A METHOD OF OXIDISING CARBOHYDRATES

Abstract: In a method of oxidising carbohydrates, particularly starch and dextrin, the oxidation is effected by molecular oxygen in an alkaline aqueous medium in the presence of a catalytic quantity of a metal ion selected from the metals of group VIII of the periodic table, copper or silver and a substance which acts as a ligand for the metal ion and is preferably constituted by a polydentate amine ligand.

Description: A method of oxidising carbohydrates The present invention relates to a method of. oxidising carbohydrates, particularly starches, dextrin and hydrolysis products thereof. Oxidised starches are used widely in the paper and textile industries. The product is generally produced by treating starch with hypochlorite in an alkaline aqueous medium. Alternatively, oxidised starches are produced by oxidation with periodate which can cleave the glucoside unit of starch between the C-2 and C-3 atoms which are converted into aldehyde groups. The starch thus produced is used mainly in the production of paper which retains good mechanical strength when wet. A further potential application of oxidised starch or cellulose, described in German patent application DE-A-24 36 843 is its use as a builder for detergents. The products produced by oxidation with hypochlorite or periodate and subsequently with chlorite contain many carboxylic groups in a chain and thus have good sequestering powers. Their use is limited, however, by the fact that these substances are less biodegradable the higher their degree of oxidation. The main object of the present invention is to provide an oxidation method which is particularly cheap and advantageous as regards the reagents used in the method. A further object is to provide a method which, with particular reference to the oxidation of starches, gives rise to an oxidation product with improved biodegradability characteristics. This object is achieved by a method of oxidising carbohydrates, characterised in that the oxidation is effected by means of an oxygen containing gps in analtøitirB q_j.τ? τ? medium in the presence of a catalytic quantity of a metal ion selected from the metals of group VIII of the periodic table, copper and silver and a substance which acts as a ligand for the metal ion. Carbohydrates, which constitute the substrate to which the oxidation method of the invention is applied, include starch, hydrolysis products thereof with up to 1 glucoside unit, and simple carbohydrates such as sorbitol. The term starch essentially means starch which has not been modified chemically and thus includes carbohydrates of natural and vegetable origin in general which are composed essentially of amylose and/or a ylopectin. Native starches extracted from various plants such as potatoes, rice, tapioca, maize and cereals may be used. Of these, maize starch is preferred. Hydrolysis products of starch are constituted by mixtures of oligomers with various numbers of glucoside units, including glucose monomer. These hydrolysis products are easily obtainable, for example, by enzymatic hydrolysis, preferably with the use of endoenzymes. Substrates usable for the invention also include polyols with carbohydrate structure, such as sorbitol. The metal ion used is preferably iin, copper,silver, ccfcaLtorι____εl and is introduced into the alkaline aqueous medium by means of a soluble salt, preferably constituted by a chloride or a sulphate. Typically, the metal ion is used in a molar ratio of between 1 and 0.25% with reference to the number of moles of glucoside units in the substrate. The ligand for the metal ion is preferably a polydentate amine ligand. Of these the following are contemplated: - monoamines of the general formula: / R l N -R 2 \ R 3 in which one of the radicals R,, R 2 anό- β is selected from the group consisting of hydrogen, C 1 -C 4 alkyl groups and carboxyalkyl radicals in which the alkyl group has from 1 to 4 carbon atoms, and the rest of the R l' R 2 or R 3 radicals are the same or different carboxyalkyl radicals in which the alkyl group has from 1 to 4 carbon atoms, and - polyamines of the general formula: in which R is an alkylene group with from 1 to 4 carbon atoms, preferably ethylene, and R, , R 2 , R 3 , and R. are the same or different and are radicals selected independently of each other from the group consisting of hydrogen, C I~ C Λ alkyl groups, aminoalkyl radicals in which the alkyl group has from 1 to 4 carbon atoms and carboxyalkyl radicals in which the alkyl group has from 1 ' to 4 carbon atoms, or alternatively, R. and R 2 and/or R_ and R. form a heterocyclic ring with the respective nitrogen atom, or alternatively, R, , R 2 , R 3 and R. form heterocyclic groups with the respective nitrogen atoms. Of the preferred amine and polyamine ligands, nitrilotriacetic acid, i inodiacetic acid, ethylenediamine, diethylenetriamine, triethylenetetramine, ethylenediaminetetra-acetic acid (EDTA) , ethylenediaminetriacetic acid, phenanthroline and 2,2'-dipyridyl are contemplated in particular. A combination of EDTA with ferrous sulphate or ferrous chloride is particularly advantageous for the oxidation of starch and hydrolysis products thereof, including glucose. The oxidation reaction is carried out by bubbling molecular oxygen or air through th alkaline aqueous medium v ichgenerallyhas apHoffrcm 8 to 14 erritypicallybetveβ.8 arύ10 atatHTp-aratute cf from 25..to 90°C and at atmospheric pressure with vigorous stirring. Example 1. 