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Amines and Amides
112. Preparation of Methylamine from Acetamide (Section 162). - Place into a 1 liter flask 1oo cc. of water and 36 grams of fresh bleaching powder. Add 10 grams of acetamide dissolved in 25 cc. of water in small portions and shake. Add slowly a cold solution of 25 grams of sodium hydroxide in 100 cc. of water. Arrange the apparatus to distil with steam (see Fig. 12, page 19), and connect an adapter by means of a tightly fitting rubber stopper with the end of the condenser. Place the end of the adapter just below the surface of 50 cc. of cold water contained in a beaker, and distil with steam. From time to time remove the adapter, and test the distillate with litmus paper. Stop the distillation when methylamine ceases to distil over. The yield in this preparation, calculated from the methylammonium chloride obtained (see experiment 113d below), should be 70 per cent of the theoretical.
Note. - In the preparation of methylamine by Hofmann's reaction, bromine and potassium hydroxide are commonly used. The use of bleaching powder, instead of these reagents, which form potassium hypobromite, avoids the handling of large quantities of bromine, and reduces the cost of the preparation. The amount of bleaching powder to be used is determined by the percentage of available chlorine which it contains. The proportions given above are based on a bleaching powder which contains about 35 per cent of available chlorine.
113. Properties of Methylamine (Sections 163, 164). - (a) Basic properties of a solution of methylamine. - Test the distillate obtained in the experiment just described with pink litmus paper.
(b) Methylamine and solutions of metallic salts. Add a little of the distillate, drop by drop, as long as any change occurs, to 1 cc. of a dilute solution of copper sulphate. Repeat with a solution of ferric chloride. Add ammonia to solutions of these salts. Write equations for the reactions in the case of ammonia and of methylamine; the reactions in the two cases are analogous.
(c) Carbylamine reaction. - Hood. - Warm 1 cc. of the distillate with 2 drops of chloroform and 2 cc. of an alcoholic solution of potassium hydroxide, which may be prepared by heating a little of the solid compound with alcohol and decanting off the solution. (Eq.) Note the odor produced. Acidify the contents of the tube before pouring into the sink.
(d) Methylammonium chloride. - Make the rest of the distillate slightly acidic with hydrochloric acid, and evaporate the solution to dryness on the steam bath. Dissolve the salt in the smallest possible amount of boiling absolute alcohol; a small amount of ammonium chloride maybe left as an insoluble residue. To dissolve the salt, add to the beaker on a steam-bath about 25 cc. of the alcohol; cover with a watch-glass, and let the salt digest with the hot alcohol for a few minutes. Filter through a funnel from which the stem has been cut (see Fig. 1, page 6). Continue the addition and digestion as long as the solvent appears to dissolve the salt. About 100 cc. of alcohol will be required. Cool the combined filtrates, and add an equal volume of ether. Filter, off the crystals by suction and dry them on a porous plate. Determine the weight and the melting-point of the methylammonium chloride obtained.
(e) Methylammonium chloride and alkalies. - Heat together in a test-tube a very small amount of the salt with 2 cc. of a solution of sodium hydroxide. (Eq.) Note the odor of the gas.
(f) Inflammability of methylamine. - Place about 0.5 gram of methylammonium chloride and an equal amount of lime in a dry test-tube, and heat. Apply a flame to the gas. Does it burn? Repeat with ammonium chloride. Does ammonia burn in air?
(g) Methylammonium chlorplatinate. - Dissolve a small amount of methylammonium chloride in a few drops of alcohol, and add, drop by drop, a 10 per cent solution of platinic chloride. Repeat, using a few drops of a strong aqueous solution of ammonium chloride. The reactions in the two cases are analogous. Write the equations for both reactions.
(h) Decomposition of methylammonium nitrite. - Mix in a test tube about 0.5 gram of methylammonium chloride with twice its weight of sodium nitrite and about 5 cc. of water. Connect the tube by means of a cork with a delivery-tube arranged to collect a gas over water. Heat the solution gently and collect two test-tubes full of the gas. (Eq.) Test the second tube for nitrogen with a glowing splinter. Distil over about 3 cc. from the tube into a second tube, surrounded by cold water. Test the distillate for methyl alcohol (experiment 77b, page 53).
