WO2019232715A1

WO2019232715A1 - Selective oxidation of alcohols

Info

Publication number: WO2019232715A1
Application number: PCT/CN2018/090110
Authority: WO
Inventors: Jingpeng ZHAO; Vitaly ORDOMSKY; Willinton Yesid HERNANDEZ ENCISO; Wen-juan ZHOU; Mickael Capron; Stéphane STREIFF
Original assignee: Rhodia Operations; Le Centre National De La Recherche Scientifique; Universite Lille 1 - Sciences Et Technologies; Centrale Lille; Ecole Nationale Superieure De Chimie De Lille
Priority date: 2018-06-06
Filing date: 2018-06-06
Publication date: 2019-12-12

Abstract

Disclosed is a catalyst system exhibiting high activity and selectivity in the oxidation of alcohols to aldehydes or ketones using molecular oxygen as a terminal oxidant. Such catalyst system comprises quinone-type compound and is particularly useful for, but not limited to, the oxidation of primary or secondary aliphatic and aromatic alcohols to the respective aldehydes or ketones. Also disclosed is a process for oxidizing said alcohols to the respective aldehydes or ketones.

Description

Selective oxidation of alcohols

Technical Field

The present invention relates to a catalyst system exhibiting high activity and selectivity in the oxidation of alcohols to aldehydes or ketones using molecular oxygen as a terminal oxidant. More specifically, the invention relates to a system comprising quinone-type catalysts, such as 2-ethylanthraquinone. Such catalysts are particularly useful for, but not limited to, the oxidation of primary or secondary aliphatic and aromatic alcohols to the respective aldehydes or ketones. The present invention is also related to a process for oxidizing said alcohols to the respective aldehydes or ketones.

Background Art

The catalytic oxidation of alcohols selectively to carbonyl compounds is essential for many important transformations in the synthetic organic chemistry. A large number of oxidants have been reported in the literature and most of them are based on transition metal oxides, such as oxides of chromium and manganese (S. Kirk-Othmer Mitchell, Encyclopedia of Chemical Technology, 4th ed., Wiley-Interscience, New York, Vol. 2, p. 481 (1992) ; Hudlicky, M. "Oxidations in Organic Chemistry" , ACS Monograph No. 186, American Chemical Society, Washington D.C. (1990) ; Sheldon R.A., Kochi J.K., Metal Catalized Oxidation of Organic Compounds, Academic Press, New York (1981) ; Ley, S.V., Madin, A., in Comprehensive Organic Synthesis, Trost B., Fleming, I., Eds.; Pergamon Press, Oxford (1991) ; Vol. 7, p. 251; Mijs, W.J., DeJonge, C.R.H.I., Eds. Organic Synthesis by Oxidation with Metal Compounds, Plenum Press, New York (1986) ) . The methods described require the use of stoichiometric amounts of inorganic oxidants, generally highly toxic chromium or manganese compounds, which creates issues related to their handling and disposal.

A convenient procedure for the oxidation of primary and secondary alcohols has been reported by Anelli et al. (J. Org. Chem. 52 (1987) , 2559; J. Org. Chem., 54 (1989) , 2970) . The oxidation has been carried out in a two-phase system (CH ₂Cl ₂/water) utilizing TEMPO ( (2, 2, 6, 6-tetramethylpiperidin-1-yl) oxidanyl) as a catalyst and cheap and readily available NaOCl as an oxidant. The co-catalyst KBr enhances the reaction rate and the aqueous phase is buffered at pH 8.5 -9.5 using NaHCO ₃. The use of a quaternary ammonium salt as a phase transfer catalyst furthers the oxidation of alcohols to carboxylic acids. The same procedure was modified by using NaClO ₂ as the oxidant in the presence of catalytic amounts of TEMPO and NaOCl. This led to the formation of the carboxylic acid as the main product (U.S. Patent No. 6,127,573) .

A particularly efficient method for the oxidation of primary and secondary alcohols was reported by Tanielyan et al in Catalysis of Organic Reactions: Twenty-first Conference, S.R. Schmidt, ed., CRC Press, Boca Raton (2007) , p. 141. The oxidation is carried out at a temperature of from -5 to 0 ℃ using TEMPO as a catalyst, Na ₂B ₄O ₇ as a co-catalyst and NaOCl as an oxidant. The procedure does not require a reaction solvent and is carried out without KBr promoter.

