Starch laurates with average degrees of substitution (DS) from 0.63 to 2.52 are obtained applying three equivalents lauroyl chloride per anhydroglucose unit (AGU). Different solvents, that is, N,N‐dimethylacetamide (DMAc), DMAc/LiCl, and N,N‐dimethylformamide (DMF)/LiCl are studied as reaction medium without and with a base. In the presence of pyridine, products of highest DS and degree of polymerization (DP) are accessible. Nuclear magnetic resonance (NMR) and Fourier Transform Infrared Spectroscopy (FTIR) reveal the presence of acetate moieties that could be caused by O‐acyl‐dimethylacetiminium generated from DMAc in a side reaction. No side reaction is found to occur in the presence of triethylamine and triphenylphosphane. Furthermore, no side reactions are detected in DMF/LiCl as solvent.
Abstract. Metalation of secondary phosphanes HPRRЈ [R = RЈ = C 6 H 4 -4-Me, C 6 H 3 -3,5-Me 2 (3), C 6 H 4 -4-NMe 2 (4); R/RЈ = Ph/cHex] with Mn 2 (CO) 10 in boiling xylene (mixture of isomers), until the evolution of gaseous carbon monoxide ceases, leads to the formation of the dinuclear complexes of the type [(OC) 4 Mn(μ-PRRЈ)] 2 [R = RЈ = C 6 H 4 -4-Me (5), C 6 H 3 -3,5-Me 2 (6), R/RЈ = Ph/cHex (7), R = RЈ = C 6 H 4 -
Unfortunately, it has poor mechanical properties and is hydrophilic. [3] Water uptake impairs the mechanical properties further. Therefore, the conversion of starch into hydrophobic materials is preferable, especially as it also improves its thermal properties. The synthesis of starch esters is an appropriate approach to get hydrophobic products with good thermal characteristics. While starch decomposes under heating up to 300 °C without melting, starch esters may exhibit thermoplastic behavior, which is also desirable for use as plastic material. [4] Especially mixed esters of starch are attractive due to the opportunity of adjusting the properties as needed. [5] Starch esters, even with high degrees of substitution (DS) up to 3, are considered as biodegradable. [6] In industrial applications, starch is chemically modified to products of low DS exclusively. A rather higher DS is needed to get starch esters with thermoplastic properties. High DS values can be obtained by the reaction of the biopolymer with carboxylic acid chlorides in pyridine. [7-13] Carboxylic acid chlorides have the advantage to be highly reactive. However, they are also difficult to handle, may undergo undesirable hydrolysis, and lead to the formation of corrosive hydrogen chloride during the reaction with hydroxyl groups. Mixed starch esters with thermoplastic behavior could be obtained in a one-step synthesis applying carboxylic acid chlorides as reagents. [14] Another appropriate path to obtain starch esters is the conversion of the biopolymer with carboxylic acids activated in situ with agents like 4-toluenesulfonyl chloride, N,N′dicyclohexylcarbodiimide/4-(1-pyrrolidinyl)pyridine, 1,1′-carbonyldiimidazole, and N,N-dimethylformamide (DMF) combined with oxalyl chloride. [15] The products are thermoplastics. Up to now, pyridine is the most common solvent for achieving starch esters of high DS. Pyridine exhibits a high vapor pressure (20.5 hPa, 20 °C), toxicity (LD 50 , rat oral is 891 mg kg-1), and can be easily taken up via inhalation and skin contact. [16] On the contrary, imidazole is less toxic (LD 50 , rat oral is 970 mg kg-1), exhibits a significant lower vapor pressure (0.00327 hPa, 25 °C), and its uptake via skin contact is very slow. Furthermore, it is readily biodegradable. [17] Recently, it was found that imidazole dissolves starch at about 100 °C and may act as reaction medium, base, and catalyst for homogeneous esterification of starch and may be Starch esters have become increasingly attractive as sustainable materials. Instead of carboxylic acid chlorides, mixtures of carboxylic acid anhydrides and carboxylic acids are used to synthesize highly substituted starch esters efficiently applying the new starch solvent imidazole. The reaction is a promising alternative to the existing protocols and leads to thermoplastic mixed starch esters. The mechanism for the reaction path is elucidated by the conversion of starch with propionic anhydride/lauric acid in molten imidazole and various model reactions applying Fourier transform inf...
Starch can be efficiently converted into the corresponding formates homogeneously using N-formyl imidazole obtained by the reaction of 1,1′-carbonyldiimidazole and formic acid in dimethyl sulfoxide as a solvent. Starch formates are soluble in polar aprotic solvents, not susceptible against hydrolysis, and not meltable. Thermoplastics could be generated by conversion of starch formates with long-chain fatty acids exemplified by the conversion with lauroyl chloride in N,N-dimethylacetamide, leading to mixed starch laurate formates. The mixed esters show melting temperatures mainly dependent on the amount of laurate ester moieties.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.