Experimental Organic Chemistry - James F. Norris, Ph. D. - Chapter XXV.

Chapter XXV

Heterocylic Compounds

230. Formation of Thiophene (Section 555). - Shake together in a test-tube 1 gram of red phosphorus and 2 grams of flowers of sulphur. Heat the mixture over a free flame until action begins. Prepare some sodium succinate by neutralizing 2 grams of succinic acid with a strong solution of sodium carbonate and evaporating to dryness. Hood. - Powder the residue and grind it with the phosphorus sulphide. Place the mixture in an 8-inch test-tube which is fitted with a glass tube bent at two right angles; the second bend of the tube should pass to the bottom of a test-tube placed in a beaker containing ice and concentrated hydrochloric acid. Heat under the hood the tube containing the mixture of sodium succinate and phosphorus trisuiphide as long as anything distils. Note whether the oil is lighter or heavier than water.

Add to a drop of the oil a trace of isatin and 1 cc. of concentrated sulphuric acid. Test a sample of commercial benzene and one of benzene purified by crystallization from thiophene.

231. Formation of Furfuraldehyde (Section 557). - Boil a small piece of gum arabic in a test-tube with 5 cc. of dilute sulphuric acid. Hold in the vapors escaping from the tube a piece of paper which has been moistened with a solution of 2 drops of aniline and 2 drops of glacial acetic acid in 2 cc. of water.

232. Properties of Pyridine (Sections 560, 561). - (a) Base-forming property of pyridine. Dissolve about 1 cc. of pyridine in 5 cc. of water and test the solution with litmus paper.

Add a solution of pyridine to a solution of ferric chloride and to one of aluminium chloride. (Eq.)

(b) Pyridine and mercuric chloride. - Add an aqueous solution of pyridine to one of mercuric chloride. The crystalline precipitate has the composition HgCl₂.C₅H₅N.

(c) Pyridine and oxidizing agents. - Determine whether pyridine is oxidized by a solution of potassium permanganate, by concentrated nitric acid, or by a mixture of potassium bichromate and sulphuric acid.

(d) Behavior of pyridine as an amine. - Determine whether pyridine is a primary, secondary, or tertiary amine. Describe in detail the tests applied.

(e) Pyridine and methyl iodide. - Mix together in a test-tube 5 drops of pyridine and 5 drops of methyl iodide. Set aside and examine after a few hours. (Eq.)

233. Preparation of Quinoline by Skraup's Synthesis (Section 563). - In a 1500 cc. flask place 24 grams of nitrobenzene and 38 grams of aniline; add cautiously 100 grams of pure concentrated sulphuric acid, and then, slowly with shaking, 120 grams of glycerol. Connect the flask with a long reflux water-condenser, the inner tube of which has a wide bore. Support the flask and condenser by means of clamps. Do not use a gauze or bath, but heat the flask directly, cautiously, with a free flame. In a short time a vigorous reaction will begin, and a large amount of heat is evolved; when this occurs remove the flame. When the spontaneous boiling ceases, place a wire-gauze under the flask, and heat to boiling for 2 hours. Cool the flask slightly, add about 100 cc. of water and distil with steam as long as an oil passes over. This distillation serves to remove the excess of nitrobenzene. Cool the flask under running water, and add a cold solution of 100 grams of sodium hydroxide in 150 cc. of water. Distil over the quinoline with steam. When an oil no longer separates in the condenser, stop the distillation.

The aqueous distillate contains the quinoline formed in the reaction and a small amount of aniline. In order to separate the latter, advantage is taken of the fact that aniline is converted into a diazo compound by nitrous acid, whereas quinoline, being a tertiary amine, is not affected by this reagent. When the aqueous solution containing the diazo compound is heated, the latter is converted into a phenol. Quinoline can be readily separated from phenol by distillation with steam from an alkaline solution, in which the phenol is present as the sodium salt and is, therefore, non-volatile. To effect this separation treat the aqueous distillate as follows: Add to the distillate 10 cc. of concentrated sulphuric acid. There should be a small excess of acid over that required to dissolve the oil. Next add a few cubic centimeters of a solution of sodium nitrite and stir vigorously. Continue the addition until the solution smells strongly of the oxides of nitrogen. The quinoline is liberated from its salt by adding a solution of 40 grams of sodium hydroxide in 50 cc. of water. Distil again with steam as long as an oil passes over. Separate the oil, dry it with solid potassium hydroxide and distil. By extracting with ether the aqueous solution, from which the quinoline was finally separated, the yield can be slightly increased.

Quinoline boils at 238°. The yield in this preparation is about 38 grams.

Alkaloids

234. General Reactions of Alkaloids (Section 571). - Dissolve the amount of quinine sulphate that can be held on the point of a pen-knife in about 20 cc. of water. Observe the appearance of the solution. Add to 2 cc. of the solution, drop by drop, a dilute (1 per cent) solution of tannic acid. Repeat using solutions of phosphomolybdic acid, picric acid, iodine in potassium iodide, and potassium mercuric iodide. The last-named solution can be prepared by adding an excess of a solution of potassium iodide to a solution of mercuric chloride.

235. Test for an Alkaloid in Tobacco: Nicotine (Section 573). - In a small distilling flask boil together one cigarette, 25 cc. of water, and 2 cc. of dilute sulphuric acid. At the end of 10 minutes, add an excess of a solution of sodium hydroxide, connect the flask with a condenser, and distil over about 10 cc. of the solution. Test the distillate by adding to separate portions of it, drop by drop, solutions of the following: mercuric chloride, tannic acid, iodine in potassium iodide, and potassium mercuric iodide.

