Synthetic urea refers to the urea that is produced artificially as distinguished from biosynthetic or natural urea.
It is an industrial product that has found many applications but primarily as nitrogen fertilizer.
Also described as synthetic or chemical fertilizer, it is an organic compound that is manufactured following an industrial process independent of living organisms.
Natural and manufactured urea have the same chemical formula CO(NH2)2.
However, natural urea is produced by living organisms, specifically, humans, other mammals, and other ureotelic organisms (excretes most nitrogen as urea; Mathews and Van Holde 1990) and subsequently excreted mostly in the urine.
Pure urea was isolated from urine many years ago.
The Discovery of Urea
The discovery of natural urea preceded that of synthetic urea but the who and when seems not clearly established.
The French chemist Hilaire Marin Rouelle (1718-1779) is commonly cited as the one who discovered urea.
Accordingly, he isolated those colorless, odorless, crystalline substances in 1773 by boiling urine (Myers 2007).
In 1797, French chemists Antoine François de Fourcroy (1755-1809) and Louis Nicolas Vauquelin (1763-1829) named the substance “urea” (Richet 1988).
However, Dutch physician-chemist Hermann Boerhaave (1668–1738) seems to have described urea much earlier.
According to Rosenfeld (2003), even before 1727 Boerhaave already obtained a crystalline residue from urine by heating, filtering, washing, and evaporating.
He called it “the native salt of urine.”
He noted that it differed from the sea salt (sodium chloride) which is also present in urine.
Further, according to the same author, Rouelle’s extract was impure, and it was British physician-chemist William Prout (1785-1850) who, in 1817, isolated pure urea from urine.
The Beginning of Synthetic Urea
In 1828, German chemist Friedrich Wöhler (1800–1882) produced synthetic urea in the laboratory from inorganic compounds.
He first heated a solution consisting of a mixture of silver cyanate (AgOCN) and ammonium chloride (NH4Cl).
As shown below, this formed ammonium cyanate is also an inorganic compound (does not originate from living organisms).
AgOCN + NH4Cl —–> NH4OCN (ammonium cyanate) + AgCl
But when ammonium cyanate was further heated, it produced clear, colorless, crystalline urea which has the same characteristics as urinary urea.
It turned out that ammonium cyanate and urea have the same elemental composition (CH4N2O) and that heating of ammonium cyanate (NH4OCN) caused the atoms to rearrange resulting to its transformation into urea (H2N.CO.NH2).
Wöhler’s teacher, Jöns Jacob Berzelius (1779-1848) who coined the term organic chemistry in 1807 for the study of compounds naturally produced by living organisms, likewise invented the term isomerism to describe the relation of distinct materials having identical elemental composition.
Apparently, Wohler also discovered that an inorganic compound (ammonium cyanate) can be an isomer of an organic compound (urea).
It was the first time that a substance of biological origin was synthesized artificially from inorganic compounds.
It eventually led to a drastic change in the definition of organic compounds and to the birth of synthetic organic chemistry.
Organic chemistry is now defined as the study of carbon compounds or carbon-containing compounds (Mark and the Editors of Time-Life Books 1966; Carey 1992; Myers 2007).
The Commercial Synthesis of Urea
The industrial synthesis of urea was conceived in 1870 upon the discovery by Bassarov that it can be produced by heating ammonium carbamate at a high temperature of 130-140°C in sealed glass tubes (Bassarov, cited by Clark et al. 1933).
Consequently, the company I.G. Farbenindustrie in Germany first engaged in commercialized production of synthetic urea from ammonium carbamate in 1920 (Tandon 2012).
On September 19, 1922, the United States Patent Office approved the patent application of Carl Bosch and Wilhelm Meiser for an improved method of producing synthetic urea.
The method involved the forced mixing of NH3 and CO2.
It also included the use of a container that was capable of withstanding high pressure and heat.
The same applies to the patent that was already filed earlier: 1916 in Germany and 1917 in Austria and Hungary (Bosch and Meiser 1922).
Subsequently, the Bosch-Meiser process (also called BASF process, for Badische Anilin & Soda Fabrik of Germany) was applied in the large-scale production of synthetic urea starting 1922.
However, it was made possible only with the commercialized production of synthetic ammonia, a raw material, following a process that was previously discovered by Fritz Haber (1868-1934) and Carl Bosch (1874-1940) in 1910 (Tandon 2012).
Commercial production of synthetic urea now involves the reaction of ammonia and carbon dioxide under high pressure (approximately 150 atm) and at high temperatures (approximately 180°C).
The product, ammonium carbamate (CO2NH4NH2), is then dehydrated to produce urea (Carey 1992; Myers 2007). A summary reaction is shown below:
2NH3 + CO2 —–> CO2NH4NH2 —–> CO(NH2)2 + H2O
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