On the mechanism of the test for thiophene via alloxan from uric acid
Department of Organic Chemistry, Faculty of Chemistry, National Autonomous, University of Mexico, Mexico City (CDMX), Mexico.
Research Article
International Journal of Scholarly Research in Chemistry and Pharmacy, 2026, 06(01), 001-004.
Article DOI: 10.56781/ijsrcp.2026.6.1.0011
Publication history:
Received on 26 November 2025; revised on 18 January 2026; accepted on 21 January 2026
Abstract:
The formation of alloxan from uric acid using bromine water has been cleared. The hydrion promoted hydration of the 1,4-system in uric acid, facilitates reaction with a bromonium ion. (addition of hypobromous acid to the double bond). There is assisted bromide elimination by the amino group at ipso carbon, and the resulting iminium ion is neutralised by water. There is a pseudo hemiaminal at C-4. The polarization of the 8,9-lactam (imidazolone ring) enhances ring opening and carbonyl formation at C-4. The second pseudo hemiaminal reacts in a similar manner as the first one. This step can also be considered as a hydrion promoted concerted mechanism involving five electron shifts. This way alloxan and urea are formed.
The mechanism of the interaction of strong nitric acid with uric acid is somewhat similar to the preceding one. A nitronium ion replaces the bromonium ion and it is protonated at the oxygen, producing a synchronous mechanism: nitrous acid is eliminated and an epoxide is formed by participation of the hydroxyl at C-4. Acid hydrolysis of the oxirane yields a vicinal diol which is precursor to alloxan. This compound had been considered also as such on theoretical grounds, but without mechanistic approach. For the ring opening of these pseudo hemiaminals to alloxan and urea, see above.
Keywords:
Alloxan; Bromonium ion; Epoxide; Hypobromous acid; Nitrous acid; Pseudo hemiaminal; Thiophene; Uric acid
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