Synthesis of Hydrophobic Starch Esters by Reaction of Starch with Various Carboxylic Acid Imidazolides
| Main Authors: | , , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0038-9056 |
| Online Access: | http://www.viks.sk/chk/star_10_02_449_453.doc |
| Abstract: | Summaries. A novel efficient method of preparing hydrophobic starch esters with a DS = 1.55-2.0 using amylose enriched starch (amylomaize starch) or potato starch and a fatty acid imidazolide in DMSO as solvent is described. The fatty acid imidazolides can be easily prepared by conversion of the corresponding acyl chloride with imidazole in toluene according to a synthesis route developed by Staab et al. [1-4]. The by-product imidazole hydrochloride could be converted to imidazole by alkaline work up with Na2CO3. As compared with the direct esterification of starch in presence of a fatty acid chloride the presented synthesis method does not need toxic amines like pyridine as catalyst. Only a catalytic amount of a methanolic KOCH3 solution is required. Furthermore no hydrolytic degradation of starch could be observed in contrast to the direct esterification reaction with a fatty acid chloride. Conclusions. Potassium methoxide catalyzed esterification of amylomaize starch or potato starch with various carboxylic acid imidazolides (C8, C12 and C16) is a powerful synthesis route to achieve hydrophobically modified starch esters with a DS from 1.55 to 2.0 in good yields (70-90 %). The carboxylic acid imidazolides can be prepared easily by conversion of the corresponding fatty acid chloride with imidazole [1-4]. The by-product imidazole hydrochloride was converted to imidazole by treatment with a saturated sodium carbonate solution. Thus the process may become as economic as the direct conversion of starch with the fatty acid chloride because imidazole can be recovered in both reaction steps. Only the fatty acid chloride is consumed. The advantage of this synthetic method is that no hydrolytic degradation of the starch could be observed. GPC determinations of the achieved starch esters compared with octanoyl amylomaize starch ester synthesized by direct esterification of starch in presence of the corresponding acid chloride demonstrated these results unambiguously. The average molar masses of the prepared starch esters were approximately five times larger than the average molar mass of the octanoyl starch ester synthesized via the acyl chloride method. Ernährung und Landwirtschaft within the research project (FKZ 97 NR 105) granted by the Fachagentur Nachwach-sende Rohstoffe e. V. in Gulzow. The determinations of the material properties were carried out within a joint research project (FKZ 97 NR 107) at the Fraunhofer Institute for Process Engineering and Packaging, in Freising by Dr. C. Schönweitz. We would like to thank Dr. K. Bergander and Mrs. K. Voss, University of Munster, for the 1H-NMR/13C-NMR measurements. |
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| ISSN: | ISSN 0038-9056 |
