Preparation method of methyl alginate with high degree of esterification

Abstract

The invention discloses a preparation method of methyl alginate with high degree of esterification; the preparation method comprises the following steps: in anhydrous methanol, adding alginic acid, starting stirring, adding a dehydrating agent having equal moles to the water content of alginic acid, adding a catalyst, and stirring and heating to reflux; after a reflux temperature is reached, starting to drip the remaining dehydrating agent, and after uniform dripping is completed within 2-4 h, continuing to carry out a reflux reaction for 6-20 h; and finishing the reaction, cooling to room temperature, then adjusting the pH to 6.5-7.0 with an alkali liquor, filtering, washing the filter cake with a methanol aqueous solution with the mass concentration more than 60%, and drying at the temperature of 40 DEG C, to obtain the methyl alginate. With adopting of the preparation method of methyl alginate, the degree of esterification of the prepared methyl alginate is more than 70%, and is obviously more than that of straight-chain alkyl alcohol alginate prepared by the prior art.

Description

Technical field [0001] The invention relates to a method for preparing alginate esters, in particular to a method for preparing methyl 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 32,000 and 200,000. 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 Carbohydrates. Alginic acid is a white or light yellow powder and is insoluble in organic solvents such as methanol, ethanol, and DMF. 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] Currently, the commercialized alginic acid derivatives mainly include so...

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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%