WöHLER, FRIEDRICH

(b. Eschersheim, near Frankfurt-am-Main, Germany, 31 July 1800; d Göttingen, Germany, 23 September 1882)

chemistry.

For three generations the Wöhlers had been equerries to the electors of Hesse, Wöhler’s mother, Anna Katharina Schröder, was the daughter of a professor of philosophy; his father, Anton August Wöhler, left Hesse and became a farmer, then a court official and leading citizen at Frankfurt . Wöhler attended the public school but had extra instruction in Latin, French, and music so that he could attend the Gymnasium from 1814 to 1820. After a year at the University of Marburg and two years at Heidelberg he qualified in 1823 for the M. D., specializing in gynecology. In 1828 he married a cousin, Franziska Wöhler, who bore him two children before her death in 1832; in 1832 he married Julie Pfeiffer, the daughter of a banker, by whom he had four children.

Wöhler’s teaching career began at an industrial school in Berlin (1825–1831). He next became professor at a similar institution in Kassel (1831–1836), and he finally settled as professor of chemistry at Göttingen (1836–1882). He was elected foreign member of the Royal Society in 1854 and was awarded its Copley Medal in 1872. From 1864 he was foreign associate of the Institut de France and in officer of the Legion of Honor.

From childhood Wöhler had a passionate interest in practical chemistry and the collection of minerals. At Heidelberg, Leopold Gmelin encouraged him to experiment on cyanates and, since it was essential for Germans to go abroad for systematic training in chemistry, he recommended Wöhler to Berzelius in Stockholm. Here Wöhler received a year’s rigorous training in mineral analysis and formed a firm friendship with Berzelius. The friendship lasted until the latter’s death in 1848 and can be followed through a voluminous correspondence. For over twenty years Wöhler translated Berzelius’ influential and often controversial annual reports, occasionally modifying their polemical tone but not their content. He also translated three editions of Berzelius’ Lehrbuch der Chemie, a labor undertaken for both love and money. Berzelius’ influence depended on accurate and prompt translation of his work, and Wöhler wrote an elementary textbook of inorganic chemistry that had fifteen editions in his lifetime and was translated into French, Dutch, Danish, and Swedish; a textbook of organic chemistry that reached thirteen editions; and a textbook of analytical methods that was translated into English.

Wöhler became acquainted with his lifelong friend Liebig as a result of what seemed in 1825 to be a minor squabble over the interpretation of analytical results but became a classic example of a new phenomenon that Berzelius in 1830 called isomerism: both silver cyanate and silver fulminate correspond to the empirical formula AgCNO. Liebig had studied the explosive fulminate and at first rejected Wöhler’s 1824 results for the stable cyanate. In the 1820’s most chemists assumed that only one chemical compound corresponded to one set of analytical percentages. Wöhler and Liebig exchanged letters, often visited each other, and sometimes took vacations together from 1829 until Liebig’s death in 1873.

Wöhler’s interest in cyanates led to a historic preparation of “artificial” urea, the circumstances of which are best described in his letter to Berzelius of 22 February 1828:

I can no longer, as it were, hold back my chemical urine; and I have to let out that I can make urea without needing a kidney, whether of man or dog: the ammonium salt of cyanic acid is urea.

Perhaps you can remember the experiments that I Performed in those happy days when I was still working with you, when I found that whenever one tried to combine cyanic acid with ammonia a white crystalline solid appeared that behaved like neither cyanic acid nor ammonia. . . . I took this up again as a subject that would fit into a short time interval, a small undertaking that would quickly be completed and – thank God – would not require a single weighing.

The supposed ammonium cyanate was easily obtained by reacting lead cyanate with ammonia solution . . . Four-sided right-angled prisms, beautifully crystalline, were obtained. When these were treated with acids, no cyanic acid was liberated, and with alkali, no trace of ammonia. But with nitric acid lustrous flakes of an easily crystallized compound, strongly acid in character, were formed; I was disposed to accept this as a new acid because when it was heated, neither nitric nor nitrous acid was evolved, but a great deal of ammonia. Then I found that if it were saturated with alkali, the so-called ammonium cyanate reappeared; and this could be extracted with alcohol, Now, quite suddenly I had it! All that was needed was to compare urea from urine with this urea from a cyanate.

