The Synthesis and Chemiluminescence of a Stable An Organic Chemistry Laboratory Experiment E. W. Meijer and Hans Wynbergl Department of Organic Chemistry, University of Groningen, 9747 AG Groningen. The Netherlands Singlet oxygen and chemilurninescence are subjects of great interest in today's organic chemistry (1-4). Both are present in the synthesis and thermal decomposition of 1,2-dioxetanes. This paper describes the synthesis and chemiluminescence of adamantylideneadamantane-1,2-dioxetane(I). The overall synthetic route is outlined in eqn. (1) and is based in part on
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syntheses originally reported by several groups ( 5 4 ) . The precursor for the 1,2-dioxetane (I) is adamantylideneadamantane (IV). This olefin is synthesized from readily available adamantanone (11) (9). Adamantanone (11) is treated with phosphorus pentabromide and as sole product, 2.2-dibromoadamantane (111) is isolated in 74% yield (5).In a Grignard type reaction 2,2-dihromoadamantane (111) is converted into adamantylideneadamantane(IV) in 84%yield by treating with magnesium (6).A photooxidation of adamantylideneadamantane (IV) with singlet oxygen affords adamantylideneadamantane-1,2-dioxetane (I)in 85%yield (7).All intermediates and produds can he identified by the undergraduate students using routine spectroscopic analysis. The table lists the results for each step in the synthesis as obtained during a normal junior level organic laboratory course. Discussion of the Singlet Oxygen Reactlon and Chemiluminescence Singlet oxygen is the first excited state of oxygen. Ground state oxveen. which is oart of the earth's atmosohere is in a triplet state. Singlet oxygen can be prepared hy photoreaction with the aid of a sensitizer (1 ). One of the most important reactions ot' singlet oxygen is the addition to electron-rich oleiins. This addition to uletinscan bedivided into twomaior paths as outlined in eqn. (2), to wit (a) the ene-reaction and (h) the 1,2-dioxetane formation. The ene-reaction needs an
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excited stste decomposition product appears to mirror natural bioluminescence to a surorisinp degree. This thermal decomposition affords, afteriuptuie ofthe central carbon-carbon hond and oxyeen-oxyeen hond, two ketone moieties, one in the ground s&ie and-one in an excited state. When this excited state ketone returns to itsground state. a bright hlue chemiluminescence (ketone fluor&ence) is observed.
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The temperature needed for this thermal decomposition is strongly structure-dependent. Most 19-dioxetanes chemiluminesce at temperatures below 75% However, adamantylideneadamantane-1,2-dioxetane(I) is stable and only starts to chemiluminesce between 151L175°C.This stabilized 1,2-dioxetane (I) can he obtained a t room temperature in crystalline form and stored for years, in contrast with almost all other known 1,2-dioxetanes.
2,2-Dibromoadamntane (Ill) All reactions are carried out in a hood. Finely divided phosphorus pentabromide can he prepared hy slowly adding 30 g phosphorus trihromide to a cold, vigorously stirred solution of 17 g bromine in 75 ml n-heptane in a 250-mlround-bottomedflask, fitted withareflux condenser, dropping funnel, and mechanical stirrer (8).When addition is comolete min). 15 e adamantanone (9) . . is added to the . (--I5 . ansoension of ohnaohnrous oentabromide in n-heotane and the re-
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allylic hydrogen atom and the possibility of a n olefin shift. Adamantylideneadamantane lacks this last opportunity for the ene-reaction (Bredt-rule), thus the only pathway for an addition of singlet oxygen to adamantylideneadamantane (IV) leads to the formation of the 1,2-dioxetane (I) (7). The interest in 1,2-dioxetanes is twofold. In the first place the chemistry of this unique, strained four-membered heterocyclic compound has intrinsic value for basic research. In the second place the chemiluminescence exhibited by the
' Author to whom correspondence should be addressed.
