Michael Oelgemöller

Recent Advances in Microflow Photochemistry

This review summarizes recent advances in microflow photochemical technologies and transformations. The portfolio of reactions comprises homogeneous and heterogeneous types, among them photoadditions, photorearrangements, photoreductions, photodecarboxylations, photooxygenations and photochlorinations. While microflow photochemistry is most commonly employed as a micro-scale synthesis tool, scale-up and technical production processes have already been developed.

Treatment options for wastewater effluents from pharmaceutical companies

In recent years, concerns about the occurrence and fate of active pharmaceutical ingredients, solvents, intermediates and raw materials that could be present in water and wastewater including pharmaceutical industry wastewater has gained increasing attention. Traditional wastewater treatment methods, such as activated sludge, are not sufficient for the complete removal of active pharmaceutical ingredients and other wastewater constituents from these waters. As a result, complementary treatment methods such as membrane filtration, reverse osmosis and activated carbon are often used in conjunction with the traditional methods for treatment of industrial wastewater. Most of the literature published to date has been on the treatment of municipal wastewater. However, there is a growing body of research that looks at the presence of active pharmaceutical ingredients in industrial wastewater, the treatment of these wastewaters and the removal rates. This article, reviews these treatment methods and includes both traditional methods and advanced oxidation processes. The paper concludes by showing that the problem of pharmaceuticals in wastewaters cannot be solved merely by adopting end of pipe measures. At source measures, such as replacement of critical chemicals, reduction in raw material consumption should continue to be pursued as the top priority.

Green photochemistry: Production of fine chemicals with sunlight

Three photochemical reactions were investigated under solar irradiation conditions with moderately concentrated sunlight: the photoacylation of naphthoquinone with butyraldehyde and the dye-sensitized photooxygenations of citronellol and 1,5-dihydroxynaphthalene, respectively. All reactions were easily performed on multigram-to-kilogram scales using cheap and commercially available starting materials, and yielded important key intermediates for industrial applications.

Titanium dioxide photocatalysis for pharmaceutical wastewater treatment

Heterogeneous photocatalysis using the semiconductor titanium dioxide (TiO2) has proven to be a promising treatment technology for water purification. The effectiveness of this oxidation technology for the destruction of pharmaceuticals has also been demonstrated in numerous studies. This review highlights recent research on TiO2 photocatalytic treatment applied to the removal of selected pharmaceuticals. The discussions are tailored based on the therapeutic drug classes as the kinetics and mechanistic aspects are compound dependent. These classes of pharmaceuticals were chosen because of their environmental prevalence and potential adverse effects. Optimal operational conditions and degradation pathways vary with different pharmaceutical compounds. The main conclusion is that the use of TiO2 photocatalysis can be considered a state-of-the-art pharmaceutical wastewater treatment methodology. Further studies are, however, required to optimize the operating conditions for maximum degradation of multiple pharmaceuticals in wastewater under realistic conditions and on an industrial scale.

Parallel microflow photochemistry: process optimization, scale-up, and library synthesis.

A novel, multimicrocapillary flow reactor (MμCFR) was constructed and applied to a series of sensitized photoadditions involving 2(5H)-furanones. The reactor allowed for rapid and energy-, time-, and space-efficient sensitizer screening, process optimization, validation, scale-up, and library synthesis.

Photoinduced electron transfer chemistry of phthalimdes: an efficient tool for CC-bond formation

A collection of intra- and intermolecular photoinduced electron transfer (PET) reactions is presented which all are based on the phthalimide chromophore as the oxidizing species. Electron-donating groups versatile for PET processes are ethers, thioethers, amines, alkenes, arenes, and carboxylates as well as α-trialkylsilyl activated heteroatom-substituents. These reactions can be efficiently applied for the synthesis of five- and six-membered ring heterocycles, medium-sized and macrocyclic products such as macrolides, cyclopeptides, crown ethers or thioethers as well as (from intermolecular processes) Grignard-alike products.

Green photochemistry: solar photooxygenations with medium concentrated sunlight

The rose bengal sensitized photooxygenations of citronellol and 1,5-dihydroxynaphthalene were performed successfully under solar irradiation conditions, and complete conversions (>95%) were achieved in almost all cases in relatively short illumination times. The selected reactions were easily performed on multigram to kilogram scales using cheap and commercially available starting materials, and yielded important key-intermediates for industrial applications.

From Conventional to Microphotochemistry: Photodecarboxylation Reactions Involving Phthalimides

A series of acetone-sensitized photodecarboxylation reactions involving phthalimides have been investigated using conventional and microphotochemistry. Both, intra- and intermolecular transformations were compared. In all cases examined, the reactions performed in microreactors were superior in terms of conversions or isolated yields. These findings unambiguously prove the advantage of microphotochemistry over conventional photochemical techniques.

Green photochemistry: solar-chemical synthesis of Juglone with medium concentrated sunlight

Dye sensitized photooxygenations of 1,5-dihydroxynaphthalene were investigated with soluble and solid-supported sensitizers and moderately concentrated sunlight. Moderate to good yields up to 79% of 5-hydroxy-1,4-naphthoquinone (Juglone) were achieved on multiple gram-scales after just 4 h of illumination. The mild and environmentally friendly reaction conditions make this application particularly attractive for ‘green photochemistry’.

Photosensitized addition of isopropanol to furanones in a 365 nm UV-LED microchip

The DMBP-sensitized addition of isopropanol to furanones was studied in a novel LED-driven microchip reactor. Complete conversions were achieved after just 2.5 to 5 min of irradiation with 6 × 365 nm high-power LEDs. The results were compared to analogous experiments using a conventional batch reactor.