Chromotropic acid reaction
The chromotropic acid reaction can detect free formaldehyde or formaldehyde that can be split off . Formaldehyde condenses in the presence of sulfuric acid with two molecules of chromotropic acid in the ortho position to the phenolic OH group. In the second step acts H 2 SO 4 as the oxidant and it forms a red, resonance-stabilized carbenium - cation .
Since some pharmacologically relevant molecules, such as metamizole , hydrochlorothiazide , cimetidine and etacrynic acid , can split off formaldehyde , these can also be identified by the chromotropic acid reaction.
The Marquis reaction is similar to the chromotropic acid reaction, only that no phenolic hydroxyl groups are condensed in this process.
application
In food analysis, the reaction is used to determine the methanol content of alcoholic beverages. Here, a distillate is again distilled over silver nitrate and potassium hydroxide to remove terpenes and aldehydes . The methanol contained is oxidized to formaldehyde with potassium permanganate . Excess potassium permanganate is removed using oxalic acid and the formaldehyde is reacted with chromotropic acid to form a red-violet reaction product, which can be measured photometrically .
Individual evidence
- ↑ Reinhard Mattisek, Gabriele Steiner, Markus Fischer: Food Analysis . 4th edition. Springer, Berlin 2010, ISBN 978-3-540-92205-6 , pp. 178 .