JP2019043869A - Manufacturing method of oxide of aromatic hydrocarbon and catalyst - Google Patents

Abstract

To provide a manufacturing method of oxide of aromatic hydrocarbon by an oxidation reaction of aromatic hydrocarbon such as toluene, and a catalyst.SOLUTION: A product mainly containing oxide of which the methyl group is converted to a carboxyl group, oxide of which the methyl group is converted to an aldehyde group, and oxide of which the methyl group is converted to hydroxymethyl group is obtained by an oxidation reaction using aromatic hydrocarbon represented by the formula (I) and having the methyl group as a substituent, under oxygen atmosphere in the presence of a catalyst in which Group 8 to Group 11 single element cluster having 4 to 60 carbon atoms is carried on a carrier, wherein at least one of R is a methyl group, n Rs are each independently the methyl group or a phenyl group, and n is an integer of 1 to 6.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a process for producing an oxide of aromatic hydrocarbon and a catalyst.

  In recent years, the catalytic activity of nanoparticles composed of noble metal elements such as platinum and gold has attracted attention. On the other hand, synthesis of subnanoparticles having a smaller number of atoms and smaller size than nanoparticles has been reported (Non-Patent Document 1, Patent Documents 1 to 4). This subnanoparticle of about 1 nm is composed of only a few tens of atoms or less, and the band gap becomes large and discrete based on the quantum size effect, and forming a unique geometrical structure unique to the element, It has an aspect that can not be captured by the conventional concept of nanoparticles that has been discussed based on simple structural features such as sheath shape, and is expected to express catalytic activity and reaction selectivity over nanoparticles.

  As a method for producing sub-nanoparticles, a method using phenylazomethine dendrimer by the present inventors as a template has been searched and developed. Phenylazomethine dendrimers are preferentially and stepwise complexed with metal salts from the innermost layer imine by an electron density gradient in which the electron density of the imine increases from the terminal imine toward the center. This enables precise accumulation of metal salts, and makes it possible to prepare dendrimer complexes in which the number and composition of metal salts are defined. By reducing the dendrimer complex to which this metal salt is coordinated, it becomes possible to form a precisely controlled metal sub-nanoparticle having a very small particle size distribution (Non-Patent Document 1, Patent Documents 1 to 4). It is reported that this subnanoparticle such as platinum exhibits a much higher oxygen reduction catalytic activity per mass than nanoparticles of 3 to 5 nm.

  On the other hand, the oxidation reaction of hydrocarbons is important in obtaining industrial raw materials and intermediates, and has been studied more than ever. The binding energy of hydrocarbons is 105.0 kcal / mol for methane, 98.6 kcal / mol for propane, 96.5 kcal / mol for isobutane for aliphatic hydrocarbons, and benzene at the aromatic ring for tertiary carbon 84.9 kcal / mol for cumene, 85.9 kcal / mol for indane with secondary carbon and 85.8 kcal / mol for ethylbenzene (Acc. Chem. Res. 2003, 36, 255. J. Phys Chem. A 2004, 108, 936.).

  The present inventors have investigated using a support of platinum sub-nanoparticles using a phenylazomethine dendrimer as a template as a catalyst for the oxidation reaction of hydrocarbons, and recently the binding energy is small and the reactivity among hydrocarbons is low. An oxygen oxidation reaction using indane having a secondary carbon in the benzene ring, which is considered to be relatively high, as a substrate is reported (Examples of Non-Patent Document 1 and Patent Document 4). However, toluene having a primary carbon in the benzene ring has a binding energy of 89.7 kcal / mol, and it is between the aliphatic hydrocarbon and an aromatic hydrocarbon having a secondary or tertiary carbon in the benzene ring. It has relatively high binding energy, and the oxidation reaction using subnanoparticles as a catalyst has not been studied yet.

  The oxidation reaction is a basic and fundamental reaction operation in the chemical fields such as resource chemistry, fuel chemistry, organic synthetic chemistry and environmental chemistry. It has been attempted to use various catalysts in both gas phase reaction and liquid phase reaction for this oxidation reaction, and various metal catalysts have been put to practical use. However, when catalytic oxidation reactions so far use air or oxygen as an oxidant, high temperature conditions are required, or liquid phase reactions require large amounts of environmental load, such as the use of organic solvents and multi-step reactions. And the catalytic reaction efficiency is not always good.

