It would be good to have some insights on how this reagent reacts with nitrogenous compounds. Also what kind of nitrogen groups will react with this reagent? Because not all the nitrogen containing compounds react with this reagent.
Hello,
Dragendorff reagent consists of (Nitrooxy)oxobismuthine (BiNO4xH2O), tartaric acid and KI and it is used for the DC detection of alkaloids and - more general - tertiary amines (and also some secundary ones). The Tertiary amine is protonated due to the tartaric acid and an ion pair is formed that consists of [BiI4]- and [HNR3]+. In dependence of the nature of the tert. amine (or alkaloid) this ion pair has a yellow...orange...red...brown collor. Secondary amines will create less colored spots.
Kind regards
Simon
Hello,
Dragendorff reagent consists of (Nitrooxy)oxobismuthine (BiNO4xH2O), tartaric acid and KI and it is used for the DC detection of alkaloids and - more general - tertiary amines (and also some secundary ones). The Tertiary amine is protonated due to the tartaric acid and an ion pair is formed that consists of [BiI4]- and [HNR3]+. In dependence of the nature of the tert. amine (or alkaloid) this ion pair has a yellow...orange...red...brown collor. Secondary amines will create less colored spots.
Kind regards
Simon
Hello
Dragendroff reagent is used for alkaloid test. It is used in plant extract for detecting alkaloid by following way------
Dragendroff’s test:
2 ml solution of the extract and 0.2 ml of dilute hydrochloric acid were taken in a test tube. Then 1 ml of Dragendroff’s reagent was added. Orange brown precipitate was formed and that was indicated as the presence of alkaloids
Alkaloid detecting reagents are solutions of the salts of heavy metals such as Dragendorff"s (potassium iodide-bismuth nitrate). The mechanism of action is proposed to occur via coupling of the reagent's heavy metal atom in the reagent with the nitrogen in the alkaloid to form ion pairs. The ion pairs form an insoluble precipitate. Using Dragendorff's reagent , a reaction occurs between BiI4- and the alkaloid -------> (alkaolid+)n(BiI4-)n. In the ppt complex, BiI4 - could determine by flam atomic absorption spectrometry. The ppt color could vary from orange-red, yellow-orange, red-black, pink-purple depending on the species or genus. [1]
Studies on false-positive alkaloid tests using Dragendroff reagent were found to result from reactions with nitrogenous (e.g. peptides) or non-nitrogenous plant constituents. All non-nitrogenous compounds that were found to give strong positive reaction with the reagent were compounds containing oxygen.[2]
[1] Coe, F.G., Anderson, G. J., J. Ethanopharm 53, 29 (1996); http://www.bio-nica.info/biblioteca/Coe1996MedicinalPlantsGarifuna.pdf
[2] Habib, A. A. M., J. Pharm. Sci., 69, 37 (1980)
Good luck
An alkaloid detecting reagent, bismuth (III) tetraiodide (Dragendorff's reagent) is a solution of the salts of heavy metals. It normally detects tertiary amines and certain secondary amines. The heavy metal ions present in reagent combine with the nitrogen present in the alkaloid normally as tertiary amine or in certain cases as secondary amines to form ion pair that forms an insoluble yellow/reddish-yellow/brick-red precipitate of the complex. Secondary amines however produce less coloured ppt. The reagent also gives false-positive alkaloid tests with protein owing to nitrogen of peptide linkage.
Primarily works well for alkaloids that have some form of basicity, as the positive result appears to be the formation of an ion pair.
Alkaloids which are not appreciably basic will most likely not stain positively.
In terms of nitrogenous functional groups, pyrroles, nitriles, nitro groups, and amides will be less likely to give a positive result.
Reaction occurs with amino-nitrogen , not with nitrate- or nitrite-nitrogen. Compounds should not be acidic. However, there are some false-positive reactions known in the literature, e.g. with steroids.
The specifics of the reaction of Dragendorff's reagent and its modifications (e.g. Munier-Macheboeuf) with alkaloids and other compounds are unclear. It seems likely that the solution contains an equilibrium mixture of different monomeric and polymeric iodobismuthate anions, the latter with bismuth atoms joined by bridging iodine atoms. Although ion pairing with basic nitrogen compounds is a possibility, ligand exchange with appropriate nucleophiles cannot be excluded. Thus, the reagent gives color reactions with non-nitrogenous compounds, some as simple as dialkyl phthalates, plasticizers commonly present as contaminants in extracts prepared when screening plants for alkaloids.
Dragondorff's reagent (potassium iodide-bismuth nitrate) is widely used reagent to detect alkaloids. The heavy metal atom (BiI4) combines with the nitrogen in the alkaloid to form ion pairs. This ion pair forms insoluble orange red colored complex.
I used this reagent on and aqueous alkaloid fraction in which i observed precipitation. Can i then filter the precipitate and reverse the reaction to get the pure alkaloids from the complex?
Adel Amer Hello Sir, with that being said, if we're going to detect all the alkaloids in the plant extract, should we be using more than one test for alkaloid? If I combine Dragendorff test with Mayer's test and Wagner's test, and it shows negative 1 out of 3, what does that actually mean?
Before me, other scientists have already answered your question, but I want to add. If you want to use the reagent of dragendorf only on alkaloids, first you need to add ammonia to the extract and rinse with chloroform. Alkaloids move to chloroform and reagent gives only a qualitative reaction alkaloids.
- Badges
- Science topic
- Similar topics
- Chemistry
- Organic Chemistry