Chloroform is a chemical compound that comes under the umbrella of organic chemistry. Many students have queries regarding the behavior and properties of chloroform. In this article, I will cover all the properties of chloroform and one main question which is generally asked is why chloroform is stored in dark bottles.
So, Why chloroform is stored in dark bottles? Chloroform is stored in dark bottles because, in the presence of light and oxygen, it reacts with oxygen to form a highly poisonous gas known as Phosgene. Therefore, chloroform is stored in the dark closed bottles so that it could not get expose to light and oxygen. IUPAC name of Phosgene is carbonyl chloride.
Chloroform is an organic compound with chemical formulae CHCl3. It is a sweet-smelling, colorless and dense liquid. It is known to be powerful anesthetic, anxiolytic and sedative when inhaled. It’s IUPAC name is trichloromethane.
The density of chloroform is around 1.489 g mL-1. It’s melting point is -63.5 degrees Celcius and the boiling point is 61.15 degrees Celcius.
Chloroform is generally used as a solvent. It is used in various chemical industries for adhesives, rubbers, resins, oil, etc.
A solvent is a substance that helps the other substances to dissolve. Hence, chloroform has got a large variety of uses in the industries.
Chloroform is a reactive chemical to moisture and it is stored in a dark-colored and tightly packed bottle so that it doesn’t get exposed to oxygen and light. This is because chloroform reacts with oxygen to form a highly poisonous gas known as phosgene when exposed to light.
Chloroform gets slowly oxidized by the air in the presence of ultraviolet rays from the sun and leads to the formation of a highly poisonous gas known as phosgene.
CHCl3 (Chloroform) + 1/2O2 —UV—–> COCl2 (Phosgene) + 2HCl (hydrochloric acid)
Chloroform consists of a single carbon atom associated with one hydrogen atom and three chlorine atoms. There are different methods to prepare chloroform. Following are the methods to form chloroform:
Methods of Preparation of Chloroform
Free radical halogenation
This is prepared by heating methane with chlorine at a high temperature of about 400-500 degrees Celcius. This method is basically by halogenation which involves repeatedly reaction of methane with the more chlorinated compounds.
CH4 + Cl2 ——–> CH3Cl + HCl
CH3Cl + Cl2 ——-> CH2Cl2 + HCl
CH2Cl2 + Cl2 ——–> CHCl3 + HCl
This method is used to form chloroform on a small scale by the reaction of acetone with sodium hypochlorite
3NaClO + (CH3)2CO ——–> CHCl3 + 2 NaOH + CH3COONa
What is Phosgene?
As explained above, Phosgene is a highly poisonous and colorless gas formed with carbon, oxygen and chlorine atoms with many different ways of reactions.
One fact about this gas was that it was used during the first world war. This gas was used as a choking agent and was responsible for the majority of deaths. This gas is highly toxic that can kill a human being. Exposure to this gas leads to throat and eye irritation as its immediate symptom at a concentration of 2-5 ppm.
Whereas at a concentration of around 25 ppm or above can be dangerous to human life.
Apart from chloroform, Phosgene can be prepared by passing carbon monoxide into chlorine through a porous carbon bed. In this reaction, the activated carbon bed acts as a catalyst.
For better understanding, have a look at the chemical reaction :
CO + Cl2 ——-> COCl2 + heat = -07.6 KJ/mol
Here, heat is liberated in the above reaction. Therefore, the reactor should be cooled down immediately as the reaction is exothermic.
Phosgene gas is mainly used for industrial purposes for preparing pesticides.
Phosgene is non-flammable in nature. It cannot be easily ignited or burned. This gas does not exist in the natural form. It can only be produced chemically. At room temperature, phosgene exists as a gas.
With the pressure and cooling, phosgene gas can be converted into liquid form and further stored for industrial use.
Phosgene gas is heavier gas therefore low lying areas are more prone to this poisonous gas.
The immediate symptoms of phosgene infected human are as following:
- Throat irritation
- Eyes irritation
- Difficulty in breathing
The loss caused by phosgene depends on:
- The timespan of exposer to phosgene
- Concentration of phosgene
Uses of Chloroform?
Chloroform consists of one carbon atom with three chlorine atoms and one single hydrogen atom also named trichloromethane (CHCl3).
Chloroform appears as a clear liquid with a sweet smell like that of ether. It is volatile in nature.
The molecular geometry of chloroform is tetrahedral. The four bonds associated with the carbon atom at the center are in a tetrahedral shape.
And it is observed that molecules that have tetrahedral molecular geometry possess sp3 hybridization. The dipole moment of chloroform is around 1.15 D. Debye is the SI unit of dipole moment denoted by D.
The chloroform is mainly used in industries in the preparation of pesticides, plastic, etc.
It is used as a solvent for fats, alkaloids, fats, and many other elements.
This has a major use in the formation of R-22 freon refrigerant. Although this is being avoided in many developed countries due to global warming due to easy availability, it is still used for making freon refrigerant R-22 in the developing counties.
Apart from use, the toxic nature of a substance formed by the chloroform has a high risk to life.
As explained above, on oxidation of chloroform in the presence of light, a highly poisonous gas is formed known as phosgene.
It is also used in the extraction of vitamins, antibiotics as it is a good solvent.
As it is a sweet-smelling, it is also used in mouthwash, toothpaste, and many other fragrances
If we talk about its biological uses, it has a variety of uses as in labs for the preservation of organic tissues in laboratories. Chloroform avoids the decay of these things hence used as a preservative.
Chloroform has great use in molecular biology, It is used in the extraction of DNA from the cell.
In industries, it is used for making pesticides and it lowers down the temperature of carbon tetrachloride. Therefore, also used as the heat transfer medium in fire extinguishers.
Conclusion: Why Chloroform is Stored in Dark Bottles?
Phosgene is a highly toxic gas that can lead to the death of a person who is exposed to as little as 2-5 ppm concentration of this gas. It is formed by the reaction of chloroform with oxygen in the presence of light. Therefore, to prevent this reaction to take place, chloroform is kept in closed dark-colored bottles.