Alkali metals as catalysts

Although the aminolysis of esters to amides is auseful synthetic operation, usually it presents some disadvantages in terms of drastic reaction conditions, long reaction times or strong alkali metal as catalyst, which are usually not compatible with other functional groups in the molecule [6]. For this reason, enzymatic aminolysis of carboxylic acid derivatives offers a clean and ecological way for the preparation of different kind of amines and amides in a regio-, chemo-, and enantioselective manner. 

The experiments with glucose show that the carbon monoxide concentration in the product gas decreases more than twenty - fold by the addition of KOH. A similar influence is observed in the experiments with vanillin where potassium carbonate was added instead of KOH, (Table 2). It is known [26-28] that the addition of alkali metals as catalyst increases the rate of the water gas shift reaction (CO + H2O CO2 + H2). 

Table 4. Structure of polybutadiene obtained in tetrahydrofuran at 0°C in the presence of naphthalene complexes of alkali metals as catalysts [68]...

The direct alkylation of ammonia and amines with olefins in the presence of alkali metals as catalysts was reported by Howk and coworkers (17), The general procedure is shown in the following reaction, where R can be a hydrogen atom or an alkyl or aryl group ... 

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... 

This type of alkoxylation chemistry cannot be performed with conventional alkali metal hydroxide catalysts because the hydroxide will saponify the triglyceride ester groups under typical alkoxylation reaction conditions. Similar competitive hydrolysis occurs with alternative catalysts such as triflic acid or other Brpnsted acid/base catalysis. Efficient alkoxylation in the absence of significant side reactions requires a coordination catalyst such as the DMC catalyst zinc hexacyano-cobaltate. DMC catalysts have been under development for years [147-150], but have recently begun to gain more commercial implementation. The use of the DMC catalyst in combination with castor oil as an initiator has led to at least two lines of commercial products for the flexible foam market. Lupranol Balance 50 (BASF) and Multranol R-3524 and R-3525 (Bayer) are used for flexible slabstock foams and are produced by the direct alkoxylation of castor oil. 

Solid-liquid phase-transfer catalyst.1 The reagent represents a new class of catalysts, acyclic cryptands or tridents. It is singled out of a group as the best compromise of efficiency/price/toxicity. It solubilizes salts of alkali metals as well as of transition metals such as RuC13 and PdCl2, probably because of the flexibility of the molecule. In addition the trident is sensitive to the nature of the anion, but anionic activation is less than that obtained with cryptands. 

Ai85,86 is discussed on p. 114. Agarwal et al.102 as well as Sharma et al.103 studied this reaction using silica-supported V2Os-alkali metal sulphate catalysts. A two-step oxidation-reduction mechanism gave the best description of the process. The activity increased with increasing atomic number of the added alkali metal for which no interpretation was offered. In an electron microscopic study of these catalysts Sharma et al.103 showed that K2 S04 and V2 05 are present as separate phases but that the sulphate causes the presence of a larger amount of V2 05 in the form of needle-like crystals which appear to be more active for the methanol oxidation. A similar result was obtained by these authors for catalytic oxidation of toluene over these catalysts.104... 

This section reports a series of examples of application of the cluster model approach to problems in chemisorption and catalysis. The first examples concern rather simple surface science systems such as the interaction of CO on metallic and bimetallic surfaces. The mechanism of H2 dissociation on bimetallic PdCu catalysts is discussed to illustrate the cluster model approach to a simple catalytic system. Next, we show how the cluster model can be used to gain insight into the understanding of promotion in catalysis using the activation of CO2 promoted by alkali metals as a key example. The oxidation of methanol to formaldehyde and the catalytic coupling of prop)me to benzene on copper surfaces constitute examples of more complex catalytic reactions. 

The use of alkali metal oxide catalysts for aldol condensation reactions has been examined for the production of 2-ethylhexenal from butanal [34]. When coupled to a hydrogenation catalyst the system can produce the plasticizer alcohol 2-ethyl-hexanol directly. When isobutyraldehyde was used as the feed to a silica-supported sodium oxide catalyst, no products were formed but a significant amount of carbon was deposited on the catalyst and in the reactor (Scheme 21.2). 

