WO2005084800A1

WO2005084800A1 - Oxidation catalysts

Info

Publication number: WO2005084800A1
Application number: PCT/GB2005/000573
Authority: WO
Inventors: Xavier Elie Baucherel; Michelle Gilhespy
Original assignee: Johnson Matthey Plc
Priority date: 2004-03-02
Filing date: 2005-02-17
Publication date: 2005-09-15

Abstract

A polymer-supported nitroxyl radical oxidation catalyst is described characterised in that the polymer supported nitroxyl radical oxidation catalyst comprises the reaction product of a functionalised nitroxyl radical compound and a polymer support containing a functional group capable of reaction with said functionalised nitroxyl radical compound. The invention further provides a method for the preparation of a polymer-supported nitroxyl radical oxidation catalyst and process for the oxidation of primary or secondary alcohols comprising the steps, (i) oxidising a primary or secondary alcohol in the presence of a polymer-supported nitroxyl radical catalyst and a co-catalyst using an oxygen-containing gas and (ii) separating the oxidised alcohol from the reaction mixture, characterised in that the polymer supported nitroxyl radical catalyst comprises the reaction product of a functionalised nitroxyl radical compound and a polymer support containing a functional group capable of reaction with said functionalised nitroxyl radical compound.

Description

Oxidation catalysts

This invention relates to catalysts for the oxidation of alcohols and in particular to polymer- supported nitroxyl catalysts.

Nitroxyl catalysts possess a nitroxyl radical, also known as an aminoxyl radical. The most widely used nitroxyl catalysts are based on 2,2,6, 6-tetramethylpiperidine-1-oxyl (TEMPO), which may additionally have a functional group bound to a carbon atom in the piperidine ring. Examples of known TEMPO nittoxyl catalysts are depicted below;

These catalysts have found use in the oxidation of primary and secondary alcohols to aldehydes and ketones, where they participate in a redox reaction involving a terminal oxidant such as copper (II) chloride, potassium ferricyanide, sodium hypochlorite (bleach), sodium chlorite, sodium bromite, tert-butyl hypochlorite, hydrogen peroxide and N-chlorosuccinimide. Alternatively, molecular oxygen itself has been used in combination with specific co-catalysts.

However, industrial-scale use of nitroxyl catalysts such as TEMPO has been limited by the complicated catalyst recovery and product purification necessary when the catalysts are homogeneous. Consequently workers have attempted to immobilise TEMPO catalysts. Heterogeneous catalysts offer particular advantages in terms of catalyst handling and recovery leading to more efficient product isolation. TEMPO has been supported on commercially available silica and aluminosilicate materials, however, their utility is limited by the low levels of functionality generally achievable on such materials (about 1 mmol/g), and by the fact that molecular oxygen is ineffective as oxidant.

Attempts have also been made to immobilise TEMPO by supporting it on polymers. Miyazawa and Endo have prepared soluble and insoluble polystyrene-supported TEMPO catalysts by radical polymerisation of monomer (I) or copolymerisation of (I) with styrene and/or divinylbenzene followed by oxidation of the amine with hydrogen peroxide (see J. Polym. Sci. Chem. Ed. 1985, 23, 2487-2494 and J. Mol. Catal. 1988, 49, L31-L34).

Such a two-step process is inefficient, but the nitroxyl catalyst cannot be directly polymerised because of the presence of the nitroxyl radical. The catalysts were used with either K₃[Fe(CN)₆] in two- or three-phase systems containing aqueous base or with two-equivalents of copper (II) chloride and copper (II) hydroxide, for the oxidation of benzyl alcohol to benzaldehyde.

These methods have not been applied successfully to less-active aliphatic alcohols. Furthermore, these methods lead to the generation of large amounts of chloride-containing waste that on an industrial scale can lead to the need for expensive pollution control measures. Therefore there is a desire to replace the conventional stoichiometric oxidations by catalytic systems that may be applied to aliphatic alcohols and use molecular oxygen and non- chlorinated solvents.

We have found that nitroxyl catalyst oxidation of aliphatic alcohols may be performed readily with high conversion and selectivity using molecular oxygen and a co-catalyst when the nitroxyl oxidation catalyst is prepared by reacting a functionalised nitroxyl radical compound with a suitably-functionalised polymer.

