共查询到20条相似文献,搜索用时 125 毫秒
1.
Cationic sugarcane bagasse hemicellulose derivatives with a relatively low degree of substitution (0.01-0.54) containing quaternary ammonium groups were prepared by etherification with 3-chloro-2-hydroxypropyltrimethylammonium chloride or preferably with 2,3-epoxypropyltrimethylammonium chloride using sodium hydroxide as a catalyst in aqueous solution. The extent of etherification was measured by yield percentage and degree of substitution (DS). The DS values of the products could be controlled by adjusting the molar ratio of etherifying agent to anhydroxylose units in hemicelluloses and the molar ratio of sodium hydroxide to etherifying reagent. In comparison, the etherified hemicellulose preparations were characterized by both degradative methods such as thermal analysis, and non-degradative techniques such as gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), and 13C nuclear magnetic resonance (NMR) spectroscopy. It was found that a significant degradation of the hemicellulose polymers occurred during etherification under the alkaline conditions used. The thermal stability of the etherified hemicelluloses was lower than that of the unmodified hemicellulose polymers. 相似文献
2.
Antje Vollmer Kristin Voiges Christian Bork Kathrin Fiege Katja Cuber Petra Mischnick 《Analytical and bioanalytical chemistry》2009,395(6):1749-1768
Dextrans from Leuconostoc ssp., α-1,6-linked glucans branched at O-3, were O-methylated in DMSO with lithium dimsyl and methyl iodide under various conditions. Methyl substituent distribution was comprehensively
studied in the terminal, internal, and branched glucosyl units and along and over the dextran macromolecules. The order of
reactivity was O-2 > O-4 ≥ O-3. The methyl pattern in the glucosyl units significantly deviates from a random distribution
with enhanced amounts of un- and trisubstituted moieties. This deviation was found to proceed on macromolecular level by means
of ESI-MS of perdeuteromethylated and partially depolymerized methyl dextrans. Heterogeneity was much more pronounced than
for methyl amylose prepared under comparable conditions. DS gradients in and over the material are discussed with respect
to dextran structure and the mechanism of Li dimsyl alkylation. For comparison, cyanoethyl dextrans were prepared by sodium
hydroxide catalyzed addition of acrylonitrile. Monomer analysis of cyanoethyl dextrans revealed that this thermodynamically
controlled reaction gave a random substitution pattern with 48% of cyanoethyl groups at O-2, 33% at O-4, and 19% at O-3.
相似文献
3.
V. O. Cirino A. L. Bullock S. P. Rowland 《Journal of polymer science. Part A, Polymer chemistry》1969,7(5):1225-1235
In order to determine the relative equilibrium constants for reactions of the hydroxyl groups at C2, C3, and C6 of the D-glucopyranosyl units, methyl vinyl sulfone was reacted with cellulose dissolved in benzyltrimethylammonium hydroxide. The reaction was carried to constancy in distribution of substituents between the 2–0– and 6–0–positions. The distributions of substituents in the D-glucopyranosyl units were measured by gas-liquid chromatographic analysis of the products from hydrolysis of the modified cellulose. Relative equilibrium constants were then evaluated, assuming complete accessibility of all three types of hydroxyl groups of the cellulose in solution. For determination of the relative accessibilities of the individual types of hydroxyl groups in heterogeneous reactions of cotton cellulose with methyl vinyl sulfone, the reactions were carried to equilibrium distributions in media of various normalities of sodium hydroxide (i.e., media of various swelling strength). The distributions of substituents in the D-glucopyranosyl units were measured. From these values and the ratio of equilibrium constants, the relative accessibilities of the hydroxyl groups at C2 versus those at C6 were calculated. Apparent accessibilities of the hydroxyl groups at C2 are approximately double those at C6 when the reaction is carried out in 1N sodium hydroxide and about triple those at C6 when the reaction is carried out in 0.5N sodium hydroxide. 相似文献
4.
