Herwig Schottenberger

Novel concepts of dissolving pulp production

Herein, we report about existing and novel dissolving pulp processes providing the basis for an advanced biorefinery. The SO2–ethanol–water (SEW) process has the potential to replace the acid sulphite process for the production of rayon-grade pulps owing to a higher flexibility in the selection of the raw material source, substantially lower cooking times, and the near absence of sugar degradation products. Special attention is paid to developments that target toward the selective and quantitative fractionation of paper-grade pulps into hemicelluloses and cellulose of highest purity. This target has been accomplished by the IONCELL process where the entire hemicellulose fraction is selectively dissolved in an ionic liquid in which the H-bond basicity and acidity are adequately adjusted by the addition of a co-solvent. At the same time, pure hemicellulose can be recovered by further addition of the co-solvent, which then acts as a non-solvent. The residual pure cellulose fraction may then enter a Lyocell process for the production of regenerated cellulose products.

Separation of Hemicellulose and Cellulose from Wood Pulp by Means of Ionic Liquid/Cosolvent Systems

Pulp of high cellulose content, also known as dissolving pulp, is needed for many purposes, including the production of cellulosic fibers and films. Paper-grade pulp, which is rich in hemicellulose, could be a cheap source but must be refined. Hitherto, hemicellulose extraction procedures suffered from a loss of cellulose and the non-recoverability of unaltered hemicelluloses. Herein, an environmentally benign fractionation concept is presented, using mixtures of a cosolvent (water, ethanol, or acetone) and the cellulose dissolving ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIM OAc). This cosolvent addition was monitored using Kamlet-Taft parameters, and appropriate stirring conditions (3 h at 60 °C) were maintained. This allowed the fractionation of a paper-grade kraft pulp into a separated cellulose and a regenerated hemicellulose fraction. Both of these exhibited high levels of purity, without any yield losses or depolymerization. Thus, this process represents an ecologically and economically efficient alternative in producing dissolving pulp of highest purity.

A cytotoxic bis(carbene)gold(I) complex of ferrocenyl complexes: Synthesis and structural characterisation

The N-heterocyclic carbene (NHC) precursors 1-[(E)-2-butenyl]-3-(4-ferrocenylphenyl)imidazolium bromide (2) and 1-[(E)-2-butenyl]-3-(4-ferrocenylphenyl)imidazolium tetrafluoroborate (3) were derived from 1-(4-ferrocenylphenyl)imidazole. Ferrocenyl complex 3 reacts with Ag2O and chloro(dimethylsulfide)gold(I) in the presence of tetraethylammonium chloride to produce the mixed metal species bis{1-[(E)-2-butenyl]-3-(4-ferrocenylphenyl)-2H-imidazol-2-ylidene}gold(I) tetrafluoroborate (4). Single crystal X-ray structure analyses of 1, 3 and 4 indicate that the NCHN-hydrogen in 3 is hydrogen bonded to the BF4− anion [C(H1)⋯F, 3.265(4) A], as is also reflected in the position of its 1H NMR chemical shift. Cytotoxicity studies show that complex 4 is selective for cancer cells and active against the tumour cell lines Jurkat and MCF 7.

Selective CC Bond Formation between Alkynes Mediated by the [RuCp(PR3)]+ Fragment Leading to Allyl, Butadienyl, and Allenyl Carbene Complexes—An Experimental and Theoretical Study

The reaction of alkynes with [RuCp(PR(3))(CH(3)CN)(2)]PF(6) (R=Me, Ph, Cy) affords, depending on the structure of the alkyne and the substituent of the phosphine ligand, allyl carbene or butadienyl carbene complexes. These reactions involve the migration of the phosphine ligand or a facile 1,2 hydrogen shift. Both reactions proceed via a metallacyclopentatriene complex. If no alpha C[bond]H bonds are accessible, allyl carbenes are formed, while in the presence of alpha C[bond]H bonds butadienyl carbenes are typically obtained. With diphenylacetylene, on the other hand, a cyclobutadiene complex is formed. A different reaction pathway is encountered with HC[triple bond]CSiMe(3), ethynylferrocene (HC[triple bond]CFc), and ethynylruthenocene (HC[triple bond]CRc). Whereas the reaction of [RuCp(PR(3))(CH(3)CN)(2)]PF(6) (R=Ph and Cy) with HC[triple bond]CSiMe(3) affords a vinylidene complex, with HC[triple bond]CFc and HC[triple bond]CRc this reaction does not stop at the vinylidene stage but subsequent cycloaddition yields allenyl carbene complexes. This latter C[bond]C bond formation is effected by strong electronic coupling of the metallocene moiety with the conjugated allenyl carbene unit, which facilitates transient vinylidene formation with subsequent alkyne insertion into the Ru[double bond]C bond. The vinylidene intermediate appears only in the presence of bulky substituents of the phosphine coligand. For the small R=Me, head-to-tail coupling between two alkyne molecules involving phosphine migration is preferred, giving the more usual allyl carbene complexes. X-ray structures of representative complexes are presented. A reasonable mechanism for the formation of both allyl and allenyl carbenes has been established by means of DFT calculations. During the formation of allyl and allenyl carbenes, metallacyclopentatriene and vinylidene complexes, respectively, are crucial intermediates.

Ionic liquids as superior solvents for headspace gas chromatography of residual solvents with very low vapor pressure, relevant for pharmaceutical final dosage forms.

