Chloroform

Chloroform is an organic compound with a complex history. It has a distinctive sweet smell and can be used for a wide range of applications. Known for its volatility, it was once used as an anaesthetic. Today, even though it is used in chemical industries and laboratories, its use is more tightly regulated. Let’s dive into the chloroform formula, structure, properties, and uses in detail.

1.0What Is Chloroform?

A member of the haloform family, chloroform is a colourless and volatile liquid that is also non-flammable. Its chemical name is trichloromethane and is often used as a solvent in industries and laboratories.

After its discovery in 1831, it gained popularity as an anaesthetic agent in the mid-19th century. However, because of its toxicity and carcinogenic potential, it is no longer used in surgery. However, in industrial applications and organic synthesis, it remains an important compound.

2.0Physical and Chemical Properties of Chloroform

Physical Properties of Chloroform

Chemical Properties of Chloroform

Chloroform demonstrates several notable chemical behaviours, particularly in the presence of bases or when exposed to air over time:

• Reactivity with Acetone in Alkaline Medium: When chloroform is mixed with acetone in an alkaline medium, the reaction can be highly explosive, requiring careful handling in lab settings.
• Reaction with Sodium Hydroxide (NaOH): Chloroform reacts with strong bases like NaOH, producing sodium formate, sodium chloride, and water.

CHCl₃ + 4NaOH → HCOONa + 3NaCl + 2H₂O

• Decomposition in Air: Over prolonged exposure to air, chloroform slowly breaks down. This oxidative decomposition produces phosgene (COCl₂) and hydrogen chloride (HCl)—both are highly toxic compounds.
• Biological Effects: In humans, chloroform has a direct depressant effect on the central nervous system. At high concentrations, it can lead to dizziness, unconsciousness, or respiratory issues.

3.0Preparation of Chloroform

Laboratory Preparation

Chloroform (CHCl₃) is prepared in the laboratory by heating bleaching powder with ethanol. This method is known as the haloform reaction, and there are three key steps involved in this:

Step 1: Generation of Chlorine Gas

First, water and bleaching power are mixed, which results in the formation of calcium hydroxide and the release of chlorine gas.

Ca(OCl)₂ + H₂O → Cl₂ + Ca(OH)₂

Step 2: Oxidation and Chlorination of Ethanol

In this step, chlorine acts as a chlorinating as well as an oxidising agent. First, it oxidises ethanol to form acetaldehyde (ethanal) and then chlorinates the aldehyde to create chloral (trichloroacetaldehyde):

C₂H₅OH + Cl₂ → CH₃CHO + 2HCll

Step 3: Formation of Chloroform

In the previous step, the end result was chloral. In this, the same chloral will undergo hydrolysis in the presence of calcium hydroxide. The resulting by-products of this would be chloroform and calcium formate.

2CCl₃CHO + Ca(OH)₂ → 2CHCl₃ + (HCOO)2Ca₂

Industrial Preparation

In industrial settings, chloroform is synthesised in large quantities using methods similar to the laboratory process, often involving ethanol or acetone, water, and bleaching powder. The production is scaled up by heating this mixture under controlled conditions.

Alternative Industrial Method:

Another commercial method involves the partial reduction of carbon tetrachloride (CCl₄) using iron filings and steam (water vapour). This reaction reduces CCl₄ to chloroform:

3Fe + 4H₂O → Fe₃O₄ + 8H₃

Purification of Chloroform

Pure chloroform can also be obtained by distilling a mixture of chloral hydrate and a concentrated solution of sodium hydroxide (NaOH) or potassium hydroxide (KOH). This method ensures a high degree of purity:

NaOH + CCl₃CH(OH)₂ → CHCl₃ + HCOONa + H₂O

4.0Uses of Chloroform

Chloroform was a vital part of the medical industry as it was used as an anaesthetic. However, after more research was done on the chemical and its toxicity was realised, it is no longer as popular in the medical domain. However, it still remains relevant across other industries, laboratories, and even certain medical domains. Let’s take a look at some of the uses of chloroform:

Medical and Dental Applications:

Historically, during surgical procedures, chloroform was used as a general anaesthetic. A mixture of 30% ether with chloroform was used to enhance the effectiveness of the compound and reduce its side effects. While it is no longer part of surgeries because of safety concerns, it is still used in root canal treatments occasionally for dissolving gutta-percha. 

Analytical Chemistry:

Pure chloroform is used as a background solvent in Fourier Transform Infrared Spectroscopy (FTIR). For spectrum analysis, it can be used to dissolve cholesterol in its powder form or extracted from dairy products.

Industrial Solvent:

Chloroform can be a powerful solvent for substances like waxes, fats, greases, rubber, oils, resins, and certain alkaloids. Once, it was used in laundry for getting rid of stains and tough spots.

Food Packaging:

Since Chloroform is used in the adhesive components of food packaging materials, you can consider it to be an indirect food additive. It ensures that certain packaging layers stick together securely without contaminating the food.

Chemical Manufacturing:

Chloroform is often used in chemical industries to produce chlorine-based compounds like chloropicrin, a pesticide. Because of its solvent properties and reactivity, it is valuable when it comes to synthesising various chemical products.