The History of Urea and Its Use in the Modern Fertilizer Industry

Iris Yan Wong

Deerfield Academy, Massachusetts, 01342-0087, U.S.A.

Keywords:

Synthetic Urea, Isomerization Reaction, Haber-Bosch Process, Industrial Process.

Abstract: From the common name of the organic compound “urea”, it can be inferred that urea is a major component

of urine. Urea naturally occurs in most mammals and is crucial for removing toxic waste products from the

human body. This work investigates the history of urea, including the discovery of the “urea cycle” in humans.

Moreover, urea was the first organic compound to be synthesized from inorganic compounds, bringing about

a new definition of organic chemistry. This work examines the specific mechanism behind Fredrich Wohler’s

synthesis of urea from inorganic compounds. Furthermore, urea is now synthesized on a large scale for

nitrogen-based crop fertilizers, and such modern processes have great implications on the environment.

INTRODUCTION

Urea is composed of a carbamide--- a carbonyl group

attached to two amide groups (see Figure 1). Its

molecular formula is CH

O, and its exact mass is

60.06g. Due to the carbonyl group in the compound,

urea is polar. Furthermore, it is highly soluble in

water and has a neutral charge overall (National

Center for Biotechnology Information, 2021).

Figure 1: Urea Molecular Diagram.

HISTORY OF UREA

DISCOVERIES

The first known description of urea is by Belgian

chemist Jean Batiste von Helmont in 1664, who

realised that there was a natural salt in urine (Raine,

1973). In 1732, Dutch chemist Hermann Boerhaave

published his chemistry textbook Ementa Chemiae,

which included the purification method of urea from

urine (Raine, 1973). Almost 50 years after

Boerhaave, French chemist Hilaire Rouelle found the

same method as his (Eknoyan, 2017). Despite

Boerhaave’s earlier work, Rouelle is frequently

attributed for the discovery and isolation of urea from

urine (Raine, 1973).

Wong, I.

The History of Urea and Its Use in the Modern Fertilizer Industry.

DOI: 10.5220/0012032100003633

In Proceedings of the 4th International Conference on Biotechnology and Biomedicine (ICBB 2022), pages 435-439

ISBN: 978-989-758-637-8

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

435

2.1

Wöhler’s Synthesis of Urea from

Inorganic Compounds

Nearly 100 years after Boerhaave’s findings were

published, German chemist Fredrich Wöhler made

the groundbreaking achievement of synthesizing urea

in a lab. Previously, scientists had believed that

naturally occurring organic compounds only

originated from living organisms from other organic

compounds (Rabinovich, 2007). This idea, known as

the “vital force theory”, expresses that a hypothetical

“vital force” in living organisms was necessary for

the formation of an organic compound (Friedmann,

1997). Upon this discovery, Wöhler wrote to his

mentor, “I can no longer, as it were, hold back my

chemical urine; and I have to let out that I can make

urea without needing a kidney, whether of man or

dog.” (Friedmann, 1997). The popularity of the “vital

force theory” declined as Wöhler’s synthesis put an

emphasis on chemical structures in compounds. Since

Wöhler’s discovery almost two centuries ago,

thorough studies continue to be conducted on

structural chemistry to further understand the

intricacy of organic compounds (Heitmann, 1989).

Wöhler’s original intention had not been to create

synthetic urea. Rather, this unanticipated discovery

came when he combined lead cyanate with ammonia

and water to form ammonium cyanate and lead

hydroxide.

Pb(OCN)

+ 2NH

+ 2H

O → Pb(OH)

2NH

(OCN)

Wöhler’s original experiment (Carr, 2018)

When Wöhler heated ammonium cyanate, he

realised that its properties aligned entirely with the

properties of urea. This, as he later found, was due to

an isomerization that had taken place after the

ammonium cyanate was formed. As Figure 2 shows,

the cyanate was the nucleophile that attacked the

hydrogen attached to ammonium. This resulted in

ammonium cyanate decomposing into ammonia and

cyanic acid and forming a reactive carbonyl. From

there, the ammonia attacked the carbonyl, leading to

the final planar urea molecule after proton transfers.

Figure 2: Reversible isomerization reaction from ammonium cyanate into urea.

2.2 Discovery of the Human Urea Cycle

This synthesis opened up a new possibility for

organic chemistry: the mass production of organic

materials. Scientists worked to find ways to

synthesize organic compounds from inorganic ones.

Amongst these included new methods of synthesizing

urea from other compounds. Further research was

also conducted on naturally occurring urea.

Figure 3: Overview of Urea Cycle (Ah Mew, 2003).

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In 1932, Hans Krebs and Kurt Heinselet

discovered the natural “urea cycle” in the human

body (see Figure 3). It was the first metabolic cycle to

be proposed, and it details the formation and

excretion of urea. When toxic ammonia is naturally

formed in digestive processes, the body relies on the

cycle to remove it safely. Specifically, ammonia is

converted into urea in the liver’s mitochondria and

cytoplasm, with the help of enzyme catalysts like

ornithine transcarbamylase and argininosuccinate

synthetase (Barmore, 2021).

