Four new hydroxybenzotriazole derivatives have been synthesized. Two of them, N-tetradecyl-1-hydroxy-1H-benzo[d][1,2,3]triazole-6-carboxamide (2) and N-tetradecyl-1-hydroxy-1H-benzo[d][1,2,3]triazole-7-carboxamide (3), possess long alkyl chains, while the other two, 1-hydroxy-1H-benzo[d][1,2,3]triazole-6-carboxylic acid (4) and 1-hydroxy-1H-benzo[d][1,2,3]triazole-7-carboxylic acid (5), have carboxylate side chains. These compounds along with their parent unsubstituted 1-hydroxybenzotriazole (HOBt), 1, have been examined for the cleavage of p-nitrophenyl hexanoate (PNPH) and p-nitrophenyl diphenyl phosphate (PNPDPP) in comicelles with monovalent cetyltrimethylammonium bromide (CTABr) and the corresponding bis-cationic gemini surfactants 16-m-16, 2Br(-) of identical chain length at 25 degrees C and pH 8.2. The apparent pK(a) values of the HOBt derivatives in the comicelles of CTABr or 16-4-16 gemini surfactant have been determined from the rate versus pH profiles and were found to be comparable. Catalytic system 4/16-4-16 demonstrated over 2200- and 1650-fold rate enhancements in the hydrolysis of PNPDPP and PNPH, respectively, for identical reactions carried out at pH 8.2 and 25 degrees C in buffered aqueous media. The second-order rate constants for such bimolecular reactions were determined employing pseudophase micellar models. Experiments in which excess substrate was taken over HOBt derivatives demonstrated that the catalysts "turned over"; hydrolysis of the putative acylated or phosphorylated HOBt intermediates was rapid in either type of host micelles.
A new series of water compatible primary-tertiary diamine catalysts derived from natural primary amino acids bearing a hydrophobic side chain have been synthesized. These new primary-tertiary diamine-Brønsted acid conjugates bifunctional organocatalysts efficiently catalyzes the asymmetric direct syn selective cross-aldol reaction of different protected hydroxyacetone with various aldehydes in high yield (94%) and high enantioselectivity (up to 97% ee of syn) and dr of 91 : 9 (syn/anti) under mild reaction conditions.
Four new tetradentate 2,6-disubstituted pyridine and tridentate 2-substituted pyridine ligands were synthesized. Two of these compounds possessed a metal ion binding subunit in the form of a 2,6-disubstituted-4-N,N'-dimethylamine pyridine moiety. Cu(2+)-complexes of these ligands incorporated in cetyltrimethylammonium bromide (CTABr) micelles speeded the cleavage of p-nitrophenyldiphenyl phosphate and p-nitrophenyl hexanoate at pH 7.6. On the basis of a kinetic version of Job plot analysis, a 1:1 ligand/Cu(2+) stoichiometry was found to be the most active species. In CTABr micelles, the pK(a) values for the Cu(2+)-coordinated hydroxyl or pendant -CH(2)OH in these ligands were between 7.8 and 7.9. The metallomicellar systems displayed catalytic (turnover) behavior in the presence of excess substrates.
A direct vinylogous Michael reaction of γ-substituted deconjugated butenolides with nitroolefins has been developed with the help of a newly identified quinine-derived bifunctional catalyst, allowing the synthesis of densely functionalized products with contiguous quaternary and tertiary stereocenters in excellent yield with perfect diastereoselectivity (>20:1 dr) and high enantioselectivity (up to 99:1 er).
The effect of viscosity variation due to temperature rise and non-Newtonian behavior of the lubricant on the performance of hole-entry and slot-entry hybrid journal bearings system is the focus of this investigation. The performance characteristics of nonrecessed hybrid journal bearings operating with different flow controlling devices, i.e., constant flow valve, capillary, orifice, and slot restrictors, have been compared. Finite element method has been used to solve the Reynolds equation governing the flow of lubricant in the bearing clearance space along with the restrictor flow equation, energy equation and conduction equation using suitable iterative technique. The non-Newtonian lubricant has been assumed to follow the cubic shear stress law. The results indicate that variation in viscosity due to rise in temperature and non-Newtonian behavior of the lubricant affects the performance of nonrecessed hybrid journal bearing system quite significantly. The results further indicate that bearing performance can be improved by selecting a particular bearing configuration in conjunction with a suitable compensating device.
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