Hemicelluloses isolated from sugarcane bagasse were converted to carboxymethyl hemicelluloses (CMH) by carboxymethylation using sodium monochloroacetate and sodium hydroxide in ethanol/water medium. The reaction was performed under various temperatures, times, times of alkaline activation, the ways of the addition of alkali, and the amounts of sodium hydroxide and sodium monochloroacetate. The product had the maximum degree of substitution (DS) of 0.56. The structure of the resulting polymers was characterized with Fourier transform infrared (FT-IR) and 13C nuclear magnetic resonance (NMR) spectroscopies. Destructive methods such as thermal analysis and non-destructive techniques such as gel permeation chromatography (GPC) were used to characterize the carboxymethyl hemicellulose preparations. It was found that a significant degradation of the polymers occurred during carboxymethylation. The thermal stability of carboxymethyl hemicelluloses was higher than that of the native hemicelluloses. 相似文献
5.
Youhei Umino Hiroshi Nozaki Hiroshi Hamana Tadashi Narita 《Journal of polymer science. Part A, Polymer chemistry》2009,47(21):5698-5708
Novel fluorinated polymer synthesis with anionic polyaddition by double Michael addition reaction of 2‐trifluoromethylacrylate derivatives with ethyl cyanoacetate (ECA) was proposed. Diaddition product of ECA with phenyl 2‐trifluoromethylacrylate was yielded in high yield by the catalysis of sodium ethoxide in tetrahydrofuran at 60 °C. Sodium hydroxide catalyzed double Michael addition reaction also produced diaddition product in high yield. Novel anionic polyaddition of 1,4‐phenylene bis(2‐trifluoromethylacrylate) [CH2?C(CF3)COOC6H4OCOC(CF3)?CH2] (PBFA) with ECA afforded the polymer of 1.2 × 104 as the highest molecular weight. The isolated polymer gave the polymer of 2.8 × 104 as a molecular weight by the reaction of the isolated polymer with PBFA in the presence of sodium ethoxide; which proved that the polymer end groups were mainly ECA moieties. The reaction mechanism that the proton abstraction from ECA followed by the addition of 2trifluoromethylacrylate was proposed. The reaction of acetylacetone with PBFA was also examined to give the polymer of 7.6 × 103 as the highest molecular weight catalyzed by sodium hydroxide at room temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5698–5708, 2009 相似文献
6.
《Tetrahedron》1986,42(4):1007-1019
Kinetic data are reported for the equilibration of the 1-methyl-3-nitropyridinium cation with its pseudobase (hydroxide adduct) and for the reduction of this cation by 1-benzyl-1, 4-dihydronicotinamide. The C-2 hydroxide adduct is the kinetically controlled product (pKR+ = 11.6) when this pyridinium cation is mixed with aqueous base, however, this species rearranges to the C-4 adduct as the themodynamically more stable product (pKR+ = 9.42). The pH-dependence of this equilibration may be analysed to give kOH = 1600 M-1s-1 for hydroxide ion attack at C-4 of this cation. Reduction of this pyridinium cation by 1-benzyl-1, 4-dihydronicotinamide appears to occur exclusively at C-4 with second-order rate constant k2 = 0.72 M-1s-1 and k2 H/k2D = 2.0 in 20% CH3CN - 80% H2O, ionic strength 1.0, 25°C.The reactivities of pyridinium, quinolinium, isoquinolinium, acridinium and phenanthridinium cations of pKR+ = 10.0 towards both hydroxide ion and 1-benzyl-1, 4-dihydronicotinamide are evaluated. Relative reactivities (K2/KOH) for these two processes are shown to be acridinium : quinolinium (C-4) : pyridinium (C-4) : quinolinium (C-2) : isoquinolinium : phenanthridinium = 1.6×105 : 3400 : 80 : (4 : 1.0 : 0.7 for predominantly aqueous reaction media. These data support the hypothesis that formation of 1, 2-dihydropyridine systems upon reduction of heteroaromatic cations by 1, 4-dihydronicotinamides occurs via direct one step hydride transfer, while formation of 1,4-dihydro-pyridines in such processes occurs preferentially by a mechanistica11y more complex process involving electron transfer. 相似文献
7.
