Catalyst alkali alkoxide

The first step for the synthesis of a melt spinnable polysilane is the alkoxylation and distillation of the residue (Figure 1). 1,2-dimethyltetramethoxydisilane and 1,1,2-trimethyltrimethoxydisilane are mixed in a special ratio and a poly silane will be obtained by a catalytic redistribution reaction. Catalysts for this reaction are alkali alkoxides like sodium methoxylate. Phenylmethoxydisilanes [22] or phenylchloride are used as additives. A mixture of methyltrimethoxysilane and dimethyldimethoxy-silane distils off as a byproduct of the redistribution reaction. Figure 2 shows the mechanism of the catalytic redistribution. 

The regenerated KOH works as a catalyst once again. If alkali alkoxides are used as catalysts instead of alkali hydroxides, the exchange of protons between the growing polymer and the dead polymer is ... 

High trimerization rates have also been observed in the presence of basic catalysts. Aliphatic and heteroaromatic amines, alkali hydroxides and alkali alkoxides have been used.247 249,256 The base presumably adds to the carbon atom of the cyanate group, and then the adduct takes part in the trimerization reaction.257 Pyridines and derivatives are superior in catalytic activity compared to tertiary alkylamines. 

Base catalysis usually is preferred in the epoxide condensation of "neutral"polyols with potassium hydroxide being the favored catalyst although other alkali hydroxides, alkali alkoxides, and various tertiary amines may be used. 

Alkali alkoxides as catalysts for carhanion reactions of hydrocarbons ... 

The rate of polymerization decreases with increasing polarity of the solvent, opposite to the behavior observed for the alkali alkoxides initiators. This observation implies that the monomer and the solvent compete for the active sites of the catalyst. 

Clalsen aldol condensation. This consists in the condensation of an aromatic aldehyde and an ester R—CHjCOOCjHj in the presence of finely divided sodium and a trace of alcohol at a low temperature. The catalyst is the alkoxide ion aqueous alkalis caimot be employed since they will hydrolyse the resulting ester. The product is an ap-unsaturated ester, for example ... 

The a -halosulfone, required for the Ramberg-Backlund reaction, can for example be prepared from a sulfide by reaction with thionyl chloride (or with N-chlorosuccinimide) to give an a-chlorosulfide, followed by oxidation to the sulfone—e.g. using m-chloroperbenzoic acid. As base for the Ramberg-Backlund reaction have been used alkoxides—e.g. potassium t-butoxide in an etheral solvent, as well as aqueous alkali hydroxide. In the latter case the use of a phase-transfer catalyst may be of advantage. ... 

Usually metal-free phthalocyanine (PcH2) can be prepared from phthalonitrile with or without a solvent. Hydrogen-donor solvents such as pentan-l-ol and 2-(dimethylamino)ethanol are most often used for the preparation.113,127 128 To increase the yield of the product, some basic catalyst can be added (e.g., DBU, anhyd NH3). When lithium or sodium alkoxides are used as a base the reaction leads to the respective alkali-metal phthalocyanine, which can easily be converted into the free base by treatment with acid and water.129 The solvent-free preparation is carried out in a melt of the phthalonitrile and the reductive agent hydroquinone at ca. 200 C.130 Besides these and various other conventional chemical synthetic methods, PcH2 can also be prepared electrochemically.79... 

The reaction between acyl halides and alcohols or phenols is the best general method for the preparation of carboxylic esters. It is believed to proceed by a 8 2 mechanism. As with 10-8, the mechanism can be S l or tetrahedral. Pyridine catalyzes the reaction by the nucleophilic catalysis route (see 10-9). The reaction is of wide scope, and many functional groups do not interfere. A base is frequently added to combine with the HX formed. When aqueous alkali is used, this is called the Schotten-Baumann procedure, but pyridine is also frequently used. Both R and R may be primary, secondary, or tertiary alkyl or aryl. Enolic esters can also be prepared by this method, though C-acylation competes in these cases. In difficult cases, especially with hindered acids or tertiary R, the alkoxide can be used instead of the alcohol. Activated alumina has also been used as a catalyst, for tertiary R. Thallium salts of phenols give very high yields of phenolic esters. Phase-transfer catalysis has been used for hindered phenols. Zinc has been used to couple... 

Alkali-immobile dye-releasing quinone compounds, 19 293-294 Alkali lignins, 15 19-20 Alkali manganate(VI) salts, 15 596 Alkali manganates(V), 15 592 Alkali-metal alkoxide catalysts, 10 491 Alkali-metal alkoxides, effects of, 14 252 Alkali-metal alkylstannonates, 24 824 Alkali-metal fluoroxenates, 17 329-330 Alkali-metal hydrides, 13 608 Alkali-metal hydroxides, carbonyl sulfide reaction with, 23 622 Alkali-metal metatungstates, 25 383 Alkali-metal perchlorates, 18 211 Alkali-metal peroxides, 16 393... 

The "Alfin" catalyst (Morton 1964 Reich 1966) is made up to a suspension, in an inert solvent like pentane, of a mixture of an alkylenyl sodium compound (such as allyl sodium), an alkoxide of a secondary alcohol (such as sodium isopropoxide), and an alkali halide (such as sodium chloride). The catalyst is highly specific for the polymerisation of dienes into the 1, 4-forms. 

