Side reaction

A side reaction is a chemical reaction that occurs at the same time as the actual main reaction, but to a lesser extent. It leads to the formation of by-product, so that the yield of main product is reduced:^[1]

${\displaystyle {\ce {{A}+B->[{k_{1}}]P1}}}$

${\displaystyle {\ce {{A}+C->[{k_{2}}]P2}}}$

P₁ is the main product if k₁> k₂. The by-product P₂ is generally undesirable and must be separated from the actual main product (usually in a costly process).