Ruzene DS Silva DP Vicente AA Gonçalves AR Teixeira JA 《Applied biochemistry and biotechnology》2008,147(1-3):85-96
The effects of alkaline treatments of the wheat straw with sodium hydroxide were investigated. The optimal condition for extraction
of hemicelluloses was found to be with 0.50 mol/l sodium hydroxide at 55 °C for 2 h. This resulted in the release of 17.3%
of hemicellulose (% dry starting material), corresponding to the dissolution of 49.3% of the original hemicellulose. The yields
were determined by gravimetric analysis and expressed as a proportion of the starting material. Chemical composition and physico-chemical
properties of the samples of hemicelluloses were elucidated by a combination of sugar analyses, Fourier transform infrared
(FTIR), and thermal analysis. The results showed that the treatments were very effective on the extraction of hemicelluloses
from wheat straw and that the extraction intensity (expressed in terms of alkali concentration) had a great influence on the
yield and chemical features of the hemicelluloses. The FTIR analysis revealed typical signal pattern for the hemicellulosic
fraction in the 1,200–1,000 cm−1 region. Bands between 1,166 and 1,000 cm−1 are typical of xylans. 相似文献
8.
The reaction of substituted phenyl isocyanates with 2‐amino‐2‐phenylpropanenitrile and 2‐amino‐2‐(4‐nitrophenyl)propanenitrile has been used to prepare substituted 1‐(1‐cyanoethyl‐1‐phenyl)‐3‐phenylureas. In anhydrous phosphoric acid the first products to be formed from 1‐(1‐cyanoethyl‐1‐phenyl)‐3‐phenylureas are phosphates of 4‐methyl‐4‐phenyl‐2‐phenylimino‐5‐imino‐4,5‐dihydro‐1,3‐oxazoles, which on subsequent hydrolysis give the respective ureidocarboxylic acids. On prolongation of the reaction time, the phosphates of 4‐methyl‐4‐phenyl‐2‐phenylimino‐5‐imino‐4,5‐dihydro‐1,3‐oxazoles rearrange to give phosphates of 5‐methyl‐4‐imino‐3,5‐diphenylimidazolidin‐2‐ones, and these are subsequently hydrolysed to the respective substituted 5‐methyl‐3,5‐diphenylimidazolidin‐2,4‐diones. The ureidocarboxylic acids were also prepared by alkaline hydrolysis of 5‐methyl‐3,5‐diphenylimidazolidin‐2,4‐diones. The 5‐methyl‐3,5‐diphenylimidazolidin‐2,4‐diones and ureidocarboxylic acids were characterised by their 1H and 13C NMR spectra. Structure of the 5‐methyl‐5‐(4‐nitrophenyl)‐3‐phenylimidazolidine‐2,4‐dione was verified by X‐ray diffraction. The alkaline hydrolysis of individual imidazolidine‐2,4‐diones was studies spectrophoto‐metrically in sodium hydroxide solutions at 25 °C. The rate‐limiting step of the base catalysed hydrolysis consists in decomposition of the tetrahedral intermediate. The reaction is faster if electron‐acceptor sub‐stituents are present in the 3‐phenyl group of imidazolidine‐2,4‐dione cycle. The pKa values of individual 5‐methyl‐3,5‐diphenylimidazolidine‐2,4‐diones have been determined kinetically. 相似文献
9.
Takahiro Gunji Satoshi Tanikawa Koji Arimitsu Yoshimoto Abe 《Journal of polymer science. Part A, Polymer chemistry》2005,43(16):3623-3630
Base‐catalyzed hydrolytic polycondensation of trialkoxymethylsilane was investigated to synthesize polymethylsilsesquioxanes (PMSs). The reaction of trimethoxy(methyl)silane and triethoxy(methyl)silane with tetramethylammonium hydroxide, tetrabutylammonium hydroxide, and also coline gave insoluble gels. Polymethylsilsesquioxane (PMS‐IP) was obtained by the reaction of triisopropoxy(methyl)silane (MTIPS) with tetrabutylammonium hydroxide as a catalyst. PMS‐IP was composed primarily of T2 and T3 units. The percentage of T3 units and the molecular weight of PMS‐IP increased with increases in the molar ratios of catalyst and water to MTIPS and with the reaction time. PMS‐IP was soluble in organic solvents, except for methanol, and was separated by extraction with hexane and methanol into low‐ and high‐molecular‐weight fractions of Mw 2800–4000 and 7300–88,300, respectively. PMS‐IP coating films were prepared by dip coating on the organic, inorganic, and metal substrates, using the acetone–isopropyl alcohol solution of PMS‐IP. Since PMS‐IP solutions prepared with tetrabutylammonium hydroxide were hardly used because of the low content of hydroxy groups in the polymer, they showed low adhesion when compared with those solutions prepared with hydrochloric acid. The dielectric constant of the coating film prepared from the high‐molecular‐weight PMS‐IP was 2.6. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3623–3630, 2005 相似文献
10.
