Starch Derivatives of High Degree of Functionalization 4. Homogeneous Tritylation of Starch and Subsequent Carboxymethylation
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0038-9056 |
| Online Access: | http://www.viks.sk/chk/star_6_01_261_268.doc |
| Abstract: | Summaries. The synthesis of monomethoxytriphenylmethyl (MMtrityl) starch and the subsequent Carboxymethylation of the 6-O-functionalized products were investigated. The trityla-tion both in N,N-dimethylacetamide (DMA)/UCI and in dimethyl sulfoxide (DMSO) occurred homogeneously. The highest degree of Substitution of trityl groups (DSTrityl) obtained after a single conversion step was 0.77 in both solvents. A complete func-tionalization of primary OH-groups was achieved only with unsubstituted triphenyl-methyl Chloride in these reaction media. In case of monomethoxytriphenylmethyl chlo-ride (MMTMC) as reagent an additional conversion step is necessary to synthesize products with a DSTrityl = 1. The structure of the products was analyzed by FTIR- and 13C-NMR spectroscopy. Subsequent Carboxymethylation of the MMtrityl starch sam-ples leads to products with a preferred functionalization of the unprotected secondary OH-groups. After removal of the trityl moieties, the DSCM and the distribution of car-boxymethyl groups within the anhydroglucose unit was investigated by means of HPLC and 1H-NMR spectroscopy. The Carboxymethylation was more effective at O-2 than at O-3. In case of ether products with DSTrityl < 1 a partial Substitution of the primary OH group took place as well. Conclusions. The present paper describes for the first time the homogeneous conversion of starch with monomethoxytri-phenylmethyl chloride (MMTMC) in N,N-dimethylacet-amide (DMA) in combination with LiCI as reaction medium. In contrast to the tritylation of cellulose, it is not possible to achieve a DSTrityl of 1 in a one-step procedure. Starch dissolved in dimethyl sulfoxide (DMSO) shows the same reactivity. Products with a fully functionalized primary position can be obtained by subsequent reaction of MMtrityl starch with MMTMC in tetrahydrofuran. A starch derivative with DSTrityl of 1 can only be synthesized with unsubstituted trityl chloride in an one-step reaction. The determination of the molecular structure of MMtrityl starch is possible by means of FTIR- and 13C NMR spec-troscopy. Carboxymethyl starch products of high DSCM and with a preferred functionalization of the secondary positions in dependence on DSTrityl were obtained by the reaction of MMtrityl starch with sodium monochloroacetate and NaOH powder in DMSO. Under controlled acidic conditions the MMtrityl moieties can be removed without further degradation of the polymer, yielding carboxymethyl starch products. Information about the DSCM and the functionalization patterns of the CMS's synthesized can be effectively obtained by means of HPLC and 1H NMR spectro-scopic measurements after complete depolymerization. The CMS samples with a new functionalization pattern are included in studies on structure-property relationships and the results will be published elsewhere. |
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| ISSN: | ISSN 0038-9056 |