Accordingly the invention provides a polymer-supported nitroxyl radical oxidation catalyst characterised in that the polymer supported nitroxyl radical oxidation catalyst comprises the reaction product of a functionalised nitroxyl radical compound and a polymer support containing a functional group capable of reaction with said functionalised nitroxyl radical compound.

The invention further provides a method for the preparation of the polymer-supported nitroxy radical oxidation catalyst comprising reacting a functionalised nitroxy radical compound with a polymer support containing a functional group capable of reaction with said functionalised nitroxyl radical compound.

The invention further provides a process for the oxidation of primary or secondary alcohols comprising the steps (i) oxidising a primary or secondary alcohol in the presence of a polymer-supported nitroxyl radical catalyst and a co-catalyst using an oxygen-containing gas and (ii) separating the oxidised alcohol from the reaction mixture, characterised in that the polymer supported nitroxyl radical catalyst comprises the reaction product of a functionalised nitroxyl radical compound and a polymer support containing a functional group capable of reaction with said functionalised nitroxyl radical compound. The functionalised nitroxyl radical compound may comprise the functionalised nitroxyl radical or a precursor thereto. Such precursors are known to those skilled in the art and include the equivalent hydroxylamine complex (i.e. N-OH) which is able to form the nitroxyl radical (i.e. N- O ) in-situ under normal reaction conditions, or the amine (i.e. N-H) which requires an oxidation step in order to convert the non-active amine to the active nitroxyl radical. Such an oxidation . step is described in the aforesaid J. Polym. Sci. Chem. Ed. 1985, 23, 2487-2494 and J. Mol. Catal. 1988, 49, L31-L34. The functionalised nitroxyl radical compound is preferably a nitroxyl radical or the hydroxylamine precursor equivalent. An advantage of the method of the present invention is that the amine plus oxidation step previously required is not necessary because the bonding of the nitroxyl radical compound to the functionalised polymer need not be by radical polymerisation. The nitroxyl catalyst is bound to the polymeric support via a functional group present in the nitroxyl radical compound that is able to react with the functionality present in the polymer. It will be apparent that the functionalised nitroxyl radical will have a functional group in a position that does not effect the ability of the nitroxyl radical to catalyse the oxidation of primary or secondary alcohols. Typically the functional groups will be bound to carbon or other atoms in the nitroxyl radical compound that are more than one, preferably more than two atoms away from the nitroxyl radical. The functionalised nitroxyl radical compound preferably comprises a functionalised 2,2,6,6-tetramethylpiperidine-1-oxyl compound, or a precursor thereto. More preferably the functionalised nitroxyl radical compound is a 2,2,6,6- tetramethylpiperidine-1-oxyl compound having a functional group, capable of reaction with the functionalised polymer, selected from hydroxyl, amine, keto, carboxyl or amide bound to a carbon atom in the piperidine ring, especially the 4-position of the piperidine ring. A particularly suitable functionalised nitroxyl radical compound is 4-hydroxy-2,2,6,6-tetramethylpiperidine-1- oxyl (4-hydroxy-TEMPO).

The polymer is preferably substantially non-porous and insoluble in the reaction medium. The insolubility and lack of porosity provides the polymers with sufficient mechanical strength to withstand use in stirred reactors without creating fines. Difficulties associated with further processing of the polymers, e.g. washing or eluting, are also mitigated.

The polymer support preferably comprises a polymer chosen from the group; polyolefins, fluorinated polyethylene, cellulose and viscose. Suitable polyolefins are those formed from units of alpha-olefins, the units having the formula -CH₂-CHR-, where R is H or (CH₂)nCH₃ and n is in the range 0 to 20. Particularly suitable polyolefins are those that are homo- or co- polymers of ethylene and propylene. In the case of fluorinated polyethylenes, those formed from units of general formula -CF₂-CX₂-, where X is H or F are suitable.

The polymers require a functionality with which the functionalised nitroxyl radical compound may react to form the polymer-bound nitroxyl radical catalyst. The functional group may be introduced onto the polymer in various ways including radiation grafting, chemical grafting or chemical modification of the polymer before or after it is formed into a catalyst support. Preferably the functional groups are introduced by radiation grafting.

