Question

In laboratory preparation of alkyl halides is least preferred by
A) Halide exchange
B) Direct halogenation of alkanes
C) Treatment of alcohols
D) Addition of hydrogen halides to alkenes

Answer 1

As we know that in organic chemistry, many substitution reactions are possible. We have to know that the halogenation is the one of the substitution in alkyl groups. Alkyl halides having many applications in our day-to-day life. Chlorine, fluorine, iodine and bromine are halogens in the periodic table. These are binding with alkyl groups to form alkyl halides in various methods.

Complete step by step answer:
We must have to know that in a theoretical way so many halogenation reactions are possible in alkyl groups. But in the laboratory many parameters are optimised to obtain the product like alkyl halide.
Halide exchange is very easy to do in a laboratory in which one alkyl halide is changed to another alkyl halide. Like methyl iodide is converted into methyl chloride.
Therefore, the option A is not correct.
Treatment of alcohols by using preparation of alkyl halide is also possible. When the hydrogen halide is reacted with alcohol to form alkyl halide with removal of water.
e.x. Hydrogen bromide reacts with ethanol to form ethyl bromide in removal of water.
Therefore, the option C is not correct.
In organic chemistry addition reaction is easy to compare another kind of reaction. One unsaturated compound is converted into saturated compound by addition of some molecules. Addition of hydrogen halide to alkene is possible to form alkyl halides. Because, hydrogen goes to one double bonded carbon and halide goes to another double bonded carbon to form alkyl halide.
Therefore, the option D is also not correct.
We need to remember that the direct halogenation of alkanes is not easy to do in the laboratory. During this kind halogenation in alkyl groups many side products are possible. Optimisation of this reaction is very complicated. In direct halogenation of alkyl groups not only one mono alkyl halide product is formed and dehalogenation, tri halogenation is also possible. Halogen are highly reactive species for the reason that more side products are formed in direct halogenation of alkyl groups.
We can write a chemical equation for this type is when methane reacts with chlorine to form methyl chloride and hydrochloric acid as,
$C{H_4} + C{l_2} \to C{H_3}Cl + HCl$
Therefore, option B is correct.

Note:
We need to know that the alkyl halides have various uses in commercials. We have to remember that the halogens are highly reactive, because they have one electron to obtain the stable electronic configuration. Direct halogenation in any organic compound forms many side products.