WO2024134691A1

WO2024134691A1 - Process for producing carbonyl compounds from olefins

Info

Publication number: WO2024134691A1
Application number: PCT/IT2023/050253
Authority: WO
Inventors: Francesco Parrino; Sandra Dire'; Riccardo CECCATO; Alessandro GOTTUSO; Leonardo Palmisano; Claudio DE PASQUALE
Original assignee: Universita' Degli Studi Di Trento; Universita' Degli Studi Di Palermo
Priority date: 2022-12-19
Filing date: 2023-11-14
Publication date: 2024-06-27

Abstract

A process for the preparation of carbonyl compounds starting from olefins is described, comprising the oxidative scission reaction of one or more carbon- carbon double bonds, where electron-poor double bonds and terminal bonds which do not have neighbouring functional groups capable of donate electronic density are excluded, wherein such reaction is carried out by means of an advanced oxidation process, in the presence of at least one nitrogen-containing additive and at least one advanced oxidation agent, the advanced oxidation process being a chemical treatment which in a reaction produces oxidation of chemical compounds through the generation of active radical species.

Description

PROCESS FOR PRODUCING CARBONYL COMPOUNDS FROM OLEFINS The present invention refers to a process for the oxidative cleavage of olefins for the synthesis of carbonyl compounds, and more particularly of aldehydes, ketones and/or compounds with both functionalities. Aldehydes are compounds characterized by the presence of a terminal carbonyl group and are generally represented by the general formula RCHO, where R represents any carbonyl (aliphatic, aromatic) chain. The strong polarity of the carbonyl group makes aldehydes particularly reactive, to the point that it is difficult to isolate them as a pure compound. They are therefore able to react with a wide range of compounds and can be used as intermediates for the synthesis of many products of industrial interest, including drugs and polymeric materials such as polyamides and polyurethanes. Furthermore, aldehydes find direct use in the cosmetic and food fields such as perfumes or fragrances. Therefore, the synthesis of aldehyde compounds is still of great industrial interest today as demonstrated by the numerous literature involved. Formaldehyde is the most produced aldehyde compound in the world (approx. 6.0x106 t/y) and is mainly used as starting material for the production of thermosetting resins and the synthesis of polyurethanes. Butyraldehyde is the second most produced aldehyde (approx. 2.5x106 t/a), used mainly for the synthesis of 2-ethylhexanol, one of the most common and used plasticizers. Acetaldehyde, although decreasing in production, remains one of the most produced aldehydes with approximately 1.0x106 t/y. For the most important aldehydes used in the perfume industry, little production data is available. The aldehydes most produced for the cosmetic field in 2009 were the following: cinnamaldehyde 3000 t/y, lilial 8000 t/y, hydroxycitronellal 1000 t/y, α- hexylcinnamaldehyde 12000 t/y, α-amylcinnamaldehyde 2100 t/y, citral 4500 t/a, citronellal 550 t/a, and cyclamenaldehyde 500 t/a. Similar to aldehydes, ketones are also compounds characterized by a carbonyl group, but have the latter in a non-terminal position, with the general formula RCOR'. This characteristic makes ketones, compared to aldehydes, decidedly more stable and consequently less reactive compounds. They are also widely used as solvents, due to their relative stability, as precursors of thermoplastic polymers (polyesters and polyamides) and pharmaceutical compounds. In 2020, the ketone most produced on an industrial scale was acetone with approx. 7.4x106 t/y of which approximately a third was used as a solvent and a quarter as a precursor of acetone cyanohydrin, a compound used for the production of methyl methacrylate. Among the most produced ketones are: cyclohexanone (with approximately 8.6x105 t/a) used mainly for the synthesis of polyamide precursors (nylon 6, nylon 6.6); butanone (with approx. 7x105 t/a), widely used as a solvent, but also as a precursor of rubbers, resins, lacquers, paints and inks. The synthesis of carbonyl compounds can be achieved by numerous methods. Industrially, the oxidative dehydrogenation of primary alcohols are of great importance, in particular for the production of formaldehyde and acetaldehyde, and the oxidation of secondary alcohols for the synthesis of ketones. Furthermore, there are several laboratory-scale processes for the synthesis of aldehydes (catalytic reduction of various organic compounds such as nitriles, carboxylic acids, amides, esters and hydrazines) and for the synthesis of ketones (Friedel-Crafts acylation, hydration of alkynes, decarboxylation ketolysis of carboxylic acids, hydrolysis of β- ketoesters or β-diketones). However, it is inconvenient to use polyfunctional or industrially interesting compounds for the formation of carbonyl compounds, which is why these methods, despite good yields, remain on a laboratory scale. Synthesis methods that instead make use of olefins, products widely accessible from petroleum refining and extraction processes from plant material, appear to be of great interest and industrial advantage. These processes therefore constitute the state of the art for the present