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PRODUCTION OF CUPRAMMONIUM RAYON

* PURPOSE

In this demonstration rayon fiber is produced by the use of four common substance: sodium hydroxide, ammonium hydroxide, copper sulfate, and paper. This method demonstrates one of the earliest techniques of producing this famous polymer, called cuprammonium rayon.

* DESCRIPTION

This demonstration is appropriate for a general or first-year college-prep course. It shows the students the method of preparation of one of the first mass-produced synthetic fibers. It would fit very well with the organic sections found in most introductory texts.

* TIME REQUIRED

One class period.

* MATERIALS

Chemicals
CuSO4·5H2O*
NaOH*
concentrated NH3 solution
1.6 M H2SO4 (88.8 ml of concentrated H2SO4
solution diluted to 1.00 liter with distilled or deionized water)*
11.0 cm filter paper*
Equipment
250-mL Erlenmeyer flask
1000-mL beaker
syringe or bulb/pipet combination
funnel
filter paper
funnel support
magnetic stirrer (optional)
Buchner funnel and filtering flask (optional)
*See Modifications/Substitutions

* HAZARDS

Avoid skin contact with all reagents. Use caution when making NaOH and H2SO4 solutions; both processes are exothermic. Avoid breathing NH3 vapors and work within hood if possible. Goggles must be worn for this demonstration.

* MODIFICATIONS/SUBSTITUTION

  1. CuSO4·5H2O can be purchased as root killer at a garden supply store.
  2. NaOH can be purchased as lye in grocery stores.
  3. Sulfuric acid is available from auto supply stores as battery acid. This solution is 4.8 M.
  4. Paper towels could be substituted for the shredded filter Paper in this reaction.

* PROCEDURE

  1. Dissolve 25.0 g of CuSO4·5H2O in 100 mL distilled water. Heat the water to accelerate the dissolving process.
  2. Dissolve 8.0 grams NaOH in 200 mL distilled water.
  3. Mix the cooled NaOH solution with the copper sulfate solution. Collect the resultant gelatinous precipitate of Cu(OH)2 by filtration. Wash the precipitate with three 10-mL portions of distilled water. If using 11.0 cm filter paper, several filtrations will be required because of the large amount of precipitate produced.
  4. Measure 70 ml concentrated NH3(aq) into a 250-mL Erlenmeyer flask. Shred four pieces of 11.0-cm filter paper. Add the Cu(OH)2 precipitate carefully along with the filter paper to this flask and stir. This should result in a deep purplish-blue solution of tetraaminecopper(II) hydroxide, referred to as Schweizer's reagent. Stopper the flask and stir periodically for 24 hours. Use a magnetic stirrer, if available.
  5. Take up the contents of the 250-mL Erlenmeyer flask in 10-mL increments in a 10-mL or 50-mL syringe. Squeeze out the contents into a 1000-mL beaker containing 300 mL of 1.6 M sulfuric acid. Be sure that the tip of the syringe or pipet is under the surface of the acid. A crude "thread" should form.
  6. The clumps or threads can be washed free of the solution to show the white color of the rayon.

* DISPOSAL

Flush the ammonia solution and the sulfuric acid solution down the drain with copious amounts of water. Dispose of rayon with solid waste.

* DISCUSSION

The primary reactions involved are:
NaOH(aq) + CuSO4(aq) ---> Cu(OH)2(s) + Na2SO4(aq)
Cu(OH)2(aq) ---> Cu2+(aq) + 2 OH-(aq)
n Cu2+(aq) + (cellulose)n + 2n OH- ---> (CuC6H8O5)n + 2n H2O
Cellulose is actually dissolved in [Cu(NH3)4](OH)2 solution and then regenerated as rayon when extruded into sulfuric acid.

* TIPS

  1. Filtration of Cu(OH)2 can be a problem; small amounts of precipitate should be filtered and then combined in one container.
  2. Samples of rayon and other synthetics could be shown and their properties discussed.

* REFERENCES

Alyea, H.N., Dutton, F.B., "Tested Demonstrations in Chemistry, Journal of Chemical Education, Easton, PA, 1965, p. 14.
- Describes another preparation of rayon.

Summerlin, L.R. and Ealy, J.L., Jr., Chemical Demonstrations - A Sourcebook for Teachers, American Chemical Society, Washington, 1985, p. 126.
- This work describes another short prep of rayon.

Submitted by Paul Hobe, Dan Holmquist, Carolyn Morse, Pat Noel, Joe Wilkins

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