Nanoreinforced hemicellulose-based hydrogels prepared by freeze–thaw treatment

A novel hybrid hydrogel was prepared from hemicelluloses, polyvinyl alcohol, and chitin nanowhiskers by the freeze–thaw technique. The hydrogel was characterized by Fourier-transform infrared (FT-IR) spectrometry, scanning electron microscopy, X-ray diffraction analysis, cross-polarization (CP)/magic-angle spinning (MAS) ¹³C nuclear magnetic resonance (NMR), and swelling property and compressive strength measurements. Atomic force microscopy images of chitin implied that the size of whiskers reached nanometer level with average length of about 200 nm and width of 40 nm. The FT-IR and NMR results indicated that physical cross-linking rather than chemical reaction occurred during the gelation process. The mechanical properties of the hydrogels were significantly improved with increasing proportion of chitin nanowhiskers, with the highest compressive stress of 9.6 MPa being found for Gel-0.5. The results showed that the repeated freeze–thaw cycles induced physical cross-linking of packed chains by hydrogen bonds among the polymers, and the concentration of chitin nanowhiskers affected the hydrogel morphology and properties. It is suggested that hydrogels with good mechanical properties can be successfully prepared by this physical method, offering promise for tissue engineering applications.     

Bacteriostatic activities of N-substituted tris-thioureas bearing amino acid and aniline substituents

A series of tri-substituted thiourea derivatives were synthesized by the reaction of 1,3,5-triacetylbenzoyl isothiocyanate with aminoacids and aniline derivatives. All thiourea derivatives were characterized by FT-IR, ¹H and ¹³C NMR spectroscopy. Antibacterial activities against wild-type Escherichia coli American Type Culture Collection 8739 were determined by use of the turbidimetric methodto evaluate the effect of varying amino groups on the synthesized thioureas. Tris-thiourea derivatives bearing ortho-chloroaryl substituents showed excellent antibacterial activity against E. coli with minimal inhibitory concentration (MIC) of 96 ppm. The optimum inhibition was dependent on the type of amines and the position of the halogen in aniline.     

Synthesis of 5-(dimethylsilyl)pentylalkylferrocene-grafted HTPB (alkylFc-HTPB) via platinum-catalyzed hydrosilylation

In this work, at first alkylferrocene derivatives were synthesized according to procedure described in the literature. (5-Chloropentanoyl)ferrocene derivatives were prepared by Friedel–Crafts acylation of ferrocene and alkylferrocene derivatives with 5-chloropentanoyl chloride in dichloromethane, and AlCl₃ was used as catalyst. The corresponding 5-chloropentylferrocene derivatives were synthesized from reduction of these products by NaBH₄ in diglyme at 0 °C. Finally (5-alkylferrocenylpentyl)dimethylsilane was synthesized from reaction of 5-chloropentylferrocene derivatives with magnesium in THF and reaction of corresponding Grignard reagents with chlorodimethylsilane in 82–87% yields. ¹H and ¹³C NMR, FT-IR spectroscopy supported the predicted structure of the product. Nine samples of alkylferrocene-grafted hydroxyl-terminated polybutadiene (alkylFc-HTPB) derivatives, containing different percent of iron, were synthesized by hydrosilylation reaction of [5-(alkylferrocenyl)pentyl]dimethylsilane with hydroxy-terminated polybutadiene (HTPB), in the presence of catalytic amount of the hexachloroplatinic acid (Speier’s catalyst). FT-IR spectroscopy was utilized to follow the progress of the reaction, by monitoring the loss of the Si–H absorption at 2110 cm^?1, and the reaction was completed in 24 h. Some properties of resulting prepolymer like viscosity, glass transition temperature and iron percentage as important parameters in production of composite propellants were investigated. For example, the viscosity increased with increasing iron content because of the greater extent of ferrocene grafting in the polymer.     