The letter goes on to describe how the discovery adds to the pairs of substances of similar composition but of different properties already known. “It is noticeable that in making cyanates (and in making ammonia) we always have to start with an organic substance. . . .”

In his published paper Wöhler referred to his work of 1823, in which he had shown that cyanogen and aqueous ammonia yielded oxalic acid and a white crystalline solid that he now realized was urea.¹ This, and his new method, he considered to be remarkable examples of the preparation “by art” of a substance of animal origin from inorganic materials.

In a widely quoted obituary, A. W. Hofmann grossly exaggerated the impact of Wöhler’s discovery on his contemporaries; there are in fact few references to the discovery in papers or letters of the time. J. H. Brooke and others refer to the literature and indicate the place of Wöhler’s discovery in the history of the decay of vitalism and the establishment of isomerism.²

Wöhler’s period in Berlin was remarkable not only for the preparation of urea but also for the extraction of aluminum.³ In Lavoisier’s Traité of 1789 there is a list of earths, including alumina: although he was confident that the fixed alkalies (soda and potash) were compound, he was less certain of the earths. In 1807 Davy succeeded in decomposing soda and potash, and in 1808 he attempted electrolysis of the earths. In his footnotes to the printed lecture the history is reviewed.⁴ Meanwhile, Berzelius succeeded in using mercury as a cathode for the electrolysis of most lime and barytes; but alumina would not yield aluminum for him or for Davy, even though the latter tried many ingenious variations. With hindsight one can perhaps see that Davy almost certainly obtained aluminum in several very impure forms: as an amalgam, as a solution in potassium, fused into molten glass, and in iron alloys, Faraday and James Stodart in 1822 made an aluminum-in-iron alloy by reduction with coal and iron. In 1824 Berzelius succeeded in extracting silicon by heating potassium with potassium fluosilicate, the potassium probably being provided by Wöhler; the method failed for aluminum.

In 1825 H. C. Oersted showed a specimen of metal, which he believed was aluminum, to the Academy of Sciences in Copenhagen (the specimen is not now available). He certainly prepared aluminum chloride by a new method, but is seems unlikely that the metal was pure aluminum; an alloy of aluminum and potassium seems probable. Oersted, a friend of Wöhler’s, never published a claim and made no objection when Wöhler tacitly assumed priority in 1827 or when he published further details in 1845. Recently, however, claims have been made for Oersted’s priority.⁵

On 10 October 1827 Wöhler wrote to Berzelius: “Oersted has told me that he does not intend to carry on with his experiments with aluminum chloride. I have already made a first repetition of his researches . . .” Later he said, “Like Oersted, I decomposed it [aluminum chloride] with potassium amalgam and distilled the product. When the mercury had gone, an iron-black lump of metal remained; but on strong heating it distilled as a green vapor.” In a paper of 1827, Wöhler emphasized that he was not saying the extraction was impossible by Oersted’s method, but that he could not repeat the process and had a better one. Oersted had, he stated, given up the work and had given him permission to go ahead – an important ethical consideration. He praised Oersted’s “most ingenios method” for the preparation of the aluminum chloride from which the metal could be extracted.

Wöhler’s technique was to cover a small quantity of potassium in a platinum crucible with excess aluminum chloride and to head the covered crucible gently to start the vigorous reaction. Nothing remained to react with water to produce alkalies when the reaction mixture was put into water. Other workers possibly had failed with similar methods because alkalies would react with the finely divided metallic product. Wöhler proved that his metal contained no potassium and described its chemical properties in considerable detail, especially its reactions with other elements, acids, and alkalies; footnotes contain many references to other metals.

In 1845 Wöhler published a supplementary paper to amplify his descriptions of 1827.

Later in the nineteenth century, when aluminum became a common metal. Wöhler was honored by Napoleon III. Twentieth-century controversies over priority in the extraction of pure aluminum have added little to history except nationalistic claims. Wöhler subsequently used the same technique to extract beryllium and what he thought was yttrium from their chlorides.

