Base catalyst, hydroxide

The product is an aldehyde with a hydroxy (ol) group whose trivial name is aldol. The name aldol is given to the whole class of reactions between enolates (or enols) and carbonyl compounds even if in most cases the product is not a hydroxy-aldehyde at all. Notice that the base catalyst (hydroxide ion) is regenerated in the last step, so it is truly a catalyst. 

Tetrahydrofurfuryl alcohol reacts with ammonia to give a variety of nitrogen containing compounds depending on the conditions employed. Over a barium hydroxide-promoted skeletal nickel—aluminum catalyst, 2-tetrahydrofurfur5iarnine [4795-29-3] is produced (113—115). With paHadium on alumina catalyst in the vapor phase (250—300°C), pyridine [110-86-1] is the principal product (116—117) pyridine also is formed using Zn and Cr based catalysts (118,119). At low pressure and 200°C over a reduced nickel catalyst, piperidine is obtained in good yield (120,121). 

Vinyl ethers are prepared in a solution process at 150—200°C with alkaH metal hydroxide catalysts (32—34), although a vapor-phase process has been reported (35). A wide variety of vinyl ethers are produced commercially. Vinyl acetate has been manufactured from acetic acid and acetylene in a vapor-phase process using zinc acetate catalyst (36,37), but ethylene is the currently preferred raw material. Vinyl derivatives of amines, amides, and mercaptans can be made similarly. A/-Vinyl-2-pyrroHdinone is a commercially important monomer prepared by vinylation of 2-pyrroHdinone using a base catalyst. 

Methyl-l-Pen ten e. This olefin is produced commercially by dimeriza tion of propylene in the presence of potassium-based catalysts at 150—160°C and - 10 MPa. Commercial processes utilize several catalysts, such as sodium-promoted potassium carbonate and sodium- and alurninum-promoted potassium hydroxide (12—14) in a fixed-bed reactor. The reaction produces a mixture of C olefins containing 80—85% of 4-methyl- 1-pentene. 

Before preparing these carbon-supported Pt-based catalysts, a support pretreatment toward granular activated carbon with an aqueous solution of NaOH (pH 14) was carried out by immersing for 24 h to promote the anion exchange between the ligand chloride of impregnated metal precursers (K2PtCl4) and the aqueous hydroxide ion (OH ) inside the micropores of the activated carbon [33]. 

Biodiesel is a mixture of methyl esters of fatty acids and is produced from vegetable oils by transesterification with methanol (Fig. 10.1). For every three moles of methyl esters one mole of glycerol is produced as a by-product, which is roughly 10 wt.% of the total product. Transesterification is usually catalyzed with base catalysts but there are also processes with acid catalysts. The base catalysts are the hydroxides and alkoxides of alkaline and alkaline earth metals. The acid catalysts are hydrochloride, sulfuric or sulfonic acid. Some metal-based catalysts can also be exploited, such as titanium alcoholates or oxides of tin, magnesium and zinc. All these catalyst acts as homogeneous catalysts and need to be removed from the product [16, 17]. The advantages of biodiesel as fuel are transportability, heat content (80% of diesel fuel), ready availability and renewability. The... 

These polystyrene-based catalysts are effective for the cyanide displacements of 1-bromooctane and 1-chlorooctane, and also for the generation of dichlorocarbene from chloroform and aqueous sodium hydroxide, giving quantitative yields of (2,2-dichlorocyclopropyl)benzene from styrene. The catalysts may be recovered simply by filtering the reaction mixture. Unfunctionalized polystyrene does not catalyse these reactions. As well as improving product purification and catalyst recovery, this approach also avoids... 

The pH dependence of the regioselectivity for the nucleophilic photosubstitution of 3,4-dimethoxy-l-nitrobenzene by n-butylamine gives21 2-methoxy-5-nitro-Af-butylaniline as the major product at pH = 11 (equation 19). At pH = 12, the ratio of the major product to 2-methoxy-4-nitro-7V-butylaniline increases to 12 1 the increased selectivity is caused by hydroxide ion, which can either promote exciplex formation or act as a base catalyst in deprotonation steps following the cr-complex formation22. 

A novel finding related to the mechanism of catalysis by the genomic HDV ribozyme is that the pKa of C75 is perturbed to neutrality in the ri-bozyme-substrate complex and, more importantly, that C75 acts as a general acid catalyst in combination with a metal hydroxide which acts as a general base catalyst (Fig. 9A) [105]. The discovery of this phenomenon provided the first direct proof that a nucleobase can act as an acid/base catalyst in RNA. As a result, as shown by the solid curve in Fig. 9B, the curve that represents the dependence on the pH of the self-cleavage of the precursor genomic HDV ribozyme has a slope of unity at pH values that are below 7 (the activity increases linearly as the pH increases, with a slope of +1). Then, at higher pH values, the observed rate constant is not affected by the pH. 

In acid catalysis (HCl), the variation in pH of the medium affects the yield of oligoorganylsilsesquioxanes to a lesser extent than in the case of alkaline catalysis. Base catalysts are used in the synthesis of oligosilsesquioxanes mainly in the thermolysis of the primary products of XSiYj hydrolysis (Table 1). The most efficient catalysts, in this case, are those which are readily decomposed upon heating to give inactive products For example, the use of tetraethylammonium 32,45) trimethyl-benzyl ammonium 23.37,41) triethylamine hydroxides has proved successful. 

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. 

The same authors (77) also investigated the Michael addition of nitromethane to a,/l-unsaturated carbonyl compounds such as methyl crotonate, 3-buten-2-one, 2-cyclohexen-l-one, and crotonaldehyde in the presence of various solid base catalysts (alumina-supported potassium fluoride and hydroxide, alkaline earth metal oxides, and lanthanum oxide). The reactions were carried out at 273 or 323 K the results show that SrO, BaO, and La203 exhibited practically no activity for any Michael additions, whereas MgO and CaO exhibited no activity for the reaction of methyl crotonate and 3-buten-2-one, but low activities for 2-cyclohexen-l-one and crotonaldehyde. The most active catalysts were KF/alumina and KOH/alumina for all of the Michael additions tested. 

The reaction is usually performed with homogeneous basic catalysts such as alkali hydroxides, alkoxides, and tetraalkyl ammonium hydroxide (161,162). The mechanism accepted for this transformation starts with the abstraction by the base catalyst of a proton from the hydroxyl group of the alcohol to generate the alkoxide anion, which reacts with acrylonitrile to form the 3-alkoxypropanenitrile anion. The 3-alkoxypropanenitrile anion abstracts a proton from the catalyst to yield 3-alkoxypropane nitrile. 

By the use of base catalysts phosphine and phenylphosphine for example can be cyanoethylated. Acrylonitrile and phosphine react together at room temperature in the presence of aqueous potassium hydroxide solution to give, depending on the reaction conditions, primary, secondary and tertiary 2-cyano-ethyl-phosphines... 

The fact that a carbohydrate can be vinylated in the presence of a base catalyst in,an aqueous system is a good argument for the existence of carbohydrate alcoholates in aqueous media. However, successful vinylation does not imply that the concentration of the alcoholate is necessarily high. Because the interaction between the carbohydrate and the hydroxide ion is rapidly reversible, the concentration of the alcoholate may not have to be large for vinylation to proceed at a moderate rate. 

In aqueous solution, protons (actually present as hy-dronium ions) or hydroxide ions are the catalysts most commonly used for nonenzymatic reactions. The way in which acid or base catalysts work in ester hydrolysis is illustrated in Figure 10b and c. As a result of the electronegativity of... 

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