The search for efficient, easily accessible catalysts and "clean" oxidants such as hydrogen peroxide, hydroperoxides or molecular oxygen for industrial applications is still a challenge (Dijksman, A., Arends, I.W.C.E. and Sheldon R., Chem. Commun., 1999, 1591-1592 ; Marko I.E., Giles, P.R., Tsukazaki, M., Brown, S.M. and Urch, C.J., Science, 274 (5295) (1996) , 2044-2046) . A large number of transition metal complexes and oxidants have been reported to catalyze the selective oxidation of primary alcohols to aldehydes with varying levels of effectiveness such as RuCl ₃-NaBrO ₃ (Konemoto, S., Tomoioka, S., Oshima, K., Bull. Chem. Soc. Japan 59 (1) (1986) , 105) , Bu ₄NRuO ₄-4-methylmorpholine-N-oxide (Griffith, W.P., Ley, S.V., Whitcombe, G.P., White A.D., Chem. Commun. 1987 (21) , 1625) , H ₂O ₂ and tert-butylhydroperoxide (t-BuOOH) (Tsuji, Y., Ohta, T., Ido, T. et al., J. Organomet. Chem., 270, (1984) , 333, Jiang, T.M., Hwang, J.C., Ho, H.O., Chen, C.Y., J. Chin. Chem. Soc., 35 (1988) , 135) . The methods described have only limited use since the overall yields are low and some of them require the application of precious metal complexes or expensive primary oxidants.

In the area of the aerobic oxidation of alcohols, very few efficient systems are currently available. A catalyst system based on TEMPO and Mn (NO ₃) ₂-Co (NO ₃) ₂ or Mn (NO ₃) ₂-Cu (NO ₃) ₂ was reported (Cecchetto, A., Fontana, F., Minisci, F. and Recupero, F., Tetrahedron Lett., 42 (2001) , 6651-6653) . The oxidation requires diluted solutions of the starting alcohol in acetic acid solvent (in the range of from 6 to 10 %v/v) and takes place at ambient temperatures and at atmospheric pressure of oxygen. A serious drawback of the method is the rapid deactivation of the catalyst at higher alcohol concentrations, resulting in the catalyst system becoming virtually inactive. Because of this, direct commercial application is not economically feasible as higher alcohol concentrations are typically required in such processes.

Wendlandt, A.E and Shannon, S.S. review quinone-catalyzed selective oxidation of organic molecules (Angew. Chem. Int. Ed. 54 (2015) , 14638 –14658) . The article focusses on stoichiometric reactants for the oxidation of organic compounds, such as DDQ (2, 3-dicloro-5, 6-dicyano 1, 4-benzophenone) and the bioinspired o-quinone catalyzed oxidation of amines.

Dehydrogenation of alcohols by stoichiometric, quinone-type molecules is further disclosed in Braude, E.A., Linstead, R.P. and Wooldridge K.R., J. Chem. Soc. 1956, 3070 –3074; Ohki, A., Nishiguchi, T., and Fukuzumi, K., Tetrahedron 35 (1979) , 1737 –1743; Becker, H. -D.,

A., and Adler, E., J. Org. Chem. 45 (1980) , 1596 –1600) .

Another review article titled Catalytic Oxidation of Organic Substrates by Molecular Oxygen and Hydrogen Peroxide by Multistep Electron Transfer –A Biomimetic Approach (Piera, J. and

J. -E., Angew. Chem. Int. Ed. 47 (2008) , 3506 –3523) covers transition metal (Pd, Ru, Os, Cu) catalyzed oxidation of organic substrates using molecular oxygen and/or hydrogen peroxide as the oxidant and further employing electron transfer mediators such as porphyrins. Metal-free catalyzed oxidations focus on TEMPO as an active agent.

