Efficient and continuous monoacylation with superior selectivity of symmetrical diamines in microreactors

Efficient and continuous monoacylation of symmetrical diamines performed in microreactors yielded superior selectivity to that predicted by statistical considerations. It is highly valuable that the kinetically controlled product in high yields was achieved without any special catalyst at ambient temperature.     

Selective monoacylation of symmetrical diamines via prior complexation with boron

[reaction: see text] Pretreatment of a symmetrical primary or secondary diamine with 9-BBN prior to the addition of an acyl chloride significantly suppressed undesired diacylation, and the product of monoacylation predominated. The reactive preference is interpreted as the result of a selective deactivation of one nitrogen atom of the diamine by 9-BBN.     

Synthesis and characterization of new polyamides derived from di(4-cyanophenyl)isosorbide

New optically active polyamides were synthesized according to two ways: using a microwave-assisted polycondensation of an optically active isosorbide-derived diacylchloride with different aromatic diamines in NMP and using interfacial polymerization from an isosorbide-derived diamine with different diacylchlorides. The polymers are obtained with inherent viscosities in the range from 0.11 to 1.05 dL/g. The DSC and TGA measurements clearly demonstrate the high thermal stability of these polymers when considering the range of the melting points from 200 °C to 300 °C and the absence of decomposition till 350 °C.     

Diglycidylphenylphosphate based fire retardant liquid crystalline thermosets

Organophosphorus liquid crystalline thermosets (LCTs) were developed using diglycidylphenylphosphate (DGPP) and various aromatic diamines. DGPP was prepared by the esterification of phenylphosphorodichloridate with glycidol. 2,5-Bis(p-aminophenyl)-1,3,4-oxadiazole (BPOD) was synthesized and three different commercial diamines, 4,4′-diaminodiphenyl sulphone (DDS), 4,4′-diaminodiphenyl methane (DDM) and biphenyl diamine (BPD) were used as curing agents. The mesomorphic behaviour of DGPP/diamine mixtures and their curing kinetics were monitored by differential scanning calorimetry and hot stage optical polarized microscopy. The thermogravimetric analysis data showed that the LCTs are stable in the range 261-292 °C and afford 36-48% char yield. The limiting oxygen index values are between 35 and 47 proving fire retardance. The mechanical properties of the cured LCTs were characterized by dynamic mechanical analysis.     

N-Acylbenzotriazole: convenient approach for protecting group-free monoacylation of symmetric diamines

Monatshefte für Chemie - Chemical Monthly - An efficient green route for monoacylation of aromatic diamines, namely o-phenylenediamine and p-phenylenediamine and aliphatic diamines...     

Greener and rapid access to bio-active heterocycles: room temperature synthesis of pyrazoles and diazepines in aqueous medium

An expeditious room temperature synthesis of pyrazoles and diazepines by condensation of hydrazines/hydrazides and diamines with various 1,3-diketones is described. This greener protocol was catalyzed by polystyrene supported sulfonic acid (PSSA) and proceeded efficiently in water in the absence of any organic solvent within 1-2 min.     

Stepwise dansyl grafting on the kaolinite interlayer surface

A block copolymer (PS-b-poly(l-Glu)) composed of polystyrene and poly(l-glutamic acid) was used as a stabilizer for dispersion polymerization of styrene. When dispersion polymerization of styrene was conducted at 70 °C in 80% dimethylformamide-water with 0.5 wt% PS-b-poly(l-Glu), spherical polystyrene particles with D_n = 0.72 μm and narrow size distribution were obtained. Whereas AIBN concentration did not have any effects on particle size, molecular weight of the polystyrene particles was strongly dependent on the initiator concentration. As concentration of the PS-b-poly(l-Glu) increased from 0.2 to 1.0 wt%, particle size decreased from D_n = 0.91 to 0.69 μm with keeping surface area occupied by one poly(l-glutamic acid) chain about S = 50 nm². On the other hand, an increase in initial concentration of styrene from 2 to 20 wt% caused an increase in particle size from D_n = 0.48 to 1.36 μm and a decrease in surface area per poly(l-glutamic acid) block from S = 91 to 45 nm². Colloidal stability of the polystyrene particles in aqueous solution was responsive to pH due to the surface-grafted poly(l-glutamic acid). For dispersion polymerization of styrene, the PS-b-poly(l-Glu) functions as both a stabilizer and a surface modifier.     

