Dilute Aqueous Alkaline Solution Research Articles

Facile Post-Carboxymethylation of Cellulose Nanofiber Surfaces for Enhanced Water Dispersibility.

To improve the water dispersibility of cellulose nanofibers without deteriorating the physical properties, it is necessary to develop methods that can selectively modify fiber surfaces. Herein, the reaction conditions for carboxymethylation of the surface of nanofibrillated bacterial cellulose were optimized using chloroacetic acid as an etherification agent. Carboxymethylation in a high-concentration alkaline solution (>5 wt %) in the presence of isopropanol caused the mercerization and carboxymethylation of not only the nanofiber surface but also the cellulose crystals within the nanofiber, resulting in nanofiber swelling and an increase in fiber width. In contrast, with a dilute alkaline aqueous solution (3 wt %), the nanofiber surface was successfully carboxymethylated without changing the inner structure. Furthermore, the morphology was not affected by the carboxymethylation reaction, and no fiber swelling occurred under these reaction conditions. When the substitution reaction proceeded only on the nanofiber surface, the maximum degree of substitution (i.e., the average number of carboxymethyl groups substituted per anhydroglucose residue in cellulose) was 0.091. After surface modification, the nanofibers became more negatively charged, which improved the dispersibility in water through electrostatic repulsion, resulting in a drastic increase in the transparency of the nanofiber dispersion. This method provides a general approach for the surface modification of cellulose nanofibers to increase water dispersibility.

Single-chain conformation of carboxylated schizophyllan, a triple helical polysaccharide, in dilute alkaline aqueous solution

Synchrotron-radiation small-angle X-ray scattering measurements were carried out for a schizophyllan (SPG) sample with the weight-average molar mass Mw of 340 kg mol−1 and five carboxylated SPG (sclerox) samples with different degrees of substitution (DS) ranging from 0.18 to 0.45 in 200 mM aqueous NaOH including 10 mM NaCl to determine Mw, the second virial coefficient A2, the particle scattering function P(q), and the radius of gyration ⟨S2⟩. Positive A2 values indicated that this alkaline solvent was a good solvent for all polysaccharide samples investigated. The resultant Mw values (~100 kg mol−1) were much smaller than that for the trimer in aqueous NaCl at neutral pH, indicating all SPG and sclerox samples dissolved as single chains in the alkaline solvent. Both P(q) and ⟨S2⟩ were consistently explained by the wormlike chain model. The obtained parameters were almost independent of DS. While the chain stiffness (12–18 nm) in terms of the Kuhn segment length or twice the persistence length was similar to those for the other single chain polysaccharides, the helix pitch per residue (0.1 nm) was quite smaller than the trimer state (0.3 nm). This shrunken main-chain helical structure is most likely due to hydrophobic interactions between helical main chain and side groups.

Photosensitive poly(vinylene carbonate)s based on reaction development patterning with dilute aqueous alkaline solution

We examined positive-tone pattern formation based on reaction development patterning (RDP) using hydrolysis of carbonate groups on the side chains of vinyl polymers. Homopolymers and copolymers with carbonate groups were prepared by radical polymerization using vinylene carbonate (VCA) as a monomer. Application of RDP to the VCA homopolymer resulted in unclear positive-tone pattern because the high reactivity of the carbonate group led to insufficient difference in solubility between the exposed and unexposed areas. When we applied RDP using 5.0 wt% NaOHaq as developer to the copolymers between VCA and vinyl acetate (P(VCA–VAc)s), clear positive-tone patterns were successfully obtained. The effect of the ratio of carbonate groups in the copolymers on the development property of the RDP process was examined, and the use of a copolymer in which the ratio between VCA and VAc was 1:0.6 was found to yield positive-tone pattern with the highest contrast. Pattern formation using more dilute developer (1.0 wt% NaOHaq) was also achieved. Though conventional photosensitive polymers are required to have acidic or protected acidic groups for alkaline development, we succeeded in addition of photosensitivity to P(VCA–VAc)s, which do not have such functional groups, by using dilute aqueous alkaline solutions as developers. © 2015 Society of Chemical Industry