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Summaw 01 Literature and Student Ylelds
with 75-ml portions of dilute sodium bisulfite and with' water. The organic layer is dried over anhydrous magnesium sulfate and thenheplane ia evaporated under reduced pressurp. The residue. 2 2 . dibromoadarnaolane (Ill).1s crystallized t'rorn 96% ethanol to afford colorless needh, mpt 162-IWC, IH (KRr,: 29iI11, 1460, 760 crn-.. Adamantylideneadamntane (IW The reaction is carried out under anhydrous conditions'and the reaction equipment is dried in a drying oven. In a 500-ml roundbottomed flask, fitted with a reflux condenser,dropping funnel, and mechanical stirrer is placed 4 g of activated magnesium turnings and 25 ml of anhydrous ether. To this suspension is added dropwise a solution of 10 g Z,2-dibromoadamantane (111) in 75 ml anhydrous ether. If, after addition of --I g of (111) the reaction has not started Volume 59 Number 12 December 1982
1071
spontaneously (evident when the ether starts to reflux), a small crystal of iodine is added, followed by gently warming. When the reaction has started the remainder of (111) is added at such a rate that gentle reflux is maintained. The reaction mixture is heated under reflux far 1hr. Then it is cooled and pouredinto 100 ml water. Theaqueous layer is separated and extracted twice with 50-ml portions of ether. The combined ether layers are washed with 100 ml water and dried over anhydrous magnesium sulfate. After evaporation of the ether under reduced pressure, the adamantylideneadamantane is washed with methanol and allowed to dry, mpt 176-184%. Sublimation (8090°C/0.002 mm) affords colorless crystals, mpt 1&1-185°C, IR (KBr): 2900,1460,1100 em-'.
A solution of 200 mg adamantylideneadamantane in 100 ml dichloromethane and 10 mg methylene hlue is irradiated. The photochemical conversion is carried out in a three-necked flask fitted with 150 W.. hieh an immersion well lamo . and ~~~~~"~ ~~, of the tvne , . Hansu ~ (80 pwsurel or llanowa ,420 W,medium precsure). 'The ultravi&t light IS filtered with a saturated (at .I°Ci potasslunl dichnmate ariution between the lamp and the dichloromethane solution. This potassium dichromate solution serves also, via a circular course in which it is cooled, as cooling system of the lamp (circulation through the well jacket is often possible). Even a simple sodium street lamp (150 W) works well when the solution is olaced in front of the lamo (20-30 cm . distance) and the glasswork (f.;. a 250-ml three-necked ronnd-hottomed flask) is coated with the glass paint silver-yellow to filter the ultraviolet light; in this case no cooling of the solution is necessary. A slow stream of oxygen is bubbled through the gentle stirred reaction mixture. The reaction can be followed by aGLC analysis (Carbowax S E 30 column, inlet temperature: 300°C and column temperature: -200'C). The high inlet temperature of the GLC unit causes decomposition of the 19-dioxetane into adamantanone. Thus, the for~
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1072
Journal of Chemical Education
mation of adamantanone and the decay of ad9mantylideneadamanlane can be detected easily. Normally a rtat.tim time of 3 hr is sufficient fur a complrte conversion o i the olefin to the d~oretane(the reaction time is strongly dependent upon the lamp used). The methylene blue is removed with activated carbon, and the dichloromethane is evaporated under reduced pressure. One crystallization from methanol affords pure adamantylideneadamantane-1.2-dioxetane (I), mpt 163-164'C, IR (Kbr) 2900,1460,1100,1065,1010,800 cm-l.
The Chemiluminescent Reaction In a 25-ml round-hottomed flask are placed 50 mgadamantylidenead~mantane-l,2-d1oxetane (11and 5 rnl ethylmeglycol. In a n m p l ~ t t l vdark room the reaction mixture id htated to 120-200°C. A bright hlue chemiluminescence is observed for several minutes, Acknowledgment T h e authors would like to acknowledge the help of the many undergraduate students of t h e organic chemistry laboratory course, who checked, repeated, a n d optimized this experi-
ment. Llterature Cited (1) Wasserman, H. H., Murray, R.W.,"Singlet Oxygen.'. AeademicPressInc.,New York. 1979. (2) Horn, K. A,, Koo, J. Y..Schmidt, S. P.. Sehuster,G. B.. MoioeulorPhofoehrmisfry,9, l(1978-1979). (3) Adam, W.,Adu. Hotwocyclic Chem., 21.437 (1977). (4) wilson,T., lnr. RW. s e i . . ~ h y sc. h e m s s r TUO. 3,265 (1976). (5) Geluk, H. W. Synthesis, 652 (1970). (6) Bsrtlctt,P. D., Ho,M. S.,J. Amor Chem. Soc.. 96,627 (1974). (7) Wierings, J. H., Strsting,J.,Wynberg, H.,Adsm. W., TefmhadmnLett.,169 (1972). (8) Fieser. L. F.. Fieser, M. F.,"Resgenta for O~ganicSynthds." Wiley, Nov York. 1967. p. 865. (91 Aldrich, cat. number 14.604-8.
