Emil Erlenmeyer

German chemist

• Born: June 28, 1825; Taunusstein, Germany
• Died: January 22, 1909; Aschaffenburg, Germany

Scientist, editor, and professor, Emil Erlenmeyer contributed to the great advances of organic chemistry in the second half of the nineteenth century. He discovered the Erlenmeyer Rule that hydrocarbon compounds will not form alcohols if the hydroxyl group is attached directly to double-bonded carbon atoms. The conical and iconic Erlenmeyer flask that he invented is still standard laboratory equipment.

Primary field: Chemistry

Specialties: Organic chemistry; quantum mechanics

Early Life

Richard August Carl Emil Erlenmeyer, who was known as Emil Erlenmeyer throughout his life, was born on June 28, 1825, in Taunusstein in Hesse, Germany. His father, Dr. Friedrich Erlenmeyer, was a Protestant minister.

Erlenmeyer’s only public schooling was from 1835 to 1839. He studied classical languages like Latin and Greek to prepare for a career as a minister. Afterward, he was home schooled by a Lutheran minister and a Catholic priest. Emil passed his high school degree examinations in 1845.

Rather than prepare for a clerical vocation, Erlenmeyer enrolled at the University of Giessen in 1845 to study medicine. At Giessen, he attended lectures in chemistry by Justus von Liebig (1803–73). These lectures fascinated him so much that he switched the focus of his studies to chemistry. Because there was no space in Liebig’s laboratory for Erlenmeyer, he went to the University of Heidelberg from 1846 to 1847 where he studied botany, mineralogy, and physics. When he returned to Giessen, however, there was still no laboratory space available. Upon the urging of his father, Erlenmeyer passed the state pharmaceutical exam in Nassau, Hesse in 1849 and bought a pharmacy in the town of Katzenelnbogen.

Erlenmeyer sold the business in 1850 and earned his PhD in chemistry from the University of Giessen. He then purchased another pharmacy in the city of Wiesbaden, where he was married and started a family.

Life’s Work

Life as a pharmacist did not satisfy Erlenmeyer, and he began teaching chemistry part-time at the Wiesbaden vocational school and invested in a small local chemical plant. In 1854, he travelled to London where he met fellow German chemist Friedrich August Kekulé (1829–96), also a Giessen graduate and a postdoctoral student in England.

In 1855 and back in Germany, Erlenmeyer sold his pharmacy after his chemical plant failed, and he moved his family to Heidelberg. He bought a plot of land with a shed on it, which he converted into his chemical laboratory. Erlenmeyer began a lifelong tradition of working as a chemical consultant for pharmaceutical and artificial fertilizer companies. In order to teach university students, Erlenmeyer needed to pass the state doctorate exam. This required research under the supervision of a full professor, and Erlenmeyer approached Rudolf Bunsen at the University of Heidelberg. Bunsen took an interest in Erlenmeyer’s proposed postdoctoral research of artificial fertilizers, and he agreed to supervise him.

In 1856, Friedrich Kekulé was back in Germany and was working as an unsalaried lecturer at the University of Heidelberg, which required him to provide his own teaching space. He rented a small lecture hall for ten students above the shop of a flour merchant in Heidelberg, which Erlenmeyer shared once he became assistant professor in May 1857.

Working with Kekulé, Erlenmeyer became interested in theoretical chemistry, particularly in structural chemistry. Erlenmeyer enthusiastically embraced Kekulé’s ideas and developed experiments and articulated theories to support them. When Kekulé left in 1859 to become chair of chemistry for the University of Ghent in Belgium, Erlenmeyer took up editorship of the third volume of the Zeitschrift für Chemie und Pharmacie (Journal for Chemistry and Pharmacy), which Kekulé had founded.

Erlenmeyer’s love for teaching and his work at the cutting edge of organic chemistry earned him a major following, particularly among the many Russian students who came to Heidelberg to study with him. At this time, his research focused on aliphatic compounds—nonaromatic hydrocarbons, which, like polyethylene, would become very important in the plastics industry in the later twentieth century.

In 1859, Erlenmeyer synthesized aminohexoic acid. He investigated the amount of the amino acids of leucine and tyrosine created during the degradation of water-soluble proteins, the albuminoids. In 1860, Erlenmeyer discovered that glycide is related to glycerol (or glycerine), both important in the pharmaceutical industry. One year later, Erlenmeyer proved that the reaction of hydriodic acid and glycerol created an isomer, isopropyl-iodide, instead of regular propyl-iodide. Conducting his experiments led Erlenmeyer to invent a new conical flask in 1861, known since as the Erlenmeyer flask.