  Production of benzaldehyde by chlorine oxidation is known as an industrial oxidation method of toluene, but the environmental load is large and a by-product acid is produced in a multistep reaction. On the other hand, a method of producing benzaldehyde from toluene by air oxidation reaction is known. This method is a one-step reaction with low environmental impact and only water as a by-product. However, further improvement is desired in consideration of product selectivity with high industrial utility, catalyst turnover frequency (TOF), and improvement of conversion rate in a short time under mild conditions. There is. For example, benzoic acid and the like have a large industrial demand compared with ester compounds such as benzyl benzoate, and from that viewpoint, it is desired that the yield ratio of benzoic acid and the like be high.

  Under such circumstances, studies using finely divided heterogeneous catalysts such as nanoparticles as catalysts for oxygen oxidation of toluene have also been reported (Non-Patent Documents 2 to 4).

  Hutchings et al. Used benzal, benzyl alcohol, benzoic acid by reacting toluene in an oxygen atmosphere for 48 hours using a catalyst in which palladium and gold alloyed nanoparticles (̃5 nm) are supported on carbon by sol immobilization. It is reported that a mixture of benzyl benzoate was obtained, and the catalyst rotation frequency was 50 to 69 (Non-patent Document 2). However, industrially useful benzaldehyde, benzyl alcohol and benzoic acid are only 5% of the total, and almost all the esterification reaction proceeds and the product is benzyl benzoate.

Zhong et al. Selected 37.5% selectivity of benzaldehyde by reacting at 180 ° C. for 1 hour using a catalyst in which manganese oxide (MnO _x ), which is an oxide of group 7 element, is supported on mesoporous silica SBA-15. The catalyst rotation frequency is about 500 (non-patent document 3).

Jiang et al. Catalyzed the oxidation of toluene at 160 ° C. for 48 hours by using Au / γ-MnO ₂ supported on γ-MnO ₂ with 10 nm gold nanoparticles as a catalyst, and benzaldehyde was obtained with a selectivity of 55 to 60%. Although it has been reported that the proportion of benzyl benzoate which has advanced to the esterification reaction is also large, the TOF is about 50 to 60 (Non-patent Document 4).

Yamamoto, K. et al. Angew. Chem. Int. Ed., 2015, 54, 9810. Hutchings, G. J. et al. Science, 2011, 331, 195. Zhong, W. et al. Chemical Engineering Journal, 2015, 280, 737-747. Jiang, F. et al. Chinese Journal of Catalyst, 2013, 34, 1683-1689.

JP, 2010-18610, A JP, 2013-159588, A International Publication No. 2004/9076531 Unexamined-Japanese-Patent No. 2017-087151

  However, there has been a demand for a novel technology that can generally improve the industrially useful product selectivity, the catalyst rotation frequency, and the point of obtaining the desired product in a high yield in a short time under mild conditions. .

  The present invention has been made in view of the above circumstances, and is industrially useful in an oxidation reaction based on an aromatic hydrocarbon in which a methyl group of primary carbon is bonded to a benzene ring such as toluene. Provided is a method and a catalyst for producing an aromatic hydrocarbon oxide capable of enhancing high product selectivity, increasing catalyst turnover frequency, and capable of improving conversion in a short time under mild conditions. The problem is that.

  In order to solve the above-mentioned subject, the manufacturing method of the oxide of the aromatic hydrocarbon of the present invention is a following formula (I):

(Wherein, at least one of R is a primary carbon methyl group, and n Rs are each independently the methyl group or a phenyl group. N is an integer of 1 to 6.) Using the aromatic hydrocarbon having the methyl group as a substituent as a substrate, a single-element cluster of groups 8 to 11 having an element number of 4 to 60 is supported on a support under an oxygen atmosphere. A product comprising an oxide in which the methyl group is converted to a carboxy group by an oxidation reaction in the presence of a catalyst, an oxide converted to an aldehyde group, and an oxide converted to a hydroxymethyl group. It is characterized by getting

  In the method of producing an oxide of an aromatic hydrocarbon, it is preferable that the aromatic hydrocarbon is toluene and the oxide of the main component is benzoic acid, benzaldehyde and benzyl alcohol.

  In the method of producing an oxide of an aromatic hydrocarbon, the single element cluster is preferably a noble metal or a cluster of copper.

