Question

The missing structures A and B in the reaction sequence are given by the set:

A.${\text{C}}{{\text{H}}_3}{\text{OH}},{\text{RCOOH}}$
B.Methanal, ${\text{RC}}{{\text{H}}_{\text{2}}}{\text{OH}}$
C.Ethanal, ${\text{RCOOH}}$
D.Methanal, ${\text{RCHOHR'}}$

Answer 1

Hint: To answer this question, you must recall the various reactions of oxygen containing organic compounds. Aluminum oxide is a lewis acid and converts alcohols to alkenes.
Complete step by step solution:
A is formed as a by- product along with an aldehyde when an alkene undergoes ozonolysis reaction.
We know that, ozonolysis reaction involves the breaking of a carbon carbon double bond wherever present with the addition of an oxygen atom on the carbon atom which forms a double bond with the carbon atom. As a result, carboxylic compounds are obtained (aldehydes or ketones). In the question, the ozonolysis of the given alkene gives${\text{RCHO}}$. Thus it is evident that the other product formed is${\text{HCHO}}$.
In the next step, the aldehyde is reduced. The mild reduction of an aldehyde leads to the formation of an alcohol. We can see it as the addition of a hydrogen molecule over the carbon oxygen double bond.
Thus, the product formed is ${\text{RC}}{{\text{H}}_2}{\text{OH}}$
Therefore we know A is ${\text{HCHO}}$(methanal) and B is ${\text{RC}}{{\text{H}}_2}{\text{OH}}$.

The correct option is B.

Note: Alkenes are oxidized with ozone to form aldehydes or ketones, or carboxylic acids. Generally, ozone is bubbled through a solution of the alkene at low temperature till the solution takes on a characteristic blue color, which indicates complete consumption of the alkene.
In the next step, a reagent is added to convert the intermediate ozonide formed in the first step to a carbonyl derivative. The reagent added is generally a reducing agent. The use of zinc dust, or dimethyl sulfide produces aldehydes and ketones while the use of hydrogen peroxide produces carboxylic acids.