Hugo Weidel, 1849-1899 A Tribute MORITZ KOHN New York City (Translated by Ralph E. Oesper, Unierersity of Cincinnati)
T.
H E slgnlficant roles played by Lieben and 'Skraup ' ' ~n the development of chemistry in Vienna were discussed in a previous paper.' Their colleague, Hugo Weidel, likewise was one of Austria's leading chemists. The writer was assistant to Lieben and Skraup from 1900 to 1910; he also studied under Weidel. This account of the latter's important contributions to organic chemistry is presented here as a token of the debt owed to a great chemist and a fine teacher. Hugo Weidel was a typical Austrianproduct. Born a t Vienna on November 13, 1849, he spent his whole career there, except the student years in Germany. His chemical training was begun a t the Vienna Polytechnical School under Hlasiwetz, and continued a t Heidelberg (Ph.D. 1870). He returned to Vienna and served as assistant to Hlasiwetz until 1874. He then was appointed section chief in the Chemical Laboratory I of the University of Vienna. The director, Schneider, was succeeded in 1876 by Ludwig von Barth, in whom Weidel found a high-minded superior, who favored the advancement of his junior colleague in e v q way possible. ' KOHN,J. CHEM.EDUC.,20,471 (1943).
Chemical Laboratory I1 of the University was headed a t this time by Rochleder, who was succeeded in 1875 by Lieben. The latter's successor (1906) was Skraup. I n 1886, Weidel was called to the Agricultural Institute as professor. His creditable record brought him the appointment as head of Chemical Laboratory I, in succession to Barth, whose untimely death came in 1891. Weidel filled this important post, with distinction, until his own death in 1899. Hlasiwetz was interested in various vegetable products, and a t his suggestion and invitation Weidel collaborated with hi. These first research efforts were soon followed by a study of the constituents of meat extract, and the findings were published in 1871. The material was furnished by none other than Liebig, whose name is still linked in the minds of the nonchemical public with his world-famous "Beef Extract." Weidel, together with Habermann, published (1873) a detailed analysis of the drinking water supplied to Vienna from a new source. Weidel's really significant work originated in another suggestion by Hlasiwetz, who thought that interesting results would be obtained if alkaloids were oxidized with nitric acid. These studies proved to be a veritable milestone in the development of the chemistry of alkaloids. Hlasiwetz at once appreciated the importance of Weidel's first findings and, without waiting for publication in Liebig's Annalen, hurriedly reported the results to the Vienna Academy of Sciences on January 16, 1873. The oxidation of nicotine with nitric acid yielded nicotinic acid (I), which Huber had obtained in 1867, but had failed to characterize chemically. In 1874, Weidel oxidized cinchonine and so discovered cinchoninic acid (11), cinchomeronic acid (III), and carbocinchomeronic acid (IV). In 1879, hediscovered berberonic acid (V) among the oxidation products of berberine.
Since all these acids on decarboxylation yielded pyridine, or quinoline, Weidel's attention was attracted
to these parent substances of the alkaloids. In this field, he, like his colleague Skraup, who was one year his junior, was to achieve great success. Their work often touched or overlapped, but also their results frequently supplerented each other. Koerner, in 1889, and Dewar, in 1871, independently proposed that the structure of pyridine is analogous to that postulated for benzene by KekulC, their revered teacher. Weidel was intrigued by the idea of searching for the possible isomeric substitution products of pyridine predicted by the Koerner-Dewar formula. Pyridine and pyridine bases had been discovered by Anderson in his investigation (1849 to 1851) of the so-called animal tar or bone oil obtained by beating bone meal. In 1879 Weidel began to restudy this oil. The rich harvest of new observations and discoveries garnered from his ambitious program is contained in a series of five papers. The researches were made possible by Joseph Loschmidt (1821-1895), the celebrated professor of physics in the University of Vienna. This gifted man, the son of poor peasants, made important contributions to chemistry, and physical chemistry as well as to his own field. He had originally studied chemistry and worked in industrial chemical plants before making his final choice of profession. Through Loschmidt, Weidel became acquainted with the industrialist Benedikt Margulies, who allowed Weidel to use his plant equipment to fractionate 1400 kg. of bone oil. This yielded 18.5 1. of pyridine bases. Even in the first paper (1879) he was able to report that the picoline obtained from bone oil is not a single substance,
but contains a- and P-picoline (VI, VII). Oxidation of the picoline had yielded not only picolinic acid (VIII), hitherto unknown, but also nicotinic acid (IX).