Laurent Jouffret Jerome Lhoste Annie Hemon‐Ribaud Marc Leblanc Vincent Maisonneuve 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(5):512-516
The title compound, (H3O)2NaAl3F12 [dihydronium sodium trialuminum(III) dodecafluoride], was obtained by solvothermal synthesis from the reaction of aluminium hydroxide, sodium hydroxide, 1,2,4‐triazole and aqueous HF in ethanol at 463 K for 48 h. The structure consists of AlF6 octahedra organized in [AlF4−]n HTB‐type sheets (HTB is hexagonal tungsten bronze) separated by H3O+ and Na+ cations. 相似文献
11.
《Journal of Inorganic and Nuclear Chemistry》1978,40(9):1661-1664
The rate of the reaction between sodium hydroxide and oxalatotetraamminecobalt(III) ion was measured for a variety of hydroxide ion concentrations and at four temperatures. The rate law below 333 K is given by kobs = k0 + k2[OH−]2 and above 333 K is shown to be kobs = k0 + k1[OH−]. The reaction proceeds with a single rate controlling step, which is interpreted as oxalate ring opening. This is followed by a rapid oxalate loss step. 相似文献
12.
Satoshi Kaneco Kenji Iiba Hideyuki Katsumata Tohru Suzuki Kiyohisa Ohta 《Journal of Solid State Electrochemistry》2007,11(4):490-495
The electrochemical reduction of CO2 with a Cu electrode in methanol was investigated with sodium hydroxide supporting salt. A divided H-type cell was employed;
the supporting electrolytes were 80 mmol dm−3 sodium hydroxide in methanol (catholyte) and 300 mmol dm−3 potassium hydroxide in methanol (anolyte). The main products from CO2 were methane, ethylene, carbon monoxide, and formic acid. The maximum current efficiency for hydrocarbons (methane and ethylene)
was 80.6%, at −4.0 V vs Ag/AgCl, saturated KCl. The ratio of current efficiency for methane/ethylene, r
f(CH4)/r
f(C2H4), was similar to those obtained in LiOH/methanol-based electrolyte and larger relative to those in methanol using KOH, RbOH,
and CsOH supporting salts. In NaOH/methanol-based electrolyte, the efficiency of hydrogen formation, a competing reaction
of CO2 reduction, was suppressed to below 4%. The electrochemical CO2 reduction to methane may be able to proceed efficiently in a hydrophilic environment near the electrode surface provided
by sodium cation. 相似文献
13.
The per-O-acylation of xylan-type hemicellulose was firstly carried out in dimethylsulfoxide/N-methylimidazole (DMSO/NMI) at room temperature without additional catalyst. The optimum conditions for esterification of xylan was investigated in terms of the molar ratio of reagents to anhydroxylose units (AXU) in xylan and the kinds of esterification reagents to obtain a high degree of substitution (DS, 1.98) and weight percent gain (WPG, 86.88 %) of xylan esters. In this solvent system, NMI acted as a solvent, a base and an excellent catalyst, therefore, the per-O-acylation of xylan (DS of 1.98) was readily accomplished in DMSO/NMI system at room temperature. Structure elucidation of xylan esters was characterized by FT-IR and NMR (1H-NMR, 13C-NMR and HSQC). FT-IR and NMR analyses provided the direct evidence of per-O-acylation of xylan under the given conditions. Furthermore, HSQC revealed the higher reactivity of hydroxyls at C-2 position than those at C-3 position of xylan. The solubility of xylan in DMSO, DMF and CHCl3 improved after esterification. TGA/DTG indicated that the thermal stability of xylan increased after the esterification with anhydrides, while decreased with acyl chlorides, probably due to degradation and hydrolysis of the acylated xylan at the presence of by-product hydrochloric acid. 相似文献
14.
