Potassium isopropoxide

Whereas most hydrogenation catalysts function very well in water (see for example Chapter 38 for two-phase aqueous catalysis), scattered instances are known of inhibition by water. Laue et al. attached Noyori s transfer hydrogenation catalyst to a soluble polymer and used this in a continuous device in which the catalyst was separated from the product by a membrane. The catalyst was found to be inhibited by the presence of traces of water in the feed stream, though this could be reversed by continuously feeding a small amount of potassium isopropoxide [60]. A case of water inhibition in iridium-catalyzed hydrogenation is described in Section 44.6.2. 

Phenyl-2//-pyrimido[ 1,2-b]pyridazin-2-one (71) is cleaved by reaction with potassium isopropoxide in refluxing isopropyl alcohol to give the pyrimidinone (72) (72M1591). 

Potassium f-pentoxide gave similar results, whereas the yield dropped to 3-4% with potassium isopropoxide and to 1.5% with potassium methoxide. 

As noted in Section 5.2.2.1.2.3., the reaction of 1,1-dichlorocyclopropanes with alkoxides does not give the ordinary alkenyl(alkylidene)cyclopropane products when the side chains of the substrate cannot accommodate the double bonds in these positions. Instead, the usual course of the reaction in these cases is double elimination followed by addition of alkoxide to the cyclopropene double bond. Thus, c -l,l-dichloro-2,3-dimethylcyclopropane (1), when treated with potassium isopropoxide in dimethyl sulfoxide at 30 °C, gave a mixture of two isomeric ethers, l-isopropoxy-l-methyl-2-methylenecyclopropane (2) and tra 5-l-isopropoxy-2-methyl-3-methylenecyclopropane (3), in 31% and 35% yield, respectively. When 1 was reacted with potassium rcrt-butoxide in the presence of sodium methoxide the corresponding methyl ethers 4 and 5 were obtained in yields of 35% and 17%. ... 

An informative and amusing background to that unique material, camphor, has appeared. Its preparation by Oppenauer oxidation of the epimeric borneols occurs without epimerization. Epimerization does not occur in the presence of potassium t-butoxide in t-butyl alcohol, but it does with potassium isopropoxide in propan-2-ol." The reaction of camphor with phosphoric acid yields a complex mixture of m- and p-cymenes, 3,4-dimethylethylbenzene, 1,2,3,4-and 1,2,3,5-tetramethylbenzene, fenchone, carvenone, and carvacrol. A very detailed examination of the metal-ammonia reduction has revealed an intermediate camphor analogue of pinacol formed by association of a camphor anion radical with the metal cation. This intermediate was isolated and characterized. Other effects are discussed, such as that of adding a large excess of metal salt (LiBr, KBr, or NH Cl)." ... 

A high concentration of a strong base in a relatively nonpolar solvent is used to carry out the dehydrohalogenation reaction. Such combinations as sodium methoxide in methanol, sodium ethoxide in ethanol, potassium isopropoxide in isopropanol, and potassium ferf-butoxide in fcrf-butanol or dimethyl sulfoxide (DMSO) are often used. 

The addition of a sodium (or potassium) isopropoxide to an appropriate LnCl3.3Pr OH in a medium of isopropyl alcohol and benzene resnlts in the precipitation of NaCl (or KCl), which is removed by filtration. From the filtrate, quantitative yields of [Ln(OlV)3L can be isolated (Eq. 2.44) ° ... 

Guido, W, and Mathre, D. J., Phase-transfer alkylation of heterocycles in the presence of 18-crown-6 and potassium tert-butoxide, J. Org. Chem., 45, 3172, 1980. Mariani, G., Modena, G., Pizzo, G. E, and Scorrano, G., The effect of crown-ethers on the reactivity of alkoxides. Part 2. The reaction of potassium isopropoxide and 2,4-dinitrohalogenobutanes in propan-2-ol-benzene, J. Chem. Soc., Perkin Trans. 2, 1187, 1979. 

The estimation of alkoxy groups is not such a simple task. One method (26,68) involves hydrolysis and oxidation of the Hberated alcohol with excess standard potassium dichromate solution. The excess may then be estimated iodometrically. This method is suitable only for methoxides, ethoxides, and isopropoxides quantitative conversion to carbon dioxide, acetic acid, and acetone, respectively, takes place. An alternative method for ethoxides is oxidation followed by distillation, and titration of the Hberated acetic acid. 

