The Kurnakov test, also known as Kurnakov's reaction, is a
chemical test
In chemistry, a chemical test is a qualitative property, qualitative or Quantitative property, quantitative procedure designed to identify, quantify, or characterise a chemical compound or substituent, chemical group.
Purposes
Chemical testing m ...
that distinguishes pairs of
''cis''- and
''trans''-isomers of
tA2X2(A = NH
3, X =
halogen
The halogens () are a group in the periodic table consisting of six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and the radioactive elements astatine (At) and tennessine (Ts), though some authors would ...
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, inorgani ...
). Upon treatment with
thiourea
Thiourea () is an organosulfur compound with the formula and the structure . It is structurally similar to urea (), with the oxygen atom replaced by sulfur atom (as implied by the '' thio-'' prefix). The properties of urea and thiourea differ s ...
, 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 chemical compound with chemical formula, formula ''cis''-. It is a coordination complex of platinum that is used as a chemotherapy medication used to treat a number of cancers. These include testicular cancer, ovarian cancer, c ...
, but it is mainly of pedagogical interest, as it illustrates the
trans effect
In inorganic chemistry, the trans effect is the increased Lability#Chemistry, lability of ligands that are Cis-trans isomerism#Inorganic coordination complexes, trans to certain other ligands, which can thus be regarded as trans-directing ligands. ...
.
The test was devised by
Soviet
The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
chemist
Nikolai Kurnakov
Nikolai Semyonovich Kurnakov (; 6 December Old_Style_and_New_Style_dates.html" ;"title="nowiki/>Old Style and New Style dates">O.S. 24 November1860 – 19 March 1941) was a Russian chemist, who is internationally recognized as the originator of ...
.
Application
The Kurnakov test is sometimes used to detect
transplatin 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