Hofmann's Benzene Tree at the Kekul6 Festivities William H. Brock Department of History, University of Leicester, Leicester LE1 7RH, England, U K
0. Theodor Benfey a n d Susanne Stark The Beckman Center for the History of Chemistry, 3401 Walnut Street, Philadelphia, PA 19104-6228
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Also. the s~eech'se m ~ h a s i son t h e interaction amone I n 1890, Friedrich August Kekule was honored by the science, trchnolom and ;ndustty isofconsiderable interest German Chemical Society at a special scientific session todnv. Finallv. the ioccch contributes to hstorical studies dinner held at the Berlin town hall. (Festsitzung) and of ~ k k u l ga t time of renewed interest and controversy This occurred 25 vears after h e ~ u b l i s h e dthe hexaeon concerning his work. We have not tried to reproduce t h e formula for benzene. Here ~ e k u l k m a d ehis famous, and complexities of Hofmann's German style i n t h e translation, currently controversial, speech on the role of dreams or but instead aimed to produce a more idiomatic text. daydreams in scientific imagination.' The chief instigators of this Benzolfest were Gustav TheA. W. von Hofmann's After Dinner Speech odor August Schultz (1851-1928), who was then Director at t h e Kekule Celebration (Vorstand) ofthe research laboratories of t h e Aktien-GesellIntroduction By Prof. Dr. G. Schultz, Munich schaftfiirAnilinfabrikationin Berlin;' and August Wilhelm Hofmann (1818-1892). t h e pupil of Liebie who had spent Everybody lucky enoughto have been personally close to the two men, A. W. von Hofmann and August KekulC, to whom the 20 years leading Hritish ch&;stry a t ~ o n h o n ' s~ o ~ a l ~ o l superb color industry owes such an enormous debt, will also remember Irecof'Chcmrstrv until hecomin~.F'nfessur of'Chemistwat the differences in their thought and the manner in which they th;! University i f Berlin in 186k3Schultz, who had been expressed it. Their academic publications are, by the way, an Kekule's assistant at Bonn 1875-1876, edited the long eloquent testimonial to this. report of t h e Benzolfest t h a t appeared in the German These differences were also prominent at the celebration in Chemical Society$ journaL4 This included a historical adhonor of August KekulC in Berlin twelve years ago, organized by the German Chemical Society and jokingly called at the time 'the dress on benzene by Adolf Baeyer given at the scientific benzene frstival" Xcnn,lfesl session. In therepunon theucmsmn, which I wrotcat the tune? I could However, since shorthand reporters h a d n o t been present only hneflv rnentwu the final pan of the Fcatwmrs, ronsisting of at the ~ r i v a t edinner, Schultz was unable to print the more a banqueGith interesting afterdinner speeches, because, unfarinfo&al speeches given. Indeed, Kekule's owk famous pretunately, no stenographer was present. dinner soeech a t the Festsitzunz was recom~oseda h r the One of the after-dinner soeeches. that bv A. W. von Hofmann. was put into my hands at the timc, and I think it would now he event foliowing special p l e a d h i b y ~chu1tz.s-Theonly other interesting Forcolleaguer mthcCeld turcnd thespccch. It went nr sneech t h a t Schultz succeeded i n wllectine for oosteritv follows. was Hofmann's banquet speech, which was not printed in 1890, perhaps for reasons of space or because Schultz did Hofmann's Speech not care to publish i t without t h e other informal speeches. Dear party guests! If I was sufficiently unselfish I would have to Instead, 1 2 i e a r s later, when Schultz had become ~ r o f e s s o r regret that circumstances have put the toast of the evening into of C h e m i c a l T e c h n o l o ~ va t Munich's Technische my hands. I can see in this gathering so many pupils of the Hochschule, h e p u b l i s h e d ~ o f m a n n ' s witty speech in a celebrated man who, because they are adorned with the attributes now-rare a n d obscure iournal of dve and textile chemist& ofyouth, would haveexpressed thegratitude weowe to him in more lively words than those available to me. It is only because, even There a r e several reasons whv a translation ofHofmann's though many years older, I also claim the honor of being one of elegant speech is justified. I t should be rescued from its KekulC's