40 g of dextrin was dissolved in 500 ml of deionised water. 0.63 g of FeCl 2 and 0.5 g of o-phenanthroline were added. The reaction was carried out at 60°C and at a pH of 9 in an atmosphere of oxygen and good stirring was maintained. A total of 15 ml of 3.4M NaOH was introduced during a reaction period of 8 hours. Upon completion of the reaction the water was evaporated and the product, recovered. Example 2. 40 g of dextrin was dissolved in 500 ml of deionised water. 0.68 g of FeS0 4 .7H 2 0 and 0.5 g of o-phenanthroline were added. The reaction was carried out at 70°C and at a pH of 9 in an atmosphere of oxygen and good stirring was maintained. A total of 35 ml of 3.4M NaOH was introduced during a reaction period of 12 hours. Upon completion of the reaction, the water was evaporated and the product recovered. Example 3. 40 g of dextrin was dissolved in 500 ml of deionised water. 0.34 g of FeS0 4 .7H 2 O and 25 g of o-phenanthroline were added. The reaction was carried out at 70 C and at a pH of 9 in an atmosphere of oxygen and good stirring was maintained. A total of 60 ml of 3.4M NaOH was introduced during a reaction period of 32 hours. Upon completion of the reaction the water was evaporated and the product recovered. Example 4. 40 g of dextrin was dissolved in 500 ml of deionised water. 0.34 g of FeS0..7H 2 0 and 0.43 g of the dihydrated disodium salt of EDTA were added. The reaction was carried out at 70 C and at a pH of 9 in an atmosphere of oxygen and good stirring was maintained. A total of 60 ml of 3.4M NaOH was introduced during a reaction period of 16 hours. Upon completion of the reaction the water was evaporated and the product recovered. Example 5. 20 g of soluble starch was dissolved in 500 ml of deionised water. 0.34 g of FeS0 4 .7H 2 0 and 0.25 g of o-phenanthroline were added. The reaction was carried out at 70°C and at a pH of 9 in an atmosphere of oxygen and good stirring was maintained. A total of 17 ml of 3.4M NaOH was introduced during a reaction period of 12 hours. Upon completion of the reaction the water was evaporated and the product recovered. Example 6. 20 g of maize starch was gelled in 500 ml of deionised water. 0.34 g of FeS0 4 _7H 2 0 and 0.46 g of EDTA were added in an atmosphere of oxygen and good stirring was maintained. A total of 17 ml of 3.4M NaOH was introduced during a reaction period of 17 hours. Upon completion of the reaction the water was evaporated and the product recovered. The recovered product was subjected to Ft-IR spectroscopy with Perkin Elmer 1760 equipment. The graph below shows the spectra of the oxidation product (2) and of untreated starch (1) in Nujol. The spectrum (2) has a band at a wavelength of 1597 cm " which is characteristic of the salified carboxyl group and is absent from the spectrum (1) . The two spectra have substantially corresponding shapes in the region between 1000 and 1100 cm " in which there are strong bands characteristic of the structure of starch. The oxidation product of a starch or a dextrin obtainable by the method which is described above and is the subject of the following claims falls within the scope of the present invention. The oxidation product of starch may conveniently be used as a binding additive for paper, as a builder for detergents, as a polyelectrolyte thickening agent, in formulations for paints and printing inks, and as a high-molecular-weight coalescent. Its use as a builder for detergents is particularly advantageous by virtue of its good sequestering properties combined with the biodegradability of the product compared with products oxidised by hypochlorite. Additionally the product may be used as a co-builder in detergent formulations in association with known builders, such as zeolites, in order to improve the anti-redepoεition properties and dispersion capacity of the detergents and achieve an improved soil removal effectiveness. Hydrolysis products of starch and particularly dextrin oxidised by the method of the invention may also be used in particular as polyelectrolyte thickening agents in formulations for paints and printing inks. These uses constitute a further subject of the invention.

