Urea. 
It is the normal terminate production of the human metabolism of nitrogen-containing foods (proteins). An adult somebody excretes almost iii grams of urea inwards urine inwards 24 hours.
Preparation of urea.
(1) Urea is made commercially past times the reaction of liquid ammonia together with carbon dioxide at 150-200°C together with almost 200 atmospheres pressure. Ammonium carbamate outset formed decomposes to shape urea.
(2) It tin hold upward prepared inwards the laboratory past times the activity of ammonia on carbonyl chloride.
(3) Wohler was the outset to synthesise urea inwards 1828 past times evaporating a solution of ammonium
cyanate. This method is of historical involvement only.
Properties of Urea.
Physical Properties.
Urea is a colorless, crystalline solid, mp 135°C. It is real soluble inwards H2O giving neutral solutions. It is less soluble inwards alcohol together with insoluble inwards ether, chloroform, together with benzene.
Chemical Properties.
Urea contains an amide grouping attached to an amino grouping together with gives reactions of both these functions. It may hold upward idea of equally having 2 amide groups alongside a mutual - CO- function.
Thus it behaves equally a diamide inwards most reactions.
Some of the reactions of urea are listed below.
(1) Salt Formation. Urea is a feeble mono acid-base (Kb= 1.5 x 10-14). Thus it reacts alongside concentrated nitric acid together with oxalic acid to shape salts.
The inwards a higher house salts comprise the oxygen-protonated cation, [HOC(NH2)2]+, which is resonance-stabilized.
(2) Hydrolysis. Like other amides, urea is hydrolysed nether both acidic or element of group I weather condition to
give ammonia together with carbon dioxide.
An enzyme called urease, acquaint inwards reason together with soya edible bean hydrolyzes urea to ammonium carbonate. This reaction is used for the quantitative estimation of urea.
(3) Reaction with HNO2. Urea, similar other amides, reacts alongside nitrous acid when nitrogen is evolved, leaving the carbonic acid behind. This is plough decomposes to carbon dioxide together with water.
(4) Reaction alongside Alkaline Hypohalites. Urea is oidised to nitrogen when it is heated alongside excess of element of group I hypochlorite or hypobromite (Br2+NaOH).
This reaction is too used to gauge urea past times mensuration the book of nitrogen envolved from a exam sample.
(5) Acetylation. Urea reacts alongside acylating agents e.g., acetyl chloride to shape N-acyl ureas or 'ureides'.
(6) Action of Heat. (a) On heating at 132°C, urea melts.Then the liquid on gentle heating at a slightly higher temperature decomposes, liberating ammonia together with leaving behind a solid chemical compound known equally Biuret.
Urea tin hold upward identified past times the Biuret Test. The meat is heated, a picayune inwards a higher house its melting point, inwards a dry out test-tube. Biuret is formed alongside the development of ammonia. When the development of ammonia begins to slacken, the balance is dissolved inwards H2O together with treated alongside a few drops of sodium hydroxide solution. To the solution is together with thence added a driblet of copper sulfate solution, when a purplish coloration is produced.
(b) When heated rapidly good inwards a higher house its melting point, urea is decomposed to isocyanic acid which trimerizes to cyanuric acid.
(7) Reaction alongside Hydrazine. Urea reacts alongside hydrazine at 100°C to shape semicarbazide.
Urea uses.
Urea is used.
- Chiefly equally fertilizer.
- As brute feed.
- For making barbiturates.
- for the industry of urea-formaldehyde resins.
- As a stabilizer for explosives (nitrocellulose).
Urea Structure.
(1) By elemental analysis together with molecular weight determination, its molecular formula has been constitute to be CON2H4.
(2) Diamide formula. Its formation from carbonyl chloride together with ammonia indicates that urea has a symmetrical diamide formula.
The diamide formula is confirmed because of urea : (a) upon hydrolysis forms 2 molecules of
ammonia (b) alongside nitrous acid it liberates 2 molecules of N2.
(3) Facts against the Diamide formula. It fails to explicate :
(a) Urea forms salts alongside acids similar HCl or HNO3 land elementary amides gain not.
(b) It forms mono-salts entirely e.g., CO(NH2)2. HCl, showing that the molecule is unsymmetrical.
(4) Tautomeric Structure Proposed. To explicate the facts listed inwards (3), Chattaway proposed that urea
exists equally a tautomeric mixture.
It is the basic imide shape which forms a tabular array salt alongside a monobasic acid at the imide grouping (= NH.HCI).
(5) Resonance Structures. Urea is to a greater extent than stable than could hold upward expected of whatever carbonic acid derivative. In damage of the modern resonance theory, this stability of urea is attributed to its beingness equally a resonance hybrid.
(6) Formation of Mono-Salts Explained. The oxygen atom of the carbonyl grouping of urea is capable of coordinating alongside 1 proton (H+). The resulting cation is resonance stabilized past times considerable delocalization of the cationic charge.
Thus urea tin shape mono-salt alongside an acid similar HCl.
X-ray diffraction studies convey confirmed that inwards the crystalline tabular array salt of urea alongside HCl is acquaint an oxonium type cation equally shown above.
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