NOVEMBER, 1949
HYDROLYSIS OF NYLON A Laboratory Experiment ROY G. BOSSERT and RICHARD C. CROFT Ohio Wesleyan University, Delaware, Ohio
CECIL E. BOORD Ohio State University, Columbus, Ohio
Tm
increased use of Nylon as a commercial material lends added interest to its study in the laboratory. The production of Nylon is not performed easily in the student laboratory and similar difficultiesare encountered in any attempt to present its production as a class demonstration. A study of the chemical properties of Nylon may be accomplished through its hydrolysis in acid solution. Nylon resists alkaline hydrolysis even after boiling several hours. The present paper offers an exercise on the hydrolysis of a Nylon hose and the isolation and purification of the products of the reaction. The E. I. DuPont Co. reclaims Nylon through the hydrolysis of waste Nylon in an acid solution.' The Nylon of hosiery results from the condensation of adipic acid and hexamethylenediamine. Upon the acid hydrolysis of Nylon, the adipic acid crystallizes from the acid solution. The free hexamethylenediamine is soluble in aqueous solutions and is isolated readily by means of its dibenzoyl derivative. This exercise not only affords added interest in Nylon but also exemplifies a number of fundamental principles: the hydrolysis of the -CONHlmkage; the separation of basic and acidic organic compounds from a mixture of the two; the liberation of a weaker base from its salt by a stronger base; the benzoylation (esterification) of an amine. It also affords further practice in the techniques of crystallization and the melting point. The experimental basis for the hydrolysis of Nylon described in this paper developed from a group of students in the organic laboratory. From this point, individual studies were made to determine the optimum conditions for maximum yields. The items studied were: coneentrat,iou of acid; time of
hydrolysis; removal of sizing from the hose; solvents for the recrystallization of the products. The student results for recrystallized products showed overall yields of 43 per cent, with sharp melting points. The yields of crude products for the optimum experimental conditions were near 90 per cent for both the adipic acid and the dibenzoyl hexamethylenediamine. The general formula for the Nylon from d i p i c acid and hexamethylenediamiue is presented below (I), together with the reactions (Z), (3), (4), which represent, the chemistry involved in t,he hydrolysis and isolation of the products.
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-NH(CH&XHCO(CH,),CONH(CH,)sNHCO(CHn)CO-
I 1I
Polysmide of the Nylon T .v. ~ e 30% H8Og COOH Nylon (CH& Reflux 6 hours COOH
+
Hexamethylenediamine
Dibenzoyl Hsxamethylenediamine
The following experimental details are presented in the fmm of a student exercise.
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THEHYDROLYSISOFNYLON
Place 140 ml. of tap water in a 500-ml. round-bottomed flask and add to it33 ml. of concentrated sulfuric acid, slowly with shak'mg. Prepare the Nylon hose as follows: Immerse the hose three or four times in 100 ml. of acetone and squeeze out the solvent after each immersion. Rinse the hose well in water and dry it thoroughly. This process removes most of the sizing from the hose. Cut the hose in pieces and weigh a sample (not over 8 g.) to the closest 0.1 g. on the trip scales. Place the sample in the hot acid mixture with 2 or 3 pieces of porous chips. Connect the flask to a water-reflux condenser with a rubber stopper and reflux the mixture for a period of six hours. The time of refluxing may be broken up into two or three periods. The mixture takes on a deep red color from the dye in the hose. The Nylon goes into solution almost completely a t the end of one hour. At the end of the refluxing, filter the hot mixture through an ord'mary filter paper in a Biichner funnel. Transfer the filtrate to a 400-ml. beaker and let stand until the next laboratory period. Cool the mixture in an ice bath to insure complete crystallization of the adipic acid and filter by suction through a fine filter paper. Save the filtrate and recrystallize the adipic acid as described in the Following section.