Grafting onto microfibrils of native cellulose

Attempts to modify the surface of oxidized cellulose microfibrils were made using amine terminated molecules. First, native cellulose was oxidized with catalytic amounts of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO), sodium hypochlorite and sodium bromide in water. The primary alcohol moieties were selectively oxidized into carboxyl groups. Then, the oxidized cellulose was coupled with amines derivatives by a peptidic reaction by using carbodiimide and hydroxysuccimide as catalyst and amidation agent. The obtained coupled cellulose showed low polarity, with stability in non-polar solvents. The products were characterized by FTIR, ¹³C NMR, rheology and conductometric titration as well as transmission electron microscopy. Their hydrophobic character was evaluated by observing their behavior in polar and non-polar solvents.     

Bis-Thiourea Bearing Aryl and Amino Acids Side Chains and Their Antibacterial Activities

Abstract

A series of symmetrical 1,3-bis thiourea 1a–e and 1,4-bis thiourea derivatives 2a–e have been successfully synthesized from the reactions of amines with 3-acetylbenzoyl isothiocyanate and 4-acetylbenzoyl isothiocyanate, respectively. All the synthesized compounds were characterized by FT-IR spectroscopy and ¹H and ¹³C NMR spectroscopy. The compounds were screened for their antibacterial activity by turbidimetric method using gram-negative bacteria (E. coli ATCC 8739) using turbidimetric method. The newly synthesized bis-thiourea derivatives bearing aryl side chains showed good antibacterial activity against E. coli. The effect of the molecular structure of the synthesized compounds on the antibacterial activity is discussed.     

Synthesis of new indolylpyrrole derivatives via a four-component domino reaction between arylglyoxals,acetylacetone, indole and aliphatic amines in aqueous media

A novel synthesis of indolylpyrrole derivatives is described by a four-component domino reaction between arylglyoxals, acetylacetone, indole and aliphatic amines in water as solvent at 60?°C without using any catalyst or promoter. The FT-IR, ¹H NMR, ¹³C NMR spectral and elemental analysis confirm the structures of the products.     

Spectroscopic and structural aspects of the reactions of 1,4-quinones with sulfur and nitrogen nucleophiles

A series of 1,4-benzoquinone derivatives from 2,5-dichloro-3,6-diethoxy-1,4-benzoquinone and 2,6-dichloro-3,5-diethoxy-1,4-benzoquinone were prepared by nucleophilic substitution reactions of sulfur and nitrogen nucleophiles. Spectral techniques (¹H NMR, ¹³C NMR, FT–IR, and LC–MS) were employed to structurally characterize the reaction products of alkoxy, chloro substituted-1,4-benzoquinones with thiols and amines in the presence of sodium carbonate in ethanol at room temperature. The orientations and the regioselectivity of the reactions of alkoxy, chloro substituted-1,4-benzoquinones with various thiol and amine nucleophiles are discussed.     

Synthesis of 5-alkoxy-4-amino-3-bromo-2(5H)-furanones containing benzene rings

Using KF as base and THF as solvent, different 5-alkoxy-3,4-dibromo-2(5H)-furanones were reacted with amines containing a benzene ring structure by Michael addition–elimination reaction at room temperature or 40 °C to give twenty-three 5-alkoxy-4-amino-3-bromo-2(5H)-furanones containing benzene rings, with yields of 21–86 % (mostly over 64 %). The structures of all the newly synthesized compounds were elucidated and confirmed by FTIR, UV, ¹H NMR, ¹³C NMR, and mass spectroscopy, elemental analysis, and X-ray single-crystal diffraction. This rapid synthesis of the series of 2(5H)-furanones derivatives with different bioactive units is not only an important synthetic strategy for 2(5H)-furanone derivatives but also a basis for synthesis of potential drug molecules for activity testing.     

Zinc templated synthesis—a route to get metal ion free tripodal ligands and lariat coronands, containing Schiff bases

A new series of tripodal receptors bearing imine linkages have been prepared in high yields, by a single step condensation reaction between tripodal aromatic amines and aldehydes, using zinc perchlorate as a template. The template cation leaves the pseudo cavity after the Schiff base condensation to give metal free multidentate ligands. These products have been characterized by ¹H, ¹³C NMR, IR, elemental analysis, UV-vis absorption spectroscopy and X-ray crystallographic studies. It has been seen that the presence of a coordinating atom such as O, S, and N at position-2 with respect to the carbonyl group, is mandatory for the reaction to proceed. The template reaction has been also successfully employed to synthesize a lariat type coronand by reacting the tripodal amine with a dialdehyde.     