students; like all of us, I went to his school and perhaps aforementioned obscuritv. It is a beautiful e x a m ~ l eof the master will testify that I learned something there. Hofmann's superb use of sustained metaphor, especially its Even though I certainly have been left behind by the majority of clever and appealing image of benzene asa fecund tree with my fellow pupils, I believe that 1am ahead of many of them in one slender OH, fork-shaped NH2. a n d cross-shaped CH3 blosrespect of which they won't he jealous. My "chemical memories" soms i n i t s derivatiGes. who can fail to be amused by already cover over half a century. For this reason I can also make known to my younger colleagues what organic chemistry looked Hofmann's beekeeping anecdote? like before KekulC spread his wings. Organic chemistry a t that time was like a menily splashing torrent; there were so many For a translation of KekulB's "dream" speech, see Japp, F. R. J. stonesin the water that one could still cmss it without gettingwet. Chem. Soc. 1898, 73,97 and Benfey, 0 . T. J. Chem. Educ. 1958,35, Today the torrent has become a deep and massive stream; the eye 21-23. The controversy is aired in The Kekul4 Riddle. A Challenge can hardly see the opposite hank, and proud, richly loaded fleets for Chemists and Psychologists; Wotiz, J., Ed.; Springer-Verlag, in rack eentlv on its broad surface. ~~~, press. With the ronccptof the henzene ring the number of organic On Schulb, see obituary Ber. Dtsch. Chem. Ges. 1928,.61A, compounds all n t once seems, one mlght almost sag. to have 82-83. increased to infinity. In the benzene nucleus we ha!,e been given On Hofmann, A. W. von, see Dictionary of ScientificBiography, a soil out of which we can see with surprise the already-known Vol. 6. realm of organic chemistry multiply, not once or twice but three, Schulb, G. "Bericht Ober die Feier der Deutschen Chemischen four, five or six times just like an equivalent numher of trees. What Gesellschar? zu Ehren August KekuM's." Ber. Dtsch. Chem. Ges. an amount of work had suddenly become necessary, and how 1890, 23, 1265-1 312. quickly were busy hands found to carry it out! First the eye moves 5Anschutz,R.AugustKekul4,2vols., Berlin, 1929,1,615-627; note up the aix stems opening out from the tremendous benzene trunk. also portrait of Schultz, p. 485. See also Rudofsky,S. F.; Traynham, But already the branches of neighboring stems have become interJ. G. The Kekui6 Riddle (note 1);Chapters 2 and 3. twined, and a canopy of leaves has developed which becomes more Z Farben Text. lnd. 1902, 1, 1-2. spacious as thegiant soars upwardsinto the air. The top of the tree
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November 1991
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rises into the clouds where the eye cannot yet follow it. And to what an extent is this wonderful benzene tree thronged with blossoms! Everywhere in the sea of leaves one can spy the slender hydroxyl bud; hardly rarer is the forked hlossom [Gabelb2irtelwhich we call the amine group, the most frequent is the beautiful eross-shaped blossom we call the methyl group. And inside this embellishment of blossoms, what a richness of fruit, same of them shining in a wonderful blaze of color, others givingoff an almost overwhelming fragrance! Understandably, there is also no dearth of industrious workers busily striving to collect the harvest. Keen climbers have already clambered up to the third or fourth hranch; same of them we can see working a t a dizzy height. Mast of them, however, are in the bottom branches of the benzene tree. Some have collected enough and are about to get dawn, others still cannot separate themselves from the rich harvest, and yet others are quarreling with their neiehbors about the harvest. But dear party kwests. I won't nttempt todepirt the benrene rrer any f ~ r t h e r , f o r r h r r ~ a r e s t , m d anwnguawhnenmem ny know the mirnculous tree in far higher regions thnn was granted to me by my weak powers. Allow me rather to descend from the dizzy heights of metaphor to the solid ground of reality in order to express a thought that impressed itselfonme again and again duringtoday's proceedings. I t concerns the close alliance between the efforts of pure science and the tasks of industry and technology, of