invention. Among these are: 1. Hydroformylation of olefins (oxo synthesis); 2. Wacker-Hoechst oxidation; 3. Oxidation of hydrocarbons in air; Hydroformylation is the most important process for the production of aldehydes containing at least three carbon atoms. In this process, the olefins react with synthesis gas (CO, H₂) to form aldehydes with one more carbon atom than that of the starting material. This reaction occurs in a range of temperatures between 40°C and 200°C, pressures between 10 atm and 100 atm, and homogeneous catalysts based on rhodium or cobalt. The most used industrial process for the production of acetaldehyde is the partial oxidation of ethylene in the aqueous phase and in the presence of palladium and copper chlorides (Wacker- Hoechst process). Direct oxidation of hydrocarbons is the most important process for the synthesis of some ketone compounds, in particular cyclohexanone and acetone (cumene process). However, this method is limited to a small number of compounds, while the oxidation of secondary alcohols is widely used. Another undoubtedly promising method at industrial level and which involves the use of alkenes is the oxidative scission of olefins, which is currently being validated at laboratory level. This reaction consists in the breaking of the carbon-carbon double bond of the olefin with consequent oxidation of the carbon atoms initially engaged in the double bond, to carbonyl groups. In particular, through this approach, it is possible, starting from cyclic olefins, to obtain α,ω- dicarbonyl compounds and, in the case of α,ω- dialdehydes, it is therefore possible to easily access a whole series of α,ω-bi-functional compounds (such as α,ω-diols, α,ω-carboxylic diacids, α,ω-diamines, α,ω-diamides etc.). α,ω-bi- functional compounds are precursors of numerous industrially produced plastic materials, in particular polyamides and polyurethanes. At present, there are several methods capable of giving oxidative scission of olefins; many of these include the use of stoichiometric quantities of strong oxidants such as KHSO₅ (oxone), KMnO₄, NaIO₄, RuCl₃, Cr(VI) salts, m-chloroperbenzoic acid, hypervalent iodine, or take place in the presence of Pd, Au, Os, or porphyrin derivatives. Others instead make use of enzymatic catalysis. Certainly more interesting is ozonolysis, a process in which ozone is added as an electrophile to an alkene to give the unstable cyclic molozonide which immediately reorganizes and splits into carbonyl products in the presence of a reducing agent such as zinc or dimethyl sulfide. The use of hydrogen peroxide, however, can lead to the formation of carboxylic acid. Ozonolysis, consequently, appears to be used more as a degradation procedure than as a synthesis method. Another method involves the use of singlet oxygen in a [2+2] cycloaddition, which however applies effectively on a laboratory scale only to electron-rich C=C double bonds. Despite the existence of numerous methods, the oxidative cleavage of olefins seems, at the moment, not suitable for industrial applications. It is desirable, in fact, that heterogeneous catalytic systems are used industrially, because they are more easily separated from the reaction mixtures, and that the operating conditions of pressure and temperature are as close as possible to the environmental ones, parameters currently not satisfied by the synthesis methods used industrially. It is also desirable in industrial applications to use non-toxic and non-harmful substances for the environment. From the above discussion of the most commonly used oxidative cleavage methods, it can be seen that the art lacks a selective, conveniently employed, economical, and low environmental impact method for the synthesis of carbonyl compounds. The present invention is therefore proposed to provide such a method of synthesis of carbonyl compounds starting from olefins, which can be carried out in mild conditions and providing, with high selectivity, primary oxidation products of an exclusively carbonyl character. There are patents on the oxidative cleavage of olefins: US3201476A, US6787671B2, US20100184174A1: the first concerns a method for the oxidative cleavage of carbon-carbon double bonds to obtain carbonyl compounds, in which the olefin is treated with Cr oxide (VI) supported by different oxide systems (silica, alumina, mixtures of silica and alumina, zirconia, thoria) in an atmosphere with humidity close to zero; the second concerns a method for the oxidative scission of carbon-carbon double bonds, in which the olefin is treated with osmium and peroxides obtaining, depending on the reaction conditions, aldehydes, ketones, esters and carboxylic acids; the third concerns a method for the oxidative scission of carbon-carbon double bonds of the vinyl-aromatic type, in which the olefin is transformed into aldehyde through the reaction with oxygen in the presence of an enzymatic catalyst. It is worth noting that, in the first two methods, the use of catalysts based on hexavalent chromium or osmium represent the major critical issues to overcome as they are dangerous materials for the environment and very expensive. The third method, however, although it presents more advantageous reaction conditions than the first two, finds application only on olefins specifically of the