Potassium hydroxide-Alumina

Potassium dichromate, 3 24 Potassium diisopropylamide, 324 Potassium ethanethiolate, 325 Potassium fluoride, 279, 325-326 Potassium formate, 329 Potassium-Graphite, 326 Potassium hexamethyldisilazide, 326-327 Potassium hydride, 327-328 Potassium hydrogen persulfate, 328 Potassium hydroxide-Alumina, 328 Potassium iodide-Boron(ill) iodide, 329 Potassium iodide-Zinc-Phosphorus(V) oxide, 329... 

By treatment of the protected 2-O-tosyl-a-D-glucopyranoside 121 under microwave irradiation conditions at 100 °C for 6 min in the presence of potassium hydroxide-alumina, Cleophax et al. [82] obtained the epoxide 122 in nearly quantitative yield. Under classical heating conditions (same conditions, oil bath), the required epoxide was obtained in 25% yield only (Scheme 12.50). 

Potassium hydroxide-alumina with 0-deacetylation s. H, 750 Sodium alcohol... 

Commerioal ether was stored over potassium hydroxide pellets and used without being distilled. Because some heat is evolved when the ether is added to the alumina, the fiask is equipped with a condenser. 

The conversion of pitrosocarbamates into a-diazosulfones is efiected also with certain bases, notably by aqueous potassium hydroxide. Potassium hydroxide, however, causes rapid decomposition of p-tolyl-sulfonyldiazomethane. Alumina is thought to act as a solid base and does not cause significant decomposition. 

It has been claimed that the elimination of tosylates of 3a-alcohols in 5jS-series gives 3-oleflns with high selectivity. However, the homogeneity of these products is questionable, in view of recent findings concerning the ehmination of 3-chloro compounds (see below) and Fieser s results with the elimination of methyl lithocholate tosylate (ref. 232, cf. ref. 233). Neutral alumina may also be used to effect elimination of tosylates of 3j5-alcohols if the alumina is pretreated with potassium hydroxide the inverted alcohol is the predominant product. 

A solution of the acylated thiocyanatohydrin in a minimal amount of 5% potassium hydroxide in diglyme (other solvents such as methanol, ethanol or tetrahydrofuran have also been used) is stirred for 2 days at room temperature. Water is added to the reaction mixture to precipitate the product which is filtered or extracted with ether (or chloroform). The ether extract is washed several times with water, dried (Na2S04), and concentrated under vacuum. The thiirane usually can be crystallized from an appropriate solvent pair. Chromatography over alumina has been used for the purification of episulfides. 

Chromatography of 3, 17jS-dihydroxypregn-5-en-20-one (82a) on alumina affords the rearranged product 3/ ,17a/ -dihydroxy-17aa-methyl-D-homo-androst-5-en-17-one (84a) in quantitative yield.On the other hand, treatment of diol (82a) or diacetate (82b) with methanolic potassium hydroxide... 

As reported by Shani and Sondheimer,1 the dehydrohalogenation of the tetrabromide by means of potassium hydroxide in ethanol at 50-55° affords a mixture, which is readily separated by chromatography on alumina, of l,6-oxido[10]annulene and the isomeric 1-benzo-xepin. The latter compound is also formed during chromatography of l,6-oxido[10]annulene on silica gel.7... 

Cyclopropyl cyanide has been prepared by therepeated distillation of 7-chlorobutyronitrile over powdered potassium hydroxide,1- 2 3 4 5 or over a mixture of sodium hydroxide and alumina. ... 

The mother liquors and the two washes containing methanol are collected and combined. A one normal solution of potassium hydroxide in methanol is added in approximately equal volume to the combined washes and mother liquors. The solution is then filtered and the filter washed with a few ml of methanol. The filtrates are allowed to stand at room temperature for two to three hours to reequilibrate the iso-lysergic acid amides from the mother liquors. About 500 ml of water is then added and the mixture extracted with 2.5 liters of methylene chloride in divided portions in a separatory funnel. The combined extracts are shaken with 25 grams of anhydrous magnesium sulfate and filtered. The filtrate is taken to dryness on the rotary vacuum evaporator, care taken not to heat above 55° C. The material is purified in the same manner as that from the original reaction mixture using approximately one fourth the quantities of solvents and alumina as for the original. 

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). 

In the absence of potassium hydroxide hydrogenation of vinylic and allylic chlorides to the saturated chlorides (with only partial or no hydrogenolysis of chlorine) is accomplished over 5% platinum, 5% palladium and, best of all, 5% rhodium on alumina [40]. 

Although hydrogenation of pyrrole over a rhodium/alumina catalyst gives some 1-pyrroline (Scheme 6.18a), a better method is to dehydro-halogenate A-chloropyrrolidine by heating it with alcoholic potassium hydroxide (Scheme 6.18b). 2,5-Dihydro-1//-pyrrole, containing 15% pyrrolidine, is obtained by the zinc/hydrochloric acid reduction of pyrrole. 

The purification of the alkali hydroxides.—Numerous impurities have been reported in commercial sodium and potassium hydroxides. Several have commented on the presence of peroxide, particularly in caustic potash.19 Various salts—carbonate, sulphate, nitrate, nitrite, chloride, and phosphate—as well as alumina, silica, organic matters, and metal oxides—e.g. arsenic, vanadium, iron, etc., have been reported. More or less of the other alkalies may also be present. 

Alumina, Calcium, and Heavy Metals. — 5 gm. of potassium hydroxide should yield a clear and colorless solution with 10 cc. of water. To this solution add 25 cc. of acetic acid (sp. gr. 1.041), followed by 10 cc. of ammonia water, dilute with 65 cc. of water, and heat the fluid on the water-bath until the odor of ammonia has entirely disappeared. Now add 2 or 3 drops of ammonia water, and allow to stand twelve hours. At the end of this time there should be no precipitate, or, at most, only an exceedingly slight, flocculent precipitate. In the latter case the precipitate is collected by filtration, washed, and ignited. Its weight should not exceed 0.0005 gm. The following tests are now carried out with the filtrate ... 

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