Polymer-solvent effects in cellulose urethane and methyl cellulose urethane solutions

The polymer-solvent interaction was studied for two similar cellulose derivatives in the semi-dilute concentration range by static and dynamic light scattering. The trisubstituted 3-chlorophenyl carbamate (3Cl-CTC) and a mixed trisubstituted derivative with methyl groups (degree of methyl substituents: DS _Me = 1.6–1.7)combined with the abovementioned 3-chlorophenyl carbamate groups filling the still open positions at the cellulose backbone were synthesized, fractionated and characterized according to standard methods. Different kinds of associations, entangled clusters with a rod-like shape on one side and entanglement networks on the other side, exist in semi-dilute dioxane solutions caused by different polymer-solvent interactions. These quite different associations lead to either a liquid crystalline or a gel-like state upon increase of concentration.     

Base catalyzed cyclization of N-aryl and N-alkyl-O-propargyl carbamates to 4-alkylidene-2-oxazolidinones

The base catalyzed cyclization of N-aryl and N-alkyl-O-propargyl carbamates is studied in detail. The effect of various bases and solvents on the efficacy of this cyclization reaction is analyzed and a new base-solvent system (LiOH in DMF) for effective cyclization of these carbamates is reported. A number of differentially substituted O-propargyl carbamates were cyclized to the corresponding 2-oxazolidinones under these conditions. The reaction conditions reported here are mild and no side reactions were observed in any of the substrates studied. A propargyl carbonate group was unaffected during the course of the cyclization of the O-propargyl carbamate group. The propargyl carbamates were prepared from the corresponding alkyl or aryl amines and the corresponding propargyl chloroformate, resulting in oxazolidinones diversely substituted at the nitrogen atom. N-Aryl-O-propargyl carbamates cyclized readily to the corresponding oxazolidinones with LiOH in DMF, whereas N-alkyl-O-propargyl carbamates reacted slowly under the same conditions. O-Propargyl carbamates substituted at the 1-position tend to cyclize faster whereas those substituted at 3-position cyclize considerably slower than the unsubstituted carbamates.     

Synthesis and characterization of hydroxypropyl cellulose from bacterial cellulose

Bacterial cellulose produced by Acetobacter xylinum has been reacted with propyleneoxide to synthesize hydroxypropyl cellulose(HPC) under different reaction conditions while diluted by toluene. The effects of mass ratio of bacterial cellulose to propyleneoxide, dilutability of toluene, reaction temperature(T) and time(t) were investigated by series of experiments. The degree of substitution(DS), hydroxypropyl content(A) and yield(η) were compared. The optimized product exhibited cold-water solubility and hot-water gelatinization in aqueous medium. Further study was carried out with FTIR, TGA, XRD, SEM and 13C-NMR for characterization. The water/air contact angle measurement reveals that it is a good hydrophobic material with good mechanical properties.     

The synthesis of unusual isocoumarin derivatives: the chemistry of homophthalic acid

Homophthalic acid was reacted with thionyl chloride/DMF and ethyl chloroformate/NEt₃ in the presence and absence of NaN₃. In all cases completely different isocoumarin derivatives were obtained. These unusual isocoumarin derivatives were characterized and their mechanism of formation is discussed.     

Synthesis of d-camphor based γ-amino acid (1S,3R)-3-amino-2,2,3-trimethylcyclopentane carboxylic acid

Synthesis of a γ-amino acid derived from (1R,3S)-camphoric acid is described. d-(+)-Camphoric anhydride, prepared from d-(+)-camphoric acid by treatment with methanesulfonyl chloride and triethylamine, was reacted with benzyl alcohol and catalytic DMAP, and subsequently reacted in a Curtius rearrangement to afford the corresponding carbamate derivative. This derivative was converted to the desired γ-amino acid through hydrogenolysis.     