vinyl-aromatic type, which represent a very limited number of compounds, and therefore the method is anything but general. Document CN-B-106 831 284 describes a process according to the prior art. Figure 1 shows the conversion of limonene (X(L)-square) and selectivity to limononaldehyde (S(LA)-sphere). The oxidative cleavage of olefins is a potentially industrially relevant process and therefore the present invention fits into an area of high interest. Therefore, object present invention is providing an improved, economically and technically sustainable alternative for the synthesis of carbonyl compounds starting from olefinic compounds, solving the already mentioned critical issues of current methods. Limonene was used as a model olefin for the present invention essentially because it is of natural origin, economically accessible (waste from the citrus industry) and has low toxicity. However, the process has been shown to be valid for other olefinic compounds. Furthermore, it would be desired that the above-mentioned process preferably allows operation at ambient pressure and temperature. A further object is providing a process with high selectivity. A further object is using a process that respects the principles of green chemistry as required by the latest European Green Deal directives. The present invention therefore provides a process for the preparation of carbonyl compounds starting from olefins, comprising the oxidative scission reaction of one or more carbon-carbon double bonds, where electron-poor double bonds and terminal bonds which do not have vicinity functional groups capable of donating electronic density are excluded, wherein this reaction is carried out through an advanced oxidation process, in the presence of at least one nitrogen-containing additive and at least one advanced oxidation agent. The advanced oxidation process is a chemical treatment that produces oxidation of chemical compounds in a reaction medium through the generation of active radical species. It can be selected from the group consisting of photocatalysis, electrocatalysis, photoelectrocatalysis, ozonation, Fenton processes, photo-Fenton processes, irradiation, oxidation by H₂O₂ or a combination thereof. Advanced oxidation agent (AOA) can be selected from the group consisting of catalyst, photo- catalyst, electro-catalyst, photo-electro-catalyst, ozone, H₂O₂, light, electric potential, metal ions or a combination thereof. The present invention also concerns a process for the synthesis of carbonyl compounds starting from olefins by means of an advanced oxidation process (AOP), in a reaction medium, in the presence of at least one olefin, at least one nitrogen-containing additive and at least one advanced oxidation agent (AOA), followed by a process step in which the nitrogen oxide generated during the reaction is removed from the reaction mixture. The present invention also concerns a process for the synthesis of carbonyl compounds from olefins by means of an advanced oxidation process (AOP), in a reaction medium, in the presence of at least one olefin, at least one nitrogen-containing additive and at least one AOA, followed from a process stage in which the nitrogen oxide generated during the reaction is removed from the reaction mixture, re-oxidized and reintroduced into the reaction mixture. A further object of the present invention is providing a reaction system consisting of any apparatus capable of carrying out the process which is the object of the present invention. The production of carbonyl compounds from olefins occurs with any advanced oxidation process and combinations thereof so that in a single general inventive concept, all equally effective alternatives, working alone or in combination, can be applied, thus making the invention unitary. Further characteristics of the present invention will be clear from the following detailed description with reference to the experimental examples and the attached drawings. The above and other objects and advantages of the invention, as will appear from the following description, are preferably achieved with a process for the production of carbonyl compounds from olefins such as that described in claim 1. Preferred embodiments and non-trivial variations of the present invention form the subject matter of the dependent claims. It is understood that all attached claims form an integral part of this description. It will be immediately obvious that countless variations and modifications can be made to what is described (for example relating to shape, dimensions, arrangements and parts with equivalent functionality) without departing from the scope of the invention as appears from the attached claims. Regarding the advantageous effects of the invention, the present process for the synthesis of carbonyl compounds from olefins is based on the interaction of the advanced oxidation agent with a nitrogen-containing additive generating highly reactive species which in turn react selectively with the olefins producing corresponding carbonyl compounds. The above reactive species may contain, together with other possible atoms, nitrogen and/or oxygen. The product of the reaction of the nitrogen-containing additive is then reconverted into the starting species in a subsequent stage and reintroduced into the