Ruthenium(III) catalyses the oxidative decarboxylation of butanoic and 2-methylpropanoic acid in aqueous sulfuric acid. ° Studies of alkaline earth (Ba, Sr) metal alkoxides in amide ethanolysis and of alkali metal alkoxide clusters as highly effective transesterification catalysts were covered earlier. Kinetic studies of the ethanolysis of 5-nitroquinol-8-yl benzoate (228) in the presence of lithium, sodium, or potassium ethoxide revealed that the highest catalytic activity is observed with Na+.iio... 

Alkyl or 1-arylbiguanides (jS97) react analogously 1-Arylbiguanides condense slowly with esters other than those of formic acid (226), but metal alkoxide-catalysts 475) or caustic alkalis (477) have again been employed (475) to good effect. The synthesis has been widely used (19, 127, 204, 221, 417, 593, 599, 601, 602, 677, 701). 

Nitroalkanols are intermediate compounds that are used extensively in many important syntheses 142). They can be converted by hydrogenation into / -aminoalcohols, which are intermediates for pharmacologically important chemicals such as chloroamphenicol and ephedrine. They are obtained by Henry s reaction by the condensation of nitroalkanes with aldehydes. The classical method for this transformation involves the use of bases such as alkali metal hydroxides, alkoxides, Ba(OH)2, amines, etc. 142-144). However, these catalysts give predominantly dehydrated products—nitroalkenes— which are susceptible to polymerization (Scheme 16). The reaction proceeds by the nucleophilic addition of the carbanion formed by the abstraction of a proton from the nitro compound to the carbon atom of the carbonyl group, finally forming the nitroaldol by abstraction of a proton from the catalyst. 

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. 

For the anionic polymerization of methacrylonitrile (MAN), many initiators have been developed, which include alkali-metal alkyls such as butyllithium [42], triphenylmethylsodium [43], phenylisopropylpotassium [43], the disodium salt of living a-methylstyrene tetramer [44], alkali-metal amides [45], alkoxides [46], and hydroxide [47], alkali metal in liquid NH3 [48], quaternary ammonium hydroxide [49], and a silyl ketene acetal coupled with nucleophilic or Lewis acidic catalysts [50]. However, only a single example of the synthesis of PMAN with narrow molecular-weight distribution can be cited, and the reported number-average molecular weights were much higher than those calculated from the stoichiometry of the butyllithium initiator [42]. 

Double alkoxides with alkali metals A[M(OR)6] (Table 8) were formed from the reaction of the pentaalkoxides with alkali metal alkoxides. The double alkoxides of Mg, Ca, Sr and Ba with Nb and Ta have been synthesized in the presence of MgCl2 as a catalyst.169 Refluxing M(OPri)5 and A(OPri)3 (A = A1 or Ga) in isopropyl alcohol afforded double isopropoxides of the type [MA(OPr )8J and [MA2(OPr1)n]170. [NbTa(OMe)10] appears to be the first mixed transition metal alkoxide isolated.171 NMR showed it to be in dynamic equilibrium with the symmetrical M2(OMe)i0 dimers in solution, with close to random distribution of the three species. 

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 synthesis of NH- and N-vinyltetrahydroindoles (1,2) is successfully performed with the cyclohexanone oxime/acetylene molar ratio 1 (2-5) at 90-140°C with bases (alkali metal hydroxides and alkoxides) taken in amounts of 10-50% of cyclohexanone oxime mass, serving as reaction catalysts. The reaction is catalyzed by potassium, rubidium, and tetrabu-tylammonium hydroxides (78MIP1). 

Significant improvement in the catalytic activity of ALB was realized without any loss of enantioselectivity by using the second-generation ALB [27] generated by the self-assembled complex formation of ALB with alkali metal-malonate or alkoxide. This protocol allowed the catalyst loading to be reduced to 0.3 mol %, for example, the Michael addition of methyl malonate to cyclohexenone catalyzed by the self-assembled complex of (ff)-ALB (0.3 mol %) and KO Bu (0.27 mol %) in the presence of MS 4A gave the adduct in 94% yield and 99% ee [28]. This reaction has been successfully carried out on a 100-g scale wherein the product was purified by recrystallization. The kinetic studies of the reactions catalyzed by ALB and ALB/Na-malonate have revealed that the reactions are second-order to these catalysts (the rate constant ALB = 0.273 M 1h 1 ALB/Na-maionate = 1-66 M 1h 1) [27]. This reaction was used as the first key step for the catalytic asymmetric total synthesis of tubifolidine (Scheme 8D. 11) [28]. 

The exchange reactions of organyltrialkoxysilanes with THEA mostly require heating of the components in an appropriate inert solvent (benzene, toluene, xylene, anisole, chloroform, methanol, ethanol etc.) for a long time. However, in some cases the reactions can be carried out at room temperature or, if necessary, with cooling. The transetherification rates and silatrane yields increase in the presence of an alkali metal hydroxide or alkoxide as a basic catalyst. 

As catalysts in the above reactions, alkali metal hydroxides or alkoxides are used (equations 15, 19-21). 

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