Also, the role of alkali metal as co-catalyst was examined. Various alkali metal -nickel catalysts were prepared by impregnation method (5wt%) using alkali metal carbonates such as LbCOj, Na2COj, K2CO3, CS2CO3 and obtained result were shown in Table 3. 

Cubic boron(lll) nitride is manufactured from hexagonal BN in a high pressure synthesis at 50 to 90 kbar and 1500 to 2200°C in the presence of alkali or alkaline earth metals as catalysts. Cubic boron(III) nitride is, after diamond, the hardest known material. It is utilized in the grinding agent sector instead of diamond, due to its better chemical resistance at high temperatures. 

For this reaction the comparison of activity of various oxides cannot be carried out because most of them transform in reaction conditions into nonactive sulfates. The exception is vanadium pentoxide whose activity strongly increases when promoted by sulfates of alkali metals. As is clear from Fig. 15, the catalytic activity of vanadium catalysts, with the addition of different sulfates of alkali metals, changes identically in reactions of isotopic exchange in molecular oxygen and in the oxidation of sulfur dioxide. 

LCB is also enhanced by the addition of alkali metal, as might be expected from its acceleration of annealing. In one test of LCB trends, a silica was impregnated with sodium ions, which caused a reduction in the surface area of 30-50% when it was heated to only 600 °C. This silica was then washed repeatedly with liquid water numerous times to remove the sodium then chromium was applied. After a second activation at only 600 °C, this catalyst produced polymer with high levels of LCB. The fusion of the silica primary particles caused a large increase in LCB. This happened although the chromium, and in this case even the silica, had never experienced a high activation temperature. 

Yamazaki and Kawai reported a study on the reaction of HCHO with acetonitrile or propionitrile using silica-supported metal salts or hydroxides as catalysts. Formalin is used as the source of HCHO. The performances are summarized in Table 15. It is concluded that silica-supported alkali metal hydroxide catalysts show the best performances. The optimum loading of alkali metals is in the range of 0.01 to 0.1 mol/60 g of silica gel. The optimum reaction conditions are nitrile/HCHO molar ratio of 5, temperature of 500 °C, and contact time of 2.5 x 10 s-g-cat/mol. The single-pass yields of acrylonitrile and methacrylonitrile are 75 and 65 mol%, respectively, based on the charged HCHO (25 and 22 mol% based on the charged nitrile) with a nitrile/HCHO molar ratio of 3. The reaction rate is first order with respect to the concentrations of both nitrile and HCHO. 

It can be seen from Fig. 6.12 that the activity of Ru-M/MgO catalysts with alkali metal as promoter is low. The main purpose of the addition of the alkali metal is to increase the basicity of the supports. But the role is not obviously due to the strong alkaline of MgO itself. The alkaline earth metals (especially Ba) can increase the specific surface areas of catalyst, on the other hand, Ba and Mg is in the same group in periodic table, so may be have the synergistic effect on each other, which can enhance the activities of the catalysts. 

The results in Refs. 91 and 127 (Table 9.7) also demonstrate that some alkali salts (nitrate, carbonate, hydroxide) give rise to efficiencies similar to the alkali metals as promoters, while others (chlorides) are almost totally inactive, which is in marked contrast to alumina>supported catalysts where the addition of alkali salts has little promoting effect. The active state of the promoter on ruthenium/carbon catalysts is unlikely to be metallic, as the high vapor pressure of the alkali metals would give rise to substantial losses under synthesis conditions. The more probable state is a charge transfer complex with the graphite... 

Cold-Box Process. In the cold-box process which takes place at room temperature, a gas catalyst is passed through the sand to promote curing. The catalysts are triethylamine or meth-ylethylamine for phenolic isocyanate binders, sulfur dioxide for vinyl-unsaturated urethane binders, and methyl formate for an alkali metal salt of a phenolic resole binder. Yii -ortho resins have been developed for the phenolic component by using water-free systems and salts of divalent metals as catalysts. A recent patent describes improvements in the two-package phe-... 

A number of stannoxy-aluminoxane polymers containing organotin side groups have been prepared from monomers of tiie type 60. These materials have good thermal stability. They are formed through heating wifli or without pressine and in flie presence of an alkali metal alcoholate catalyst. A sample structure is given as 61. 

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