Bhalchandra M. Bhanage

Synthesis of dimethyl carbonate and glycols from carbon dioxide, epoxides, and methanol using heterogeneous basic metal oxide catalysts with high activity and selectivity

Abstract This paper gives a comprehensive report on a two-step synthesis of dimethyl carbonate (DMC) from epoxides, carbon dioxide and methanol using various basic metal oxide catalysts. The first step is the reaction of ethylene oxide or propylene oxide with CO 2 to form the corresponding cyclic carbonates, and the second step is the transesterification reaction of the cyclic carbonates with methanol to DMC and glycols. Among the catalysts examined, MgO is the most active and selective for both these reactions. Other alcohols can be used for the second step, but the activity decreases as the carbon number of the alcohol increases. Although a one-pot synthesis of DMC, i.e. the sequential reaction of the epoxide, CO 2 and methanol, is also possible with MgO, the selectivity is low because of the alcoholysis of the epoxide. In contrast with the reactions of ethylene oxide and propylene oxide, when styrene oxide is used for the first reaction and for the one-pot synthesis, mandelic acid is produced. Basic properties of the metal oxide catalysts were measured by temperature programmed desorption of CO 2 . The relationship between the catalytic performance and the basic property is discussed.

Heck reactions of iodobenzene and methyl acrylate with conventional supported palladium catalysts in the presence of organic and/or inorganic bases without ligands

The vinylation of iodobenzene with methyl acrylate has been studied with several supported palladium catalysts in N-methylpyrrolidone in the presence of triethylamine and/or sodium carbonate. The reaction can be performed in air without any solubilizing or activating ligands. It was found that significant amounts of palladium leach out into the solvent and these dissolved Pd species essentially catalyze the reaction. It is interesting, however, that almost all the palladium species in the solution can redeposit onto the surface of the supports after the reaction has been completed (at 100% conversion of iodobenzene). Thus, the catalysts were recyclable without loss of activity. The use of both inorganic and organic bases is very effective in the promotion of the palladium redeposition as well as in the enhancement of the reaction rate. For Heck reactions with bromobenzene and chlorobenzene it was found that the use of triethylamine and sodium carbonate increases the selectivity of the Heck coupling product (benzene is also produced for these two substrates), but the mixed bases do not affect the overall rate of reaction as much.

CATALYST PRODUCT SEPARATION TECHNIQUES IN HECK REACTION

The Heck reaction finds several applications in industry because it is one of the effective tools for the formation of a new C─C bond. In addition to the catalytic activity and selectivity, catalyst–product separation strategies are very important for the industrial application. There are various methods of interest ranging from conventional heterogeneous catalysts to heterogenization of homogeneous catalysts. The heterogeneous catalysts are classified into supported metal catalysts, zeolite-encapsulated catalysts, colloids–nanoparticles, and intercalated metal compounds. The homogeneous metal complexes catalysts are heterogenized using modified silica catalysts, polymer-supported catalysts, biphasic catalysts, supported liquid-phase catalysts, nonionic liquids solvents, perfluorinated solvents, and reusable homogeneous complexes. In general, heterogeneous catalysts are effective and stable at higher temperatures, which may be important for the activation of less reactive but less expensive chloroaryls substrates. However, the heterogeneous catalysts have a major drawback of poor selectivity toward Heck coupling products. The heterogenized metal complexes catalysts operate under relatively mild conditions as compared with heterogeneous catalysts, and so they can be applied to the production of pharmaceuticals and fine chemicals. Catalysis using supercritical solvents with catalyst separation techniques is promising for the development of green chemistry processes. Although the concepts described in this article have been reviewed mainly for Heck reactions, they should be applicable to a wide range of other chemical transformations (hydrogenation, carbonylation, hydroformylation, and so on) that, currently, are homogeneously catalyzed reactions.

Recent developments in palladium catalysed carbonylation reactions

Recently, carbonylation reactions have gained considerable interest as they are becoming a versatile tool in the synthesis of pharmaceuticals, agrochemicals and their intermediates. Nowadays, a plethora of transition metal catalysts are available for the synthesis of various functional groups like ureas, carbamates, oxamates, oxamides, α-keto amides, ketones, esters, etc. using carbonylation methodology. Several carbonylation reactions such as aminocarbonylation, alkoxycarbonylation, double carbonylation and oxidative carbonylation, provide efficient and attractive alternatives to the conventional synthetic routes on a laboratory or industrial scale. Oxidative carbonylation is an important reaction as it allows direct carbonylative C–H bond activation. A double carbonylation reaction provides a one step alternative route for the synthesis of α-keto amides, oxamides, and oxamates. It also eliminates the use of conventional thermally unstable and toxic reagents like oxalyl chloride. Several recent studies have focused on the various aspects of these reactions, including catalyst–product separation, and catalyst recoverability and reusability. In view of this, developments in anchoring homogeneous catalysts using various techniques like biphasic catalysis and supported liquid phase catalysis are gaining importance. Carbonylation routes using these techniques are simple, efficient, economical, avoid the use of ligands, and give the desired products in excellent yields. The use of phosphine ligands is disadvantageous as it leads to air/moisture sensitivity, tedious work-up procedures and high work-up costs. Several phosphine-free carbonylation routes eliminate the use of phosphine ligands, and provide economical and simple methods for these transformations. In this review we have summarized the recent trends in carbonylative transformations, which have undergone a rapid development.

