Igor V. Elmanovich

A biphase H2O/CO2 system as a versatile reaction medium for organic synthesis

We review activity on the usage of a biphase H2O/CO2 system in organic synthesis as a reaction medium of green chemistry. The formation of self-neutralizing carbonic acid in such a system eliminates the problem of salt disposal, typical for acid-catalyzed reactions with the usual mineral and organic acids. A large variety of different reactions to be performed in the biphase H2O/CO2 system are discussed in detail, including cyclization/cycloaddition, hydroformylation, hydrogenation, reduction, coupling, rearrangement, substitution, addition, halogenation, hydrolysis, oxidation and others. These reactions cover a significant part of modern organic synthesis. The main physical properties of carbonic acid being formed in the biphase H2O/CO2 system and their dependence on the temperature and pressure of saturating CO2 are analyzed. The problem with the search for the most optimal reaction conditions from the viewpoint of selection of appropriate pressure and temperature regions for the best yields and selectivity achievable is addressed in general. Comparison with formation and utilization of peroxycarbonic acids, alkylcarbonic acids and carbamic acids by means of saturation with pressurized CO2 of some other biphase systems is discussed in relationship to organic synthesis as well. The influence of a CO2 admixture on the unique properties of high temperature water, another promising green solvent, is also considered.

Hydrolytic polycondensation of diethoxydimethylsilane in carbonic acid

A new process for producing silicones based on chlorine-free reagents is suggested. Carbonic acid at elevated pressure and temperature is shown to be an effective reagent for converting alkoxysilane to silicones. The process conditions make it possible to control the ratio between linear and cyclic products.

Electrocatalysts for fuel cells synthesized in supercritical carbon dioxide

We applied the method of directly depositing an organometallic precursor from a solution in supercritical carbon dioxide on a dispersed carbon substrate surface followed by reduction to obtain a number of electrocatalytic materials in the form of nanoscale platinum particles on dispersed carbon supports (Vulcan XC72r carbon black, acetylene black, nanotubes). The synthesized materials persistently showed a monodisperse size distribution of platinum particles with an average diameter of 2–3 nm, regardless of the substrate nature, and a uniform distribution over the support surface. The synthesized electrocatalysts (ECs) were tested as part of an operating cathode electrode of a phosphoric acid fuel cell (FC) with a PBI matrix. In this case, the membrane-electrode assembly with this cathode showed current-voltage characteristics as good as the reference characteristics achieved with electrodes produced by BASF.

Organosilicon compounds in supercritical carbon dioxide: Synthesis, polymerization, modification, and production of new materials

The main promising opportunities for the advantageous combination of organosilicon compounds and supercritical carbon dioxide both as a solvent and as a reagent in chemical processes are analyzed. The main processes of polymerization and modification of polymer matrices that are performed in supercritical СО2 with the use of organosilicon materials of various types are outlined. Methods for the obtaining organosilicon polymers and polymer-inorganic composites and methods for the application of siloxane stabilizers in the dispersion polymerization of monomers in supercritical СО2 are described. Studies of the insertion of a СО2 molecule into Si–H, Si–N, and Si–O–Me bonds in reactions that feature exceptionally high chemical selectivity and afford a wide spectrum of products potentially useful for application in the chemistry of polymer materials are considered. It is shown that the silylation of surfaces of various types and morphologies in the medium of supercritical СО2 is a rapidly developing green approach that makes it possible to obtain highly uniform defect-free coatings with variable desired functionality.

Hydrolytic polycondensation of methylalkoxysilanes under pressure

Hydrolytic polycondensation of methytrialkoxysilanes under the pressure in water and in carbonic acid was investigated. It is shown, that both processes proceed with full conversion of the monomer to form a low molecular soluble polymethylsilsesquioxanes. However, they have a different structure: in water branched compounds were produced and in carboxylic acid polycyclic compounds were synthesized. A type of alkoxy group affects the course of the process. In the case of hydrolytic polycondensation of methyltriethoxysilane under the pressure, unlike methyltrimethoxysilane, full conversion is observed only when additional homogenization of the reaction mixture takes place by vigorous stirring or increasing temperature of the process.

Interaction of organodialkoxysilanolates with carbon dioxide

A series of organo(alkoxy)disiloxanes was obtained by the reaction of carbon dioxide with sodium alkoxy(organo)silanolates under high pressure as well as by bubbling CO2 through the reaction mixture. It has been suggested that the reaction involves the intermediate formation of carbonate derivatives of sodium alkoxy(organo)silanolates.

Synthesis of macrocyclic tris-cis-tris-trans- dodeca[(phenyl)(hydroxy)]cyclododecasiloxane in carbonic acid solution

ABSTRACT The possibility to synthesize stereoregular tris-cis-tris-trans- dodeca[(phenyl)(hydroxy)]cyclododecasiloxane (tris-cis-tris-trans-[PhSi(O)OH]12) in an inorganic liquid medium – aqueous carbonic acid solution – was shown. The interaction of polyhedral phenylcoppersodiumsiloxane, {[(C6H5Si(O)O−]12(Cu2+)4(Na+)4}*(L)m (L = Bun OH, H2O), with carbonic acid can be considered as a new ‘green’ method to obtain functional organosiloxane macrocycles. In contrast to the known methods, no organic solvents were used during the reaction. The identification of the structure of the end compound was performed by means of NMR and Infrared spectroscopy as well as X-ray crystallography. GRAPHICAL ABSTRACT

Hydrophobic Properties of Thin Films of Comb-Shaped Perfluorohexylethyl Methacrylate-Polydimethylsiloxane Copolymers Deposited from Supercritical Carbon Dioxide Solutions

Comb-shaped copolymers of perfluorohexylethyl methacrylate and methacryloxypropyl-terminated polydimethylsiloxane are synthesized by radical polymerization in supercritical carbon dioxide, solubility of the copolymers in supercritical carbon dioxide is studied, and hydrophobic properties of thin films obtained via precipitation of the copolymers from trifluorotrichloroethane and supercritical carbon dioxide solutions on substrates are examined. On the basis of water and dimethyl sulfoxide contact angle measurements, the specific free surface energy of the formed films is calculated. It is shown that the thin films of the copolymers have a lower surface energy and are characterized by a smaller water contact angle hysteresis than the films based on homopolymer poly(perfluorohexylethyl methacrylate). A comparative testing of coatings based on the homopolymer and copolymer deposited from solutions in supercritical carbon dioxide on the surface of nylon fabrics is performed. It is found that copolymer-coated fabrics have on average higher water contact angles.

Non-catalytic hydrolytic polycondensation of dialkoxydiorganosilanes under elevated pressure

The process of non-catalytic hydrolytic polycondensation of dialkoxydiorganosilanes under elevated pressure has been investigated. It is shown that non-catalytic hydrolytic polycondensation of diethoxydimethylsilane in an autoclave proceeds with complete monomer conversion for 10 min forming predominantly linear oligomers. Complete conversion of diethoxymethylphenylsilane is achieved by stirring or by increasing of the process temperature. In the hydrolytic polycondensation of dialkoxydimethylsilanes in the autoclave without stirring the reactivity of monomer is regularly decreased with increasing of length of the alkoxy-groups in the series of MeO—EtO—PriO—PrnO—BunO.