Model reactions of functionalization of polycarbonate. Reactions of phenyl chloroformate with nucleophiles and cationic polymerization behavior of bicyclo orthoesters containing carbonate group

Some model experiments for functionalization of a polycarbonate were carried out. At first, reactivity of phenyl chloroformate with a few nucleophiles was examined. Reaction with alkyl amines gave corresponding carbamates, but in the case of aniline, formation of a byproduct diarylurea was observed. Reactions with alcohols and phenols afforded carbonates in moderate yields, in which p-nitrophenol and isopropyl alcohol were less reactive. On the basis of these results, 1-ethyl-4-phenoxycarboxymethyl-2,6,7-trioxabicyclo[2.2.2]octane (2) and 1-ethyl-4-ethoxycarboxymethyl-2,6,7-trioxabicyclo[2.2.2]octane (3) were prepared by the reaction of phenyl and ethyl chloroformates with 1-ethyl-4-hydroxymethyl-2,6,7-trioxabicyclo[2.2.2]octane in the presence of tert-amine. 2 polymerized cationically with BF₃OEt₂ at more than 80°C to give a polyether containing both ester and carbonate groups in the side chain, with contamination of a gelled polymer.     

Production of Microbial Cellulose by a Bacterium Isolated from Fruit

This study presents the production of bacterial cellulose (BC) by a bacterium isolated from a rotten fruit and its process optimization. Here, isolation and screening of potent cellulose producers were carried out from different natural sources, viz., soil, rotten fruits, and vegetables and vinegar. A total of 200 bacterial isolates were obtained, which were screened for cellulose production using Hestrin?CSchramm medium. A novel and potent cellulose-producing bacterium was newly isolated from a rotten fruit and identified as Gluconacetobacter sp. F6 through 16S ribosomal DNA sequencing and morphological, cultural, and biochemical characteristics. After optimization of culture conditions, including pH, temperature, agitation, carbon/nitrogen sources, and inducers, the BC production was greatly increased from 0.52 to 4.5?g/l (8.65-fold increase). The optimal culture medium contained 1% (w/v) glucose, 1.5% (w/v) yeast extract, 0.5% (w/v) peptone, 0.27% (w/v) disodium hydrogen phosphate, 0.115% (w/v) citric acid, and 0.4% (w/v) ethanol. BC produced was analyzed for the presence of cellulose fibrils by epiflourescent microscopy using Calcofluor white stain and scanning electron microscopy and confirmed by NMR. There are very scanty reports about the optimization of BC production by bacteria isolated from rotten fruits.     

Readily hydrolysable cellulose esters as intermediates for the regioselective derivatization of cellulose; II. Soluble,highly substituted cellulose trifluoroacetates

Cellulose trifluoroacetate (CTFA) with DS values of 1.5 and 2.1 and DP values ranging from 170 to 800 have been prepared free from impurities of the reaction mixture (weakly bound trifluoroacetic acid) and of the procedure of isolation (diethyl ether). The CTFAs are soluble in DMSO, DMF, pyridine, and THF and thermostable up to 250 °C. A convenient synthetic method for CTFAs with DS 1.5 involves the acylation of cellulose with mixtures of trifluoroacetic acid (TFA) and trifluoroacetic anhydride (TFAA, 33% v/v) at room temperature for 4 h and subsequent treatment of the crude polymer at 150 °C and 80 Pa for 40 min. The preparation of CTFAs with DS-values up to 2.1 requires the addition of chloroform and 16 h reaction time.¹³ C-NMR studies as well as HPLC analyses after methylation and chain degradation show a preferred trifluoroacetylation of the primary hydroxy groups of the cellulose. The extent of depolymerization during the trifluoroacetylation was investigated for various cellulose materials. The cleavage of the trifluoroacetyl groups is possible by treating the derivative with a protic medium like water. Total hydrolysis of CTFA dissolved in DMF with water (room temperature) takes 6 min. The first paper on this topic was concerned with cellulose formates (Schnabelrauchet al., 1992).     