Silica immobilized TEMPO as a catalyst in conjunction with nitrosium tetrafluoro borate was shown to convert alcohols into the corresponding aldehydes or ketones employing molecular oxygen as the final oxidant (Shakir, A.J., Paraschivescu, C., Matache, M., Tudose, M., Mischie, A., Spafiu, F., Ionita, P., Tetrahedron Lett. 56 (2015) , 6878 –6881) .

Photooxidation of alcohols to obtain carboxylic acids and ketones using catalysts such as 2-chloroanthrachinone as an inorganic catalyst under visible light irradiation in a air atmosphere is disclosed by Shimada, Y., Hattori, K., Tada, N., Miura, T. and Itoh, A., Synthesis 45 (2013) , 2684 –2688. The reaction mixtures are mild, such as ambient pressure and temperature. Yield of ketones are low as under the reaction conditions mainly carboxylic acids are being formed.

Aerobic organocatalytic oxidation of alcohols was achieved by using water-soluble sodium anthraquinone sulfonate. Under visible light activation, this catalyst mediated the selective aerobic oxidation of alkanes or alcohols to aldehydes and ketones (Zhang, W., Gacs, J., Arends, I.W.C.E., and Hollmann, F., ChemCatChem. 9 (2017) , 3821-3826, hereinafter referred to as Reference A) .

Despite the extensive work reported in the area of the selective oxidation of primary and secondary alcohols there is still a continuous need for developing highly efficient and economical oxidation methods using molecular oxygen as an environmentally friendly oxidant. It is the object of the present invention to provide such an oxidation method.

Invention

It has unexpectedly been discovered that primary and secondary alcohols can be selectively oxidized to the respective aldehydes or ketones with molecular oxygen in the presence of a catalyst system, which comprises quinone-type catalysts, such as anthraquinone, naphthoquinone, phenanthraquinone and benzoquinone type catalysts.

The quinone catalyzed oxidation is described by the reaction scheme shown in Figure 1. The catalytic process involves hydrogen abstraction from the alcohol by the quinone with concomitant formation of the hydrogenated quinone and selective production of the respective aldehyde or ketone. Molecular oxygen was used as terminal oxidant, which provokes the regeneration of the quinone and probably formation of H ₂O ₂.

The reaction preferably takes place in solution employing an atmosphere of pure oxygen or air and at a temperature in the range of from 80 to 200 ℃ and a pressure in the range of from 0.1 to 40 MPa.

The term primary or secondary alcohols as used in the present invention describe organic compounds having primary or secondary hydroxyl groups. The term lower alcohol as used herein refers to alcohols having 1 to 10 carbon atoms while the term higher as used herein refers to alcohols having 11 or more carbon atoms. Examples of primary and secondary alcohols thereof include alcohols aliphatic alcohols such as methanol, ethanol, n-and isopropyl alcohol, n-, iso and sec-butyl alcohol, pentyl alcohol, hexyl alcohol, neopentyl alcohol, neohexyl alcohol, heptyl alcohol, octyl alcohol, Iauryl alcohol, tridecyl alcohol, myristyl alcohol, nonadecyl alcohol, eicosyl alcohol; alicyclic alcohols, including but not limited to cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol; heteroocyclic alcohols, including but not limited to 2, 2-dimethyl-1, 3-dioxolane-4-methanol (also referred to as acetone glycerol) ; unsaturated alcohols including but not limited to 3-methyl-3-buten-1-ol, allyl alcohol, crotyl alcohol and propargyl alcohol; and aromatic alcohols including but not limited to benzyl alcohol, phenyl ethanol, phenyl propanol, and hydroxymethyl furfural.

The term quinone-type catalyst as used herein refers to a catalyst selected from the group comprising anthraquinone, naphthoquinone, phenanthraquinone and benzoquinone.

In a preferred embodiment, the catalyst is selected from the group comprising 1, 2-benzoquinone, 1, 4-benzoquinone, 1, 4-naphthoquinone, 9, 10-phenanthraquinone and 9, 10-anthraquinone which may be un-substituted or substituted by at least one substituent. Substituents are selected from the group comprising alkyl, alkylaryl, alkenyl, alkynyl, halogen, hydroxyl, alkoxy, hydroxyalkyl, oxyaryl, oxyheteroaryl, amino, substituted amino, aryl, arylalkyl, heteroaryl, silyl, nitro, sulfonic, or cyano group, and wherein the term alkyl denotes a C ₁ -C ₁₂ hydrocarbon group which may be linear, branched or cyclic.

