Liebig, Justus (1803–1873)
German organic chemist who extended chemical research into other scientific fields, such as agricultural chemistry and biochemistry. He introduced the theory of compound radicals and discovered chloroform and chloral, and demonstrated the use of fertilizers.
Isomers
In the 1820s, Liebig began a long collaboration with Friedrich
Wöhler. Liebig investigated
fulminates, at the same time that Wöhler was independently working with cyanates. In 1826, Liebig prepared silver fulminate (modern formula AgCNO) and Wöhler made silver cyanate (AgNCO). When they reported their results they assigned the same formula to the two different compounds, which stimulated Jöns Berzelius' work that led to the concept of
isomers.
Compound radicals
Liebig and Wöhler became friends and continued their researches together. They introduced the idea of
compound radicals in organic chemistry– the idea that a family of chemicals can be made from the same molecular unit, or radical. In 1832, from a study of oil of bitter almonds (benzaldehyde; phenylmethanal), they discovered the benzoyl radical (C
6H
5CO–). They showed that benzaldehyde can be converted to benzoic acid and made a number of other related compounds, such as benzyl alcohol and benzoyl chloride. The benzene ring had, in fact, conferred unusual stability to the benzoyl grouping, allowing it to persist in the various reactions. Although they found no other radicals that supported their theory as convincingly, they introduced a degree of systematization into the confused field of organic chemistry. Liebig devised many new methods of organic analysis, specifically ways of determining hydrogen, carbon and halogen content in organic compounds.
Biochemistry
From 1838 Liebig's work centred on what we would now call biochemistry. He studied fermentation, but would not acknowledge that yeast is a living substance, a view to which Berzelius also subscribed. Their view brought them both into contention with Louis Pasteur. Liebig analysed various body fluids, and calculated the calorific values of foods, emphasizing the role of fats as a source of dietary energy and developing a beef extract – marketed as Liebig extract.
Agricultural chemistry
Liebig also applied his chemical knowledge to agriculture. He demonstrated that plants absorb minerals, water, and nitrogen from the soil, although he incorrectly thought that the nitrogen came from ammonia in rainwater. He demonstrated that the carbon used by plants does not come from humus in the soil, postulating instead that the carbon comes from carbon dioxide in the air. He was also correct in thinking that adding minerals and nitrates to the soil would improve plant growth and advocated the use of artificial fertilizers in agriculture.
| Liebig was born in Darmstadt, Hesse, and studied at Bonn (where he was arrested for his liberalist political activity), Erlangen, and Paris, where Alexander von Humboldt (1769–1859) obtained a position for him in Joseph Gay-Lussac's laboratory at the Arsenal. At the age of 21, he became professor at Giessen and stayed there for 27 years (1825–52), building up a prestigious teaching laboratory. In 1840 he founded the journal Annalen der Chemie; he was made a baron in 1845. His students, assistants and co-workers included such famous chemists as Edward Frankland, Joseph Gay-Lussac, August von Hofmann, Friedrich Kekulé, Friedrich Wöhler, and Charles Wurtz. |