Radiation grafting is an especially suitable method for graft modification of polymers suitable for the present invention. Radiation grafting is generally known, and involves the irradiation of polymer in a suitable form to introduce reactive sites (free radicals) into the polymer chain. These free radicals can be utilised to initiate graft copolymerisation under specific conditions. Three different methods of radiation grafting have been developed; (i) direct radiation grafting of a vinyl monomer onto a polymer (mutual grafting); (ii) grafting on radiation-peroxidised polymers (peroxide grafting); and (iii) grafting initiated by trapped radicals (pre-irradiation grafting). Pre-irradiation grafting is most preferred since this method produces smaller amounts of homopolymer in comparison to mutual grafting. Particularly suitable methods for the production of graft co-polymers suitable for use in the present invention are described in WO 02/36648, page 4, line 8-page 7, line 4.

Preferably, the functionalised polymer comprises at least one functional group selected from carboxylic acid, acid-chloride, anhydride, hydroxyl, halide (CI, Br, F or I), triflate, sulphonic, pyridinium, amine, amide, thiol or the like. Preferably the functionalised polymer comprises carboxyl, anhydride or acid chloride functional groups, especially carboxyl. The functional groups are preferably introduced using vinyl monomers such as acrylic acid, methacrylic acid, acrylates, methacrylates, styrene, substituted styrenes (such as alpha-methylstyrene), inylbenzyl derivatives (such as vinylbenzyl chloride, vinyl benzyl boronic acid and vinylbenzyl aldehyde), vinyl acetate, vinyl pyridine and vinyl sulphonic acid. If the groups introduced by the graft copolymerisation process do not possess functional groups capable of reaction with the functionalised nitroxy radical compound, they may be further reacted to introduce such functional groups using known chemical transformations, e.g. phenyl rings introduced using styrene may be functionalised using a Friedel-Crafts acylation reaction.

The amount of functionality present on the polymer is such that a suitably small volume of supported catalyst may be used to effect the catalytic reaction. Too low a concentration and an undesirably large volume of supported catalyst may be required, too high and possible mass- transport effects may be observed. Preferably the polymer comprises functional groups at a level of 2-15 mmol/g, preferably 5-10 mmol/g.

Thus according to one preferred embodiment of the present invention a carboxyl-functional polyolefin polymer, e.g. an acrylic acid-grafted polyethylene is reacted with an amino or hydroxyl-functionalised nitroxy radical compound, e.g. a 4-hydroxyl-1-oxo- 2,2,6,6- tetramethylpiperidine (4-hydroxy-TEMPO) to give a polymer-supported catalyst. Accordingly the functionalised nitroxyl radical compound is preferably bound to the functionalised polyolefin via an ester or amide link. It will be understood by those skilled in the art that the same bonds may be formed if the functionalities were reversed, i.e. an amino or hydroxy-functional polyolefin may be reacted with a carboxyl-functionalised nitroxy radical compound.

The reaction between the functionalised nitroxy radical compound and the functionalised polyolefin may be performed using any suitable coupling chemistry. For example, a carboxy- functional polymer dispersed in a suitable solvent may be reacted with diisopropylcarbodiimide (DIC), dimethylaminopyridine (DMAP), triethylamine and 4-hydroxy-TEMPO over 16 hours at room temperature. Alternatively, the polymer may first be converted to the acid chloride in a suitable solvent, using e.g. thionylchloride (SOCl₂) or oxalyl chloride, followed by direct reaction of the acid chloride with 4-hydroxy-TEMPO in a suitable solvent in the presence of excess triethylamine.

The polymer-supported catalyst of the present invention may be in the form of film, fibres, pellets, powder, foam, honeycomb or other structure suitable for use in stirred tank or continuous flow reactors. Preferably the polymer-supported catalyst is in the form of fibres. The fibres may be used without further processing and be on any suitable length. Compared to polymer beads, fibres have the advantage that they may be converted using conventional technology into a variety of useful forms. Thus fibres may be spun, woven, carded, needle- punched, felted or otherwise converted into threads, ropes, nets, tows or woven or non-woven fabrics of any desired form or structure. Short fibres can easily be stirred in a liquid medium and filtered off or otherwise separated therefrom. If desired, fibres of different characteristics can readily be combined in threads or fabrics in order to optimise the catalytic properties for a particular alcohol. In an alternative embodiment, fibres may be combined with inorganic fibres such as silica or alumina fibres in order to achieve, e.g. threads, of increased mechanical strength. This may be of particular use when the fibres are used in processes that involve high degrees of agitation or high turbulence.

