Synthesis of an lsolable Quinodimethane Stuart Rosenfeld and Sarah VanDyke Smith College. Northampton. MA 01063 Quinodimethanes', e.g., the parent member of the series 1 and its dibenzologue 2, are highly reactive species that typically undergo cyclodimerization or polymerization below room temperature in the absence of other reagents. While this lability precludes room temperature isolation, there have been numerous studies of their chemistry at low temperature (1, 2) as well as reports of their electronic (3), vibrational (3). nuclear maenetic resonance (4). and photoelectron ( 5 )&&troscopic behavior. A small n k h e r oiiso~able derivatives of 2 with suhstituents in the . ~ e r -~ositions i have been reported, and a dipole moment measurement on one of these is consistent with a n o n ~ l a n a r(boat) eeometrv (6,7). MNDO calculations also suppbrt a nonplanir geometry for 2 (8).The simplest isolable derivatives of 2 have alkyl groups in the peri positions (7), and we have modified the procedures for the synthesis of one of these (3) t o fit the time and equipment l i m h o n s of an advanced synthetic lab.
T h e focus in developing this new lab sequence around the chemistry of quinodimethanes was to provide lab experience with arealistic research component. The primary goal was to generate a situation in which students have the ability to extend knowledee indenendentlv usine the tools and models available followl'ng a y e d o n g o"rganicchemistry course. T o accom~lishthis. we created a structured lab within a relatively poorly &died area s o that some independent work could be done in a settine that is neither contrived nor too loosely defined to afforda useful experience for most individuals. Exparlrnetal Phthalic anhydride (Fisher) and p-xylene (Aldrich) were obtained commercially and used without further purification. NMR spectra were recorded on a Bruker WPlOOSY NMR spectrometer as CDC13 solutions (TMS reference). IR spectra were recorded on a Nicolet 20 DXC FTIR spectrometer. Melting points are uncorrected. 242,5-Dimethyibenzoyl )benzoic Acid (lo) A 250-mL, three-necked (24/40), round-bottom flask was equipped with magnetic stir bar, hollow glass stopper, condenser with drying tube, and a 5-in..long piece oi Tygon tubing or Gooch tuhine attached to one neck of the flask. Finelv mound ~hthalir anhy&ide (14.8g, 0.1 mol),p-xylene(13.5mL, ~ . i l & o l )and , 80mL of 1,1,2,2-tetrachloroethane(Caution: toxic, hood) were added to the round-hottom flask. Aluminum chloride (30 g, 0.48 mol) wss placed in an Erlenmeyer flask, which was quickly attached to the Tygon tuhing. While stirring, aluminum chloride was added to the reaction mixture over a 10-min period. The thick orange-yellow mixture was stirred for 1h after the vigorous exothermic reaction had subsided. The reaction mixture was poured into a separatory funnel containing 300 mL of ice water and 30 mL conc. hydrochloric
acid (Caution: ezothermic).The two layers were separated,and the organic layer (bottom) was washed twice with water. The solvent and remaining xylene were steam stripped in an apparatus consisting of a 500-mL,single-neck (24/40),round-bottom flask with adaptor for distillation and a 12-in. piece of glass tubing reaching from the bottom of the flask to the top of the adaptor, where it was attached to rubber tubing connected to a steam outlet via a t-tube that acted as a water trap and pressure release. The solid residue was light yellow, thick, and sticky and hardened upon cooling. The remaining water was poured off. The solid was dissolved in 250 mL of 12%aq. NaOH (may require as much as 1h) and the solution was neutralized by cautiouslypouring into -90 mL ice-cold eonc. hydrochloric acid with vigorous stirring. The white precipitatewas colleeted by vacuum filtration (sintered glass funnel) and then allowed to air dry (829yield); mp 145-146'C; IR (nujol mull) 1680 em-', 1645; NMR S 2.2 ppm (a), 2.6 (s1,I.O-8.3) (m). 1,4-Dimethyl-9,1O-anthraqulnone A 100-mL,single-neck (24/40), mund-bottom flask was equipped with magnetic stir bar and condenser with drying tube. Concentrated sulfuric acid (-50 mL) was poured into the flask and chilled. 2(2,5-Dimethylbenzoyl)benzoicacid (10.0 g, 0.039 moll was added to the cold sulfuric acid while stirring. Once thesolid was dissolved, the flaskwas gently lowered into a45 OC water bath. The temperature of the bath was quickly raised to 70 OC, and the reaction mixture was stirred for an hour. The dark red reaction mixture was cooled to room temperature, chilled in an ice bath, and then poured into 250mL ice water (exothermic).A green precipitate immediately formed and was collected via vacuum filtration (sintered glass funnel). It was washed on the filter with water, 5%aq. NazC03 (approximately 100 mL or until foaming stops), and with water again. The crude product was purified by dry-column flash chromatography (9) on silica gel (CHC13. The first band, after evaporation of solvent, afforded bright yellow crystals (72%yield); mp 138-140 OC (lit. 142 "C) (10); IE (nujol mull) 1680cm-I; NMR 8 2.8 ppm (s), 7.4 (s), 7.95 (m). 