Controlled Radical Polymerization of Vinyl Acetate Mediated by a Bis(imino)pyridine Vanadium Complex

Source type: Prin

The Contribution of Molecular Modeling to the Knowledge of Pesticides

Non

Thermochemische Einsicht in einige "Green Chemistry" Prozesse: Experiment und Ab Initio Berechnungen

This work is addressed to the experimental investigation, analysis, and predicting of energetic effects of chemical compounds and reactions. Thermodynamic properties of cyclic alkylcarbonates and ionic liquids have been studied. The subject under study is aimed for generating a broad and reliable database of enthalpies of formation. Such database is required in order to get insight into quantitative structure-energy relationships in organic compounds in terms of group-additivity values.Diese Arbeit ist der experimentellen Untersuchung, Analyse und Vorhersage von energetischen Effekten chemischer Verbindungen und Reaktionen gewidmet. Es werden allgemeine thermodynamische Eigenschaften von zyklischen Alkylcarbonaten und ionische Flussigkeiten untersucht. Die Arbeit leistet ein Beitrag zur Schaffung einer zuverlassigen Datenbasis von Standardbildungsenthalpien. Solche Datenbasis ermoglicht, Einsicht in quantitative Verhaltnisse der Struktur-Energie-Beziehung zu bekommen und fur organische Stoffe gruppenadditive Werte zu ermitteln

Lignin Hydrothermal Liquefaction into Bifunctional Chemicals: A Concise Review

Lignin, the second largest biomass after cellulose is underutilized. Yet, it remains the only natural source of aromatic, and phenolic compounds. It is imperative to, amidst the expanding interest on biomass conversion, to accord the necessary attention towards lignin degradation into value added chemicals. Specifically, its phenyl, guaiacyl, and syringyl derivatives. Understanding lignin degradation chemistry, goes a long way in its selective valorization into fuels and chemicals via thermochemical routes such as hydrothermal liquefaction (HTL). Therefore, development of technologies targeting value addition of products and by-products from lignin, would undoubtedly give way to emerging markets in the industry. Previous review papers focused on the general HTL of biomass, food waste, algae, and their model compounds. However, review on HTL of lignin is scarcely available. This paper presents the detailed literature analyses of the current trend in lignin degradation via HTL. Effect of HTL conditions including temperature, heating rate and catalyst has been reviewed. In-depth discussion on use of ionic liquids as catalyst for HTL of lignin has also been compiled. Other lignin degradation techniques such as pyrolysis and hydrolysis were also discussed. This is aimed at bringing together an up-to-date information on lignin degradation into selected chemical intermediates

Development of thermodynamic frameworks for the reliable prediction of properties of key compounds and intermediates obtained from biomass

The reliable thermochemical data are required for the design and development of new technologies for valorisation biomass. Based on the conducted thermochemical research, a “centerpiece” approach to predict thermodynamic properties was developed. The evaluated thermochemical properties of substituted benzenes, glycerol ethers, and indole derivatives were used for validation and refinement of the “centerpiece” approach.Die zuverlässigen thermochemischen Daten werden für das Design und die Entwicklung neuer Technologien zur Steigerung des Werts von Biomasse benötigt. Basierend auf erweiterten experimentellen Arbeiten wurde ein „Herzstück“-Ansatz zur Vorhersage thermodynamischer Eigenschaften entwickelt. Die evaluierten thermochemischen Eigenschaften von substituierten Benzolen, Glycerinethern und Indolderivaten wurden zur Validierung und Verfeinerung des „Herzstück“-Ansatzes verwendet

Palladium(II) and platinum(II) synthetic peptidases: residue- and sequence-selective hydrolysis and the photochemistry of sulfoxides, S,C-sulfonium ylides, and sulfilimines: unimolecular bond cleavage

In this dissertation the photochemistry of sulfoxides, sulfilimines, and S,C-sulfonium ylides was explored both computationally and experimentally. Dibenzothiophene-S-oxide has been previously shown to undergo deoxygenation to form dibenzothiophene and a reactive intermediate believed to be O(3P). In this study, the photochemistry of S,C-sulfonium ylides of thiophenes was explored and shown to result in unimolecular bond scission of the S-C ylidic bond to give the corresponding sulfide and a reactive intermediate, analogous to the chemistry of dibenzothiophene -S-oxide. Chemical trapping studies provide indirect evidence that the reactive intermediate produced upon photolysis is a carbene.;The mechanism of unimolecular bond cleavage for sulfoxides was further explored computationally by generating the potential energy surfaces (PES) of thiophene-S-oxide and selenophene-Se-oxide as a function of S-O and Se-O bond length using the CASSCF method. Energy corrections were obtained with a second-order perturbation theory (MRMP2). The results for thiophene-S-oxide and selenophene -Se-oxide indicate that the second triplet excited state of each provide nearly barrierless route toward S-O and Se-O bond dissociation. The potential energy diagrams offer a new explanation for the experimentally observed unimolecular bond cleavage of DBTO and DBSeO, in which intersystem crossing from an excited singlet state to a dissociative T2 state provides a pathway to deoxygenation products. This mechanism is consistent with the increased quantum yields of deoxygenation that were experimentally observed for heavy-atom substituted sulfoxides.;The bond dissociation enthalpies (BDEs) of several sulfoxides, sulfilimines, S,C-sulfonium ylides, and selenoxides were also estimated by applying MP2/6-311++G(3df,2p)//MP2/6-31G(d,p), G3, and other computational methods. Selenoxides have the weakest ylide bond strengths, followed by N- H sulfilimines and CH2-S,C-sulfonium ylides. Sulfilimine and S,C-sulfonium ylides are stabilized by electron withdrawing substituents on N or C, respectively. Incorporation of the S or Se atom into a ring system that stands to gain aromaticity upon deoxygenation results in weaker BDEs.;Finally, the elimination reactions of sulfoxides, sulfilimines, and S,C-sulfonium ylides were studied computationally. We report the reaction enthalpies and activation barriers of the forward and reverse reactions for related sulfilimines, S,C-sulfonium ylides, and a sulfoxide. Our results indicate that a major factor affecting the relative ease of reactivity is the strength of the S-Calpha bond. Resonance stabilization of the ylide nitrogen of sulfilimines and the ylide carbon of sulfonium ylides with electron-withdrawing groups effectively delocalizes the charge rendering the ylide less nucleophilic and thereby less reactive toward eliminations. Additionally, our results show that among the compounds tested, the S-C alpha bond of compounds with electron-withdrawing substituents is the strongest, further limiting the reactivity of these ylides. The estimated reaction enthalpies of S,C-sulfonium ylides from this study suggest that these compounds would be viable reactants for mild preparation of a variety of alkenes