Harald Schmidt

Levoglucosan, cellobiose and their acetates as model compounds for the thermally assisted hydrolysis and methylation of cellulose and cellulose acetate

Levoglucosan (1,6-anhydro-β-d-glucopyranose), cellobiose (β-d-glucopyranosyl-[1→4]-d-glucopyranose), tri-O-acetyl-levoglucosan (1,6-anhydro-β-d-glucopyranose-2,3,4-triacetate) and cellobiose octaacetate have been studied with regard to their suitability as model compounds for thermally assisted hydrolysis and methylation with tetramethylammonium hydroxide of cellulose and cellulose acetate. In addition, the results of analytical pyrolysis of methyl cellulose were compared with those of thermally assisted hydrolysis and methylation, to distinguish between products arising from alkaline hydrolysis and pyrolytic cleavage, respectively. Parameters such as surplus of tetramethylammonium hydroxide, water content prior to pyrolysis and pyrolysis temperature were varied to find the optimal thermochemolysis procedure for cellulosic samples.

Cannizzaro reaction of aldehydes in TMAH thermochemolysis

Abstract Recently, tetramethylammonium hydroxide (TMAH) has been advantageously used in the analytical pyrolysis of polymers, but yielded a great amount of carboxylic acid methyl esters which were absent in conventional pyrolysis. Our experiments with model compounds such as furaldehyde, benzaldehyde, hydroxy-, methoxy-, dimethoxybenzaldehyde and vanillin show that TMAH can react not only as a methylating and/or hydrolysing agent but also with aldehydes according to a Cannizzaro reaction and the reaction products can be in-situ methylated to the corresponding esters and ethers.

The effect of tetramethylammonium hydroxide in comparison with the effect of sodium hydroxide on the slow pyrolysis of cellulose

Abstract The effect of two bases, tetramethylammonium hydroxide (TMAH) used in thermally assisted hydrolysis and methylation (THM) analysis of biopolymers and NaOH generally used in cellulose and textile industry, was compared in the pyrolysis of cotton cellulose at very low concentrations using differential thermal analysis, data obtained from thermogravimetry/mass spectrometry and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) to get more information about the reactive decomposition of cellulose. Highly purified cotton cellulose was impregnated with NaOH or TMAH to various weight levels up to 5%, immediately dried and pyrolysed in He atmosphere. The interaction with cellulose has a stabilizing effect on TMAH. Both bases decrease the temperature of the decomposition with increasing concentration, however, the decomposition patterns are different. The differences in the pyrolysis are enhanced by the methylating effect of TMAH.

The behavior of aldehydes—produced as primary pyrolysis products—in the thermochemolysis with tetramethylammonium hydroxide

Abstract Aromatic aldehydes are well known products in the pyrolysis of humic substances, polysaccharides, lignins and wood species. Our studies with model compounds show that these aldehydes undergo a disproportionation/methylation or disproportionation/butylation reaction if pyrolysis is carried out in the presence of tetramethylammonium hydroxide (TMAH) or tetrabutylammonium hydroxide (TBAH), respectively. Methoxy-, trimethoxy- and benzyloxy-benzaldehydes were subjected to TMAH or TBAH pyrolysis. Due to this side reaction, aldehydes contribute to the artefact appearance of benzenecarboxylic acid species in the TIC chromatogram of the thermochemolytic products of humic substances, lignin, wood, etc.

THM-GC/MS analysis of model uronic acids of pectin and hemicelluloses

Abstract The thermally assisted hydrolysis and methylation (THM) reaction of hexuronic acids and xylobiose using tetramethylammonium hydroxide (TMAH) was studied. The results were compared to the THM of the corresponding matrix polymers. Glucuronic and galacturonic acids—which we take as model substances—produce unique products, namely 2,4,6-tri- O -methyl-3-deoxy-glucaric acid dimethyl ester and tri- O -methyl-3-deoxy-galactaric acid dimethyl ester, respectively, together with their epimers. The EI mass spectrum, as well as a proposed fragmentation pathway, are presented. These markers, however, are not detectable in the THM of the corresponding polymers, i.e. the hemicellulose xylan and pectin.

Pyrolysis–gas chromatography/mass spectrometry and thermally assisted hydrolysis and methylation (THM) analysis of various cellulose esters

Abstract Cellulose is being derivatized to change its properties and improve usability for special purposes. Its esters with phthalic acid, citric acid, maleic acid, and nitric acid were examined with analytical pyrolysis and thermally assisted hydrolysis and methylation using tetramethylammonium hydroxide. With traditional analytical pyrolysis the free acid or an anhydrous and decarboxylated thermally stable form could be proved in organic cellulose esters with a low degree of substitution, whereas for the high substituted cellulose nitrate also completely new products were produced through this method. Using thermally assisted hydrolysis and methylation the sensitivity of the method could be improved especially for cellulose derivatives with a low degree of substitution and characteristic products could be identified for most samples.

QUATAM PROCESS—NEW SULFUR-FREE DELIGNIFICATION

ABSTRACT An essentially new alkaline chemical pulping process—the Quatam process—has been introduced using an organic base for producing cellulose fibers from wood and annual plants. Solutions of quaternary ammonium compounds, preferably tetramethylammonium hydroxide (TMAH), serve as pulping liquors. The process produces high quality pulp with low kappa number, high brightness and good viscosity—without using sulfur-containing compounds. The process is suitable for both hardwood and softwood. The pulping selectivity of TMAH is demonstrated. Bleachability and mechanical properties of the resulting pulp are compared to those of conventional Kraft pulp.

ZUM REAKTIONSVERHALTEN VON 2,4-DIOXOHEXAHYDRO-1,3,5-TRIAZIN

Summary2,4-Dioxohexahydro-1,3,5-triazin (DHT) reacts with formaldehyde and secondary amines (Mannich reaction) to the corresponding 1,3,5- or 1,5-aminomethyl-DHTs (1a–8a or1b–11b).DHT and formaldehyde give the methylol compounds12a,12b, and12c. Alkylation ofDHT with alkyl halides in presence of base and dimethyl-sulfoxide as the solvent affords the tri-N-alkyl derivatives14–22. 1,5-Dimorpholinomethyl-DHT (1b) can be alkylated in position 3 with alkyl halides. The morpholinomethyl groups in positions 1 and 5 behave as protecting groups and are easily removable. Thus, it is possible to introduce different alkyl substituents into the molecule. The reaction of1b with dihaloalkanes results in a coupling of twoDHT moleculesvia the nitrogen in position 3 (compounds26–29).