Potassium carbonate,a support for the green synthesis of azoles and diazines

A novel potassium carbonate mediated synthesis of 2‐amino‐1,3‐thia/oxa zoles, 2‐amino‐1,3,4‐thia/oxa diazines and 2‐hydrazino‐1,3,4‐thiadiazines has been described here. The use of K₂CO₃ allows for an aqueous workup thereby eliminating the organic solvent from both the reaction step and post reaction stage, without compromising the yield and reaction time.     

Large‐scale extrusion processing and characterization of hybrid nylon‐6/SiO2 nanocomposites

Solution impregnations, pulltrusion and film stacking are widely used methods to prepare thermoplastic composite materials. Extruders are used to melt the polymer and to incorporate fibers into the polymer in order to modify physical properties. In this article, the compounding of colloidal silica nanoparticles filled polyamide‐6 (PA‐6) is achieved using a twin‐screw extruder, which has a significant market share due to its low cost and easy maintenance. The experiments were performed at 250 rpm and the bulk throughput was 6 kg h^?1 with a pump pressure of 30 bars. The composites were characterized with nuclear magnetic resonance (NMR), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). As determined by WAXD, the PA‐6 showed higher amounts of γ‐phase when compared to other synthesis methods such as in situ polymerization. TEM pictures showed that the silica particles aggregated nevertheless, upon addition of 14% (w/w) silica the E‐modulus increased from 2.7 to 3.9 GPa indicating that an effective mechanical coupling with the polymer was achieved. The behavior, illustrated with dynamic mechanical analysis (DMA) curves, indicated that in general when a filled system is compared to unfilled material, the values of the moduli (E′ and E″) increased and tan δ decreased. Determination of molecular mass distribution of the samples by means of size exclusion chromatography (SEC) coupled to a refractive index (RI), viscosity (DV) and light scattering (LS) detector revealed that the addition of silica did not decrease the average molecular weight of the polymer matrix, which is of importance for composite applications. Copyright © 2004 John Wiley & Sons, Ltd.     

Facile route to 3,5-disubstituted morpholines: enantioselective synthesis of O-protected trans-3,5-bis(hydroxymethyl)morpholines

[reaction: see text] (3R,5R)-1 R1 & R2 = TBDPS, (3S,5R)-2 R1 = Bn,R2 = TBDPS, (3S,5S)-3 R2 & R2 = Bn. trans-3,5-Bis(benzyl/tert-butyldiphenylsilyloxymethyl)morpholines, promising candidates for the C(2)-symmetric class of chiral reagents, were prepared with excellent optical purity. A key step in the synthesis is the coupling of a serinol derivative with 2,3-O-isopropylideneglycerol triflate or its equivalent. This methodology was extended to the synthesis of chiral trans-3-(benzyloxymethyl)-5-(tert-butyldiphenylsilyloxymethyl)morpholine, a potentially useful chiral building block.     

Nanostructured Ion-Selective MCM-48 Membranes

Templated MCM-48 silica was prepared using CTAB as surfactant. The MCM-48 powders and thin films were characterized by different techniques. MCM-48 layers were deposited on macroporous α-alumina supports and silicon nitride microsieves. The water permeability of MCM-48 was compared with the permeability of conventional mesoporous γ-alumina membranes. The applicability of MCM-48 as ion-selective electric field-driven switchable interconnect for microfluidic devices was demonstrated.     

1,3‐Dimethyl‐2‐oxo‐4,6‐diphenyl‐1,2,3,4‐tetrahydropyridine‐3‐carbonitrile

The crystal structure of the title compound, C₂₀H₁₈N₂O, reveals a distorted half‐chair conformation of the central tetra­hydro­pyridine (THP) ring, with the cyano‐ and adjacent phenyl‐substituted C atoms displaced by 0.329 (1) and ?0.315 (1) Å, respectively, from the THP best plane. Steric interactions force the phenyl rings out of the THP plane by 49.21 (9) and 65.76 (5)°. The cyano moiety is coplanar with the THP plane.     

C—H⋯N and C—H⋯π interactions in 2‐ethoxy‐4,6‐diphenylpyridine‐3‐carbonitrile

The title compound, C₂₀H₁₆N₂O, has two mol­ecules in the asymmetric unit and the crystal structure shows that the central pyridine ring of each mol­ecule has a flat boat conformation. The terminal C atom in one of the mol­ecules is disordered over two positions, with relative occupancies of 0.594 (14) and 0.398 (14). Intermolecular C—H?N and C—H?π interactions and π–π stacking, along with intramolecular C—H?N and C—H?π interactions, help to stabilize the structure.     

Glass fiber reinforced composites of phenolic–urea–epoxy resin blends

The present work aims to modify conventional epoxy resin by blending with four different phenolic–urea oligomers. These oligomers are similar to phenolic–urea resin matrix and simultaneously function as amino curing agent for epoxy matrix. In this context, phenolic–urea oligomers were prepared respectively by polycondensation reaction of four phenols namely phenol, m-cresol, resorcinol and 1,5-dihydroxy naphthalene, respectively with formaldehyde and urea in presence of acid catalyst. The resulting oligomers were characterized by elemental analysis, spectral studies (IR & NMR), number average molecular weight $(\overline{M}n)$ estimated by non-aqueous conductometric titration and thermal stability by thermogravimetric analysis (TGA). Each of these oligomers was used in resin matrix as a blending component for the modification of commercial epoxy resin for fabricating glass fiber reinforced laminates. Finally these laminates were evaluated for their synergetic thermal stability, mechanical properties and chemical resistance to different reagents.     

Synthesis of isomeric triazolopyrrolopyrimidines

4‐Hydrazino‐7H‐pyrrolo[2,3‐d]pyrimidines ( 4 ) were cyclocondensed with formic acid or triethyl orthoformate to give 7H‐1,2,4‐triazolo[1,5‐c]pyrrolo[3,2‐e]pyrimidines ( 5 ) and 7H‐1,2,4‐triazolo[4,3‐c]pyrrolo‐[3,2‐e]pyrimidines ( 6 ) respectively. The [4,3‐c]‐isomers ( 6 ) were rearranged into thermodynamically more stable [1,5‐c]‐isomers ( 5 ). The identical compounds ( 5 ) were prepared using another route by reacting 3‐amino‐4‐imino‐7H‐pyrrolo[2,3‐d]pyrimidines ( 3 ) with formic acid or triethylorthoformate. Reaction of 2‐amino‐3‐cyanopyrroles ( 1 ) with triethyl orthoformate followed by hydrazinolysis afforded ( 3 ) via the formation of N‐ethoxymethylene‐2‐amino‐3‐cyanopyrroles ( 2 ).     

Magnetically Aligned Supramolecular Hydrogels

The magnetic‐field‐induced alignment of the fibrillar structures present in an aqueous solution of a dipeptide gelator, and the subsequent retention of this alignment upon transformation to a hydrogel upon the addition of CaCl₂ or upon a reduction in solution pH is reported. Utilising the switchable nature of the magnetic field coupled with the slow diffusion of CaCl₂, it is possible to precisely control the extent of anisotropy across a hydrogel, something that is generally very difficult to do using alternative methods. The approach is readily extended to other compounds that form viscous solutions at high pH. It is expected that this work will greatly expand the utility of such low‐molecular‐weight gelators (LMWG) in areas where alignment is key.