The bubble size and rate of hydrogenation have been measured in the mass transfer controlled regime in a 3L stirred reactor agitated by a Rushton turbine at 2 bar absolute pressure and 35C. The reaction in question is the hydrogenation of 2-butyne-1,4-diol with pure hydrogen using a range of solvents from water through to isopropanol (IPA) and mixtures in between and different mean specific energy dissipation rates have been utilised. The results have been analysed in the context of a film model. The different solvents lead to different bubble sizes, which also differ from those under non-reactive conditions; and also different hydrogen solubilities. The reaction leads to first butene-diol and then butane-diol and the 2nd step is the faster. Both steps are enhanced at a concentration of approximately 5% IPA/95% water as the solvent compared to the compositions around that as the the smallest bubbles and hence the highest surface area for mass transfer are found at that composition. However, overall the highest rates are found at 100% IPA because though the bubbles are much larger and hence the interfacial area is significantly smaller, the hydrogen solubility is the highest, thus maximising the overall rate of mass transfer. In water, both the area and solubility is small and the rate is lowest at about half the maximum value.