2NH

+ CO

+ 3ATP → H

N(CO)NH

+ H

O +

3ADP

Overall reaction from ammonia to urea

(Cheriyedath, 2019)

3 MODERN PROCESSES OF

SYNTHESIZING UREA AND

ITS IMPLICATIONS

On the other hand, synthetic urea is found in various

products, such as instant cold packs, skin care

products and resins, but it is most used in nitrogen-

based fertilizers. This is because urea has the highest

nitrogen content amongst solid nitrogen fertilizers

(Bradley, 2018). In fact, due to its properties, more

than 90% of urea production is used for agricultural

purposes (American Chemical Society, 2021).

3.1 Employment of Haber-Bosch

Process to Synthesize Urea from

Ammonia

To facilitate global production of urea, a specific

process known as the Haber-Bosch process is

employed. As seen in Figure 4, hydrogen is first

formed by reacting methane or other natural gases

with steam. Under high temperatures, the hydrogen is

synthesized with gaseous nitrogen to make ammonia.

Ammonia is subsequently combined with carbon

dioxide to form ammonium carbamate, which then

decomposes into urea and water (Copplestone, 2017).

Though this synthesis equation was always known,

German chemists Fritz Haber and Carl Bosch found

ideal conditions for it to happen with much higher

yield than before: high temperatures, high pressures

and typically an iron-based catalyst. The process also

removes substances such as carbon monoxide, water,

and other carbon oxides during synthesis

(Copplestone, 2017). This developed industrial

process is key to the global output of 220 million tons

of urea per year (American Chemical Society, 2021).

Figure 4: Overview of the Haber-Basch process (Boerner, 2019).

+ H

O → CO

+ H

Hydrogen synthesis in industrial processes

(Copplestone, 2017)

+ 3H

⇌ 2NH

Ammonia synthesis in industrial processes

(Copplestone, 2017)

2NH

+ CO

⇌ NH

COONH

(ammonium

carbamate)

COONH

⇌ H

O + NH

CONH

(urea)

Urea synthesis in industrial processes

(Copplestone, 2017)

3.2 Existing Issues with Mass

Production of Synthetic Urea and a

Possible New Method

Such a wide-scale level of production comes at a

global cost, though. The multitude of problems begins

from the compound itself and extends all the way to

its industrial process. For instance, Christer Aakeröy

from Kansas State University explains that urea is

highly soluble in water, offering an unfavorable

property for storage and transport (Sandhu, 2018).

Farmers therefore tend to overuse urea fertilizer to

compensate for potential losses, leading to

The History of Urea and Its Use in the Modern Fertilizer Industry

437

inefficiencies and increased nitrogen concentration in

the air (Bradley, 2018). The most pressing issue,

however, is the copious amounts of energy needed to

produce urea. 80% of ammonia produced globally is

used specifically for urea synthesis (Chen, 2020), yet

ammonia production through the Haber-Bosch

process accounts for 1-2% of worldwide energy

consumption and 1.44% of CO

emissions (Kyriakou,

2020). This makes it the industrial process that emits

the most CO

worldwide (American Chemical

Society, 2021).

The harsh impacts of the process on the

environment have propelled scientists to investigate

more energy-efficient methods of urea synthesis.

Figure 5: Electrocatalysis to synthesize urea (Chen, 2020).

In 2018, chemical engineer Shaungyin Wang and

his colleagues from Hunan University in Changsha,

China used an electrochemical reaction to develop a

method of urea synthesis. Its synthetic route, as

shown in Figure 5, directly combines nitrogen, CO

and water to form urea at ambient temperature and

pressure (American Chemical Society, 2021). While

this process is still in its preliminary stage, it offers a

possibility of producing urea fertilizers with lower

energy consumption rates and higher yields.

4 CONCLUSION

The simple organic compound urea has had an

unbelievable impact on the scientific community. The

urea cycle was also the first metabolic cycle

discovered by Krebs and Henseleit, which was even

earlier than their renowned Krebs (tricarboxylic)

cycle. As French chemist Louis Pasteur once said,

“Chance favors only the prepared mind” (Gibbons,

2013). In such a vast field of organic chemistry,

serendipitous discoveries happen when one is ready

to recognize. Wöhler was able to identify the

isomerization of ammonia to urea because he was

familiar with the compound from studying medicine

before (Shampo, 1985). Without Wöhler’s synthesis,

the idea of producing organic compounds from

inorganic ones would not even exist.

The transformative understanding of urea

synthesis now seeps into people’s everyday lives,

most prominently in fertilizers that pillar the

agricultural system worldwide. What may the next

step be? Perhaps a more resource and energy efficient

form of synthesis may be witnessed and fully

developed in the near future.

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