Vanadic acid as demethylation catalyst in Mandelin’s test for brucine
Organic Chemistry Department, Faculty of Chemistry, National Autonomous University of Mexico, Mexico City (CDMX), Mexico.
* Corresponding Author
ORCID Details
F. Sánchez-Viesca: https://orcid.org/0009-0003-9528-0104
Luz Clarita: https://orcid.org/0009-0008-6362-3826
Research Article
International Journal of Scholarly Research in Chemistry and Pharmacy, 2026, 07(01), 001–004.
Article DOI: 10.56781/ijsrcp.2026.7.1.0018
Publication history:
Received on 03 September 2026; revised on 10 October 2026; accepted on 12 October 2026
Abstract:
The Mandelin test for brucine (dimethoxy strychnine) and for strychnine are very different, giving blood-red and blue-violet colour, respectively. These results indicate that in brucine the methoxy groups are reacting. However, these ethers are commonly very stable, requiring strong experimental conditions for demethylation. Since brucine reacts in different form than strychnine, we can conclude that the methoxy groups in brucine intervene in some manner. Vanadic acid, coming from ammonium vanadate in acidic medium, can act as demethylation agent and catalyst. The reactive species is protonated vanadic acid. A coordination compound is formed with concomitant elimination of water. The oxonium intermediate can separate a methyl group with assistance of a bisulphate anion and formation of a vanadate. Acidolysis of this mixed ester forms a phenolic group.
The second methoxyl in brucine also forms a vanadate, but protonation of this group gives rise to a concerted reaction mechanism. A redox reaction form vanadous acid and a red o-benzoquinone.
Keywords:
Acidolysis; Brucine; Coordination Compound; Demethylation Catalyst; Mandelin Test; Redox Reaction
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