. The decrease in CHCl to 0.15 mol L −1 led to a decrease in the rate of the condensation reaction of α- The maximum yields of the products proved to be at C HCl = 0.37 mol L −1 . With the decrease of C HCl to a value of 0.037 mol L −1 , the yields decreased drastically. Figure 10 gives the 29 Si NMR spectra of α-naphtylsiloxane products obtained at C HCl = 0.37 and 0.15 mol L −1 ; for C HCl = 0.37 mol L −1 , two broad signals were observed in the regions of −59.0 to −59.3 and −66.4 to −69.1 ppm (Figure 10a). This means that a great number of siloxane products with one and two hydroxyl groups at the silicon atoms were present in this time precipitate. The decrease in C HCl to 0.15 mol L −1 led to a decrease in the rate of the condensation reaction of α-naphtyltrihydroxysilane and 1,1,3,3-tetrahydroxy-1,3-di-α-naphtyldisiloxane, and two singlets at −61.34 and −60.68 ppm clearly manifested themselves in the region characteristic of siloxanes containing only RSi(OH) 2 fragments. Most likely, the singlets belonged to 1,1,3,3-tetrahydroxy-1,3-di-α-naphtyldisiloxane in different conformations. However, a broad signal at −69 to −71 ppm (region for products bearing one hydroxyl at each silicon atom) was detected, but with a significantly less intensity that in the case of C HCl = 0.37 mol L −1 . Interestingly, a signal of organocyclosiloxanes with no hydroxyl groups at −78.0 to −81.0 ppm was also observed but on the background level only. The same singlets were found for the case of C HCl = 0.037 mol L −1 , but in another ratio that produced a slight shift in their positions. In this case, other products in the precipitates were determined by PI APCI-MS ( Figure 11 and Figure S4). The maximum yields of the products proved to be at CHCl = 0.37 mol L −1 . With the decrease of CHCl to a value of 0.037 mol L −1 , the yields decreased drastically. Figure 10 gives the 29 Si NMR spectra of α-naphtylsiloxane products obtained at CHCl = 0.37 and 0.15 mol L −1 ; for CHCl = 0.37 mol L −1 , two broad signals were observed in the regions of −59.0 to −59.3 and −66.4 to −69.1 ppm (Figure 10a). This means that a great number of siloxane products with one and two hydroxyl groups at the silicon atoms were present in this time precipitate. The decrease in CHCl to 0.15 mol L −1 led to a decrease in the rate of the condensation reaction of αnaphtyltrihydroxysilane and 1,1,3,3-tetrahydroxy-1,3-di-α-naphtyldisiloxane, and two singlets at −61.34 and −60.68 ppm clearly manifested themselves in the region characteristic of siloxanes containing only RSi(OH)2 fragments. Most likely, the singlets belonged to 1,1,3,3-tetrahydroxy-1,3di-α-naphtyldisiloxane in different conformations. However, a broad signal at −69 to −71 ppm (region for products bearing one hydroxyl at each silicon atom) was detected, but with a significantly less intensity that in the case of CHCl = 0.37 mol L −1 . Interestingly, a signal of organocyclosiloxanes with no hydroxyl groups at −78.0 to −81.0 ppm was also observed but on the background level only. The same singlets were found for the case of CHCl = 0.037 mol L −1 , but in another ratio that produced a slight shift in their positions. In this case, other products in the precipitates were determined by PI APCI-MS ( Figure 11 and Figure S4).   The precipitates from the reactions of 3 conducted at C HCl = 0.037, 0.15, and 0.37 mol L −1 from several time points were isolated. Recrystallization of them from CH 3 CN gave white powders, each with m.p. 162 • C (compound 7; see below). Compound 7 was characterized by 1 H and 29 Si NMR. If in the 29 Si NMR spectra of compounds 4, 6a, and b were signals at −70.16, −71.63, and −71.89 ppm, respectively, for compound 7, the signals shifted downfield to −60.0-−61.0 ppm.
