edited by ARDEN P. ZlPP SUNY-Conland Conland. NY 13045
illustrate how synthetic organic chemistry ran play a supporting rule in medical researrh. This experiment involves the use of ICI and organohorme intermediates to prepare iodohexsne and parallels similar methods that introduce iodine radonuclides into fatty acids for use as heart imaging agents via positron emission tomography (1-3). These substitu-~~~~~oreanoborane-mediated "~ tions have several advantages over rhr previous use of ICI to intrudure radioiodine: they generate ICI m situ, avoiding the handling of a corrasive, unstable reagent; they are "cry tolerant of other funcrional groups: they provide a means of adding H I in an anti-Markovnikov fashion ro an alkene, and
Synthesis of lodohexane via Hvdroboration-lodination: A hli&oscale Organic Laboratory Experiment Involving AirSensitive Compounds E. Eugene Gooch Elon College NC 27244 At Elon college, a microscale hydroboration-iodination experiment has been introduced in the second semester organic lab to
proceed with complete regio- and stereoselectivity with > 90% radiochemical yield in < 5 mi". The reactions themselves are quite appropriate for an introductory organic lah. The use of radioiodine ('251 or 1311) is more appropriate for an advanced undergraduate or graduate lab where both synthesis of iodohexane and a determination of the radiochemical yield could be carried out. Special techniques for handling air-sensitive reagents (4) can be demonstrated a t the beginning of lab. Product yield can he determined by GC; analysis is complete in < 3 min, one instrument suffices for 24 students, and the experiment can be completed in asingle 3-h period.
Experimental' (Eye protection is mandatory, andgloves are recommended. B H s T H F reacts uigorously with water to liberate H2. Chloramine-T is a n irritant. Methanol is toxic. Exercise care in handling syringes and needla. \
THF
0
R = cyclohexyl
A232
Journal
of Chemical Education
A clean, oven-dried (110 'C), 25-mL 19/22 round-bottom flask (RBF) is quickly fitted with a rubber septum while~hotand secured.zThe flask is allowed to cool for 2 min with Ng flowine. then immersed in an ice hath. slight p&itive pressure of Nz should he left in the flask. An oven-dried syringelneedle is coded and Nz-flushed. Then 1.5 mL of 2 M l-hexene in onhydrous T H F is injected into the RBF, and 1 mL of 1 M BH3-THF is added dropwise with ~wirling.~ After 10 min, a vent needle is inserted, and 2 mL of 1M methanolic sodium acetate is slowly injected (HI evolved-hood). The ice hath is removed, and 2 mL of 1M aqueous NaI is added. Finally 4 mL of 0.5 M methanolic chloramine-T is slowly added with swirling.' The septum is removed. After 2 min, 2 mL of 5%aqueous NaSS203 and 2 mL of 5% HCL are added. The reaction mixture is ~ o u r e d into 10 mL of water. The mixture is extra&ed twice with 15 mLof petroleumether. The combined organic layers are washed with s a t u r a t e d a q u e o u s NaCl a n d d r i e d (MgSOd. Octane (1-2 mmol) is added as external standard, and the yield of product is determined by GC5
Concluslon In the years this experiment has been used, students have h a d l i t t l e difficulty w i t h this method: a few were somewhat i n t i m i dated b y the needles a n d used extra caution! A typical class of 25 students obtained good (17 students, 70-98%) t o fair yields (four students, 40-69s). Lower yields (4 students, < 25%) were traceable to poor l a b technique o r errors in following instructions. Student response to this laboratory has been consistently positive, their view ofthe relevance of oreanie chemistm is enhanced. and t h w e who contmue i n t o undergraduate research already h a w experience i n the handling of air-sensitive compounds.
Lnerature Clted 1. Kabalka, G. W.: G a r b , E. E.J. Or& Chem. 1980.43, 3578. 2. Kabalb, G. W.: G-h.
E. E. J Org. Chem. 1981.46,
2582.
3. Kabalb.G.W.;Gooeh.E.E.;Mta.C.H. JRadioanal. Chrm. 1981,65,115.
4. Brown. H. C. Orgonir Synthesis uia Bomnes: Wiley: New York. ,975; Chapter 9.
Anhydrous THF and 1 M BH.-THF (Sure-Seal bottles). 1-hexene. chloramine-T. septa far 19/22 joints, syringes. and needles were purchased from Aldrich Chemical Co. Normallv ssota are secved with 1-2 wraos of PO-gauge copper wire. Several tlght wraps of a rubber band were adequate and more rapidly applied. After each group has finished wlm it, the bome-THF syringe should be immediately rinsed with melhanol or water (hydrogen evolved-hood) to avoid damage to me plunger and barrel. Prompt wllection of all syringes and nesdles helps prevent
.
IDS
-
or men.
The wlor of ICi Is evldent: disappearance of wlor is a g w d preilmlnw iMicamr of prcduct yield. Analysis was pwformed on capillary GC with FID(0.25 mm X 15 m DB-1 wlumn. He 3 mL1min. injector and detector 250 'C, oven 50-150 ' C at 20 'C1mln)or conventional GC with TCD (6 ft X % in.. Chromosorb W with 5% SE-30. He 60 mumin. oven 100 OC1. ~, Some reaction moduch did not eiuta under mare condit8onr. Aner analyses were linaneb, t h , column war h e a M lo 250°C lor 2-4 h w~ se-I in/ections 01 sdvent to remove 4
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Volume
67
Number 9
S e p t e m b e r 1990
A233
