A Novel Thermomorphic System for Electrocatalytic Diels‐Alder Reactions

The discovery that lithium bis(trifluoromethane)sulfonamide (LiTFSI)/1‐nitropropane (PrNO₂) solution functions as a less polar alternative to lithium perchlorate (LiClO₄)/nitromethane (MeNO₂) solution has led to the development of a novel thermomorphic system for electrocatalytic Diels‐Alder reactions. Methyl cyclohexane (Me‐c‐Hex) can form a monophasic condition with LiTFSI/PrNO₂ solution at room temperature, enabling the use of hydrophobic dienophiles. After the electrochemical reaction, a biphasic condition can be formed at –50°C, where the cycloadducts are selectively recovered from the upper Me‐c‐Hex phase and the remaining lower LiTFSI/PrNO₂ solution can be reused.     

Computer-assisted design and lactonization of model seco-acid derivatives of lankanolide

In some cases, seco-acid derivatives (a precursor of macrolactone) did not cyclize to form the corresponding macrolactone. To design easily cyclizable seco-acid derivatives of lanaknolide, the conformation of several model seco-acids was calculated, and lactonization experiments of the seco-acids prepared from oleandomycin were carried out to elucidate the efficiency of the cyclization of the model seco-acid. The easily cyclable seco-acid was designed to be C8 exomethylene derivative of lankanolide seco-acid. On the other hand, seco-acid derivative having tertiary alcohol at C8 was predicted not to cyclize to form macrolactone.     

Reaction of o-carboxyphenyl sulfoxides with acetic anhydride : Kinetic studies on the neighboring group effect of ortho-carboxyl group in the oxygen exchange and Pummerer reactions

Kinetic studies on the concurrent oxygen exchange and racemization reactions and Pummerer reaction of o-carboxyphenyl sulfoxides with acetic anhydride were carried out. In the reaction of o-carboxyphenyl phenyl sulfoxide, ortho-carboxyl group was found to enhance the rates of both oxygen exchange and racemization about 180 times, and the rate of racemization was nearly twice that of oxygen exchange. In the reaction of alkyl o-carboxyphenyl sulfoxides, an intramolecular Pummerer reaction took place to give 3,1-benzoxathian-4-one derivatives, and the Pummerer reaction was accelerated about 140 times that of the usual unassisted Pummerer reaction of aryl methyl sulfoxide. A very small deuterium kinetic isotope effect (k_H/k_D = 1.07 with trideuterated-methyl o-carboxyphenyl sulfoxide) and the rate-enhancing effect of α-alkyl group were also noticed. The markedly large rate-enhancement of both oxygen exchange and the Pummerer reactions is undoubtedly caused by the neighboring group participation of carboxyl group in the rate-determining intramolecular acylation of sulfinyl O atom.     

Picosecond time-resolved fluorescence studies of intramolecular heteroexcimers

Intramolecular heteroexcimer formation processes in the excited state of p-(CH₃)₂N-C₆H₄-(CH₂)₃-(9-anthryi) (A₃) as well as p-(CH₃)₂N-C₆H₄-(CH₂)₃-(1-pyrenyl)(P₃ in hexane and 2-propanol have been investigated by means of picosecond time-resolved fluorescence measurements.     

Predictability of transport equations for pervaporation on the basis of pore-flow mechanism

In this paper a transport model for pervaporation based on the pore-flow mechanism was tested by examining whether it could describe main features observed in pervaporation experiments. The pervaporation systems used for the above test include mixtures of ethanol/n-heptane, methanol/ethanol, 2-propanol/water and cyclohexane/benzene. Membrane polymeric materials such as cellulose, cellulose diacetate-triacetate blend, polyamide, polyethylene and poly(γ-methyl- -glutamate) are also included in this study. Membranes are either asymmetric or homogeneous but not of composite nature. Separation of organic mixtures by vapor permeation was also discussed in relation to pervaporation.     

Mechanism of aerobic decomposition of Angeli's salt (sodium trioxodinitrate) at physiological pH

The recent determination that Angeli's salt may have clinical application as a nitrogen oxide donor for treatment of cardiovascular diseases such as heart failure has led to renewed interest in the mechanism and products of thermal decomposition of Angeli's salt under physiological conditions. In this report, several mechanisms are evaluated experimentally and by quantum mechanical calculations to determine whether HNO is in fact released from Angeli's salt in neutral, aerobic solution. The mechanism of product autoxidation is also considered.     

Stereochemistry of aldols: configuration and conformation of aldols derived from cycloalkanones and aldehydes

The structures of cycloalkanone-based threo and erythro aldols were investigated by systematic introduction of stereo-determining factors. The combination of single-crystal X-ray analysis and cryoscopic measurement and solution NMR and IR studies elucidated the detailed geometry of these typical aldols. Currently, X-ray diffraction is the only reliable spectroscopic method to determine the relative configuration of aldols. Empirical NMR analysis can be safely applied in only limited cases. In hydrocarbon solvents, many aldols exist as monomers with an intramolecular OH...O=C hydrogen bond, but some compounds are in an equilibrium with higher aggregates via intermolecular hydrogen bonds. The aldols take various staggered conformers, where the relative stabilities are controlled largely by torsional strain affected by the size and nature of substituents. The intramolecular and intermolecular hydrogen bonds, gauche interactions between the vicinal substituents, and sometimes CH/pi attractions significantly influence the distribution of conformers. The preferred structure in solution often differs greatly from the crystalline-state geometry.     

One-pot synthesis of nylon 6–clay hybrid

Nylon 6–clay hybrid is a molecular composite of nylon 6 and uniformly dispersed silicate layers of montmorillonite. One-pot synthesis of the hybrid was carried out by the following procedures. Montmorillonite was dispersed in water, and then ε-caprolactam, acid (phosphoric acid, hydrochloric acid, benzenesulfonic acid, isophthalic acid, trichloroacetic acid, or acetic acid), and 6-aminocaproic acid were added to the dispersion. The mixtures were reacted at 260°C for 6 h, yielding the nylon 6–clay hybrids (1potNCHs). X-ray diffraction revealed that the silicate layers of 1potNCH by phosphoric acid were uniformly dispersed in the nylon 6 matrix. The 1potNCH had excellent mechanical properties. The strength and the modulus of the hybrid increased compared with previously reported nylon 6–clay hybrid (NCH) synthesized by montmorillonite intercalated with 12-aminolauric acid. The heat distortion temperature (HDT) of the 1potNCH was 160°C, which was 8°C higher than that of NCH. In other 1potNCHs, montmorillonite had a smaller effect on the increase of those properties, and interlayer spacing of montmorillonite was observed at ca. 20 Å. © 1993 John Wiley & Sons, Inc.