Alkali metal hydroxides, supported

The total yield of 2-vinylpyridine formed from 2-methylpyridine can be as high as 90%. 2-Vinylpyridine may also be obtained in almost quantitative yields by heating 2-alkylaminopyridine derivatives (which are directly available by cobalt catalysis) with a supported (e.g., AI2O3) alkali metal hydroxide [Eq.(8) R = R = alkyl, cyloalkyl, etc., RR N = heterocycle] (76SZP14399 78MI1). 

When the Diels-Alder reaction between butadiene and itself is carried out in the presence of alkali metal hydroxide or carbonate (such as KOH, Na2C03, and K CC on alumina or magnesia supports) dehydrogenation of the product, vinylcyclohexene, to ethylbenzene can occur at the same time (134). The same reaction can take place on simple metal oxides like Zr02, MgO, CaO, SrO, and BaO (135). 

Amides with electron-withdrawing substituents can be sufficiently labile towards nucleophilic attack to enable their use as protective groups. This is the case, for example, with trifluoro- [102,290] and trichloroacetamides [163], which are readily hydrolyzed under mild conditions (Figure 10.13). Suitable nucleophiles are hydrazine [291], aliphatic amines, and hydroxide, but if a hydrophobic support has been chosen, it must be borne in mind that the reactivity of alkali metal hydroxides will be reduced because of poor diffusion into the support. Amides of electron-poor amines (e.g. anilides) can also be readily cleaved by nucleophiles [292],... 

Trends in the dimerization energies for the higher alkali metal hydroxides, as well as for the dimeric alkali fluorides and chlorides, suggest that the enthalpy of dimerization for LiOH from the work of Berkowitz et al. (2) may be slightly high. Such a comparison results in A H (dimerization, 298.15 K) values in the range -(52-61) kcal mol". Further support for a lower value comes from the mass spectral work of Porter and Schoonmaker (JL). They investigated the reaction of H 0(g) with a mixture of... 

Vinylpyridine may also be obtained in almost quantitative yields from 2-alkylaminopyridine derivatives (directly available through cobalt catalysis) using a supported (e. g., AI2O3) alkali metal hydroxide [29]. 

Pearson also reported that the reaction over silica-supported alkali metal hydroxide catalysts is promoted markedly by the presence of water in the range of water/HCHO molar ratio = 1 to 5. With an acetic acid/HCHO/water molar ratio of 4.9/1/2.7, an SV of 750 h and a temperature of 405 °C, the yield of acrylic acid reaches 41.4 mol% based on the charged HCHO (8.5 mol% based on acetic acid) at the conversion of 53% the selectivity to acrylic acid is 78 mol% based on HCHO. 

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 is seen from Fig. 6.24 that the alkali metal hydroxide can be easily absorbed by carbon support due to its low melting point and its large fluidity. Therefore, only with enough quantity, the alkali metal can be accreted on the interface between ruthenium and carbon support and then plays the promotional roles effectively. As alkaline earth metal oxides have high melting point and poor fluidity, small amounts of them can be accreted on the interface between ruthenium and carbon support, which can produce effective active sites. The excessive promoters might cover the active sites of catalyst smface, which can influence the effective contact between active sites of ruthenimn smface and reactant gases and therefore decrease the catalytic activity. 

Alkali moderation of supported precious metal catalysts reduces secondary amine formation and generation of ammonia (18). Ammonia in the reaction medium inhibits Rh, but not Ru precious metal catalyst. More secondary amine results from use of more polar protic solvents, CH OH > C2H5OH > Lithium hydroxide is the most effective alkah promoter (19), reducing secondary amine formation and hydrogenolysis. The general order of catalyst procUvity toward secondary amine formation is Pt > Pd Ru > Rh (20). Rhodium s catalyst support contribution to secondary amine formation decreases ia the order carbon > alumina > barium carbonate > barium sulfate > calcium carbonate. 

This review is a summary of the work done and potential opportunities for inexpensive and easily accessible base catalysts, such as alkaline earth metal oxides and hydroxides, as well as alkali metals and oxides supported on alkaline earth metal oxides. Preparation methods of these materials, as well as characterization of basic sites are reported. An extensive review of their catalytic applications for a variety of organic transformations including isomerization, carbon-carbon and carbon-oxygen bond formation, and hydrogen transfer reactions is presented. 

Figure 8.11 Electrochemistry of nanotubes solubilized by direct sodium reduction. Background of the supporting electrolyte solution is shown with dashed line. The star indicates the irreversible anodic peak due to the oxidative stripping of the reduced alkali metal film. 2 mM tetrabutylammonium hydroxide/DMSO working electrode Pt disk (r = 25 pm) data recorded at 298K scan rate 1 V/s. Potentials are referenced to SCE. Reproduced with permission from Ref. 122. Copyright 2008 American Chemical Society.

For depressing the overhydrogenation of aromatic aldehydes and ketones over nickel or copper-chromium oxide at elevated temperatures and pressures, the presence of an aqueous alkali metal carbonate or hydroxide is effective.44 Thus, 60 g of benzaldehyde was hydrogenated over 1.5 g of a supported nickel in the presence of 2 ml of 10% aqueous sodium carbonate at 90-115°C and 3.2 MPa H2 to give 91.5% of benzyl alcohol and 7.7% of toluene, compared to 48.7 and 49.5%, respectively, without aqueous sodium carbonate. 

---