In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...
, Keller's reagent is a mixture of
anhydrous
A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...
(glacial)
acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main compone ...
, concentrated
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
, and small amounts of
ferric chloride
Iron(III) chloride describes the inorganic compounds with the formula (H2O)x. Also called ferric chloride, these compounds are some of the most important and commonplace compounds of iron. They are available both in anhydrous and in hydrated f ...
, used to detect
alkaloids
Alkaloids are a broad class of naturally occurring organic compounds that contain at least one nitrogen atom. Some synthetic compounds of similar structure may also be termed alkaloids.
Alkaloids are produced by a large variety of organisms i ...
. Keller's reagent can also be used to detect other kinds of alkaloids via reactions in which it produces products with a wide range of colors.
[. An extract of heartwood reacts with the reagent to produce a yellow-brown color.][. Certain compounds "can be detected by means of a bright blue color formed with Keller's reagent".][. "With Keller's reagent there is first a pale red, later a blue violet color."] Cohn describes its use to detect the principal components of
digitalis
''Digitalis'' ( or ) is a genus of about 20 species of herbaceous perennial plants, shrubs, and Biennial plant, biennials, commonly called foxgloves.
''Digitalis'' is native to Europe, Western Asia, and northwestern Africa. The flowers are ...
(note that they may not be alkaloids). The reaction with this reagent is also known as the Keller–Kiliani reaction, after C. C. Keller and H. Kiliani, who both used it to study digitalis in the late 19th century. It can be used for
digitoxin
Digitoxin is a cardiac glycoside used for the treatment of heart failure and certain kinds of heart arrhythmia. It is a phytosteroid and is similar in structure and effects to digoxin, though the effects are longer-lasting. Unlike digoxin, whic ...
's quantitative analysis.
Another method of visualizing the Keller-Kiliani reaction is to treat the test solution with ferric chloride-containing glacial acetic acid, followed by the addition of concentrated sulfuric acid, which sinks to the bottom (like in
the brown ring test for nitrates). A brown ring in the interface indicates the presence of
cardenolides
A cardenolide is a type of steroid. Many plants contain derivatives, collectively known as cardenolides, including many in the form of cardenolide glycosides (cardenolides that contain structural groups derived from sugars). Cardenolide glycoside ...
.
List of color changes with various compounds
*
Digoxin
Digoxin (better known as digitalis), sold under the brand name Lanoxin among others, is a medication used to treat various heart disease, heart conditions. Most frequently it is used for atrial fibrillation, atrial flutter, and heart failure. ...
: olive-brown without red traces
*
Digitoxin
Digitoxin is a cardiac glycoside used for the treatment of heart failure and certain kinds of heart arrhythmia. It is a phytosteroid and is similar in structure and effects to digoxin, though the effects are longer-lasting. Unlike digoxin, whic ...
: green, then blue
*
Digoxigenin: greenish-yellow
*
Vindolicine: bright blue
*
Uleine: yellow-brown
*
Hunteria eburnea alkaloid J (C
39H
46N
4O
2): pale red, later blue violet
See also
*
Dische test
*
Baljet reaction
References
{{reflist
Chemical mixtures
Organic reactions