Angela Köckritz

Synthesis and Application of Carbonated Fatty Acid Esters from Carbon Dioxide Including a Life Cycle Analysis

Carbon dioxide can be used in various ways as a cheap C1 source. However, the utilization of CO2 requires energy or energy-rich reagents, which leads to further emissions, and therefore, diminishes the CO2-saving potential. Therefore, life cycle assessment (LCA) is required for each process that uses CO2 to provide valid data for CO2 savings. Carbon dioxide can be incorporated into epoxidized fatty acid esters to provide the corresponding carbonates. A robust catalytic process was developed based on simple halide salts in combination with a phase-transfer catalyst. The CO2-saving potential was determined by comparing the carbonates as a plasticizer with an established phthalate-based plasticizer. Although CO2 savings of up to 80 % were achieved, most of the savings arose from indirect effects and not from CO2 utilization. Furthermore, other categories have been analyzed in the LCA. The use of biobased material has a variety of impacts on categories such as eutrophication and marine toxicity. Therefore, the benefits of biobased materials have to be evaluated carefully for each case. Finally, interesting properties as plasticizers were obtained with the carbonates. The volatility and water extraction could be improved relative to the epoxidized system.

Fundamental calculations on the surface area determination of supported gold nanoparticles by alkanethiol adsorption.

Surface area determination is a crucial step for the characterization of the activity of noble metal catalysts. Not only the development of useful determination methods but foremost the understanding of surface properties and their conversion into mathematical expressions are essential to obtain reliable results. A selective method to gain access to the specific surface area of gold on oxidic supports is the chemisorption of alkanethiol from suspensions. Therefore, the concentration of a 1-dodecanthiol solution before and after immersion of supported gold catalysts was determined by gas chromatography. To convert the concentration information into a specific surface area, the surface coverage, the surface atom concentration, the interatomic Au-Au distance, and the particle morphology were considered. Further calculations afforded the determination of a mean particle diameter. A good agreement was found between gold particle sizes obtained from transmission electron microscopy and thiol adsorption. The given mathematical expressions are highly valuable for a broad range of chemisorption methods and noble metal catalysts.

Reaction Monitoring of Heterogeneously Catalyzed Hydrogenation of Imines by Coupled ATR‐FTIR, UV/Vis, and Raman Spectroscopy

Coupled ATR‐FTIR, UV/Vis, and Raman spectroscopy has been introduced for the monitoring of liquid phase hydrogenation reactions under elevated H2 pressure by implementation of spectroscopic immersion probes into a modified autoclave reactor. The setup was successfully tested for the heterogeneously catalyzed hydrogenation of several imine substrates under H2 pressures up to 20 bar. The conversion of the imines could be analyzed by Raman spectroscopy and the product formation was observable by attenuated total reflectance FTIR spectroscopy (ATR‐FTIR), which illustrates the benefits of coupling complementary spectroscopic methods. Separate spectroscopic investigations show that imines intensively interact with the phosphoric acid ester that is used as catalyst modifier, indicated by a shift of the original ν(CN) band of the imine to higher wavenumbers. UV/Vis spectroscopic investigations reveal a distinct shift of the absorption edge to a higher wavelength. Furthermore, the formation of adsorbates on the surface of used Pt/Al2O3 catalysts, resulting mainly from adsorbed imine, was detected by FTIR spectroscopic analysis. The potential of UV/Vis spectroscopy in transmission mode for analyzing the organic components was tested. Due to its high sensitivity at low concentrations this method offers an additional possibility for a quantitative in situ analysis of the reaction progress in real time.

Insights into gold-catalyzed synthesis of azelaic acid

A novel green route for the synthesis of azelaic and pelargonic acid via aerobic gold-catalyzed cleavage of 9,10-dihydroxystearic acid (DSA) was investigated recently. In this study, the examination of the reaction mechanism is described. The results of the application of 18O-labeled molecular oxygen and sodium hydroxide as well as of diastereomeric pure erythro- and threo-DSA were discussed. Assumed reaction intermediates were synthesized and subjected to the same reaction conditions as with DSA. As a conclusion from the obtained data, an oxidative dehydrogenation mechanism was postulated. Additionally, the aging of the gold catalyst used under different storage conditions was explored.

Oxidation of Citronellal to Citronellic Acid by Molecular Oxygen Using Supported Gold Catalysts

The oxidation of citronellal to citronellic acid was studied using molecular oxygen as oxidant and gold-containing supported catalysts under aqueous conditions. The reactions were carried out at 60-90 degrees C, with 200 Nml min(-1) O2 and at pH values from 9 to 12. The alumina- or titania-supported catalysts were synthesized according to the deposition-precipitation procedure using urea or NaOH. Mechanistic studies have revealed that radical-initiated reactions lead to undesired by-products especially at pH <9, that is, the C=C bond is attacked and a diol is primarily formed probably via an epoxide intermediate. This side reaction can be suppressed to a large extent by increasing the pH to 12 and by raising the catalyst/oxygen ratio. Furthermore, detailed studies on the influence of reaction time, pH value, reactant concentration and amount of catalyst show that citronellic acid can be obtained in over 90% yield with total conversion of citronellal at pH 12 and a temperature of 80 degrees C.