Düsseldorf, Universiẗat, Diss., 2002.

In previous work done in our laboratories, a method was discovered to produce phenolic mono-ethers from 4-hydroxyacetophenone and other 4-hydroxyketones by treating with ammonium peroxy-disulfate in an alcohol as a reaction solvent and in the presence of concentrated sulphuric acid or other strong protonic acids. Since this method of producing 4-alkoxyphenol ethers provides a very convenient way to modify hydroquinone and substituted hydroquinones to produce a variety of phenol mono-ethers, it was of interest to study the general scope of this reaction, including a more detailed investigation of the reaction mechanism. In previous studies, it was suggested that interaction between the aromatic pi-system of hydroquinone and the cyclohexa-2,5-diene structure of benzoquinone plays a significant role during the reaction. It was therefore of interest to investigate whether other compounds that are also capable of forming the cyclohexa-2,5-diene structure, will interact in a manner analogous to the hydroquinone/benzoquinone couple. Two specific compounds were selected for this purpose, namely 4-nitrosophenol and 4- (diphenylmethylene)cyclohexa-2,5-dien-1-one . The scope of etherification reactions of hydroquinone-benzoquinone or hydroquinone/benzoquinone like substrates such as 4-nitrosophenol and 4- (diphenylmethylene)cyclohexa-2,5-dien-1-one in the presence of acid catalyst and alcohols was investigated. These studies showed that hydroquinone, 4- nitrosophenol and 4-(diphenylmethylene)cyclohexa-2,5-dien-1-one successfully affords the phenolic ethers in good to excellent yield. For example, quantitative yield of 4-methoxyphenol could be obtained from a 1:1 mixture of hydroquinone and benzoquinone at the reflux temperature of methanol. In order to study the reaction mechanism, the cross-over reaction between tertbutylhydroquinone and benzoquinone (or hydroquinone and tertbutylbenzoquinone) was studied in detail. The results of these cross-over reactions were used to propose a mechanistic pathway that could explain the requirement for pi-interaction between the hydroquinone and benzoquinone molecules, the role of the acid catalyst, as well as the relative rates of hydroquinone and benzoquinone consumption during these reactions. The mechanism was also capable of explaining all the reaction products observed during these reactions. The work was then extended to reactions of 4-nitrosophenol and 4- (diphenylmethylene)cyclohexa-2,5-dien-1-one with methanol in the presence of either hydroquinone or benzoquinone. The results of these investigations strongly suggest the presence of similar interactions between these molecules that also influence the outcome of the reactions. The exploitation of pi-interactions between two molecules of these types investigated during this work opens an interesting field of chemistry. Clearly, the level of understanding developed during this work is only beginning to address this interesting field of chemistry and much work will need to be done to gain a fuller understanding of the chemistry involved as well as the potential synthetic value of these interactions.

Düsseldorf, Universiẗat, Diss., 2000.

Düsseldorf, Universiẗat, Diss., 2000.

Inaug.-Diss.--Erlangen.

Thesis (Ph. D.)--Columbia University, 1945. / "Lithoprinted ... Edwards Brothers, Inc., Ann Arbor, Michigan, 1946." Vita. Bibliography: p. 59-60.

The project was concerned with the investigation of the electrochemical oxidation of various phenols, and to develop a viable reaction system for the production of the respective hydroquinones. Current production routes utilizing phenol as starting material have the limitations of using large amounts of acids, having to be stopped at low conversions and producing a mixture of the hydroquinones and catechols. Of the possible routes to the respective hydroquinones from the various phenols, the electrochemical oxidation of these phenols offers commercial and environmental advantages and hence formed the theme of the investigation. The synthetic possibilities proved to be more prevalent in a system when the electrochemical oxidation of these phenols was performed in an aqueous medium utilizing an organic co-solvent. Results obtained during this investigation made it possible to make certain predications about the mechanism taking place. This was found to depend on the anode material used for the oxidation. The results showed that the process developed for the electrochemical oxidation of these phenols, yields mainly the para-isomers of the respective hydroquinones and benzoquinones in good yields and selectivities, with fair current efficiencies and good mass balances at high conversions. For example: * Phenol (batch) 8 F: 345% current efficiency, 70% hydroquinone, 6% catechol, 9% benzoquinone, 9% phenol and 94 mass balance. * 2-Tert-butylphenol (flow) 10 F: 37% current efficiency, 65% hydroquinone, 33% benzoquinone, 2% phenol and 100% mass balance. * 2,6-Di-tert-butylphenol (flow) 11 F: 23% current efficiency, 92 % hydroquinone, 6% benzoquinone, 1% phenol and 99% mass balance. The developed electrochemical oxidation system offers the following advantages over previous and current methods: simplified isolation and extraction procedures, smaller amounts of acid usage, reasonably selective synthesis of the para-isomer and a less corrosive system all at high conversions.

The electrochemical oxidation of phenol can be considered as an important process for either producing value added products such as hydroquinone and catechol or for the removal of the phenol from waste water streams to form carbon dioxide. This process had been extensively studied with the main focus on type of anode material used. Even though the anode material could be made from a range of materials, this study focused on using PbO2 as anode material that was made by using Pb-acid battery principles in designing a microporous electrode. In this study, the focus was on using lead dioxide as an anode material that was made by using the formation principles used in the manufacturing of Pb-acid batteries. This allowed for the construction of an electrochemical flow-through micro-porous reactor that contained PbO2 as the anode and Pb as the cathode, allowing for a solution containing phenol to flow through the cell continuously. By applying a suitable potential across the cell, the almost complete oxidation of phenol would occur to form benzoquinone, which was followed by the sequential reduction to other products such as hydroquinone and catechol. The system was shown to be made up of tightly packed micro-porous material that had a very high surface area-to-volume ratio. The study showed that between 80 to 90 percent successful conversion of a 50 mM solution of phenol could be achieved by optimizing the continuous flow process of up to 500 minutes. The main reaction product from this process was hydroquinone, of up to 60 percent with a number of the minor products of which not all could be identified. In order to utilize the characteristics of this reactor system, its design and reaction conditions such as applied potential, phenol concentration, co-solvent concentration and support electrolyte concentration were investigated to optimize the convection of phenol and the yield of hydroquinone.

No description available.

No description available.