Dorine L. Verraest

Carboxymethylation of inulin

Inulin was carboxymethylated in aqueous alkaline medium with monochloroacetic acid as the reagent. The degree of substitution of the reaction product was determined by titration, LC analysis and 13C NMR spectroscopy. Carboxymethylinulin with a degree of substitution between 0.2 and 1 was obtained depending on the molar ratio of inulin-monochloroacetic acid. Increasing the concentration of the reaction mixture and lowering the reaction temperature resulted in higher selectivities towards carboxymethylinulin. Determination of the molecular weight distribution was performed by GPC and by multi-angle laser light scattering. Carboxymethylation caused little or no degradation of the chain length of the starting material.

Carboxymethyl inulin: A new inhibitor for calcium carbonate precipitation

A new polysaccharide-based polycarboxylate, carboxymethyl inulin (CMI), was synthesized recently. The influence of small amounts (0.1–200 ppm) of this material on the crystallization of calcium carbonate, an important scale-forming salt, is studied. The effects of CMI are compared to those of a commercial inhibitor (a copolymer of acrylate and maleate) and of other carboxymethylated saccharides. It is shown that CMI is a good calcium carbonate precipitation inhibitor. CMI influences the spontaneous precipitation of calcium carbonate, the morphology of the formed crystals (vaterite and calcite), and the growth rate of calcium carbonate seed crystals. The effect is related to the carboxylate content, the chainlength, and the concentration of the additive. For the application of CMI as crystallization inhibitor, products with a high degree of substitution (degree of substitution>1) and a high degree of polymerization (average degree of polymerization = 30) are the most effective. Also, other carboxymethylated polysaccharides (dextrins, cellulose) show good crystallization-inhibition properties, although the performance of the copolymer of acrylate and maleate is not met. A great advantage of CMI, as compared to carboxymethyl cellulose (CMC), is that aqueous solutions of CMI display, contrary to those of CMC, a very low viscosity. A carboxymethylated disaccharide (carboxymethyl sucrose) has no influence on the calcium carbonate crystallization which shows that the long-chain character is essential for a polycarboxylate inhibitor.

The platinum-catalyzed oxidation of inulin.

The oxidation of inulin with Pt/C as catalyst was studied. Methyl alpha-D-fructofuranoside was used as a model compound for the monomeric unit of inulin. Oxidation occurred selectively at the C-6 position in a high yield (79%). The rate of oxidation and the degree of oxidation obtained for inulin oligosaccharides decreased upon increase of the chain length of the substrate. Inulin could only be oxidized partially: the oxidation degree obtained was 20% of the primary hydroxy groups for inulin with an average dp 30. Possible explanations for these relatively low conversions are discussed. Adsorption and desorption phenomena appear to play and important role during the oxidation process.

Modification of inulin with amidoxime groups and coordination with copper(II) ions

Inulin modified with amidoxime groups was prepared by reaction of the nitrile groups of O-(cyanoethyl)inulin with hydroxylamine. This material has good chelating properties for Cu(II) ions. The coordination of the inulin derivative with Cu(II) has been studied using potentiometry, polarimetry and 17 O NMR spectroscopy. At low molar ratio of Cu(II):amidoxime groups (ρ L < 0.25), stable complexes are formed. The optical rotation measurements indicate folding of the backbone to form intramolecular complexes. At higher ρ values, no additional Cu(II) ions are bound by the polymeric ligand. Presumably, no defolding to form 1:1 1 Cu(II)-amidoxime complexes occurs.

Methyl α-D-fructofuranoside: Synthesis and conversion into carboxylates

Abstract Methyl α- D -fructofuranoside was synthesized by methylation of D -fructose and subsequent isolation of the α-furanoside from the anomeric mixture. This fructofuranoside was used as a starting material for the syntheses of several carboxylates, applying glycolic oxidation, selective oxidation of the primary alcohol function at the C-6 position and carboxymethylation.

Preparation of O-(Aminopropyl)inulin.

Inulin ethers carrying primary amino groups have many potential applications. O-(Aminopropyl)inulin is obtained from O-(cyanoethyl)inulin by reduction of the nitrile groups. Heterogeneously catalyzed hydrogenation using Raney-cobalt as the catalyst resulted in only partial conversion of the O-cyanoethyl into O-aminopropyl groups. Complete conversion of the nitriles to primary amines was achieved by a homogeneous reduction with an excess of sodium borohydride and cobaltous chloride or with metals in liquid ammonia-methanol. Optimal results were obtained with the latter method; 83% of the substituents were converted into primary amines and 17% were lost by dealkylation.

Distribution of substituents in O-carboxymethyl and O-cyanoethyl ethers of inulin

Abstract The distribution of substituents in O -carboxymethyl and O -cyanoethyl ethers of inulin was studied using 13 C NMR spectroscopy and HPLC analysis. For both types of inulin derivatives, the distribution of substituents can be described by the statistical model of Spurlin, showing that the substituents are uniformly distributed along the inulin chains and that the reactivities of the hydroxyl groups in the sugar units are independent upon substitution of a neighbouring hydroxyl group. The 4-position of the d -fructofuranosyl units was found to be the most reactive in the etherifications.

Synthesis of Carbamoylethyl Inulin and Carboxyethyl Inulin

Inulin etherified with carbamoylethyl groups and with carboxyethyl groups is described. Both materials were prepared by hydrolysis of the nitriles of cyanoethyl inulin, which was obtained from reaction of inulin with acrylonitrile.