A particularly preferred functionalised polymer is a fibrous acrylic acid-functionalised polyolefin having a polyolefin content of 30-40% and a carboxyl functionality of 5-10 mmol/g. Such fibrous materials are available commercially, for example as Smopex-102pp (carboxyl functionality 6.5 mmol/g) available from Johnson Matthey PLC.

The process of the present invention comprises oxidising a primary or secondary alcohol in the presence of a polymer-supported nitroxyl radical and a co-catalyst using an oxygen-containing gas. The polymer supported nitroxy radical oxidation catalysts of the present invention may be used for the oxidation of a range of different primary and secondary alcohols, including diols, triols and the like. The alcohol may be a primary or secondary aliphatic, e.g. alkyl C1-C30, or non-aliphatic alcohol which may contain one or more aryl groups, e.g. benzyl alcohol, or allyl groups such as allyl alcohol. Preferably the alcohol is a branched or linear primary or secondary alcohol having ≥7 carbon atoms such as heptanol, octanol, decanol, dodecanol, octadecanol, benzyl alcohol, phenyl-ethanol and phenyl propanol. Furthermore, the alcohol may comprise one or more carbon-carbon double bonds in a beta-, gamma- or other position in the carbon chain distanced from the hydroxyl-bearing carbon atom, e.g. 1-undecanol. Although effective for oxidation of secondary alcohols, the catalysts of the present invention have been found to be particularly active and selective for primary alcohols.

The process of the present invention may be performed without solvents using the alcohol as the reaction medium or may be performed in the presence of solvents, which act to dissolve or dilute the reactant alcohol and act as a heat-sink for any exotherm. Suitable solvents are hydrocarbons, such as hexanes, heptanes or octanes, aromatic hydrocarbons such as toluene or xylene, chlorinated hydrocarbons such as dichloromethane or chlorobenzene, ethers such as diisopropyl ether or methyl-tert-butyl ether, ketones such as acetone or 3-pentanone, water, acetic acid, dimethylformamide, acetonitrile and benzonitrile and mixtures of these. One advantage of the process of the present invention is that it is not necessary to use chlorinated solvents. An aqueous phase may also be used if desired to effect separation of product, alcohol or co-catalyst. Where the process is carried out under acidic conditions, a particularly preferred acid is acetic acid, particularly glacial acetic acid, and this may constitute part or all of the solvent used in the process. Where acetic acid is used as part of the solvent, it is preferably present in an amount greater than 25% by volume of the solvent.

The molecular oxygen may be provided as substantially pure oxygen, air, or diluted in an inert gas, e.g. 5% v/v 0₂ in nitrogen.

A co-catalyst is required. Suitable co-catalysts comprise salts of divalent metals (particularly manganese (II), cobalt (II) and copper (II)); ruthenium-phosphine complexes or polyoxometallates. In previous methods, two equivalents of copper (II) chloride was used alone as stoichiometric terminal oxidant to 'activate' the alcohol, e.g. benzyl alcohol. Although relatively inexpensive, the requirement for large amounts of copper salt results in waste disposal and handling issues on an industrial scale. Alternatively a combination of cobalt or copper and manganese nitrates has been used, under acidic conditions, with molecular oxygen in homogeneous systems. (Minisci et al, Tetrahedron Lett., 2001 , 42, 6651 ). In the present invention cobalt/manganese or copper/manganese combinations are effective. We have found that a particularly suitable co-catalyst is a combination of copper and manganese salts. This has the advantage of replacing the cobalt salts, which may be harmful, with relatively harmless copper compounds. Surprisingly we have found this combination to be as effective or more effective than the cobalt/manganese system. The salts used are preferably the nitrates. We have found that partial replacement of the nitrate with acetate may lead to a reduced activity although the original activity may be recovered by addition of sodium nitrate. Previously copper chloride has been used in stoichiometric amounts (to the alcohol) as the chloride. In the present invention we have surprisingly found the nitrate to be more effective. Thus in the present invention the preferred salts of copper, cobalt and manganese are the nitrates. An alternative copper (II) co-catalyst system comprises a copper (II) halide, preferably CuBr₂, in conjunction with bipyridine (bipy) and a base such as KO'Bu, KOH or NaOH. Alternative non- cόpper co-catalysts are ruthenium phosphine complexes such as RuCI PPh₃ or polyoxometallates such as H₅PV₂Mo₁₀O ₀.