reaction system. Preferably, the nitrogen-containing additive is silver nitrate which, by interacting with the advanced oxidation agent, produces the oxidative splitting of the olefin, transforms into a nitrogen oxide which in turn can be converted back to nitrate and reintroduced into the reaction system. Nitrate does not present particular safety problems and after the reaction it can be easily re-obtained without losses of material, as instead happens in the case of peroxy oxidants used in stoichiometric quantities. The process can take place in a heterogeneous phase, in the presence of a stable catalyst preferably based on TiO₂, pure, modified or coupled in all its phases and forms. The process takes place at ambient temperature and pressure in the presence of pure or mixed oxygen. The process takes place without any stoichiometric addition of peroxides and/or other co-oxidants. The process for the oxidative cleavage of olefins, object of the present invention, therefore, not only proceeds catalytically and with high selectivity towards double bonds, but takes place without the addition of expensive and dangerous compounds, and without additions in stoichiometric quantities of peroxides and/or other co-oxidants. Furthermore, unlike the currently most used processes, the process for the synthesis of carbonyl compounds from olefins which is the object of the present invention, takes place at ambient temperature and pressure in the presence of pure or mixed oxygen and/or another electron acceptor. Furthermore, the catalyst, preferably TiO₂, is stable, inexpensive and abundant. The invention can be used by industries operating in the chemical sector for the production of carbonyl compounds, i.e. compounds used in the polymer industry, detergents, cosmetics and as intermediates in numerous chemical syntheses. A process for the synthesis of carbonyl compounds from olefins takes place in a reaction fluid via an AOP advanced oxidation process, in the presence of at least one olefin, at least one nitrogen-containing additive, at least one advanced oxidation agent. The AOP advanced oxidation process is selected from the group consisting of photo-catalysis, electro-catalysis, photo-electro-catalysis, ozonation, Fenton process, photo-Fenton process, irradiation, oxidation with H₂O₂ or a combination thereof. The Advanced Oxidation Process, AOP, involves an Advanced Oxidation Agent, AOA, which can be selected from the group consisting of photo- catalyst, electro-catalyst, photo-electro-catalyst, ozone, H₂O₂, electric potential, irradiation or a combination thereof. The product of the reaction of the nitrogen- containing additive is easily re-oxidized or reacted in an appropriate way to reform the precursor of the active radical species, and introduced into the reaction fluid to support the reaction. Preferably, the process of the invention is characterized by the presence of the nitrate radical (NO₃ ^.). More preferably, the process of the invention is characterized by the presence of the nitrate radical (NO₃ ^.), where the nitrate radical is generated in situ starting from the additive comprising nitrogen, through the advanced oxidation process and/or the advanced oxidation agent. According to one aspect, the process provides that the nitrogen-containing additive is an inorganic or organic nitrate or is a nitrate salt of an alkaline, alkaline earth or transition element, or is nitrated silver. According to one aspect, the process provides that the advanced oxidation process is selected from the group consisting of photo-catalysis, electro-catalysis, photo-electro-catalysis, ozonation, Fenton process, photo-Fenton process, irradiation, oxidation with H₂O₂ or a combination thereof . According to one aspect, in the process of the invention, the advanced oxidation process is photo- catalysis, in which the light has a wavelength in the range from 200 nm to 800 nm, or from 280 nm to 380 nm, or is 365 nm. According to one aspect, in the process of the invention, the advanced oxidation agent is selected from the group consisting of photo-catalyst, electro-catalyst, photo-electro-catalyst, ozone, H₂O₂, electric potential, irradiation or a combination thereof. According to a preferred aspect, the process of the invention provides that the advanced oxidation agent is TiO₂, in each of its phases or variously modified. According to a more preferred aspect, in the process of the invention, the nitrogen-containing additive is silver nitrate and the advanced oxidation agent is TiO₂, in each of its phases or variously modified. According to one aspect of the process, the advanced oxidation process is photo-catalysis, in which the light has a wavelength of 365 nm, in which the nitrogen-containing additive is silver nitrate and the advanced oxidation agent is TiO₂, in each its phase or variously modified. According to one aspect, the process can take place in the presence of air, as an advanced oxidation agent, and at ambient temperatures and pressure. According to one aspect, the process is carried out without any addition of stoichiometric quantities of peroxides and co-oxidants. According to one aspect of the process, the oxidative cleavage reaction of an olefin is carried out in an organic solvent or is carried out in acetonitrile. According to one aspect, the