NL9300540A - Method for oxidizing carbohydrates. - Google Patents

Description

Method for oxidizing carbohydrates

The invention relates to a method of oxidizing carbohydrates which have two neighboring secondary alcohol functions.

The oxidation of such carbohydrates can lead to dicarboxy carbohydrates. Such dicarboxy compounds are useful as metal ion complexing agents, such as calcium and magnesium, and can therefore be used, for example, as phosphate substitutes in detergents.

The oxidation of carbohydrates has been described in various variants. Known oxidizing agents for this purpose are periodic acid, lead (IV) salts, chlorite and hypochlorite. It is also known to oxidize carbohydrates with hydrogen peroxide in the presence of sodium tungstate as a catalyst (M. Floor et al, Starch, 4l, 303 ~ 309 (1989)); This process also produces oxidation products other than dicarboxy carbohydrates and chain degradation also takes place.

In 27ΕΡ ^ 27 27 · ·99 and WO-91.17189, the oxidation of polysaccharides with a catalytic amount of bromide to form dicarboxy polysaccharides is described. The bromide is converted into hypobromite by hypochlorite or electrochemically.

The known processes for the oxidation of carbohydrates have the drawback that they lead to at least equivalent amounts of salt in the final product, which causes separation problems and / or limits the application possibilities of the product. In addition, yield of dicarboxy product is sometimes insufficient or long reaction times are required.

A process has now been found for the oxidation of carbohydrates in which no or only small amounts of salt are formed, and which lead to a yield of more than 90% of desired dicarboxy carbohydrates within short reaction times.

According to the method of the invention, the carbohydrate is oxidized in an aqueous medium with hydrogen peroxide or electrochemically in the presence of a catalytic amount of a metal salt which is a metal halide or a transition metal salt,

The carbohydrates to be oxidized by the process of the invention include all mono-, oligo- and polysaccharides and derivatives thereof containing a vicinal diol group, such as ribose, glucose, galactose, fructose and the oligo- and polysaccharides based thereon. Important examples of useful carbohydrates are starch (poly-a-anhydro-glucose), cellulose (poly-a, β-anhydroglucose) and inulin (mainly poly-anhydrofructose).

The process of the invention results in high yields of dicarboxy carbohydrate, typically more than $ 0% of the theoretical yield. The oxidation hardly leads to chain breakdown. In addition, the crude product contains only small amounts of salts, namely the amounts corresponding to the catalytic amount of metal salt used. Dicarboxy carbohydrate is understood to mean the original carbohydrate of which the vicinal diol group has been converted into two carboxyl groups by breaking the C-C bond, and thus usually by ring opening.

According to a variant of the process according to the invention, the carbohydrate is oxidized with an approximately equivalent amount of hydrogen peroxide in the presence of a catalytic amount of metal halide, which in this case can advantageously be an alkali or alkaline earth metal halide such as sodium chloride or magnesium bromide. An equivalent amount of hydrogen peroxide is an amount of 3 moles of hydrogen peroxide per mole unit of monosaccharide, according to the gross equation: -CHOH-CHOH- + 3 H 2 O 2 - 2 -C00H + k H 2 O.

A catalytic amount of metal salt is here understood to mean an amount which is considerably less than an equimolar amount relative to the monosaccharide units, i.e. less than 50% of the equimolar amount, in particular less than 25% thereof. Preferably 0.02-0.20 mol, more preferably 0.05-0.15 mol metal halide per mol mono-saccharide unit is used.

In this variant of the process, a virtually quantitative conversion to dicarboxy product is obtained in a few hours to a few days. The reaction temperature can vary from 0 ° C to 100 ° C, in particular from 20-80 ° C. The pH appears to be variable over a wide range from about 4 to high pH; preferably a pH between 5 and 9 is used.

According to another variant of the method according to the invention, the metal salt is a transition metal salt, in which case the oxidation can be carried out with hydrogen peroxide or electrochemically. The transition metal can be any metal that can assume different oxidation states, such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu from the fourth series of the periodic table of elements and the corresponding metals from higher series of the periodic table . Copper, iron, nickel, cobalt, manganese and ruthenium salts are preferred. In particular, halides, more particularly chlorides, bromides or iodides of the transition metals are used. A catalytic amount of metal salt can here be an amount of, for example, 1-25 #, in particular 2-10 #, of an equimolar amount of carbohydrate monomer.

