The first step is the hydroboration reaction, which is the reaction between propylene and borane (BH3). The reaction reagent is diborane, which is a dimer of borane, so it essentially reacts with BH3. The addition at this time is consistent with the electrophilic addition of olefin and hydrogen bromide, but the electrophilic reagent at this time is +BH2, not H+. Because the electronegativity of B is less than H, BH2+ attacks as an electrophilic reagent, and B is added to the terminal carbon atom of olefin. At the same time, because of its large volume and large space barrier, B is always added to the terminal carbon atoms of olefins.

Next, it should continue to react with 2 molecules of propylene to form trialkylboron (CH3CH2CH2)3B.

In the second step, hydrogen peroxide is oxidized under alkaline conditions to obtain trialkoxyboron (CH3 CH2 O) 3b, and finally hydrolyzed to obtain n-propanol. Remember, the oxidation of hydrogen peroxide should be under alkaline conditions, and your reaction conditions are neither fish nor fowl.

Hydroboration is a good method to prepare primary alcohols with high yield and few by-products.