An organic synthetic process was monitored on-line by mid-infrared spectroscopy. The Orthogonal Projection Approach (OPA) and Principal Component Analysis (PCA) were used to detect time regions in the synthesis process where the reaction reached a steady state (constant temperature and concentration of compounds). Multivariate Curve Resolution Alternating Least Squares (MCR-ALS) was applied on the steady state regions to obtain information about the chemical composition of the reaction medium.