DMF-water System Research Articles

Selective Synthesis of Spirooxindoles by an Intramolecular Heck-Mizoroki Reaction.

We report a highly diastereoselective synthesis of cyclopentene-spirooxindole derivatives via an intramolecular Heck-Mizoroki reaction using aryl bromides as precursors. The reactions were performed under dry conditions or in a DMF-water system. This protocol can be useful to introduce several functionalities to the aromatic nucleus of the spirooxindoles. DFT calculations were performed to rationalize the high antiselectivity. A functionalized spiroproduct was transformed into a cyclic amino acid derivative.

Perfluoropolymer membrane behaves like a zeolite membrane in dehydration of aprotic solvents

Dehydration of aprotic solvents, frequently needed in pharmaceutical processing, can be implemented easily by vacuum-based pervaporation employing a novel perfluoropolymer-based membrane: perfluoro-2,2-dimethyl-1,1,3-dioxole copolymerized with tetrafluoroethylene (PDD-TFE). Possessing one of the highest fractional free volumes, this polymer is resistant to most solvents including N,N-dimethyl formamide (DMF), N,N-dimethylsulfoxide (DMSO), and N,N-dimethylacetamide (DMAc). Results were obtained using a 25 μm thick dense polymeric membrane supported by a porous polytetrafluoroethylene (PTFE) sheet. Maximum water flux values found for a 90 wt% aprotic solvent feed were as follows: 77 g/(m2 h) for DMF–water mixture at 50 °C; 9.8 g/(m2 h) for DMSO–water mixture at 30 °C; 9 g/(m2 h) for DMAc–water mixture at 50 °C. Excellent pervaporation separation factors for water over these aprotic solvents were obtained for mixtures containing 1, 5 and 10 wt% water in the temperature range 30–60 °C. The separation factors varied between 1000 and 12,000 depending on the water content, temperature and the solvent species. Such highly selective water removal in pervaporation has been achieved earlier in dehydration of ethanol by NaA zeolite membranes which however achieve an order of magnitude lower selectivity in for example, DMF–water system.

Phase behavior and mechanism of formation of protofiber morphology of solution spun poly(acrylonitrile) copolymers in DMF-water system

Phase diagrams of a series of copolymers of acrylonitrile (AN) and acrylic acid (AAc) were constructed using linearized cloud point correlation. The miscibility region in the phase diagram was found to increase with the increase in AAc content of the copolymers. For various compositions, χ13 (polymer–water interaction parameter) values were estimated by sorption experiment. As the hydrophilic nature of the polymer increased with the increase in the content of acrylic acid, the χ13 interaction parameter was found to decrease from poly(acrylonitrile) homopolymer to its copolymer with 50 mol % acrylic acid (AA50B). The polymer–solvent interaction parameters (χ23) and composition at the critical points for all the polymers were determined by fitting the theoretical bimodal curves to the experimental cloud point curves using Kenji Kamide equations. The polymer composition at the critical point was found to increase by 400% with increasing AAc content. The polymers were solution spun in DMF-water coagulation bath at 30°C and their protofiber structures were investigated under scanning electron microscopy. The observed morphological differences in protofibers were explained on the changes brought about in the phase separation behavior of the polymer–solvent–nonsolvent systems. The copolymers with higher acrylic acid content could be solution spun into void free homogeneous fibers even at conditions that produced void-filled inhomogeneous fibers in poly(acrylonitrile) and its copolymers with lower AAc content. The experiments demonstrate the important role of thermodynamics in deciding the protofiber morphology during coagulation process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Nanoparticles formed from PNIPAM- g-PEO copolymers in the presence of indomethacin

