Catalysis of Organic..

Tanielyan et al. 143TEMPO catalyst, eliminate the bromine-based co-catalyst, significantly reduce thevolume of the buffer solution and avoid the use of organic solvents. With just a tenfoldbuffer reduction, the volume which the substrate occupies is now close to 40%of the initial charge (bar B in Figure 1b).Yield, DMBALD, %100(a)901:12:1803:15:17010:1[Br - ] : [ TEMPO ]00 5 10 15 20 25 30 35Time, minVolume Reactants, L8.06.04.02.00.0(b)2.3%of V tA37.5%of V tBNaOClSolventBufferROHFig 1. Effect of the KBr:[MeO TEMPO] ratio on the yield of 3 (a) and graphicalpresentation of the volumes of each reactant used (b). Reaction conditions:[MeO TEMPO] = 0.08mM, [3,3-Dimethylbutanol] = 8mM, [NaOCl] = 10mM,CH 2 Cl 2 20mL, T = 0ºCScreening for an efficient TEMPO catalystThe various commercially available TEMPO’s were screened for activity in thisreaction with the following order the result.OMeNHCOCH 3OHN(CH 3 ) 2NONONONONOMeO-TMP~=AA-TMP > TMP > HO-TMP>DMA-TMPSolvent effectAttempts were made to replace the CH 2 Cl 2 solvent without sacrificing the reactionrates and the selectivities to the target aldehyde, 2. The screening was done at [MeO-TEMPO] :Br - =1. High reaction rates and complete conversion of 1 was recorded inacetone and toluene. When we carried the reaction in acetone, even after complete