Heterogeneous alkali metals

Cg.Me(.)2Sm(THF)2 also shows high reactivity in its reactions with C,H C=CCgH and CgHj-NzNC H- and the subsequent reactions of these products With CO 5 The clH CECC.H reaction (65), which forms [(C Me )2Sm]2C2(CgH )2 (Equation 8 may have a parallel in alkali metal chemistry, except that in the heterogeneous alkali metal systems, polymerization or dimerization of the intermediate radical... 

The existence of such associated organolithium compounds has been estabhshed in various cases (19, 20, 24), In addition to isotactic polystyrene, a considerable amoimt of atactic material is always present it is formed by starting the polymerization on the nonassociated part of the organolithium compounds which probably promote a nonstereospecific anionic polymerization. The stereoregulation of the polymerization of styrene by heterogeneous alkali metal aUcyl initiators is limited by the forces on the surface of the catalyst while the dissolved organolithium initiators in their associated form cause the stereospecific polymerization. 

Alkali Metal Catalysts. The polymerization of isoprene with sodium metal was reported in 1911 (49,50). In hydrocarbon solvent or bulk, the polymerization of isoprene with alkaU metals occurs heterogeneously, whereas in highly polar solvents the polymerization is homogeneous (51—53). Of the alkah metals, only lithium in bulk or hydrocarbon solvent gives over 90% cis-1,4 microstmcture. Sodium or potassium metals in / -heptane give no cis-1,4 microstmcture, and 48—58 mol % /ram-1,4, 35—42% 3,4, and 7—10% 1,2 microstmcture (46). Alkali metals in benzene or tetrahydrofuran with crown ethers form solutions that readily polymerize isoprene however, the 1,4 content of the polyisoprene is low (54). For example, the polyisoprene formed with sodium metal and dicyclohexyl-18-crown-6 (crown ether) in benzene at 10°C contains 32% 1,4-, 44% 3,4-, and 24% 1,2-isoprene units (54). 

A three-step process developed hy Snamprogetti is based on the reaction of acetylene and acetone in liquid ammonia in the presence of an alkali metal hydroxide. The product, methylhutynol, is then hydrogenated to methylhutenol followed hy dehydration at 250-300°C over an acidic heterogeneous catalyst. 

Electron transfer reactions involving alkali metals are heterogeneous, and for many purposes it is desirable to deal with a homogeneous electron transfer system. It was noticed by Scott39 that sodium and other alkali metals react rapidly with aromatic hydrocarbons like diphenyl, naphthalene, anthracene, etc., giving intensely colored complexes of a 1 to 1 ratio of sodium to hydro-... 

Protons are not the sole species that can be incorporated into the lattices of different host materials. At the beginning of the 1960s, Boris N. Kabanov showed that during cathodic polarization of different metals in alkaline solutions, intercalation of atoms of the corresponding alkali metal is possible. As a result of such an electrochemical intercalation, either homogeneous alloys are formed (solid solutions) or heterogeneous polyphase systems, or even intermetallic compounds, are formed. 

Interaction of the CO molecule with CuX-FER zeolites (X is an alkali-metal or proton as a co-cation) was investigated by IR spectroscopy and DFT calculations. An absorption band at 2138 cm 1 observed in IR spectra of CO on CuK- and CuCs-FER zeolites was assigned to a new type of CO adsorption complex on heterogeneous dual cation sites. CO molecule interacts simultaneously with Cu+ and alkali metal cations (via C- and O-end, respectively) in this type of complex. Interaction of CO with the secondary (alkali metal) cation led to a slight destabilization of the carbonyl complex. 

The production of sulphuric acid by the contact process, introduced in about 1875, was the first process of industrial significance to utilize heterogeneous catalysts. In this process, SO2 was oxidized on a platinum catalyst to S03, which was subsequently absorbed in aqueous sulphuric acid. Later, the platinum catalyst was superseded by a catalyst containing vanadium oxide and alkali-metal sulphates on a silica carrier, which was cheaper and less prone to poisoning. Further development of the vanadium catalysts over the last decades has led to highly optimized modem sulphuric acid catalysts, which are all based on the vanadium-alkali sulphate system. 