1,4-dlmethyl-9,lO-d~hydr0-9,lO,dlhydroxy9,10dimelhyanthmcene (1 1) A 25-mL, three-neck (14/20), round-bottom flask was equipped with stir bar, condenser with drying tube, and septum. Magnesium turnings (0.25 g, 0.01 mol) were placed in the flask, and the apparatus was flamed out with a Bunsen burner. Once the apparatus had cooled, 1,4-dimethylanthraquinone(0.5 g, 2 mmol) and 10 mL of diethyl ether were added to the magnesium. Finally iodomethane (0.63 mL, 0.01 mol) was injected into the flask while stirring. The reaction should begin in ahout 5 min. When the reaction began to subside, the mixture was heated (hot water bath) for an additional 4: min. The reaction mixture was added rlowly with swirling to an Erlenmeyer flask containing an ice-cold solution of 1.5 g NH,CI in 10 mL H.0. Vacuum filtration2afforded a yellow solid whi~hwas
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The compounds have also been referred to as qulnane dlmethIdes and pxylylenes. Compound 2 Is 9,lO-anthraqulnodimethane or 9.10-bis(methy1ene)-9,lOdlhydroanthracene.
Evaporation of the ether layer of the filtrate yields only a small additional amount of pmduct, which may be combined with the rest of the materlai prior to chromatography. (Alternatively, additlon of acetone to the filtrate causes precipltatlon of this material, which can then be isolated by vacuum filtration.) Florisii must be used for this separation since slllca and alumlna promote dehydration and other reactions of 6. The compound was preadsorbed on florlsiland applied to the top of the dry column as a plug because of poor solubility in the eluting solvent. Volume 68
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purified by dry-column flash chromatography (9) on florid (10% etherlnet. ether)." Asmall amount of startine ouinone 3 elutesfirst. followed by whfw powdery d~olfi (ROar y i e i i mp 192 193 T; IR (CC1,) :3598 rm 3 5 3 . 2984, 2969, 1489, 1454, 1386, 1X0, 1:31;1, 126fi;N M H 6 1.6 ppm Is), 1 . 3 Is) 2.88 (31, 7.1 W, 7.55 r m ~C'rystals . of 6 from recrystallization (benzenelpet.ether, 60%recovery) are a mixture of two crystalline forms.
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1,4-Dimethyl-9,lO-bis(methylene)-9,lOdihydroanthracene (7) The apparatus consisted of a 10-mL,three-neck (14120), roundbottom flask and a 25-mL, two-neck, pear-shaped flask. The two flasks were connected via a 5-in.-lone - niece . of Tveon ." tuhine with a shorr-~remmeddisporalde piper on each rnd. The piper was firwd intothsr~~~nd.I,ottom nark wirharubbrr~fopper~nd infothe pearshaped flask with a rubber rhermomrrer adapwr. The round-hottam flask was also equipped with a magnetic stir har, condenser with drying tube, and a septum. (If this procedure is not done in a fume hwd, a water scrubber to trap escaping HCI should be added.) Sodium chloride (2.21 g) was placed in the pear-shaped flask, and the flask was equipped with a septum. The diol(0.l g, 0.37 mmol) was dissolved in 5 mL dry THF and injected into the 10-mL,roundbottom flask (make sure the tip of the pipet is below the surface of the THF solution), which was then cooled in an ice-water bath. Concentrated sulfuricacid (1mL) was injected into the pear-shaped flaskdrop by drop to produce HCI gas, which bubbled into theTHF solution. The THF solution immediately changed from clear to bright yellow. After most of the gas had entered the THF solution (apprax. 10 min), the pipet was replaced with a stopper, and the cooling bath was removed. The reaction mixture was stirred for another 2 hand then poured into 10 mL ice water (exothermic).The yellow precipitate was immediately vacuum filtered (sintered glass funnel),washed with cold water, 5%aq.sodium carbonate, and with cold water again and then allowed to air dry (55%yield) mp 96-99'C (lit. 105 OC (7)). This material gives fairly clean NMR and IR spectra, but recrystallization from ethanollH20 provides colorless crystals with good recovery; mp 104-104.5 'C; IR (CCld 3064 cm-', 3033,2979,2956,2928,1623,1460,1448,1445; NMR 6 2.55 ppm (s), 5.5 (d, poorly resolved splitting), 5.8 (d, poorly resolved splitting), 7.1 (s), 7.45 (m). ~
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conformations. Experimental probes of this area, e.g., dipole moment measurement for 3, mav be available but molecular mechanics modeling (13) d s o provides some insight. For example, the lowest energy calculated geometry for 3 is a boat (and the corresponding calculated dipole moment is about 0.6 D).