  In the method for producing an aromatic hydrocarbon oxide, preferably, the single element cluster is a reduced product of a dendrimer in which the metal salt of the single element is accumulated.

  In the method for producing an aromatic hydrocarbon oxide, the oxidation reaction is preferably performed at a temperature of 90 to 180 ° C. and an oxygen pressure of 0.1 MPa or more.

  The catalyst of the present invention has the following formula (I):

(Wherein, at least one of R is a primary carbon methyl group, and n Rs are each independently the methyl group or a phenyl group. N is an integer of 1 to 6.) An oxide in which the methyl group is converted to a carboxy group, an oxidation in which the methyl group is converted to an aldehyde group by performing an oxidation reaction in an oxygen atmosphere using an aromatic hydrocarbon having the methyl group as a substituent as a substrate And a catalyst for obtaining a product containing an oxide converted to a hydroxymethyl group as a main component, the single-element cluster of groups 8 to 11 having 4 to 60 elements It is supported by a carrier.

  According to the present invention, it is possible to increase the selectivity of a product having high industrial utility in an oxidation reaction based on an aromatic hydrocarbon in which a primary carbon methyl group is bonded to a benzene ring such as toluene, and a catalyst The frequency of rotation can be increased, and the conversion can be improved in a short time under mild conditions.

It is a graph which shows the result of having changed the number of platinum elements of the cluster in a catalyst to 10-60, carried out the oxygen oxidation reaction of toluene, and measured the kind and conversion ratio of a product, and catalyst rotation frequency. Using a support of platinum element number 12 cluster (Pt ₁₂ ) and a platinum element number 28 cluster (Pt ₂₈ ), the amount of platinum carried on ketjen black is changed to carry out an oxygen oxidation reaction of toluene It is a graph which shows the result of having measured the kind of product, conversion rate, and catalyst rotation frequency. The oxygen oxidation reaction of toluene is carried out by using a support of platinum element number 19 cluster (Pt ₁₉ ) and a platinum element number 13 cluster (Pt ₁₃ ), and the oxygen oxidation reaction of toluene is carried out to select the type of product and conversion It is a graph which shows the result of having measured the rate and catalyst rotation frequency. Using a support of platinum element number 19 clusters (Pt ₁₉ ), the reaction temperature is changed from 130 ° C. to 180 ° C. every 10 ° C. to carry out an oxygen oxidation reaction of toluene, the type and conversion of products and catalyst rotation It is a graph which shows the result of having measured frequency. Using a support of platinum element number 13 clusters (Pt ₁₃ ), the reaction temperature is changed from 130 ° C. to 180 ° C. every 10 ° C. to carry out an oxygen oxidation reaction of toluene, and the type and conversion of products and catalyst rotation It is a graph which shows the result of having measured frequency. Using a support of a platinum ₁₉ cluster (Pt ₁₉ ) and a platinum 13 cluster (Pt ₁₃ ), the oxygen oxidation reaction of toluene is carried out under the conditions of a reaction temperature of 160 ° C. and an oxygen pressure of 1 MPa. It is a graph which shows the result of having measured the time-dependent change of the conversion ratio and catalyst rotation frequency in reaction time 5-40 hours. Oxygen oxidation reaction of toluene is carried out using various single metal species in the metal cluster of the catalyst (metal element number 28: in addition to Pt (platinum), Au (gold), Ru (ruthenium), Rh (rhodium) as noble metals It is a graph which shows the result of having measured Pd, palladium (palladium), copper (Cu) as a base metal, the kind of product, conversion rate, and catalyst rotation frequency. Oxygen oxidation reaction of toluene was carried out using various single metal species in metal clusters of catalyst (metal element number 60: in addition to Pt (platinum), Au (gold) as noble metal, copper (Cu) as base metal) formed It is a graph which shows the result of having measured the kind of substance, conversion rate, and catalyst rotation frequency.

  Hereinafter, the present invention will be described in detail.

  In the catalyst of the present invention, single element clusters of groups 8 to 11 each having an element number of 4 to 60 are supported on a support.

