Potassium hydroxide as catalyst

As in the previous sections, secondary enamines in which either the nitrogen or the double bond is further conjugated with an electron-withdrawing or electron-donating substituent are not reviewed. Metal derivatives of imines (metalloenamines) are discussed in Chapter 25. We are only concerned with secondary enamines, in equilibrium with their imine tautomer, form by condensation of a primary amine with an aldehyde or ketone. Such condensations can readily be carried out using potassium hydroxide as catalyst or by azeotropic distillation in the presence or absence of add catalysts or, for more hindered or acid-sensitive ketones, titanium tetrachloride or dibutyltin dichloride, respectively, may be used. 

By using sodium or potassium hydroxides as catalysts of aminolysis, it is possible to regenerate the initial monoethanolamine (a bifunctional compound in the conditions of PU chemistry and to destroy the oxazolidone formed (reaction 20.11) [33] ... 

When the asymmetric carbon is a part of a heterocyclic monomeric system, the polymerization of such a compound may lead to optically active products. For example, in the case of the polymerization of 1-propylene oxide with potassium hydroxide as catalyst, a low molecular weight crystalline optically active polymer formed. When the same monomer was polymerized by use of a ferric chloride-propylene oxide complex catalyst, a high molecular weight product was formed. This polymer could be separated into an amorphous form with little or no optical activity and a crystalline resin with optical rotation similar to that observed for the potassium hydroxide-catalyzed process [106]. 

Ethoxylation reactions are normally initiated with sodium or potassium hydroxide as catalyst. When the reaction is complete, the catalyst may be removed by filtration or liquid-liquid extraction, or may simply be neutralized and left in the product. The presence of neutralized catalyst may cause problems in certain applications, or may sometimes be detectable as turbidity or even crystals in the product. Normally, if the catalyst is removed, inorganic residues are reduced to the low parts per million level. If the catalyst is simply neutralized, the resulting salt is present in the 0.5-1.0% range. 

As a demonstration of the complete synthesis of a pharmaceutical in an ionic liquid, Pravadoline was selected, as the synthesis combines a Friedel-Crafts reaction and a nucleophilic displacement reaction (Scheme 5.1-24) [53]. The allcylation of 2-methylindole with l-(N-morpholino)-2-chloroethane occurs readily in [BMIM][PF6] and [BMMIM][PF6] (BMMIM = l-butyl-2,3-dimethylimida2olium), in 95-99 % yields, with potassium hydroxide as the base. The Friedel-Crafts acylation step in [BMIM][PF6] at 150 °C occurs in 95 % yield and requires no catalyst. 

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... 

Osmium This metal had already been found by Haber to be an excellent ammonia catalyst. Its activity is further increased by alkali metal oxides, especially by potassium hydroxide. As the pure metal 2% ammonia, promoted, 4%. 

The acidic nature of the SiO2 (AI2O3) catalysts over the whole range was explored by Thomas (78) using a titration procedure with potassium hydroxide as neutralizer. A general relationship was observed between the amount of catalytic cracking and acidity. His method of determining the acid nature of the catalyst has been criticized by Miesserov (79) whose work indicated that NaOH solutions reacted with other protons... 

The first of these relates to the differences between reactions catalyzed by these materials in the presence and absence of hydroxyl compound initiators. Polymerization with added amounts of such initiators proceeds slower than without them at the same catalyst concentration. This is in contrast to polymerization of epoxides and to copolymerization of epoxides and anhydrides using potassium hydroxide as the catalyst. In the latter cases, little or no reaction occurs in the absence of an initiator. Hydroxyl compounds also retard the activation of the catalyst that is, the induction periods are longer in their presence. Finally, the molecular-weight distribution of the polymer prepared without the initiators is much broader than that of the polymers made with the initiators. 

A similar approach was reported by Lygo and co-workers who applied comparable anthracenylmethyl-based ammonium salts of type 26 in combination with 50% aqueous potassium hydroxide as a basic system at room temperature [26, 27a], Under these conditions the required O-alkylation at the alkaloid catalyst s hydroxyl group occurs in situ. The enantioselective alkylation reactions proceeded with somewhat lower enantioselectivity (up to 91% ee) compared with the results obtained with the Corey catalyst 25. The overall yields of esters of type 27 (obtained after imine hydrolysis) were in the range 40 to 86% [26]. A selected example is shown in Scheme 3.7. Because the pseudo-enantiomeric catalyst pairs 25 and 26 led to opposite enantiomers with comparable enantioselectivity, this procedure enables convenient access to both enantiomers. Recently, the Lygo group reported an in situ-preparation of the alkaloid-based phase transfer catalyst [27b] as well as the application of a new, highly effective phase-transfer catalyst derived from a-methyl-naphthylamine, which was found by screening of a catalyst library [27c],... 

Rapeseed methyl ester (RME) is another alternative biofuel that can be used in diesel engines. RME has the advantages that it is renewable compared to diesel, non-toxic and less flammable compared with many other fuels, like ethanol. RME has the same cetane number, viscosity and density as diesel, contains no aromatic compounds and is biologically degradable with minor contamination in soil. RME can be produced from vegetable oils, but is mostly produced from rapeseed oil by pressing of the seeds or by extraction. Up to 3 tons of rapeseed can be produced from one hectare. The fatty acids in rapeseed oil are mostly oleic acid, linoleic acid and linolenic acid. The oil is pressed from the plant and after some purification allowed to react with methanol in the presence of potassium hydroxide as a catalyst, to produce a methyl ester, see Figure 6.6. 