Removal of uranium(VI) from dilute aqueous solutions using novel sequestering sorbent poly-acryl hydroxamic acid

A novel sorbent, poly-acryl hydroxamic acid was prepared in-house from acrylamide monomer by solution polymerization method. Surface morphology and energy dispersive X-ray spectroscopy revealed that the sorbent was capable of encaging uranium from aqueous solution. Sorption potentials of uranium ions were investigated using the sorbent in dilute alkaline aqueous solution by varying pH of solution, sorbent quantities, contact time, initial uranium ion concentration and temperature of solution. Results from batch sorption experiment with simulated nuclear plant effluent showed the sorbent could remove uranium(VI) ions efficiently in presence of competitive ions such as Ca(II), Mg(II), Mn(II), Cu(II), Fe(III) and nitrate. Sorption characteristics were studied using Langmuir and Freundlich isotherms. The evaluated thermodynamic parameters indicated the present sorption process was endothermic and spontaneous. This work provided a promising and new sorbent for removing hazardous material like uranium from industrial wastewater.

A convenient method for the reductive degradation of mono-, di-, and tribromodiphenyl ethers, tetrabromo- and tetrachlorobisphenol A with Raney Ni-Al alloy

Raney Ni-Al alloy in a dilute aqueous alkaline solution of NaOH, KOH, CsOH, LiOH, or Ca(OH)2, or of alkali metal carbonates such as Na2CO3, K2CO3 and Cs2CO3, becomes a very powerful reducing agent and dehalogenates mono-, di and tribromodiphenyl ethers (BDPEs), tetrabromobisphenol A (TBBPA) and tetrachlorobisphenol A (TCBPA) effectively. Polybromodiphenyl ethers are reduced to give diphenyl ether as sole product. TBPPA and TCPPA are debrominated to bisphenol A and other dehalogenated compounds. The C-C bond of bisphenol A is broken easily under the reaction conditions. An almost quantitative removal of halogen from BDPEs, TBBPA and TCPPA can be realized in aqueous media under mild reaction conditions without the use of organic solvents. The reductive dehalogenation of TBBPA and TCBPA with a Raney Ni-Al alloy under ultrasonication is also described.

Raney Ni–Al alloy-mediated reduction of benzils in water

Raney Ni–AI alloy in a dilute aqueous alkaline solution has been shown to be a powerful reducing agent and is highly effective for the reduction of alkylbenzils and alkoxybenzils to afford the corresponding 1,2-diarylethers at 90°C, in the absence of organic solvents. 4,4′-Dinitrobenzil was transformed selectively to 1,2-bis(4-aminophenyl)-ethane.

Raney Ni-Al alloy mediated hydrodehalogenation and aromatic ring hydrogenation of halogenated phenols in aqueous medium

Raney Ni-Al alloy in a dilute aqueous alkaline solution has been shown to be a very powerful reducing agent and is highly effective for the reductive dehalogenation of polyhalogenated phenols and aromatic ring hydrogenation of phenols to the corresponding cyclohexanols.

A facile method for the dechlorination of mono- and dichlorobiphenyls using Raney Ni–Al alloy in dilute aqueous solutions of alkali hydroxides or alkali metal carbonates

Raney Ni–Al alloy in a dilute aqueous alkaline solution of NaOH, KOH, CsOH, LiOH, or Ca(OH) 2 or of alkali metal carbonates such as Na 2CO 3, K 2CO 3 becomes a very powerful reducing agent and dechlorinates the polychlorobiphenyl(PCB) congeners mono- and dichlorobiphenyls effectively to afford biphenyl and/or phenylcyclohexane, respectively. The reactions are run under mild conditions without the use of organic solvents. The reductive dechlorination of dichlorobiphenyls with a Raney Ni–Al alloy under ultrasonication was investigated, also.

Raney Ni–Al alloy-mediated reduction of alkylated phenols in water

Raney Ni–Al alloy in a dilute aqueous alkaline solution has been shown to be a very powerful reducing agent in the hydrogenation of phenol and alkylated phenols to the corresponding cyclohexanol derivatives.