Synthesis of dimethyl carbonate and glycols from carbon dioxide, epoxides and methanol using heterogeneous Mg containing smectite catalysts: effect of reaction variables on activity and selectivity performance

This paper reports the effect of various reaction variables on the activity and selectivity performance on a two-step synthesis of dimethyl carbonate (DMC) and glycol from propylene oxide, carbon dioxide and methanol using a heterogeneous Mg containing smectite catalyst. The first step, the reaction of propylene oxide with CO2 to form propylene carbonate, and the second step, the transesterification reaction of the cyclic carbonate such as ethylene carbonate with methanol to DMC and ethylene glycol, have been studied. The catalyst was found to be effective for one-pot synthesis of DMC, i.e. the sequential reaction of the epoxide, CO2 and methanol.

Trifluoromethylchlorosulfonylation of Alkenes: Evidence for an Inner-Sphere Mechanism by a Copper Phenanthroline Photoredox Catalyst†

A visible-light-mediated procedure for the unprecedented trifluoromethylchlorosulfonylation of unactivated alkenes is presented. It uses [Cu(dap)2]Cl as catalyst, and contrasts with [Ru(bpy)3]Cl2, [Ir(ppy)2(dtbbpy)]PF6, or eosin Y that exclusively give rise to trifluoromethylchlorination of the same alkenes. It is assumed that [Cu(dap)2]Cl plays a dual role, that is, acting both as an electron transfer reagent as well as coordinating the reactants in the bond forming processes.

Palladium-Catalyzed Carbon-Monoxide-Free Aminocarbonylation of Aryl Halides Using N-Substituted Formamides as an Amide Source

A carbon-monoxide-free aminocarbonylation of various N-substituted formamides with aryl iodides and aryl bromides using palladium acetate and Xantphos is described. The developed methodology is applicable for a wide range of formamides and aryl halides containing different functional groups furnishing good to excellent yield of the corresponding products. N-substituted formamides are used as an amide source wherein a Vilsmeier-type intermediate plays a major role, thus eliminating the need of toxic carbon monoxide gas.

Efficient synthesis of cyclic carbonate from carbon dioxide using polymer anchored diol functionalized ionic liquids as a highly active heterogeneous catalyst

A highly efficient catalytic protocol using polymer supported diol functionalized ionic liquids (PS-DFILX) was developed for cyclic carbonates synthesis from carbon dioxide and epoxide providing remarkable yields of desired products under solvent free conditions. The developed methodology was found to be applicable for a wide variety of epoxides producing the corresponding cyclic carbonate in good to excellent yields. Besides this, the catalyst could be reused for five consecutive recycles without any significant loss in its catalytic activity. The hydroxyl groups present on the vicinal carbon of the catalyst seems to be vital for efficiency of the catalyst endowing high activity, stability and recyclability. The present protocol thus offers appreciable advantages with respect to excellent yield, short reaction time, operational simplicity and environmentally benign characteristics.

Transesterification of urea and ethylene glycol to ethylene carbonate as an important step for urea based dimethyl carbonate synthesis

Two-step synthesis of dimethyl carbonate (DMC) from urea has been investigated with various solid catalysts. The first step involves reaction of urea with ethylene glycol (EG) to form ethylene carbonate (EC) and the second step transesterification of EC formed with methanol to give DMC and EG. It has been found that ZnO is highly active and selective for the two steps, of which the former should be conducted under reduced pressure. At around ambient pressure, 2-oxazolidone and ethyleneurea are formed in the first step. Similar to EG, other glycols such as 1,2- and 1,3-propanediols can also be transformed to corresponding cyclic carbonates.

Synthesis of cyclic ureas and urethanes from alkylene diamines and amino alcohols with pressurized carbon dioxide in the absence of catalysts

Clean synthesis to imidazolidone and oxazolidone compounds using direct reaction of carbon dioxide with diamine or amino alcohols can be achieved at 6 MPa CO2 and 150 °C without use of any catalyst.