Examples of quinone-type catalysts compounds contemplated for use in the present invention include, but are not limited to compounds of formulas (I) or (II)

wherein R ¹ to R ⁸ independently are hydrogen, alkyl, alkylaryl, alkenyl, alkynyl, halogen, hydroxyl, alkoxy, hydroxyalkyl, oxyaryl, oxyheteroaryl, amino, substituted amino, aryl, arylalkyl, heteroaryl, silyl, nitro, sulfonic, or cyano group, and wherein the term alkyl denotes a C ₁ -C ₁₂ hydrocarbon group which may be linear, branched or cyclic.

In a preferred embodiment, the catalyst is selected from the group consisting of 1, 4-benzoquinone, anthraquinone, 2-ethylanthraquinone, 2, 6-dihydroxyanthraquinone, and disodium anthraquinone-2, 6-disulfonate

In a still preferred embodiment, the catalyst is selected from the group consisting of 1, 4-benzoquinone, and 2-ethylanthraquinone.

The immobilized forms of any of the above-described compounds can also be used. As a solid support one can use materials such as polymers, composites, carbon materials, or inorganic carriers such as aluminum oxide or titanium oxide or silica. The immobilization of the quinone-type catalyst can be accomplished, for example, by physical adsorption on the surface or via tethering through organic or inorganic linkers.

The term oxidant as used herein means compounds capable of directly oxidizing the reduced form of the quinone type catalyst (see scheme of Figure 1) . Suitable oxidizing agents that can be employed include, but are not limited to molecular oxygen, air, hydrogen peroxide, chlorite, chlorate, bromate, hypochlorite, hypobromite, organic hydroperoxides, percarboxylic acids and the like. More particularly, the preferred oxidants are molecular oxygen and air. If oxygen or air are used, ambient pressures may be used. However, pressurized oxygen or air may have benefits in certain applications. If oxidizing agents such as hydrogen peroxide, chlorite, chlorate, bromate, hypochlorite, hypobromite, organic hydroperoxides, or percarboxylic acids are used, a molar percentages of from 10 %to 200 %may be used, based on the alcohol substrate used.

The presence of solvents in the process of the invention may be beneficial to dissolve the catalyst. Particularly prefened solvents include but are not limited to toluene, acetic acid, ethyl acetate, butyl acetate, acetonitrile, tetrahydrofuran, methylene chloride, chloroform, acetone, diethyl ether, methyl tert-butyl ether. Especially preferred solvent is toluene.

The solvent is present in an amount of from 0 %to 80 %, preferably from 20 to 80 %based on the volume of the reaction mixture of the present invention.

In the inventive processes, the quinone-type catalyst preferably is used in a concentration of from 0.01 to 10 mol %, more preferably from 0.1 to 5 mol %.

If air or molecular oxygen are the terminal oxidant, the process pressure is preferably in the range of from 0.1 -40 MPa, most preferably from 0.5 to 5 MPa.

The reaction can be carried out in a temperature range of from 80 ℃ to 200 ℃, preferably from 90 ℃ to 180 ℃, more preferably from 100 ℃ to 150 ℃.

The process of the invention can be carried out in any conventional batch, semi-batch or continuous flow reactor capable of bringing the two phases (the organic phase and the gas phase) in sufficient contact and at the same time being capable of maintaining the reaction temperature and pressure within the desired range.

Once the reaction is completed, the crude aldehyde or ketone is isolated by phase split by addition of appropriate amount of water, saturated salt solution or by extraction. The solvent used in extraction can be selected from a group of aprotic inert solvents such as methylene chloride, chloroform, ethyl acetate, butyl acetate, methyl acetate, toluene, diethyl ether, methyl tert-butyl ether, pentane, hexane, heptane. Excess solvent may be recycled after isolation of the desired aldehyde or ketone. Especially preferred solvents are methyl tert-butyl ether and ethyl acetate. The crude aldehyde or ketone can be recovered in several ways, including distillation, fractional distillation, either batch or continuous, or use of a thin-film evaporator to concentrate the aldehyde or ketone. The crude aldehyde or ketone can also be purified as described in US patent No. 5,905,175.

