Mid-IR spectroscopy has long been a powerful tool to elucidate molecular structures and reaction mechanisms. With the advent of optical fibers, it became possible to move the spectroscopic experiment close to the chemical process, rather than transferring the chemistry into the spectrometer. The combination of novel high-duty probes with dedicated spectrometers opens up whole new possibilities for monitoring, studying and even controlling chemical processes. This is e.g. demonstrated for a technically relevant N-alkylation in liquid phase.