Chen-Kao reaction

The Chen-Kao reaction (named after Ko Kuei Chen and Chung-Hsi Kao, Madison, Wisconsin 1926) is a chemical method for determining the presence of pseudoephedrine, ephedrine, and similar phenylalkylamines. The reaction is used in spot tests and is also known as Chen-Kao test (or simply as Chen, Test T in UN Precursor Test Kit). The test is often used to distinguish ephedrine, pseudoephedrine, norephedrine, cathinone and methcathinone from amphetamine and methamphetamine, which do not react with Chen’s test reagent. The Chen-Kao test is performed by creating an acidic solution of the compound to be tested and adding dilute Copper (II) Sulfate and Sodium hydroxide solutions.The procedure is as follows: Place small amount of material to be tested on a spot plate. Add 2 drops of reagent A Add 2 drops of reagent B Add 2 drops of reagent C A violet color indicates presence of ephedrine or pseudoephedrine Reagent A - 1% (vol/vol) aqueous acetic acid solution Reagent B - dissolve 1g Copper(II) sulfate in 100ml water Reagent C - dissolve 8g of NaOH in 100ml of water (that is 2N NaOH solution) Further, the coordination complex might be extracted with organic solvent like diethyl Ether or n-butanol (see Table II), as proposed in the literature, which provides additional confirmation of the original results, but no further differentiation. This modification is not included in the UN Precursor Test Kit and other spot tests alike. In order to further differentiate between ephedrine enantiomers - ephedrine, pseudoephedrine and other ephedrine-related compounds, Simon’s test (with acetaldehyde) and Simon’s test (with acetone) are used. (see Table III) When acidic solution of ephedrine or pseudoephedrine is mixed with copper sulfate and sodium hydroxide solutions, a violet color is formed. Upon shaking with ether, the organic phase turns red/purple and the aqueous phase turns blue. The staining is based on the formation of a coordination complex of two ephedrine molecules and a copper ion Cu2+ This works, because, in an alkaline solution, the hydroxyl and amine groups are de-protonated, leaving a negative charge on the central atoms.