Mechanochemistry involves milling reagents to induce reactions and is considered a greener alternative to solution-based synthesis. This work will address the mechanochemical syntheses of the α- and β-isomers of ditetradecyl 2,2'-bipyridine-4,4'- dicarboxylate complexes of palladium as well as the kinetics of these reactions. This work will also address the improved mechanochemical synthesis of 1,3-dimethyl benzimidazolium iodide as well as its kinetics.
The study of ditetradecyl 2,2'-bipyridine-4,4'-dicarboxylate complexes of palladium utilized 1H NMR spectroscopy for kinetic analysis. The total reaction completion time for PdLα14I2 was 55 minutes while the total reaction completion time for PdLβ14I2 was 600 minutes. Based on coefficients of determination, it was ascertained that only the Johnson-Mehl-Avarami-Yerofeev-Kolmogrov (JMAYK) model could be used to fit both reactions.
Values of the rate constant, 𝑘 obtained from the JMAYK model for PdLα14I2 were 0.05±0.01 min-1 while values of 𝑘 from the JMAYK model for PdLβ14I2 were 0.011±0.008 min-1 and 0.005±0.004 min-1 for mixing and non-mixing, respectively. These decreased values for PdLβ14I2 were consistent with the rate differences observed during milling for both complexes. Average values of 𝑛 obtained for PdLα14I2 were 1.1±0.2 and indicate pre-existing nucleation sites are present on the material before milling as well as two-dimensional growth. While average 𝑛 values obtained for PdLβ14I2were 0.5±0.1 and 0.30±0.06 for mixing and non-mixing, respectively. These values also indicate pre existing nucleation sites are present on the material prior to mixing, however, growth is one-dimensional. The differences in growth cause the differences in observed reaction rates between the two complexes.
Values of nucleation, 𝑘1 and autocatalytic growth, 𝑘′2 for PdLα14I2 were 0.04±0.02 min-1 and 0.02±0.03 min-1. While values of 𝑘1 for PdLβ14I2 were 0.01±0.01 min-1 and 0.004±0.002 min-1 for mixing and non-mixing, respectively. However, values of 𝑘′2 were consistently negative, therefore; restricted modeling was utilized to only yield positive values. This gave values of zero for both mixing and non-mixing, which would indicate autocatalytic growth does not occur during the synthesis of PdLβ14I2. Differences in the physical properties of the complexes were observed throughout milling as α-substituted reactions yielded products that were soft while β-substituted reactions yielded products that were hard and sticky.
Finally, this work will address the improved mechanochemical synthesis of 1,3 dimethyl benzimidazolium iodide where both LAG (liquid assisted grinding) and neat methods were utilized. Kinetic analysis for this study also utilized 1H NMR spectroscopy. For neat methods, complete conversion occurred within 350 minutes, whereas complete conversion for LAG methods occurred at 600 minutes. Coefficients of determination were found to be between 0.9834-0.9951 and 0.9450-0.9912 for JMAYK and Finke Watzky (FW) models, respectively. Values of 𝑘 from the JMAYK model for neat methods were 5.644x10-3 min-1and 5.246x10-3 min-1while the 𝑘 value obtained for the LAG methods were smaller. This was consistent with the differences in rates observed during the course of the reactions. Values of 𝑛 cannot be broken down to give information of nucleation and growth as the values obtained were larger than four for the neat methods. This would indicate, however, that increasing nucleation is occurring.
Values of 𝑘1 and 𝑘′2 for neat methods were also similar to each other while the values of 𝑘1 were in between those of neat methods. Values of 𝑘′2 were smaller than that of the LAG methods which was consistent with the reaction rates observed. Due to the slow reaction times for LAG methods, it was determined that LAG methods actually hindered conversion to product.
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Year degree awarded
Rachel J. Allenbaugh
Robert D. Johnson
Harry B. Fannin
Kevin M. Miller
Underwood, Alexandra Nicole Ms, "KINETIC STUDY AND MECHANOCHEMICAL SYNTHESES OF α- AND β- ISOMERS OF DITETRADECYL 2,2'-BIPYRIDINE-4,4'- DICARBOXYLATE COMPLEXES OF PALLADIUM AND 1,3-DIMETHYL BENZIMIDAZOLIUM IODIDE" (2019). Murray State Theses and Dissertations. 157.