New Method for the Reduction of Benzophenones with Raney Ni‐Al Alloy in Water

Raney Ni‐Al alloy in a dilute alkaline aqueous solution has been shown to be a powerful reducing agent, which is highly effective in the reduction of benzophenones to the corresponding hydrocarbon derivatives, in the absence of any organic solvents.

Reductive degradation of tetrabromobisphenol A (TBBPA) in aqueous medium

Raney Ni–Al alloy in a dilute alkaline aqueous solution has shown to be a powerful reducing agent and is highly effective for the hydrodebromination of tetrabromobisphenol A (TBPPA) to bisphenol A (BPA) and other debrominated alicyclic compounds. The C–C bond of bisphenol A is cleaved easily under the reaction conditions. An almost quantitative removal of TBBPA can be attained at 90 °C.

ChemInform Abstract: Organic Reaction in Water. Part 3. A Facile Method for Reduction of Aromatic Rings Using a Raney Ni-Al Alloy in Dilute Aqueous Alkaline Solution under Mild Conditions.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Organic reaction in water. Part 3: A facile method for reduction of aromatic rings using a raney Ni–Al alloy in dilute aqueous alkaline solution under mild conditions

Reduction of aromatic rings such as phenol, naphthalenes, biphenyls, acenaphthene, and acenaphthylene was smoothly performed using a Raney Ni–Al alloy in dilute aqueous alkaline solution without any organic solvents at 90°C under atmospheric pressure, and the corresponding reduced compounds were obtained in high yields.

Organic reaction in water. Part 2. A new method for dechlorination of chlorobiphenyls using a Raney NiAl alloy in dilute aqueous alkaline solution

Use of a Raney NiAl alloy in dilute aqueous alkaline solution gave rise to strong reducing power and chlorobiphenyls were reduced easily to biphenyl and/or phenylcyclohexane, respectively, without any organic solvents.

The cathodic reduction of oxygen on n-type UO 2 in dilute alkaline aqueous solution

The cathodic reduction of O 2 on ceramic UO 2 that exhibits an n-type photocurrent response has been studied in dilute alkaline aqueous solution using rotating disc and ring-disc electrodes. Steady state polarization measurements were made using the current-interrupt method to compensate for the potential drop caused by ohmic resistance, mainly in the electrode. Overall, four-electron reduction to OH − has been shown to predominate in perchlorate solution, with only a slight pH dependence. Although the reaction order with respect to the O 2 concentration in solution has been determined to be near square-root under these conditions, dissociative adsorption of O 2 appears very unlikely. Instead, the same basic reaction mechanism as proposed for p-type UO 2, involving consecutive single electron and proton transfer steps in a classic series route, is thought to apply. Reaction is presumed to occur exclusively at active sites formed by uranium ions in different valence states, after the theory originally developed by Presnov and Trunov for transition metal oxides with p-type semiconductivity. The near square-root reaction order, as well as unusually large Tafel slopes, can then be interpreted on the basis that the first electron-transfer step is tightly coupled with O 2 adsorption under Temkin conditions. This treatment follows ideas previously developed by Calvo and Schiffrin to explain similarly anomalous kinetics for O 2 reduction on passive iron in alkaline solution. In the present case, the observed behaviour is thought to reflect microscopic heterogeneity in the degree of hyperstoichiometry of the UO 2 + x electrode. Pronounced effects caused by gentle surface oxidation and the presence of carbonate in solution are consistent with the reaction scheme outlined.

