High esterification degree ethyl alginate preparation method

Abstract

The invention discloses a high esterification degree ethyl alginate preparation method, which comprises: adding alginic acid to anhydrous ethanol, stirring, adding a dehydrating agent having the same molar water content as the alginic acid, adding a catalyst, carrying out stirring heating to achieve a reflux state, adding the remaining dehydrating agent in a dropwise manner when the reflux temperature is achieved, continuously carrying out a reflux reaction for 6-18 h after the remaining dehydrating agent is uniformly added in the dropwise manner within 2-4 h, completing the reaction, cooling to a room temperature, adjusting the pH to 6.5-7.0 with an alkali liquid, filtering, washing the filter cake by using an ethanol aqueous solution with a mass concentration of higher than 60%, and drying at a temperature of 40 DEG C to obtain the ethyl alginate. According to the present invention, with the ethyl alginate preparation method, the esterification degree of the prepared ethyl alginate is higher than 68% and is significantly higher than the esterification degree of the straight chain alkanol ethyl alginate prepared by using the existing technology.

Description

technical field [0001] The invention relates to a method for preparing alginate, in particular to a method for preparing ethyl alginate with a high degree of esterification. Background technique [0002] Alginic acid is mainly derived from brown algae plants and bacteria, and its molecular formula is (C 6 h 7 o 6 Na) n , the relative molecular weight is between 32000-200000, the molecule is composed of β-D-mannuronic acid and α-L-guluronic acid linked by (1→4) glycosidic bonds, it is a linear polyanion water-soluble carbohydrate. Alginic acid is white or light yellow powder, insoluble in methanol, ethanol, DMF and other organic solvents. Degradation reactions occur under acidic, alkaline and high temperature conditions, resulting in a rapid decrease in molecular weight. Therefore, it should be placed in a low temperature, dry, ventilated, and dark environment during storage. [0003] Alginic acid derivatives with a high degree of commercialization currently mainly inc...

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Problems solved by technology

However, for small-molecular direct alkanols, since the esterification reaction will generate water molecules, and the water molecules have compatibility or high compatibility with small-molecular raw material alcohols, it is difficult to separate each other, so even if an excessive amount of alcohol is used To promote the positive direction of the esterification reaction, the esterification reaction is also difficult to obtain alginate with a high degree of esterification, and the degree of esterification is usually less than 20%.

For example Broderick Eilish et al. (Broderick E, Lyons H, Pembroke T, et al. The characterization of novel, covalently modified, amphiphilic alginate derivative, which retainsgelling and non-toxic properties[J]. Journal of colloid and interfacescience, 2006, 298(1 ): 154-161.) Using sulfuric acid as a catalyst, the direct esterification reaction of alginic acid and excess butanol is used to prepare butyl alginate. When the esterification reaction reaches equilibrium, the degree of esterification is lower than 20%; for long-chain alkanols In other words, due to poor compatibility with alginic acid and low reactivity, even if it is easy to separate from the water molecules generated by the esterification reaction, the degree of esterification reaction is relatively low

For the preparation of alginic acid long-chain alcohol esters, the Ugi reaction is usually used at present (Ugi I. The α‐Addition of Immonium Ions and Anions to Isonitriles Accompanied by Secondary Reactions[J]. Angewandte Chemie International Edition in English, 1962, 1(1) :8-21) to prepare, but the degree of esterification of alginate prepared by this method is usually lower than 20%