process provides that the carbonyl compound is limononaldehyde and that the olefin is limonene. The nitrogen-containing compound is an inorganic or organic nitrate. The process for the synthesis of carbonyl compounds from olefins takes place at ambient temperature and pressure in the presence of air. The process for the synthesis of carbonyl compounds from olefins takes place without any stoichiometric addition of peroxides and co- oxidants. The photocatalyst is pure TiO₂, in each of its phases or variously modified. The olefin is limonene as a model molecule. The role of AOA in the process of the present invention is to generate active species that can oxidize olefins to carbonyl compounds. The above active species may contain, together with other possible atoms, nitrogen and/or oxygen. Oxidation can occur directly or indirectly through interaction with intermediates produced by the presence of a nitrogen-containing compound. Furthermore, the advanced oxidation process allows, in situ or in a subsequent stage, to re-oxidize or react in an appropriate manner the reaction product of the nitrogen-containing additive, to reform the precursor of the active radical species, and then reintroduce it into the reaction system. The process for the synthesis of carbonyl compounds from olefins is characterized by mandatory essential parameters for the quantitative formation of the desired product which are: presence of olefin in a reaction medium, presence of nitrogen-containing additives, preferably silver nitrate, capable of inducing and supporting the reaction directly or indirectly, an advanced oxidation process and an advanced oxidation agent. Preferably, the advanced oxidation process is photo-catalysis. Preferably, the advanced oxidation agent is photo-catalyst. When the advanced oxidation process is photo- catalysis and the advanced oxidation agent is a photo-catalyst, the photo-catalytic process requires the presence of oxygen, or another electron acceptor, and light. The presence of oxygen or an electron acceptor is mandatory because it reduces charge recombination and contributes to the formation of active species, which in turn react selectively with olefins producing the corresponding carbonyl compounds. The process works for various concentrations of the olefin in the reaction medium including even the case of pure olefin. For the photocatalytic reaction, O₂ is preferably added pure or in a mixture with other inert gases such as nitrogen. Preferably, the photocatalyst is a heterogeneous or homogeneous photocatalyst, organic or inorganic, more preferably it is a semiconducting metal oxide, even more preferably it is a polycrystalline TiO₂ Evonik (approx. 20% rutile and 80% anatase, specific surface area approx. 50 m² g^-1) pure or surface modified. Preferably, the photocatalyst is added in an amount between 0.1 and 5 g L^-1, more preferably in an amount between 0.5 and 1 g L^-1, even more preferably the amount is 0.5 g L^-1. Preferably, the light has a wavelength from 200 nm to 800 nm depending on the photocatalyst used, more preferably from 280 nm to 380 nm, even more preferably in the case of TiO₂, the main wavelength is 365 nm. The light can be solar or light emitted by a light emitter such as a lamp. The extraction of the reaction products of the nitrogen-containing additive can be carried out by mild heat treatment or pressure control or any other known extraction process. The technical conditions can be chosen to facilitate the reaction and avoid the formation of unwanted products. Preferably, the processes of the present invention are carried out at an appropriate temperature based on the physical-chemical characteristics of the olefin, the reaction medium, the photocatalyst and the nitrogen-containing additive. Preferably, the temperature is room temperature. In a preferred embodiment of the present invention, the reaction is carried out in the presence of UV light with a wavelength of 365 nm. The irradiated and magnetically stirred reaction mixture contains TiO₂ as photo-catalyst, air, silver nitrate as nitrogen-containing additive, limonene as olefin, and acetonitrile as reaction fluid. The initial concentration of limonene is 2 mM, the initial concentration of silver nitrate is 10 mM, the initial concentration of TiO₂ is 0.5 g L^-1. Preferably TiO₂ is TiO₂ Evonik. The reaction system includes at least one reactor, a power supply, a light emitter, a gas tank containing pure or mixed oxygen for photocatalysis. Furthermore, a system is needed to collect the reaction products of the nitrogen- containing compound which must be appropriately transformed or re-oxidized and reintroduced into the reaction system. In a preferred embodiment of the present invention, the reaction system comprises a reactor, a magnetic stirrer, a reserve of pure or mixed oxygen, a power supply connected to the light emitter and a system for collecting and re- oxidation or transformation of the reaction products of the nitrogen-containing compound. All chemicals were purchased and used as received without further purification. Referring to the reaction in Figure 1, the main product is shown resulting from the oxidative cleavage of limonene, i.e. limononaldehyde (LA). The diagram below shows the main product of the oxidative cleavage of limonene.

