A. P. Hagen, T. S. Miller a n d D. L. Terrell The University of Oklahoma Norman, OK 73019 B. Hutchinson, R. L. H a n c e and L. Daniels Abilene Christian university Abilene. TX 7 9 m i
High Pressure Synthesis of Transition Metal Carbonyls I
T h e use of increased pressure a s a synthetic tool has been described recently in this Journa1.l However, there a r e few experiments available in teaching guides which outline t h e equipment and procedures necessary for high pressure reactions. This experiment uses readily available starting materials and inexpensive apparatus for a synthesis a t 1000 atm. T h e nrocedure eives t h e student imoortant hackeround experience in basic techniques which are used i n research and industrv. This exoeriment is sueaested for use a s a special project in inorganic, organic, o r physical chemistry laboratories. Transition metal carbonyls are synthesized normally from metal halides suspended in organic solvents which are treated with carbon monoxide in thepresence of a reducing agent. Reducing agents include hydrogen gas, triethylaluminum in ether, zinc, or magnesium powder i n pyridine, a n d sodium i n diethyleneglycol dimethyl ether.2 I n this procedure carbon monoxide serves a s t h e ligand as well a s t h e reducing agent."
.
+ + WOJ + 9CO
---
2CoO 18CO Ma03 9CO
CodC0)s + 2C02 MO(CO)B+ 3C02
+
W(C0k 3C02 T h e reaction also readily takes place with iron a n d nickel oxides, b u t t h e products are difficult t o handle without a vacuum line constructed in a fume hood. Safety In our laboratorv t h e sueeested hieh Dressure reactors and valves have never ;upture&t tempeiat&es u p t o 500°C and a t pressures u p t o 4000 atm; however, t h e fittings d o break occasionally. Therefore, t h e r e a c t o r assembly m u s t a l w a y s b e kept behind a safety shield w h e n the p r e s s u r e is above 1800 isi (the normal &essure of a comm&cial carbon monoxide cylinder), and t h e m i c r o r e a c t o r should b e inside of n m e t a i c a s e d t u b e f u r n a c c . C a r b o n monoxide and the t r a n s i t i o n m e t a l c a r b o n y l s a r e toxic; therefore, a n effic i e n t f u m e hood s h o u l d a l w a y s b e used. Apparatus The figure shows the assembled apparatus and is complete except for the gland nuts and collars which are e part of the high pressure closures. The MRA-114R reaction vessel is supplied with all fittings up to the high pressure valve4and the high pressure valves (60-llHF4) comes with collars and glands to fit the 8 inch nipple5 (60-8M4-3).The manual control valve should he purchased with a gauge and a 114 inch NPT female outlet6 (52C-350)so that an adapter5 for the high pressure fittings can be installed (30-21HF4NMB).The entire assembly should cost less than $300. Catalogs are available from each of the listed suppliers which describe the apparatus components in more detail. Procedure Place 0.300 e of MOOTor W01. in a elass .. liner and nack the ooen end #,f the tulw with glass UWI l n s ~ r tthe liner into the hlgh pressure mmmcactur and then spa1 the cover 1,y tightening the r a p nut. Attnrh the mirnresctor wlvr to the carhon monoxide cylinder manual
control valve, turn on, and then turn off the carbon monoxide tank valve. If thegauge pressure doesnot drop within 15 min the reaction vessel assembly most likely does not haves leak. If the gauge pressure decreases within 15-30 mi", apply a liquid soap solution (30%liquid dishwashing soap in water) to the seals: bubbles will form from the escaping gas. When the system is tight, turn on the CO tank valve and cool the bottom 8 in. of the microreactor with liquid nitrogen for 1hr to condense carbon monoxide into the reactor. Close off the bomb valve and the tank valve. Then disconnect the reaction assembly from the carhon monoxide valve and place in the tube furnace. Heat the bottom 8 in. of the reactor a t 350DCfor at least 3 hr. This gives a pressure in excess of 1000 atm. Allow the reactor to cool to room temperature. This coaling rate is increased by blowing compressed air over the reactor. When the reactor reaches room temperature, vent the carhon monoxide into the hood, and then remove the reactor cover and recover the glass liner. The microreactor may have some carbon present due to the decomposition of carbon monoxide, hut the liner will contain beautiful colorless transparent crystals of MO(CO)~ or W(CO)e.The product may he recovered from a small amount of unrractrd oxld~.hy 'crysrnl picking" ur hy srlmrntmn id tlw product through s u h l m n t ~ mat WY' IrI~''l'orr. I.hlh :i\ei a 65% yield. 'l'h
