Sidereaction

Sidereaction is a term that describes a secondary chemical reaction that occurs concurrently with the intended primary transformation in a synthesis. In practice, it refers to reactions that compete with the desired pathway, generating byproducts or otherwise altering yield and purity. The term is not widely used in current English literature, where side reaction is the more common formulation.

Causes and mechanisms of sidereactions include competing mechanistic pathways for reactive intermediates, unintended interactions with reagents, solvents, or catalysts, and the influence of impurities. Factors such as temperature, concentration, solvent polarity, catalyst choice, moisture, and the presence of oxygen can promote sidereactions. Because these reactions can proceed in parallel to the main reaction, they often become more significant as conversion increases or under less selective conditions.

Impacts of sidereactions encompass reduced yield, diminished selectivity, and the formation of complex mixtures that complicate purification and downstream processing. In pharmaceutical and fine chemical manufacture, sidereactions can affect regulatory compliance and product consistency, making control of selectivity a central concern.

Examples of sidereactions occur across organic and inorganic chemistry. In electrophilic aromatic substitution, unwanted polyalkylation or over-oxidation can occur. In esterifications, hydrolysis or transesterification may proceed alongside the target reaction. In metal-catalyzed couplings, homocoupling or debonding side processes can compete with cross-coupling. In polymerization, chain-transfer or termination events act as sidereactions that alter molecular weight distributions.

Mitigation strategies focus on reaction optimization and control. Approaches include adjusting stoichiometry and temperature, selecting more selective catalysts or ligands, using protecting groups or scavengers, altering solvent choice, and implementing real-time monitoring to stop the process before significant sidereaction occurs.