From the first letters exchanged between Wöhler and Liebig the possibility of a joint work was discussed; but when it came, it was not, as might have been expected, on cyanates but, rather, on mellitic acid. In 1825 Wöhler became interested in the mineral honeystone sent to him by Heinrich Rose. (Its true structure, as the aluminum salt of mellitic acid–C₆(COOH)₆– was established by Adolf von Baeyer in 1865). He isolated the pure acid, a calcium salt, and other metallic derivatives; and qualitative observations led him to believe that the acid contained little or no hydrogen and might be related to benzoic acid. (By “the acid,” workers at that time usually meant the acid anhydride.) Liebig took over the practical work in 1829, and a joint paper eventually was published. Wöhler returned to the subject in 1839; was helped by Berzelius with supplies of the rare material in 1840; and prepared the ammonium salt, an amide, euchronic acid, and some unidentified colored derivatives.

In January 1830, Liebig wrote to Wöhler that he would prefer their joint work to be on cyanates instead of honeystone. While he was still a student Wöhler had already published four papers on cyanates; one on mercuric thiocyanate (“Pharaoh’s serpent”) and perthionic acid, two more after his year with Berzelius, and a fourth in 1829 on the products of dry distillation of urea and uric acid. Urea yielded an acid that he recognized as cyanic acid, already discovered and named by Serullas. But whereas Serullas gave C₂N₂O₂ as an empirical formula. Wöhler decided that the acid of the cyanates must be C₂N₂O. Liebig and Wöhler set to work separately. Wöhler doing the preparation and Liebig the analyses. They struggled for a year and were remarkably successful in sorting out the complex products of dry distillation of urea. In 1845 they returned to the study of the product obtained when cyanic acid reacts with alcohol and decided, with irony, to call it allophanic ether (literally, “unexpected” ether).

The correspondence shows that a joint paper consisting of miscellaneous observations in inorganic chemistry was based solely on Wöhler’s work. From the letters that each exchanged with Berzelius it can be seen that at this time both men were considering a study of oil obtained by pressing bitter almonds. Wöhler suggested it to Liebig as a joint study, and they began to collect materials. After Wöhler’s first wife died in June 1832, he went for about seven weeks to Giessen and worked feverishly with Liebig: although they published other joint works, this was the only time they actually shared a laboratory. A letter to Berzelius shows that in the first four weeks, they had carried out most of the experimental work and tentatively drawn what were to be their final conclusions.

In 1832 the two workers left open the relationship between the oil and the material from which it was extracted. In their classic paper–which was actually written by Wöhler although Liebig is listed as coauthor–they summarized their achievements; “. . . we make the general assertion that as a result of our experiments, it is established that there is a body, composed of three elements, that remains stable in the presence of reagents and that can be regarded not only as the radical of benzoic acid but, perhaps with slight variations, as the radical of a large number of similar compounds.”⁶

Wöhler and Liebig overcame considerable practical and theoretical difficulties. They had, for example, no thermometer that could measure temperatures over 130°C. Misunderstanding over the relative atomic weights of heavý metals metals and oxygen led to formulas double the modern ones (for instance, C¹⁴H¹⁰O² instead of C₇H₅O for the benezoyl radical); their analysis of benzoic acid therefore gave a result different from that established by Berzelius. The last of these difficulties was overcome after correspondence with Berzelius and analysis of the silver salt. They established the relation between the oil (now called benzeldehyde) and its aerial oxidation product (already known as benzoic acid). Then the reaction of the oil with potassium hydroxide was studied and a new “oil” (now called benzyl alcohol) extracted with potassium benzoate.

By passing chlorine through the oil, Wöhler and Liebig obtained benzoyl chloride, which they converted into the bromide and iodide; they also studied its reaction with alkalies, water, alcohol, and dry ammonia gas. Among many derivatives they obtained were benzoyl sulfide, benzoyl cyanide, benzamide, ethyl benzoate, benzonitrile, and benzoin. They did not analyze all of these, and some of their tentative formulas are incorrect; but the paper established beyond doubt what they claimed: the existence of a body that was constant from one compound to another. Incidentally, many of the compounds they first prepared and described (such as benzoyl chloride) were important in the future development of organic chemistry. Berzelius was prepared to accept the benzoyl radical, oxygen included; but he later felt that oxygen could not possibly be present in an electropositive radical and withdrew his support for such a view.