In accordance with one embodiment of the present invention, the oxidation is carried out as follows:

1. Preparing a solution of quinone-type catalyst in toluene.

2. Addition of the alcohol substrate to the catalyst solution.

3. Placing the reaction mixture of catalyst, alcohol and solvent in an autoclave.

4. Pressurization of the autoclave to the desired pressure employing pure O ₂.

5. Heating the stirred reaction mixture to the desired temperature.

6. Cooling the reaction after the oxygen uptake is completed.

7. Phase splitting the reaction mixture by addition of water and collecting the organic phase.

In accordance with another embodiment of the present invention, the oxidation is carried out using immobilized quinone-type catalyst and consists of the following steps:

1. Placing commercially available aminopropyl-functionalized silica in a reactor, adding solution of quinone-type catalyst in toluene, followed by required amount of NaBH ₃CN.

2. Stirring the obtained reaction mixture overnight at ambient temperature.

3. Removing the mixture from the reactor and removing any liquids by centrifugation.

4. Washing obtained solids repeatedly with toluene and ethanol to remove any physically adsorbed quinone. Drying the solids at 80 ℃ under vacuum.

5. Preparing a solution of alcohol substrate in toluene.

6. Addition of the immobilized quinone-type catalyst to said solution.

7. Heating the stirred reaction solution to the desired temperature under oxygen atmosphere.

8. Cooling the reaction after the oxygen uptake is completed.

9. Filtering the reaction mixture to remove immobilized catalyst.

10. Phase splitting of the reaction mixture by addition of water and collecting the organic phase.

It is the great advantage of the process of the present invention that selective oxidation of alcohols to the respective aldehydes or ketones and reoxidation of the formed hydroquinone with molecular oxygen can be achieved at the same time in the same reactor. The utilization of additional electron transfer mediators (ETM) , such as metal porphyrin, metal phthalocyanine, or metal-salen complexes to effect reoxidation of the hydroquinone is unnecessary. Also TEMPO-catalyzed selective oxidation reactions of alcohols require ETM’s for the reoxidation of the reduced TEMPO.

High reduction potential quinones, such as 2, 3-dichloro-5, 6-dicyano-1, 4-benzoquinone (DDQ) and chloranil can only oxidize activated alcohols (e.g. allylic and benzylic alcohols) , and the high reduction potential quinone is used as a stoichiometric oxidant (not a catalyst) .

The recently reported (Reference A) aerobic organocatalytic oxidation of alcohols to aldehydes and ketones at ambient conditions under oxygen atmosphere employs sodium anthraquinone sulfonate as the photocatalyst. Visible light (λ > 400 nm) is used to activate the H-abstraction from the starting alcohol to the photoexcited catalyst. As with the present invention, reoxidation of formed hydroquinone with molecular oxygen can be achieved at the same time in the same reactor.

The following examples are provided for illustrative purposes only; the claimed invention shall not be construed as limited to the examples set forth below.

Examples

All reactions were conducted in a 30 ml stainless steel autoclave.

GC analyses: Filtered samples were analyzed using an Agilent 7820A gas chromatograph (GC) equipped with a HP-5 column at a temperature gradient from 50 ℃ to 290 ℃ at 6 ℃ min ^-1.

GC/MS analyses: Filtered samples were injected into a gas chromatography-mass spectrometry (GC/MS) apparatus (Agilent Technologies) with Inert Mass Selective Detector: 7890A gas chromatograph, 5975C Mass Selective Detector, 7693 autosampler. Column: HP-5, 30 m × 320 μm × 0.25 μm) . The injector was set at 325 ℃ and splitless injection was used. The column oven temperature was programmed at 80 ℃ for 1 min, then increased to 325 ℃ at 20 ℃/min for 3 min.