Chiroptical properties of S-alanine conformational isomers

The chiroptical properties of several S-alanine (zwitterionic and nonzwitterionic), S-alanine cation, and S-alanine anion structural isomers are calculated from LCAO-MO-SCF-CI wave functions constructed on the semiempirical CNDO MO model. Electronic excited states are constructed in the virtual orbital-configuration interaction approximation. We calculate and report the transition energies, dipole strengths, reduced rotatory strengths, and dissymmetry factors for the four lowest energy singlet-singlet transitions as a function of a single conformational variable (the angle between the C_αCOO′ plane and the CC_αN plane, where C ≡ carboxylate C atom, N ≡ ammonium or amino N atom, and C_α ≡ α-carbon atom) for zwitterionic and nonzwitterionic S-alanine, the S-alanine anion, and the S-alanine cation. The ground state dipole moments and first three ionization potentials are also computed and reported for the various S-alanine species. Electric dipole transition integrals are calculated in the dipole velocity formalism and all two-center contributions to these and the magnetic dipole transition integrals are included. The calculated rotatory strengths are compared with experimental circular dichroism spectra reported for S-alanine and with predictions based on sector rules which have been proposed for α-amino acids.     

Studies on Non-natural Deoxyammonium Cellulose

Summary: Ammonium group containing cellulose derivatives are prepared from homogeneously synthesized cellulose p-toluenesulfonic acid esters (tosyl cellulose) by conversion with sodium azide and subsequent reduction of the azido moiety applying NaBH₄/CoBr₂/2,2′-bipyridine as reagent. Regarding the tosylation, cellulose samples of different degree of polymerization and hemicellulose content possess a different reactivity. The deoxyamino cellulose is water soluble in the protonated state. Elemental analysis, FTIR- and NMR spectroscopy were carried out to analyze the degree of substitution and functionalization pattern. It was also studied to synthesize deoxyazido celluloses without isolation of the tosyl cellulose. However, a predominant formation of deoxychloro moieties occurs.     

Studies on the molecular flexibility of novel dendronized carboxymethyl cellulose derivatives

Water-soluble deoxy-azido cellulose derivatives were synthesized by heterogeneous carboxymethylation, applying 2-propanol/aqueous NaOH as slurry medium. The novel, carboxymethyl deoxy-azido cellulose provides a convenient starting material for the selective dendronization of cellulose via the copper-catalyzed Huisgen reaction yielding water-soluble carboxymethyl 6-deoxy-(1-N-[1,2,3-triazolo]-4-polyamidoamine) cellulose derivatives of first (degree of substitution, DS 0.51), second (DS 0.44) and third generation (DS 0.39). The novel biopolymer derivatives were characterized by FT-IR and NMR spectroscopy, intrinsic viscosity, sedimentation coefficient and weight average molar mass. Solution conformation and flexibility were estimated qualitatively using conformation zoning and quantitatively (persistence length) using the combined global method. Sedimentation conformation zoning showed a semi-flexible coil conformation and the global method applied to each carboxymethyl deoxy-azido cellulose and carboxymethyl 6-deoxy-(1-N-[1,2,3-triazolo]-4-polyamidoamine) cellulose derivative yielded persistence length all within the range of 2.8-4.0 nm with no evidence of any change in flexibility with dendronization.     

Some chemical transformations of alkyl (4-aminophenyl)carbamates

Azo coupling of diazonium salts derived from alkyl (4-aminophenyl)carbamates with ethyl α-methylacetoacetate gave ethyl 5-alkoxycarbonylamino-1H-indole-2-carboxylates. The condensation of aminophenylcarbamates with aromatic aldehydes in ethanol afforded the corresponding Schiff bases. Cyclohexyl {4-[(4-methoxyphenyl)methylidene]aminophenyl}carbamate reacted with chloroacetyl chloride in dioxane in the presence of triethylamine to produce cyclohexyl {4-[3-chloro-2-(4-methoxyphenyl)-4-oxoazetidin-1-yl]phenylcarbamate, and the reaction of benzyl {4-[(4-nitrophenyl)methylidene]aminophenyl}carbamate with sulfanylacetic acid in DMF led to the formation of benzyl {4-[2-(4-nitrophenyl)-4-oxo-1,3-thiazolidin-3-yl]-phenyl}carbamate.     

