Step 1: Bromination of p-Isopropylbenzene The first step is to brominate p-isopropylbenzene to introduce a bromine atom (Br) onto the benzene ring. This reaction can be carried out using bromine (Br2) in the presence of a Lewis acid catalyst, such as iron (Fe):

Reaction: p-Isopropylbenzene + Br2/Fe → p-Bromoisopropylbenzene

Step 2: Oxidation of p-Bromoisopropylbenzene to p-Isopropylbenzaldehyde The second step involves the oxidation of p-bromoisopropylbenzene to form p-isopropylbenzaldehyde. This can be accomplished using a mild oxidizing agent like sodium dichromate (Na2Cr2O7) in an acidic medium (e.g., sulfuric acid, H2SO4):

Reaction: p-Bromoisopropylbenzene + Na2Cr2O7/H2SO4 → p-Isopropylbenzaldehyde + NaBr + Cr2(SO4)3 + H2O

Step 3: Oxidation of p-Isopropylbenzaldehyde to p-Isopropylbenzoic Acid The final step is the conversion of p-isopropylbenzaldehyde into p-isopropylbenzoic acid. This can be achieved through further oxidation using a stronger oxidizing agent like potassium permanganate (KMnO4) in an acidic medium:

Reaction: p-Isopropylbenzaldehyde + KMnO4/H+ → p-Isopropylbenzoic acid + MnO2 + H2O

After these three steps, you will have successfully converted p-bromoisopropylbenzene into p-isopropylbenzoic acid. Please note that proper safety precautions and laboratory techniques should be followed when conducting these reactions, especially when working with chemicals like bromine and strong oxidizing agents.