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Aromatic Compounds Containing Two or More Unlike Groups
215. Preparation of o-Nitrophenol (Section 498). - (a) In a small beaker melt 20 grams of phenol on the steam-bath, and add it slowly with stirring to a mixture of 30 cc. of pure concentrated nitric acid and 100 grams of ice contained in a beaker. Stir the mixture and then let it stand for at least 3 hours; if more convenient it can be set aside until the next laboratory exercise. Decant off as much of the acid layer as possible through a funnel containing a filterpaper, which serves to collect the part of the oil that is suspended in water. Add about 200 cc. of water to the oil, stir, and decant off the liquid as before. Repeat the washing with 200 cc. of water. Place the filter-paper with the adhering oil in a liter flask, arranged for steam distillation (see Fig. 12, page 19). Wash the oil in the beaker into the flask using for the purpose 200 cc. of water, which should be measured. (This is done to facilitate the isolation of the p-nitrophenol which is not volatile with steam.) Distil with steam as long as any oil or solid condenses (about 30 minutes). If the oil solidifies in the condenser, turn off the water from the latter; when the water in the condenser becomes heated, the solid melts and runs into the receiver. Filter, dry, and weigh the o-nitrophenol. Recrystallize the product by dissolving it in 40 cc. of hot alcohol and adding 40 cc. of water; set aside over night to crystallize. Filter by suction and wash with a small amount of cold alcohol. Heat the filtrate to boiling and add an equal volume of water. Set aside and collect as before.
o-Nitrophenol melts at 45°. The yield is from 7 to 8 grams.
(b) The p-nitrophenol, which is not volatile with steam, may be obtained from the residue in the flask as follows: Cool in running water the solution in the flask to 40° and filter it rapidly through a large funnel. The volume of the solution should be about 300 cc. Add 2 grams of bone-black to the filtrate and boil it for about 15 minutes. Filter hot, and place in cold water. The solution should be cooled to at least 10°, and ice should be used if necessary. If crystals do not form, scratch the side of the beaker with a glass rod. After standing for about half an hour, filter off the crystals by suction and wash them with a little cold water. The yield is about 3 grams. By evaporating the mother-liquor to dryness on the steam-bath and extracting the residue with about 50 cc. of boiling benzene, about 2 grams more of the product can be obtained.
p-Nitrophenol melts at 114°; it crystallizes well from benzene in which it is readily soluble hot and difficultly soluble cold. When pure it crystallizes readily from hot water.
Compare the conditions used in the nitration of phenol with those used in making nitrobenzene (experiment 170, page 135), dinitrobenzene (experiment 172, page 137), and nitroacetanilide (experiment 219, page 178).
Note. - The yields are small in this preparation on account of the fact that compounds other than o- and p-nitrophenol are formed; among these are substances of a tarry nature from which it is difficult to separate the paracompound. It is on this account that special precautions are necessary in order to obtain p-nitrophenol in a crystalline condition.
216. Isolation of Eugenol from Cloves (Section 505). - Distil 25 grams of cloves with steam as long as an oil separates in the condenser; during this time about 600 cc. of water will distil. Give the vessel containing the mixture a rotary motion so that the oil settles. Decant off most of the water, and pour the oil into a test-tube. By means of a pipette transfer about one-half the oil to a small test-tube, cover it with about 2 cc. of water, and add a dilute solution of sodium hydroxide (10 per cent) as long as it appears to dissolve the oil. (Eq.) Is a clear solution obtained? Add to a few cubic centimeters of the alkaline solution, bromine-water in excess. What does the reaction indicate? Divide the rest of the alkaline solution into two equal portions. To one add an excess of dilute hydrochloric acid. (Eq.) Set the two tubes aside and examine them carefully at the next exercise for an oil. Explain why sodium hydroxide did not dissolve the oil to a clear solution.