which KekulB's life work has convincingly made us aware. Liebig had never walked behind aplow and yet he helped agriculturemare thangenerations of farmers. Something similar can be said about Kekul4. The wonderfully developed tinetorial industries which process coal t a r belanz to the most remarkable achievements of chemistry. The ~ 1 know, ncvcr had a dye m hi* hero of the r v m m g h w , as 1 : as hand.;. Yet thruu~rhthe drvrlnpment o f h u benzene theory he hna vcrnovs funhered thp coal-tar dye industry more than all of us laken-together who dedicated years of our lives to the analysis of dyes. The advances which Kekule gained for the industry are therefore no less than the ones for science. I can see in our midst the geniuses of this industry which has become so important for
our country, and the celebrated guest of the evening has already heard from their mouths and will hear further tonight how much gratitude they owe to him. Esteemed party guests! I could now ask you to drink a toast to the one we celebrate. However, once a German professor has been given permission to speak, he won't finish soon. I don't want to sit down without having told you how moved the committee members of the German Chemical Society were by the fact that their invitation to tadav's celebration received such a iuhilant resoonse. For a long rime the commmee has felt the desire lo recogrude KrkulB'sachie\emenrs in widcrcireles than thnre purely scientrfir. Th~r-the commmre believes-has now bccn nchwvrd through this party. For weeks this celebration has been the subiect of eeneral " discussion. For wecks Kekule's name has been on everybody'* hpr. Huw often have my colleagues on the committee, how often have I m y d f been asked abuut benlene. I'coplc have wrnrkrd thcir brains far a n explanation of benzene and how the celebrated man managed to come up with the concept of his benzene theory. With reeard to the last voint esveciallv.. s friend of mine who is a farmer and has a hvely interest m chemistry has a s w d me a question fnend" which 1 *,odd like to share wnh you. My '"a&~,l-rcultural apparentlv belleves hehostraced throriginsafthr henrenethenry. W a s Kckule." ro ran the questron. "once been 3 beekeeprr'> You certainly know that becs roo huild hexagons: they know well that the" canstore the ereatest amount ofhoLevthat wavwith theleast nrnonnt nfwnx. I always hked it," my agrrcultural friend went on. 'when I rcrcivcd a new issue of the Berrchte; admittedly, I don't redd the art~cles,but I like rhr pictures very much. The patterns of benzene, naphthalene and especially anthracene are indeed wonderful. When I look a t the pictures I always have to think of the honeycombs of my bee hives." You see, honored colleagues, how benzene and its relatives have alreadybecomepopularin allcircles. Therefore we want to hesitate no longer before giving jubilant expression to our admiration for benzene.
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1992 Dexter Award The Division of the History of Chemistry of the American Chemical Society and the Dexter Chemical Corporation wish to solicit nominations for the 1992 Dexter Award for the outstandine accomdishment in the historv of chemistrv. 'lhe nwnrd, which ir; usually presenrrd at the Fall Nati~malMeeting ofthe American Chemiral Soc~ety,conslsts of a prim of S200tr and an eug-roved plaque. It should he emphasrwd that the award is intcrnntmnal in rcope and that numinatruns are wrlromr from all quarters. Prev~ouswinners hnvr included h ~ r t o n a n sand h he mists form Germany, France, Holland, Hungary, and Great Britain. Nominations should include the following: a cover letter that summarizes the nominee's achievements in the field of the history of chemistry, citing unique contributions that merit a major award, and the scholar's impact on the field; three copies of a complete vita that includes personal data, educational background, awards and honors, publications, and other services to the profession; a t least two seconding letters; and appendices containing no more than three reprints of recent publications. All nominations should be sent to James G. Traynharn, Louisiana State University, Department of Chemistry, Batan Rouge, LA 10803-1804 by January 1,1992. ~
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