Example 1.1 –1.3

Typically, 2.0 g of benzyl alcohol or cyclohexanol (or 0.5 g of HMF) and 1.0 g of toluene solvent were introduced into the autoclave, together with 50.0 mg of 2-ethylanthraquinone (EQ) as the catalyst. The reactor was sealed and pressurized with 1 MPa of pure O ₂. The reaction mixture was then vigorously stirred at a given temperature for 2 to 24 h and oxygen uptake monitored. After completion of reaction, the products were analyzed by GC and GC-MS. Reaction conditions and conversion of the alcohol and selectivity as to the respective aldehyde or ketone are listed in Table 1.

Table 1. Selective oxidation of alcohols employing EQ

*benzaldehyde /**cyclohexanone /***diformyl furan

Example 2.1 –2.9

The selective oxidation capacity of further types of quinones was evaluated employing the same reaction conditions as used in Examples 1.1 to 1.3. Table 2 summarizes the reaction conditions and catalytic results obtained with the selective oxidation of benzyl alcohol and cyclohexanol.

Table 2. Selective oxidation of alcohols employing further quinones

*BQ = 1, 4-benzoquinone /**DQ = 1, 5-dihydroxy anthraquinone ***SQ = anthraquinone-2 6-disulfonic acid disodium salt

Example 3.1 –3.2

The selective oxidation capacity of anthraquinone (AQ) grafted on the surface of silica (8 -10 wt. %) was evaluated by using the same reaction conditions as described in Examples 1.1 –1.3. Table 3 summarizes the reaction conditions and catalytic results obtained with the selective oxidation of benzyl alcohol, cyclohexanol and HMF.

AQ/silica catalyst was synthesized starting from commercially available aminopropyl-functionalized silica (Aldrich) having a relatively high degree of functionalization (1 mmol/g) . 0.3 g of aminopropyl-functionalized silica was placed in a reactor, a solution of 50 mg anthraquinone-2-carboxylic acid in toluene was added, followed by 1.25 g of NaBH ₃CN in toluene. The obtained mixture was stirred overnight at ambient temperature. The mixture was removed from the reactor and any liquids removed by centrifugation. The obtained solids were washed repeatedly with toluene and ethanol to remove any physically adsorbed quinone. The solids were dried at 80 ℃ under vacuum.

Table 3. Selective oxidation of alcohols employing immobilized anthraquinone

*benzaldehyde /**cyclohexanone /***diformyl furan

Example 4.1 –4.2

The stability of the grafted AQ/silica catalyst in the oxidation of cyclohexanol was tested by filtering off the catalyst after a reaction cycle and addiing recovered catalyst to a fresh alcohol mixture for a subsequent reaction as described in Examples 1.1 –1.3. Table 4 summarizes the reaction conditions and catalytic results obtained with the selective oxidation of cyclohexanol.

Table 4. Selective oxidation of alcohols employing immobilized anthraquinone

Comparative Example C1.1 –C1.3

Reaction conditions corresponded to those of Examples 1.1 –1.3 with the exceptions that no catalyst was employed, and air was used to pressurize the reactor. No aldehyde or ketone formation was observed via GC or GC/MS.

Comparative Example C2.1 –C2.3

Reaction conditions corresponded to those of Examples 1.1 –1.3 with the exception that TEMPO (2 molar equivalents per mol of alcohol) was employed as the oxidant. Conversion to aldehyde or ketone was higher than 90 %, however, fresh TEMPO had to be added to the reactor for each new reaction cycle.

Claims

A process for oxidizing alcohols selected from the group consisting of primary and secondary alcohols to the respective aldehydes or ketones comprising the following steps:

(a) providing said alcohol and a catalyst selected from the group comprising anthraquinone, naphthoquinone, phenanthraquinone and benzoquinone type catalysts;

