Activation conditions, conversion

Kragl and coworkers investigated using organic-solvent-free systems to overcome the thermodynamic limitations in the synthesis of optically active ketone cyanohydrins. With organic-solvent-free systems under optimized reaction conditions, conversions up to 78% with > 99.0 enantiomeric excess (ee) (S) were obtained. Finally, 5 mL of (S)-acetophenone cyanohydrin with an ee of 98.5% was synthesized using MeHNL [52]. 

Because the composition and nano-scale structure of a catalyst depend on the temperature and the gas environment, it is important to measure catalyst activity under conditions experienced in the industrial converters. For the sulphuric acid catalysts, the activity for conversion of S02 to S03 was measured in the set-up shown in Fig. 9. 

The potential activation of different Lewis acid catalysts and their load effect when used in combination with this solvent were explored, in order to determine the improvement of rates and selectivity to the endo and exo isomers. The list of Lewis acid catalysts included Li(OTf), Li(NTf2), Znl2, AICI3, BF3, HOTf, HNTf2, Ce(0Tf)4 5H20, Y(OTf)3, Sc(OTf)3, Sc(NTf2) and a blank without any Lewis acid. The reaction conditions were as follows 2.2 mmol of cyclopentadiene + 2.0 mmol of dienophile + 0.2 mol% of catalyst in 2 mL [hmim][BF4]. When no catalyst was added, the two ketones (R =Me-C=0 R2 = R3 = H and Ri=Et-C=0 R2 = R3 = H) showed modest activity ( 50% in 1 h) with endojexo selectivity = 85/15. Whereas acrolein showed modest activity (59% conversion in 2 h), methacrolein and crotonaldehyde were inert without a Lewis acid catalyst. Acrylonitrile and methyl acrylate underwent low conversions in 1 h (16-17%) whereas, N-phenylmaleimide, maleic anhydride and 2-methyl-1,4-benzoquinone showed complete reaction in 5 min with high endo isomer yields. 

In a previous patent, Bayense et al. reported the use of ETS-10 and ETS-4 for the transesterification of TGs with alcohols.In their studies, both batch and fixed bed reactors were used to conduct the reaction. Under batch conditions, reactions were carried out at 220°C, 21 bar, and a catalyst loading of 0.23 wt% based on total autoclave content. Experiments with soybean oil and methanol, at a methanol/oil ratio of 4.2, resulted in 69.0% total oil conversion with an ester yield of 52.6% for ETS-10 and 96.9% conversion with an ester yield of 85.7% for ETS-4. When tallow was used under the same conditions, conversion and ester yield were 30.6% and 19.1% for ETS-10 and 44.1% and 29.6% for ETS-4, respectively. The slightly better activity shown by ETS-4 might imply that only basic sites at the pore opening of these zeolites were catalyzing the reaction. The effective radius of the TG molecule is such that it can not enter through the small pore openings of ETS-4 (diameter of 3.7 A) or even ETS-10... 

Protected-amino phosphonic acid monoesters 51 are usually activated by conversion to the phosphonochloridates 52, then coupled with appropriate amine components such as C-protected amino adds or peptides to give phosphonoamidates 53 (Scheme 17). This procedure is in contrast to typical peptide coupling conditions, in which carboxylic acid chlorides are avoided because of their susceptibility to epimerization at the a-carbon. Since enolate-... 

Whereas the triester reacts with a range of sulfur nucleophiles, the corresponding diester does not react with thionucleophiles under ambient conditions (Eq. 8), suggesting that the precursor, which is a diester, must be activated for conversion to MPT. This activation could involve the C3 hydroxyl group of the precursor, which is missing in the model, or Lewis acidic groups present in molybdopterin synthase. 

Supercritical C02 has also recently attracted much attention as a reaction medium for C-H bond activation, because C02 is miscible with organic compounds, including organometallic compounds, and potentially stable toward alkane activation conditions. We have successfully applied supercritical C02 to the carbonyla-tion and dehydrogenation of hydrocarbons [34], The technique is effective for conversion of gaseous substrates such as methane and ethane [35]. 

Platinum (IV) Structures. The oxidation state of the platinum atom in platinum coordination compounds determines the steric configuration of the molecule platinum(II) structures are planar molecules, while platinum(IV) derivatives assume an octahedral shape. Though it was hoped that these differences could be used to circumvent platinum resistance, the two compounds developed in the clinic, iproplatin and ormaplatin, have not proven useful. In the case of the former, testing in Phase-II trials failed to reveal activity. In the case of ormaplatin, the platinum(IV) configuration is not maintained under biological conditions conversion to a platinum(II) metabolite occurs within minutes [14], A series of novel platinum(IV) and mixed ammine/amine derivatives being developed at the Institute for Cancer Research are described in this volume by Kelland. 