This single element cluster is a sub-nanoparticle consisting of only one type of element. Conventionally, as platinum nanoparticles synthesized from a platinum compound by a reduction method under conditions such as simple concentration control and addition of a carrier, those having a particle size of 2 to 5 nm and 1000 or more in number of platinum elements are known. There is. On the other hand, single-element clusters of sub-nanoparticles used in the present invention have a particle size of, for example, 0.8 to 1.8 nm, particularly 1.2 nm or less. Platinum sub-nanoparticles (Pt ₁₂ , Pt ₂₈ and Pt ₆₀ ) of ₁₂ , ₂₈ and ₆₀ elements precisely synthesized using phenylazomethine dendrimer as a template have particle sizes of 0.9, 1.0, and 1. each having a small size distribution. It has been confirmed to be a 2 nm cluster. Although a polyhedral atomic group formed by direct bonding of some or all of the atoms is generally referred to as a cluster, in this sense, this sub-nanoparticle is a cluster.

  Considering that the catalyst rotation frequency can be increased and the conversion rate can be improved in a short time under mild conditions etc., the number of elements of a single element cluster is 10 to 60, among which the number of elements is 19 15 to 25 centered on are preferred ranges.

  Iron, ruthenium, an osmium etc. are mentioned as an 8th group element among the constituting elements of a single element cluster. Examples of the group 9 element include cobalt, rhodium, iridium and the like. Examples of the group 10 element include nickel, palladium, platinum and the like. Examples of the group 11 element include copper, silver, gold and the like.

  Among these, preferred single element clusters include noble metal or copper clusters.

  Here, the noble metals are gold, silver, platinum, palladium, rhodium, iridium, ruthenium and osmium. In view of industrial use and the like, preferred noble metals include gold, silver, platinum, palladium, rhodium, iridium and ruthenium. The oxidation reaction involves the formation of reactive oxygen species bound to the catalytic metal, the formation of radical species of the substrate, and the radical reaction, so the oxygen affinity of the metal is important, but the metal with high affinity is an oxide Stabilization reduces reactivity. The noble metals tend to have low affinity, and are considered to be difficult to adsorb oxygen and to be highly reactive. Noble metals carry out dissociative adsorption of oxygen even at room temperature to form highly oxidative atomic oxygen. However, although the oxidation reaction of an organic substance at room temperature generally using a noble metal as a catalyst tends to be inactivated without being sustained, the catalyst of the present invention is characterized by a high catalyst turnover frequency.

  In industrial production, mild reaction conditions are required at temperature and pressure. Until now, it has been recognized that catalyst design is difficult because the base metal element forms a stable oxide with high oxygen affinity. Recently, research on catalyst development containing inexpensive base metal elements from the viewpoint of elemental strategy has attracted attention, but in the present invention, copper clusters of base metal elements increase the selectivity of products having high industrial utility, It is preferable in that the catalyst rotation frequency can be increased, and the conversion can be improved in a short time under mild conditions.

  In the catalyst of the present invention, by supporting single element clusters on a support, it is possible to suppress aggregation of sub-nano metal particles and the like, and to effectively suppress a decrease in catalytic activity.

  The shape of the carrier on which the single element cluster is supported is not particularly limited, and may be various types such as granular, fibrous, granular, film, plate and the like. Granules (powdery) are preferred in view of the large surface area per unit weight and the suitability of the catalyst.

  As the carrier, carbon materials, for example, carbon black (ketjen black, oil furnace black, gas black, acetylene black, lamp black, thermal black, channel black, etc.), amorphous carbon such as activated carbon and carbon fiber (microcrystal) Carbon, fullerene, nano-carbon such as nanotube, graphene, graphene oxide, etc., three-dimensional crystal such as graphite, etc. may be mentioned. These carbon materials may be porous materials, and can support single element clusters on the pore surface.

  Besides, inorganic materials can be used as a carrier. Examples of the inorganic material include silica gel, alumina, titania, magnesia, zirconia, iron oxide, copper oxide, glass, silica sand, talc, mica, clay, wollastonite and the like.

Ketjen black (KB), graphitized mesoporous carbon (GMC), graphene oxide (GO), aluminum oxide as a preferable carrier according to the present invention from the viewpoint of the internal area, affinity, versatility, stability, and durability of the carrier (Al ₂ O ₃ ) and the like.

  The carrier is supported by, for example, using a solution in which a dendrimer containing a single element cluster is dissolved in an appropriate solvent such as an organic solvent, and contacting with the carrier by mixing with a carrier dispersion, impregnation, coating, dropping, etc. It can be done by drying. Pulverization may be performed as necessary.