The process of the present invention is effective for the oxidation of a range of primary or secondary aliphatic and non-aliphatic alcohols, including diols, triols and the like. The oxidation in the case of primary alcohols leads to aldehydes and then, if desired, carboxylic acids. In the case of secondary alcohols, the oxidation yields ketones.

The reaction may be performed by mixing the polymer-supported nitroxyl radical catalyst and co-catalyst with the alcohol and an oxygen-containing gas for a suitable period of time to effect the oxidation reaction. The reaction may conveniently be followed by gas chromatography using standard methods known to those skilled in the art, e.g. by internal standards. The reaction temperature may range from about 10°C to <70°C, especially 40-60°C and the reaction pressure may conveniently be about atmospheric pressure but may be reduced or increased depending upon the physical properties of reactants and products and of any solvents. Once the reaction has reached the desired conversion, usually >90%, the catalysts may be separated e.g. by filtration or centrifugation, followed, if necessary, by separation of the product aldehyde or ketone from unreacted alcohol by e.g. distillation.

The invention is further illustrated by reference to the following examples.

Example 1. Immobilisation of TEMPO

4-hydroxy-TEMPO was immobilised ^' using Smopex-102pp fibres (30-40% polyacrylic acid grafted polyolefin/ functionalised with carboxylic acid groups (functionality = 6.5 mmol/g)) provided by Johnson Matthey PLC, according to the following method.

Polymer C0₂H

a) DIC coupling method

The technique used for immobilisation of 4-hydroxy-TEMPO involved suspending Smopex- 102pp (30g) in anhydrous dichloromethane (300mL) before addition of diisopropylcarbodiimide (DIC) (65mL) and dimethylaminopyridine (DMAP) (2.48g). 4-hydroxy-TEMPO (35g) dissolved in anhydrous dichloromethane (60mL) was then added followed by triethylamine (57mL). The reaction mixture was stirred at room temperature under an atmosphere of nitrogen for 16 hours. The solid catalyst was collected by filtration and successively washed using dimethylformamide, methanol and dichloromethane. The solid was air-dried before being soxhlet-extracted using dichloromethane to remove any non-reacted 4-hydroxy-TEMPO. Finally the polymer-supported TEMPO was dried under vacuum (40°C) for 16 hours. This method achieved a TEMPO loading of 1.9 mmol/g (as determined by recovered 4-hydroxy- TEMPO). Repeated examples have given TEMPO loadings up to 2.8 mmol/g.

b) Acid chloride method Smopex-102pp (2g) was transferred into a 100mL round bottom flask before addition of thionyl chloride (10mL). The reaction was stirred at 80°C for 6 hours under nitrogen atmosphere. The unreacted thionyl chloride was removed by filtration. The solid material was washed with n- hexane under nitrogen. Anhydrous dichloromethane (20ml) and triethylamine (18ml) were added to the flask and the mixture was stirred for 5 minutes followed by the addition of 4- hydroxyTEMPO (2.44g) in a solution of anhydrous dichloromethane (15ml). The mixture was stirred at room temperature under nitrogen for 16hours. The reaction mixture was filtered, washed with toluene and dichloromethane. The solid was air-dried before being soxhlet- extracted using dichloromethane. Finally the solid was dried under vacuum (40°C) for 16 hours. The TEMPO loading obtained was measured at 1.6 mmol/g.