In this variant of the process, almost quantitative yields of dicarboxy carbohydrate are obtained within a few hours. The reaction temperature and pH can be the same as indicated above.

In electrochemical oxidation, the usual conditions can be maintained, for example using platinum electrodes. In electrochemical oxidation, the transition metal is continuously brought from a lower to a higher oxidation state, it being assumed that the metal in the higher oxidation state oxidizes the carbohydrate.

Example 1 10 g of Inulin isolated from chicory with a DP of about 9. is dissolved in 300 ml of water. 300 mg of sodium chloride are added to this. The system is brought to 50 ° C. To this mixture is added 18 g of hydrogen peroxide (35 # w / v) in one hour. The reaction mixture is kept at pH 5. After 2 hours, the reaction mixture is evaporated. After drying, the product is obtained in a yield of more than 90 #. This was analyzed, after dissolving in D20, using XH and 13C NMR. The spectra show that the dicarboxyinulin has been obtained.

Example 2 10 g of Inulin, isolated from dahlia, with a DP of about 30, is dissolved in 300 ml of water. The same procedure is followed as described in Example 1. The yield of dicarboxyinulin, after drying, is determined to be more than 90%. Product characterization was done in the same manner as described in Example 1.

Example λ 10 g Inulin, isolated from Jerusalem artichoke (Jerusalem Artichoke) with a DP of approx. 8, is dissolved in 300 ml. water. The same procedure is followed as described in Example 1. The yield of dicarboxyinulin, after drying, is determined to be more than 90%. Characterization of the product was carried out in the same manner as described in Example 1. Example 4 10 g Inulin isolated from chicory with a DP of approx. 9 · was converted into dicarboxyinulin as described in Example 1, with the exception that the reaction was carried out at pH 7 · Yield more than 90 #, characterization of the product with 1 H NMR and 13 C NMR.

Example 5 10 g of Inulin, isolated from dahlia with a DP of about 30, was converted to dicarboxyinulin as described in Example 1, except that the reaction was carried out at pH 7 · Yield over 90 #, characterization of the product with 1 H NMR and 13 C NMR.

Example 6 10 g Inulin, isolated from Jerusalem artichoke with a DP of about 8, was converted into dicarboxyinulin as described in example 1, with the difference that the reaction was carried out at pH 7 · Yield more than 90 #, characterization of the product with 1 H NMR and 13 C NMR.

Example 7 10 g Inulin isolated from chicory with a DP of about 9% was converted to dicarboxyinulin as described in example 1, except that the reaction was carried out at pH 9 Yield over 90 #, characterization of the product with 1 H NMR and 13 C NMR.

Example 8 10 g of Inulin, isolated from dahlia with a DP of about 30, was converted to dicarboxyinulin as described in Example 1, except that the reaction was carried out at pH 9 · Yield over 90 #, characterization of the product with 1 H NMR and 13 C NMR.

Example 9 10 g Inulin, isolated from Jerusalem artichoke with a DP of about 8, was converted into dicarboxyinulin as described in example 1, except that the reaction was carried out at pH 9 · Yield over 90 #, characterization of the product with 1 H NMR and 13 C NMR.

Example 10 10 g of Inulin isolated from chicory with a DP of approx. 9i is dissolved in 300 ml of water. 0.2 mmol of copper (II) chloride is added to this. Then the pH is brought to 5 and the temperature at 60 ° C. To this reaction mixture is added 18 g of hydrogen peroxide (35% w / v) for 15 minutes. After two hours, the reaction mixture is evaporated. After drying, the yield is more than 90 #. The product is characterized as dicarboxyinulin using 1 H and 13 C NMR. In addition, * H and 13 C-NMR of a sample from the reaction mixture show that virtually no formic acid (or its salt) or carbonate salts are formed as reaction byproducts.