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The synthesis of 1,Cdimemyl-9.10-anthraquinodimethane. Of course, the best result is for students to generate their own ideasduring thestructured Dart of thelah seuuence and to discuss the& in class so that a well-defined problem is selected. Even if the plan is simply to see if the methods for synthesis of 3 can be-used to prepare an unknown quinodimethane from quinone 5, i t will be instructive for the student to consider the expectations for the spectra of the new compound. I n the course for which this lab was developed, students often Dresent and discuss ex~erimentalresultsand ~~-~~~ proposed expe;iments. Final reports are written in the style of journal articles with an audience defined as havine the same academic background as the student author but k t h out specific knowledge of the chemistry being described. ~
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Acknowledgment Dlscus~lon The authors wish t o thank the Howard Hughes Medical Institute for a grant to Smith College, which provided supThis synthesis, illustrated in the figure, provides a vehicle port forthis work. Partial support for tbis work was provided for introducing independent work. A number of advanced by the National Science Foundation's Instrumentation and techniques are used, but the conceptual material should be Laboratory Improvement Program through grant :USEeasily accessible tostudents with a background of one year of 905088. organic chemistry. The chemistry represents a fascinating area with a very limited literature and so provides opportuLiterature Clted nities to formulate questions, devise and execute experi1. For the initial report of I see Szwarc, M. Discussions Foradoy Soc. 1947.2.46. ments, and evaluate results without a distracting focus on 2. Errede, L. A,: Hoyt. J. M. J, Am. Chem. S o c 1960,82,436. the "correct result". During the course of the synthesis one 3. Poars0n.J. M.:Six,H.A.:Wiiiiams,0. J.:Levy,M . J . A m . Chem.Soc. 197i,93,5034. 4. Wi1lisms.D. J.;Pearson, J. M.: Levy, M. J A m . C h s m Soc. 1970.92, 3436. mieht lead students to the limited ~ r i m a r vliterature of 5. Al1an.M.; Heilbronner, E.: Ksupp,G. Hdu. Chim. Aclo 1976.59, 1949. direct observation of quinodimeth&es, emphasizing also 6. Dickerman,S.C.:Borg,J.H.;Hsase.J.R.;Vsrma,R.J.Am.Chem.Soc. l967,89,5467. 7. Bowden, B. F.;Csmcron,D.W. TefmhrdronLetts. 1577,383. that the isolable auinodimethane 3 is described briefly in 8. Oewar. M. J. S. J . Am. C h e m Sor. 1982,IM. 1447. only one communication (7) and its immediate precu&or, 9. (a) H a r w o d L . M.Aldriehmieio Acta 1986,18,25. (b) Sharp. J. T.;Gosney. l.;Rowley. A. G . P r o r l i d 0rganicChemistry;Chapmanand Hall: New York, 1989: pp 16h183. diol 6, has not been described a t all. Students should be 10. Stephan. V.; Vodehnal. J. Coil. Cmhoslau. Chem. Comrnun. 1971,36.3964. directed to make models of each of the four compounds and 11. Beekatf,A.H.: Lingard, R. G. J . Chem.Soc. 1961.588. to use this exercise to generate questions regarding the 12. (a) Khsrash, M. S.; Reinmuth, 0.Crignord Reorlions o/ Nonm~lollicSubafonees: Prenfice~Hsll:NewYark, 1954;p529. (b)Clarke.A.L.;Carleton,P. W . J . A m Chem. chemistry involved in thi
