Facile Two-Phase Catalysis: From Dimethoxymethane and Monomeric Formaldehyde towards Oxymethylene Ethers (OMEs)

An efficient, biphasic route towards oxymethylene dimethyl ethers (OMEs) allowing for catalyst recycling and reuse is presented (OMEs=CH3(-OCH2-)nO-CH3, n=3-5). OMEs are an interesting novel class of non-toxic, diesel-like synthetic fuels with soot-free combustion properties. A solution of commercial OMe3+BF4- in the ionic liquid (IL) 1-ethyl-3-methylimadazolium tetrafluoroborate acts as the immobilized catalyst. Upon addition of dimethoxymethane (OME1) and anhydrous formaldehyde (FA) very pure OMEs form in the upper phase of the biphasic mixture. In the lower IL-phase, the catalyst remains immobilized. After phase separation and removal of the top OME layer, the catalytically active IL-phase is reusable for at least ten times without loss of activity and selectivity.