Capillary zone electrophoresis with pre-column NDA derivatization and amperometric detection for the analysis of four aliphatic diamines

A method was developed for the analysis of four aliphatic diamines by capillary zone electrophoresis using pre-column derivatization with naphthalene-2,3-dicarboxaldehyde (NDA)/CN⁻ and amperometric detection. The pre-column derivatization reaction conditions including the molar ratio of NDA to amines, the cyanide concentration, the pH value of derivatization buffer, and the reaction time, were investigated. The separation of four derivatives of aliphatic diamines has been optimized by capillary zone electrophoresis (CZE) using end-column amperometric detection with a carbon fiber microelectrode, at a constant potential of 0.7 V versus SCE. The optimum conditions for the separation were 10 mM Tris-H₃PO₄ (pH 4.0) for the running buffer solution, 15 kV for the separation voltage. The detection limits for diaminopropane, putrescine, cadaverine, diaminohexane were 6.7×10⁻⁸, 5.1×10⁻⁸, 1.9×10⁻⁷ and 3.8×10⁻⁷ M, respectively (S/N=3). The proposed method was applied to the determination of aliphatic diamines in a lake water sample by the standard addition method. The recovery of these amines in water was 89.9-107%.     

Preparation and properties of new ortho-linked polyamide-imides bearing ether, sulfur, and trifluoromethyl linkages

A CF₃-containing diamine, 2,2′-thiobis-[4-methyl(2-trifluoromethyl)4-aminophenoxy) phenyl ether] (DA), was successfully synthesized from 2-2′-sulfide-bis-(4-methyl phenol) and 2-chloro-5-nitrobenzotrifluoride. The sulfur containing diimide-diacid (DIDA) was prepared by condensation reaction of diamine DA and trimellitic anhydride. A series of novel organic-soluble polyamide-imides (PAIs) bearing flexible ether and sulfide links, electron-withdrawing trifluoromethyl groups and ortho-phenylene units were synthesized from DIDA, by direct polycondensation with various aromatic diamines in N-methyl-2-pyrrolidone using triphenyl phosphite and pyridine as a condensing agent in the presence of dehydrating agent (LiCl). The polyamide-imides were obtained in high yields and possessed inherent viscosities in the range of 0.42-0.95 dL g⁻¹. All of the polymers were amorphous in nature, showed outstanding solubility and could be easily dissolved in amide-type polar aprotic solvents (e.g., N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide) and even dissolved in less polar solvents (e.g., pyridine and tetrahydrofuran). They showed good thermal stability with glass transition temperatures between 195-245 °C, 10% weight loss temperatures in excess of 485 °C, and char yields more than 50% at 700 °C in nitrogen atmosphere. Moreover, these PAIs possessed low refractive indexes (n = 1.57-1.59) and low birefringence (Δ ≈ 0.02) due to the trifluoromethyl pendent groups and thioether bridged ortho-catenated aromatic rings that interrupt chain packing and increase free volume.     

Heterogeneous bimetallic Pt-Sn/γ-Al2O3 catalyzed direct synthesis of diamines from N-alkylation of amines with diols through a borrowing hydrogen strategy

Direct synthesis of diamines has been efficiently realized from the N-alkylation of amines with diols by means of heterogeneous bimetallic Pt-Sn/γ-Al₂O₃ catalyst (0.5 wt % Pt, molar ratio Pt:Sn = 1:3) through a ‘Borrowing Hydrogen’ strategy under ligand-free conditions. The present methodology provides an environmentally benign route to diamines.     

Degradation of crosslinked unsaturated polyesters in sub-critical water

The degradation of unsaturated polyesters crosslinked with styrene was performed in sub-critical water (SCW) in the absence and presence of organic additives. The unsaturated polyesters were de-crosslinked by hydrolysis of ester chains to form polystyrene derivatives on SCW treatment at 300 °C. With an increase in treating time, carboxylic acid groups in the polystyrene derivatives were turned into carboxylic anhydride groups in SCW. The de-crosslinking rate was much enhanced on SCW treatment in the presence of hydroxy compounds with a long alkyl chain and alkylamines, while carboxylic acids, benzenesulfonate salts, and quaternary ammonium salts were ineffective even though they had a long alkyl chain. The degree of de-crosslinking was reduced in the presence of diamines and amino acids because re-crosslinking at both ends of the additive molecules proceeded.     