Example 2. Oxidation of primary alcohols using polymer-supported TEMPO

a) Comparison with silica-supported or homogeneous TEMPO catalysts

Mn(N0₃)₂ (29mg), Co(N0₃)₂ (29mg), 4-Methoxyacetophenone (350mg, as internal standard for gas chromatographic analysis), and the polymer-supported TEMPO catalyst of Example 1a were added to a round bottom flask along with 5mL of glacial acetic acid. The flask was flushed with pure oxygen before addition of 1-octanol (650mg)'. The reaction mixture was stirred at 40°C for 3 hours before analysis of the crude mixture by gas-chromatography (GLC). Comparative experiments (run 2 and 3) were performed using a silica-supported catalyst prepared according to the method of Bolm & Fey (see Chem. Comm. 1999, 1795-1796) and homogeneous non-functionalised TEMPO (run 4).

Without wishing to be bound by any theory, we believe that the hydrophobic nature of the polymer support improves the, interaction between a rather lipophilic long chain alcohol with the supported TEMPO and therefore improves the activity compared to the silica-supported catalysts. Furthermore the Smopex 102pp has a higher potential for loading TEMPO catalysts (6.5 mmol/g acid group versus ca. 1 mmol/g for the commercially available silica material). We have found that the activity of the polymer supported TEMPO catalysts is so pronounced that the reaction is preferably stopped immediately after full conversion to prevent over oxidation of the alcohol to the acid. b) The results using different immobilisation techniques Mn(N0₃)₂ (29mg), Co(N0₃)₂ (29mg), 4-Methoxyacetophenone (350mg, internal standard for GLC analysis), and polymer-supported TEMPO catalysts of Example 1a and 1b (250 mg) were added to a round bottom flask along with 5mL of glacial acetic acid. The flask was flushed with pure oxygen before addition of 1-octanol (650mg). The reaction mixture was stirred at 40°C for 3 hours before analysis of the crude mixture by GC. The results are given below;

Example 3. Recycling of the polymer supported TEMPO

Mn(N0₃)₂ (58mg), Co(N0₃)₂ (58mg), 4-Methoxyacetophenone (500mg, internal standard for GLC analysis) and polymer-supported TEMPO prepared as example 1a (500mg) were added to a round bottom flask along with 10mL of glacial acetic acid. The flask was flushed with pure oxygen before addition of 1-octanol (1.3g). The reaction mixture was stirred at 40°C for 3 hours. The reaction mixture was then filtered and the filtrate analysed by GC. The solid catalyst was collected was washed with acetic acid and directly re-used in an identical run. The results are given below. The results show that the catalyst can be effectively recovered and re-used for at least 5 cycles.

The filtrates from run 1 and 2 were tested for leaching by adding alcohol and monitoring the reaction at 40°C by GLC: filtrate 1 gave 8% conversion after 3 hours, filtrate 2 produced no conversion.

Example 4. Variation in catalyst level The method of Experiment 2b was repeated reducing the amount of polymer-supported TEMPO from 50mg of heterogeneous TEMPO per mmol/alcohol. Mn(N0₃)₂ (29mg), Co(N0₃)₂ (29mg), 4 Methoxyacetophenone (350mg, internal standard for GC analysis) and non- functionalised TEMPO or polymer-supported TEMPO prepared according to the method of example 1a, were added to a round bottom flask along with 5mL of solvents. The flask was flushed with pure oxygen before addition of 1-octanol (650mg). The reaction mixture was stirred at 40 or 60°C. Samples were regularly taken for analysis by GC. The results are given below;

The results demonstrate the polymer-supported catalysts of the present invention are effective at extremely low levels for the oxidation of aliphatic alcohols.

Example 5. Oxidation of primary alcohols

The method of Experiment 2b was repeated for the oxidation of primary alcohols. Mn(N0₃)₂ (58mg), Co(N0₃)₂ (58mg), 4-Methoxyacetophenone (500mg, internal standard for GLC analysis), and the polymer supported TEMPO catalyst (500 mg) prepared according to the method of Example 1a were added to a round bottom flask along with 10mL of glacial acetic acid. The flask was flushed with pure oxygen before addition of the alcohol (10 mmol). The reaction mixture was stirred at 40°C. Samples of the reaction mixture were taken out regularly to monitor the reaction by GLC. The results are given below;