  The amount of the single-element cluster supported on the carrier is not particularly limited. However, considering the increase in the supported amount to improve the catalytic activity, the difficulty in causing aggregation of the single-element cluster, etc. 1 Wt% or more is preferable, 0.2 Wt% or more is more preferable, 0.3 Wt% or more is more preferable, and 0.4 Wt% or more is particularly preferable. The upper limit is not particularly limited, but in view of suppressing a decrease in the catalyst rotation frequency, 3 Wt% or less is preferable, 2 Wt% or less is more preferable, and 1.5 Wt% or less is more preferable.

  In a preferred example of the catalyst of the present invention, the single element cluster is a reduced product of a dendrimer in which the metal salt of the single element is accumulated.

  A dendrimer is a dendritic polymer having a regularly branched structure from the center, and is composed of a core molecule serving as a core and a dendron serving as a side chain moiety. Also, the number of branches of the dendron part is also called a generation. The part branched one step from the central molecule of the dendrimer is called the first generation, and the part branched two steps is called the second generation. In general, a dendrimer is a polymer that is regularly and completely tree-like branched from the core, is sparse near the center and has a dense spherical structure near the surface, and the number of generations increases as branching is repeated from the center . Hyperbranched polymers, on the other hand, are polymers with incomplete dendritic branching, unlike dendrimers with a perfect dendritic structure. In the present invention, the dendrimer may be a hyperbranched polymer having such a partially branched unit defect.

  The dendrimer can be produced by the divergent method, the convergent method or the like. The divergent method is a method in which a molecule having a plurality of functional groups is used as a core, and a branch is extended outward from the center. The convergence method is a method in which a branch is extended from the outside to the inside and is finally adhered to the core to form a spherical polymer, and the synthesis of dendron is promoted from the part to be the outer shell of dendrimer toward the inside. Finally, attach some dendrons to the core.

  Dendrimers have different sites of environment that interact with metal salts. Here, "a different site of environment" of the dendrimer means a site at which the metal salt in the dendrimer can be accumulated and which has different interaction with the metal salt. The site includes a complexing site with a metal salt, an ionic binding site, and a covalent binding site. The “complex formation site” means a site that forms a complex with a metal salt in a dendrimer, and is a part to be a Schiff base. In one-direction electron density gradient type dendrimers, the strength of interaction such as complexing strength changes stepwise so as to become weaker gradually from the inner layer to the outer layer, and forms different sites in the environment, but, for example, When a dendrimer having an electron-donating ligand in the outer layer has a strong coordination environment only in the outermost layer, the interaction in the inner layer is higher than that in the outermost layer, so that the site with the strongest interaction is the outermost layer. Together with the weak sites, they form different sites in the environment.

  Different parts of the above environment may be included in the core itself. Therefore, in addition to the said site | part of the 1st generation, a core shall also be included in the inner layer of a dendrimer. In one-direction electron density gradient type dendrimers, a basic gradient is generated from the core to the end, so the complex formation constant of the core and the first generation complex formation site closest to it is the highest, and it is stepwise toward the outside The complexation constant decreases. The difference in the complexation constant becomes the driving force, and the metal salt is gradually accumulated from the first generation to the second generation to the third generation, which are close to the center. The number of layers filled is 4, 12, 28 and 60 when the number of core branches is four, and 3, 9, 21 and 45 when the number of core branches is three, and the number of core branches is In the case of 2, it becomes 2, 6, 14, 30. In a pyridyltriphenylmethane core dendrimer in which one coordination site is added to the core, it becomes 1, 1, 3, 2, 6. In this case, complexation is first performed at the pyridine site of the core and then stepwise complexation from the inner layer to the outer layer. At that time, in each layer, it is thought that the complexation site (imine site) of the dendron first bound to the pyridine moiety of the pyridyltriphenylmethane core is formed, and then the complexation site is formed with other complexation sites of each layer.

  In the present invention, the dendrimer preferably contains an electron donating bond or atom as a complexing site at the branch point of the dendritic structure. For example, a dendrimer containing a nitrogen atom or an oxygen atom having a lone electron pair to be an electron donor can be mentioned. As a nitrogen atom which a metal salt can coordinate, the nitrogen atom in an azo methine bond (-CH = N-) etc. are mentioned. In the present invention, in the dendrimer, it is preferable that the complexing site thus contains an imine site.