When Wöhler moved to Göttingen in 1836, he wrote to Liebig and proposed a joint study of amygdalin. Within two days of sending this letter he mailed another showing that he had virtually solved the problem. In 1830 P. J. Robiquet and Antoine Boutron-Charlard had found that crushed bitter almonds smell of bitter almonds only when moistened and that, from the crushed nuts, fats, a resin, a liquid sugar, and the substance they called amygdalin could be extracted by addition of boiling alcohol. Wöhler showed in 1836 that the crystalline amygdalin could be decomposed by a vegetable emulsion, providing the emulsion had not been coagulated by boiling. Liebig took over the quantitative work and showed that a sugar was the other product of the decomposition. Amygdalin, the first example of a glycoside, was the subject of a joint paper.

Wöhler and Liebig collaborated on one more major piece of work, a study of uric acid. Wöhler suggested the subject, and the idea seems to have come from his medical interests. Uric acid was not easily obtainable–snake excrement was the only substantial source–and relationships with urea and allantoin were suspected by Wöhler. As a student he had won a prize in 1828 for an essay on the conversion in the human body of chemicals taken orally and excreted in urine. The technique adopted by Liebig and Wöhler was to subject uric acid, ad the derivatives they prepared, to oxidation and reduction by reagents of different concentrations and strengths. Wöhler seems to have been the first to heat reagents together in sealed glass tubes, but after an explosion he thought metal ones safer.

Their 100-page paper described fourteen new compounds and their preparation and analysis.⁷ An attempt to establish a new radical called “uril” (C₈N₄O₄)was less successful. Perhaps even more significant than the sophisticated, practical and theoretical organic chemistry was the new spirit revealed. Writing to Berzelius in 1828, Wöhler was doubtful whether animal substances could be prepared in the laboratory. In 1832 he began the paper on the benzoyl radical with a description of organic chemistry as “the dark region of organic nature.” But in 1838 his work with Liebig led him to write (at Liebig’s suggestion):

The philosophy of chemistry will conclude from this work that it must be held not only as probable but [as] certain that all organic substances, insofar as they no longer belong to the organism, will be prepared in the laboratory. Sugar, salicin, morphine will be produced artificially. It is true that the route to these and products is not yet clear to us, because the intermediaries from which these materials develop are still unknown, but we shall learn to know them.

Although the two friends published further joint papers, they did no more major investigations together, Liebig turning to agricultural and physiological chemistry and Wöhler to inorganic studies. Although at the age of forty Wöhler had published only a quarter of the papers he was to present, none of the later ones was as important for the development of chemistry as those before 1840. As professor of chemistry and pharmacy, director of the laboratories, and inspector general of all the apothecaries in the kingdom of Hannover, he had to spend a great deal of time from 1836 to 1848 on inspection tours of apothecary shops. During these years translation of Berzelius’ texts also took much time. The school of chemistry at Göttingen grew steadily, and Wöhler estimated that about 1,750 students heard his lectures between 1845 and 1852, 2,950 between 1853 and 1859, and 3,550 between 1860 and 1866. He thus had all the duties of a government official, translator, and teacher, as well as father of a growing family; and later in his life he told Kolbe that he had not kept up with theoretical developments. Nevertheless, during his forty-six years as professor at Göttingen he produced a stream of interesting papers.

Wöhler was always fascinated by geological samples, which were sent to him from all over the world by friends and ex-students. Meteorites were equally absorbing, and he published some fifty papers on minerals, meteorites, and their analyses: he noted the passivity of meteoric iron. Wöhler’s lively curiosity and ingenuity shine through these papers, as well as through the fifteen papers on general analytical methods.