Novel poly(amide-imide)s from 2,6-bis(5-amino-1-naphthoxy) pyridine

Reaction of 5-amino-1-naphthol with 2,6-dichloropyridine resulted in preparation of 2,6-bis(5-amino-1-naphthoxy) pyridine (AN). This pyridine-based ether diamine was reacted with two moles of trimellitic anhydride (TMA) to synthesize related diimide-diacid (DIDA). Direct polycondensation reaction of DIDA with different diamines in the presence of triphenyl phosphite (TPP) afforded seven different poly(amide-imide)s. All the polymers were characterized and their physical and thermal properties were studied. The inherent viscosity of the polymers was about 0.44-0.50 dl g⁻¹ and they showed high thermal stability.     

Synthesis of polystyrene beads loaded with dual luminophors for self-referenced oxygen sensing

Dispersion polymerization has been successfully applied to synthesize monodisperse polystyrene beads loaded with SiOEP and PtOEP for self-referenced oxygen sensing. The polystyrene beads became larger in size as the concentration of initiator was increased due to the reduction of primary particles precipitated from the polymerization medium. The dual luminophors showed similar absorption spectra but two distinctive emission spectra with peaks at 580 and 650 nm for SiOEP and PtOEP, respectively. While the emission of SiOEP exhibited no response to oxygen, the luminescence intensity of PtOEP was monotonically dependent on the concentration of oxygen. From the Stern-Volmer plot, we observed a linear correlation between the intensity ratio of SiOEP at 580 nm to PtOEP at 650 nm and the concentration of oxygen, which could be used to reliably monitor the partial pressure of oxygen in a system.     

Crosslinking and characterization of commercially available poly(VDF-co-HFP) copolymers with 2,4,4-trimethyl-1,6-hexanediamine

Fluorinated copolymers are well known for their large range of applications. These applications can be improved by grafting or crosslinking of several agents. The mechanism of crosslinking of hexamethylene diamine and 2,4,4-trimethyl-1,6-hexanediamine is well known and occurs in four different steps. To elaborate a film of commercially available poly(VDF-co-HFP) copolymer crosslinked by 2,4,4-trimethyl-1,6-hexanediamine, a step of press cure under air is necessary. Temperature, time and pressure were optimised by regarding the solubility of the press cured films, the mechanical properties, the swelling rate in methyl ethyl ketone, and the degradation of the films. The best temperature, time and pressure for press cure were 150 °C, from 15 to 30 min, and 20 bars, respectively. Other properties of crosslinked poly(VDF-co-HFP) copolymers containing 10 mol.% and 20 mol.% of HFP were characterized. First, all films were insoluble in concentrated HCl. Secondly, swelling rates of different amounts of diamine crosslinked copolymers were measured in ethylene carbonate/dimethyl carbonate and in methyl ethyl ketone; it was proved that the higher the molar percentage of diamine, the higher the crosslinking density, so the lower the swelling rate. Concerning thermal properties, glass transition temperature mainly increased when the amount of diamine increased. Thermal stability measurements showed a higher decomposition temperature when the percentage of diamine was very low (5 mol.%). Finally, mechanical properties were measured by dynamic mechanical analysis; the storage tensile modulus (E′) of a diamine crosslinked Kynar^® copolymer versus temperature exhibited a high drop because Kynar^® was a highly amorphous copolymer. Moreover, the higher the amount of diamine, the higher the rubbery modulus.     

Synthesis of three novel chiral diamines derived from (S)-proline and their evaluation as precursors of diazaborolidines for the catalytic borane-mediated enantioselective reduction of prochiral ketones

A series of chiral diazaborolidine catalysts are readily prepared in situ at 75 °C in toluene solvent and under microwave irradiation (100 W, 15 min, air cooling) using chiral diamines derived from inexpensive and commercially available (S)-proline and borane-dimethyl sulfide. Special mention deserves the synthesis of potentially versatile diamine (S)-8 [(S)-(pyrrolidin-2-yl)diphenylmethanamine], with the key step being the conversion of tertiary alcohol (S)-(1-benzylpyrrolidin-2-yl)diphenyl methanol, (S)-12, to azide (S)-13. The chiral diazaborolidine/BH₃ reagent system was successfully employed in the enantioselective reduction of prochiral ketones to give the corresponding secondary alcohols in excellent yield and with up to 96% enantiomeric purities.     