  Examples of the dendrimer used in the present invention include phenylazomethine dendrimers, polyalkylenimine dendrimers such as polyamidoamine dendrimers, polypropylenimine dendrimers and the like, polyarylalkylether dendrimers such as polybenzyl ether dendrimers, and the like.

  Among these, phenylazomethine dendrimers are preferred. Phenylazomethine dendrimers are characterized by a very rigid structure because they have a rigid structure by π conjugation, and a sufficiently wide space is secured inside the molecule, and there are many coordination sites that form complexes with metal salts. Therefore, it is suitable for precise accumulation of many metal salts from the inner layer to the outer layer at the complexation site of each step.

  As a phenyl azo methine dendrimer, the compound represented by following formula (1) is mentioned, for example.

  A in the above formula (1) is a core molecular group to be the core of the phenyl azomethine dendrimer, and the phenyl azomethine dendrimer molecule is represented by B in the formula (1) toward the outside centering on this core molecular group. Grow a chain of units to be As a result, the phenylazomethine dendrimer molecule after growth has a structure in which the B is radially grown with the A at the center. The number of times B is linked is called "generation", and the generation adjacent to the core molecular group A is the first generation, and the number of generations increases outward. A in the above equation (1) is the following equation

R ² is a monocyclic or polycyclic aromatic group, heteroaromatic group, porphyrin group, phthalocyanine group, cyclam group or the like, and these may have a substituent.

  B in the above formula (1) is a formula which forms one azomethine bond to the above A

R ³ represents an aromatic group which may have the same or different substituents. This B constitutes the generation of phenylazomethine dendrimers, and B directly bonded to the core molecular group A becomes the first generation.

  R in the above general formula (1) forms an azomethine bond in the above B as a terminal group.

And R ⁴ represents an aromatic group which may have the same or different substituents. R ¹ will be located at the end of the radially extended structure of the phenylazomethine dendrimer molecule.

In the above formula (1), q represents the number of generations of the phenylazomethine dendrimer through the structure of B, p represents the number of terminal groups R ¹ of the phenylazomethine dendrimer, and p = 2 ^q r .

Each of R ² , R ³ and R ^{4 which} is an aromatic group which may have a substituent may be independently a phenyl group or a structure similar to that of a phenyl group as its backbone structure, for example, a phenyl group or biphenyl Examples include various groups such as groups, biphenyl alkylene groups, biphenyl oxy groups, biphenyl carbonyl groups, and phenyl alkyl groups. These skeletons have, as a substituent, a halogen atom such as chlorine atom, bromine atom or fluorine atom, an alkyl group such as methyl group or ethyl group, a haloalkyl group such as chloromethyl group or trifluoromethyl group, a methoxy group or an ethoxy group And various substituents such as an alkoxyalkyl group such as methoxyethyl group, an alkyl alkyl group, an alkylthio group, a carbonyl group, a cyano group, an amino group and a nitro group. The skeleton may optionally have one or more of these substituents.

Although it does not specifically limit in the core part represented by said Formula R < ² > (-N =) _r , For example, the integer of 1-4 is mentioned. Moreover, q in the said Formula (1) is although it does not specifically limit, It is preferable that it is 2-6.

  The phenylazomethine dendrimer represented by the above formula (1) is a relatively large molecule as a monomolecular compound (for example, in the case of a 4-generation (q = 3) phenylazomethine dendrimer, the diameter is about 2 nm). In the molecule, a plurality of nitrogen atoms to which metal atoms can be coordinated are provided at predetermined intervals. Therefore, in the phenylazomethine dendrimer, a plurality of metal elements can be regularly arranged one by one in a relatively large molecular size as a monomolecular compound.

  The size of the phenylazomethine dendrimer can be adjusted by appropriately selecting the number of generations, the size of the aromatic group bonded to the terminal, and the size of the substituent that the aromatic group bonded to the terminal has. By adjusting the size of the phenylazomethine dendrimer based on its structure, the size of the metal salt aggregate of the dendrimer formed using the phenylazomethine dendrimer can be adjusted.

  In producing a metal salt assembly of dendrimer, as a first step, a solution containing the dendrimer is prepared. The solvent for dissolving the dendrimer and the metal salt aggregate thereof is not particularly limited as long as it can dissolve these. For example, chlorine-containing organic solvents such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1-dichloroethane and carbon tetrachloride, aromatic organic solvents such as benzene, toluene, xylene, chlorobenzene, anisole and acetophenone, cyclohexanone, Organic solvents such as tetrahydrofuran, limonene, propylene glycol monoethyl ether acetate, acetonitrile and the like can be mentioned. These may be used in combination of 2 or more types.