Separate from water, by means of a pipette, the rest of the oil obtained in the distillation with steam. Put it in a dry test-tube, avoiding getting water into the tube. Add about 2 cc. of carbon tetrachloride, and filter into a dry test-tube through a small funnel containing a paper moistened with carbon tetrachloride. Add a solution of bromine in carbon tetrachloride, drop by drop. What does the behavior indicate?
217. Preparation of Sulphanific Acid (Section 510). - In a small round-bottomed flask containing 25 grams of aniline, pour cautiously 80 grams of pure concentrated sulphuric acid. Heat the mixture for from 4 to 5 hours in an oil-bath at 180°190°. In order to determine whether the reaction is complete, remove a drop of the mixture on a glass rod, and mix it on a watch-glass with a few drops of a solution of sodium hydroxide. If any aniline sulphate is present in the mixture, the aniline will separate as an oil; if sulphonation is complete, the sodium salt of sulphanilic acid, which is soluble in water, is formed. When the reaction is complete, pour the product into about 300 cc. of cold water. Filter, wash the precipitated sulphanilic acid with cold water, dissolve it in boiling water, avoiding an excess of the latter, add about 2 grams of bone-black, and boil for 5 minutes, stirring occasionally. Filter the hot solution and set aside to crystallize. Dry the crystals in the air; weigh them as soon as dry as the acid slowly loses its water of crystallization on standing. Calculate the percentage yield.
Sulphanilic acid crystallizes from water in plates, which contain 2 molecules of water of crystallization; it is converted into tribromaniline by an excess of bromine water. The yield in this preparation is about 25 grams.
218. Preparation of m-Nitraniline (Section 511). - In a 100 cc. flask dissolve 10 grams of m-dinitrobenzene in 50 cc. of hot alcohol; cool the solution under running water so that small crystals are formed, and add, 10 cc. of a concentrated solution of ammonia in water. Hood. - Pass into the solution a rapid stream of hydrogen sulphide as long as heat is evolved by the reaction (Eq.); this requires about one-half hour. Heat on the steam-bath for 10 minutes. Pour the product into 200 cc. of water, filter by suction, and wash the precipitate with water. Put the mixture of m-nitraniline and sulphur into a beaker, add 100 cc. of water and 20 cc. of concentrated hydrochloric acid, stir, and filter off the residue of sulphur by suction. Set the filtrate aside. Determine whether all the nitraniline has been extracted from the sulphur by treating it on the filter with a little dilute hydrochloric acid, and adding ammonia to the filtrate. To the original filtrate from the sulphur add an excess of concentrated ammonia. Cool in running water, filter off the precipitated m-nitraniline by suction, and wash it with a little cold water. Dissolve the nitraniline in the smallest amount of boiling water (about 500 cc.), filter the hot solution, and set it aside to crystallize. Filter off the crystals, wash them with a little cold water, and dry on filter-paper. Calculate the percentage yield and determine the melting-point of the product.
m-Nitraniline crystallizes in yellow needles, which melt at 114°. The yield in this preparation is from 5 to 6 grams.
219. Preparation of p-Nitraniline (Section 511). - Add slowly in small amounts with stirring, 20 grams of finely powdered acetanilide to 60 grams of fuming nitric acid (sp. gr. 1.52) contained in a beaker surrounded by ice and concentrated commercial hydrochloric acid. The temperature of the nitric acid should not be allowed to rise above 10°. The addition of the acetanilide requires about 20 minutes. When the substance has dissolved, pour the solution into about 300 cc. of cold water, stir vigorously, and filter by suction. p-Nitroacetanilide is precipitated, and the ortho compound formed remains in solution. Wash the precipitate three or four times with hot water. Remove as much water as possible by pressing the compound on the funnel, and then crystallize it from boiling alcohol. Let the solution cool, and filter off the crystals. By evaporating the filtrate to a small bulk, a further amount of the anilide can be obtained. Determine the melting-point and yield of the p-nitroacetanilide obtained.
p-Nitroacetaniide melts at 207°. The yield should be about 14 grams. The ortho compound can be obtained from the original solution in dilute nitric acid by extraction with chloroform.