Biocompatible double-hydrophilic PNIPAM- g-PEO copolymers containing 0.3–3.2 mol% PEO grafts were synthesized and utilized to prepare indomethacin (IMC)-loaded core–shell nanoparticles by dialysis and nanoprecipitation methods. IMC loading was conducted at room temperature using the organic solvents ethanol and DMF, which induced phase separation in the copolymers aqueous solutions due to the cononsolvency of PNIPAM. In ethanol–water solutions, the cononsolvency-induced phase separation of the copolymers promoted effective drug incorporation into the formed micellar structures. In DMF–water system, the formation of the nanoparticles did not correspond to the cononsolvent region of PNIPAM- g-PEO. In this case, hydrophobic interactions between PNIPAM and IMC allowed the copolymer self-association and drug loading. Irrespective of the solvents or preparation methods applied, the drug loading content (DLC) depended on the drug-to-copolymer feed weight ratio. DLC was relatively low at the 0.5:1 ratio but it significantly increased at the ratios of 0.75:1 and 1:1 (DLC∼90%). The particle size was strongly affected by the different mechanisms of nanoparticles formation. The nanoprecipitation from ethanol produced significantly smaller particles (<150 nm) with narrow size distribution than the dialysis from DMF. The velocity of indomethacin release from the nanoparticles was influenced by the amount of encapsulated drug, the process being faster at lower DLC.

Discovery of a unique dual response in acrylonitrile copolymers

Poly(acrylonitrile) is not reversibly sensitive to either changing temperature or changingpH. However, the addition of acrylic acid (AA) as a comonomer induces the pH response tothis polymer. In this study, for the first time, the copolymers of acrylonitrile and acrylicacid were shown to possess a unique dual response to pH and temperature. For this, aseries of acrylonitrile-based copolymers were synthesized with varying AA contentfrom 10 to 50 mol% using free radical copolymerization. These copolymers weresolution-spun from a DMF–water system and heat-set to give stable fine fibers of120 ± 3 µ diameter without any chemical crosslinking. The fibers showed temperature sensitivity in anaqueous alkaline bath. At pH 10, the volumetric swelling of fibers containing 30 mol% of AAinitially increased from 3810% to 6440% with increase in temperature of the bath from 30 to49 °C,and suddenly decreased to 4200%, near to the original swelling level, when the temperature reached50 °C. The copolymer was found to have a clear and sharp transition temperature between 49 and50 °C.The behavior shown was unlike other temperature-responsive polymers, where it is a step transitionfrom the swollen to deswollen state. The transition temperature could be tuned in the range of 40 to62 °C by varying the composition of acrylic acid from 10 to 50 mol% in the copolymers.The transition temperature was also found to increase with increasing pH of thesurrounding bath. All transitions were reversible and stable to repeated cycling.

Effect of copolymer architecture on the response of pH sensitive fibers based on acrylonitrile and acrylic acid

Copolymers of acrylonitrile and acrylic acid with high acrylic acid feed ratio of 43 mol% were synthesized using free radical polymerization. The architecture of copolymers was modified by regulating the dosing of more reactive comonomer-acrylic acid. 13C NMR analysis confirmed that two copolymers – one (A) containing enriched blocks of individual monomer-residues (architecture close to a block copolymer) and the second (B) having nearly random distribution of the comonomers, could be successfully synthesized. The resultant acrylic acid content was determined to be nearly 50 mol% for both the copolymers. These copolymers were converted to fine fibers by solution spinning in DMF-water system, drawn in coagulation bath, and annealed at 120 °C for 2 h. The fibers were evaluated for pH response behavior, mechanical stability, and retracting stresses. The fiber A was found to have significantly higher swelling percentage (3300–3700%), faster response, and higher stability to repeated cycling compared to fiber B. Also, Fiber A showed lower thermal shrinkage, better mechanical properties during swelling and higher retracting forces during deswelling. These results indicate that the copolymer with enriched block architecture could possibly form segregated domain structure with acrylic acid domains facilitating enhanced pH response while acrylonitrile domains providing physical crosslinks for stronger mechanical strength. The study suggests that above approach may be more useful than chemically cross-linked gel rods in producing artificial muscles with faster response and good mechanical properties.