Structure–reactivity relationships of alkyl α‐hydroxymethacrylate derivatives

A series of alkyl α‐hydroxymethacrylate derivatives with various secondary functionalities (ether, ester, carbonate, and carbamate) and terminal groups (alkyl, cyano, oxetane, cyclic carbonate, phenyl and morpholine) were synthesized to investigate the effect of intermolecular interactions, H‐bonding, π–π interactions, and dipole moment on monomer reactivity. All of the monomers except one ester and one ether derivative are novel. The polymerization rates, determined by using photo‐DSC, showed the average trend (aromatic carbamate > hydroxyl > ester > carbonate ～ aliphatic carbamate ～ ether), with several exceptions due to the differences in terminal groups. There is a correlation between the chemical shift differences of the double bond carbons, the calculated dipole moments, and the reactivities only for nonhydrogen bonded monomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Characterization of Highly Porous Materials from Cellulose Carbamate

Highly porous cellulose was formed by gelation of cellulose carbamate solutions in caustic soda. Two methods for gel preparation were optimized for the formation of beads and bulky materials – the chemical precipitation from dilute sulfuric acid and the thermal gelation by annealing at elevated temperatures. Various methods were used for characterizing of the pores of low density materials: scanning electron microscopy, small angle X-ray scattering, mercury intrusion and nitrogen sorption. These methods were optimized and used for characterizing the complete pore system from micro to macro pores. The effects of different preparation (cellulose carbamate concentration in caustic soda) and processing (precipitation, drying and pyrolysis) on the pore structure were studied by the set of complementary methods. Aerocell samples with a minimum density of 0.06 g/cm³ were prepared from cellulose carbamate. They are characterized by a broad pore size distribution ranging from 0.5 nm to 1 mm, specific internal surfaces of up to 660 m²/g and total pore volumes of up to 18 cm³/g.     

Effect of the nature of the tetrapyrrole macrocycle on the transmetallation of Zn2+ and Cd2+ porphyrins with PdCl2 in dimethylformamide

Transmetallation of zinc (Zn²⁺) and cadmium (Cd²⁺) complexes of 5,10,15,20-tetraphenylporphin, 5,10,15,20-tetra(4-chlorophenyl)porphyrin, 5,10,15,20-tetra(4-methoxyphenyl)porphyrin, tetrabenzoporphyrin, and octaphenyltetraazaporphyrin with PdCl₂ in DMF was studied by spectrophotometry. The influence of the nature of the tetrapyrrole macrocycle on the reactivity of Zn²⁺ porphyrins toward palladium chloride in boiling DMF was established. Palladium(II) complexes of 5,10,15,20-tetraphenylporphyrin, 5,10,15,20-tetra(4-chlorophenyl)porphyrin, 5,10,15,20-tetra(4-methoxyphenylporphyrin), and tetrabenzoporphyrin were prepared and identified.     

Direct sulfation of bacterial cellulose with a ClSO3H/DMF complex and structure characterization of the sulfates

Bacterial cellulose (BC) is a form of cellulose synthesized by microorganisms, which has unique structure properties and differs from plant cellulose. Up to now, chemical modification of BC has not been studied widely. This paper aims to prepare sodium bacterial cellulose sulfate (SBS) in N,N‐dimethylformamide (DMF) with a ClSO₃H/DMF complex as the sulfating agent. SBSs with diverse degree of sulfation (DS, 0.04–0.86) were synthesized. The system could change from heterogeneous to homogeneous during the sulfation. Regarding to the DS, the optimal ClSO₃H amount and reaction time were 6 mol/mol anhydroglucose unit and 4 h, respectively. DS increased a little when increasing the temperature, while the yield decreased significantly. SBSs with DS > 0.24 were soluble in deionized water. Carbon nuclear magnetic resonance spectroscopy revealed that the sulfation prefers to take place in the order of C‐6 > C‐2 > C‐3. The X‐ray diffraction profiles indicated that the crystalline structure of BC was destroyed during sulfation. BC has better reactivity than microcrystalline cellulose in both sulfation and depolymerization processes. SBS is a potential biomaterial. However, BC depolymerized obviously in present sulfation, which forbids application of SBS in material. Moisture of the reaction mixture should be removed as completely as possible to guarantee efficient sulfation and decrease depolymerization. Copyright © 2013 John Wiley & Sons, Ltd.     

