Intrinsic barriers for H-atom transfer reactions

Hydrogen transfer reactions play a well-recognized role in coal liquefaction. While H-abstraction reactions between radicals and H-donors have been well-studied, understanding of structure-reactivity relationships remains surprisingly incomplete. Another form of hydrogen transfer known as radical hydrogen transfer (radical donation of H to an unsaturated compound) is currently the subject of much speculation. The barriers for identity reactions are key parameters in the Evans-Polanyi equation for estimating reaction barriers and are fundamentally significant for the insight they provide about bond reorganization energies for formation of transition state structures. Although knowable from experiment, relatively few H-abstraction identity barriers and no barriers for hydrocarbon radical hydrogen transfer reactions have been measured. This paper seeks to supplement and extend existing experimental data with results obtained by calculation. The authors have used ab initio and semiempirical molecular orbital methods (MNDO-PM3) to calculate barriers for a series of H-atom abstraction and radical-hydrogen-transfer identity reactions for alkyl, alkenyl, arylalkyl and hydroaryl systems. Details of this methodology and analyses of how barrier heights correlate with reactant and transition state properties will be presented and discussed

Organic tanks safety program waste aging studies. Final report, Revision 1

Uranium and plutonium production at the Hanford Site produced large quantities of radioactive byproducts and contaminated process chemicals that are stored in underground tanks awaiting treatment and disposal. Having been made strongly alkaline and then subjected to successive water evaporation campaigns to increase storage capacity, the wastes now exist in the physical forms of saltcakes, metal oxide sludges, and aqueous brine solutions. Tanks that contain organic process chemicals mixed with nitrate/nitrite salt wastes might be at risk for fuel-nitrate combustion accidents. This project started in fiscal year 1993 to provide information on the chemical fate of stored organic wastes. While historical records had identified the organic compounds originally purchased and potentially present in wastes, aging experiments were needed to identify the probable degradation products and evaluate the current hazard. The determination of the rates and pathways of degradation have facilitated prediction of how the hazard changes with time and altered storage conditions. Also, the work with aged simulated waste contributed to the development of analytical methods for characterizing actual wastes. Finally, the results for simulants provide a baseline for comparing and interpreting tank characterization data

Preliminary economic evaluation of the Alkox process

A new chemical process has been invented at Battelle Pacific Northwest Laboratories for converting alkanes to alcohols. This new chemistry has been named the Alkox Process.'' Pacific Northwest Laboratory prepared a preliminary economic analysis for converting cyclohexane to cyclohexanol, which may be one of the most attractive applications of the Alkox process. A process flow scheme and a material balance were prepared to support rough equipment sizing and costing. The results from the economic analysis are presented in the non-proprietary section of this report. The process details, including the flow diagram and material balance, are contained in separate section of this report that is proprietary to Battelle. 7 refs., 4 tabs

Hydrogen shutting pathways in thermal hydroliquefaction: Solvent-induced scission of coal model compound structures

It has been demonstrated that donor solvents play a key role in the scission of thermal stable bonds in coal model compounds and therefore it has been speculated that they will improve liquefaction efficiencies. The authors have been studying the transfer of hydrogen from dihydroarene donor solvents to arene model compounds to quantify the barriers of competing hydrogen transfer mechanisms. Hydrogen can be transferred between arene rings by a variety of pathways. The specific hydrogen transfer pathway or pathways can be predicted given an understanding of the thermochemistry of the reactants intermediates and products. The individual pathways that contribute to strong bond scission have been shown to be dependent on the dihydroarene donor and the arene acceptor. In this paper they quantify the hydrogen pathways between the solvent components anthracene and phenanthrene. In addition, they describe reaction conditions requiring consideration of an additional hydrogen transfer pathway: a multi-step nonipso hydrogen transfer to coal model compounds to evaluate the hydrogen transfer steps to cleave strong diarylmethane bonds in coal structures

Investigation of the potential of silica-bonded macrocyclic ligands for separation of metal ions from nuclear waste. [Macrocyclic ligands covalently bonded to silica gel]

This report describes the testing of some novel separations materials known as SuperLig{trademark} materials for their ability to separate efficiently and selectively certain metal ions from a synthetic, nonradioactive nuclear waste solution. The materials, developed and patented by IBC Advanced Technologies, are highly selective macrocyclic ligands that have been covalently bonded to silica gel. The SuperLig{trademark} materials that were tested are: (1) SuperLig{trademark} 601 for barium (Ba{sup 2+}) and strontium (Sr{sup 2+}) separation, (2) SuperLig{trademark} 602 for cesium (Cs{sup +}) and rubidium (Rb{sup +}) separation, (3) SuperLig{trademark} 27 for palladium (Pd{sup 2+}) separation, and (4) SuperLig{trademark} II for silver (Ag{sup +}) and ruthenium (Ru{sup 3+}) separation. Our observations show that the technology for separating metal ions using silica-bonded macrocycles is essentially sound and workable to varying degrees of success that mainly depend on the affinity of the macrocycle for the metal ion of interest. It is expected that ligands will be discovered or synthesized that are amenable to separating metal ions of interest using this technology. Certainly more development, testing, and evaluation is warranted. 3 figs., 11 tabs

Potential uses of silica-bonded macrocyclic ligands for separation of metal ions from nuclear waste

This paper explores the potential of a relatively new separation material that is obtained by covalently binding macrocyclic ligands to silica gel. Fortunately, neutral macrocyclic ligands can be bound to silica gel such that metal binding constants do not differ significantly from the binding constants of the free ligands so that selectivities of free macrocyclic ligands can be used in designing silica-bound materials with appropriate selectivities. Accordingly, macrocyclic ligands known to have selectivities for Pd{sup +2}, Ag{sup +}, Ru{sup +3}, Sr{sup +2}, and Cs{sup +} were covalently bound to silica gel. These materials were then tested for their ability to separate these ions from a synthetic test solution representative of a nuclear process waste stream. Cs{sup +} and Sr{sup +2} are of interest because their radioactive isotopes are major radioactive constituents of defense nuclear wastes accumulated at the Hanford site. Removal of precious metals such as Pd{sup +2}, Ag{sup +} and Ru{sup +3} present in nuclear defense waste are of interest not just because of their obvious economic value, but also because these metals may hinder the waste vitrification process for confining radionuclides