Chemical reactions and reactivity of primary,secondary, and tertiary diamines with acid functionalized polymers

Reactive melt processing of different types of diamines with polyethylene containing carboxylic acid groups and polystyrene containing anhydride groups was carried out. The reactivity of primary, secondary, and tertiary diamines with these acid polymers was determined using various techniques. Molecular weight increases due to crosslinking were observed through (1) changes in the torque during the reactive processing, (2) decrease in melt flow indices, and (3) decrease in solubility of the reaction products. The chemical compositions of the reaction products were examined by Fourier transform infrared (FTIR) spectroscopy. Thermal analysis using differential scanning calorimetry (DSC) was carried out to determine the crystallization behavior, glass transition temperatures, and thermal stabilities of the reaction products. Results show that the primary amine is the most reactive towards carboxylic acid or anhydride groups followed by the secondary and then the tertiary amine. Anhydride groups on polymers are of higher activity towards secondary or primary amino groups than carboxylic acid groups in the nucleophilic acyl substitution reactions. Reaction products crosslinked with the primary diamine are less stable than their parent acidic polymers. On the other hand, crosslinking with the secondary or tertiary diamine gives products with higher thermal stability than the parent acidic polymers. The formation of reversible and irreversible crosslinks with different types of diamines is also reported. © 1992 John Wiley & Sons, Inc.     

Synthesis and characterization of new polyimides containing ethynylene linkages

We have synthesized a series of new diamines containing bis(ethynylaniline) linkages by bromine substitution reaction of ethynylaniline with 4,4′-bis(4-bromophthalimido)diphenylether (PODA) or 1,4-bis(4-bromophthalimido)benzene (PPDA). The intermediates were separated at each step, purified and characterized by the spectroscopic techniques. The model compound having imide and triple bond moiety was synthesized in order to elucidate the nature of the products formed from the ethynyl curing by FT-IR spectroscopy. The polymerization reaction of ethynylaniline diamines with various dianhydrides gave fully imidized and soluble aromatic polyimides. The thermally cured polyimide samples displayed good solvent resistance. The thermal crosslinking of triple bond moieties in the main chain was carried out by heating in the temperature range from 150 to 400 °C. The glass transition temperature of polyimide completely disappeared after heat treatment at 400 °C for 5 min. The polyimides derived from diamines containing bis(ethynylaniline) groups were thermally stable after heat treatment.     

Selective Monoacylation of a Diamine Using Intramolecular Delivery by a DMAP Unit

[reaction: see text] Regioselective monoacylation of a diamine is achieved by including a suitably positioned 4-(dimethylamino)pyridine (DMAP) group within the molecule.     

Immobilization of uricase within polystyrene using polymaleimidostyrene as a stabilizer and its application to uric acid sensor

A novel amperometric uric acid (UA) sensor has been developed by coating the surface of a gold electrode with a polystyrene (PS) membrane formed by 30 μL of a 30 mg mL⁻¹ PS chloroform solution combined with 30 μL of a 5 mg mL⁻¹ polymaleimidostyrene (PMS) solution as a dispersant for enzyme, uricase; this membrane has been successfully employed as an immobilization support for uricase. In the PS membrane, PMS forms micelle-like structures containing uricase in an active state. This immobilized uricase membrane permits the permeation of oxygen, which is consumed by the uricase reaction. A good linear relationship is obtained over the concentration range of 5-105 μM. The concentration of uric acid was determined at a negative potential based on the decrease in the reduction current of oxygen and the interference of l-ascorbic acid can be completely eliminated.     

The mean activity coefficients of LaCl3 in dilute aqueous solution at 298.15 K

The electromotive forces of a symmetrical concentration cell with transference, Ag; AgCl|LaCl₃ (m*):LaCl₃ (m)|AgCl; Ag, were measured over the concentration range from 8.762 × 10⁻⁴ mol kg⁻¹ to 6.788 × 10⁻² mol kg⁻¹ at 298.15 K to obtain the mean activity coefficients of LaCl₃. The mean activity coefficient for reference solution at 298.15 K and the ion size parameter for LaCl₃ in the extended Debye–Hückel equation are evaluated by using an approach extrapolating concentration to unlimited dilution. A modified Debye–Hückel equation with new parameters has been established for the studied concentration range. A comparison is done of the thermodynamic data of LaCl₃ that are determined by this experiment with those reported by previous literatures, and evaluated by some models.