I
Addison Ault, Rachel Kooet.. and Arthur Serianz
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Mount
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Cornell College Vernon, Iowa 52314
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Two Thermorhrotnir Compounds Preparations for the introductory organic laboratory
zinc duat
-"-"."-".-
2 xanthone dixanthylene (I) Believing that students enjoy preparing .."., compounds with interesting or unusual properties, we Dianthraquinone may be prepared by bromination of have develo~edore~arationsof two com~oundswhich anthrone to give 9-bromoanthrone, followed by treatexhibit a pronounced thermoohromism. ~ i x a n t h ~ l e n e ment of this product with diethylamine in chloroform 0) A
. '
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anthrone
is a pale yellow-green solid a t room temperature, but becomes dark blue when melted or heated in solution; at liquid nitrogen temperature, it is completely colorless. Dianthraquinone (11) 0
0
n is a bright canary yellow a t room temperature, but becomes a brilliant parrot green when heated in solution. The thermochromism of both compounds can be observed very nicely during recrystallization from boiling mesitylene. The preparation of dixanthylene (I) may be carried out by the light-catalyzed addition of xanthene to xanthone to give 9-hydroxydixanthyl, followed by elimination of water
xanthene
xanthone
TsOH
Shydmxydixanthyl AcO ,
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2 Shrornoanthrone E&NH CHCI,
dianthraquinme (11)
Procedures 8-Hydrozydizanthyl from X a n t h a e and X a n t h a e (1). Place 3.23 g. (16.5 mmole) xanthone and 3.00 g (16.6 mmole) xanthene in a 125-ml Pyrex erlenmeyer flask. Add 75 ml of benzene and bring the solids into solution with swirling and gentle heating. Stopper the flask and allow it to stand in bright sunlight until it appears that the formation of the coarse granular crystalline materid has ceased.' At this time, collect the crystalline 9-hydroxydixanthyl by suction filtration and wash it with a little benzene. Yield: about 5.3 g. (85%); mp, 193.5-194.5"C (lit.z, 194')~ --- ,. Dizanthylae ( I ) from 9-Hydrozydizanthyl. Place 1.0 g (2.65 mmole) of 9-hydroxydixanthyl in a. 25-ml erlenmeyer flask. A d d 14 ml of acetic anhydride and boil the mixture under reflux until dl the solid has dissolved. Add 7.0 g (3.7 mmole) of p-toluenesulfonic acid monohydrate down the condenser and continue to boil the mixture until no more solid appears to form and no further color change occurs; about 3 min will be required; the color ohanges from red to dark brown to dark green. Allow themixture to cool to room temperature for one hour and then collect the dixanthylene by suction filtration, washing it with a little Zcetic acid. Itecrystdise the dixanthylene by heating it under reflux with about 10 ml of mesitylene (adding mare down the condenser, if necessary, to bring d l the solid into solution) and allowing the blue solution to cool to room temperature. Yield: about 400 mg (about 40%) of yellowish crystals; (lit.3 mp: 315"). Dizanthylne from X ~ n t h o n e .Place ~ 2.5 g (12.7 mmole) of xanthone in a 250-ml boiling flask, add 100 ml of glacial acetic acid and swirl until most of the solid has dissolved. Add 0.8 g (12 mmole) of zinc dust, 2 drops of conc. hydrochloric acid, and boil the mixture under reflux for about 90 mi". Every 5 minor so, add 2 drops of conc. hydrochloric acid dawn the condenser,
Shydroxydixanthyl dixanthylenel(1)
Alternatively, dixanthylene may be prepared by the reductive dimerization of xanthone by means of zinc and acid 410
H Br Sbromoanthrone
Journal o f Chemical Education
This work was supported in part by funds from the National Science Foundation (COSIP) and from the Sloan Foundation. 1 Three to fourteen days in the sunlight will be required; overexposure does apparent harm' 2 SCHONBERG, A,, A N D MUSTAFA, A,, J. Chen. Soc., 67 (1944). a GURGENJANZ, G., A N D YON KOSTANCCKI, S., Ber., 28, 2310 (189.5).
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taking carenot to add the acidso often that the solution takes on a red color. Add three more 0.8 g portions of zinc dust, one a t a time at intervals of about 20 min, adding the first about 20 min after the mixture has been brought to a boil. At the end of the period of boiling under reflw, allow the solution to cool completely to room temperature, collect the solid by suction filtration, and wash it thoroonhlv .. . with water. S e ~ a r a t eanv zinc from the prodllrr hy I h , i l ~ nir ~with mwi~).lmr. di-3rlve therlirnnthyle~w nl,out 2: ml wll he required , filtering rhe hot, blue d t ~ t i o nby gravity, reheating the filtrate if necessary to redissolve any material which may have crystallized, and allowing the filtrate to cool to room temperature. Collect the very pale yellow-green cryatdls by suction filtration and wash them with s. little benzene. Yield: about 0.8 g (35%). The thermochromism of dixmthylene (I) may be observed by heating a. sample in a. melting point capillary over a. small burner flame, or, better, by recrystallization from boiling mesitylene, nsingabout 19 ml/g (recovery: about 90%). g-Bromaanthraefrom Anthrone.' Suspend 5.0 g (26 mmole) of anthrone in 15 ml of carbon disulfide and add bromine dropwise with stirring over a period of about 15 minutes until the bromine color persists; about 4.1 g (1.4 ml; 1 equivalent) will be required.* Collect the tan crystalline product by suction filtration and wash it with a little benzene. Yield: 6.0 g (85%). Dianthrquinone jvom 9-Bromoanth~onc.~Dissolve 2.0 g (7.3
mmole) of 9-bromoanthronel in 30 ml of chloroform.' Add 2.0 ml (1.4 g; 19 mmole) of diethylamine, swirl to mix, and allow the resulting warm solution to stand for two hours. During this time, the color of the solution will change from yellow to a dark redbrown. At this time, add 75 ml of ether slowly with swirling. After 5 min, collect the yellow precipitate by suction filtration and wash it thoroughly with ether. Suspend the precipitate in about 10 ml of 95% ethanol and then collect the canary yellow dianthraquinone by suction filtration, washing it with a little ethanol. Yield: about 0.8 g (55%). The thermochromism of dianthraquinone (11) can be observed very nicely upon recrystallization from boiling mesitylene using about 50 ml/g.
IBARNET~. E.. COOK.J. W..
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AND MATHEWS. M. A.. J . Chen. .\tr.vFn, K. H., ,Inn., 379.02 1191 I . Sinre hydrogru bmwide gas is evdveJ i u tlri* rcnvtiun, it must be iwrriwl out i n the hood or sowe pruvisim n ~ i ltw made 10nb-
.Tor., 123,l!l!i4 ,iw3
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sorb the gasproduced. ' BARNETT,E., COOK,J. W., AND GRAINGER, H. H., J. Chem. Soc., 121,2059 (1922). 'The 9-bromoantbrone m w t be prepared just before use; otherwise the vield of dianthraauinone is ereatlv reduced. Any insol;ble material shoild be removedMatthis point by gravity filtration.
Volume 48, Number 6, June 1971
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