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Chapter XXV Heterocylic Compounds 230. Formation of Thiophene (Section 555). - Shake together in a test-tube 1 gram of red phosphorus and 2 grams of flowers of sulphur. Heat the mixture over a free flame until action begins. Prepare some sodium succinate by neutralizing 2 grams of succinic acid with a strong solution of sodium carbonate and evaporating to dryness. Hood. - Powder the residue and grind it with the phosphorus sulphide. Place the mixture in an 8-inch test-tube which is fitted with a glass tube bent at two right angles; the second bend of the tube should pass to the bottom of a test-tube placed in a beaker containing ice and concentrated hydrochloric acid. Heat under the hood the tube containing the mixture of sodium succinate and phosphorus trisuiphide as long as anything distils. Note whether the oil is lighter or heavier than water. Add to a drop of the oil a trace of isatin and 1 cc. of concentrated sulphuric acid. Test a sample of commercial benzene and one of benzene purified by crystallization from thiophene. 231. Formation of Furfuraldehyde (Section 557). - Boil a small piece of gum arabic in a test-tube with 5 cc. of dilute sulphuric acid. Hold in the vapors escaping from the tube a piece of paper which has been moistened with a solution of 2 drops of aniline and 2 drops of glacial acetic acid in 2 cc. of water. 232. Properties of Pyridine (Sections 560, 561). - (a) Base-forming property of pyridine. Dissolve about 1 cc. of pyridine in 5 cc. of water and test the solution with litmus paper. Add a solution of pyridine to a solution of ferric chloride and to one of aluminium chloride. (Eq.) (b) Pyridine and mercuric chloride. - Add an aqueous solution of pyridine to one of mercuric chloride. The crystalline precipitate has the composition HgCl₂.C₅H₅N. (c) Pyridine and oxidizing agents. - Determine whether pyridine is oxidized by a solution of potassium permanganate, by concentrated nitric acid, or by a mixture of potassium bichromate and sulphuric acid. (d) Behavior of pyridine as an amine. - Determine whether pyridine is a primary, secondary, or tertiary amine. Describe in detail the tests applied. (e) Pyridine and methyl iodide. - Mix together in a test-tube 5 drops of pyridine and 5 drops of methyl iodide. Set aside and examine after a few hours. (Eq.) 233. Preparation of Quinoline by Skraup's Synthesis (Section 563). - In a 1500 cc. flask place 24 grams of nitrobenzene and 38 grams of aniline; add cautiously 100 grams of pure concentrated sulphuric acid, and then, slowly with shaking, 120 grams of glycerol. Connect the flask with a long reflux water-condenser, the inner tube of which has a wide bore. Support the flask and condenser by means of clamps. Do not use a gauze or bath, but heat the flask directly, cautiously, with a free flame. In a short time a vigorous reaction will begin, and a large amount of heat is evolved; when this occurs remove the flame. When the spontaneous boiling ceases, place a wire-gauze under the flask, and heat to boiling for 2 hours. Cool the flask slightly, add about 100 cc. of water and distil with steam as long as an oil passes over. This distillation serves to remove the excess of nitrobenzene. Cool the flask under running water, and add a cold solution of 100 grams of sodium hydroxide in 150 cc. of water. Distil over the quinoline with steam. When an oil no longer separates in the condenser, stop the distillation. The aqueous distillate contains the quinoline formed in the reaction and a small amount of aniline. In order to separate the latter, advantage is taken of the fact that aniline is converted into a diazo compound by nitrous acid, whereas quinoline, being a tertiary amine, is not affected by this reagent. When the aqueous solution containing the diazo compound is heated, the latter is converted into a phenol. Quinoline can be readily separated from phenol by distillation with steam from an alkaline solution, in which the phenol is present as the sodium salt and is, therefore, non-volatile. To effect this separation treat the aqueous distillate as follows: Add to the distillate 10 cc. of concentrated sulphuric acid. There should be a small excess of acid over that required to dissolve the oil. Next add a few cubic centimeters of a solution of sodium nitrite and stir vigorously. Continue the addition until the solution smells strongly of the oxides of nitrogen. The quinoline is liberated from its salt by adding a solution of 40 grams of sodium hydroxide in 50 cc. of water. Distil again with steam as long as an oil passes over. Separate the oil, dry it with solid potassium hydroxide and distil. By extracting with ether the aqueous solution, from which the quinoline was finally separated, the yield can be slightly increased. Quinoline boils at 238°. The yield in this preparation is about 38 grams. Alkaloids 234. General Reactions of Alkaloids (Section 571). - Dissolve the amount of quinine sulphate that can be held on the point of a pen-knife in about 20 cc. of water. Observe the appearance of the solution. Add to 2 cc. of the solution, drop by drop, a dilute (1 per cent) solution of tannic acid. Repeat using solutions of phosphomolybdic acid, picric acid, iodine in potassium iodide, and potassium mercuric iodide. The last-named solution can be prepared by adding an excess of a solution of potassium iodide to a solution of mercuric chloride. 235. Test for an Alkaloid in Tobacco: Nicotine (Section 573). - In a small distilling flask boil together one cigarette, 25 cc. of water, and 2 cc. of dilute sulphuric acid. At the end of 10 minutes, add an excess of a solution of sodium hydroxide, connect the flask with a condenser, and distil over about 10 cc. of the solution. Test the distillate by adding to separate portions of it, drop by drop, solutions of the following: mercuric chloride, tannic acid, iodine in potassium iodide, and potassium mercuric iodide.