edited b' GEORGEL. GILBER' DenIran Universit Granville. Ohio 4302:
A Demonstration ot the Cuprammonium Rayon Progress SUBMITTEDBY
George 6. Kauffman and Mohammed Karbassi Calnornla State Unlverslty, Fresno Freono, CA 93740
Wayne L. Felty The Pennrylvanla State Unlversiiy Wllkea-Barre, PA 18708
A few years before his death, Matthias Eduard Schweizer (1818-1860), Professor of Chemistry a t the Universitat Zurich (1841-1860) (11, discovered that a strongly ammoniacal solution of copper(1I) hydroxide, now known as Schweizer's reagent, dissolves cellulose (cotton, silk, or linen) (2). T h e reagent was used in analytical chemistry as a test for wool, which it does not dissolve. Rayon (a generic name for synthetic textile fiber produced from cellulose) was developed in an attempt to produce artificial silk (3).I t was first made by denitration of cellulose nitrate (Chardonnet process, 1891), but production of this nitrocellulose fiber was discontinued because of its high flammability. Most rayon is now made by the viscose (cellulose xanthate) process (1892), but the oldest known type (cuprammonium, Cupra, or Bemherg process, 1890), made by dissolving cellulose in Schweizer's reagent, extruding the solution through fine holes in a spinneret, and regenerating the cellulose in an acidic solution, is still used to produce the most expensive rayon most resembling silk. Cuprammonium rayon finds application in knitted and woven wearing apparel, upholstery, and decorative fabrics. Since both the tetraamminecopper(I1) ion and the shifting of equilibria (Le Chatelier's principle) are dealt with in general chemistry courses, the preparation of cuprammonium rayon makes a simple, interesting, and relevant demonstration (4). Cellulose dissolves in Schweizer's reagent because of the formation of complex compounds between Cu2+ and (CsH&- ions (5).T h e equilibrium reaction
+
+
nCuz+ (CsHloOs), 2nOH-
P
[CuCsHsOsl,
+ 2nH20
is p H dependent; cellulose ions are present in appreciable concentration only in a rather strongly alkaline solution. If the hydroxide ion concentration is lowered, the cellulose is reprecipitated. If it is increased by addition of NaOH solution, the cellulose redissolves. T h e physical properties and chemical reactions of Schweizer's reagent have been extensively investigated (6).
878
Journal of Chemical Education
Procedure Caution: This demonstration should be performed in a well-ventilated hood. Two hundred milliliters of 1Msodium hydroxide (or 8.00 g of NaOH in 200 ml of HzO)is added with magnetic stirring to 100ml of 1M copper (11) sulfate (or 25.0 g of CuSO.. 5H20 in 100 ml of HzO).The resulting light blue gelatinous precipitate of hydrated copper(I1) hydroxide is collected by suction filtration on a 30-ml medium-porosity sintered-glass funnel. After being washed with three 10-ml portions of distilled water, the precipitate is transferred to a 250-ml Erlenmeyer flask, and 70 ml of concentrated aqueous ammonia is added with magnetic stirring, whereupon the precipitate dissolves to form a deep purplish blue solution ol tetraamminecopper(I1) hydroxide (Schweizer's reagent). Small pieces of filter paper (- 2.4 g or three 11.0-em circles of Whatman No. 1 qualitative paper) are added, the flask is stoppered ([Cu (NH~frl(0H)n ahsorhs C02from the air), and the mixture is magnetically stirred until the next lecture or laboratory period (at least 24 h). If desired, in order to demonstrate that the filter paper has actually dissolved and is not merely suspended, the viscous deep ~urplishblue cuprammanium-cellulosesolution may he filtered by suction (30-ml medium-porosity sintered-glass funnel). The solution (or filtrate) is added from a beaker or pipet to a beaker containing 1.5 Msulfuric acid, whereupon the rayon (regenerated cellulose) foms a6 a flocculent precipitate or film. Caution: Neutralization causes heat evolution. If the solution is forced into the acid with a rubber bulh while the tip of the pipet is below the surface of the acid, a crude "thread" is formed. The clumps or "threads" may be washed free of the blue solution to show the white color of the cellulose. If a Petri dish or watch glass is used tc contain the acid, the demonstration can be performed for large lecture classes on an opaque projector. In the commercial production of rayon fiber, the cuprammonium-cellulose solution is allowed to age. During this period, absorption of atmospheric oxygen causes degradation of the cellulose and reduces the viscosity of the solutian. When the propel viscosity has been attained, the solution if filtered, aerated, and extruded into a bath of dilute sulfuricacid. (1) "75 Jahre chemischer F F F F ~ w ddd ~.U ~ n i i i i i i ~ Ziuiih: t Fe~trtrhhiftttt ErOflfluq des neuen Chemiachen 1nstituts. verfssst "on den Studierenden d.r Chemie? n,d [Zurich. 19091, pp. 14-16:Kauffman, 0. B, J. CHEM EDUC.,GI. GW19841. (21 Sehweirsr, E.,J. prakt. Chem.. 72 1"J (1857): 76,344 (18591; 78 370 (18591. (31 Clark, G. L.,end Hswley, G. G. lEditors.l."The Encyclopedia of Chemistry? md ed. Van Nostrand Reinhold Co.. New Yolk, 1966. pp. 415420. 1081-1082:Reinthaler F.. "A~tifieialSilk? Chapman & Hall. London. 1928, pp. 3 2 4 7 . (4) Fowlca, G . . ' k t u r e Experiments in Chemistry? 5th ed., Basic Bwks,New York, pp
wiehtigen vemendunpsgehiete.'. Juliue Springer. Berlin, 1935. pp. 2529-2638. re printed by Edwards Bras., Ann Arbor. Mieh.. 1943: 0%E. (Editor), 'Cellulose am rplllllnap nrrivativer*:' intcmience. N~~ YO&. 1943. on. m&mh: ~ i e s e r .T ~~, ..Kurxca Lphrbuch der cellulmeehe&? oebruder Boii&er, B&, 1953, py 97.121; "Gmelina Hsndbuch deranorganisehen Chemie? 9th ed., System-Nr.6( Kupfer, Teil B, Liefarung I, Vcrlag Chemie, WeinheimiBergntia=e, 1958, PC 18&132. and references therein. ~~