As aforesaid, the compositions of the unrecrystallized precipitates, obtained at several time points from the reaction conducted at C HCl = 0.037 mol L −1 , were determined by the PI APCI-MS. Figure 11 presents the mass spectrum of α-naphthylsiloxane compounds obtained when the reaction was carried out at C HCl = 0.037 mol L −1 for 24 h. Two main compounds were registered: 1,1,3,3-tetrahydroxy-1,3-di-α-naphtyldisiloxane (7 and probably, its other conformational isomers) as its (M + H − 2H 2 ) + ion with the nominal mass 391 Da (see below), and α-naphtyl-T 8 as the hydrate of its radical cation (nominal mass 1450 Da). Besides, small abundance peaks of ions of some other products were present in the spectrum, the monohydrate and the dihydrate of  Figure S4). Both spectra showed that in these precipitates the main products proved to be α-naphtyl-T 8 and α-naphtyl-T 10 registered again as the hydrates of their radical cations. With that, a small abundance ion peak of 7 at m/z 391 was still present in the former spectrum, while virtually absent in the latter one. The structures of other products formed in essentially less amounts and registered as the radical cations or their hydrates are depicted in the figure (Note 8 in the SM). A similar set of mass spectra was taken for the reaction implemented at C HCl = 0.15 mol L −1 . For the precipitate obtained from the reaction conducted for 24 h, a negative ion mode (NI APCI) mass spectrum was also obtained. The spectrum displayed an abundant ion peak of radical anion of 7 at m/z 394. This finding evidenced that the 391 Da ion in the PI APCI mass spectra (Figure 11and Figure  S4a) really belonged to species 7 in spite of its rather unusual type. Fragmentation of its protonated molecule with elimination of two hydrogen molecules was likely to have occurred, as an 'in-source collision-induced dissociation' process [38,39]. The PI APCI mass spectrum of the precipitate obtained after 192 h is depicted in the SM as Figure S5. This time, the main products turned out to be α-naphtyl-T 8 ; cyclosiloxanes [(α-naphtyl)Si(OH)O] 4,5 , registered as the hydrates of their radical cations (nominal masses 1450, 958, and 788, 770 Da, respectively); linear trisiloxane (α-naphtyl) 3 Si 3 (OH) 5 O 2 , registered as its radical cation and the monohydrate of the latter; and/or cyclosiloxane [(α-naphtyl)Si(OH)O] 3 , registered as both the monohydrate and the dihydrate (nominal masses 582 and 600 Da, respectively). Some other products giving small abundance peaks were also detected.
As mentioned above, the 24, 48, and 192 reaction time precipitates were recrystallized from acetonitrile to give a compound with a m.p. 162-164 • C (common yield 48%). The 1 H and 29 Si-NMR spectra (see Section 3.2) spoke in favor of the isolated compound being 1,1,3,3-tetrahydroxy-1,3-di-α-naphtyldisiloxane. Its structure (trans-isomer, 7) and the type of packing were revealed by X-ray powder diffraction analysis. The crystal data, data collection, and refinement parameters are given in Table 1. The molecular structure of 7 and a portion of the crystal packing prepared with mercury [40] are shown in Figure 12 and Figure S6 (in the SM), respectively. Therein, the diffraction profile after the final, bond-restrained Rietveld refinement is shown as Figure S7. naphtyl)3Si3(OH)5O2, registered as its radical cation and the monohydrate of the latter; and/or cyclosiloxane [(α-naphtyl)Si(OH)O]3, registered as both the monohydrate and the dihydrate (nominal masses 582 and 600 Da, respectively). Some other products giving small abundance peaks were also detected.
