adit+ by
'
-
Denisan University Granville. Ohio 43023
Synthesis and Decomposition of Zn12 Submitted by:
Checked by:
Noojin Walker Pensacola Junior College Pensacola, F L 32504 Richard F. Jones Sinclair Community College 444 West 3rd Street Dayton, OH
Preparation Obtain Zn dust (3 g), Iz crystals (2 g), water (10 ml), small gauge insulated Cu wire (30 cm), two 100 mm watch glasses, dropper, funnel, filter paper, stirring rod, and a DC power source, (1.5 V AA dry cell is the minimum.) Demonstration 1) Mix the Zn and 12 on a dry watch glass. No reaction. 2) Add 10 ml of water drop by drop (hood).Copious violet vapors. 3) Stir the mixture well. Filter. Pour the filtrate into a watch glass. The solution should he relatively clear and colorless. 4) Connect Cu wires to the DC source. An amber coloration of the filtrate occurs immediately at the anode; Zn accumlatea on the cathode. Remarks The simplicity, the controlled violence, and the visual excitement makes ZnIp an excellent demonstration. In a very few moments it can he used to show direct combination, decomposition, the effect of a catalyst, recrystallization of sublimed 1%and electrolysis. The demonstration is enhanced by the use of an overhead projector. The violet color is more dramatic, the silvery sparkles of cjstalline I2 in the violet vapors are visible, amber droplets of aqueous I p are apparent, and the produds accumulating around the electrodes and the diffusion rates are easily observed ("Tested Demonstration," 6th ed., p. 161). The reaction is reported to occur also when scrupulously clean and dry Al and Mg are used (Antelman, M., J. CHEM. EDUC., 30, 134 (1953)). What would he the electrolytic products?
788 1 Journal of Chemical Education
The Preparation and Properties of Poiybutadiene (Jumping Rubber) Bassam Z. Shakhashiri Glen E. Dirreen and Lloyd G. Williams' University of Wisconsin-Madison Madison, WI 53706 A violet suspension of an "alfin" catalyst is added to a pop bottle containing a solution of 1,s-hutadiene in pentane. The bottle is corked and shaken for several seconds. The mixture sets to a gel and the contents erupt from the bottle within two minutes.
I
1
T H E CHEMICALS USED I N THIS DEMONSTRATION ARE FIRE HAZARDS.
Materials Jumping rubber kit available from Orgmet, Inc., Route 111, East Hampstead, NH 03282 The ....kit: .....
Small pop b o k mntainii l$-hutadiene digsolved in dry pentane War-sealed, screw capped bottle containing the alfin catalyst Cork for pop bottle Bottle opener Glass stirring rod Tonga Procedure WARNING! The alfin catalyst is extremely reactive with moisture. Perform this demonstration in a well-ventilated room to minimize inhalation of pentkne vapor. Open the catalyst vial and use the glass rod to stir its contents. Quickly remove the crown seal from the pop bottle and add all the catalyst. Immediately cork the bottle and shake. The temperature increases slightly (to about 50°C) and the pressure increases (perhaps 2-3 atm) until, within two minutes, the cork is forced from the mouth of the bottle and a polymer "snake" shoots out into the air. The hottle is left al-
' Present address: Hampshire College, Amherst, MA 01002
most dry and the liquid is trapped in the polymer. Use a pair of tongs to handle the polymer. Over a period of an hour or so the trapped pentane will evaporate and the polymer will shrink. Hazards This dramatic demonstration should be performed only by individuals who understand the fire hazard and reactivity of organosodium reagents. Under hot or extremely humid conditions the catalyst could ignite in air or ignite the butadiene-pentane solution. A carbon dioxide f i r e extinguisher must be available. Pentane is a highly flammable and volatile liquid (b.p. 36'C). Pentane can cause severe exolosions when ex~0Sed to heat, sparks, o r flame. Avoid inhiation of pentane vapors since thev are sliehtlv - concentration Dentane - toxic. I n hieh is a narcotic. 1.3-hutadiene ( b . ~ -. 5 W may be irritating to skin and mucous membr&s and is a narcotic in high concentrations. Disposal Since pentane is trapped in the product, the polymer should he kept away from flames. Pentane evaporates after several hours and the shrunken polymer may be discarded. The empty screw capped bottle may he rinsed carefully with water and discarded.
