Chlorination

Alkanes like methane, propane, and decane are super useful. We use them for fuel because they release a lot of energy when we burn them. They're also used in aerosols and to make roads. But they're not very reactive because they only have nonpolar C-C and C-H single bonds. This is where chlorination comes in. By adding chlorine to alkanes, we make them way more reactive. Chlorination is when we add chlorine atoms to a molecule. To do this, we use a process called free radical substitution. Free radicals are super reactive atoms, molecules, or ions with an unpaired outer shell electron. Antioxidants can help fight the damage caused by free radicals. In free radical substitution, we take off a hydrogen atom from the alkane and replace it with a chlorine atom. This makes the molecule a halogenoalkane.

‍

Chlorination is a process of adding chlorine or chlorine-containing compounds to water to disinfect it and kill any harmful bacteria, viruses, and protozoa that may be present. Chlorination is a common method of disinfecting drinking water, swimming pool water, and wastewater. The process works by releasing chlorine into the water, which then reacts with the organic matter present in the water to form a variety of disinfection byproducts (DBPs) . Chlorination is a relatively simple and cost-effective process that can be used to provide safe drinking water to large populations .

Sources:

"Chlorination is a process of adding chlorine or chlorine-containing compounds to water to disinfect it and kill any harmful bacteria, viruses, and protozoa that may be present."
"Chlorination is a relatively simple and cost-effective process that can be used to provide safe drinking water to large populations."

Propagation I

One of the chlorine free radicals takes a hydrogen atom from methane by breaking one of the C-H bonds. It forms the stable compound hydrochloric acid. A methyl free radical is left behind. Once again, this radical is extremely reactive.

Study tip: Notice how the radical is represented. The small dot is located on the carbon, as this is where we find the unpaired electron.

Propagation II

The methyl free radical reacts with a second chlorine molecule. One of the chlorine atoms adds onto the methyl radical to form chloromethane, and the other chlorine atom is left behind as the regenerated radical. This means the reaction can happen again and again until the radical is destroyed in the final step, termination. We call this a chain reaction. A chain reaction is a reaction that produces a by-product which then goes on to react further.

Termination

Termination is the final step in free radical substitution. This step removes any remaining free radicals by having them react with each other to form a stable compound. There are different ways this can happen, but in each case, two radicals react together. For instance, two chlorine radicals can react to form a chlorine molecule. Alternatively, two methyl radicals can react to form ethane. Sometimes, a methyl free radical and a chlorine free radical can react to form chloromethane. These reactions help to prevent the formation of too many unwanted by products.

The products of chlorination

Our example of methane and chlorine initially produces chloromethane and hydrochloric acid. Chloromethane is an example of a halogenoalkane. Halogenoalkanes are organic molecules formed from alkanes, where halogen atoms have replaced one or more hydrogen atoms.

‍

Halogenoalkanes are organic molecules that contain a carbon atom bonded to a halogen atom. This bond makes them much more reactive than alkanes, and they can be used as starting materials for synthesizing a variety of organic compounds, such as alkenes, alcohols, nitriles, and amines. However, the use of free radical substitution reactions to produce halogenoalkanes can be challenging. These reactions are chaotic and difficult to control, resulting in the production of many different products. For example, when methane reacts with chlorine, a mixture of products can be produced, including ethane, dichloromethane, trichloromethane, and carbon tetrachloride. Furthermore, when longer-chain alkanes react with chlorine, many isomers can be formed due to the non-specific nature of the reaction. As a result, the use of halogenoalkanes in industry requires careful control and optimization to produce the desired product.

‍

The chlorination of alkanes using free radical substitution involves four stages and is catalyzed by UV light. The reaction produces a mixture of products and can be a chain reaction due to the highly reactive nature of free radicals, which have an unpaired electron in their outer shell. The process can be challenging to control, and the resulting mixture of products can be difficult to separate and purify. Therefore, careful optimization and control are necessary when using chlorination as a method to produce specific organic molecules.