In organic chemistry Wöhler studied quinone and hydroquinone, established the relationship between them, and discovered quinhydrone (which he compared for beauty of color with the feathers of the hummingbird). He distrusted theoretical speculation and in 1840 published a paper under the pseudonym S. C. H. Windler satirizing Dumas’s substitution theory. Had he allowed the developing theories to guide his research, it is possible that his time spent on organic chemistry might have been more fruitful: many of his papers are on topics already absorbed into the current theories (such as chloroform) or too far beyond the tide of research to affect it (such as alkaloids). Like other workers, including Berzelius, he spent time on ill-characterized substances of biological or medicinal interest that failed to yield clear chemical results even to his superb manipulative technique.

Mid-nineteenth-century inorganic chemistry was relatively static, and many workers simply collected data and prepared new compounds. Their interest was in the materials themselves: rocks, crystals, or chemicals. There is hardly a metal for which Wöhler did not prepare new salts, and he was particularly fond of colored derivatives . Some of his methods, such as the preparation of phosphorus by heating calcined bones with sand, have since been developed industrially. He was the first to make acetylene from calcium carbide (1862), by heating together zinc, calcium, and carbon. Copper-colored cubic crystals from blastfurnace slag, which had been thought to be metallic titanium, were shown by Wöhler in 1850 to be a compound of titanium. carbon, and nitrogen.

Working with Deville, Wöhler used aluminum to extract crystalline boron from boric acid, and crystalline silicon from potassium fluosilicate. Heinrich Buff consulted Wöhler about the gas, which ignited explosively and spontaneously in air, that he obtained during the electrolysis of dilute acids with aluminum electrodes. Wöhler realized that the aluminum contained silicon and went on to discover and describe silicon hydride. Wöhler and Buff were the first to prepare organosilicon compounds, silicon chloroform, iodoform, and bromoform.

Unlike his close friends Liebig and Berzelius–and, indeed, many of the eminent chemists of the time–Wöhler rarely made enemies kept a cool good humor, avoided rancorous argument, and did his best to bring together even such immovable objects and irresistible forces as Berzelius and Liebig. His efforts to counsel Liebig to lead a quieter life were unsuccessful.

Wöhler was popular with students from throughout the world. An account of his American pupils, many of whom obtained important chemical posts, was published.⁸ His most distinguished student probably was Hermann Kolbe, who became professor at Marburg and remained a close friend until Wöhler’s death. Unlike Liebig. Wöhler remained interested in what went on his laboratory even in old age.

NOTES

1. “Über künstliche Bildung des Harnstoffs,” in Annalen der Physik und Chemie, 2nd ser., 12 (1828), 253–256.

2. John H. Brooke, “Wöhlers Urea and Its Vital Force?–A Verdict From the Chemists,” in Ambix, 15 (1986), 84–114. The significance of the preparation of urea from inorganic sources has been pressed by (among others) W. H. J. Warren. in “Contemporary Reception of Wöhler’s Discovery of the Synthesis of Urea,” in Journal of Chemical Education, 5 (1928), 1539–1552; and dismissed by the following: D. McKie, “Wöhler’s Synthetic Urea and the Rejection of Vitalism, a Chemical Legend,” in Nature, 153 (1944), 608–610; P. Mendelssohn-Bartholdy, “Wöhler’s Work on Urea,” ibid., 154 (1944), 150–151; and E. Campaigne, “Wöhler and the Overthrow of Vitalism,” in Journal of Chemical Education, 32 (1955), 403, an attempt to reestablish the significance of the discovery. A balanced review of the literature is in T. O. Lipman, “Wohler’s Preparation of Urea and the Fate of Vitalism,” ibid., 41 (1964), 452–458.

3. “Über das Aluminium,” in Annalen der Physik und Chemie, 2nd ser., 11 (1827), 146–161.

4. Humphry Davy, “Electrochemical Researches on the Decomposition of the Earths . . .,” in Philosophical Transactions of the Royal Society, 98 (1808), 333–370.

5. N. Bjerrum’s claim for oersted in “Die Entdeckung des Aluminiums,” in Zeitschrift für angewandte Chemie, 39 (1926), 316–317, was countered by K. Goldschmidt in “Nochmals die Entdeckung des Aluminiums,” ibid., 375–376. Oersted’s notes were published by Kirstine Meyer, in H. C. Oersted Naturvidenskabelige skrifter, 11 (Copenhagen, 1920), 467–470.