The chemical characteristics of limonene make it an ideal model molecule for carrying out oxidative cleavage; in fact, the highly substituted endocyclic double bond is easily oxidized, while the exocyclic double bond is not attacked, allowing good selectivity of the process. The results obtained can be easily extended to most olefinic substrates whose primary oxidation is of industrial interest. Regarding the reaction conditions, 14 mg of limonene was dissolved in 50 mL of acetonitrile to form a solution with a concentration of 2 mM. Subsequently, 25 mg of TiO₂ (P25 Evonik, 0.5 g/L) and 85 mg of silver nitrate (10 mM) were added to the solution. The mixture was stirred until a stable suspension was formed and then irradiated using UV light, with a maximum emission of the lamps at 365 nm. Limonene (L) and limononaldehyde (LA) concentrations were measured by gas chromatography mass spectrometry on samples taken at fixed time intervals. The results are shown in Figure 1. From the results of a test shown in Figure 1 it can be seen that: limonene is almost completely converted after the first three hours of reaction; the reaction is selective with respect to limononaldehyde with selectivity up to 72% after 30 min of irradiation, when the conversion is about 30%, which indicates a fast formation of the sought product. After the maximum, the selectivity decreases with a slight slope up to 50% at two hours of irradiation when the conversion has reached 83%, indicating that the degradation of limononaldehyde to further oxidation products is relatively slow compared to its formation. Reaction parameters were varied including: temperature, pressure, molar ratios between the reactants (relative quantities of nitrate, TiO₂, olefin), nitrate source (NaNO₃, KNO₃, Ca(NO₃)₂, Mg(NO₃)₂, LiNO₃) and solvent (dimethyl sulfoxide, cyclohexane, toluene, dichloromethane, propyl carbonate and dimethyl carbonate). The best reaction conditions were found to be 10 mM AgNO₃, 0.5 g/L TiO₂ and 2 mM olefin in acetonitrile at room temperature and pressure. Other commercial catalysts (Merck) were also tested and functionalized (fluorinated P25, silylated P25), or with deposited noble metals (Ag, Au, Pt, Pd, Rh, Ru) at 2% by weight, which allowed to obtain similar or better performances. The same reaction was carried out in the photo-electro-catalytic regime with the application of a potential equal to +2.00V vs Saturated Calomel Electrode, SCE, obtaining similar results to the reaction in the photocatalytic regime. The same reaction was carried out in the presence of ozone (O₃) in addition to the described photocatalytic system, resulting in similar or better results. The same reaction was carried out in the presence of stoichiometric quantities of H₂O₂ in addition to the described photocatalytic system, resulting in similar results. Olefin oxidation has also been achieved by using ozone (O₃) as an advanced oxidation agent in the presence of NO₂ as a nitrogen-containing additive. Other olefins with different characteristics were tested: aromatic olefins with internal or terminal double bond (stilbene conversion 95% selectivity 40%; styrene conversion 80% selectivity 25%), non-terminal linear aliphatic olefins (4- octene conversion 70% selectivity 40%) and cyclic olefins (cyclohexene conversion 82% selectivity 37%) for which the reaction proceeds similarly. The process of the invention excludes olefins in which the double bonds are electron-poor and the terminal ones, which do not have vicinity functional groups capable of donating electronic density, for which the reaction occurs with unsatisfactory results or does not occur at all. These results were obtained in laboratory- scale batches. The selectivity and reaction yield, already significantly high at the current state of research, can be further optimized in a similar way to what the inventors have done for other partial oxidation reactions, in particular, by implementing the reaction in continuous or semi-continuous systems and by coupling advanced separation techniques. The nitrogen oxides in the gas phase produced following oxidation (N_xO_y) were conveyed to a further reactor for the oxidation of the same to nitrates (NO₃-) to be subsequently recycled and reintroduced into the first reactor. Definitions In the context of the present invention, an olefin is any chemical compound containing at least one carbon-carbon double bond not involved in aromatic cycles. In the context of the present invention, an electron-poor carbon-carbon double bond is defined as any double bond between two carbon atoms which has a reduced electron density by virtue of the nearby presence of a functional group capable of attracting electron