An Advanced Undergraduate Lab Alan R. Newmanl and Craig A. Hackworth Ohio Wesleyan University. Delaware, OH 43015 One exneriment t h a t has been successfullv. emploved . - in our Advanced Integrated Laboratory course for upperclass chemistry majors is the synthesis and characterization of M o ( d p ~ e ) ~ ( N(dppe=l,2-his(diphenylphosphino)eth~)~ ane), which has been detailed in THIS JOURNAL.^ We have extended t h e procedure one step by requiring t h a t the student synthesize the ligand dppe. T h e reaction, following t h e procedure of Hewertson and Watson3, takes place in liquid ammonia and requires two consecutive lab periods. If the yield of the ligand is insufficient to proceed t o the synthesis of the molybdenum complex, additional dppe may be supplied from commercial sources. Experlmenlal Caution: All experimental steps involving liquid ammonia should he performed in an efficient fume hood. Gloves are recommended when adding reagents to the solution. A 500-mL, three-neck, round-bottomed flask equipped with an overhead mechanical stirrer was flushed with dry nitrogen gas and flame dried to remove traces of water. The flask was then immersed in a dry ice-acetone (-78 *C) bath. Dry ammonia gas was passed over a dry ice-acetone cold finger connected to the flask and condensed. Depending upon gas flow rate, it took from a half hour to an hour to collect approximately 300 mL of liquid ammonia." Sodium (5.15 g, 0.25 mol) was added to the solvent in small chunks and then 'Author to whom correspondence should be addressed. Present address: Bldq. - 6. COEH; 3100 Wyman Park Drive. Baltimore. MD 21211. *Archer, L. T.; George, T. A.; Nobel. M. E. J. Chem. Educ. 1981,56, 727. Busby, D. C.; Fendrick,C. M.;George, T.A. J Chem. Educ. 1981, -5R-, 7. 7-R-. Hewertson. W.; Watson, H. R. J. Chem. Soc. 1962, 165, 1490. Alternatively, liquid ammonia may be dispensed directly from a cylinder equipped with a eductor tube. For details see either Jolly, W. J. "The Synthesis and Characterization of inorganic Compounds"; Prentice-Hall: Englewood Cliffs, NJ, 1970: or Anyelici, R. J. 'Synthesis and Technique in Inorganic Chemistry', 2nd ed.; Saunders: Philadelphia, 1977. Wagner, R. I.; Burg. A. 6. J. Amer Chem. Soc. 1953, 75.3869.
stirred for 15 min. During this time the solution turned deep blue. Triphenylphosphine (32.7 g, 0.12 mol) was then added over al0-min period and the solution turned orange. After 1 h of stirring, 12dichloroethane (10 mL, 0.12 mol) in 20 mL of dry diethyl ether was added to the solution. The reaction was then allowed to warm to room temperature. The orange color immediately began to disappear and eventually the solution turned white. After the loss of the liquid ammonia, the remaining solid was washed with a liter of water and 200mL of methanol. Thedried whitesolid wascrystallizedfrom hot I-propanol. One or two additional recrystallizations from 1propanol were needed to obtain a pure product. The purified product was stored in a vacuum dessieator. Typical yield: 18.4 g (74%). M.P. 139-142 "C (lit value 142-143 W3'H NMR (CDCb, Varian T60): 2.1 ppm (t, -CHz-), 7.2 ppm (m, -CsHs).
T h e first step in the synthesis is the attack of sodium on triphenylphosphine, Ph3P
+ 2 Na
-
+
NaPPhn NaPh
T h e orange color t h a t develops a t this point is due to sodium d i p h e n y l p h ~ s p h i d eMost . ~ of t h e other product, phenyl sodium, is lost in the following equilibrium t h a t favors the formation of sodium amide3, NaPh
+ NH3 = PhH + NaNHz
Half of the dichloroethane added to the reaction mixture destroys sodium amide and any remaining phenyl sodium. T h e additional dichloroethane reacts more slowly with the sodium phosphide salt t o produce dppe,
Phenyl sodium and sodium amide can also be removed by addition of an ammonium halide salt wrior to the addition of dichluruethane. Howww, there is no imprwemenr in yield a i t h this n ~ w o a c h . I'urification wrocedures remove the trvproducts Gelding t h e ligand.
Volume 63
Number 9
September 1966
817
