Dimethoxymethylphenylsilane: Conformations and Binary Mixture Properties

Dimethoxymethylphenylsilane is an important organosilicon compound. Its molecule contains silicon atoms, methoxy groups, methyl groups, and phenyl groups, combining reactivity with aromatic properties. It is commonly prepared by the alcoholysis of methylphenyl dichlorosilane with methanol. Industrially, dimethoxymethylphenylsilane is used as a structure modifier for silicone rubber, a crosslinking agent for silicone polymers, and a synthetic monomer. It enhances materials’ resistance to high and low temperatures, as well as their insulation and radiation resistance, and is widely used in the chemical, electronics, and aerospace industries.

Conformations of dimethoxymethylphenylsilane

A great deal of attention has been paid to the systematic study of the conformations of molecules containing adjacent polar bonds, such as carbohydrates, organic phosphates, acetals and ketals. One of the motivations for such studies has been the realization that the reactivity of these molecules depends largely on their conformations. Therefore a program was launched in our laboratory to study the anomeric effect in silicon systems. Trimethoxymethylsilane (TMMS), dimethoxymethylsilane (DMMS) and dimethoxydimethylsilane (DMDMS) were studied using matrix isolation infrared spectroscopy and ab initio computations. The results on the conformations of dimethoxymethylphenylsilane will be discussed in this paper. DMMPS (98%, Lancaster), without further purification, was taken in a sample bulb and treated as described below, before every experiment. We realized during these studies, that dimethoxymethylphenylsilane undergoes hydrolysis, which was evident from the appearance at 1034 cm−1 of the feature due to methanol, one of the products of hydrolysis. To minimize this impurity, the sample was chilled to a low temperature (such as −30 °C), and pumped for several hours to remove the volatile methanol. The sample was then subjected to several freeze–pump–thaw cycles. This procedure was repeated every time the matrix gas/DMMPS mixture was prepared.[1]

It can be noted that the lowest energy conformer has a dipole moment of ∼0.5 D. TT conformer has the largest dipole moment value of ∼2.3 D. Based on the computations, which indicated the higher energy conformers to contribute about 11% to the overall population at room temperature, the net dipole moment of dimethoxymethylphenylsilane, weighted for the population of the different conformers, was computed to be 0.8 D. No reports are available in the literature for comparison. Dimethoxymethylphenylsilane was trapped in Ar and N2 matrixes. Supported by ab initio computations, the spectral features were assigned to various vibrational modes of DMMPS. The room temperature effusive source spectrum agrees well with the computed spectrum of the lowest energy conformer, which was indicated by our computations to have G±G∓ structure. Conformers with G−G−, G+T, GT, G+G+ and TT structures were also computationally located on the potential energy surface but would have very little contribution to the room temperature population to be of any experimental significance. It is clear from this work that anomeric effect in silicon systems appear to be important enough to determine that G±G∓ structure to be the lowest energy conformer in dimethoxymethylphenylsilane. The relative ordering of the other conformers appears to be due to the operation of both anomeric and steric effects.

Binary systems of dimethoxymethylphenylsilane with dimethyldimethoxysilane

One general class of monomers and oligomers with a large variety of organic functionalization, called alkoxysilanes, were identified early by researchers as excellent coupling agents, a material which assists in adhesive bonding between dissimilar surfaces, allowing for better bulk and interface properties. In continuation of our study on mixing and excess properties of binary mixtures contain alkoxysilanes, the density and refractive index were determined for four binary mixtures of dimethoxymethylphenylsilane with dimethyldimethoxysilane, dimethyldiethoxylsilane, methylvinyldiethoxysilane and ethenyltrimethoxysilane at different temperatures T = (298.15, 303.15, 308.15, 313.15 and 318.15) K and atmospheric pressure. In addition, the isobaric coefficient of thermal expansion, excess molar volume , the deviations in refraction indices , molar refractions and the deviations in molar refraction  for these binary systems were calculated and correlated using these data. The densities for the mixtures of {dimethoxymethylphenylsilane (1) + dimethyldimethoxysilane (2)} as a function of mole fractions and temperature are shown. The density of the mixtures decreased with temperature for each composition. Rodríguez and Brennecke reported that the densities do not decrease linearly with temperature. Therefore, a second-order polynomial was used to correlate the density with temperature and provide a significantly better fit (0.99983 ⩽ R2 ⩽ 1 and 6.53 × 10–14 ⩽ σ ⩽ 4.51 × 10–5).[2]

References

[1]V. Kavitha ,  K. S. V. (2009). Conformations of dimethoxymethylphenylsilane: A matrix isolation infrared and ab initio study. Journal of Molecular Structure, 920 1, Pages 355-362. https://doi.org/10.1016/j.molstruc.2008.11.025

[2]Yuqian Hu. (2017). Excess molar volume along with refractive index for binary systems of dimethoxymethylphenylsilane with dimethyldimethoxysilane, dimethyldiethoxylsilane, methylvinyldiethoxysilane and ethenyltrimethoxysilane. Journal of Chemical Thermodynamics, 109, Pages 82-90. https://doi.org/10.1016/j.jct.2016.10.033