Download General properties of urea : It is water

General properties of urea :
It is water-soluble crystalline compound acting only as a weak base giving
sparingly soluble salts with HNO3 and ethanedioic acid (COOH)2 .
In its chemical properties, urea gives the typical reaction expected from an
amide (twice over)
Its properties are essentially those of amides .
Synthesis of urea :
Urea or carbamide, H2NCONH2, being an important industrial amide .
Classically it was the first naturally occurring “organic” compound to be
prepared from inorganic compounds traversing for the first time the great
divide that appeared to classify all substances known at the time.
Evaporation of an aqueous solution of ammonium cyanate to dryness was
observed to give the formation of the organic urea.
Wöhler's Synthesis :
Although this is still a method that can be used for its production, it can also be
obtained from reaction of carbonyl chloride (COCl2, “phosgene”) with ammonia
and industrially from direct combination of ammonia with carbon dioxide :
Its commercial importance lies in the fact that it finds use as a fertilizer and is
used in the formation of plastics and adhesives.
Reactions of urea :
(1) Basic nature (Salt formation):
Despite having two NH2 groups urea behaves as a monobasic entity precipitating
out urea (carbamide) nitrate and urea ethanedioate with the respective acids :
Urea is a stronger base than ordinary amide. It is because of the resonance
stabilization of cation, the negatively charged oxygen atom is capable of
coordination with one proton.
** Aqueous solvent of urea is neutral.
(2) Hydrolysis
An enzyme, urease, present in soyabean and soil also brings hydrolysis .
(3) Action of heat
Urea is identified by the test known as biuret test. The biuret residue is dissolved
in water and made alkaline with a few drops of NaOH. When a part of copper
sulphate solution is added to the alkaline solution of biuret, a violet colouration is
produced.
when heated rapidly at 170o C, polymerisation takes place:
(4) Reaction with nitrous acid
(5) Reaction with ethanol
(6) Reaction with chlorine water
(7) Dehydration
(8) Reaction with fuming sulphuric acid
(9) Hoffmann degradation
with urea as the reagent gives N2 and water (via the formation of hydrazine H2NNH2, which is immediately oxidized in the oxidizing medium to nitrogen and
water)
(10) Formation of cyclic ureides
(11) Reaction with formaldehyde
(12) Reaction with acid chlorides – formation of ureides
Acid chlorides give compounds known as ureides in these reactions :