To obtain p-nitraniline from the anilide proceed as follows: Hood. - In a beaker covered with a watch-glass boil the aceto-nitranilide with ten times its weight of dilute hydrochloric acid (sp. gr. 1.12) for about 20 minutes. Cool the solution, add about an equal volume of water and an excess of concentrated ammonia. When the solution is cold, filter off the p-nitraniline, wash it with cold water, recrystallize from boiling water, using about 60 cc of water for each gram of anilide hydrolyzed. Weigh the compound, determine its melting-point, and calculate the percentage yield from the p-nitranilide used.
p-Nitraniline melts at 147°.
220. Hydrolysis of the Salts of the Nitranilines. - Prepare a sample of aniline hydrochloride as follows: Mix together 1 cc. of aniline and 1 cc. of concentrated hydrochloric acid. Cool under running water, and place the solid which separates on a porous plate. When the liquid has been absorbed pour a little ether on the salt. Repeat the treatment with ether, and let the salt dry in the air. Prepare samples of the hydrochlorides of meta- and para-nitranilines as follows: Mix together about 1 gram of the amine with 5 cc. of concentrated hydrochloric acid and 5 cc. of water. Heat to boiling, and then cool in running water. Filter the salt by suction, and wash the crystals with 10 cc. of alcohol and then with 10 cc. of ether. Dry the salts for a few minutes on filter-paper.
Shake up a little of the three salts with about 2 cc. of water and test the solutions for acid with litmus paper and with Congo paper. Explain the results.
Note. - Litmus is much more sensitive to hydrogen ions than the dye on Congo paper.
221. Properties of Salicylic Acid (Section 516). - (a) Salicylic acid and ferric chloride. - Add a dilute solution of ferric chloride (see note to experiment 197d, page 163) to a dilute aqueous solution of a salicylic acid. To one-half of the solution add dilute hydrochloric acid, drop by drop, and to the other half dilute acetic acid. Add a drop of ferric chloride to an alcoholic solution of salicylic acid. Repeat these tests with phenol and compare the results.
(b) Salicylic acid and bromine. - Add bromine water to a solution of the acid. (Eq.)
(c) Formation of methyl salicylate. - Warm together on a watchglass about 0.05 gram of salicylic acid, 3 drops of methyl alcohol and 3 drops of concentrated sulphuric acid. (Eq.) Note. the odor of the compound formed.
(d) Decomposition of salicylic acid on heating. - Heat rapidly in a dry test-tube a little of the acid (Eq.) and note the odor.
(e) Detection of salicylic acid and benzoic acid in foods. - If the sample to be tested is a liquid, acidify 100 cc. of it with 10 drops of dilute sulphuric acid, and extract the solution twice with ether or petroleum ether, using 50 cc. each time. If the material contains a substance insoluble in water, grind 50 grams of it with 100 cc. of water, and add enough of a dilute solution of sodium hydroxide to make the mixture alkaline. Mix thoroughly, filter through 3 layers of cheese-cloth, acidify with dilute sulphuric acid, and extract twice with ether or petroleum ether using 50 cc. each time. Separate the ethereal extract and filter it through a dry filter-paper. Shake 5 cc. of the extract with 5 cc. of water and add to the aqueous solution a dilute solution of ferric chloride containing no free acid; if salicylic acid is present, the characteristic color will develop. Evaporate the rest of the ethereal extract to dryness, dissolve the residue in the smallest possible amount of hot water. Let the solution cool, and remove the crystals by means of a spatula to a porous plate. When dry, determine their melting-point. Test a crystal with ferric chloride as in (a) above. Dissolve a crystal in a drop of ammonia, evaporate on the steam-bath, dissolve in a few drops of water, and add a drop of a solution of ferric chloride. If benzoic acid is present, a buff-colored precipitate of basic ferric benzoate is formed.
222. Properties of Tannic Acid (Section 523, 524). - For the following experiments make a 1 per cent solution of tannic acid, by dissolving 0.5 gram of the acid in 50 cc. of water.
