Byron L. Hawbecker, David A. Radovich, and Loyal G. Tillotson Ohio Northern University Ada, 45810
I
I
Preparation of Phenanthridone A multipurpose experiment for the organic laboratory
The laboratory experience in the typical undergraduate organic chemistry course is expected to provide the student with the opportunity to learn and to practice proper laboratory techniques. Furthermore, each student is expected to gain some proficiency in handling organic substances in the process of synthesizing, separating, and identifying appropriate compounds. It is also desirable to use the laboratory to reinforce the understanding of reaction chemistry as presented in the lecture portion of the course, whenever suitable experiments for making such correlations are available. Typically, there is insufficient laboratory time to allow adequate illustration of all the reaction chemistry that mieht be examined via the laboratorv- Dronram. . - Thus, it is deiirable to have available some multipurpose experiments which can illustrate a varietv of reaction tvDes within a single three-hour laboratory period. The pr;paration of phenanthridone provides such an experiment while giving the student the added experience of running a reaction a t low temperature. The instructor can easily use the experiment to illustrate addition to the carbonyl function with resulting derivative formation, diazotization, molecular rearrangement involving a l,Z.shift, and formation of a heterocycle via a ring expansion. The first step in the experiment involves the conversion of the cyclic ketone, 9-fluorenone, to its hydrazone a s illustrated by eqn. (1).
T h e hydrazone is then allowed to react under diazotizing conditions. This resulta in the loss of nitrogen and rearrangement to produce the final heterocyclic product, phenanthridone, as shown in the sequence represented by eqn. (2).
N-NH,
N-N-N
The ability of ketone hydrazones to rearrange under diazotizing conditions was first studied in detail by Pearson, Carter, and Greer (1, 2). Later work by Lansbury, Colson, and Mancuso (3, 4) demonstrated the applicability of the 398 / Journal of Chemical Education
diazotization-rearrangement process to hydrazones derived from cyclic ketones. Additional studies by Hawbecker, et al. (5-7) have served to define more carefully the mechanism of the reaction tvoe as well as the eeneral aoolicability of the process to a wide variety of ietone hGdrazones. The hvdrazone diazotization-rearrangements eenerailv have been found to be first-order in dLappearance of h i . drazone and in formation of nitroeen -eas. In addition. when geometric isomers of ketone hydrazones have been studied, the rearraneement steo has roved to be stereos~ecificwith migration 2 the group anti to the NH2. Thus, eqn. (2) illustrates the roba able mechanism for the conversion of 9-fluorenone hyhrazone into phenanthridone. The loss of nitrogen is thought to be concerted with the rearrangement step, and reaction of the resulting intermediate with water followed by a tautomeric shift produces the desired product. Both the hydrazone formation and the diazotizationrearrangement occur readily giving products which are easily purified. The diligent laboratory worker will generally have no difficulty in completing the sequence within one three-hour laboratory period. Experimental Preparation of 9-Floorenone Hydrazone
Place 3.0 g t0.011 mole) of 9-fluorenone.6.0 ml of 64% aqueous hydrazine, and 10 ml of anhydrous ethanol in a 5 0 4 boiling flask. (CAUTION!Avoid contact of hydrazine solution with the eyes or skin. It may cause irritation or burning. If contact is made, wash thoroughly with water.) Allow this mixture to reflux for 40 min. Transfer the reaction mixture to a 50-ml beaker and chill it in an ice harh to produce crystellization of rhe 9-fluorenonehydrazone. Recover the product by vacuum filtration and recrystallize ir from 40 ml of hot anhydrous ethanol. The tsn-yellow needles thus recovered melt at 150-151DC.Typical yields (which generally can be increased somewhat by longer reflux time) for this preparation are in the 70-9096 range. Preparation of Phenanthridone Place 10 ml of 90% HzSOa in a 250-ml Erlenmeyer flask and place the flask in an ice bath which rests upon a magnetic stirrer. When the acid has cooled to near O°C, add 0.85 g (0.012 mole) of NaNOz with stirring. The addition should be made in increments which allow the temperature to be maintained between 0 and 5°C (a thermometer may remain in the reaction mixture during the entire process). To this cooled mixture, add with constant stirring 0.80 g (0.004 mole) of 9-fluorenone hydrazone in sufficientlysmall increments to maintain the temperature below 10DC.Allow the mixture to stir for about 5 min after the addition is complete. (It is advisable to grind the 9-fluorenone hydrazone to a powder with a mortar and pestle prior to adding it to the acidic mixture. This greatly improves the solubility of the hydrazone and, thus, facilitates the reaction. The reaction mixture will become a dark red or brawn in color as the diazotization progresses.) While the diazotization is taking place, prepare an ice-cold solution of 20 ml of concentrated ammonia and 25-30 g of crushed ice in a 100-ml beaker. When the diazotization reaction is complete, carefully pour the entire ice-cold ammonia solution into the reaction flask. (It is advisable to keep the ammonia solution packed in ice until ready for use. Likewise, it is best to keep the reaction flask packed in ice as the ammonia solution is added to it.) Some foaming may occur as a suspension of the phenanthridone product is formed. Filter the suspension by vacuum filtration and boil the crude phenanthridone in 40 ml of ethanol for 5-10 min. Filter out the undissolved inorganic material, quickly transfer the filtrate to
a clean beaker. and chill t o oroduce the oroduct crvstals. Recover ~~
~
~~
the purified product via vacuum filtration and press between filter (In 'Ome cases it may be papers to to the product to dry until a subsequent laboratory period before weighing and checking the melting point.) The produd, a yellow powder, melts at 2 8 3 . 2 8 5 0 ~with the yield based upon starting bydrazone hein~rin the 50-70% ranxe.
Literature Cited (11 Pea-n.D E..and Greer.C. M.. J. Amer Chem. Soe. 71.1895 11%91. 121 Pesmon. D. E.. Carter. K.N., and GIPOI,C. M.. J. Am07 Chem Soe., 76,5905 (19531. (31 ~ ~ ~P. T~ ..colson, b ~J. G.. r and ~ ~ a. n e u ~ N o.. R., J. mar c h a m sot, 86,5225 (19641. ( 4 L a ~ s b u c P.T..and ~. Mencuno, N. R..J . A m s r Cham. Sor.. 88.1205 (19661. 151 Fishel, D. L.. and Havbecker, B. L., Abstracts of Papen. Divbion of Organic Chemin~ r,v American . Chemical Soeietu. 156th National ~ e e t i n z .tia antic Citv. Sootomber 1968. paper 170. I61 Hawbeeker.B. L.. J. CHEM. EDUC.. 17.218 119701. (7) Hawbecker. B. L.. Gladon, R. J., Hitchcock. R. H., Nardeen, D. H.,snd Wylpa, L. R., Ohio rl Sci., 72.276 iL9721.
.
..
.. .
Volume 53,Number 6, June 1976 / 399
