Juglone: A Comparison of Natural and Synthetic Products
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The allelooathic aeent from the black walnut tree (Juelons niero) has been .. iuelone (5-hvdroxv-1.4-naohthwuinone) . . . reviewed in ~ h ; ~s o u r n o l ( 1and , elrewhere (2).~svaightforwardsynthesis ofjugloneand ademonatration ofnr phy~otoxic activity have also been reported (3,. We have used juglune as a subject fur the organicchemistry teaching laboratory. cornbining thesynthesisof juglone with iu: isolation from walnut hulls. The idationof natural juglunenupled with the nvailahility of the synthetic material affords an opportunity t o make some interesting comparisons of the two substances by melting point and tlc techniques. We have also incorporated into this study a demonstration of the pharmacological activity (4,5) of juglone which requires only a few minutes of observation as opposed to the weeks of observation required to observe phytotoxic activity. Juelone mav be isolated from three black walnut hulls bv extractine crushed hull nieces with about 100 ml oetroleum rthrr 6; 30 min,followed by decantntion and evaporation of thesolrent in a hood at rook temperature ( 4 ) . ~ e c r y s h i z a t i o n of thr orang? residue from hrranr affords 50-100 mg of orange needles of juglonr, melting in the range 153 159'C (when inserted at 140°C). It should be noted that the yield and mpof theextraction product vary depending upon theconditim of thr hulls. Hulls that are softened but nor split and blarkened give thedescribed results. Howrver, our experience indicates that extrnctlon ofpreen, hard hulls results in low yirld and is complicated by coextraction of yellow pigments, presumably rarotenoids. Ihy, blackened hulls y~eldlittle or no juglone. As reported, juglone melts with derompusitiun 16); howewr. insertion at 14O0C affords a sharp mp of 161-163T for the synthetir product and 162-16;i0(' fur commercially purrfied iuelonr from Aldrirh Chemiral Comoanv. Tlcon Eastman Chromarraoh sheets (6060Silira Gel1 in CHCI. of both extraction and synthetic products affords a bright orange spot of R, = 0.7 which corresponds to juglone (7):while th; synthetic product is normally shown to be relatively pure, mast extraction products are shown to be contaminated with a grey-brown material which gives a faint spot or streak of Rf = 0.3-0.4.The comparison of the extraction and synthetic products by tlc and melting point provides an excellent example of the relationship between melting point and purity. A rather dramatic demonstration of the pharmacological activity of juglone is easily accomplished by addition of juglone to the water environment of a goldfish (5).About 10 ml of a saturated aqueous solution of juglone per liter of tank water produces a depressant effect within five minutes. The sedated goldfish will normally be reviewed by transfer t o fresh water if exposure to juglone is not prolonged.
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Literature Cited
J a m e s M. Wilbur Southwest Missouri State University Springfield, Missouri 65802
156 I Jwmal of Chemical Education
K e r r y Lyn Sublett Tulsa J u n i o r College Tulsa, Oklahoma 74119