As mentioned above, the 24, 48, and 192 reaction time precipitates were recrystallized from acetonitrile to give a compound with a m.p. 162-164 °C (common yield 48%). The 1 H and 29 Si-NMR spectra (see Section 3.2) spoke in favor of the isolated compound being 1,1,3,3-tetrahydroxy-1,3-di-αnaphtyldisiloxane. Its structure (trans-isomer, 7) and the type of packing were revealed by X-ray powder diffraction analysis. The crystal data, data collection, and refinement parameters are given in Table 1. The molecular structure of 7 and a portion of the crystal packing prepared with mercury [40] are shown in Figures 12 and S6 (in the SM), respectively. Therein, the diffraction profile after the final, bond-restrained Rietveld refinement is shown as Figure S7.   In the crystal structure, molecule 7 is situated in the center of symmetry at (1/2, 1/2, 1/2). However, the molecule is not centrosymmetric because atom O1 is disordered over two positions ( Figure 12 (Table 2) which link the molecules into layers parallel to the bc plane ( Figure S6 in the SM). The search in the Cambridge Structural Database (ConQuest, version 1.21 [41]) for close molecules resulted in only one hit with refcode MOQMOU [25] that contains the molecule of 1,1,3,3-tetrahydroxy-1,3-bis(2-naphthyl)disiloxane included in the framework.
Scheme II. The hydrolysis-condensation reaction of compound 3.

Materials
Scheme 2. The hydrolysis-condensation reaction of compound 3.
Commercial grade organic solvents (acetone, acetone-d 6 , diethyl ether, benzene, and hexane) were cleaned and dried (if necessary) according to conventional procedures. Acetonitrile, acetonitrile-d 3 , and CDCl 3 were used without additional purification.

Methods
The 1 H and 29 Si NMR spectra were taken on Bruker AV-400 and AV-600 spectrometers (Bruker Corporation, Karlsruhe, Germany) in aceton-d 6 solutions at 20 • C.
The PI and NI APCI mass spectra were obtained with a Thermo Finnigan LCQ Advantage tandem dynamic mass spectrometer (Thermo Finnigan, 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 (Schmidlin-Lab, Neuheim, Switzerland). Both sheath and auxiliary gases were nitrogen. The temperature of the vaporizer was 400 • C; the flow rate of acetonitrile was 350 µL min −1 . The heated capillary temperature was 150 • C; the corona discharge current was 5 µA. Samples were dissolved in acetonitrile and introduced into the ion source through a Reodyne injector with a 5 µL loop. The program Xcalibur, version 1.3, was used for the data collection and treatment.
The molecular structure of compound 7 was confirmed by X-ray structure determination from powder data measured at room temperature on a diffractometer Huber G670 Guinier camera (Cu K α1 radiation, λ = 1.54059 Å) equipped with an imaging-plate detector. The powder pattern was indexed in the monoclinic unit cell parameters, and the crystal structure was solved with the use of simulated annealing technique [45] and refined with the program MRIA [46] following the known procedures described by us earlier [47,48]. The crystal data, data collection, and refinement parameters are given in Table 1. The molecular structure of 7 and a portion of the crystal packing prepared with mercury [40] are shown in Figure 12 and in Figure S6 of the SM, respectively.
General procedure. A solution of organotrichlorosilane (1 or 2, or 3) in acetone was added at 2-4 • C under stirring to a mixture of water and ice (1:1) taken in an amount that was necessary to get the required C HCl after the complete hydrolysis of the organotrichlorosilane. The mixture was then placed into a fridge operated at 4 • C. Products precipitated from the solution in time. The precipitates were isolated at several time periods. Each precipitate was dissolved in diethyl ether; the ether layer was separated, washed with water until the neutral reaction of washing water, and dried over Na 2 SO 4 . The solvent was then removed and the yield of the product mixture was determined by the equation: S p = 100m p M cl /m cl (M h − 18), where S p is the yield of precipitate in percent; m p -the mass of the precipitates deposited up to and including the specified time point; M cl -the molecular mass of the corresponding organotriclorosilane; m cl -its mass taken for the reaction; M h -the molecular mass of its hydrolysate; and 18-the molecular mass of water (see Note 1 in the SM and Figures 1, 7 and 9). The compositions of the precipitates were analyzed by APCI-MS, 1 H, and 29 Si NMR.

Conclusions
The results obtained showed that the acidity of the solutions affected the rate of the hydrolysis-condensation reaction of organotriclorosilanes and the yields of the products, and also, which products formed.
