Mass spectrometry in the characterization of reactive metal alkoxides

Abstract

Metal alkoxides are metal-organic compounds characterized by the presence of MOC bonds (M = metal). Their chemistry seems to be, in principle, relatively simple but the number of possible reactant species arising as a consequence of their behavior is very remarkable. The physico-chemical properties of metal alkoxides are determined by many different parameters, the most important ones being the electronegativity of the metal, the ramification of the ligand, and the acidity of the corresponding alcohol. Their reactivity makes them suitable and versatile candidates for many applications, including homogeneous catalysis, synthesis of new ceramic materials through the sol-gel process and, recently, also for Cultural Heritage. Metal alkoxides are characterized by a strong tendency to give clusters and/or oligomers through oxo-bridges. Mass spectrometry has been successfully employed for the characterization of metal alkoxides in the gas-phase. Electron ionization (EI) allowed the assessment of the molecular weight and of the most relevant decomposition pathways giving information on the relative bond strength of differently substituted molecules. On the other hand, information on the reactivity in solution of these molecules have been obtained by electrospray ionization (ESI)-matrix assisted laser desorption ionization (MALDI) experiments performed on their reaction products. These data were relevant to investigate the sol-gel process. In this review, these aspects are described and the results obtained are critically evaluated. © 2016 Wiley Periodicals, Inc. Mass Spec Rev.

Strontium Isopropoxide: A Highly Active Catalyst for the Ring‐Opening Polymerization of Lactide and Various Lactones

“…The dispersity decreased to values below 1.2 for monomer conversions above 50%, ruling out commonly observed transesterification processes as reason for this unusual polymerization behavior. One could speculate that catalyst rearrangements or oligomers with varying activity present in the reaction solution might cause this effect, which clearly requires extensive additional studies.…”

Kinetics of Alkoxysilanes and Organoalkoxysilanes Polymerization: A Review

“…The use of MS to study the hydrolysis and condensation of metal alkoxides (e.g., silicon alkoxide) was discussed previously [10]. In our work, we try to discuss the principles, which will help in using the technique, as well as TOF, which is not discussed in the mentioned publication.…”

“…Because the use of GC is limited by the volatility and thermal stability of the compounds, it is used to determine the silane itself or the hydrolysis and early stage condensation products. A good combination between the detectors and GC columns can be used to investigate the kinetics of silane polymerization, especially GC/MS, because it does the separation and identification (Figure 25) [4,10]. Yevchuk et al [38] used GC with a thermal conductivity detector (GC/TCD) to conduct kinetic studies of the hydrolysis and early stage condensation of TEOS, while Chen et al [36] used GC/MS and GC with a flame ionization detector (GC/FID) to study the kinetics of the formation of monodispersed silica particles after extracting the TEOS with n-heptane.…”

“…The GC/MS chromatograms of methyl triethoxysilane and its species in the presence of alcohol, water, and HCl. Reprinted with permission from [10]. Copyright John Wiley and Sons, 2016.…”

“…For a more general understanding of the sol-gel process, and a more specific understanding of the polymerization of alkoxysilanes, there are a number of texts and literature reviews, which cover developments in the sol-gel technique up to 1997 [4,5,6,7,8,9,10,11,12,13,14,15]. Although this review covers developments after 1997, we shall periodically refer to these works because of their importance in understanding the basics of the technique.…”