Molecular interactions in β-alanine-water-methanol solutions at 308.15 K on volumetric, viscometeric, and acoustic data

The density, viscosity and ultrasonic velocity for β-alanine solutions in aqueous and aqueous methanol medium at different concentrations has been determined at 308.15 K. The experimentally obtained data were used to evaluate the apparent molal volume and apparent molal adiabatic compressibility. The related thermodynamic parameters like partial molal volume as well as partial molal adiabatic compressibility at infinite dilution along with their corresponding constants S _v and S _k , respectively, give an insight to the nature of molecular interactions. The viscosity coefficient has also been calculated using Jones-Dole equation.     

Short Review on the Synthesis of Thiophene,Pyrazole, and Thiazole Derivatives

The review summarizes the synthesis of different thiophene, pyrazole, and thiazole derivatives by refluxing 9a in ethanol with a catalytic amount of TEA or leaving it in DMF containing potassium carbonate at room temperature overnight to afford the corresponding thiophene derivative 10a . In addition, cyclization of Schiff bases with thioglycollic acid in the presence of a catalytic amount of ZnCl₂ yielded novel thiophene derivatives. Condensation of 2‐substituted‐4‐methylythio semi‐carbazides 92 with carbonyl compounds under strong acidic conditions afforded 2‐thiazolines. Also, carboxylic acid reacted with 2‐thioethylamine in the presence of triphenylphosphine and triethylamine to afford 2‐thiazolines 98 .     

Reactive poly(glycidyl methacrylate) microspheres prepared by dispersion polymerization

Poly(glycidyl methacrylate) [poly(GMA)] microspheres of narrow size distribution were prepared in a simple one‐step procedure by dispersion radical polymerization. Depending on the solvent used, poly(GMA) particle size could be controlled in the range of 0.5–4 μm by changing the solubility parameter of the reaction mixture. In N,N′‐dimethylformamide (DMF)/methanol mixture, the particle size increased and the size distribution broadened with decreasing initial solubility parameter. While in the DMF/methanol solvent system, hydroxypropyl cellulose (HPC) or cellulose acetate butyrate (CAB) were taken as steric stabilizers of the dispersion polymerization, poly(vinylpyrrolidone) (PVP) was used in alcoholic media. Contrary to the DMF/methanol system, narrow particle size distributions were obtained with PVP‐stabilized polymerizations in ethanolic, methanolic, propan‐1‐olic or butan‐1‐olic medium. Both the particle size and polydispersity were reduced with increasing stabilizer concentration. If lower molecular‐weight PVP was used, larger microspheres were obtained. Poly(GMA) samples prepared in a neat alcoholic medium virtually quantitatively retained oxirane group content after the polymerization. Reactivity of the poly(GMA) microspheres was confirmed by their hydrolysis and aminolysis. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3855–3863, 2000     

Mechanism of hydrolysis and aminolysis of homocysteine thiolactone

Homocysteine thiolactone (tHcy) is deemed a risk factor for cardiovascular diseases and strokes, presumably because it acylates the side chain of protein lysine residues (“N‐homocysteinylation”), thereby causing protein damage and autoimmune responses. We analysed the kinetics of hydrolysis and aminolysis of tHcy and two related thiolactones (γ‐thiobutyrolactone and N‐trimethyl‐tHcy), and we have thereby described the first detailed mechanism of thiolactone aminolysis. As opposed to the previously studied (thio and oxo)esters and (oxo)lactones, aminolysis of thiolactones was found to be first order with respect to amine concentration. Anchimeric assistance by the α‐amino group of tHcy (through general acid/base catalysis) could not be detected, and the Brønsted plot (nucleophilicity versus pK_a) for aminolysis yielded a slope (β^nuc) value of 0.66. These data support a mechanism of aminolysis where the rate‐determining step is the formation of a zwitterionic tetrahedral intermediate. The β^nuc value and steric factors dictate a regime whereby, at physiological pH values (pH 7.4), maximal reactivity of tHcy is exhibited with primary amine groups with a pK_a value of 7.7; this allows the reactivity of various protein amino groups towards N‐homocysteinylation to be predicted.