Example 11 10 g. Inulin, isolated from dahlia, with a DP of about 30 * is dissolved in 300 ml of water. The same procedure is followed as described in example 10. The yield of dicarboxyinulin, after drying, is determined to be more than 90%. The product and reaction mixture were characterized in the same manner as described in Example 10. Example 12

10 g Inulin, isolated from Jerusalem artichoke with a DP of approx. 8, is dissolved in 300 ml of water. The same procedure is followed as described in Example 10. The yield of dicarboxyinulin, after drying, is determined to be above 90%. The product and reaction mixture were characterized in the same manner as described in Example 10. Example IR

10 g of inulin isolated from chicory with a DP of approx. 9 is has been converted to dicarboxyinulin as described in example 10, except that the reaction is carried out at pH 7 · Yield over 90%, characterization of the product with 1H- NMR and 13 C-NMR.

Example 14 10 g of Inulin isolated from dahlia with a DP of about 30 * is converted to dicarboxyinulin as described in Example 10, except that the reaction is carried out at pH 7. Yield over 90%, characterization of the product with 1 H NMR and 13 C NMR.

Example IR

10 g Inulin, isolated from Jerusalem artichoke with a DP of about 8, has been converted into dicarboxyinulin as described in example 10, except that the reaction is carried out at pH 7 · Yield over 90%, characterization of the product with 1H- NMR and 13 C-NMR.

Example 16 10 g of inulin isolated from chicory with a DP of about 9 µ is dissolved in 300 ml of water. 0.2 mmol of copper (II) chloride is added thereto. Then the pH is brought to 5 and the temperature at 60 ° C. The copper (II) chloride is constantly oxidized by electrochemical oxidation. After two hours, the reaction mixture is evaporated. After drying, the yield is more than 90%. The product is characterized as dicarboxyinulin using XH and 13 C NMR. In addition, * 11 and 13 C NMR of a sample from the reaction mixture shows that no formic acid (or its salt) or carbonate salts are formed as by-products of the reaction.

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10 g of Inulin, isolated from dahlia, with a DP of about 30, is dissolved in 300 ml of water. The same procedure is followed as described in example 16. The yield of dicarboxyinulin, after drying, is determined to be more than 90%. The product and reaction mixture were characterized in the same manner as described in Example 16. Example 18

10 g Inulin, isolated from Jerusalem artichoke with a DP of approx. 8, is dissolved in 300 ml of water. The same procedure is followed as described in example 16. The yield of dicarboxyinulin, after drying, is determined to be more than 90%. The product and reaction mixture were characterized in the same manner as described in Example 16. Example IQ

10 g of Inulin isolated from chicory with a DP of approx. 9% has been converted and characterized as dicarboxyinulin as described in Example 16, except that the reaction is carried out at pH 7 · Yield over 90%, characterization of the product with 1 H NMR and 13 C NMR.

Example 20 10 g of Inulin, isolated from dahlia with a DP of about 30, has been converted and characterized as dicarboxyinulin as described in Example 16, except that the reaction is carried out at pH 7 · Yield over 90%, characterization of the product with 1 H NMR and 13 C NMR. Example 21 10 g Inulin, isolated from Jerusalem artichoke with a DP of about 8, has been converted and characterized as dicarboxyinulin as described in Example 16, except that the reaction is carried out at pH 7 · Yield over 90%, characterization of the product with 1 H NMR and 13 C NMR.

Claims (6)

A method of oxidizing carbohydrates to dicarboxy carbohydrates by reacting the carbohydrate in an aqueous medium with hydrogen peroxide or electrochemically, in the presence of a catalytic amount of a metal salt which is a metal halide or a transition metal salt. The method of claim 1, wherein the metal salt is an alkali or alkaline earth metal halide and the oxidation is performed with hydrogen peroxide. The method of claim 1, wherein. the metal salt is a halide of a transition metal. h. The method of claim 1 or 3, wherein the transition metal is copper, iron, nickel, cobalt, manganese or ruthenium. A method according to any one of the preceding claims, wherein a pH between 5 and 9 is used. The method of any preceding claim, wherein the carbohydrate is a glucan or a fructan. The method of claim 6, wherein the carbohydrate is starch, cellulose or inulin or a fraction thereof.