Three-component reaction between amines,carbon disulfide and electron-deficient derivatives of chloropyridine or chlorobenzene: synthesis of 3,6-diazaspiro[4.5]deca-2,7,9-trien-6-ium chloride and dithioylcarbamates derivatives

In this study, three-component reaction of some primary and secondary amines with carbon disulfide in the presence of electron-deficient derivatives of chloropyridine or chlorobenzene in the CH₃CN as a solvent is reported. The reaction of primary amines with carbon disulfide and electron-deficient compounds of chloropyridine or chlorobenzene after 6–8 h afforded the three-component addition product. The reaction of secondary amines with carbon disulfide and electron-deficient compounds of chloropyridine or chlorobenzene after 3–4 h afforded the two-component addition product. The product(s) of reactions were purified by recrystallization or column chromatography and their structures were identified by spectroscopy techniques such as ¹H-NMR, ¹³C-NMR, IR, UV and elemental analysis. The reactions were carried out under mild conditions and without using a catalyst.     

Acid-base bifunctional catalysis of silica-alumina-supported organic amines for carbon-carbon bond-forming reactions

Acid-base bifunctional heterogeneous catalysts were prepared by the reaction of an acidic silica-alumina (SA) surface with silane-coupling reagents possessing amino functional groups. The obtained SA-supported amines (SA-NR2) were characterized by solid-state 13C and 29Si NMR spectroscopy, FT-IR spectroscopy, and elemental analysis. The solid-state NMR spectra revealed that the amines were immobilized by acid-base interactions at the SA surface. The interactions between the surface acidic sites and the immobilized basic amines were weaker than the interactions between the SA and free amines. The catalytic performances of the SA-NR2 catalysts for various carbon-carbon bond-forming reactions, such as cyano-ethoxycarbonylation, the Michael reaction, and the nitro-aldol reaction, were investigated and compared with those of homogeneous and other heterogeneous catalysts. The SA-NR2 catalysts showed much higher catalytic activities for the carbon-carbon bond-forming reactions than heterogeneous amine catalysts using other supports, such as SiO2 and Al2O3. On the other hand, homogeneous amines hardly promoted these reactions under similar reaction conditions, and the catalytic behavior of SA-NR2 was also different from that of MgO, which was employed as a typical heterogeneous base. An acid-base dual-activation mechanism for the carbon-carbon bond-forming reactions is proposed.     

Preparation and Properties of Novel Cyclophosphazenes Containing Cyanato Groups

Abstract

Novel cyclotriphosphazenes containing cyanato group (PZCN) derivatives were synthesized by a substitution reaction of 4-hydroxyphenoxycyclotriphosphazenes and cyanogen bromide (BrCN) in the presence of triethylamine (TEA). The PZCNs were characterized by FT-IR, liquid chromatography–mass spectrometry (LC-MS), ¹H NMR, ¹³C NMR, and ³¹P NMR spectroscopy. Curing reactions of the PZCNs were evaluated by FT-IR spectroscopy, thermogravimetry/differential thermal analysis (TG/DTA), and differential scanning, calorimetry (DSC). The PZCNs exhibited an exothermic peak due to curing within the temperature range of 140–300°C by DSC. The PZCNs were completely cured at 220°C. The cured PZCNs exhibited high thermal stability up to 350°C, a high char-forming capability, and electrical properties, such as dielectric constants (Dks) between 2.68 and 2.87, and dissipation factors (Dfs) between 0.008 and 0.013 at 1 MHz.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Preparation of novel symmetrical bistetrazole-carbazole derivatives through a one-pot Ugi-azide reaction

A series of new symmetrical tetrazole-based carbazole derivatives starting from the initially generated 3,6-diformyl-N-alkylcarbazoles were successfully synthesized through a one-pot Ugi-azide reaction in moderate to high yields. Simplicity, easily accessible chemicals, mild reaction conditions, and fast separation of the products with the formation of bistetrazole-based carbazole derivatives in one step are some advantages of this method. The structure of the products was characterized and confirmed by using spectroscopic techniques such as ¹H NMR, ¹³C NMR, FT-IR, and MS spectroscopy.     

