Question

An organic compound which produces a bluish-green coloured flame on heating in presence of copper is:
A. Chlorobenzene
B. Benzaldehyde
C. Aniline
D. Benzoic acid

Answer 1

The organic compound that has halogen gives a positive result for Beilstein’s test. The bluish-green coloured flame indicates the presence of halogen in the organic compound.

Complete answer:
The organic compound that has halogen gives the bluish-green coloured flame during Beilstein’s test.
The organic compound is heated on the copper wire on the burner. As the organic compound burns it decomposes. The halogen of organic compounds reacts with copper and forms copper halide and produces a bluish-green coloured flame.
The structures of all the compounds are as follows:

In chlorobenzene, chlorine is attached with a benzene ring, so chlorobenzene can produce bluish-green coloured flame on reacting with copper, so option (A) is correct.
In benzaldehyde, an aldehyde group is attached with a benzene ring so, benzaldehyde does not have halogen, so it will not produce a bluish-green coloured flame on reacting with copper, so option (B) is incorrect.
In aniline, ammine is attached with a benzene ring so aniline does not have halogen, so it will not produce a bluish-green coloured flame on reacting with copper, so option (C) is incorrect.
In benzoic acid, carboxylic groups are attached with benzene rings so benzoic acid does not have halogen, so it will not produce a bluish-green coloured flame on reacting with copper, so option (D) is incorrect.

Therefore option (A) chlorobenzene, is correct.

Note: Beilstein’s test is used for the detection of halogens in the organic compound. The bluish-green coloured flame indicates the formation of copper halide. Beilstein’s test does not determine the presence of fluorine.