University thesis:
Dissertation, Universität Freiburg, 2020
Footnote:
Description:
Abstract: In this work, a new type of minireactor and a nickel chip-based microreactor with sub-millimeter channel hydraulic diameters (280 μm) were developed together with the group of Prof. Woias (Department of Microsystems Engineering, University of Freiburg). In addition, the direct fluorinations of cyclic carbonates with F2 diluted with N2 in these reactors have been investigated. For the minireactor, we studied the fluorination of fluoroethylene carbonate (FEC) and obtained four fluorinated products: 4,4-F2EC, trans-F2EC, cis-F2EC and F3EC. trans- and cis-F2EC were the main products, while trifluorinated F3EC has been fully characterized for the first time. In the microreactor, FEC and of propylene carbonate (PC) were tested for the direct fluorination. In the reaction with FEC, a high efficiency for the formation of the four fluorinated products (4,4-F2EC, trans-F2EC, cis-F2EC and F3EC) was demonstrated (65 % F2 usage). Moreover, twelve fluorinated compounds were obtained and characterized in the direct fluorination of PC. Compared to the initial studies in 2013 employing a minireactor, two new difluorinated compounds, E- and Z-4,5-Difluoro-4-methyl-1,3-dioxolan-2-one, and even trifluorinated compounds, E- and Z-4,5-difluoro-4-fluoromethyl-1,3-dioxolan-2-one, were synthesized in the microreactor. These new compounds were claimed to be applied as potential additives for Li-ion batteries, but for none of them has any characterization or proof of synthesis been provided. For all direct fluorinations in the microreactor, the yield of the fluorinated cyclic carbonates, the selectivity of the reactions, the product distributions as well as the space-time-yields of the fluorinated cyclic carbonates were studied by varying the ratio of fluorine and the cyclic carbonates as well as the fluorine concentrations. <br>Besides, initial theoretical and experimental work was dedicated to the establishment of synthesis of perfluorinated salts with perfluoroalkyl and perfluoroaryl cations. The thermodynamic stability of perfluoroalkly and perfluoroaryl cations of the elements of the fifth main group (N to Sb) were calculated by quantum chemical calculations. The theory suggested that it will be difficult to quaternize the perfluorinated A(RF)3 systems. Experimentally, the F3C-CH2-N2+ diazonium ion was chosen as a promising candidate for quaternization. However, this reaction is also only slightly exergonic and side reactions dominated the experiments. Alternatively, 1-Ethyl-1-methyl-pyrrolidinium tetrafluoroborate, [EMPy][BF4] dissolved in CH3CN or fluorinated cyclic carbonates was directly fluorinated in the capillary, mini- and microreactors to obtain perfluoralkyl salt. Three mono-fluorinated products were obtained in all reactors with very low yields. However, the main products were the fluorinated solvents. Further, the minireactor exhibits much higher yields when compared with the capillary reactor. The use of the microreactor is challenging as [EMPy][BF4] contains sodium cations so that the by-product NaF caused blocking of the microchannels. Overall, the synthesis of “repulsive salts” in amounts suitable to measure their potentially unique properties could not be achieved, and preliminary work suggests this to be a difficult task in general