Synthesis and stabilization mechanism of novel stabilizers for fullerene-malonamide derivatives in nitrocellulose-based propellants

Nitrocellulose (NC)-based propellants require stabilizers to avoid early decomposition or even explosion during storage. A series of novel fullerene-malonamide derivatives with different carbon chain lengths on the p-position of the benzene ring was synthesized as stabilizers for NC-based propellants through the Bingel reaction because of the excellent thermal stability and strong ability of these derivatives to eliminate free radicals. The molecular structures of these fullerene-malonamide derivatives were verified via ¹H nuclear magnetic resonance (NMR) spectroscopy, ¹³C NMR spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, ultraviolet–visible spectroscopy, and high-resolution mass spectrometry. Meanwhile, their stability was investigated using methyl violet, vacuum stability, and weight loss tests. Results indicated that the stability of the novel fullerene-malonamide derivatives was considerably better than that of traditional stabilizers, such as N,N′-dimethyl-N,N′-diphenylurea and diphenylamine. Moreover, these derivatives exhibited excellent thermal stability at high temperatures. The stability of the fullerene-malonamide derivatives also improved as the carbon chain length on the p-position of the benzene ring on C₆₀ increased. In addition, the stability mechanism of the fullerene-malonamide derivatives was studied through electron paramagnetic resonance spectroscopy, FT-IR spectroscopy, and liquid chromatography-mass spectrometry. Results turned out that the fullerene-malonamide derivatives could react with nitroxide radicals released from the pyrolysis of NC. Hence, these novel fullerene-malonamide derivatives can be used as promising stabilizers for NC-based propellants.     

Synthesis of some acylated 2-pyrazoline and chalcone derivatives

α-Haloesters containing the chalcone structure and α-haloamides containing the pyrazoline ring have been synthesized by reaction of substituted hydroxy chalcones and pyrazoline derivatives (prepared as reported elsewhere; J Chem 8(4):1574–1581, 2011) with chloroacetyl chloride in dry THF in the presence of Et₃N. The structures of the synthesized compounds were confirmed by IR, ¹H NMR, and (for some compounds) ¹³C NMR spectroscopy.     

Novel Regioselectively 6‐Functionalized Cationic Cellulose Polyelectrolytes Prepared via Cellulose Sulfonates

The synthesis of new 6‐deoxy‐6‐trialkylammonium cellulose derivatives obtained by nucleophilic displacement reactions of p‐toluenesulfonyl celluloses with various amines is described. Water soluble cellulosics could be prepared using a N,N‐dimethylformamide/water mixture as the reaction medium. Detailed studies concerning the influence of reaction time and temperature as well as the water content on the solubility of the products were carried out. Even the synthesis of large sample amounts was possible using optimized reaction conditions. The 6‐deoxy‐6‐trialkylammonium cellulose derivatives are water‐soluble even at low degrees of substitution, i. e., in the range of 0.2 and 0.5. The structure was confirmed by means of ¹H and ¹³C NMR spectroscopies.     

Synthesis of O‐(2,3‐dihydroxypropyl) cellulose in NaOH/urea aqueous solution: As a precursor for introducing “necklace‐like” structure

O‐(2,3‐dihydroxypropyl) cellulose (DHPC) samples were synthesized by etherification of cellulose with glycidol (GLY) in a NaOH/urea aqueous solution system under different reaction conditions, so that they had different degrees of ether substitution (DS) in both the overall and regional distributions. The characterization was made by NMR spectroscopy in order to clarify the effects of the molar ratio of in‐fed GLY to anhydroglucose unit and of the reaction temperature not only on the total and regional DSs but also on the molar substitution (MS_dhp) for the multireactive dihydroxypropyl group. The evaluation of MS_dhp was performed after complete propionylation of each DHPC sample. Determination of molecular weights was also conducted on the propionylated DHPCs by GPC analysis. As a preliminary extension, butyralization of DHPC was undertaken in aqueous solution by using p‐toluenesulfonic acid as catalyst together with butyraldehyde (BuA). Two‐dimensional NMR (¹H–¹³C gHSQC) spectra measurements revealed that the products contained butyral groups, owing to dehydration‐cyclization between the BuA‐carbonyl and the duplicate hydroxyls in the side chain of DHPC. Such butyral derivatives of cellulose are expected to be a promising functional material parallel or superior to poly(vinyl butyral) available for safety glass interlayers, etc. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3590–3597     