The cathodic reduction of oxygen on uranium dioxide in dilute alkaline aqueous solution

The cathodic reduction of oxygen on uranium dioxide (UO 2) in dilute alkaline aqueous solutions has been investigated using rotating UO 2 disc and Au ring-UO 2 disc electrodes. Steady state polarization measurements were made using the current-interrupt method to compensate for the potential drop caused by ohmic resistance, mainly in the electrode. Tafel slopes of 130–280 mV decade −1 were observed spanning 2–3 decades of current. At high overpotentials, the (transport-compensated) kinetic-limiting current invariably approached a constant value. The reaction order with respect to the O 2 concentration was determined to be unity. In perchlorate solutions, an overall four-electron reduction process was observed, with only a weak dependence on pH. In carbonate solutions, O 2 reduction currents were suppressed by up to an order of magnitude (compared with those in perchlorate) and copious amounts of peroxide were released to solution. The theory developed by Presnov and Trunov for O 2 reduction on transition metal oxides with p-type semiconductivity was adapted to interpret the results for UO 2. Variations in the number density of surface donor—acceptor sites as a function of applied potential can then be invoked to explain a diverse range of experimental observations. These claims are consistent with the conclusions of previous voltammetric experiments, which showed that the degree of oxidation of the UO 2 surface changes substantially over the region of Tafel behaviour for O 2 reduction.

Competitive intramolecular aminolysis: Relative rates of 5- and 6-membered lactam ring closure

Methyl 4,5-diaminopentanoate (4,5-Dape Me) undergoes competitive intramolecular aminolysis to 5-aminomethyl-2-pyrrolidinone (L5) and 5-amino-2-piperidinone (L6) in dilute alkaline aqueous solution at 25°C. Use of this single compound provides an ideal case for assessing the relative rates of 5- and 6-membered lactam ring closure. Assessments are also made using the intramolecular aminolysis of pairs of compounds: methyl 2,4-diaminobutanoate (2,4-Dab Me) and methyl 2,5-diaminopentanoate (2,5-Dape Me); methyl 4-aminobutanoate (4-Ab Me) and methyl 5-aminopentanoate (5-Ape Me).

Dimerization: First step for micelle preorganization of bile salts

The dimerization constants of sodium cholate, sodium deoxycholate and sodium chenodeoxycholate have been determined in dilute alkaline aqueous solution. The high stabilities of the dimers cannot be explained by single hydrogen bonds but multiple interactions must be involved simultaneously.

Reactivity effects in the oxidative dissolution of UO 2 nuclear fuel

Abstract The known energy-level scheme for UO 2 and the nature of electron transport in UO 2+ x have been assessed with regard to their influence on electrochemical reactions. An unusually negative flat-band potential permits conventional electrochemical experiments to be conducted at considerably more cathodic potentials than would be feasible with a normal p-type semiconductor. The unique electronic properties of UO 2+ x can also be seen to accommodate cathodic and anodic photocurrents simply by changing the degree of hyperstoichiometry. Cathodic reduction of O 2 in dilute alkaline aqueous solution has been studied intensively on two kinds of UO 2+ x (with p-type and n-type photocurrent response) and a UO 2-based SIMFUEL. The kinetics of this reaction appear to control the corrosion (oxidative-dissolution) rate of UO 2 and are a sensitive probe of surface reactivity: a significant range of behaviour has been observed as a function of the properties of the electrode material and its interactions with solution. Anomalous features in Tafel plots can be correlated with qualitative changes in the composition of the surface oxide film. A theory developed to describe O 2 reduction on transition-metal oxides with p-type semiconductivity has been adapted to provide a basis for understanding this process at UO 2+ x surfaces. Electron-transfer reactions are presumed to occur exclusively at active sites, formed by adjacent cations in different valence states, where O 2 and any intermediates are adsorbed.

The J-aggregate 5,5′,6,6′-Tetrachloro-1,1′-diethyl-3,3′-bis(4-sulfobutyl)benzimidazolocarbocyanine Sodium Salt in Aqueous Solution

Abstract The aggregation of the title dye in a dilute alkaline aqueous solution is investigated at 283–303 K by measuring the electronic absorption spectra. The association number is estimated to be 8, the heat of formation and the entropy change for the association are found as ΔH=−91.5 kcal mol−1 (1 cal=4.184J) and ΔS=−139.3 cal K−1 mol−1, respectively. The structure of the octamer is discussed from a view of spectral shift, intermolecular force and the crystalline structural data. The lifetimes, quantum yields and polarization of fluorescence are investigated on the monomeric and the J-aggregate state of the dye. The energy transfer between several J-aggregate units is indicated in the excited state.