Question

How is chloroform prepared from ethyl alcohol? Describe giving chemical equations. Why is chloroform stored in dark-coloured bottles?

Answer 1

Chloroform or trichloromethane is a colourless organic compound having the chemical formula as $CHC{{l}_{3}}$with strong-smelling liquid. It is a very powerful anaesthetic when inhaled or ingested.

Step by step answer:

-Chloroform is a dense liquid that is chiefly produced on a large scale as a precursor to polytetrafluoroethylene (PTFE).

-Chloroform is a powerful euphoriant, a substance that gives the intense feeling of pleasure, excitement, and happiness. It is also used as a medication that inhibits anxiety. It also works like a sedative or tranquillizer which reduces irritability by depressing the central nervous system.

-Chloroform is known by many names like Methane trichloride, Methyl trichloride, Methenyl trichloride, TCM, Freon 20, and Refrigerant-20.

-The chloroform molecule exhibits tetrahedral geometry.

-Chloroform is produced naturally by many kinds of seaweeds and fungi in soil.

-Chloroform can be produced from ethyl alcohol. In the process of preparing chloroform in the laboratory, a mixture of bleaching powder $(CaOC{{l}_{2}})$ is heated with ethanol or acetone. Bleaching powder here acts as an oxidizing chlorinating and hydrolyzing agent.

$CaOC{{l}_{2}}+{{H}_{2}}O\to Ca{{(OH)}_{2}}+C{{l}_{2}}\uparrow$

Chlorine gas evolved from the bleaching powder oxidizes and chlorinated ethanol.

$C{{H}_{3}}C{{H}_{2}}OH\xrightarrow[-2HCl]{C{{l}_{2}}}C{{H}_{3}}CHO\xrightarrow[-3HCl]{3C{{l}_{2}}}C{{l}_{3}}CCHO$

Trichloroethane also is known as Chloral further reacts with calcium hydroxide formed in the first step forming chloroform.

$Ca{{(OH)}_{2}}+2C{{l}_{3}}C-CHO\to {{(HCOO)}_{2}}Ca+2CHC{{l}_{3}}$
-Chloroform in the presence of light, air, or moisture undergoes oxidation and forms phosgene $COC{{l}_{2}}$ which is a poisonous gas. Hence chloroform is stored in dark-coloured bottles to avoid this reaction.

$2CH{{C}_{3}}+2{{H}_{2}}O\to 2COC{{l}_{2}}+6HCl$

Note: While handling chloroform, one must follow safety procedures. Chloroform is often formed as a by-product during the process of water chlorination along with a range of other disinfection by-products and thus is present in municipal tap water and swimming pools. Chloroform when orally ingested, inhaled, or on dermal exposure can cause sores as a result of defatting. The accidental splashing of chloroform into the eyes is found to cause severe irritations. Chloroform is also found to be carcinogenic to humans.