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Aromatic Alcohols, Phenols, and Ethers
193. Preparation of Benzyl Alcohol from Benzaldehyde (Section 439). - Place in a 250 cc. bottle 20 grams of benzaldehyde and a cold solution of 18 grams of potassium hydroxide in 12 cc. of water. Close the bottle with a cork or a rubber stopper, shake it vigorously until an emulsion is formed, and set aside over night or longer. (Eq.) Add enough water to dissolve the crystals of potassium benzoate formed, and extract the solution three times with ether, using about 50 cc. each time. Save the aqueous solution. Dry the ethereal solution with anhydrous copper sulphate - distil off the ether (§34, page 22), and distil the benzy alcohol. Weigh the alcohol and calculate the percentage yield.
Benzyl alcohol boils at 206°. The yield in the preparation should be about 7 grams.
Add an excess of hydrochloric acid to the filtered aqueous solution of potassium benzoate, filter off the precipitate of benzoic acid, and wash it with cold water. Crystallize the acid from boiling water. Weigh the acid and calculate the, percentage yield.
Benzoic acid melts at 121.4°; it is soluble in 345 parts of water at 20°, and in 17 parts at 100°.
194. Properties of Benzyl Alcohol (Section 439). - (a) Benzyl alcohol and hydrochloric acid. - Mix 2 cc. of benzyl alcohol and 4 cc. of concentrated hydrochloric acid. Heat the mixture slowly and note any change produced. (Eq.) Observe the odor of the substance formed.
(b) Oxidation of benzyl alcohol. - Mix together, 1 cc. of concentrated nitric acid, 4 cc. of water, and 3 drops of benzyl alcohol. Boil the mixture for about 2 minutes and note the odor from time to time. The characteristic odor of benzaldehyde is first served, and then disappears as the aldehyde is oxidized further to benzoic acid, Cool the solution in running water; if the oxidation has progressed far enough benzoic acid will crystallize out. (Eq.)
(c) Benzyl alcohol and acetyl chloride. - Add acetyl chloride drop by drop, to about 2 cc. of benzyl alcohol as long as evident reaction takes place. Pour the product into cold water and shake. (Eq.)
195. Preparation of Diphenylcarbinol from Benzophenone (Section 440). - In a 500 cc. flask dissolve 15 grams of benzophenone and 15 grams of potassium hydroxide in 150 cc. of alcohol. Add 15 grams of zinc dust, connect the flask with a reflux condenser and boil for 1 1/2 hours. (Eq.) Filter hot, add water until the solution clouds, and set aside to crystallize. Filter off the crystals by suction, and wash with dilute alcohol. A second crop of crystals may be obtained from the filtrate.
Diphenylcarbinol melts at 67.5°-68°. The yield is nearly theoretical.
Warm a few of the crystals with concentrated hydrochloric acid. (Eq.)
196. Preparation of Diphenylethylcarbinol by the Grignard Reaction (Section 349). - In a 200 cc. flask surrounded by cold water and provided with a return condenser, place 5 grams of magnesium powder, and add slowly through the condenser from a separatory funnel a solution of 38 grams of ethyl iodide dissolved in 50 cc. of ether which has been dried over sodium. If a reaction does not take place promptly, add a small crystal of iodine. Toward the end of the reaction it may be necessary to heat the flask by surrounding it with warm water. When the magnesium has passed into solution add, drop by drop, through the condenser, a solution of 10 grams of benzophenone in 10 grams of dry benzene. If the reaction ceases, place warm water around the flask for a few minutes. Cool the reaction-mixture, and pour it slowly into about 200 cc. of ice-water which contains about 10 cc. of dilute sulphuric acid. Extract twice with ether, using about 100 cc. each time. Shake the ether with a little sodium hydroxide solution if it is colored by iodine. Filter the ether solution, and distil off the ether; dissolve the residue in 50 cc. of hot petroleum ether and set the solution aside to crystallize. Weigh the product and calculate the yield from the benzophenone used.
Diphenylethylcarbinol melts at 95°. The yield should be from 10 to 12 grams.
197. Properties of Phenol (Sections 444, 445). - (a) Solubility of phenol. - Caution. - Do not touch phenol; it causes painful blisters when brought into contact with the skin. Determine the solubility of phenol in the following: Water, a solution of sodium hydroxide, and a solution of sodium carbonate. Use about 1 gram of phenol in each case, and add the liquids in portions of about 2 cc. until solution is complete; shake thoroughly after each addition of the solvent.
