Lower selectivities were measured when coarse magnesium turnings were used (figure , columns 1-4) compared to the case when fine magnesium turnings were used (figure , columns 5-8). Fine magnesium turnings possess a larger magnesium surface compared to coarse turnings. Since the Grignard reagent formation is a surface reaction between halide and metallic magnesium, the reaction between magnesium and 4 on a large Mg surface proceeds fast. The data show that not only the size of the magnesium particles has an influence on the selectivity, but also the type of pump used. The influence of the particle size is more pronounced than the influence of the pump type. All pumps used were calibrated before use, so that a wrong volumetric flow rate can be ruled out and the influence can be attributed to the pumping principle alone. The following order of selectivity towards 5 when using coarse magnesium turnings was found: pump A > pump D > pump C > pump C + pump B. For the fine magnesium turnings, the following order was obtained: pump C > pump C + pump D > pump A > pump D. Considering only single pumps, the lowest selectivity was measured for pump C for the coarse magnesium turnings. In contrast to that, the best selectivity was found for the fine turnings and the same pump. Similar contradictory results were obtained for pump A: the highest selectivity was registered for the coarse magnesium turnings, while for fine turnings the low selectivities were found. Pronounced formation of the Wurtz product 6 may result from limited magnesium surface accessibility, limiting the conversion of the educt 4. The available Mg surface in a bed of fine turnings is more than twice as high as in a bed of coarse turnings (see part 1). Another reason for an increasing formation of 6 might be an enhanced backmixing that widens the contact zone where 4 and 5 are simultaneously present. The effect of the available Mg surface is clearly observable when comparing the results of coarse and fine turnings. When assuming that Mg beds with similar sized turnings are comparable, the available Mg surface cannot be the reason for the differences in selectivity when using the same turnings. Therefore, differences in the residence time distribution are likely the reason for pronounced Wurtz product formation.