Ethanol, absolute, preparation oxidation

The requisite intermediate, ethyl 4-dimethylaminocyclohexylcarboxylate is prepared as follows 33 g of ethyl p-aminobenzoate dissolved in 300 cc of absolute ethanol containing 16.B cc of concentrated hydrochloric acid is hydrogenated at 50 pounds hydrogen pressure in the presence of 2 g of platinum oxide. The theoretical quantity of hydrogen is absorbed in several hours, the catalyst removed by filtration and the filtrate concentrated to dryness in vacuo. The residue Is dissolved in water, made alkaline with ammonium hydroxide and extracted with chloroform. After removal of the solvent, the residual oil is distilled to yield ethyl 4-aminocyclohexylcarboxylate, boiling point 114°C to 117°C/10 mm. 

Preparation of Sodium Bisulphide. Assemble an apparatus as shown in Fig. 66. Fill drying columns 4 with. phosphorus(V) oxide placed on glass wool. Weigh 2-2.5 g of metallic sodium, wash it with benzene and diethyl ether, thoroughly remove the oxide film from its surface, cut the sodium up into small pieces, and put them into test tube 2. Pour 75 ml of absolute ethanol into 150-200-ml round-bottomed flask 1. Fill the apparatus with dry argon (nitrogen) via tube 3. 

Super-dry ethanol. The yields in several organic preparations (e.g. malonic ester syntheses, reductions involving sodium and ethanol, etc.) are considerably improved by the use of ethanol of 99.8 per cent purity or higher. This very high grade ethanol may be prepared in several ways from commercial absolute alcohol or from the product of dehydration of rectified spirit with calcium oxide. 

Reactivity of (HPS)VO(OH). A variety of coordination complexes catalyze the oxidation of bromide by hydrogen peroxide. The first and most studied catalyst is the hydroxooxovanadium(V) complex of hydrox-yphenylsalicylideneamine (H2HPS, shown in Figure 4) (35). The proposed mechanism is shown in Scheme 3. The catalyst precursor is the crystalline (HPS)VO(OEt)(EtOH) compound, which is readily prepared from VO(iOPr)3 and H2HPS (36) in absolute ethanol. Dissolution of this solid in N,N-dimethylformamide (DMF) gives rise to five species (HPS)VO(OEt), the active catalyst (HPS)VO(OH), and three stereochemically distinct di-... 

Not all liquids form ideal solutions and conform to Raoult s law. Ethanol and water are such liquids. Because of molecular interaction, a mixture of 95.5% (by weight) of ethanol and 4.5% of water boils below (78.15°C) the boiling point of pure ethanol (78.3°C). Thus, no matter how efficient the distilling apparatus, 100% ethanol cannot be obtained by distillation of a mixture of, say, 75% water and 25% ethanol. A mixture of liquids of a certain definite composition that distills at a constant temperature without change in composition is called an azeotrope 95% ethanol is such an azeotrope. The boiling point-composition curve for the ethanol-water mixture is seen in Fig. 4. To prepare 100% ethanol the water can be removed chemically (reaction with calcium oxide) or by removal of the water as an azeotrope (with still another liquid). An azeotropic mixture of 32.4% ethanol and 67.6% benzene (bp 80.1 °C) boils at 68.2°C. A ternary azeotrope (bp 64.9°C) contains 74.1% benzene, 18.5% ethanol, and 7.4% water. Absolute alcohol (100% ethanol) is made by addition of benzene to 95% alcohol and removal of the water in the volatile benzene-water-alcohol azeotrope. 

Ethanol is commonly obtained in a 95 per cent and an absolute grade. The former has the composition of the azeotrope with water (bp 78.2°) and except for the water is quite pure. If absolute ethanol (bp 78.3°) is required, it may be prepared by heating the 95 per cent ethanol to reflux with calcium oxide for several hours and then distilling. However, absolute ethanol is available at a reasonable cost and is rarely prepared in a laboratory. The commercial absolute ethanol often contains a small amount of benzene, since it is prepared from 95 per cent ethanol by removing the water through the ternary azeotrope of benzene-ethanol-water (bp 65°). The absolute ethanol is therefore not suitable for use as a solvent for ultraviolet spectroscopy, and the 95 per cent ethanol is usually used. 

Absolute ethanol is very hygroscopic, and thus the commercial absolute ethanol and that prepared by treating the 95 per cent alcohol with calcium oxide usually contain about 0.5 per cent water. A common method for removing the residual water has been to add sodium, which reacts with water to form sodium hydroxide. However, since water is not much more acidic than ethanol, the equilibrium... 

F.H. Kohnke and co-workers prepared novel heterocyclophanes from cyclic poly-1,4-diketones, which were obtained by the oxidation of calix[6]furan and calix[4]furan. " One of the heterocyclophanes, calix[6]pyrrole, was prepared by the Paal-Knorr pyrrole synthesis from the corresponding dodecaketone. The substrate was heated with excess ammonium acetate in absolute ethanol. Interestingly, the analogous synthesis of calix[4]pyrrole under identical conditions failed, while calix[5]pyrrole is obtained only in 1% yield. 

Dimedon, 5,5-dimethylcyclohexane-l,3-dione, is prepared by an interesting process discovered by Vorlander. The reaction of 1 mole each of diethyl malonate, mesityl oxide, and sodium ethoxide in absolute ethanol probably involves a Michael addition followed by an intramolecular ester condensation to close the ring to give the diketo ester formulated (procedure of Shriner and Todd. Aqueous potassium... 

Oxidation. The use of iodine as an oxidant is exemplified by a procedure for the preparation of dibenzoyl disulfide. A solution of potassium hydroxide in absolute ethanol is saturated with hydrogen sulfide and treated with benzoyl chloride at 15°. The potassium chloride formed is removed by filtration, and iodine is added to the filtrate in the amount required to complete the oxidation. 

Nitrobenzoic acid, may be prepared by nitration of toluene and oxidation of the resulting /(-nitrotoluene, is esterified to the eorresponding ethyl ester by heating with absolute ethanol and a few drops of sulphurie acid. The resulting ethyl/>-nitrobenzoate is redueed with tin and hydrochloric acid to give the oflfieial compound. 

Arachidonyl ethanolamide (2-AG) (NIDA-Research Triangle Institute) 26.4 mAf in absolnte ethanol, MW 378.5. Prepare 2-AG aliquots in silica-coated vials. Purge vials containing 2-AG with N2 gas and store at -70 C. Do not use the cannabinoid solutions if there is suspicion of oxidation. After aliquotting, use within 6 mo. Working solutions are prepared by dilution in absolute ethanol. 

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