Structure Determination of Uric Acid
Structure of Uric Acid can be determined by the following facts, evidences and its synthesis-
1. Elemental analysis and molecular weight determination shows that the molecular formula of uric acid is C5H4N4O3.
2. Mild oxidation of uric acid with nitric acid gives alloxan and urea.
Since alloxan C4H2N2O4 does not have any free amino group or carboxyl group and on hydrolysis gives mesoxalic acid and urea. So, it must be mesoxalyl urea whic is confirmed by its synthesis involving the direct combination of urea and mesoxalic acid.
The formation of alloxan rom uric acid confirms the uric acid has a pyrimidine nucleus.
3. Vigorous oxidation of uric acid with neutral or alkaline KMnO4 gives allantoin and CO2.
Structure of Allantoin
i. When hydrolysis with alkali, allantoin forms two molecules of urea and one molecule of glyoxalic acid. The formation of these products suggest that the allantoin is the diureide of glyoxalic acid.
ii. On oxidation with HNO3, allantoin forms urea and parabanic acid in equimolecular proportions.
iii. When reduced with HI at 100° C, allantoin produces urea and hydantoin.
From the above facts, the structure of allantoin may be -
and is confirmed by its synthesis from urea and glyoxalic acid on heating-
4. On exhaustive methylation, uric acid gives tetramethyluric acid in which all the four hydrogen atoms of uric acid have been replaced by methyl groups. On hydrolysis with dil. HCl, tetramethyluric acid loses all the four nitrogen atoms as methyl amine. This indicates that in tetramethyluric acid, all the methyl groups are directely attached to nitrogen atoms. So, it indicte that all the four hydrogen atoms of uric acid are attached to nitrogen atoms and shows that uric acid has four imino groups (-NH-)
From the above mentioned facts and evidences, Two structures of uric acid was proposed. One by Medicus and other by Fitting but the Medicus structure was accepted.
This structure of uric acid was confirmed by its synthesis.
1. Elemental analysis and molecular weight determination shows that the molecular formula of uric acid is C5H4N4O3.
2. Mild oxidation of uric acid with nitric acid gives alloxan and urea.
Since alloxan C4H2N2O4 does not have any free amino group or carboxyl group and on hydrolysis gives mesoxalic acid and urea. So, it must be mesoxalyl urea whic is confirmed by its synthesis involving the direct combination of urea and mesoxalic acid.
The formation of alloxan rom uric acid confirms the uric acid has a pyrimidine nucleus.
3. Vigorous oxidation of uric acid with neutral or alkaline KMnO4 gives allantoin and CO2.
Structure of Allantoin
i. When hydrolysis with alkali, allantoin forms two molecules of urea and one molecule of glyoxalic acid. The formation of these products suggest that the allantoin is the diureide of glyoxalic acid.
ii. On oxidation with HNO3, allantoin forms urea and parabanic acid in equimolecular proportions.
iii. When reduced with HI at 100° C, allantoin produces urea and hydantoin.
From the above facts, the structure of allantoin may be -
and is confirmed by its synthesis from urea and glyoxalic acid on heating-
4. On exhaustive methylation, uric acid gives tetramethyluric acid in which all the four hydrogen atoms of uric acid have been replaced by methyl groups. On hydrolysis with dil. HCl, tetramethyluric acid loses all the four nitrogen atoms as methyl amine. This indicates that in tetramethyluric acid, all the methyl groups are directely attached to nitrogen atoms. So, it indicte that all the four hydrogen atoms of uric acid are attached to nitrogen atoms and shows that uric acid has four imino groups (-NH-)
From the above mentioned facts and evidences, Two structures of uric acid was proposed. One by Medicus and other by Fitting but the Medicus structure was accepted.