The Reaction Activity of Aromatic Carbonyl Compounds with Diphenylphosphine Oxide Studied by 31P NMR

Abstract

A series of α-hydroxyphosphine oxides were prepared by the reactions of diphenylphosphine oxide and aromatic carbonyl compounds and characterized by ¹H NMR, ¹³C NMR, ³¹P NMR, FT-IR, ESI-MS, and HR-MS spectra. The reaction rates and experimental conditions of aromatic aldehydes and aromatic ketones were obviously different due to the activity of their carbonyls. The different substituents of the aromatic aldehydes affected the reaction rate too, and the quantitative reactivity of their substituent conformed to the Hammett equation. The results were confirmed by ³¹P NMR spectroscopy.     

Preparation and characterization of novel hyperbranched poly(amido amine)s from Michael addition polymerizations of trifunctional amines with diacrylamides

Novel hyperbranched poly(amido amine)s containing tertiary amines in the backbones and acryl as terminal groups were synthesized via the Michael addition polymerizations of trifunctional amines with twofold molar diacrylamide. The hyperbranched structures of these poly(amido amine)s were verified by ¹³C NMR (INVGATE). The polymerization mechanisms were clarified by following the polymerization process with NMR method, and the results show that the reactivity of secondary amine formed in situ is much lower than that of the secondary amine in 1‐(2‐aminoethyl) piperazine (AEPZ) ring and the primary amine. The secondary amine formed in situ was almost kept out of the reaction before the primary and secondary amines in AEPZ were consumed, leading to the formation of the AB2 intermediate, and the further reaction of the AB2 yielded the hyperbranched polymers. The molecular weights and properties of poly(amindo amine)s obtained were characterized by GPC, DSC, and TGA, respectively. Based on the reaction of active acryl groups in the polymers obtained with glucosamine, hyperbranched polymers containing sugar were formed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5127–5137, 2005     

Bifunctional Heterogeneous Catalysis of Silica–Alumina‐Supported Tertiary Amines with Controlled Acid–Base Interactions for Efficient 1,4‐Addition Reactions

We report the first tunable bifunctional surface of silica–alumina‐supported tertiary amines (SA–NEt₂) active for catalytic 1,4‐addition reactions of nitroalkanes and thiols to electron‐deficient alkenes. The 1,4‐addition reaction of nitroalkanes to electron‐deficient alkenes is one of the most useful carbon–carbon bond‐forming reactions and applicable toward a wide range of organic syntheses. The reaction between nitroethane and methyl vinyl ketone scarcely proceeded with either SA or homogeneous amines, and a mixture of SA and amines showed very low catalytic activity. In addition, undesirable side reactions occurred in the case of a strong base like sodium ethoxide employed as a catalytic reagent. Only the present SA‐supported amine (SA–NEt₂) catalyst enabled selective formation of a double‐alkylated product without promotions of side reactions such as an intramolecular cyclization reaction. The heterogeneous SA–NEt₂ catalyst was easily recovered from the reaction mixture by simple filtration and reusable with retention of its catalytic activity and selectivity. Furthermore, the SA–NEt₂ catalyst system was applicable to the addition reaction of other nitroalkanes and thiols to various electron‐deficient alkenes. The solid‐state magic‐angle spinning (MAS) NMR spectroscopic analyses, including variable‐contact‐time ¹³C cross‐polarization (CP)/MAS NMR spectroscopy, revealed that acid–base interactions between surface acid sites and immobilized amines can be controlled by pretreatment of SA at different temperatures. The catalytic activities for these addition reactions were strongly affected by the surface acid–base interactions.