6. “Untersuchungen über das Radikal der Benzoesäure,” in Justus Liebigs Annalen der Chemie, 1 (1832), 249–282, written with Liebig; also reprinted separately as Ostwalds Klassiker der Exacten Wissenschaften, no. 22 (Leipzig, 1891).

7. “Untersuchungen über die Natur der Harnsäure,” in Justus Liebigs Annalen der Chemie, 26 (1838), 241–340, written with Liebig.

8. H. S. van Klooster, “Freidrich Wöhler and His American Pupils,” in Journal of Chemical Education, 21 (1944), 158–170.

BIBLIOGRAPHY

I. Original Works. A. W. Hofmann’s complete bibliography of Wöhler’s publications (see below) includes details of the translations of his books. The Royal Society Catalogue of Scientific Papers, VI , 410–419; VIII , 1258–1259; XI , 836–837; and XII , 790; lists all the translations of the papers.

Wöhler’s book include Grundriss der unorganischen Chemie (Berlin, 1831; 15th ed., 1873); Grundriss der organischen Chemie (Berlin, 1840; 13th ed., 1882); Beispiele zur Übung in der analytischen Chemie (Göttingen, 1849), published anonymously; Practische Übungen in der chemischen Analyse (Göttingen, 1853), also published anonymously; and Die Mineralanalyse in Beispielen (Göttingen, 1861), published as a 2nd ed. of the last work.

Wöhler’s translation of Berzelius’ Lärbok i kemien appeared as Lehrbuch der Chemie, 4 vols. (Dresden, 1825–1831); the 3rd ed., rev., appeared in 10 vols. (Dresden, 1833–1841). and the 4th ed. in 10 vols. (Dresden–Leipzig, 1835–1841). Vols. 4–20 of Berzelius’ annual surveys of progress in the sciences, Årsberättleser öfver Vetenskapernas Framsteg, 27 vols. (Stockholm, 1822–1848), were also translated by Wöhler.

The voluminous correspondence between Wöhler and Berzelius was published almost in its entirety by O. Wallach, ed., Briefwechsel zwischen J. Berzelius und F. Wöhler, 2 vols. (Wiesbaden, 1901), with scholarly footnotes.

Extracts from the Liebig-Wöhler correspondence were published six years after Wöhler’s death. Wöhler selected and often polished the extracts, probably intending publication as a tribute to his friend: A. W. Hofmann, ed., Aus Justus Liebig’s und Friedrich Wöhler’s Briefwechsel 1829–1873, 2 vols. (Brunswick, 1888). The extracts represent perhaps a quarter of the total correspondence, the bulk of which is at the Bayerische Staatsbibliothek, Munich. Wöhler’s (and Liebig’s) publisher, Vieweg, in Brunswick, has about 100 letters exchanged between the two men. The Deutsches Museum, Munich, and the University Library, Göttingen, hold letters exchanged by Wöhler and other chemists, such as Kolbe and Bunsen.

II. Secondary Literature. A. W. Hofmann, “Zur Erinnerung an Friedrich Wöhler,” in Berichte der Deutschen chemischen Gesellschaft, 15 (1882), 3127–3290; and Johannes Valentin, Friedrich Wöhler (Stuttgart, 1949), 159–170, both include bibliographies of Wöhler’s writings. See also Th. Kunzmann, Die Bedeutung der wissenschaftlichen Tätigkeit Friedrich Wöhler’s für de Entwicklung der Deutschen chemischen Industrie (Berlin, 1830), which gives a list of papers published by Wöhler’s students between 1837 and 1863; and Poggendorff, VII A (1970), 779–783, with a full list of papers published on Wöhler and his work.

Robin Keen

Wöhler, Friedrich

GERMAN CHEMIST
1800–1882

Friedrich Wöhler was born on July 31, 1800, at Eschersheim, near Frankfurt-am-Main, Hesse. The son of a veterinary surgeon, young Wöhler attended public schools in Frankfurt and passed exams qualifying him for admission to a university in 1820. During his earlier school years Wöhler had acquired an all-consuming interest in practical chemistry and mineralogy. He chose to study medicine at Heidelberg University and obtained an M.D. degree from that institution in 1823.