density. In the context of the present invention, a terminal carbon-carbon double bond is defined as any double bond between two carbon atoms of which one is bonded to two hydrogens. In the context of the present invention, a reaction fluid is any medium of organic, inorganic nature or combination thereof, in liquid, solid, gaseous phase, plasma or combination thereof, in which the oxidative splitting reaction of the olefin takes place. In the context of the present invention, a nitrogen-containing additive, capable of initiating and sustaining the process of the present invention, is a compound added to the other components of the reaction system or formed in situ, containing at least one nitrogen atom, the oxidation of which produces intermediates capable to interact with the species directly or indirectly involved in the oxidative fission mechanism, generating the reaction products. The nitrogen-containing additive can be inorganic, organic or a combination thereof. The nitrogen-containing organic additive can be amines, diazonium salts, amides, nitro compounds, imines, imides, enamines, azoles, amino acids, peptides, proteins, nitriles, nitrogen- containing heteroaromatic compounds, urea polymers, melamine, nitrophenol, aminophenol, butylamine, aminoethanoic acid, benzamide, polyamides, pyridine, or combination thereof. The inorganic nitrogen-containing additive may be inorganic amines, inorganic imides, metalamides, nitrogen hydrides, nitrogen oxides, nitrogen-containing oxyacids or combination thereof such as ammonia, nitric acid and nitrous acid, nitrogen oxides (N_xO_y), N2, hydrazine, azides and complexes comprising at least one metal and at least one ligand wherein the metal can be copper, iron, manganese, silver, cobalt, cerium, tungsten, vanadium, silver, palladium, and where the ligand is an organic or inorganic additive containing at least a nitrogen atom as previously defined. In the context of the present invention, nitrate can be added to the reaction fluid or generated in situ by oxidation of nitrogen- containing additives. In the context of the present invention, an Advanced Oxidation Process, AOP, is a chemical treatment that produces oxidation of compounds in a reaction mixture via generation of intermediate active species. In the context of the present invention, Advanced Oxidation Processes may be photo- catalysis, electro-catalysis, photo-electro- catalysis, ozonation, Fenton processes, photo- Fenton processes, irradiation, oxidation by H₂O₂ or a combination thereof. In the context of the present invention, an Advanced Oxidation Agent is an agent that enables the progression of an Advanced Oxidation Process, AOP. In the context of the present invention, Advanced Oxidation Agents may be photo-catalyst, electro-catalyst, photo-electro-catalyst, ozone, H₂O₂, irradiation, electric potential, plasma or a combination thereof. In the context of the present invention, photo-catalyst means any catalyst that exerts its catalytic effect when irradiated with radiation of appropriate wavelength without its chemical nature being substantially modified. In the context of the present invention, photo-catalyst means homogeneous photo-catalyst, heterogeneous photo-catalyst, organic photo- catalyst, inorganic photo-catalyst, or a combination thereof. In the context of the present invention, homogeneous photo-catalyst means that, in the photo-catalytic reaction, the photo-catalyst is in the same phase as the reactants, such as metal complexes, substances generating singlet oxygen or active oxygen species, organic or inorganic dyes. In the context of the present invention, heterogeneous photo-catalyst means that, in the photo-catalytic reaction, the photo-catalyst is present in a separate phase from the reaction mixture as metal particles or metal oxides. In the context of the present invention, organic photo-catalyst means that the photo- catalyst can be selected from the class of organic substances such as organic dyes, nitrogen- containing compounds such as iminium salts, imidazolinones, piperidine, metalorganic complexes such as pure or variously modified trisbipyridyl ruthenium complex. In the context of the present invention, inorganic photo-catalyst means that the photo- catalyst can be selected from the class of inorganic substances such as metal particles such as Ag, Au, Pt, Pd, Rh, metal ions, or metal oxides, nitrides, carbides or chalcogenides, such as for example C₃N₄, ZrO₂, Bi₂WO₆, NbO, Ta₂O₅, ZnS, KTaO₅, SnO₂, ZnWO₄, NiO, GaN, SrTiO₃, BaTiO₃, ZnO, LaFeO₃, TiO₂, CuTiO₃, FeTiO₃, In₂O₃, SiC, WO₃, CdS, CdSe, CdFe₂O₄, Fe₂O₃, pure CdO, mixed Cu₂O, CuO, MoS₂, variously doped or doped in different polymorphic phases and in different