Double metal cyanides

Co/Zn double metal cyanide catalyzed ring-opening polymerization of propylene oxide effect of cocataiysts on polymerization behavior... 

Higher molecular weight materials are typically prepared using coordination catalysts, such as the calcium amide-alkoxide system developed by Union Carbide,932 and double metal cyanide initiators, e.g., [Zn(Fe(CN)6)].933 The nature of the active sites in these catalysts is not well understood and only a few studies have been published outside the patent literature.810,934,935... 

Table 10.4 Esterification—transesterification of different oils in the presence of Fe-Zn double metal cyanide.

Terpolymers of maleic anhydride (MA) and PPC could be prepared using a double-metal cyanide (DMC)-type catalyst. The polymer was amorphous like most terpolymers of propylene carbonate [39]. For terpolymers with up to 50 50 (mol/ mol) of PO/CO2 and MA, it could be shown by TGA that the observed degradation temperature was again raised by about 20-30°C and that the maximum rate of decomposition even exceeded 300°C. 

Kruper WJ, Swart DJ (1985) Carbon dioxide oxirane copolymers prepared using double metal cyanide complexes. US Patent 4500704... 

Robertson NJ, Qin Z, Dallinger GC, Lobkovsky EB, Lee S, Coates GW (2006) Two-dimensional double metal cyanide complexes highly active catalysts for the homopolymerization of propylene oxide and copolymerization of propylene oxide and carbon dioxide. Dalton Trans 5390-5395... 

Conventional polyether polyol technology involves alkoxylation of the starters with PO and EO using an alkali metal hydroxide catalyst such as potassium hydroxide. The catalyst can be neutralized and the neutral salt can be left in the final polyol, or optionally the catalyst can be extracted by washing with water or by deposition on an ion exchange medium. In recent years, a new catalyst technology has become widely adopted within the polyols industry, using zinc hexacyano-cobaltate (double metal cyanide catalyst, or DMC), which runs at very high... 

Discovery. These catalysts were discovered during a study of the use of transition metal cyanides in combination with metal alkyl and hydride reducing agents in polymerizations. The combination of nickel cyanide and lithium aluminum hydride complexed very strongly with tetrahydrofuran. A similar complexing action occurred with propylene oxide and nickel hexacyanoferrate(II)-lithium aluminum hydride. This led to speculation as to the role of the double-metal cyanide itself. 

Synthesis of High Molecular Weight Polyether Polyols with Double Metal Cyanide Catalysts (DMC Catalysts)... 

Double metal cyanide catalysts (DMC catalysts) were developed 40 years ago by General Tire Rubber [1]. These catalysts have the following general formula of a nonstoichiometric substance ... 

Longer reaction times are usually required for propoxylation reactions due to the preference for lower reaction temperatures necessary to maintain product color and avoid troublesome side reactions such as elimination of a terminal alcohol to generate allyl ethers. Propoxylation reactions can be selectively accelerated at lower temperatures with the use of a double metal cyanide catalyst. The catalyst is extremely sensitive and easily deactivated by moisture and conventional groups I and II catalysts, and will not effectively catalyze ethoxylation reactions. 

The reaction of hydroxyl dehydration, which eliminates the chain terminal hydroxyl is a drawback in the case of production of polyols for polyurethane industry, therefore several catalysts apart from potassium and sodium hydroxide have been proposed. These catalysts, including hydroxide of rubidium, cesium, barium and strontium, or double metal cyanide, are much more expensive and toxic than classical catalysts [11], Recently, a new class of catalyst has been... 

Lee K, Ha JJY, Cao C, Park DW, Ha C-S, Kim I (2009) Effent of complexing agents of double metal cyanide catalyst on the copolymerizations of cyclohexene oxide and carbon dioxide. Catal Today 148 389-397... 

Rapid and controlled PO polymerization has recently become effective for industrial application through the commercially available double-metal cyanide (DMC) compounds, whose... 

ENSEL [The name is probably derived from NCL, the National Chemical Laboratory in Pune, India, whose former director, Paul Ratnasamy, was the prime inventor of the catalyst for this process] A transesterification process for making biodiesel from vegetable oils, using a solid double metal cyanide catalyst. Developed in 2006 by the National Chemical Laboratory, India, and commercialized by Benefuel, a joint venture of Seymour Biofuels with SUd-Chemie. The first plant was built in Seymour, IN, from 2008. The novel catalyst was provided by Siid-Chemie India. 

Impact A continuous process for making long-chain polyether polyols as precursors for polyurethanes. Uses a double metal cyanide catalyst. 

Double Metal Cyanides as Heterogeneous Catalysts for Organic Reactions... 

Double metal cyanides (DMCs), also known as Prussian blue analogues, are a class of molecular salts built up of a crystalline metal cyanide framework [1], As their name suggests, DMCs feature two different metal centers, one coordinating via the carbon atom of the CN ligand and the other via the nitrogen atom. DMCs have a general structural formula M [M (CN) Jv A typical selection of M metals is Zn(II), Fe(II), Co(II), or Ni(II), whereas Co(ni), Fe(n), Fe(in), Cr(in), or Ir(III) is often used as M [2]. Typical u-v combinations... 

TABLE 5.6 Catalytic activity of double-metal cyanide (DMC) complexes for co-polymeiization of CO and epoxides. 

Tharun, J. Dharman, M. M. Hwang, Y Roshan, R. Park, M.S. Park,D.-W. Tuning Double Metal Cyanide Catalysts with Complexing Agents for the Selective Production of Cyclic Carbonates over Polycarbonates. Appl. Catal A Gen. 2012,419 20, 178-184. 

Dharman, M. M. Ahn, J.-Y. Lee M.-K. Shim, H.-L. Kim, K.-H. Kim, IL Park, D.-W. Moderate Route for the Utilization of COj-Microwave Induced Copolymerization with Cyclohexene Oxide using Highly Efficient Double Metal Cyanide Complex catalysts Based on Znj[Co(CN)J. Green Chem. 2008,10,678-684. 

Dong, Y Wang, X. Zhao, X. Wang, F. Facile Synthesis of Polyfether carbonate)s via Copolymerization of COj and Propylene Oxide Under Combinatorial Catalyst of Rare Earth Ternary Complex and Double Metal Cyanide Complex. J. Polymer Sci. Part A Polymer Chem. 2012,50,362-370. 

Gao, Y Qin, Y. Zhao,X. Wang,F. Wang,X. Selective Synthesis of Ohgo(Carbonate-Ether) Diols from Copol3mierization of CO and Propylene Oxide under Zinc-Cobalt Double metal Cyanide Complex. JPolym Res 2012,19, 9878-9886. 

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