Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B31/00—Preparation of derivatives of starch
  • C08B31/18—Oxidised starch

Definitions

• the invention relates to a method for the oxidation of starch with periodate. More in particular, the invention relates to a method for the oxidation of starch using periodate, wherein the spent periodate is regenerated.
• the product of this method is dialdehyde starch.
• Oxidized polysaccharides such as oxidized starch
• these products possess excellent properties with respect to the complexing of metal ions, such as calcium ions. These properties are advantageously utilized in, e.g., detergent formulations .
• oxidizing agents for this purpose are (air) oxygen, hydrogen peroxide, peracetic acid, perborate, persulfate, periodic acid, potassium permanganate, lead (IV) salts, cerium (IV) salts, NO 2 /N 2 O 4 , chlorite and hypochlorite .
• electrochemical methods have been described.
• dialdehyde starch (DAS) by subjecting starch to an oxidation with periodate has been examined extensively. In this connection, reference can be made to, e.g., Mumbleretter, Starch Chemistry and Technology 2, ed. R.L. Whistler, E.F. Paschall, Chapter 18, 433, Acad. Press NY (1967) .
• the chemical oxidation of iodate is mainly carried out using chlorine compounds, e.g. hypochlorite .
• Iodate and hypochlorite are reacted at basic pH and a high temperature. Periodate thereby precipitates and can be recovered in relatively pure form.
• U.S. patent 3,703,508 describes a method for the regeneration of spent periodate after the oxidation of polysaccharides.
• An aqueous solution with spent periodate is separated from the oxidized product, followed by regeneration in an electrodialysis device.
• the regenerated product is then reused in a next oxidation step.
• An important disadvantage of this method is the high consumption of expensive periodate which is used in equimolar amounts with respect to the starch and must be regenerated in very diluted form after different washing steps .
• WO 95/12619 teaches a method for the oxidation of carbohydrates with a sub-stoichiometric amount of periodate to dialdehyde carbohydrates, wherein the iodate ions or other iodine-containing ions formed, with a state of oxidation other than periodate, are electrochemically regenerated during the reaction in a separate reaction cell .
• This reaction cell is separated from the reaction vessel by a membrane permeable to the periodate, but not to the carbohydrate.
• the disadvantages of this method are that the carbohydrate is contaminated by the metal of the electrode and that the conventional membranes are not, at least insufficiently, resistant to periodate.
• DD-A-87778 describes a method for the preparation of water-soluble dialdehyde polysaccharides using electrochemically regenerated periodate.
• the water-soluble polysaccharide dextran is oxidized with 0.2 equivalents of periodate, obtaining a product with a degree of oxidation of 10%.
• the reaction mixture is contacted with an ion exchanger in acetate form to separate the dextran product from the (per) iodate.
• the ion exchanger is eluted with caustic solution, and the eluted (per) iodate is purified, freeing it from, inter alia, acetate, which originates from the ion exchanger, and from the reaction byproduct formate by means of evaporation.
• the invention is directed to a method for the oxidation of starch, wherein a starch suspension is subjected to a reaction with periodate, the reaction mixture is subjected to a separation step in which the solid constituents are separated from the liquid medium, the solid constituents being recovered as a product, and the liquid medium is treated with ozone, in a manner such that periodate is regenerated.
• dialdehyde starch is selectively obtained.
• the present method renders it possible to prepare dialdehyde starch in all desired degrees of oxidation, mainly by varying the reaction time and the concentrations of the reagents. Generally, within a few minutes a degree of conversion of some tens of percents is obtained, by degree of conversion being meant the number of C2-C3 bonds converted into dialdehydes, based on the total number of C2-C3 bonds. Within a few hours a degree of conversion of the order of 50% is obtained, after which the reaction continues to proceed slowly.
• dialdehyde starch product such as the complexing capacity and the reactivity
• additional advantages over a degree of conversion of 50% are hardly obtained if dialdehyde starch with a conversion percentage of more than 50% is used, while properties such as water solubility, water absorption and biodegradability are exactly greater at degrees of oxidation of 40-60%.
• the reaction medium does not come into contact with electrodes, so that no contamination by electrode metal can occur, while, furthermore, no complicated electrochemical devices are required, the electrodes of which are subject to wear when used.
• the method according to the present invention is a method that can be carried out both batch-wise and semi- continuously, in which the iodine-containing compounds successively oxidize starch, are separated, are regenerated and can be added again to the starch suspension to be oxidized.
• the above renders it possible in the method to restrict to deficient periodate based on the starch, which is likewise one of the advantages of the above-discussed method in the international patent application 95/12619.
• the starch oxidized using the method according to the invention is generally present in the reaction mixture in solid form. There is started from a suspension of starch in a suitable liquid medium, usually water. The above is necessary to readily carry out the separation step of the solid constituents and the liquid medium. When the starch is present in liquid dissolved form, the separation step is substantially more complicated, which renders it difficult to design an economically interesting process.
• a suitable liquid medium usually water.
• the starches may originate from any sources, such as starch from potatoes, wheat, maize, tapioca, peas, rice and sorghum orache, as well as genetically modified variants thereof.
• the starch may consist of amylose and/or amylopectin; amylose and amylopectin may occur in all possible mutual ratios.
• This starch may be chemically modified, with derivatives such as cationic and anionic starch, starch ethers such as hydroxyethyl and hydroxypropyl starch, starch esters such as starch acetates etc. being obtained.