Aggregation behavior and catalytic activity of systems based on calix[4]resorcinarene derivatives and surfactants. 1. Mixed micellization of aminomethylated calix[4]resorcinarenes with cetyltrimethylammonium bromide in aqueous dimethylformamide

Mixed micellization of amphiphilic aminomethylated calix[4]resorcinarenes and phenols, which are their structural units, with the cationic surfactant cetyltrimethylammonium bromide (CTAB) in aqueous 10—70 vol % DMF decreases the critical micelle concentration; the resulting aggregates are larger than those in the CTAB—DMF—water systems. The micellization of CTAB with aminomethylated calix[4]resorcinarenes proceeds in two steps, while its micellization with phenols is a single-step process. The micellization characteristics depend on the structure and hydrophobicity of the amphiphilic compound and the concentration of DMF.

高圧力の可能性に挑む ホルムアミド類‐水混合溶液の密度・粘度に対する圧力効果

Densities and viscosities of formamide (FA)-, N-methylformamide (NMF)-, andN, N-dimethylformamide (DMF)-water mixtures were measured at 25°C under high pressure up to 200 MPa. The isothermal compressibility of the FA-water system decreases monotonously with an increase in the FA content at each pressure, but those of NMF-and DMF-water systems show a minimum against the composition in the water-rich region. Although the excess viscosity of the FA-water system is negative in the whole composition range, those of NMF-and DMF-water systems are positive. Such trends become remarkable with an increase in pressure. These results are discussed in terms of the hydrogen bonding between water and amide molecules and the hydrophobic hydration.

Partial Molar Volumes of Some Multicharged Electrolytes in Aqueous Dimethylformamide at Various Temperatures

Partial molar volumes of ammonium aluminium sulfate and potassium aluminium sulfate in DMF-water mixtures (5-20 wt.% of DMF) have been determined from solution density measurements at various temperatures and electrolyte concentrations. The data were evaluated by using Masson equation and the obtained parameters were interpreted in terms of ion-solvent and ion-ion interactions. Both electrolytes have been found to act as the structure makers/promotors in DMF-water systems.

Thermodynamic properties of liquid mixtures. II. Dimethylformamide-water

The excess enthalpy of mixing of DMF-water was measured at 25° C in the 0–1 molar fraction range. The maximum of heat is developed for a 0.33 DMF molar fraction. The excess partial molar and other excess quantities were also calculated for the DMF-water system at 25° C. The results suggest a strong interaction between DMF and water.

The protonation of aromatic hydrocarbon radical anions: III. Elucidation of electrode process of aromatic hydrocarbon reduction

Summary The rates of protonation of aromatic hydrocarbon radical anions with water in the DMF—water systems were measured by the stopped flow method. Apparent first-order rate constants of the order of 10 s−1 were obtained by this method. These rate constants were compared with those calculated from the polarographic limiting currents on the basis of two possible mechanisms, i.e. the e.c.e. mechanism: R + e ⇌ R ⨪ R ⨪ + H 2 O → R H ⋅ + O H − R H ⋅ + e ⇌ R H − and the regeneration mechanism: R + e ⇌ R ⨪ R ⨪ + H 2 O → k R H ⋅ + O H − R H ⋅ + R ⨪ → fast R H − + R Good agreement was found between the rate constants of protonation measured by the stopped flow method and those calculated on the basis of the regeneration mechanism. The regeneration mechanism was justified also by the observation that it leads to rate constants which are independent of drop-time.

The Effect of Water on the Reduction Potentials of Some Aromatic Compounds in the DMF-Water System

Abstract From the viewpoint of the interaction between the oxidized or the reduced form of a depolarizer and solvents, the solvent effect on the half-wave potentials was studied. Another factor affecting the E1⁄2, i.e., pH or ion-pair formation, was also examined. The correction for the liquid junction potential was carried out by the use of the ferrocene standard. The reduction products, radical anions or dianions, were found to be stabilized by the hydrogen-bonding with water where the hydrogen-bond interaction of the dianion was stronger than that of the monoanion. Aromatic hydrocarbon radical anions, whose charges are dispersed over the molecule, were less susceptible to this solvent transfer than were the anthraquinone radical anion and the dianion, whose charges are strongly localized.