1-n-Butyl-3-methylimidazolium dimethyl phosphate (BMIM DMP) was identified as the most suitable ionic liquid as solvent for the headspace gas chromatographic analysis of solvents with very low vapor pressure such as dimethylsulfoxide, N-methylpyrrolidone, sulfolane, tetralin, and ethylene glycol in a realistic matrix of commonly used excipients (carboxymethylcellulose, magnesium stearate, guar flour, and corn starch) in pharmaceutical products. Limits of quantification and limits of detection were in the low microgram per gram range. The detection of traces of sulfolane in a real sample of tablets containing the drug cefpodoxim proxetil demonstrated the applicability of the method.

Dialkyl Phosphate-Related Ionic Liquids as Selective Solvents for Xylan

Herein we describe a possibility of selective dissolution of xylan, the most important type of hemicellulose, from Eucalyptus globulus kraft pulp using ionic liquids (ILs). On the basis of the IL 1-butyl-3-methylimidazolium dimethyl phosphate, which is well-known to dissolve pulp, the phosphate anion was modified by substituting one oxygen atom for sulfur and selenium, respectively. This alteration reduces the hydrogen bond basicity of the IL and therefore prevents dissolution of cellulose fibers, whereas the less ordered xylan is still dissolved. (1)H NMR spectra of model solutions and Kamlet-Taft parameters were used to quantify the solvent polarity and hydrogen bond acceptor properties of the ILs. These parameters have been correlated to their ability to dissolve xylan and cellulose, which was monitored by (13)C NMR spectroscopy. It was found that the selectivity for xylan dissolution increases to a certain extent with decreasing hydrogen-bond-accepting ability of anions of the ILs.

Ethynylcobaltocenium compounds as precursors for bridged, heteronuclear oligometallocenes: Preparation and reactions of ethynyl-, trimethylsilylethynyl- and ferrocenylethynylcobaltocenium salts

Abstract A general procedure for introducing substituents into cationic sandwich complexes by nucleophilic attack of suitable carbanions and subsequent hydride abstraction has been applied to the preparation of ethynyl-substituted cobaltocene species. Ethynylcobaltocenium hexafluorophosphate, trimethylsilylethynylcobaltocenium hexafluorophosphate, and salts of ferrocenylethynylcobaltocenium, a rigidly-bridged, conjugated heteronuclear bimetallocene, have been prepared. These compounds and isolated exo-diene intermediates have been characterized by NMR and IR spectroscopy, mass spectrometry and cyclic voltammetry. The new two-centered sandwich cation ferrocenylethynylcobaltocenium exhibits diamagnetism, indicating a situation not involving asymmetric averaging of the formal oxidation states on the NMR time scale. The electrochemical potentials and halfwave separations fall within the expected ranges.

Semimasked 1,1′-diethynylferrocenes: synthetic concepts, preparations, and reactions

Abstract Due to the inherent instability of 1,1′-diethynylferrocene, the respective coupling chemistry for the access of oligonuclear systems requires stepwise preparative sequences involving consecutive ethyne deprotection, or the conversion of latent ethyne precursor functionalities, respectively. The new derivatives 1-acetyl-1′-ethynylferrocene, 3 , and, preferably, 1-ethynyl-1′-formylferrocene, 9 , turned out to be the most favorable starting compounds. The subsequent synthetic chemistry, as well as the X-ray structures of selected starting and target derivatives are presented. A unique intramolecular coupling product, 12 , represents the first ladder-type tricyclic metallocenophane system exhibiting high ring strain. Supplementary novelties concerning monoacetylenic parent systems are also presented.

X-ray structural investigations and conformational particularities of ethyne-derived organometallics based on ferrocene and fluorene

Abstract The X-ray structures of eight different ethyne-based organometallic compounds, 1-trimethylsilylethynylferrocene [55997-95-0] (I), 1-iodoethynylferrocene [94598-10-4] (II), 1,1′-bis(2-hydroxy-2-methylbut-3-yn-4-yl)ferrocene [144975-44-0] (III), novel (5-hydroxy-5-methylhexa-1,3-diyn-1-yl)ferrocene-co-3-hydroxy-3-methyl-1-iodobut-1-yne (IVb), endo-1-hydroxy-1-ethynylferroceno[2.3.a]indene (V), 9-ethynyl-9-hydroxyfluorenedicobalthexacarbonyl [148943-14-0] (VI), ethynylferrocene-derived (Z)-[2-(4-nitrophenyl)-1chloroethenylferrocene [151305-19-0] (VII) and (Z)-[2-(4-acetylphenyl)-1-chloroethenyl]ferrocene [151305-20-3] (VIII) are presented. Selected crystallographic data, particular structural features as well as the syntheses of IVa, IVb and V are reported. The importance of hydrogen bonding for the lattice formation of the ferrocenylpropargylalcohols III and IV as well as the relevance of hydrogen bonding and π-stacking in VII and VIII are discussed in detail.

The reaction of ferrocenyl acetylene with [RuCp(PR3)(CH3CN)2]PF6 (R=Me, Ph, Cy). Formation of the first allenyl carbene complexes

Abstract The reaction of [RuCp(PR3)(CH3CN)2]PF6, where R=Ph and Cy, with ferrocenyl acetylene (HCCFc) affords the first η2-allenyl carbene complexes [CpRu(C(Fc)-η2-CHCCH(Fc))(PR3)]PF6. The new type of CC bond formation is affected by the strong electronic coupling of the ferrocenyl moiety with the conjugated allenyl carbene unit, which facilitates transient vinylidene formation with subsequent alkyne insertion into the RuC double bond. The vinylidene intermediate appears to occur only in the presence of bulky substituents of the phosphine co-ligand. For small R=Me, head-to-tail coupling between two alkyne molecules involving phosphine migration is preferred, giving the more usual η3-allyl carbene complex [CpRu(C(Fc)-η3-CHC(Fc)CHPMe3)]PF6. The X-ray structure of an η2-allenyl carbene complex is presented.