Therefore, to compare the catalytic activity, or better the catalytic performance, of a series of catalysts, several factors such as reaction conditions, conversion, and selectivity must be taken into account. 

Block Polymer Made with Active and Inactive Polypropylene. Inactive polypropylene powder in hexane suspension was treated with (CH3CH2)2A1C1, TiCl3, water, N,N-dimethylaminoethyl methacrylate, and benzoyl peroxide under the same conditions used to prepare AFR polymer. Just as for the polypropylene-methylvinylpyridine-acrylonitrile system, the inactive polypropylene did not show evidence of incorporation of the free radical polymer (Table XIV). When inactive polypropylene was used, the —COOR absorbance of the polymer was only about 10-30% as great as the —COOR absorbance with active polypropylene. With active polymer conversion to block formation increased as the... 

In these examples, precursors of the enzyme-catalysed reaction act as feed-forward inhibitors (AMP for PFK and citrate for FBPase). The plenty signal F26BP (elevated as a result of the precursor elevated blood glucose conditions) also activates PFK. Conversely, down the track , end products act as feedback inhibitors (ATP and citrate for PFK and F26BP - that can be loosely seen as an end product of blood glucose elevation by gluconeogenesis - for FBPase). 

Fig. 17 shows that a large amount of carbon was deposited without loss of much catalytic activity. The conversion of both ethane and propane declined gradually to a similar degree, possibly indicating that some encapsulated carbon was forming in parallel with weakly or non-deactivating filamentous carbon (Fig. 18). At higher steam-to-carbon ratios under otherwise similar conditions, the conversion curves are almost stable, indicating that carbon was the main cause of deactivation.

The specific reaction ( activation ) conditions for the conversion of catalyst precursors to unsupported catalysts have a direct effect on the catalytic activity and dispersion. The importance of reaction intermediates in decomposition of ammonium heptamolybdate and ammonium tetrathiomolybdate, and the sensitivity of these intermediates to reaction conditions, were studied in coal liquefaction systems. Recent results indicate that optimization of activation conditions facilitates the formation of a highly dispersed and active form of molybdenum disulfide for coal liquefaction. The use of the catalyst precursors ammonium heptamolybdate, ammonium tetrathiomolybdate, and molybdenum trisulflde for the conversion of coal to soluble products will be discussed. 

The degree of ionization of acidic and basic antimicrobial agents depends on pH. Some compounds are active only in the unionized state (e.g., phenolics) whereas others are preferentially active as either the anion or cation. It therefore follows that the activity of a particular concentration of an agent will be enhanced at a pH that favors the formation of the active species. Thus, cationic antibacterials such as acridines and quaternary ammonium compounds are more active under alkaline conditions. Conversely, phenols and benzoic acid are more active in an acid medium. Chlorbutol is less active above pH 5 and unstable above pH 6. Phenylmercuric nitrate is only active at above pH 6 whereas thiomersal is more active under acid conditions. The sporicidal activity of glutaraldehyde is considerably enhanced under alkaline conditions whereas hypochlorites are virtually ineffective at above pH 8. 

In other words, under standard-state conditions in which the concentrations of glucose-6-phosphate, glucose, and Pi are all maintained at a steady-state level of unit activity, the conversion of 1 mole of glucose-6-phosphate to 1 mole of glucose and 1 mole of Ps liberates 3138 cal. 

Experience has shown the experimental conditions in which all the above cited catalysts are very active. Tar conversions... 

Heat shock transcription factor (HSF) is part of the family of heat shock factors that are activated and bind to DNA induced by OS. Several chemicals, heat shock, or conditions that generate abnormally folded proteins activate HSFl conversion from a monomer to a trimer state (Liu et al., 1996). lodoacetamide (IDAM), an alkylating agent, activates the transcription of Hsp 70 gene (Liu et al., 1996). The depletion of GSH induces oxidation of protein thiols, denaturation, and aggregation of proteins (Freeman et al., 1997). Alkylating agents that deplete GSH increase HSFl (Liu et al., 1996) and induce trimerization of HSFl. 

In addition, the tetrafluoroborate salt of P-NH-NH-P complex 22 showed slightly better activity (95% conversion) than the diimine precatalyst 29 under identical conditions. This... 

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