As a student at Heidelberg Wöhler attended the chemistry lectures of Leopold Gmelin, and the experience prompted Wöhler to choose chemistry over medicine. On the advice of Gmelin, Wöhler spent a year at the laboratory of Jöns Jakob Berzelius in Stockholm, where he honed his experimenter's skills. Wöhler developed a lifelong friendship with Berzelius and acted as the translator into German of Berzelius's influential Textbook of Chemistry (1808–1818, published in six parts over ten years) as well as of his annual reports of new developments in chemistry. Wöhler himself was a prolific writer of textbooks; his organic and inorganic chemistry texts went through thirteen and fifteen editions, respectively, in his lifetime.

Returning to Germany in 1825 Wöhler held positions in technical schools in Berlin and Kassel. In 1832 he was offered the professorship of chemistry of the medical faculty at the University of Göttingen, where he stayed until his death (on September 23, 1882). Wöhler is best known for his synthesis of urea and the isolation of aluminum. He is also known for his important studies of the elements boron, silicon, beryllium, and titanium.

Wöhler's synthesis of urea was the result of experiments begun in 1823, in which he investigated the salts of cyanic acid, known as cyanates. In 1824 Wöhler showed that the empirical formula of silver cyanate was AgNCO. Justus von Liebig, who had studied the compound silver fulminate, had come up with the same formula for an entirely different compound. (These two compounds were structural isomers .) Isomerism was a novel idea at that time, as it was believed that each compound had a unique formula: No two compounds could have the same formula. (Berzelius had first described the phenomenon of isomerism in 1831.)

In 1828 Wöhler attempted to synthesize ammonium cyanate via the treatment of silver cyanate with aqueous ammonium chloride. The reaction produced a white crystalline solid that did not possess the properties of ammonium cyanate. Wöhler then attempted to synthesize ammonium cyanate using lead cyanate and ammonium hydroxide. This produced the same white powder, but with fewer contaminants so that it could be analyzed. Upon analysis this white powder proved to have the composition and properties of urea, a compound that had been isolated from urine.

Pb(OCN)₂ + 2 NH₃ + H₂O → PbO + NH₄OCN → H₂NCONH₂

Wöhler recognized in the urea he had synthesized the phenomenon of isomerism, and, incidentally, that he had prepared an organic compound outside a living system. At that time it was believed that all organic (carbonbased) compounds could be made within living organisms only. Vitalism was a theory that developed as a reaction to mechanistic explanations of physical phenomena, which were viewed as a threat to belief in the unique nature of life. It held that living processes could not be understood according to totally mechanistic models, and that it was a material invisible force in organisms that made life possible. August W. von Hofmann, in his obituary notice for Wöhler, alleged that it was Wöhler's synthesis of urea that led to the demise of the theory of vitalism.

Wöhler's other major achievement was his isolation of the element aluminum in 1827. Attempts by chemists Humphry Davy and Berzelius to prepare aluminum from alumina (Al₂O₃) via electrolytic decomposition had all failed. Wöhler employed a chemical approach that included the reduction of anhydrous aluminum chloride by potassium amalgam , followed by treatment with water. It produced a gray powder that Wöhler was able to identify as the element aluminum.

3K + AlCl₃ → Al + 3KCl

see also Aluminum; Berzelius, JÖns Jakob.

Martin D. Saltzman

Bibliography

Hoffman, August (1961). "Friedrich Wöhler." In Great Chemists, ed. Eduard Farber. New York: Interscience.

Keen, Robin (1972). "Friedrich Wöhler." In Dictionary of Scientific Biography, Vol. 14. New York: Charles Scribner's Sons.

Wöhler, Friedrich (1800–82) German chemist who first isolated aluminium and beryllium, and discovered calcium carbide. In 1828, his synthesis of urea (from ammonium cyanate) was the first synthesis of an organic chemical compound from an inorganic one; it contributed to the foundation of modern organic chemistry.

Wöhler, Friedrich (1800–1882) German chemist; his synthesis of urea from inorganic compounds (1828) was the first evidence that organic compounds produced by living organisms do not contain a ‘vital force’.