• the starch can be partially broken down chemically or enzymatically or treated otherwise, e.g. cross-linked. As stated, these derivatives are preferably non-soluble, at least difficultly soluble.
• the term starch also comprises debranched starch.
• the method is analogously applicable to cellulose and the corresponding derivatives thereof.
• the treatment of the starch with periodate is carried under acid conditions (pH ⁇ 4), and preferably at a pH between 2.5 and 3.5. Depending on the temperature, the pH must not be so low that hydrolysis of starch occurs. This degradation can, as those skilled in the art know, occur at a pH below 1.
• ozone can also be passed through during the treatment of starch with periodate, as described in Dutch patent application 1002527.
• the content of solid matter in the reaction medium is not critical and can readily be optimized by those skilled in the art depending on the desired degree of conversion and the other reaction conditions.
• the solid contents will generally be between, e.g., 1 wt . % and 50 wt . % , based on the weight of the total suspension.
• the aqueous solution with the iodine-containing compounds which remains after a separation step m which the solid constituents of the treated suspension are separated from the water phase, is treated with ozonee. From the iodine compounds periodate is formed again at pH > 6.5.
• the treatment with ozone is carried out at basic pH, that is to say at a pH above 7.
• the treatment with ozone is carried out at a somewhat higher pH, because periodate then forms a precipitate.
• a precipitate of periodate is formed at pH > 8.
• the pH In the regeneration step the pH must not be above 10.5, because at higher pH's ozone disintegrates.
• the periodate After the regeneration the periodate can be subjected to a purification step.
• a purification step When the periodate is recovered as precipitate, e.g. by carrying out a filtration step, this can suitably be done by means of a recrystallization.
• the advantage of the purification step is that the yield of the recirculation step, based on the spent ozone, does not decrease too rapidly.
• an aqueous suspension of potato starch is prepared.
• solid periodic acid at a pH of 3.
• the liquid phase is suitably separated from the solid phase, the product phase.
• This separation step may be, e.g., decantation, a filtration or a centrifugation step.
• the solid fraction may, if desired, be subjected to washing steps and further desired reprocessing steps.
• the pH of the liquid phase is increased to, e.g., 8.5-9 with a suitable base, such as caustic soda, and substantially bubbled through with ozone.
• a precipitate is thereby formed which mainly consists of periodate salt.
• This salt can be recovered by, e.g., filtration and be subjected, if required, to a recrystallization in basic water.
• the periodate product may then be introduced into the reactor vessel containing a starch suspension.
• the oxidation of the starch is preferably carried out with stirring, at a constant pH and at a temperature between -10°C and 100°C, preferably between 0 and 35°C, most preferably between 5 and 20°C.
• the regeneration with ozone is preferably carried out at a temperature between 0 and 100°C, more preferably at a temperature between 5 and 40°C.
• the percentage of DAS (the percentage of C2-C3 dialdehydes based on the total number of C2-C3 bonds) is demonstrated with a combination of gas chromatography and mass spectroscopy (Hewlett Packard, gas chromatographic device GC 5890 series II and mass spectrometer MS 5989A) conform to the procedure as described in the Dutch patent application 1002527.
• ozone is generated by means of a Fischer OZONE Generator 502.
• feed gas technical oxygen is used.
• This oxygen is pre-dried over a KOH (Merck) and Sicapent (Merck) column (0.5 m) .
• the ozone concentration in the gas stream was about 4 wt . % .
• the flow rate was about 100 1/h.
• the gas was dosed via two (2 x 2 x 2 cm) outflow pebbles (aquarium pebbles) .
• the oxidation of starch is carried out in a double- walled reaction vessel of 2 liters capacity.
• the contents of this vessel were stirred by means of a magnetic stirrer. Over the reaction vessel an excess pressure of 0.125 bar was applied by means of a water column of 1.25 m.
• Example 1 Generation of periodate from iodate with ozone in basic medium, followed by the reaction of periodate with potato starch in acid medium.
• the filtered product was suspended in 1 1 water and neutralized to pH 5.5.
• the product was filtered off once again, washed with 3 1 water and dried (322 g; 5.4 % moisture; 5.0 % product loss).
• Example 1 The filtrate from Example 1 was supplemented with water to 2 kg and then treated as described in Example 1. Subsequently, 374 g potato starch were suspended in this water phase. The filtrate was used again in Example 3. The product was suspended in 1 1 water and neutralized to pH 5.5. Finally, the product was filtered off, washed with 3 1 water and dried (327 g; 5.5 % moisture; 3.4 % product loss).
• Example 3 Regeneration of the periodate in the filtrate of Example 2 with ozone in basic medium, followed by the reaction of periodate with potato starch.
• the product was filtered off, washed with 3 1 water and dried (339 g; 6.3 % moisture; 0.6 % product loss) .
• the filtered suspension liquid and the washing water were collected and then evaporated to 2.0 1.
• the pH of the solution was adjusted to 8.5 by means of a 25% and a 4.4% NaOH solution.
• the filtered suspension liquid and the washing water were collected and then evaporated to 2.0 1.
• ozone was bubbled through for 8 hours at 35°C and pH 8.5 (by means of 4.4% NaOH) . A precipitate of periodate was formed.

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• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Biochemistry (AREA)
• Materials Engineering (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Polysaccharides And Polysaccharide Derivatives (AREA)

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Cited By (6)

Citations (1)

• 1996
  • 1996-12-16 NL NL1004793A patent/NL1004793C2/nl not_active IP Right Cessation
• 1997
  • 1997-12-15 WO PCT/NL1997/000697 patent/WO1998027118A1/en active Application Filing
  • 1997-12-15 AU AU53476/98A patent/AU5347698A/en not_active Abandoned

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