The Kurnakov test, also known as Kurnakov's reaction, is a
chemical test
In chemistry, a chemical test is a qualitative or quantitative procedure designed to identify, quantify, or characterise a chemical compound or chemical group.
Purposes
Chemical testing might have a variety of purposes, such as to:
* Determine ...
that distinguishes pairs of
''cis''- and
''trans''-isomers of
tA2X2(A = NH
3, X =
halogen or
pseudohalide
Pseudohalogens are polyatomic analogues of halogens, whose chemistry, resembling that of the true halogens, allows them to substitute for halogens in several classes of chemical compounds. Pseudohalogens occur in pseudohalogen molecules, inorganic ...
). Upon treatment with
thiourea
Thiourea () is an organosulfur compound with the formula and the structure . It is structurally similar to urea (), except that the oxygen atom is replaced by a sulfur atom (as implied by the '' thio-'' prefix); however, the properties of ur ...
, the ''trans''-dihalides give less soluble white products, whereas the ''cis''-dihalides give more soluble yellow products. The test is still used to assay samples of the drug
cisplatin
Cisplatin is a chemotherapy medication used to treat a number of cancers. These include testicular cancer, ovarian cancer, cervical cancer, breast cancer, bladder cancer, head and neck cancer, esophageal cancer, lung cancer, mesothelio ...
, but it is mainly of pedagogical interest, as it illustrates the
trans effect In inorganic chemistry, the trans effect is the increased lability of ligands that are trans to certain other ligands, which can thus be regarded as trans-directing ligands. It is attributed to electronic effects and it is most notable in square p ...
.
The test was devised by
Soviet
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...
chemist
Nikolai Kurnakov
Nikolai Semyonovich Kurnakov (russian: Николай Семёнович Курнаков; 6 December 1860 – 19 March 1941) was a Russian chemist, who is internationally recognized as the originator of physicochemical analysis. He also was one ...
.
Application
The Kurnakov test is sometimes used to detect
transplatin
''trans''-Dichlorodiammineplatinum(II) is the trans isomer of the coordination complex with the formula ''trans''-PtCl2(NH3)2, sometimes called ''transplatin''. It is a yellow solid with low solubility in water but good solubility in DMF. The ex ...
in samples of the drug cisplatin. In hot aqueous solution, the ''cis''-compound reacts with aqueous thiourea (tu) to give a deeper yellow solution, from which yellow needles of
t(tu)4l
2 chloride deposit on cooling. The ''trans''-compound gives a colourless solution, from which snow-white needles of ''trans''-
t(tu)2(NH3)2l
2 deposit on cooling.
References
{{Reflist, 2
Chemical tests