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Haloalkanes are the alkanes that have one or more halogen substituents and come as a subset of halocarbons. These are widely used in multiple chemical and industrial applications. These typical applications are pharmaceuticals, solvents, fuels, refrigerants, fire extinguishants, flame retardants, etc. Haloalkanes have the general formula RX, where R is the alkyl group while X is the halogen like I, Br, Cl, F, etc.
This section will cover all about the popular haloalkanes called 2-bromobutane. We’ll cover its properties, followed by the dehydrohalogenation of the 2-bromobutane. The quick list of the top questions related to the same helps students understand the importance of 2-bromobutane.
2- Bromobutane
The molecular formula of 2-bromobutane is C4H9Br. It is the isomer of 1-bromobutane, The other names of 2-bromobutane are methyl-ethyl bromomethane or sec-butyl bromide. It belongs to the large section of chemical compounds called alkyl halides with at least one halogen, i.e., bromine. The carbon atom attached to the bromine is connected to the other two carbon atoms, and hence the molecule is called the secondary alkyl halide. Hence, 2-bromobutane is called secondary alkyl halide.
It has a pleasant odour and is a colourless liquid. It is a stable chemical compound but is highly toxic and flammable. It is an irritant and harmful to skin, eyes; and if ingested. The reaction of 2-bromobutane with a strong base yields 2-butene which is an alkene. This reaction is the bimolecular E2 elimination reaction.
Elimination reaction
It is an elimination reaction in which saturated compounds are formed into the unsaturated compounds having double or triple carbon-carbon bonds. There are two types of the elimination reaction which include:
1.Dehydrohalogenation: In this method of elimination reaction, there is the removal of both a halogen atom and a hydrogen atom.
2.Dehydration: In this method of elimination reaction, the water molecule is eliminated from alcohol. It is called a beta elimination reaction. In the dehydration, the leaving group and H are placed at the neighbouring carbon atoms.
Elimination reaction can occur in two forms-
- E1 mechanism: It is the unimolecular elimination reaction and consists of two steps- ionisation and deprotonation. It occurs in the presence of a base leading to the formation of a pi-bond in the molecule. It has first-order kinetics, and the reaction rate is proportional to the concentrations of the substance to be transformed.
- E2 mechanism: It is the bimolecular elimination and has a one-step mechanism. The carbon-hydrogen and carbon-halogen bonds break to form the new double bond. Here, the base is the rate-determining step of the reaction. It has second-order kinetics, and the reaction rate is proportional to the concentrations of the substrates and the eliminating agents.
Dehydrohalogenation of 2-bromobutane
The chemical reaction for the dehydrohalogenation of the 2-bromobutane is:
CH3 – CH (Br) – CH2 – CH3 → CH3 – CH = CH – CH3
The products of the dehydrohalogenation of the 2-bromobutane reaction are given by Satyzeff’s rule. According to this rule, in the dehydrohalogenation of the 2-bromobutane, 2-butene is the major product. This reaction takes place in the presence of alcoholic KOH only. Satyzeff’s rule states that in any reactions, the preferred product is the one alkene having a large number of alkyl groups attached to the doubly bonded carbon atoms in the molecule.
Conclusion
Hence, it is easy for our students to understand the basic idea of the dehydrohalogenation of 2-bromobutane. Starting with the haloalkanes, we cover all the important topics like the making of 2-bromobutane, followed by its properties, and the reaction.
It becomes quick and smooth learning for the students when they can access the details of 2-bromobutane. The structural and chemical composition understanding lays a strong foundation for the understanding of complex reactions like dehydrohalogenation or dehydration.
