Katarina Gibson

Difluoromethylene-containing compounds have attracted substantial research interest over the past decades for their ability to mimic biological functions of traditional functional groups while providing a wide variety of pharmacological benefits bestowed by the C–F bond. We report a novel strategy to access RCF2Br-containing heterocycles by regio- and enantioselective bromocyclization of difluoroalkenes enabled by chiral anion phase-transfer catalysis. The utility of this methodology was highlighted through a synthesis of an analogue of efavirenz, a drug used for treating HIV. Additionally, the synthetic versatility of the CF2Br intermediates was showcased through functionalization to a variety of enantioenriched α,α-difluoromethylene-containing products.

The authors examine the effective hydro-processing of residuum from heavy crude oils, through proper catalyst selection. Utilizing proper catalyst selection and application can make residuum hydroprocessing an attractive process route to lighter products, allowing flexibility to handle a wide range of feedstock properties. Chevron has analyzed the important catalyst properties and how they affect catalyst selection for, and catalyst application to, different residuum processing routes to transportation fuels. They have also examined the role of hydroprocessing in those routes. Data were obtained from commercial operation in Chevron's Richmond, Calif., and Pascagoula, Miss., refineries.

A central practice in the discipline of organic chemistry is the ability to solve certain fundamental problems, including predicting reactivity, proposing mechanisms, and designing syntheses. These problems are encountered frequently by both students and practitioners, who need to utilize vast amounts of content knowledge in specific ways to generate reasonable solutions. To gain insight into how one of these major problem types can be solved, we have investigated student approaches to complex predict-the-product problems through the detailed analysis of think-aloud interviews. This work led to the creation of a general workflow model that describes the reasoning pathways of students with varying levels of expertise when attempting to predict organic reactivity. The problems used in this study were designed to be non-trivial and potentially ambiguous to elicit “true” problem solving and discourage a purely memorization-based approach, even from more experienced organic chemists. Rich descriptions of undergraduate and graduate student interviews are provided, and student thought processes are characterized in terms of common problem-solving actions. These actions were developed into the workflow model using an iterative method that combined results from our analysis with the experiences of instructors and feedback from both undergraduate focus groups and graduate students. The workflow serves as both a potential instructional tool and a model for student thinking. This model is general enough to be applied to both successful and unsuccessful solution pathways by both novice undergraduates and more expert-like graduate students. Characteristics of more successful and more experienced problem solvers are investigated, and concrete strategies that can be recommended to students are discussed. The results of this study complement existing work on other fundamental problem types in organic chemistry and suggest a variety of teaching interventions to develop students into more successful organic problem solvers.

Deteriorating crude quality plus lower heavy fuel demand have encouraged refiners such as Chevron USA to consider conversion of residuum to more valuable light products. Chevron residuum hydrotreating unit will substantially improve conversion. Specifically tailored, noncylindrical systems of crude mixtures 10% Maya/ 90% Arab heavy for example, were designed to improve catalyst life. CCH system can perform better than standard RDS catalyst systems. The conversion of the vacuum bottoms fraction of the residuum feedstock is also discussed, few tailored catalysts giving better results.

Recent improvements in the Rheniforming process enable refiners to conserve petroleum by increasing efficiency for production of gasoline blending stocks, aromatic chemicals and hydrogen. These advances are based upon the development and commercial demonstration of an improved catalyst and new operating procedures. A new, less costly catalyst, Type E, is more active and even more stable and selective than previous Rheniforming catalysts. The high stability of the new catalyst makes its use advantageous for low pressure reforming, which gives high yields of blending stocks, aromatics and hydrogen. Improved catalyst stability allows operation at reduced gas circulation rates and decreased recycle compressor power requirements. The new operating procedures involve optimization of on-stream catalyst chemistry. Effective regeneration can be ensured through the use of catalyst samplers. New procedures have been developed for control of catalyst and recycle gas properties to maximize selectivity and run length. Experimental evidence indicates that long-cycle, semi-regenerative Rheniforming can maintain higher average selectivity than cyclic or continuous reforming processes using platinum-rhenium catalysts. Cyclic and continuous processes were developed in response to the high deactivation rates of platinum catalysts and their decline of selectivity with time on-stream. In contrast, with many feedstocks the far more stable platinum-rhenium catalysts showmore » large, gradual increases in selectivity that continue through an appreciable portion of each cycle. These selectivity increases are particularly large for feedstocks having low to moderate end points, including those used for production of aromatic chemicals. Consequently, platinum-rhenium catalysts can produce higher run-average liquid and hydrogen yields in long-cycle reforming than in processes involving frequent regeneration.« less