(b) Acidity of phenol. - Test an aqueous solution of phenol with litmus paper and with Congo paper. Test a dilute solution of hydrochloric acid with the two indicators. Do you observe a difference? A much higher concentration of hydrogen ions is required to affect the coloring matter on the Congo paper than to affect litmus. From the results obtained in experiment (a) above what conclusion can be drawn in regard to the relative acidity of phenol and carbonic acid? Test a solution of picric acid (trinitrophenol), acetic acid, benzoic acid, and salicylic acid, with the two indicators.
(c) Phenol and acetyl chloride. - Add acetyl chloride, drop by drop, as long as an evident reaction takes place, to about 0.5 gram of phenol. (Eq.) Pour the product into water and note the odor.
(d) Phenol and ferric chloride. - Add a few drops of a dilute aqueous solution of ferric chloride (1 part of the 10 per cent reagent with 3 parts of water) to an aqueous solution of phenol.
(e) Identification of phenol by converting it into s-tribromphenol. - Dissolve about 0.1 gram of phenol in 5 cc. of water and add an aqueous solution of bromine until a permanent yellow color is formed. Filter off the precipitate and wash it with a solution of sulphur dioxide or of acid sodium sulphite until there is a strong odor of sulphur dioxide. Wash with water. Dissolve the compound in 10 cc. of hot alcohol, filter, add 20 cc. of hot water, and set aside to crystallize. Filter off the crystals and dry them on a porous plate. Determine the melting-point of the crystals; the 2,4,6-tribromphenol which is formed melts at 93°.
Notes. - (d) If the ferric chloride solution contains much free acid it will not give the usual test - the production of a marked color. If this occurs makeup a reagent for this and the following experiments as follows: Add to a 10 per cent solution of ferric chloride a solution of sodium hydroxide, drop by drop, until a permanent precipitate is just formed on shaking. If too much alkali is added, a little of the solution of ferric chloride can be used to almost dissolve it. Filter the solution, which should have a deep yellow color and mix with three volumes of water.
(e) When bromine is added in excess to an aqueous solution of phenol, a compound of the formula Br3C6H2.OBr, is formed, which is converted by sulphur dioxide into tribromphenol, Br3C6H2.OH. On account of the great insolubility of this compound in cold water, it is of value in detecting the presence of phenol in dilute aqueous solutions. Salicylic acid, sulphanilic acid, and a few other compounds are converted into tribromphenol by bromine water.
198. General Reactions of Phenols (Section 456). - (a) With ferric chloride. - Add a dilute aqueous solution of ferric chloride (see note to experiment 197d, above) to dilute aqueous solutions of pyrocatechol quinol, resorcinol, cresol, a-naphthol, b-naphthol, and pyrogallol. If no color appears, dissolve a little of the substance in alcohol and add a drop of ferric chloride solution.
(b) With bromine water. - Add bromine water to the solutions of the phenols listed above.
(c) Preparation of phthaleins from phenols (Section 473). - Put in a dry test-tube about 0.1 gram of phenol, in a second tube 0.1 gram of resorcin, and in a third 0.1 gram of thymol. To each tube add about 0.1 gram phthalic anhydride and 2 drops of concentrated sulphuric acid. Place the tube for 3 minutes in an oil-bath heated to 160°. Cool, add 5 cc. of a solution of sodium hydroxide, and observe the color by transmitted and reflected light. If the solution appears to be too concentrated, pour off a little and dilute with water. (Eqs.)
Notes. - (a) Most phenols give a color when treated with a solution of ferric chloride. The reaction is valuable in testing for compounds of this class.
(b) Most monatomic phenols which dissolve in water give a precipitate when treated with bromine water.
199. Preparation and Properties of Anisol (Section 457). - (a) Add to 50 cc. of methyl alcohol, contained in a 250 cc. flask, 2.5 grams of sodium; the metal should be cut into about half a dozen pieces and added slowly, and the flask should be kept cold by immersion in water. When the sodium has reacted, add to the solution 10 grams of phenol and 20 grams of methyl iodide. Attach a reflux condenser to the flask, and heat on a water-bath until a drop of the solution, when diluted with water, no longer shows an alkaline reaction. The reaction is complete in about an hour. Distil off the excess of methyl alcohol on a water-bath, and add about 25 cc. of water to the residue. Extract with a small amount of ether, dry the ethereal solution with calcium chloride, and distil off the ether on a water-bath. Distil the residue over a free flame. Calculate the percentage yield from the phenol used.
Anisol boils at 155°. The yield is nearly the theoretical.
(b) Solubility of anisol. - Determine if anisol is soluble in the following: dilute hydrochloric acid, dilute sodium hydroxide, and cold concentrated sulphuric acid.