Cleavage of lignin model compounds using ruthenium/KOH or KOH-only systems

Interest in conversion of lignin to value-added, aromatic compounds has led to studies with lignin model compounds (LMCs), including polymers, showing their conversion to monomers using in situ homogeneous Ru catalysts (in toluene) such as Ru(H)xCly(CO)(PPh3)3/xantphos, where x = 1 = y, or x = 2 and y = 0. One paper reported that the xantphos could be replaced by the much cheaper KOH, but limitations within the experimental methodology and discussion have led us to re-investigate this KOH system. Our studies show that the catalysts decompose over 2 or 4 h, respectively, and further LMC conversion is due solely to the KOH. A key factor is the solubility of the KOH in the toluene, which is determined by the amount of trace water in the KOH used (i.e. commercial vs. flame-dried); in some cases, complete conversion of an LMC can result from use of 2 equivalents of KOH without the use of any Ru catalyst.