In the case of m-tolyltrichlorosilane (1), e.g., all cis-(tetrahydroxy)(tetra-m-tolyl)tetracyclosiloxane (4) was obtained as the main final product when the reaction was conducted at C HCl = 0.054 mol L −1 for 475 h. Meanwhile, a mixture containing many m-tolylcyclosiloxanes was separated from the 24 h reaction mixture, but APCI-MS showed two main peak groups corresponding to 4 and m-tolylcyclosiloxanes 5a and/or 5b when the reaction was carried out at C HCl = 0.40 mol L −1 for 48 and more hours.
When α-naphtyltriclorosilane (3) was reacted with C HCl = 0. 15 mol L −1 for 192 h, recrystallization of the combined precipitates obtained at 24, 48, and 192 time points from acetonitrile gave trans-isomer of 1,1,3,3-tetrahydroxy-1,3-di-α-naphtyldisiloxane (7) which was characterized by 1 H and 29 Si-NMR spectroscopy, and X-ray powder diffraction. The conformers of this compound should be the products of the first act of the condensation, and they were detected by PI APCI-MS as a peak at m/z 391 in the precipitates obtained in the cases of the reactions implemented at all values of the acidity employed. However, the corresponding disiloxanes were not found in the case of m-tolyltrichlorosilane (1) since they seemed to be more soluble than 7 and its stereoisomers, and thus, rapidly entered into the following condensation. As aforesaid, tetracyclosiloxane 4 was isolated instead.
The difference in products obtained at different acidities of the solutions was also observed in the case of 3. Thus, in the PI APCI mass spectrum obtained for the precipitates collected after 48 and 240 h when the reaction was carried out at C HCl = 0.037 mol L −1 , two main ion peak groups were found corresponding to the monohydrates of α-naphtyl-T 8 and α-naphtyl-T 10 , whereas in the case of C HCl = 0.15 mol L −1 after 192 h, the most abundant peaks turned out to be the ion peaks of four or five compounds [α-naphtyl(HO) 2  In summary, it should be pointed out that the use of both 29 Si NMR and APCI-MS proved to be a good tool for monitoring the hydrolysis-condensation reaction studied. We believe that it can be used for the investigation of other similar reactions.
Supplementary Materials: The following are available online. Notes 1-7. Figure S1: PI APCI mass spectrum of products from the hydrolysis-condensation reaction of compound 1 carried out in a water-acetone solution at C HCl = 0.40 mol L −1 for 120 h. Figure S2: PI APCI mass spectrum of products from the hydrolysis-condensation reaction of 1 carried out in a water-acetone solution at C HCl = 0.15 mol L −1 for 48 h. Figure S3: 29 Si NMR spectra of the precipitates deposited from the reaction mixtures of the hydrolysis-condensation reaction of 2 conducted at 4 • C: (a) at C HCl = 0.032 mol L −1 for 90 h and (b) at C HCl = 0.056 mol L −1 for 72 h. Figure S4: PI APCI mass spectra of products from the hydrolysis-condensation reaction of α-naphtyltrichlorosilane (3) carried out in water-acetone solutions with C HCl = 0.037 mol L−1 at 4 • C for: (a) 48 h and (b) 240 h. Figure S5: PI APCI mass spectrum of the precipitate collected from the reaction of species 3 conducted at 4 • C and C HCl = 0.15 mol L −1 for 192 h. Figure S6: A portion of the crystal packing of 7 viewed approximately along [011] and showing the hydrogen-bonded (thin blue lines) layers of the molecules with the naphthalene bicycles protruding in the opposite directions. Figure S7: The final Rietveld plot for 7. The experimental and difference (experimental minus calculated) diffraction profiles are shown as the black and red lines, respectively. The vertical blue bars correspond to the calculated positions of the Bragg peaks. The structure of compound 7 was registered in the database of the Cambridge Crystallographic Data Centre (CCDC) (http://www.ccdc.cam.ac.uk.") under the number 1867122. The data can be obtained free of charge from it.