A general solvent system for the analysis of lignosulfonates by ³¹P NMR

Abstract

The new solvent system [emim]Cl/DMF/pyridine enables the quantitative determination of hydroxy groups of previously insoluble lignosulfonates by means of 31P-NMR.

High-Resolution Profiling of the Functional Heterogeneity of Technical Lignins

“…Sample preparation was adapted from the literature. 34 − 36 Due to differences in solubility, different solvent mixtures were used to dissolve kraft lignins or lignosulfonates. Kraft lignins (30 mg) were dissolved in a 1:1.6 mixture of chloroform (deuterated) and pyridine (anhydrous, nondeuterated).…”

“…For HWNSSC samples, the addition of the ionic liquid 1-ethyl-3-methylimidazolium chloride (>99%, [emim]Cl) was necessary to achieve adequate dissolution. 36 Internal standard (4 mg of N -hydroxy-5-norbornene-2,3-dicarboxylic acid imide) and 0.5 mg of NMR relaxation agent, chromium (III) acetylacetonate (Cr(acac) 3 ) were added along with the solvent mixture. For phosphitylation, 150 μL of 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane was used.…”

“…Aliphatic hydroxy, aromatic hydroxy, and carboxylic acid group contents were determined by inverse gated 1 H-decoupled 31 P NMR spectroscopy. Sample preparation was adapted from the literature. − Due to differences in solubility, different solvent mixtures were used to dissolve kraft lignins or lignosulfonates. Kraft lignins (30 mg) were dissolved in a 1:1.6 mixture of chloroform (deuterated) and pyridine (anhydrous, nondeuterated).…”

“…Lignosulfonates (30 mg) were dissolved in a mixture of N , N -dimethylformamide and pyridine (anhydrous, nondeuterated; for locking and shimming, 100 μL of CDCl 3 was added); the ratio varied between 4:1 and 5:1 to ensure optimal dissolution of the samples. For HWNSSC samples, the addition of the ionic liquid 1-ethyl-3-methylimidazolium chloride (>99%, [emim]­Cl) was necessary to achieve adequate dissolution . Internal standard (4 mg of N -hydroxy-5-norbornene-2,3-dicarboxylic acid imide) and 0.5 mg of NMR relaxation agent, chromium (III) acetylacetonate (Cr­(acac) 3 ) were added along with the solvent mixture.…”

“…For phosphitylation, 150 μL of 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane was used. Spectra evaluation was carried out as described in the literature. − …”