Cylodextrins effects in the substitution reaction of 4,4′-bpy for the aquo ligand in aquopentacyanoferrate (II): An estimation of the binding constants of the reactant and the transition state to cyclodextrins

The substitution reaction of 4,4′-bpy (4,4′-bipyridine) for the aquo ligand in aquopentacyanoferrate (II) was studied in solutions containing -, β- and γ-cyclodextrins. We conclude that the well-known pseudophase model is equivalent to the Brönsted equation in regard to the interpretation of the cyclodextrins effects on reactivity. The equivalence follows from the fact that both pseudophase and Brönsted approaches can be used to rationalize kinetic data and permit to quantify the inclusion of the aromatic ligand in the cyclodextrins.     

Brønsted acid-mediated opening of nitroso cycloadducts under anhydrous conditions

An unusual bicyclic hydroxamate resulted from C-O bond cleavage of acylnitroso hetero-Diels-Alder cycloadducts when treated with catalytic Brønsted acids under anhydrous conditions. Similarly, the formation of a nitrone was observed using one equivalent of triflic acid.     

Synthesis and Surface Acidity of MeAPO-5 Molecular Sieves

Metal substituted aluminum phosphate molecular sieves, MeAPO-5 (Me = Co, Mn, Fe(II), Fe(III), and Mg) were synthesized and characterized with X-ray diffraction and scanning electron microscopy. The acidity was determined by temperature programmed desorption of ammonia, Desorption peaks at around 200°C were observed for all the MeAPO samples studied. Additional desorption peaks at around 300°C were found in MnAPO-5, CoAPO-5, and MAPO-5. MnAPO-5, CoAPO-5, and MAPO-5 also show good activities toward the cracking reaction of cumene at 350°C, while Fe(II)APO-5 and Fe(III)APO-5 show some activity at 500°C. The order of the cracking activity correlates with the presence of strong acidic sites in MnAPO-5, CoAPO-5, and MAPO-5 as indicated by the TPD of ammonia.     

富硅超稳八面沸石研究：制备,表征,稳定性,羟基酸性及催化活性

用(NH_4)_2SiF_6二次合成法制备了Si/Al=4.2～7.1、结晶度大于94％的系列八面沸石(FSY样品),再于500℃水热处理得到相应的US-SY样品。XRD、DTA及IR研究发现US-SY样品较FSY样品有更高的热稳定性、骨架稳定性和酸强度,其裂解、歧化活性也优于FSY样品。     

The solubility of argon in aqueous solutions of a complex-ion electrolyte

From measurements of the solubility of argon in aqueous solutions of the complexion electrolyte t-[Co(en)₂NCSCl]Br at 25°C, the Setschenow parameter for this system is found to be +0.33₆. Using the scaled-particle theory of the salt effect with this value ofk ₅ and the Waddington crystal radius of the Br^– ion, 1.98 Å, the radius of the complex cation is calculated to be 3.71 Å. This value is in reasonably good agreement with that estimated from scale models of the t-[Co(en)₂-NCSCl]⁺ cation, about 3.9 Å. It is somewhat larger than the radius calculated from various semiempirical equations relating the molal volume of an ion at infinite dilution to its radius; values of r obtained in this manner range from 3.32 to 3.66 Å.Abstracted, in part, from D.P.'s M.S. thesis, June 1971.     

Nucleophilic reactivity of thiolate, hydroxide and phenolate ions towards a model O-arylated diazeniumdiolate prodrug in aqueous and cationic surfactant media

The kinetics of aromatic nucleophilic substitution of the nitric oxide‐generating diazeniumdiolate ion, DEA/NO, by thiols (L ‐glutathione, L ‐cysteine, DL ‐homocysteine, 1‐propanethiol, 2‐mercaptoethanol, and sodium thioglycolate) from the prodrug, DNP‐DEA/NO, has been examined in aqueous solution and in solutions of cationic DOTAP vesicles. Second‐order rate constants in buffered aqueous solutions (k_RS‐ = 3.48–30.9 M^?1 s^?1; 30 °C) gave a linear Brønsted plot (β_nuc = 0.414 ± 0.068) consistent with the rate‐limiting S_NAr nucleophilic attack by thiolate ions. Cationic DOTAP vesicles catalyze the thiolysis reactions with rate enhancements between 11 and 486‐fold in Tris‐HCl buffered solutions at pH 7.4. The maximum rate increase was obtained with thioglycolate ion. Thiolysis data are compared to data for nucleophilic displacement by phenolate (k_PhO‐ = 0.114 M^?1 s^?1) and hydroxide (k_OH‐ = 1.82 × 10^?2 M^?1 s^?1, 37 °C) ions. The base hydrolysis reaction is accelerated by CTAB micelles and DODAC vesicles, with the vesicles being ca 3‐fold more effective as catalysts. Analysis of the data using pseudo‐phase ion‐exchange (PIE) formalism implies that the rate enhancement of the thiolysis and base hydrolysis reactions is primarily due to reactant concentration in the surfactant pseudo‐phase. Copyright © 2009 John Wiley & Sons, Ltd.