(a) Tannic acid and ferric chloride. - Add a few drops of a dilute solution of ferric chloride (see note to experiment 197d, page 163) to about 5 cc. of a solution of tannic acid. Dilute some of the solution of the acid with 50 parts of water and add a drop of ferric chloride.
(b) Tannic acid and the salts of heavy metals. - Add to a solution of the acid a solution of lead acetate. Repeat using copper sulphate.
(e) Tannic acid and gelatin. - Dissolve about 0.1 gram of gelatin in about 10 cc. of warm water, and add to one-half of the cold solution a solution of tannic acid. Reserve the rest of the solution for experiment (f) below.
(d) Reducing action of tannic acid. - Test a solution of the acid with Fehling's solution. Add a solution of tannic acid to an ammoniacal solution of silver nitrate.
(e) Oxidation of tannic acid by air. - Mix a little of the solution of the acid with a solution of sodium hydroxide and shake the mixture in contact with air.
(f) Tannic acid in tea (Section 526). - Pour about 50 cc. of boiling water onto about 1 gram of tea. After 2 minutes decant off the clear solution; to 5 cc. of it add 2 drops of ferric chloride solution. If the shade of the color produced can not be clearly seen, dilute with water. Compare the color with that produced by the gall-nut tannic acid in experiment (a) above. Add 5 cc. of the solution to a dilute solution of gelatin. Compare the behavior of the tannic acid from tea with that from gall-nuts.
To the rest of the tea-infusion add a dilute solution of lead acetate, drop by drop, from a pipette as long as a precipitate is formed.
Devise and carry out an experiment to determine whether the amount of tannic acid present in a tea-infusion is greater when the, tea is steeped for 2 minutes, or when it is boiled with water for 15 minutes.
(g) Preparation of a tannin ink: removal of ink-stains (Section 525). - Dissolve 1 gram of tannic acid in 10 cc. of hot water, 0.5 gram of ferrous sulphate in 5 cc. of hot water, and 0.05 gram gum arabic in 5 cc. of hot water. Cool the solutions and mix them. Write on a piece of paper with some of the ink, using a new pen. Add a few drops of ferric chloride to a little of the ink and write with the mixture. Compare result in the two cases. Explain. Put the paper away, and examine the writing with the two samples of ink at the next exercise. Explain.
Put on a piece of cotton cloth some of the iron ink and on another piece some ordinary ink which probably contains a dye. When the ink-spots are dry, cut each piece of cloth into three parts in such a way that the pieces containing the iron ink can be distinguished from those containing the dye. Wash the pieces in water. Add a piece of each kind to a dilute solution of oxalic acid. Explain the result. Add a piece of each kind to a dilute solution of sodium hypochlorite. Place these pieces alternately in the solution of oxalic acid and sodium hypochlorite until the color is destroyed in both cases.
Prepare a 0.5 per cent solution of potassium permanganate by dissolving about one-fourth gram of the salt in 50 cc. of water. Add to the solution 5 drops of concentrated sulphuric acid. Place in the solution pieces of cloth containing the two kinds of ink. After about 2 minutes remove them, wash with water, and place them in a strong solution of sodium hydrogen sulphite. Repeat the treatment with the permanganate and sulphite until the ink is destroyed. If ink is removed in this way the fabric should be washed thoroughly in water, and then placed in a dilute solution of ammonia.
Notes. - (b) The formation of insoluble compounds from tannic acid and the salts of metals is used in preparing mordants in dyeing. (See experiment 228, page 187.)
(c) The use of tannin in tanning leather is based on the fact that it forms a compound with the proteins in the hide, of which gelatine is an example.
(g) The removal of ink-spots from fabrics made of silk is best accomplished by means of potassium permanganate. If sodium hypochlorite is used, the chlorine present attacks the material, and converts it into a chlorinated product which has a faint yellow color that can not be readily destroyed. A neutral solution of potassium permanganate oxidizes ink; the reaction takes place more rapidly in a very faintly acid solution.