phases or technological arrangements. In the context of the present invention, the Fenton process is an advanced oxidation process based on the presence of iron or other metal with similar action and hydrogen peroxide. In the context of the present invention, Photo-Fenton process means a Fenton process in the presence of irradiation. In the context of the present invention, radiation means any irradiation of energy capable of producing active species for the oxidative cleavage of olefins for the production of primary oxidation species, directly or indirectly. In the context of the present invention, oxidation with H₂O₂ means any process in which the direct or indirect oxidant is hydrogen peroxide. In the context of the present invention, electrocatalysis means a catalytic process that occurs in the presence of an applied electrical potential. In the context of the present invention, photo-electro-catalysis means a catalytic process that occurs in the presence of an applied potential and irradiation. In the context of the present invention, the system is any apparatus capable of performing the synthesis of carbonyl compounds from olefins according to the process of the present invention, further comprising the steps of separation of nitrogen-containing additives, reoxidation and reinjection into the system.

Claims

CLAIMS 1) Process for the preparation of carbonyl compounds starting from olefins, comprising the oxidative scission reaction of one or more carbon-carbon double bonds, where electron-poor double bonds and terminal bonds which do not have neighbouring functional groups capable of donate electronic density are excluded, characterized in that said reaction is carried out by means of an advanced oxidation process, in the presence of at least one nitrogen- containing additive and at least one advanced oxidation agent, wherein said advanced oxidation process is a chemical treatment which in a reaction medium produces oxidation of chemical compounds through the generation of active radical species. 2) Process according to claim 1, characterized by the presence of the nitrate radical (NO₃ ^.). 3) Process according to claim 2, wherein the nitrate radical (NO₃ ^.) is generated in situ starting from the additive comprising nitrogen, through the advanced oxidation process and/or the advanced oxidation agent. 4) Process according to any of the previous claims characterized in that the nitrogen-containing additive is an inorganic or organic nitrate or is a nitrate salt of an alkaline, alkaline earth or transition element, or is nitrated silver. 5) Process according to any of the previous claims, characterized in that the advanced oxidation process is selected from the group consisting of photo-catalysis, electro- catalysis, photo-electro-catalysis, ozonation, Fenton process, photo-Fenton process, irradiation, oxidation with H₂O₂ or a combination of the same. 6) Process according to any of the previous claims, in which the advanced oxidation process is photo-catalysis, in which light has a wavelength in the range from 200 nm to 800 nm, or from 280 nm to 380 nm, or is 365 nm. 7) Process according to any of the previous claims, wherein the advanced oxidation agent is selected from the group consisting of photo- catalyst, electro-catalyst, photo-electro- catalyst, ozone, H₂O₂, electric potential, irradiation or a combination thereof. 8) Process according to any one of claims 1 to 6, characterized in that the advanced oxidation agent is TiO₂, in each of its phases or variously modified. 9) Process according to any one of claims 1 to 8, wherein the nitrogen-containing additive is silver nitrate and the advanced oxidation agent is TiO₂, in each of its phases or variously modified. 10) Process according to any one of claims 1 to 9, wherein the advanced oxidation process is photo- catalysis, wherein light has a wavelength of 365 nm, wherein the nitrogen-containing additive is nitrated silver and the advanced oxidation agent is TiO₂, in each of its phases or variously modified. 11) Process according to any of the previous claims, characterized in that it takes place in the presence of air, as an advanced oxidation agent, and at ambient temperature and pressure. 12) Process according to any of the previous claims, characterized in that it is carried out without any addition of stoichiometric quantities of peroxides and co-oxidants. 13) Process according to any one of the previous claims, wherein the oxidative cleavage reaction of an olefin is carried out in an organic solvent or is carried out in acetonitrile. 14) Process according to any of the previous claims, characterized in that the carbonyl compound is limononaldehyde and that the olefin is limonene.