114. Isolation of Lecithin from Egg-yolk (Section 174). - Grind the yolk of one hard-boiled egg with 50 cc. of ether. Filter and wash the solid residue twice with 10 cc. of ether. Evaporate off the ether on the steam-bath, or distil it off from a small flask. Extract the residue twice with hot alcohol, using 10 cc. each time. Pour off the alcohol from the heavy oil through a small filter. Evaporate off the alcohol, dissolve the residue in 10 cc. of cold ether, and add 10 cc. of acetone. Stir until the particles of the precipitated lecithin adhere together and form a ball. Place the latter on a filter-paper. Describe its properties. Boil about one-fourth of the lecithin with about 10 cc. of a 10 per cent solution of sodium hydroxide. Note the odor of the gas evolved. What is it? Cool the solution. Is there any evidence of the formation of a soap? Filter, dissolve the precipitate in warm water and add dilute hydrochloric acid to the solution. What is precipitated? Test a part of the lecithin for nitrogen and for phosphorus (§58, §59, §61, page 39).
Note. - Ether dissolves from egg-yolk, in addition to lecithin, some fat and protein. The protein and a part of the fat are removed by extracting the residue from ether with alcohol. The lecithin is finally separated by adding acetone to an ethereal solution of the lecithin and fat. The latter is soluble in acetone while the lecithin is insoluble.
115. Preparation of Acetamide from Ethyl Acetate (Section 178). - Mix in a 250 cc. distilling flask 50 grams of ethyl acetate and 100 cc. of a concentrated aqueous solution of ammonia (sp. gr. 0.90). Close the flask with corks and let the mixture stand over night, until the two layers first formed have disappeared. (Eq.) Arrange the flask for distillation with a thermometer and water condenser, and use as a receiver a distilling flask or a filter-bottle, the side-arm of which is provided with a tube which dips under water; the latter precaution is taken to absorb the large quantity of ammonia which is given off in the distillation. Distil carefully; collect the first part (about 10 cc.) of the distillate separately and test it for ethyl alcohol. When the thermometer registers 160°, replace the water-condenser by an air-condenser, change the receiver, using this time a beaker, and collect what distils at 160°-225°. As the temperature rises the acetamide solidifies in the condenser to a crystalline mass, which can be readily liquefied by warming the condenser cautiously with a free flame. When the distillate is cold pour off from the crystals in the receiver any liquid present, and dry the crystals on a porous plate. Weigh the product obtained and determine its melting-point. Calculate the percentage yield obtained. The slightly impure acetamide may be purified by a second distillation, or by crystallizing it from a mixture of one volume of alcohol and two volumes of ether. If the product obtained in the first distillation does not melt sharply, recrystallize a small portion of it.
Acetamide melts at 82°, and boils at 222°. The yield obtained in the preparation should be about 65 per cent of the theoretical.
Note. - The odor of the amide prepared as directed above is due to an impurity which is present in small quantity. By a single recrystallization the compound is obtained in an odorless condition.
116. Properties of Acetamide (Section 178). - (a) Hydrolysis of acetamide. - Mix about 0.5 gram of acetamide with about 5 cc. of a solution of sodium hydroxide, shake and observe whether the odor of ammonia is present. Heat the solution to boiling. Is ammonia set free? (Eq.)
(b) Heat to boiling for 1 minute about 0.5 gram of acetamide with 2 cc. of dilute sulphuric acid. Cool, and make alkaline with a solution of sodium hydroxide. Does the solution smell of ammonia? Explain.
(c) Mercury salt of acetamide. - Add an excess of a solution of sodium hydroxide to 2 cc. of a solution of mercuric chloride. (Eq.) Determine whether the precipitate dissolves when a little acetamide is added. (Eq.) Test the solution for mercury with hydrogen sulphide.
(d) Acetamide and nitrous acid. - To an aqueous solution of acetamide add a few crystals of sodium nitrite and a few drops of dilute sulphuric acid. (Eqs.)