Example 6. Oxidation of secondary alcohols

The method of Experiment 2b was repeated for the oxidation of secondary alcohols. Mn(N0₃)₂ (58mg), Co(N0₃)₂ (58mg), 4-Methoxyacetophenone (500mg, internal standard for GLC analysis), and the polymer supported TEMPO catalyst (500 mg) prepared according to the method of Example 1a were added to a round bottom flask along with 10mL of glacial acetic acid. The flask was flushed with pure oxygen before addition of the alcohol (10 mmol). The reaction mixture was stirred at 40°C. Samples of the reaction mixture were taken out regularly to monitor the reaction by GLC. The results are given below;

These results demonstrate that the functionalised nitroxyl radical compound 4-hydroxy-TEMPO can be successfully immobilised onto suitably functionalised organic polymer support to form an active polymer supported nitroxyl radical oxidation catalyst. The polymer supported TEMPO is effective for the oxidation of aliphatic and benzylic primary and secondary alcohols under mild conditions using molecular oxygen without the need for a chlorinated solvent. Furthermore, the supported TEMPO can be recycled for at least 5 runs without significant loss of conversion and minimal or no leaching of TEMPO. The supported catalyst can be used with either Mn/Co or Mn/Cu as co-catalyst in an acidic medium. The quantity of immobilised TEMPO required can be as little as 10mg per mmol of alcohol.

Claims

Claims.

1. A polymer-supported nitroxyl radical oxidation catalyst characterised in that the polymer supported nitroxyl radical oxidation catalyst comprises the reaction product of a functionalised nitroxyl radical compound and a polymer support containing a functional group capable of reaction with said functionalised nitroxyl radical compound.

2. A catalyst according to claim 1 when the nitroxyl radical compound is a functionalised 2,2,6,6-tetramethylpiperidine-1-oxyl compound having a functional group bound to a carbon atom in the piperidine ring selected from the list consisting of hydroxyl, amine, keto, carboxyl or amide.

3. A catalyst according to claim 1 or claim 2 wherein the nitroxyl radical compound is 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-hydroxy-TEMPO). ^'

4. A catalyst according to any one of claims 1 to 3 wherein the polymer support comprises a polyolefin, fluorinated polyethylene, cellulose or viscose.

5. A catalyst according to any one of claims 1 to 4 wherein the polymer support comprises carboxyl, anhydride or acid chloride functional groups.

6. A catalyst according to any one of claims 1 to 5 wherein the functionality is present on the polymer support in an amount between 2 and 15 mmol/g.

7. A catalyst according to any one of claims 1 to 6 wherein the functionalised nitroxyl radical compound is bound to the functionalised polymer via an ester or amide link.

8. A catalyst according to any one of claims 1 to 7 wherein the polymer is in the form of a fibre.

9. A method for the preparation of a polymer-supported nitroxyl radical oxidation catalyst according to claims 1 to 8 comprising reacting a functionalised nitroxyl radical compound with a polymer support containing a functional group capable of reaction with said functionalised nitroxyl radical compound.

10. A method according to claim 9 wherein the functionalised nitroxyl radical compound is an amino or hydroxy-functionalised nitroxyl radical compound and the functionalised polymer is an acrylic acid grafted polyolefin.

11. A process for the oxidation of primary or secondary alcohols comprising the steps (i) oxidising a primary or secondary alcohol in the presence of a polymer- supported nitroxyl radical catalyst and a co-catalyst using an oxygen- containing gas and (ii) separating the oxidised alcohol from the reaction mixture, characterised in that the polymer supported nitroxyl radical catalyst comprises the reaction product of a functionalised nitroxyl radical compound and a polymer support containing a functional group capable of reaction with said functionalised nitroxyl radical compound.

12. A process according to claim 11 wherein the co-catalyst comprises at least one compound selected from divalent salts of manganese, cobalt and copper, a ruthenium-phosphine complex or a polyoxometallate.

13. A process according to claim 11 or claim 12 wherein the co-catalyst is a combination of copper and manganese salts.

14. A process according to any one of claims 11 to 13 wherein the alcohol is an aliphatic or non-aliphatic linear or branched C1-C30 primary or secondary alcohol.

15. A process according to any one of claims 11 to 14 wherein the alcohol is a branched or linear primary or secondary alcohol having ≥7 carbon atoms.