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Many years later it was found that this careful study of the preparation and properties of nicotinic acid had an extremely high practical v a h . I t and some of its derivatives are now known to be important with respect to biochemist~yand medicine; in the treatment of pellagra, for instance. The third pyridine mono-carboxylic acid predicted by the Koerner-Dewar formula was discovered in 1879 by Skraup, who was then working in Lieben's laboratory. In the third paper (1880), Weidel and Herzig reported another method of preparing this pyridine4-carboxylic acid (X). They named it isonicotinic acid. The fourth paper contained an account of the work of Weidel and Ciamician on the dry distillation of boneglue (gelatin). In the course of this study they discovered pyrocoll. I t is the dimolecular tricyclic anhydride (XI) of pymole-a-carboxylic acid. /CH-N CH \CH=C
I
'C%kCH
I \CH ,Co,~-~~R ~
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(XI)
THE
WORLD-RENOWNED
Weidel left to Ciamician the investigation of the nonbasic portions of bone oil. The young chemist was highly appreciative of this considerate action. Even as a student in Vienna he thus began his important work on the pyrroles. He continued this field when he returned to his native country and became one of the leading authorities on these compounds. Ciamician (1857-1922) developed into the leading organic chemist of Italy. This early recognition of his talents and the confidence in his abilities exhibited by his teacher, Weidel, doubtless were significant factors in setting Ciamician on the path that led to his later achievements. An early sequel to Weidel's discovery of cinchomeronic acid was his observation that this compound lost ammonia when treated with sodium amalgam in warm alkaline solution. A nitrogen-free tribasic acid is formed. In time he demonstrated that this is a fairly general reaction of pyridine mono- and dicarboxylic acids. Almost 20 years of persistent labor were necessary to elucidate this reaction completely, a success that demonstrated the high quality of his chemical thinking. ~h~ reaction is an interesting example of transition from the pyridine to the aliphatic series. I t involves the remarkable change:
This method can be used in a great many cases. For instance, Weidel and Wenzel used it to prepare methyl phloroglucinol (XIX) from toluene, dimethyl phloroglucinol (XX) from meta xylene, and trimethyl phloroglucinol (trihydroxy mesitylene) (XXI) from 1,3,5-trimethyl benzene (mesitylene).
\----,
The Weidel method, the best and simplest for ~ r e ~ a r i n g phloroglucinol and its homologs, was the basis of a Patent issued to Cassella and CO. Weidel was an enthusiastic teacher. Although he expended most of his energy in laboratory instruction, he was nevertheless an excellent lecturer. He was a I II I I man of vision and avoided one-sided specialization. I I1 I 1 CH=N-CH-+CO-SCH?, in that the third double Though primarily an organic chemist, he was also well bond of the pyridine nucleus is also hydrogenated a t the versed in the theory and methods of the inorganic and same time and aliphatic lactone acids are formed. analytical fields. The writer followed, with great Thus cinchomeronic acid (XII) yields a-methyloltri- interest and profit, his lectures on inorganic chemistry carballyic acid (XIII), which goes over into its lactone, and his course on the tri- and quadrivalent metalloids. cinchonic acid (or-valerolactone-p,ydicarboxylicacid) The lectures were of the highest quality, both in form (XIV). The latter, when subjected to dry distillation, and content, and were accompanied by excellent demloses water and carbon dioxide, and the anhydride of onstration experiments. His able dqmonstrator was pyrocinchonic acid (dimethyl maleic anhydride) (XV) Franz Wenzel, who had collaborated with him in the preparation of phloroglucinols. Under Weidel's guidresults. ance, Wenzel(1894) synthesized kynurine and so proved COOH COOH i t to be 4-quinolinol, COOH
CH,/~~\CHCOOH
C H/~ C
COOH
CO.,CH1
I
CHnOH
I
H \ ~ ~ ~ o o ~ I
Weidel's interests, in his last years, turned especially to the hydroxilated benzenes. His teacher Hlasiwetz had discovered phloroglucinol in 1855. I n Weidel's laboratory it had been observed that sometimes amino groups were replaced by hydroxyls. This led Weidel to suggest t o his student Flesch an examination of the action of water on the hydrochloride of 1,3,5-triamino benzene (XVII). It was found (1897) that complete exchange occurs and phloroglucinol (XVIII) forms. The preparation was accomplished in three stages with benzene as starting material through 1,3,5-trinitrobenzene (XVI).
Weidel's diligence and continued effort were almost incredible. At noon he left the laboratory briefly to take coffee with a few intimates in a nearby cafe and to glance through the newspapers. He could then be seen hastening hack t o his work. His countenance disclosed his comolete immersion in the uroblem a t hand. Absolutely unpretentious, his dominant desire was to go through life in a simple fashion. The world could give him no distinctions; to h i there was only one worthwhile honor: the opportunity to serve science and education with unselfish devotion. On June 7, 1899, he delivered, as usual, a lecture on pharmaceutical chemistry from 7 to 8 A.M. He then went to his laboratory. Suddenly he had a painful heart attack to which he quickly succumbed. Liebeu, in the obituary t o his respected colleague said: "The days were too short for him, and he borrowed from the (Cmtinued on pape 379)
AUGUST,
1944
379
HUGO WEIDEL, 1849-1899 (Co ntin ued from page 376)
nights; the weeks were not long enough, and he sought help from Sundays and holidays; the academic year was too brief, and he took from the vacation. He obviously sensed t hat the time at his disposal was to be short. He was always to be found in the laboratory; like a hero he fell at his post."
This condensed account of Weidel's extensive researches gives a picture. admittedly incomplete and inadequate, of the brillian t things he accomplished in his regrettably short career. However, he was granted enough time to earn a place of honor in the annals of chemistry.
