Thesis (Ph. D.)--Columbia University, 1916. / Biographical.

Thesis (Ph. D.)--Columbia university, 1916. / Biographical.

The oxidation of cymene with dioxygen has been investigated in some detail with the view of establishing the feasibility of improving the efficiency of the oxidation process. Of particular interest were the rate of cymene oxidation and the selectivity of the oxidation process for the tertiary cymene hydroperoxide, especially at conversions above 15%. In order to be able to evaluate the selectivity of oxidation processes, a reliable method for analysis of the individual hydroperoxides had to be established. Two methods were investigated, namely reduction of the hydroperoxides to alcohols using ferrous sulphate and reduction using triphenylphosphine, and analysing the reduction products by gas chromatography. Of these two methods, the triphenylphosphine method proved to be superior to the ferrous sulphate method and was used as the method of choice for this investigation. A number of oxidation systems were evaluated in an initial screening experiment for the oxidation of p-cymene. The results of this screening experiment showed that three-phase oxidation systems, i.e. systems containing an organic phase, an aqueous phase and gas, gave significantly lower activities than two-phase oxidation systems. In addition, the use of a base in the aqueous layer does not improve the overall selectivity of the oxidation process, but improves the selectivity towards the tertiary hydroperoxide to some extent due to the decomposition and extraction of primary hydroperoxide into the basic aqueous phase. Oxidation systems using a non-autoxidation catalyst, i.e. a catalyst that does not catalyse the conventional autoxidation of organic compounds, gave by far the most promising results. These systems gave both a high selectivity as well as high reaction rate. From the initial screening experiment, and using multi-factorial statistical techniques, two catalyst systems were selected for investigation, namely vanadium phosphate and boron phosphate. The results of these investigations showed that these two catalysts are remarkably active and selective for the oxidation of p-cymene, giving the cymene tertiary hydroperoxide in selectivities exceeding 85% and at substrate conversions as high as 25%. These results are a considerable improvement over currently known oxidation systems and may offer opportunities for further commercial exploitation.

