Urea in the history of organic chemistry

Urea is one of the most important chemicals in use today – as a fertiliser and industrial raw material. It is also the chemical that gave birth to the science of organic chemistry. Let’s see how.

Until the early 19th century, people – including many scientists – believed in a theory called vitalism. Those who believed in this theory held that life was not subject to the laws of physics and chemistry. They believed that there was an unknown, even divine principle, that governed living organisms, called the ‘life spark’.

Because of this belief, it was thought that chemicals found in plant and animal bodies – like proteins and carbohydrates – were completely different from other chemicals like salts, acids and gases. Therefore, people thought that ‘organic’ chemicals (because they came from organs) could not be made artificially, but had to be extracted from living animals. This theory also stopped people from using inorganic chemicals to treat diseases.

Organic chemistry
The Wohler synthesis is the conversion of ammonium cyanate into urea. This chemical reaction was discovered in 1828 by Friedrich Wohler in an attempt to synthesize ammonium cyanate. It is considered the starting point of modern organic chemistry.

There was a huge amount of resistance to the idea that vitalism wasn’t correct. Indeed Wohler himself did not like it. Influential scientists like Justus von Liebig and Louis Pasteur weren’t convinced either. Many organic compounds still could not be made in the lab at all, from inorganic ones. (Even today, some very complicated molecules like insulin cannot be made in the lab without using living organisms.) The tide changed only in 1845, when Hermann Kolbe showed that carbon disulfide could be converted to acetic acid, the main ingredient of vinegar.

But meanwhile a whole lot of scientists saw the practical uses of Wohler’s discovery. For many organic chemicals like urea (till then obtained from kidneys), citric acid (obtained from lemons) and benzene (obtained from gum benzoin) were industrially very useful. If they could be made from inorganic chemicals, then they could be made cheaper and on a large scale.

Soon a huge industry had sprung up, with synthetic dyes (see the articles on Perkin and indigo) and drugs (see the article on salvarsan) being made on a large scale. Today, organic chemistry makes more than a million chemicals every year!