Discussion We have performed this demonstration over 100 times without a single accident. I t is a dramatic demonstration which, along with other demonstrations, serves the purpose of discussing polymers, their methods of preparation, their properties, and their uses. Polymer chemistry should become an important aspect of general chemistry courses because of its own richness and because of the importance of polymers in our daily lives. We urge that this and other related demonstrations he used to focus attention on polymer chemistry and to increase the students' knowledge and awareness of chemical systems. We discourage its use only as a magic trick. Alfin catalysts are a class of heterogeneous catalysts which cause rapid polymerization of hutadiene, isoprene, and other monomers resulting in polymers with very high molecular weights (1-2 million or higher). The alfin catalyst used in this demonstration is a solid surface catalyst developed by A. A. Morton (1,2,3) and co-workers a t M.I.T. I t is produced by reacting amyl chloride with sodium, which is then reacted with isopropyl alcohol. The resulting mixture contains amyl sodium, sodium isopropoxide, and sodium chloride. Propylene is added to produce ally1 sodium from amyl sodium. The following sequence (4) shows the necessary stoichiometry 1.5
CsHllCl 3 Na
-
1.5 CsHllNa 1.5
NaCl
The sodium isopn~poxide-allylaodiumcombination gives the highest polymer yields. The role of the sodium chloride is not clear, although it could be acting as a support for the catalyst. The catalyst is the mixture of the three sodium compounds; allyl sodium, sodium isopropoxide, and sodium chloride. All of these are essential constituents. The name, alfin, was taken from the fact that analcohol and an olefin are involved in the preparation of the reagent. The alfin catalyst is believed (5,6)to adsorb and orient the monomer prior to the chain-growth process. Surface effects presumably influence the stereochemistry (4), and the poly-
mer consists mainly of trans-1,4 repeating units. Since one ally1 group is incorporated into each polymer chain, the process resembles Ziegler-Natta catalysis (4). a l f l n catalyst nCIf2=CHeH=CH2 CH l,3-butadiena
lH>c=C CHI
trans-1,C polybutadiene The predominance of 1,4-polymerization has been suggested as evidence for a free radical propagation mechanism. I t has heen proposed (4) that complexes such as CH,-CH-CH, CH,-CH-CH,
I
I
are formed and that adsorbed monomer displaces the aUyl anion from the comolex to form an ion oair which then reacts to form a radical pa'ir.
[CHI-CH-2CH-CHaaF-[CH2=CH=CH2] .CH2-CH=CH-CH,-Na+ +.CH,-CH=CHI The radical anion initiates polymerization which continues until combination with an ally1 radical occurs. This does not occur very readily hecause the allyl radical is bound to the catalyst surface (4), and hence very high molecular weights are obtained. CH, CH,R CHI CHs
+
II CH I
6+CH
//
I
I
II
R- CH
+
/
6%H R'Na+
-CH,
I
1
~a+~l--Na+-oR
4'"catalyst surface
II
CH
CH
CH
II
CH
+
/
-CH,
1
+
I
~'CH
+
//
6%H,
"7
catalyst surface CH,-CH,-CH=CH-CH,R
.
I
1I
CH
and so on
Nnt
1
catalyst surface Others have proposed an ionic mechanism for polymerization with the alfin catalyst. Discussion of the ionic hypotheses may he found in the references cited, particularly in Reich and Schindler (7). Literature Cited (1) MoMn, Avery A., Mwat,E., Leteinger, R. L., J Amen Chem. Sac, 69,950 (1947). (2) Morton,AwryA.. Welehcr,R.P.,CoEns.F.,Penner.S.E..Comhi.RD., J A W . Chen.
(3) ~ o m o s & ~ a & R:, and Campbell, Tod W. '"Preparative MeUlada of Polymer Chemistry," SecondEdition. lntemienee, New York,1968. pp. 305307. (41 Stevens. Mdmlm P., "Polymer Chemia~y:An Intmduction:' Addilon-Wnley Publishing Company, Inc., Reading, Massachwtta, 1915, pp. 179-180. (5) Morton.AveryA. andlanpher.E.J.. J . Polymer Seiencea. 44.233(1960) andrrf.mneea
Volume 57, Number 10, October 1980 1 739