The selective, liquid phase oxidation of p-cymene is an important synthetic route for the production of p-cresol via the tertiary cymene hydroperoxide (TCHP). The industrial-scale oxidation process is characterised by slow oxidation rates due to limitations in the mass transfer of oxidant (gaseous oxygen) into the liquid phase. However, like all other autoxidation reactions, the oxidation reaction is exothermic, following the typical free radical autoxidation reaction mechanism, which implies that careful temperature control is critical in order to prevent the further reaction of the initially formed hydroperoxide species. In the presence of metal catalysts, the limiting oxidation rate is the transfer of oxygen from the gas to liquid boundary interface. As a result, low product yields and poor productivity space-time yield are typically experienced. At high substrate conversions, by-products resulting from the decomposition of the formed hydroperoxides predominate. For this reason, the conversion of substrate is restricted to preserve the TCHP selectivity. The slow rates in industrial-scale p-cymene oxidations results in long oxidation times, typically 8-12 h. Substrate conversions are typically between 15-20 percent, and the TCHP selectivity ranges between 65-70 percent. The work described in this thesis concerns the oxidation of p-cymene in a microstructured falling film reactor (FFMSR). These reactor systems facilitate chemical reactors to have high mass and heat transfer rates because of high surface area-to-volume ratios. Due to their small internal volumes, these reactors are inherently safe to operate. These properties were exploited to improve the p-cymene oxidation rate and, consequently, the space-time yield. In order to evaluate the suitability of vanadium phosphate oxide (VPO) catalysts for use as supported catalyst in the FFMSR, different catalysts prepared from VOHPO4∙0.5H2O and VO(H2PO4)2 precursors was first evaluated for the oxidation of p-cymene in a well-stirred batch reactor. The results of the two activated catalysts, (VO)2P2O7 and VO(PO3)2 when used as powders in their pure form, showed a significant improvement in p-cymene oxidation rates with conversions up to 40 percent in 3-4 h reaction time with a TCHP selectivity of 75-80 percent. The (VO)2P2O7 catalyst showed better oxidation rates and selectivity when compared to the VO(PO3)2 catalyst obtained from the VO(H2PO4)2 precursor. The (VO)2P2O7 catalyst was supported on a stainless steel plate and the coated plate used to study the long-term stability and catalytic perfornance of the catalyst during p-cymene oxidations in a batch reactor. Comparable oxidation rates and TCHP selectivity were obtained with the stainless steel coated VPO catalyst when compared to the “free powder” (VO)2P2O7 catalyst. The results also showed that the stainless steel coated catalyst displays a slow, yet significant deactivation over extended reaction periods (250 h onstream). Characterization of the exposed (VO)2P2O7 catalyst to p-cymene oxidation conditions by powder XRD, SEM and TGA-MS showed that (VO)2P2O7 phase undergoes structural transformation back to VOHPO4∙0.5H2O phase over time. The (VO)2P2O7/-Al2O3 catalyst was used to coat the micro-channel reaction plates of the FFMSR. Both uncoated and coated micro-channel reaction plates were evaluated in the FFMSR for the oxidation of p-cymene. The FFMSR showed effective improvement of oxidation rates in terms of productivity space-time-yield at comparable batch p-cymene conversions. A Typical 10 percent conversion in catalysed batch oxidations at 1-2 h reaction time was achieved in few seconds (19 s) reaction time in FFMSR. The comparison of uncoated (i.e. uncatalysed) and coated (i.e. catalysed) FFMSR oxidations showed slight differences in oxidation rates. No clear explanation could be established with the present results for the observed same behaviour. However, the insufficient contact time between the gas and liquid reactants with the wall-coated solid catalyst is one of the possible causes for the observed behaviour of the coated and uncoated micro-channel plates. A simple developed kinetic model was used to confirm the obtained batch oxidation results using cumene as probe compound due to its similarity to p-cumene oxidation and extensive studied kinetics. With the estimated K values and available rate constants from literature, it was possible to predict the conversions in a batch reactor at the same typical micro-structured reactor residence time (i.e. of 19 s). The predicted conversions in the batch reactor were less than 0.1 percent even at harsh conditions such as 170 oC when compared to about 10 percent achieved in the micro-structured reactor at the same reaction temperature, reactants concentration and reaction time of 19 s. This difference in the reactor systems performance indicates the unique advantages offered by micro-structured reactors (e.g. improved mass transfer, temperature management and high surface-to-volume ratios) to perform typical gas/liquid mass transfer limited reactions such as cumene and p-cymene autoxidations.

Thesis (Ph. D.)--Columbia University, 1930. / Vita. "Literature cited": p. [44].

