Well-stirred batch reactors show a maximum degree of backmixing, representing one extreme case of residence time behaviour. The batch synthesis of 5 from 4 in THF is carried out using various procedures, which are described in detail in the experimental section. Significant amounts of Wurtz product 6 were obtained using the general literature procedure for the synthesis of Grignard reagents (table 4, batch procedure 1). The Wurtz product 6 has a melting point of 52 °C and in this synthesis it was present in such a high concentration that it precipitated in the flask, formed a thick layer of precipitate and stirring of the reaction mixture by means of a magnetic stirrer was hardly possible (picture within ESI). Due to the large amount of Wurtz product, only a low concentration of Grignard reagent would be available for a subsequent synthesis. The poor stirability of the reactor contents also means that targeted temperature control was hardly possible. If the synthesis parameters from the continuous synthesis of 5 were adapted to batch synthesis (batch procedure 2), the formation of 6 was reduced compared to the literature reaction conditions. This was partly a result of the lower halide concentration. It must be noted that intense mixing was hardly possible due to the high magnesium content in the flask (picture within ESI). The small volume of the halide solution initially introduced was not sufficient to completely cover the magnesium turnings. For this reason, the subsequently added halide solution initially only met the bare magnesium surface and rinsed from top to bottom through only magnesium turnings before eventually meeting the Grignard reagent in the sump of the flask. Even in a continuous synthesis process, the halide reactant is in more intense contact with the Grignard reagent. Due to the high magnesium excess, there is a high magnesium surface area available for Grignard reagent synthesis per drop of halide solution. Coarse and fine magnesium turnings have similar yields in batch synthesis since formation of the Wurtz product can only occur when the halide reactant comes into contact with the Grignard reagent. Conducting the Grignard reagent synthesis in a batch under the investigated reaction conditions exhibited inadequate temperature control of the exothermic Grignard synthesis due to the poor stirability of the magnesium turnings, exhibiting a safety hazard. Considering that Grignard reagents are rarely the desired final product and that in laboratory syntheses in batch flasks, the subsequent synthesis such as the Grignard reaction is carried out in the same flask, the high magnesium excess requires separation of the magnesium turnings from the Grignard reagent. The influence of remaining magnesium turnings can lead to problems ranging from issues with stirring to insufficient heat dissipation to undesired reactions with the magnesium turnings (e.g. in the case of a halogen atom on the electrophilic substrate for the subsequent synthesis), so that separation of the magnesium turnings may be necessary. Separation of a solid from a batch flask is not easy to achieve preparatively and, moreover, opening the flask can lead to contamination with e.g. oxygen and moisture. The latter would lead to yield losses due to the reaction with the Grignard reagent and must be avoided urgently. To handle these challenges, laboratory syntheses in batch flasks are typically conducted with stoichiometrically amounts of magnesium, so that at the end of the Grignard synthesis the magnesium is completely consumed. These points were considered during a further adjustment of the literature conditions (batch procedure 3) as a compromise between the previously investigated conditions. The adjustment of the conditions corresponds to what is expected from a laboratory synthesis in a batch flask: In the optimum case, complete conversion of the magnesium turnings and complete mixing of the reactants are batch procedure 1 (coarse Mg turnings) achieved so that uniform tempering is possible. Independent of the size of the magnesium turnings, 5% of the halide reactant could not be converted in the flask at the end of the synthesis with conditions 3, although the flask was tempered and stirred for additional 30 minutes after the addition of the complete halide solution and magnesium turnings were still present (picture within ESI). This comparatively low conversion is related to the lower magnesium surface, although it is not clear why remaining 4 did not or could not react with the remaining magnesium. When using fine turnings, a higher selectivity was achieved. Assuming complete backmixing and since all other reaction conditions were constant for both types of Mg turnings, the influence of the magnesium surface is particularly evident here: a larger magnesium surface area leads to a higher yield of the Grignard reagent. The formation of side product 6 was found to be higher compared to the batch procedure 2, which is also reasoned by the lower Mg surface.