Sulphuric acid catalysts are not truly heterogeneous catalysts but so-called supported liquid phase (SLP) catalysts, where the oxidation of S02 takes place as a homogeneous reaction in a liquid film covering the internal surface of the support material [2], This was proposed already in 1940 by Frazer and Kirkpatrick [6], who found that the promoting action of the common alkali metals was due to their ability to form relatively low-melting pyrosulphates, which dissolve vanadium oxides, e.g. for potassium... 

Free radicals are atoms or groups of atoms possessing an odd (unpaired) electron. Radical recombination occurs when active flame propagating species (O , H and OH) recombine (heterogeneously) on particle surfaces or (homogeneously) as a result of gas phase reactions catalysed by alkali metal atoms in the flame, e.g. 

Electron-transfer initiation also occurs in heterogeneous polymerizations involving dispersions of an alkali metal in monomer. Initiation involves electron transfer from the metal to monomer followed by dimerization of the monomer radical-anion to form the propagating... 

The effect of the addition of alkali metal b-butoxides on the lithium morpholinide-initiated heterogeneous butadiene polymerization was also studied at 30°C in hexane. The data in Table III show that the 1,2 content of the polybutadiene is sensitive to the type of alkali metal used. For example, by changing metal alkoxides from Li to Na to K, the 1,2 content of polybutadiene changes from 46.0% to 58.2% to 55.4%, respectively, at an initiator concentration of about 10 mmoles. However, the 1,2 content of the polybutadienes is unaffected by the metal alkoxide concentration (1,2 content, 42-46% for LiOtBu, 55-58% for NaOtBu, 53-55% for KOtBu) when the alkoxide/ morpholinide ratio is greater than 1 1. 

The most active heterogeneous catalysts that are effective at room temperature are alkali metals supported on activated alumina. Simple C4-Cg alkenes, for example, were shown to yield equilibrium mixtures in short contact time over sodium on alumina.112116 Partial conversion of 1-butene at low temperature and in very short contact time (—60°C, 14 s) led to the stereoselective formation of m-2-butene.112 The changes in isomeric composition in the transformation of 4-methyl-l-pentene112 are as follows ... 

At this stage, it is still difficult to determine whether the conclusion is appropriate for the fundamental part of the multicomponent bismuth molybdate catalyst. Unfortunately, we have no available information on the number of active reaction sites on the catalyst system. In the heterogeneous catalysis, apparent activation energy does not necessarily correspond to the real energy barrier of the elementary slow step of the reaction. Multicomponent bismuth molybdate catalyst has been established industrially, whereas only parts of the fundamental structure and working mechanism have been elucidated. In addition, important roles of alkali metals and other additives such as lanthanides remain unknown. Apparently, further investigations should be done to clarify the complete working mechanism of the multicomponent bismuth molybdate catalyst. 

Bismuth is an important element in many of the new high-temperature, oxide superconductors and in a variety of heterogeneous mixed oxide catalysts. Some of the methods employed in the preparation of these materials, namely sol-gel and chemical vapor deposition processes, require bismuth alkoxides as precursors and a number of papers on these compounds have recently been published.1 One synthetic route to bismuth alkoxides, which avoids the more commonly used trihalide starting materials and the often troublesome separation of alkali metal halides, involves the reaction between a bismuth amide and an alcohol according to the following equation ... 

The polymerization of isoprene hv alkali metal and organometullic compounds (other than organolilhiumI is a heterogeneous reaction both in hulk and hydrocarbon solvents. 

The mechanism of the anionic polymerization of styrenes and 1,3-dienes initiated by alkali metals has been described in detail (3,20) as shown in equations 3—5 where Mt represents an alkali metal and M is a monomer molecule. Initiation is a heterogeneous process occurring on the metal surface. The... 

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