Katsunori Teranishi Kayo Watanabe Makoto Hisamatsu Tetsuya Yamada 《Journal of carbohydrate chemistry》2013,32(3):489-494
Abstract Cyclodextrins are cyclic oligosaccharides consisting of six or more α-1,4-linked D-glucopyranose units, which possess primary hydroxyl groups at the C-6 positions and secondary hydroxyl groups at the C-2 and C-3 positions. Because cyclodextrins have a hydrophobic and optically active interior, they have been utilized as transporters of hydrophobic molecules and small molecular mimics of enzymes. The chemical modification of cyclodextrins has been investigated in order to improve these characteristics. Sulfonations of the primary or secondary hydroxyl groups of cyclodextrin have been applied for further functionalization of cyclodextrin, and several methods for regioselective sulfonations have been developed. Among these strategies, selective monotosylation of the C-6 hydroxyl group is done relatively easily by reaction of α or β-cyclodextrin and p-toluenesulfonyl chloride in pyridine1,2 or in alkaline aqueous solution.3,4 However, sulfonation of the secondary hydroxyl groups is more difficult and new sulfonation methods must be developed to provide precursors for cyclodextrin analogues such as amino and sulfide analogues. Several strategies for the sulfonation of one C-2 hydroxyl group have been reported. However, because reaction conditions can require specific sulfonation reagent,5 alkaline condition,3-7 strict anhydrous conditions,8,9 or use of protected C-6 hydroxyl groups,10,11 the methodology is not convenient to employ. 相似文献
15.
Robin F. Weitkamp Beate Neumann Hans‐Georg Stammler Berthold Hoge 《Angewandte Chemie (International ed. in English)》2019,58(41):14633-14638
The reaction of a strongly basic phosphazene (Schwesinger base) with water afforded the corresponding metastable hydroxide trihydrate [OH(OH2)3]? salt. This is the first hydroxide solvate that is not in contact with a cation and furthermore one of rare known water‐stabilized hydroxide anions. Thermolysis in vacuum results in the decomposition of the hydroxide salt and quantitative liberation of the free phosphazene base. This approach was used to synthesize the Schwesinger base from its hydrochloride salt after anion exchange in excellent yields of over 97 %. This deprotonation method can also be used for the phosphazene‐base‐catalyzed preparation of the Ruppert–Prakash reagent Me3SiCF3 using fluoroform (HCF3) as the trifluoromethyl building block and sodium hydroxide as the formal deprotonation agent. 相似文献
16.
Shin-Ichi Takahashi Tetsuya Fujimoto Basu M. Barua Takeaki Miyamoto Hiroshi Inagaki 《Journal of polymer science. Part A, Polymer chemistry》1986,24(11):2981-2993
13C-NMR spectra of trityl cellulose (Tr-Cell), tosyl cellulose (Ts-Cell), cellulose S-methyl xanthate (Cell-M-Xan), and cellulose formate (CF) in dimethylsulfoxide-d6 were analyzed at 50.4 MHz. It was found that the distribution of substituents in the anhydroglucose units of these cellulose derivatives can be estimated from their ring carbon spectra. The results showed that (i) in Tr-Cell having degree of substitution (DS) lower than 1, the hydroxyl groups at C-6 carbon position are selectively tritylated, (ii) in the case of Ts-Cell, the difference in the relative DS value among three different types of hydroxyl groups is not large, although the relative reactivities of hydroxyl groups toward tosylation decrease in the order C-6 > C-2 > C-3, (iii) in Cell-M-Xan, the hydroxyl groups at C-3 carbon position are mainly substituted, and (iv) the ease of formylation is C-6 > C-2 > C-3. The 100.8 MHz 13C-NMR spectra of O-methyl cellulose (MC) revealed that the reactivity order in commercial MC prepared from alkali cellulose is C-6 ? C-2 > C-3. Concerning MC, its water solubility was also discussed in terms of the distribution of substituents along the cellulose chain. 相似文献
17.