Chelation of the enolate and orientation of the acceptor chain away from the chclatc, seems to be essential as the use of potassium tert-butoxide in to / -butyl alcohol (nonchelated enolate) results in a 1 1 mixture of cis- and tram-2132-I33. The diastereomeric ratio furthermore depends on the alcohol (R20) moiety134- 136-386, whereas the use of zirconium(IV) isopropoxide also results in high tram-selectivity (cisjtrans ratio, 1 25) 137. 

Addition of potassium ferf-butoxide or of sodium isopropoxide to the solvent led to ignition of the latter. This was attributed to presence of free metal in the alkoxides, but a more likely explanation seems to be that of direct interaction between the powerful bases and the sulfoxide. 

The IPA system is convenient in being almost thermo-neutral. All of the components can be mixed safely at the start of the reaction, and the reaction is initiated with small amounts of potassium hydroxide, or isopropoxide. The reaction is clean and no side reactions seem to occur. There is no apparent formation of hydrogen. 

Potassium methylselenide, 0451 Rhenium hexamethoxide, 2603 Sodium ethoxide, 0878 Sodium isopropoxide, 1270 Sodium methoxide, 0464... 

Abundant evidence has been gathered to show that pure alumina, prepared either from aluminum isopropoxide or aluminum nitrate and ammonia and calcined at 600-800°, has intrinsic acidic sites. Several physical methods have been used to study the acidity of alumina. Titration with butylamine (33), dioxane (34), and aqueous potassium hydroxide (35) as well as chemisorption of gaseous ammonia (35), trimethylamine (36), or pyridine (37) gave apparent acidity values which approximated those of silica-alumina. On the other hand, the indicator method for testing the acidity of solids as developed by Walling (3S) showed no indication of even weak acids (39, 40). 

The study of the product distribution from the isomerization of 3,3-dimethylbutene proved useful for evaluating the strength of the acid centers in aluminas (36). Pure alumina from aluminum isopropoxide which was calcined at 700° showed optimum activity. Heating at higher temperatures decreased the number of acid sites as well as their acid strength. Aluminas obtained from potassium or sodium aluminate contained alkali in amounts of 0.08 to 0.65%, depending on the way of precipitation and on the number of washings. 

Pure alumina catalyst prepared either by hydrolysis of aluminum isopropoxide or by precipitation of aluminum nitrate with ammonia, and calcined at 600-800°, contains intrinsic acidic and basic sites, which participate in the dehydration of alcohols. The acidic sites are not of equal strength and the relatively strong sites can be neutralized by incorporating as little as 0.1 % by weight of sodium or potassium ions or by passing ammonia or organic bases, such as pyridine or piperidine, over the alumina. 

Potassium peroxomonosulfate, 259 Titanium(IV) isopropoxide, 311 of allylic, homoallylic alcohols t-Butyl hydroperoxide-Dialkyl tar-trate-Titanium(IV) isopropoxide, 51 t-Butyl hydroperoxide-Dibutyltin oxide, 53... 

Butyl hypochlorite, 55 of phenols to quinones Benzoyl /-butyl nitroxide, 28 2,3-Dichloro-5,6-dicyano-l, 4-benzoqui-none, 104 Periodic acid, 238 of phosphorus compounds Dimethyldioxirane, 120 of selenium compounds Potassium permanganate, 258 of sulfides to sulfoxides and sulfones /-Butyl hydroperoxide-Dialkyl tar-trate-Titanium(IV) isopropoxide, 51 ra-Chloroperbenzoic acid, 76, 112 Dimethyldioxirane, 120 of thiols to sulfur compounds Trimethylsilyl chlorochromate, 327... 

TRANSAMINATION 4-Pyridinecarboxaldchyde. TRANSESTERIFICATIONS Titanium(IV) ethoxide. Titanium(lV) isopropoxide. TRIFLUOROMETHYLATION Zinc. TROFIMOV REACTION Potassium hydroxidc-Dimethyl sulfoxide. 

Codeine sulfate trihydrate Ammonium hydroxide Aluminum isopropoxide Potassium sodium tartrate tetrahydrate Palladium on carbon... 

The secondary alcohols are oxidized to ketones by refluxing with aluminium isopropoxide, A1[0CH(CH3)2]3 [or Al(0-iPr)3], or potassium t-butoxide, KOC(CH3)3 [or KO-t-Bu]. A ketone such as acetone used in the reaction as refluxing agent is reduced to alcohol, 2-propanol. The reaction is known as the Oppenauer oxidation. The reverse reaction known as the Meerwein-Ponndorf-Verly reduction is the reduction of ketones to alcohols in the presence of alcohol such as 2-propanol. Potassium fert-butoxide can be used for the oxidation of primary alcohols. Aluminium isopropoxide in acetone is particularly used for... 

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