$\ce{CaO}$ being a basic oxide should not react with $\ce{NaOH}$. Then how come decarboxylation takes place using soda lime? I am confused.
2 Answers
Sodalime when used in decarboxylation, the reaction does not take place between NaOH and CaO. In Oakwood reaction, Carboxyl group is the one which gets reduced by NaOH being base.
The decarboxylation using soda lime does not involve any reaction between $\ce{NaOH}$ and $\ce{CaO}$.
It is in fact the $\ce{NaOH}$ which reacts with the carboxylic acid to form the alkane, alongwith the formation of $\ce{Na_2CO_3}$.
$\ce{CaO}$ is simply used to make the reagent easier to handle. $\ce{NaOH}$ is highly hygroscopic and easily forms a concentrated sodium hydroxide solution when exposed to air. Sodalime does not absorb moisture that easily.