117. Preparation of Urea from a Cyanate (Section 180). - Dissolve 8 grams of potassium cyanate in 20 cc. of hot water and 13 grams of ammonium sulphate in 20 cc. of hot water. Mix the solutions and evaporate to dryness on the steam-bath. (Eq.) Grind the product to a fine powder and dry on the steambath for 15 minutes. Place the solid in a dry beaker and add 25 cc. of alcohol. Cover with a watch-glass, and let the mixture digest just below the boiling-point of alcohol for a few minutes. Decant off the liquid through a filter and digest a second time. If the solution is colored, boil the combined filtrates with a little bone-black. Filter and evaporate on the steam-bath to crystallization (see §9, page 6). When the solution is cold, filter off the crystals by suction (see §12, page 7) and dry them on a porous plate. From the filtrate a second crop of crystals may be gotten by evaporation and the addition of an equal column of ether to the cold solution. Weigh the urea obtained and determine its melting-point.
Urea melts at 132°, and can be crystallized from hot amyl alcohol.
Note. - The blue substance formed at times in this preparation is probably produced as the result of the following cause: Commercial potassium cyanate may contain potassium ferrocyanide. If this is the case, when a solution of the salt is evaporated in the air with ammonium sulphate containing a trace of iron, Prussian blue is formed.
118. Properties of Urea (Sections 180, 181). - (a) Nitrate of urea. - Dissolve a crystal of urea in a drop of water on a microscope slide; place near this solution a drop of concentrated nitric acid, and bring the two together by touching with a glass rod. (Eq.) Examine the crystals under the microscope.
(b) Urea and oxalic acid. - Repeat (a) above but use a saturated solution of oxalic acid in place of nitric acid. (Eq.)
(c) Hydrolysis of urea. - Treat about 0.5 gram of urea with 5 cc. of a solution of sodium hydroxide. Note whether ammonia is given off. Explain. Boil the solution for a minute or two and observe if ammonia is given off freely. (Eq.) Test the vapor with litmus paper.
(d) Urea and nitrous acid. - Place in a test-tube 0.1 gram of sodium nitrite and 10 cc. of water; in another tube put 0.1 gram sodium nitrite, 10 cc. of water and 0.2 gram of urea. Add to each tube 1 cc. of dilute acetic acid. Compare the amount and color of the gas given off in each case. (Eqs.)
(e) Urea and sodium hypobromite. - Prepare an alkaline solution of sodium hypobromite by adding 3 drops of bromine to 5 cc. of a dilute solution (10 per cent) of sodium hydroxide. Add this solution to a dilute solution of urea. (Eq.)
(f) Urea and mercuric nitrate. - To a dilute solution of urea add a 1 per cent solution of mercuric nitrate. A compound of the formula CO(NH2)2.Hg(NO3)2.HgO is precipitated.
(g) Action of heat on urea: biuret (Section 181). - Heat cautiously about 0.5 gram of urea in a dry test-tube; continue the heating until a white opaque solid is formed. The residue is a mixture of biuret and cyanuric acid (Section 201). Treat the residue when cold with about 5 cc. of water, shake, pour off the aqueous solution of biuret, and add 5 cc. of a solution of sodium hydroxide and a few drops of a dilute (1 per cent) solution of copper sulphate.
Dissolve the residue insoluble in water in a little ammonia, add a few cubic centimeters of a solution of barium chloride and shake. A precipitate of barium cyanurate is formed.
Notes. - (a) The nitrate of urea is difficultly soluble in cold water and in nitric acid. This fact is made use of in the isolation of urea from urine.
(c) Ammonium salts can be distinguished from amides by means of sodium hydroxide; the former yield ammonia in the cold.
(e) Ammonium salts give nitrogen when treated with a solution of sodium hypobromite; they must, therefore, be absent when applying the test to urea. This reaction is used in the clinical examination of urine for urea.
(f) Many substances related to acid amides, for example the proteins, give precipitates with solutions of mercuric salts.
(g) This test for biuret is not characteristic; it is given by many substances in which there is a linking of atoms similar to that in biuret. The test is useful in the study of proteins.