Friedrich Wohler's Synthesis of Urea: Mechanism & Experiment

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

Friedrich Wohler performed an experiment attempting to form ammonium cyanate, instead he dispelled a commonly held theory and created urea. We will learn about this experiment in this lesson.

An Important Experiment

In chemistry, we often separate the study of organic and inorganic compounds. This is because the types of reactions and how they react tend to be really different between the two fields of chemistry. They are so different, in fact, that prior to the 1820s scientists believed that there was something fundamentally different between organic and inorganic compounds. They believed that the only way that something could become organic was through a 'vital force' which was found in living creatures. This entire belief was completely dispelled when Friedrich Wohler created urea from non-organic compounds.

Wohler was not attempting to dispel the vital force theory during this experiment, he was simply trying to make ammonium cyanate. When he ended up making urea it dispelled the vital force theory. This was an important experiment which led to the start of organic chemistry as we know it today.

Urea is a great fertilizer, and comes from the urine of animals. It contains a carbon, doubled bonded to an oxygen, and bound to two nitrogen atoms, the nitrogen atoms each have two hydrogen atoms.

The Mechanism

The first step in this reaction takes lead cyanate (silver or potassium cyanate can also be used) and reacts it with ammonia and water. Wohler expected the ammonia to form a salt with the cyanate, forming ammonia cyanate. The first step of this reaction occurred just as he expected it, with the salts rearranging to form ammonia cyanate:

Prior to the salt rearrangement, the ammonia and water needs to rearrange hydrogen atoms to form a negative and positive charged particles, this reaction actually occurs twice, with two water molecules and two ammonia molecules
Mechanism step 1

The positive charge on the lead combines with two hydroxide molecules, and the negative charge on the cyanate forms with the ammonium to form ammonium cyanate
Mechanism step 2

But, the reaction doesn't stop there, instead the ammonium decomposes, forming ammonia and cyanic acid:

The ammonium cyanate quickly decomposes, with ammonia and cyanic acid forming
Mechanism step 3

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