Periodate oxidative decrystallization of cotton cellulose

Cotton cellulose is decrystallized by periodate oxidation to essentially zero crystallinity index (CI) at 100% oxidant consumption. The decrease in CI is pseudo zero-order over 60% of the reaction and consistent with a diffusion-controlled mechanism. The attack on regions of high order is indicated to be 100% in the latter phase of oxidation and 13% in the initial phase. Data allow an estimate that approximately 60% of the structural segments of the cotton cellulose under investigation lies in highly ordered arrangements.     

Temperature-concentration conditions of liquid-crystalline-phase formation in cellulose ethers and esters in trifluoroacetic acid

The temperature-concentration conditions of formation and regions of liquid-crystalline-phase existence in concentrated solutions of methyl cellulose, hydroxypropylmethyl cellulose, cellulose diacetate, and cellulose triacetate in trifluoroacetic acid are studied via optical methods. It is shown that the type of anisotropic structures is largely determined by the pitch of the cholesteric helix. An increase in the strength of acetate films corresponding to the maximum optical anisotropy in the two-phase region of transition of cellulose acetates solutions to the LC phase is found.     

Mesomorphic solutions of cellulose triacetate in halogenated organic acids and mixtures of trifluoroacetic acid and dichloromethane

Cellulose triacetate (CTA) forms liquid-crystalline solutions in trifluoroacetic acid, dichloroacetic acid, and mixtures of trifluoroacetic acid and dichloromethane. Brilliant iridescent coloration, high optical rotations, and birefringent regions with swirl-like fingerprint patterns suggested the formation of cholesteric liquid crystals. Trifluoroacetic acid–dichloromethane is a particularly excellent solvent mixture to form liquid-crystal solutions of cellulose acetate. Crude bulk viscosity measurements confirm the formation of an anisotropic phase, and the temperature dependence of the critical concentration for formation of the anisotropic phase, obtained by bulk viscosity measurements at various temperatures, provides confirming evidence. Viscosity decreases with aging, suggesting that CTA is slowly degraded in the solvents studied. This is also confirmed by optical rotatory measurements and by polarizing microscope observations. The miscibility gap is observed as a function of molecular weight, and the differences between the experimental data and Flory's prediction are discussed.     

Chemical transformations of methane in trifluoroacetic acid

The reaction of methane conversion in anhydrous trifluoroacetic acid (TFA) is shown to take place at room temperature and atmospheric pressure and to result in the formation of a resinous product. Signals of ions with molecular weights of 684 and 700 are observed in MALDI-TOF spectra of the dry residue of methane conversion products.     

Activation of molecular oxygen in trifluoroacetic acid

The interaction of molecular oxygen with aqueous trifluoroacetic acid (TFA) led to an increase in pH. This effect was explained by a decrease in the concentration of the protonated CF₃CO₂H₂⁺ and H₃O⁺ species after oxygen was fed in the reactor. Quantum-chemical calculations show that a radical pair can be formed in an activation-free exothermal reaction involving the radical residue of the acid, the CF₃CO₂H₂⁺...³O₂...CF₃CO₂⁻ peroxide radical, and the acid molecule in the CF₃C₂^·...HOO^· collision complex. It was assumed that the activation of molecular oxygen in aqueous TFA solutions, providing the activity of the system in oxidations of various organic and inorganic substrates, is related to the formation of peroxide radicals in them.     

Activation of molecular oxygen in trifluoroacetic acid

The possibility of the formation of the H₂O₂^+· cation-radical was determined according to the data from nonempirical calculations for liquid trifluoroacetic acid, which forms a hydroperoxide radical after deprotonation. A catalytic cycle was obtained in which CF₃COOH serves as a catalyst in the oxidation of a substrate by dissolved molecular oxygen.     

Reaction of indoles with trifluoroacetic acid

3-Trifluoroacetyl indoles are formed by the action of trifluoroacetic acid on indole-2-carboxylic acid and its benzo-substituted derivatives. When unsubstituted indole is refluxed with trifluoroacetic acid, it gives 3-trifluoroacetylindole in 30% yield.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1233–1235, September, 1981.     