The current interest in the preparation of crown ethers is due to their extensive application in many different areas.2 Published synthetic procedures3 that have appeared since Pedersen's first report4 are based mostly on the reaction promoted by strong base between two polyoxaethylene units of varying length, one of which bears two terminal OH groups, and the other two leaving groups. We now report a different approach, based on the action of hydroxide ion on polyethylene-glycol dibromides BrCH2(CH2OCH2)x-1 CH2Br, with X = 5, 6, and 7, in highly concentrated water solution in the presence of Ba++ ion. The most significant feature of the present method is that it requires only one building block, bearing one less oxygen atom than the crown ether to be formed.5 The last oxygen 相似文献
18.
《Journal of Saudi Chemical Society》2020,24(12):934-941
An expedient regioselectivesynthesis of novel mono, C2-symmetric bis-triazole and acridinedione bridged macromolecules has been achieved in good yields employing intermolecular Cu(I) catalyzed azide and alkyne click reaction. Synthesis of O-propargyl acridinedione was achieved in three good yielding steps starting from dimedone, while the symmetrical aliphatic and aryl bis-azides were derived from appropriate dibromides in the presence of sodium azide in dry DMF. The synthesized mono and C2-symmetric bis-macromolecules have been elucidated by 1H, 13C, elemental and mass spectroscopic analysis. The antioxidant activity of synthesized compounds has also been investigated. 相似文献
19.
Gabriela A. Rodrigo Sergio G. Renou Diana G. Bekerman M. Ins Abasolo Beatriz M. Fernndez 《Journal of heterocyclic chemistry》1997,34(2):505-508
Some novel 3-substituted benzoquinoxalinones [R = H, CH3, C6H5, (CH2)2COOH] were synthesized by the Hinsberg reaction between 2,3-diaminonaphthalene and several α-dicarbonyl compounds. The course of the reactions was followed by the second uv/visible Derivative Spectroscopy Method at different pH values (-0.89 to 9.0) and also in organic solvents at 25°. The compound non-substituted at C-3 was the only one that could be obtained in every media in good yields (80%), having pseudo first-order anelation rate constants of relative high values (1 × 10?1 — 1 × 10?2 min?1). On the other hand, only methanol could be used as the organic solvent for the synthesis of all of the other compounds; aqueous media always provided better results. In the 3-methyl derivative, as well as in the 3-phenyl derivative the change of the reaction pH medium modified the stoichiometry of the anelation, turning a non-quantitative reaction into a quantitative one. This is explained by a change in the mechanism of the reaction on going to lower hydrogen concentrations, a fact that was supported by complementary quantitative hptlc experiments. In general, pseudo first-order rate constants for the anelation were one or two logarithmic units lower than those of the non-substituted compound (RC-3 = H), but yields were above 60% in every case. A reaction scheme is presented which includes a probable mechanism. 相似文献
20.
On the structure and cure acceleration of phenol-urea-formaldehyde resins with different catalysts 总被引:2,自引:0,他引:2
Phenol-urea-formaldehyde (PUF) resins with different catalysts [calcium oxide (CaO), sodium carbonate (Na2CO3), zinc oxide (ZnO), and magnesium oxide (MgO)] were prepared to accelerate the cure of the resin at low temperature. The cure-acceleration effects of catalysts on chemical structure and cure characteristics of PUF resins were investigated by using both liquid 13C nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC). The liquid 13C NMR analysis indicated that the catalyst such as CaO seemed to present a retarded effect on the polycondensation reaction of phenolic components with urea units, while the Na2CO3 appeared to promote the self-condensation reaction of phenolic methylol groups at para position toward the formation of para-para methylene linkage. Both ZnO and MgO in PUF resins promoted self-condensation reaction of para methylol groups and condensation reaction of ortho methylol groups with para methylol groups. The catalysts such as Na2CO3, ZnO, and MgO can make PUF resins cure at a low temperature. Among these catalysts, the MgO had the most significant accelerating effect on polycondensation and cure reaction of PUF resin. 相似文献