Claims: CLAIMS 1. A method of oxidising carbohydrates, characterised in that the oxidation is effected by means of anαx t i -.-rrtainirg g β e in an alkaline aqueous medium in the presence of a catalytic quantity of a metal ion selected from the metals of group VIII of the periodic table, copper and silver and a substance which acts as a ligand for the metal ion. 2. A method according to Claim 1, characterised in that the ligand is a polydentate amine ligand. 3. A method according to Claim 2, characterised in that the ligand is a monoamine of the general formula: in which one of the radicals R, , R 2 and R_ is selected from the group consisting of hydrogen, C,-C 4 alkyl groups and carboxyalkyl radicals in which the alkyl group has from 1 to 4 carbon atoms and the rest of the R. , R 2 and R_ radicals are the same or different carboxyalkyl radicals in which the alkyl group has from 1 to 4 carbon atoms. 4. A method according to Claim 2 , characterised in that the ligand is a polyamine of the general formula: in which R is a C,-C 4 alkylene group, preferably ethylene, and R., R 2 , R,, and R 4 are the same or different and are selected independently of each other from the group consisting of hydrogen, C. -C . alkyl groups, aminoalkyl radicals in which the alkyl group has from 1 to 4 carbon atoms and carboxyalkyl radicals in which the alkyl group has from 1 to 4 carbon atoms, or alternatively, R, and R 2 an /or R- and R. form a heterocyclic ring with the respective nitrogen atom, or alternatively, R. , R 2 , R 3 and R 4 form heterocyclic groups with the respective nitrogen atoms. 5. A method according to Claim 2 , characterised in that the amine ligand is selected from the group consisting of nitrilotriacetic acid, iminodiacetic acid, eth lenediamine, diethylenetriamine, triethylenetetramine, eth lenediaminetriacetic acid, ethylenediaminetetra-acetic acid, phenanthroline and 2,2'-dipyridyl. 6. A method according to Claim 5 in which the ligand is ethylenediaminetetra-acetic acid and the metal ion is iron. 7. A method according to Claim 5 in which the metal ion is copper and the ligand is o-phenanthroline. 8. A method according to Claim 1 in which the molar concentration of the metal ion in the reaction medium is from 1 to 0.25% with reference to the number of moles of glucoside in the oxidation substrate. 9. A method according to Claim 1 wherein the oxidation reaction is carried out at a temperature of from 25 to 90°C and at atmospheric pressure with vigorous stirring. 10. A method according to Claim 1 wherein the carbo¬ hydrate subjected to oxidation is selected from starch, dextrin, hydrolysis products of starch or dextrin, and sorbitol. 11. An oxidation product of starch, a hydrolysis product of starch or dextrin obtainable by a method according to any one of Claims 1 to 9. 12. The use of an oxidation product of starch, a hydrolysis product of starch or dextrin obtainable by a method according to any one of Claims 1 to 9 as a builder or co-builder for detergents. 13. The use of an oxidation product of starch, a hydrolysis product of starch or dextrin obtainable according to any one of Claims 1 to 9 as a binder for paper, as a polyelectrolyte thickening agent or as a coalescent.

Inventors: BRUSSANI GIANFRANCO, CONCA ESTERINO, BRUSSANI, GIANFRANCO, CONCA, ESTERINO
Applicants: NOVAMONT SPA, NOVAMONT S.P.A.
Application year: 1992
Main classification: D21H17
IPC codes: C07H7, C08B31, C09D7, C09K3, C11D3, D21H17