Organomagnesium halides, also known as Grignard reagents, are important intermediates for the formation of new carboncarbon-bonds in synthetic chemistry. In the pharmacy sector they became especially useful for the formation of active pharmaceutical ingredients, e.g. pain-reliever ibuprofen and breast cancer drug tamoxifen. Grignard reagents originate from an exothermic reaction of metallic magnesium (mostly powder or turnings) and a halide in a water free ethereal solvent. Side product formation due to the Wurtz coupling reaction can occur, in which a Grignard reagent molecule (product) reacts with a halide molecule (educt), diminishing the yield of the Grignard reagent. Therefore, reducing the contact between the formed Grignard reagent and the halide educt would prevent Wurtz coupling. Consequently, residence time distributions (RTD) in tubular flow reactors equipped with a packed bed of magnesium turnings will have an impact on product distribution. To minimize the contact between the halide educt and the Grignard reagent, a plug-flow like behaviour is favourable, ideally having a constant velocity across the cross-section of the tube and no backmixing, resulting in a narrow residence time distribution. The residence time distributions of chemical reactors depend on the flow and mixing conditions and is a long-known tool of reactor development to estimate the hydrodynamic characteristics of a reactor. The data obtained can also be used to make statements about the average residence time of a volume element within the investigated system and by applying a model the dimensionless Bodenstein number Bo can be estimated. To narrow residence time distributions and minimize backmixing, finally approaching plug flow behaviour and with this high Bodenstein numbers under laminar conditions, continuous oscillatory baffled reactors (COBR) can be used. The COBR is a tubular reactor with internal baffles, which are equidistantly spaced. By superimposing an oscillating flow on the main flow, vortices are generated at the backside of the baffles that cause intense mixing within the vortices and improved heat and mass transfer. This oscillatory flow concept utilising baffles or even without baffles has been used for gasliquid and liquid-liquid reaction systems but also for solid-containing reaction systems. The platform SciFinder refers to 3782 publications from 1950 to 2022 considering the term "oscillatory flow" with a steady increase in publications per year, showing the rising interest in and application of this reactor concept. Some literature reviews do exist, dealing with the concept of oscillatory flow reactors (OFR) and giving an overview of the broad potential and applications of this specific reactor type. Investigated solid-containing reaction systems operated under oscillating flow conditions consider on the one hand solid particles being suspended in the fluid and on the other hand being placed in packed beds. In the case of the flow tube reactor used in this publication, it is not a COBR type reactor, but a tubular reactor fitted with a packed bed of magnesium turnings. The magnesium turnings in the reactor cartridge present obstacles to the flow through the reactor, influencing flow behaviour, so the fluid usually does not flow through the reactor in a uniform way. By using different pumps (syringe pump, pulsating valveless rotary piston pump and pulsation-free micro annular gear pump) and by applying oscillating flow conditions, the residence time distribution of the magnesium-filled reactor cartridge and its dependence on the pump-induced flow behaviour were determined and Bodenstein numbers and mean residence times were calculated. In part 2 of this publication, the impact of residence time distribution and backmixing on the selectivity of Grignard reagent formation was investigated by utilizing the synthesis of benzylmagnesium bromide, an exemplary synthesis prone to Wurtz coupling.