Mesomorphic solutions of cellulose triacetate in trifluoroacetic acid halogenated solvent mixtures: Phase separations and factors affecting the cholesteric pitch

Cellulose triacetate (CTA) forms cholesteric mesophases in trifluoroacetic acetic acid (TFA) and mixtures of TFA and CH₂Cl₂, 1,2-dichloroethane (1,2-DCE), and CHCl₃. Cholesteric pitches and solution flow times indicate that the order of solvent powers is TFA-CH₂Cl₂ > TFA-1,2-DCE > TFA > TFA-CHCl₃, which is the order of decreasing acidity of the solvent systems. With TFA-CH₂Cl₂ as solvent, the one-fourth power of the pitch varies inversely with the CTA concentration, and increases linearly with temperature. The pitch increases exponentially with time and increases faster the more acidic the solvent. In a magnetic field a cholesteric to nematic transition occurs. A minimum in solution viscosity occurs at 34% w/v of CH₂Cl₂ for solutions in TFA-CH₂Cl₂. The miscibility gap as a function of molecular weight depends on the solvent composition and is smaller the higher the acidity of the solvent. Agreement between the experimentally observed A and B points and the theoretical points is better for the Khokhlov and Semenov theory for semiflexible chains than for the original Flory theory or the Flory-Ronca modification.     

Improved sulfuric acid decrystallization of wheat straw to obtain high yield carbohydrates

Wheat straw is an abundant residue of agriculture which is increasingly considered as a feedstock for the production of fuels, energy and chemicals. The concentrated acid hydrolysis of wheat straw has been investigated in this work. Hemicellulose and cellulose have been efficiently converted into monomers of pentoses and glucose in high yields by a one-pot decrystallization-hydrolysis procedure. This process differs from usual concentrated acid biomass fractionation methodologies as a low quantity of acid is used and the supplementary use of a costly acid is not necessary to yield efficiently carbohydrates. The influence of the acid native concentration, and of the time of the decrystallization step have been studied so as to optimise yields of carbohydrates using a minimum of sulfuric acid so as to preserve a potential market value of the process. One can also imagine that this procedure will not impact dramatically the subsequent purification costs. In view of the growing importance of renewable resource-based molecules in the chemical industry, and the necessity to produce fermentable substrate for biofuels, this approach may open a new avenue for the use of wheat straw as raw material for various applications.     

Lyotropic mesomorphic formation of cellulose in trifluoroacetic acid-chlorinated-alkane solvent mixtures at room temperature

Mixtures of trifluoroacetic acid (TFA)-1,2-dichloroethane (1,2-DCE); TFA-dichloromethane (CH₂Cl₂); and TFA-trichloromethane (CHCl₃) are excellent cellulose solvents at room temperature. TFA-1,2-DCE and TFA-CH₂Cl₂ are superior to pure TFA. Lyotropic cellulose mesophases were obtained in (20% w/v) solutions of cellulose in these solvent mixtures. The optical and optical rotatory powers of the solutions suggest that the lyotropic mesophase of cellulose is cholesteric. This implies that cellulose molecules are arranged in helical form in these solvent systems.     

Transformation of organic and inorganic compounds in trifluoroacetic acid

It is established that the effectiveness of fluorine-containing acids in the transformation of organic and inorganic substrates is due to the ability of the acid to perform several functions: to accumulate relatively high concentrations of molecular oxygen, to activate it, and to serve as a hydrogen-containing medium.     

Adamantylation of N-aryl and N-arylalkyl acetamides in trifluoroacetic acid

Russian Chemical Bulletin - Alkylation of N-aryl and N-arylalkyl acetamides with hydroxy adamantane derivatives in trifluoroacetic acid was studied. The differentiating effect of trifluoroacetic...     

AgOAc-mediated rearrangement of gem-dibromospiropentanes in trifluoroacetic acid

AgOAc-mediated intramolecular skeleton rearrangement reaction of gem-dibromospiropentanes produced the corresponding naphthalene and indene derivatives in moderate to good yields under mild conditions.     

Chemical transformations of CO2 in trifluoroacetic acid solutions

It is established that a conversion reaction of carbon dioxide takes place at room temperature and atmospheric pressure in aqueous solutions of trifluoroacetic acid (TFA), which leads to the formation of oxalic acid and heavier polymerized products.     

Kinetics of heptene-I interaction with formaldehyde in trifluoroacetic acid

A mechanism for formation of hydrogenated furans in the reaction of α-olefins with formaldehyde is suggested. Based on kinetic data, it involves the equilibrium addition of protonated formaldehyde to the olefin.     

Some further observations on the systems cellulose/trifluoroacetic acid/CH2Cl2 and cellulose triacetate/TFA/CH2Cl2

There is little or no trifluoroacetylation of cellulose dissolved in TFA-CH₂Cl₂ admixtures. Both cellulose and cellulose triacetate (CTA)are slowly degraded in the solvent. Cellulose forms a mesophase as low as 4%(w/w)concentration, but CTA has a much higher critical concentration, 20% (w/w), in TFA-CH₂Cl₂. The cellulose behaves as a rigid rod in TFA-CH₂Cl₂ (70/30v/v) and its persistence length calculated using the lattice model approximates its chain length, presumably due to extensive interaction with the solvent. As expected, due to low polymer-solvent interactions, the persistence length of CTA in TFA-CH₂Cl₂ is only one-fourth the chain length.