Friedrich Wöhler

A sample of aluminium

A sample of beryllium in elemental form

Samples of yttrium in elemental form

Wöhler investigated more than twenty‐five chemical elements during his career.[6] Hans Christian Ørsted was the first to separate out the element aluminium, in 1825, using a reduction of aluminium chloride with a potassium amalgam.[7] Although Ørsted published his findings on the isolation of aluminium in the form of small particles, no other investigators were able to replicate his findings until 1936. Ørsted is now credited with discovering aluminium.[8] Ørsted's findings on aluminium preparation were developed further by Wöhler, with Ørsted's permission. Wöhler modified Ørsted's methods, substituting potassium metal for potassium amalgam for the reduction of aluminium chloride. Using this improved method, Wöhler isolated aluminium powder in pure form on 22 October 1827. He showed that the aluminium powder could be solidified balls of pure metallic aluminium in 1845. For this work, Wöhler is credited with the first isolation of aluminium metal in pure form.[9][10]

In 1828 Wöhler was the first to isolate the element beryllium in pure metallic form (also independently isolated by Antoine Bussy).[3][11] In the same year, he became the first to isolate the element yttrium in pure metallic form.[12] He achieved these preparations by heating the anhydrous chlorides of beryllium and yttrium with potassium metal.[4]

In 1850, Wöhler determined that what was believed until then to be metallic titanium was in fact a mixture of titanium, carbon, and nitrogen, from which he derived the purest form isolated to that time.[13] (Elemental titanium was later isolated in completely pure form in 1910, by Matthew A. Hunter.)[14] He also developed a chemical synthesis of calcium carbide and silicon nitride.[15]

Wöhler, working with French chemist Sainte Claire Deville, isolated the element boron in a crystalline form. He also isolated the element silicon in a crystalline form. Crystalline forms of these two elements were previously unknown. In 1856, working with Heinrich Buff, Wöhler prepared the inorganic compound silane (SiH₄. He prepared the first samples of boron nitride by melting together boric acid and potassium cyanide. He also developed a method for preparation of calcium carbide.[4]

Wöhler had an interest in the chemical composition of meteorites. He showed that some meteoric stones contain organic matter. He analyzed meteorites, and for many years wrote the digest on the literature of meteorites in the Jahresberichte über die Fortschritte der Chemie. Wöhler accumulated the best private collection of meteoric stones and irons then existing.[4]

In 1832, lacking his own laboratory facilities at Kassel, Wöhler worked with Justus Liebig in his Giessen laboratory.[6] In 1834, Wöhler and Liebig published an investigation of the oil of bitter almonds. Through their detailed analysis of the chemical composition of this oil, they proved by their experiments that a group of carbon, hydrogen, and oxygen atoms can behave chemically as if it were the equivalent of a single atom, can take the place of an atom in a chemical compound, and can be exchanged for other atoms in chemical compounds. Specifically, in their research on the oil of bitter almonds, they showed that a group of elements with chemical composition C₇H₅O can be thought of as a single functional group, which came to be known as a benzoyl radical. In this way, the investigations of Wöhler and Liebig established a new concept in organic chemistry referred to as compound radicals, a concept which had a profound influence on the development of organic chemistry. Many more such functional groups were later identified by subsequent investigators with wide utility in chemistry.[4]

Liebig and Wöhler explored the concept of chemical isomerism, the idea that two chemical compounds with identical chemical compositions could in fact be different substances because of different arrangements of the atoms in the chemical structure.[1] Aspects of chemical isomerism had originated in the research of Berzelius. Liebig and Wöhler investigated silver fulminate and silver cyanate. These two compounds have the same chemical composition, yet are chemically different. Silver fulminate is explosive, while silver cyanate is a stable compound. Liebig and Wöhler recognized these as being examples of structural isomerism, which was a significant advance in the understanding of chemical isomerism.[16]

Wöhler has also been regarded as a pioneer in organic chemistry as a result of his 1828 demonstration of the laboratory synthesis of urea from ammonium cyanate, in a chemical reaction that came to be known as the "Wöhler synthesis".[3][17][18] Urea and ammonium cyanate are further examples of structural isomers of chemical compounds. Heating ammonium cyanate converts it into urea, which is its isomer. In a letter to Swedish chemist Jöns Jacob Berzelius the same year, he wrote, 'In a manner of speaking, I can no longer hold my chemical water. I must tell you that I can make urea without the use of kidneys of any animal, be it man or dog.'[19]

Wöhler synthesis of urea by heating ammonium cyanate. The Δ sign indicates heat.

Wöhler's demonstration of urea synthesis has become regarded as a refutation of vitalism, the hypothesis that living things are alive because of some special "vital force". It was the beginning of the end for one popular vitalist hypothesis, the idea that "organic" compounds could be made only by living things. In responding to Wöhler, Jöns Jakob Berzelius clearly acknowledged that Wöhler's results were highly significant for the understanding of organic chemistry, calling the findings a "jewel" for Wöhler's "laurel wreath". Both scientists also recognized the work's importance to the study of isomerism, a new area of research.[20]

Wöhler's role in overturning vitalism is at times said to have become exaggerated over time. This tendency can be traced back to Hermann Kopp's History of Chemistry (in four volumes, 1843–1847). He emphasized the importance of Wöhler's research as a refutation of vitalism, but ignored its importance to understanding chemical isomerism, setting a tone for subsequent writers.[20] The notion that Wöhler single-handedly overturned vitalism also gained popularity after it appeared in a popular history of chemistry published in 1931, which, "ignoring all pretense of historical accuracy, turned Wöhler into a crusader".[21] [22] [23] [24] [25][26] [27] [28]