Crown ether catalysis of the reduction is also useful (Table I), with potassium hydroxide as the base and 18-crown-6 as the catalyst (18). 

The literature procedure for condensation of benzil with 1,3-diphenyl-acetone in ethanol with potassium hydroxide as basic catalyst suffers from the low boiling point of the alcohol and the limited solubility of both potassium hydroxide and the reaction product in this solvent. Triethylene glycol is a better solvent and permits operation at a higher temperature. In the procedure that follows, the glycol is used with benzyl-trimethylammonium hydroxide, a strong base readily soluble in organic solvents, which serves as catalyst. 

The interaction of a catalyst with impurities can also lead to an increase in catalyst activity. Polyether polyols prepared from ethylene oxide or propylene oxide are often prepared with potassium hydroxide as a catalyst. Residual catalyst in the polyol has been shown to increase the reaction rate with DBTDL. 

Arylselenocyclopropanes 6 were prepared from aryl chloromethyl selenides and alkenes in a solid-liquid phase-transfer catalytic system, under sonication. The best results were obtained using solid potassium hydroxide as the base, methyltrioctylammonium chloride as catalyst and the alkene as solvent ( 10 fold excess in respect to carbene precursor). 

Thus, heating methyl 2-aminonicotinate under reflux for 16 hours with methyl isocyanate in pyridine gave a 76% yield of 3-methylpyrido[2,3-rf]pyrimidine-2,4(l//,3/f)-dione (R1 = H R2 = Me), whereas the method using ethanolic aqueous potassium hydroxide as catalyst88 could not be repeated.83 The cyclization of 2-(arylamino)nicotinic acid methyl esters with various alkyl isocyanates requires 6 days at reflux in xylene with camphorsulfonic acid as catalyst.91,92... 

The reaction of aminothioltriazoles (147) with 3-formylchromone (154) under phase-transfer catalysis, consisting of aqueous potassium hydroxide as a base, methylene chloride or benzene, and t-butylammonium hydrogensulfate as a phase-transfer catalyst, furnished the triazolo[3,4-ft]-1,3,4-thiadiazepines (156) (60-75% yield), via the condensation intermediates (155) (Scheme 27) <87SC185l>. 2-(Dicyanomethylene)-l,3-indanedione (157) also reacted with (147) to give the tetracyclic thiadiazepines (159) (ca. 20% yield) via the intermediates (158) <93BCJ2612>. 

Worldwide, 94% of the chlorine is made by the electrolysis of brine. Sodium hydroxide and hydrogen are prodnced as by-products. A few plants produce potassium hydroxide as well as, or instead of, sodinm hydroxide by the electrolysis of potassium chloride solutions. Abont 3% of the chlorine is made by other processes. These include electrolysis of hydrochloric acid electrolysis of molten sodinm or magnesium chloride, which, respectively, produce sodium or magnesium metal as well as chlorine " nitric acid oxidation of potassinm chloride to make nitrosyl chloride, which is further oxidized by oxygen to make potassium nitrate, and the oxidation of hydrochloric acid directly with oxygen or air using a catalyst, or indirectly throngh the formation and snbsequent oxidation of metal chlorides. ... 

The factors affecting the choice of catalyst are cost and efficacy. In the Haber process the main catalyst used has been iron with potassium hydroxide as promoter. In the AMV process the iron catalyst has been improved with a new combination of promoters which gives longer life and higher activity. Many catalysts can easily be poisoned and iron is no exception. It is poisoned by H2O vapour, H2S, CO and CO2, and therefore these must be excluded from the process if long life is to be assured. 

On an industrial scale, the reaction in aqueous solution is a disadvantage because concentrated water-free products cannot be obtained without additional working-up steps. Therefore, a water-free process was developed, which is outlined in Fig. 44. The alkyl polyglycoside is initially introduced into the reactor with an excess of butyl chloride and heated to 80 °C. The reaction is initiated by addition of potassium hydroxide as the catalyst. On completion of the reaction, the reaction mixture is neutralized, the potassium chloride precipitate is filtered off, and the excess butyl chloride is distilled off. The product is composed of various alkyl polyglycosides and alkyl polyglyco-... 

The nature of the potassium promoter will now be discussed. It is clear that potassium is present on the catalyst only in the oxide state. No metallic potassium is formed during the activation stage, during which the dispersion of the potassium oxide is increased markedly (see Fig. 2.42, which shows an increase in intensity and the loss of broadening due to differential charging). These findings render the suggested mechanism of the formation of potassium hydroxide as the active phase formed via hydrolysis of potassium amide to be unlikely, since it requires the intermediate presence of metallic potassium. 

Monomer is synthesized by heating acetylene and methanol rmder pressure in the presence of potassium hydroxide as a catalyst. Polymer is obtained using BFj, I2, and AICI3 as cationic polymerization catalysts. Maintain monomer under pressure at 5°C and add dioxane solution of boron trifluoride and heat gradually to 100°C. When this is polymerized, an atactic polymer like a thick malt syrup is formed. When dried propane is used as a solvent at —78°C, and when boron trifluoride diethyletherate is used as a catalyst, a crystalline isotactic polymer is obtained. Water... 

Optically active propylene oxide was polymerized by potassium hydroxide as a catalyst and the polymer of an osmometric molecular weight of 3200 was obtained [5]. Optical rotation of the polymer was measured in 35 different solvents at ambient temperature at a fixed concentration of 2.5 g/100 ml. 

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