The decomposition of 1-phenyl-3-chloro-nortricyclene and 1-phenylnortricyclene on reduction in 1,2-dimethoxyethane. The EPR spectra of the radical ions

Radical anions of 1-phenyl-3-chloronortricyclene and 1-phenylnortricyclene were produced by reduction with potassium in 1,2-dimethoxyethane under a high vacuum. The initially formed radical anion of 1-phenyl-3-chloronortricyclene was very unstable, and decomposed finally to the anions of naphthalene and biphenyl. The only product of the reduction of 1-phenylnortricyclene was the biphenyl anion. The EPR spectra of the reaction mixtures were measured at temperatures from —80°C to room temperature.     

Accessibility of hydroxyl groups in birch kraft pulps quantified by deuterium exchange in D2O vapor

Deuterium exchange in a deuterium oxide (D₂O) atmosphere (95 % relative humidity), quantified by a dynamic vapor sorption (DVS) apparatus, was applied for assessing the accessibility of hydroxyl groups in birch kraft pulps. Achieving the maximum deuteration level exhibited slower kinetics than was earlier reported for experiments with ground wood and bacterial cellulose. The deuterium exchange process followed two parallel phenomena. Applying multiple drying and rewetting cycles gave kinetic information also on the hornification phenomenon occurring during these cycles. Dry birch pulps treated with sodium hydroxide solution of varying alkalinities at elevated temperatures were assessed for their accessible hydroxyl groups by DVS with deuterium exchange. This method was evaluated against deuteration combined with Fourier transform infra-red spectroscopy and water retention value (WRV). DVS measurements were in correlation with WRV and both the methods indicated that an alkaline treatment of dry birch pulp improves cellulose accessibility. The level of irreversible deuteration also decreased as the alkalinity was increased. DVS was shown to provide quantitative information on the accessibility but to be a time-consuming method for the pulp samples. A potential means to decrease the duration of the measurement is increased D₂O exposure by excluding the drying phases.     

Release of K,Cl, and S during combustion and co-combustion with wood of high-chlorine biomass in bench and pilot scale fuel beds

Studies of the release of critical ash-forming elements from combustion of biomass are typically conducted with small sample masses under well controlled conditions. In biomass combustion on a grate, secondary recapture and release reactions in the fuel-bed may affect the overall release and partitioning of these elements. Earlier work by the authors on the release of K, Cl, and S from a high-chlorine biomass (corn stover) in a lab-scale setup is, in the present work, supplemented with novel results from a bench-scale fixed bed reactor and a 100 kW moving grate pilot facility. The results from the bench-scale reactor indicate that S and K release are not significantly affected by secondary reactions, while Cl is partly recaptured by secondary reactions in the char. A linear increase in K-release was observed from 50% at 906 °C to almost 80 wt.% at 1234 °C when firing only corn stover. A similar release profile was observed for Cl, from 65% to nearly 100%. Complete release of S was achieved at 1234 °C with a linear increase from 70% at 906 °C. Co-combustion of corn stover with low-Cl wood chips served to increase the bed temperature, resulting in complete and close to complete release of Cl and S, respectively. An increase in the relative K-release was observed when increasing the wood chip fraction from 40% to 100% (energy basis). Pilot scale flue gas results indicate that the share of Cl released as HCl decreases towards 0% as the share of wood chips is increased towards 100%. Hence, co-combustion of corn stover with wood chips is expected to decrease the absolute release of KCl due to the lower feedstock quantity of Cl, however, increase the relative release of Cl as KCl.     

Three nuclei n.m.r. spectroscopy of dimethoate compounds. A large solvent effect on the 31P?S?C?1H vicinal coupling

Proton, phosphorus and carbon magnetic resonance spectra of dimethoate, dimethoxon, des-N-methyldimethoate, ω-hydroxydimethoate, trimethyldithiophosphate and O,O-dimethyldithiophosphate in different solvents have been measured. Most of the n.m.r. parameters were characteristic of the structural environment of the corresponding nucleus and solvent-independent. However, in the amide structures dimethoate, dimethoxon, des-N-methyldimethoate and ω-hydroxydimethoate the ³¹P? S? C? ¹H vicinal coupling showed an unusually large solvent effect of a 2.3 to 6.5 Hz decrease when CDCI₃ was replaced by acetone-d₆ or DMSO-d₆.     

1H and 13C n.m.r. spectra of dichloro(trans-2-chlorovinyl)arsine

Proton and carbon magnetic resonance spectra of Lewisite or dichloro(trans-2-chlorovinyl)arsine have been measured and the results are compared with the n.m.r. spectral parameters of other trans-1,2-substituted ethylenes. The coupling constants can be rationalized by substituent electronegativity. The chemical shifts show an unusually large paramagnetic effect from the AsCl₂ group.     

Effect of xylan in hardwood pulp on the reaction rate of TEMPO-mediated oxidation and the rheology of the final nanofibrillated cellulose gel

alkali-washed nanofibrillated cellulose (NFC) samples, obtained from hardwood kraft pulp, with different amounts of retained xylan were prepared to study the influence of xylan on the water-retention properties of NFC suspensions. In this study, NFC was produced using an oxoammonium-catalyzed oxidation reaction that converts the cellulosic substrate to a more highly oxidized material via the action of the nitroxide radical species 2,2,6,6-tetramethylpiperidine-1-oxyl. Reduction of the xylan content in NFC was achieved by cold alkali extraction of kraft pulp. The pulps were then oxidized to a set charge under constant chemical conditions, and the reaction time was determined. The xylan content of the feed pulp was found to have a large negative influence on the oxidation rate of the pulp, as the oxidation time shortened when xylan was removed, from 220 min (for 25.2 % xylan content) to 28 min (for 7.3 % xylan content). Following fibrillation by homogenization, the swelling of the NFC was determined by a two-point solute exclusion method. The distribution of hemicellulose over the fibril surface was observed by atomic force microscopy. Xylan was found to be distributed unevenly over the surface, and its presence increased the water immobilized within flocs of NFC, i.e., so-called network swelling. The swelling of the NFC had a large impact on its rheology and dewatering. Comparison of the morphological and swelling properties of the suspensions with their rheological and dynamic dewatering behavior showed that reducing the xylan content in NFC results in a weaker gel structure of the nanocellulose suspension. The results indicate that most of the water is held by the swollen structure by means of xylan particles trapped within the hemicellulose layer covering the fibril surface. Samples with high xylan content had high shear modulus and viscosity and were difficult to dewater.     

Alkali treatment of birch kraft pulp to enhance its TEMPO catalyzed oxidation with hypochlorite

Alkali treatment was used to increase the reactivity of birch kraft pulp prior to its 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) catalyzed oxidation with hypochlorite, which is a process commonly applied to prepare nanofibrillated cellulose. On contrary to the traditional use of NaBr as a cocatalyst, TEMPO was activated with HOCl prior to the oxidation. Commonly, the lack of bromide increases the oxidation time and impairs the formation of carboxylic groups. However, the reaction time of the bromide-free TEMPO catalyzed oxidation could be shortened from 2.5 to 0.5 h when the pulp was treated with 1 M NaOH prior to the oxidation (2.4 mmol NaOCl/g pulp). The beneficial effect was obtained even if the alkali treatment was executed at room temperature and only for few minutes. Moreover, the alkali pretreatment enabled selective production of a pulp with carboxylate content as high as 1.6 mmol/g with NaOCl dosage of 4.4 mmol/g. The changes in the cellulosic raw material during the alkali treatment were assessed by water retention value and carbohydrate analysis.