In 1862, Erlenmeyer proposed a new definition to describe carbon atom bonding in molecules. Using the example of hydrocarbons, Erlenmeyer defined that there were not only single carbon bonds, as in ethane, but also double bonds as in ethylene (ethene), and triple bonds as in acetylene (ethyne). This theory supported Kekulé’s groundbreaking discovery of the benzene ring structure in 1865.

Erlenmeyer was appointed “extraordinary professor,” or adjunct professor, at Heidelberg in 1863. In 1864, he used unripe grapes to obtain pure glycolic acid, which would become an important ingredient in dermatological products.

Erlenmeyer proved to be a highly abrasive editor, even when he was editing articles submitted by his friends and like-minded colleagues. In 1864 he gave up editorship of the Zeitschrift für Chemie und Pharmacie. The journal had only 150 subscribers, half of whom were Russians fiercely loyal to Erlenmeyer.

In his research in 1865, Erlenmeyer used isopropyl-iodide to discover isobutyric acid. Like many of the organic chemicals Erlenmeyer investigated, it would later be used in the pharmaceutical and food industry. In 1867, Erlenmeyer published the first volume of Lehrbuch der Organischen Chemie (Textbook for organic chemistry, 1867–94). However, his subsequent volumes failed to keep current with newly discovered organic compounds, the number of which had increased from three thousand to fifteen thousand at the time of Erlenmeyer’s last, still incomplete volume.

In 1868, Erlenmeyer was made full professor at the newly founded Munich Polytechnic School; in 1873, he was appointed a coeditor of another chemical journal, Justus Liebig’s Annalen der Chemie (Annals of Chemistry). Liebig himself appointed Erlenmeyer despite some reservations among other chemists about his aggressive style. That year, Erlenmeyer became a member of the Bavarian Academy of Sciences. When the Polytechnic School was upgraded and became the Technical University of Munich in 1877, Erlenmeyer became its first director and served in that position until 1880.

Erlenmeyer defined in 1880 what would become the Erlenmeyer rule. Based on his 1866 description of the chemical formula for naphthalene, Erlenmeyer proved that there can be no stable alcohols in which the characteristic hydroxyl group is attached directly to a double-bonded carbon atom. Instead, these compounds react immediately to form aldehydes or ketones.

The Erlenmeyer rule, also known as keto-enol tautomerism, proved valid with only a few rare exceptions. They occur only where hydrogen atoms of the hydroxyl group have been substituted. Their existence is the reason why Erlenmeyer’s discovery is considered a chemical rule rather than a chemical law.

Erlenmeyer also contributed to the growing knowledge of organic chemical compounds and was the first to synthesize several. He approached his research by first defining the compound’s structural formula then conducting experiments to synthesize it. This approach led to his synthesis of guanidine in 1868 and continued to his final synthesis of tyrosine in 1883.

In 1883, Erlenmeyer was semi-retired from teaching and research, but in 1884, he was elected President of the German Chemical Society. He also invested in a chemical laboratory services company founded by his former student Ludwig Belli in Frankfurt, Germany. Toward the end of his life, Erlenmeyer moved to Aschaffenburg, Germany, where one of his daughters, Maria, was married to the botanist Hermann Dingler. On January 22, 1909, Erlenmeyer died in Aschaffenburg.

Impact

Emil Erlenmeyer aggressively supported fresh advances in chemical structural theory and helped lay the foundation of the contemporary system for writing chemical formulas. Erlenmeyer’s support of the theories of August Kekulé helped them find wide acceptance. Much of Erlenmeyer’s basic research and discoveries concerned organic compounds such as glycerol, glycolic acid, and isobutyric acid, which have many applications in the pharmaceutical, cosmetic, and food industries. One of his lasting contributions to practical chemical work has been the conical Erlenmeyer flask, which is still standard equipment in modern chemical laboratories.

Bibliography

Gordin, Michael D. “Beilstein Unbound: The Pedagogical Unraveling of a Man and his Handbuch.” Pedagogy and the Practice of Science: Historical and Contemporary Perspectives. Ed. David Kaiser. Cambridge, MA: MIT P, 2005. 11–40. Print. Examines Erlenmeyer’s professional relationship with fellow organic chemist Friedrich Beilstein and illustrates how scientists struggled to propagate and find professional acceptance for their ideas in the late nineteenth century.

Perkin, William Henry. “Emil Erlenmeyer, 1825–1909.” Journal of the Chemical Society, Transactions 99 (1911): 1649–51. Print. Contemporary obituary illustrates the international importance Erlenmeyer had gained at the time of his death.

Rocke, Alan J. Image and Reality: Kekulé, Kopp, and the Scientific Imagination. Chicago: U of Chicago P, 2010. Print. Discusses Erlenmeyer’s influence on August Kekulé and the importance of Erlenmeyer’s propagation of Kekulé’s discovery of the benzene ring structure. Describes Erlenmeyer’s contributions to theoretical chemistry.