JOURNAL OF CHEMICAL EDUCATION
the dibenzoyl hexamethylenediamine by adding 10 ml. of benzoyl chloride under a hood with vigorous stirring. Continue the stirring and maintain an alkaline solution (litmus test) by the addition of further quantities of the 20% NaOH solution. When the odor of benzoyl chloride has disappeared filter the mixture by suction and press it well on the filter by means of a spatula or small beaker. Transfer the product to a 600-ml. beaker containing 400 ml. of water and stir vigorously to remove free alkali from the product. Filter the product again by suction and press it well on the funnel. Wash the product on the filter paper with 100 ml. of water and press well under suction. Transfer the product to a 200-ml. round-bottomed flask and add 60 ml. of ethyl alcohol. Attach the flask to a reflux condenser and heat to boilmg. If the product does not dissolve readily after refluxing 10 minutes add a further 20 ml. of alcohol and reflux the mixture again. Upon complete solution of the product (Note: A slight amount of insoluble material may remain a t this point) transfer the hot solution (CARE--no flames) to a beaker (treat with charcoal again if necessary) and add water, dropwise, with stirring, until the mixture becomes cloudy. Set the mixture aside until crystallization is complete. The dibenzoyl derivative crystallizes in a heavy mass of colorless crystals. When the crystals are dry weigh them and take a melting point, as follows.
THE PURIFICATION OF ADIPIC ACID
Dissolve the adipic acid in the least possible amount of hot water (10-15 ml.) and treat the hot solution with 0.1 g. of decolorizing charcoal if the original material was dark. Filter the mixture (keep hot) and cool the filtrate in an ice bath. Filter the crystals by suction and spread them on a filter paper to dry. When the crystals are dry, weigh them and take a melting point. ISOLATION AND PURIFICATION OF DIBENZOYL HEXAMETHYLENEDIAMINE
The deep red filtrate from the hydrolysis contains the sulfate salt of hexamethylenediamine. Remove the color as follows: Prepare a solution of NaOH by dissolving 50 g. of NaOH pellets in 200 ml. of tap water. Stir the solution until the pellets are entirely dissolved. Add this NaOH solution with stirring to the red filtrate until the solution is barely alkaline to litmus (it will require most of the solution). The resulting hot solution is treated with 0.2 g. of decolorizing charcoal and the mixture is stirred well a t 8090°C. (Heat if necessary.) Prepare a Biichner funnel with a fine filter paper and set the paper on the funnel with water. Start the suction and filter the mixture. The filtrate contains the purified diamine in solution. Add the remainder of the prepared NaOH solution (or a further 20 ml. of 20% NaOH) to the purified solution of the diamine. Now, precipitate the diamine as
MELTING POINTS OF THE PRODUCTS AND THE DATA ON YIELDS
Refer to the laboratory manual and prepare an apparatus for the determination of the melting points. Powder the dry samples of the adipic acid and dibenzoyl hexamethylenediamine and place them in separate capillary tubes. Mount the tube of adipic acid on the left and that of the dibenzoyl hexamethylenediamine on the right side of the thermometer. eat the melting point bath rapidly to 140°C. (with stirring) and then a t a rate of not more than 2' per minute. Observe the melting point ranges of the products and record them in the table. Pure adipic acid melts a t 149-150°C. and the pure dibenzoyl hexamethylenediamine melts a t 155OC. Record the data for your preparations in the following table: 1. Weight of washed, dry Nylon hose.. . . . . . . . . . . . --g. 2. Weight of adipic acid isolated.. ............... 3. Weight of dibensoyl diamine isolated.. ......... 4. Actual weight of dimnine (from 3). ............ (Note: The weight from 3 must be multiplied by the factor 0.358). ....................... 5. Total weight of products isolated (2 plus 4). . . . 6. Percentaee recovew: Total ;eight (2 plus 4) X 100.. ............. Weight of hose 7. Melting point nmge of adipic acid (uncorr.). .... 8. Melting point range of dibenaoyl hexamethylene....... diamine (uncorr.)................. .
--g. --g. g.
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--g. --g. --% -OC. -"C.
