Chloroform is a sickly, sweet-smelling, colorless liquid, b.p. 61oC. it is sparingly soluble in water but readily soluble in ethanol and ether. It does not burn in air under usual conditions, but its vapour may be ignited, when it burns with a green-edged flame. According to Hine, chloroform undergoes alkaline hydrolysis to produce the formate ion and carbon monoxide by what Hine calls the alpha-elimination mechanism: this involves the removal of hydrogen and chloride ions from the same carbon atom.

Preparation of Chloroform

Chloroform may be prepared in the laboratory or industrially by heating ethanol or acetone with bleaching powder, or with chlorine and alkali (yield about 40 per cent). The reaction is extremely complicated, and the mechanism is obscure.

The equations usually given for the action of bleaching powder on ethanol are: (i) oxidation of ethanol to acetaldehyde; (ii) chlorination of acetaldehyde to trichloroacetaldehyde; (iii) decomposition of trichloroacetaldehyde (choral) by free calcium hydroxide (present in the bleaching powder) into chloroform and formic acid:

(i)                CH3CH2OH   +Cl2    →    CH3CHO   +   2HCl
(ii)              CH3CHO   +   3Cl2    →   CCl3CHO   +   3HCl
(iii)            2CCl3CHO   +   Ca(OH)2    →    2CHCl3   +   (HCO2)2Ca

When acetone is used, the first product given is trichloroacetone, which is then decomposed by the calcium hydroxide into chloroform and acetic acid:

(i)                CH3COCH3   +   3Cl2    →    CCl3COCH3   +   3HCl
(ii)              2CCl3COCH3   +   Ca(OH)2    →   2CHCl3   +   (CH3CO2)2Ca

Chloroform is also prepared industrially by the chlorination of methane. 

Reaction of Chloroform

When chloroform is treated with zinc and hydrogen chloride in ethanolic solution, methylene dichloride (q.v.) is obtained; when treated with zinc and water, methane is obtained:
When chloroform is warmed with silver powder, acetylene is obtained:

2CHCl3   +   6Ag   →    C2H2   +   6AgCl

When treated with concentrated nitric acid, chloroform forms chloropicrin:

CHCl3   +   HNO3    →    CCl3NO2   +   H2O

Chloropicrin or nitrochloroform (liquid, b.p. 112oC) is used as an insecticide, and has been used as a war-gas. Chloroform adds onto the carbonyl group of ketones in the presence of potassium hydroxide, e.g., with acetone it forms chloretone (colorless needless, m.p.97oC), which is used as a drug. The mechanism is possibly:

use of Chloroform

Chloroform has been used in surgery as an anesthetic, and for this purpose it has to be pure. In the presence of air and light, chloroform slowly forms carbonyl chloride, which is extremely poisonous:
Chlorine, water and carbon dioxide are also produced. Anesthetic chloroform was therefore kept in well-Stoppard dark-brown bottles. Ethanol was also added but its function is not quite clear. According to some authors, it retards the decomposition of the chloroform. This is supported by the fact that infra-red measurements of such mixtures show that absence of the carbonyl frequency.

A delicate test for chloroform is the ‘isocyanide test’. This is carried out by heating chloroform with ethanolic potassium hydroxide and aniline, whereby phenyl isocyanide is formed, and is readily detected by its nauseating odor.

CHCl3   +   3KOH   +   C6H5NH2    →    C6H5NC   +   3KCl   +   3H2O

Chloroform is widely used in industry as a solvent for fats, waxes, resins, rubber, etc.