 We know that phenols can be prepared by several methods. From aryl halides, from disinium salts, from benzene-sulfonic acids and so on. In this video we are going to see how to prepare phenols from cumene also called isopropyl benzene. Now this method is not discussed in details in many textbooks but it is important to understand this because this is the industrial method by which phenols are primarily prepared and not just that. This process also generates another commercially important chemical called acetone as the byproduct. So let's go ahead and see how we can prepare phenols from cumene. Now to give you an overall idea this is what happens in the entire reaction. Cumene or isopropyl benzene undergoes catalytic aryl oxidation to give cumene hydroperoxide which on treatment with acid gives us phenol and acetone. Now if you look at the products it is not intuitive as to how we would arrive at these products from the starting material right. Looks like something more is happening here and we are going to figure out what exactly that is. Now we arrive at this important chemical which is cumene hydroperoxide through a free radical mechanism and as we know free radical mechanism involves initiation propagation and termination steps correct. So we start with HBr which reacts with oxygen in the presence of a catalyst to form bromine radical and hydroperoxide radicals. Now the actual radical mechanism begins when this bromine radical abstracts this hydrogen atom from cumene that is we have a chomolytic cleavage here and this process generates a hydrocarbon radical and HBr. Now in the propagation step this hydrocarbon radical reacts with oxygen and generates this particular radical. So here again the bond breaking happens and we get another radical. This radical further reacts with HBr regenerating the bromine radical and look what we have here we got our cumene hydroperoxide intermediate. In the termination step all of these radicals combine with each other giving us a myriad of minor products. Now this cumene hydroperoxide is treated with acid to give phenol and acetone. So let's go ahead and see what that mechanism looks like. When we treat cumene hydroperoxide with acid the lone pair of electrons on the oxygen atom abstracts a proton from the medium and here we have a protonated intermediate. With the loss of water molecule we get an intermediate where oxygen atom has a positive charge. Now this is quite unstable because oxygen is highly electronegative and an electronegative atom like oxygen having positive charge makes this very unstable. So through a phenyl shift the phenyl group gets attached to the oxygen atom and the positive charge gets transferred to the carbon atom as you can see here. As this bond gets broken we get a positive charge or a carbocation. A nucleophilic attack takes place next where the water molecule attacks the carbocation and in the next step the lone pair of electrons on the oxygen atom abstracts a proton from the acidic medium. So this is kind of a reversible step. In the last step the oxygen atom forms a double bond with the carbon atom eliminating this particular group. The eliminated group here is nothing but phenol and the side product we get here is the acetone. So this is how phenol is prepared commercially from cumene.