Formation of hydrogen peroxide by VUV-photolysis of water and aqueous solutions with methanol.

The hydrogen peroxide production upon vacuum ultraviolet (VUV) irradiation of water is reviewed, because published results from the last 10 years lead to conflicting mechanistic interpretations. This work confirms that in pure water, hydrogen peroxide is only produced in the presence of molecular oxygen. Mechanistic schemes explain these findings and confirm earlier statements that recombination of hydroxyl radicals is kinetically disfavoured. In agreement with other recent publications, this work confirms that enhanced hydrogen peroxide production takes place upon VUV irradiation of aqueous solutions of organic compounds. For these investigations, methanol was chosen as an organic model compound. During photolyses, hydrogen peroxide, dissolved molecular oxygen, pH-value of the reaction system, methanol and its products of oxidative degradation were analyzed, and kinetic studies were undertaken to explain the evolution of the concentrations of these components.

A hybrid process for chiral separation of compound-forming systems.

The resolution of chiral compound-forming systems using hybrid processes was discussed recently. The concept is of large relevance as these systems form the majority of chiral substances. In this study, a novel hybrid process is presented, which combines pertraction and subsequent preferential crystallization and is applicable for the resolution of such systems. A supported liquid membrane applied in a pertraction process provides enantiomeric enrichment. This membrane contains a solution of a chiral compound acting as a selective carrier for one of the enantiomers. Screening of a large number of liquid membranes and potential carriers using the conductor-like screening model for realistic solvation method led to the identification of several promising carriers, which were tested experimentally in several pertraction runs aiming to yield enriched (+)-(S)-mandelic acid (MA) solutions from racemic feed solutions. The most promising system consisted of tetrahydronaphthalene as liquid membrane and hydroquinine-4-methyl-2-quinolylether (HMQ) as chiral carrier achieving enantiomeric excesses of 15% in average. The successful production of (+)-(S)-MA with a purity above 96% from enriched solutions by subsequent preferential crystallization proved the applicability of the hybrid process.