(b) reacting said alcohol in the presence of said catalyst with an oxidant to produce said aldehyde or ketone.
The process as claimed in claim 1, wherein primary and secondary alcohols are selected from the group comprising aliphatic alcohols, including but not limited to methanol, ethanol, n-and isopropyl alcohol, n-, iso and sec-butyl alcohol, pentyl alcohol, hexyl alcohol, neopentyl alcohol, neohexyl alcohol, heptyl alcohol, octyl alcohol, Iauryl alcohol, tridecyl alcohol, myristyl alcohol, nonadecyl alcohol, eicosyl alcohol; alicyclic alcohols, including but not limited to cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol, heteroocyclic alcohols, including but not limited to 2, 2-dimethyl-1, 3-dioxolane-4-methanol, unsaturated alcohols including but not limited to 3-methyl-3-buten-1-ol, allyl alcohol, crotyl alcohol and propargyl alcohol, and aromatic alcohols including but not limited to benzyl alcohol, phenyl ethanol, phenyl propanol, and hydroxymethyl furfural.
The process as claimed in claim 1 or 2, wherein the catalyst is selected from the group comprising 1, 2-benzoquinone, 1, 4-benzoquinone, 1, 4-naphthoquinone, 9, 10-phenanthraquinone and 9, 10-anthraquinone which may be un-substituted or substituted by at least one substituent.
The process as claimed in claim 3, wherein substituents are selected from the group comprising alkyl, alkylaryl, alkenyl, alkynyl, halogen, hydroxyl, alkoxy, hydroxyalkyl, oxyaryl, oxyheteroaryl, amino, substituted amino, aryl, arylalkyl, heteroaryl, silyl, nitro, sulfonic, or cyano group, and wherein the term alkyl denotes a C ₁-C ₁₂ hydrocarbon group which may be linear, branched or cyclic.
The process as claimed in one or more of claims 1 to 4, wherein the catalyst is selected from the group consisting of compounds having the formulas (I) and (II) :

wherein R ¹–R ⁸ are independently hydrogen, alkyl, alkylaryl, alkenyl, alkynyl, halogen, hydroxyl, alkoxy, hydroxyalkyl, oxyaryl, oxyheteroaryl, amino, substituted amino, aryl, arylalkyl, heteroaryl, silyl, nitro, sulfonic, or cyano group, and wherein the term alkyl denotes a C ₁-C ₁₂ hydrocarbon group which may be linear, branched or cyclic.
The process as claimed in one or more of claims 1 to 5, wherein the catalyst is selected from the group consisting of 1, 4-benzoquinone, anthraquinone, 2-ethylanthraquinone, 2, 6-dihydroxyanthraquinone, disodium anthraquinone-2, 6-disulfonate.
The process as claimed in one or more of claims 1 to 6, wherein the catalyst is selected from the group consisting of 2-ethylanthraquinone and 1, 4-benzoquinone.
The process as claimed in one or more of claims 1 to 7, wherein the catalyst is present in an amount of from 0.01 to 10 mol %, based on the molar amount of the employed alcohol.
The process as claimed in one or more of claims 1 to 8, wherein the catalyst is immobilized on a solid support.
The process as claimed in claim 9, wherein the solid support is selected from the group comprising polymers, composites, carbon materials, or inorganic carriers, the latter including but not limited to silica, aluminum oxide or titanium oxide.
The process as claimed in one or more of claims 1 to 10, wherein the oxidant is selected from the group comprising molecular oxygen, air, hydrogen peroxide, chlorite, chlorate, bromate, hypochlorite, hypobromite, organic hydroperoxides, and percarboxylic acids.
The process as claimed in one or more of claims 1 to 11, wherein the reaction mixture further comprises a solvent.
The process as claimed in claim 12, wherein the solvent is selected from the group comprising: acetic acid, ethyl acetate, butyl acetate, acetonitrile, tetrahydrofuran, methylene chloride, chloroform, toluene, acetone, diethyl ether, methyl tert-butylether and mixtures thereof.
The process as claimed in claims 12 or 13, wherein the solvent is present in an amount of from 0 %to 80 %based on the volume of the reaction mixture of claim 1.
The process as claimed in one or more of claims 1 to 14, wherein the reaction temperature is maintained in a range of from 80 ℃ to 200 ℃.
The process as claimed in one or more of claims 1 to 15, wherein the reaction pressure is maintained in a range of from 0.1 MPa to 40 MPa.
The process as claimed in one or more of claims 1 to 16, further comprising the step of purification of said aldehyde or ketone by one or more of the group comprising batch or continuous distillation, batch or continuous fractional distillation, or a thin film evaporation.
Use of anthraquinone, naphthoquinone, phenanthraquinone and benzoquinone type catalysts for the selective oxidation of of primary and secondary alcohols to the respective aldehydes or ketones.