Thesis (Ph. D.)--University of Wisconsin--Madison, 1931. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 250-254).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1931. / Typescript. With this is bound: Brom derivatives of hydroxythymoquinone / By Samuel R. Chechik. Reprinted from Journal of the American Pharmaceutical Association, vol. XXII, no. 6 (June 1933), p. [506]-510. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis(M.Sc. (Chemistry)) -- University of Limpopo, 2019 / Imidazolyl-ethanamine Schiff base ligands of the N^N type were prepared by condensation reaction of histamine dihydrochloride with para-substituted aldehyde derivatives to yield: (E)-N-benzylidene-2-(1H-imidazol-4-yl)ethanamine 119a, 4-((E)(2-(1H-imidazol-4-yl)ethylimino)methyl)phenol 119b, E)-N-(4-fluorobenzylidene)-2(1H-imidazol-4-yl)ethanamine 119c and (E)-N-(4-nitrobenzylidene)-2-(1H-imidazol-4yl)ethanamine 119d, which were characterised by 1H and 13C-NMR, FTIR specroscopy and HRMS. 2D-NMR experiments (1H-1H COSY and 2D-HMBC) for representative ligand 119b were performed to qualify success in the condensation reaction. An attempted reaction to coordinate Schiff base ligand 119c to zinc chloride was carried out in an NMR tube and traces of the product were observed between 12 and 24 h monitoring using 1H-NMR. Iodine promoted cyclocondensation reaction of anthranilamide and para-substituted aldehyde derivatives afforded 2-aryl-quinazolin4(3H)-ones 120a-e and subsequent chloro-aromatisation reaction in SOCl2 afforded electrophilic C4-(Cl) 2-aryl-4-chloro-quinazolines 121a-e and the compounds were characterised by 1H and 13C-NMR and FTIR spectroscopic techniques. The 2-aryl-4chloro-quinazolines served as prerequisites for de-chloro amination on the C4-(Cl) position by 2-amino-3-nitropyridine to yield 2-aryl-N-(3-nitropyridin-2-yl)quinazolin-4amine derivatives 123a-e in good yield and the derivatives were characterised by 1H and 13C-NMR, FTIR and HRMS spectroscopic techniques. The C4-(Cl) position further allowed for Sonogashira cross-coupling with ethynylpyridine to yield 2-aryl-4(ethynylpyridine)quinazoline derivatives 125a-e which were characterised by 1H and 13C-NMR, FTIR and HRMS spectroscopic techniques. The 2-aryl-4(ethynylpyridine)quinazoline served as ligands for coordination to monomeric pcymene ruthenium(ll) which yielded (ɳ6-p-cymene)RuCl2-2-aryl-4(ethynylpyridine)quinazoline derivatives 126a-e in good yield. Compounds 126a-e were characterised by 1H and 13C-NMR, FTIR and HRMS spectroscopic techniques. 2D-HMBC NMR of representative ligands 126c and 126e showed long range couplings from 1JCH to 9JCH and this was confirmed by coordination induced shifts (CIS) ranging from 1 ppm to 11 ppm. Compounds 119a-d, 123a-e and 125a-e were inductively docked into the active receptors of tyrosine kinase (PDB:2SRC), glutamine synthetase (PDB:1HTO) and oxidoreductase (PDB:3F8P). The docking scores obtained gave hits ranging from -5 to -10 Kcal/mol. Compounds 119a-d, 121a-e, 123a-e, 125a-e and 126a-e were assayed employing the broth-dilution method which gave promising anti-Mycobaterium tuberculosis activity. Compound 125e gave good activity of <0.244 µg/mL over 7 day and 14 day sampling. Coordination of ligands 125a-e to Ru(ll) group resulted in loss of activity, notably for ligand 125e. / NRF and Sasol Inzalo Bursary

Using photochemical and emulsion pro­cedures, a study has been made of the liquid-phase oxida­tion of p-cymene with respect to the nature of the result­ing hydroperoxides and their decomposition products, and the relative extent of oxidative attack at the methyl and iso­propyl groups. Hydroperoxide decomposition was negligible in the photochemical oxidations at 60C, and the product was shown to consist of 20% primary and 80% tertiary hydroper­oxide by reduction of the total product and fractionation of the resulting alcohols. The following compounds were shown to be present in the emulsion oxidation product in addition to the above mentioned hydroperoxides: dimethyl-p-tolylcarbinol, p-methylacetophenone, p-isopropylphenylcarbinol, cumic acid, p-acetobenzoic acid, p-A-hydroperoxyisopropyl, benzoic acid, and p-(I-hydroxyisopropyl) benzoic acid. By chromatographic separation of the acids and reduction of the other products, the relative extent of attack at the two positions was shown to be 1:4, identical with that of the photochemical oxidation. Pure tertiary hydroperoxide has been obtained for the first time. / Thesis / Master of Science (MS)

Seventeen novel osmium cymene complexes with O,O′- and P,P′-chelating ligands as well as N- and P-monodentate ligands are reported. The osmium cymene complexes were synthesised and characterised by spectroscopic techniques (NMR, IR and Raman), elemental analysis, thermal analysis, conductivity studies and X-ray crystallography. The molecular structures of complexes 1(b), 2, 4, 6, 7(a)-(d) and 11 in this study are reported. The cymene rings of these complexes show different conformations due to loss of planarity influenced by the ancillary ligands as a result of ML back bonding. Osmium cymene complexes of the type [Os(η6-p-cymene)BrL2]+ (where L2 = chelating P,P′ ligand) and binuclear [{Os(η6-p-cymene)Br2}2 L2] (where L2 = bridging P,P′ ligand) were evaluated for anticancer activity against renal, melanoma, breast and HeLa cancer cells. The chelated-diphosphine osmium cymene complexes exhibited significant anticancer activities relative to the bridged-diphosphine osmium analogues. A series of O,O′-chelated osmium complexes exhibited moderate and poor anticancer activities. / Chemistry / M. Sc. (Chemistry)