  The concentration of the dendrimer in the solution before mixing the metal salt is not particularly limited, but is preferably 0.001 to 100 μmol / L, and more preferably 0.01 to 10 μmol / L.

  As a next step, the metal salt is mixed with the solution to obtain a metal salt assembly of dendrimer in which the metal salt is accumulated. The metal elements in the metal salt to be accumulated in the dendrimer are those described above as metal species of single element clusters. The counter anion or ligand in the metal salt is not particularly limited, and examples thereof include halogen ions such as chloride ion, bromide ion and iodide ion, trifluoromethanesulfonic acid, acetic acid, acetylacetone, acetonitrile, salen, tetrafluoro A borate ion etc. are mentioned.

  The method for mixing the metal salt with the dendrimer solution is not particularly limited, and examples include dropping of the metal salt solution into the dendrimer solution.

  When the dendrimer and the metal salt are mixed, the metal element is coordinated to the complexing site of the dendrimer and is incorporated inside the dendrimer. In the unidirectional electron density gradient type dendrimer, at this time, the metal element is preferentially coordinated to the complexing site on the central side of the dendrimer, and thus the complexation existing outside from the complexing site existing on the central side Coordinate in order of site. That is, the metal salt coordinates in a generation order from the core of the dendrimer or the complex formation site of the first generation to the outside. Therefore, the metal element can be disposed at a desired position of the dendrimer by controlling the molar ratio of the dendrimer and the metal salt.

  The metal salt assembly of the dendrimer can be reduced to produce sub-nanoparticles of the metal element.

  The reduction of the metal salt aggregate of the dendrimer can be carried out in solution, for example, using a reducing agent which has a reducing action on the metal salt and can be reduced to a zero-valent state. As such a reducing agent, for example, sodium borohydride, sodium cyanoborohydride, hydrogen, hydrazines, lithium aluminum hydride, diisobutylaluminum hydride, lithium borohydride, tetra n-butylammonium borohydride, Methyl ammonium borohydride, lithium triethylborohydride, borane complexes, sodium triacetoxyborohydride, zinc borohydride, lithium tributylborohydride, potassium tributylborohydride, Schwartz's reagent, Stryker's reagent, tributyltin hydride, hydrogenation Sodium, lithium hydride, calcium hydride, benzophenone ketyl radicals, metal naphthalenides, hydrogen peroxide and the like can be mentioned.

  By reducing the metal salt aggregate of the dendrimer in this way, sub-nano metal particles of a size corresponding to the number of metal salts collected can be prepared as included in the dendrimer.

  Such sub-nano metal particles are supported on a support as described above to obtain the catalyst of the present invention.

  The substrate used in the method for producing an oxide of an aromatic hydrocarbon of the present invention is represented by the above formula (I).

  In formula (I), at least one of R is a primary carbon methyl group. According to the catalyst of the present invention, by oxidizing the methyl group bonded to the benzene ring, an oxide in which the methyl group is converted into a carboxy group, an oxide converted into an aldehyde group, and a hydroxymethyl group are converted It is characterized in that a product based on the above oxide is obtained.

  Each of n R's is independently a methyl group or a phenyl group.

  Among them, 1 to 3 methyl groups are preferable, 1 to 2 methyl groups are more preferable, and 1 is more preferable.

  n is an integer of 1 to 6; Among them, n is preferably an integer of 1 to 3, and more preferably an integer of 1 to 2.

  The aromatic hydrocarbon can be used alone or in combination of two or more as a substrate. As an aromatic hydrocarbon, toluene, O-xylene, m-xylene, p-xylene etc. are mentioned, for example. Among them, preferred is toluene, in consideration of industrial utility and the like.

In the method of the present invention, the oxidation reaction is carried out in the presence of the catalyst of the present invention in an oxygen atmosphere using an aromatic hydrocarbon as a substrate. The amount of the catalyst of the present invention to be used is not particularly limited, but it is 1.0 × 10 ^{−3 to} 1.0 × 10 ⁻² mole percent as mole percent of single-element cluster with respect to substrate (single-element cluster / substrate) Is preferable, and 1.2 × 10 ^{−3 to} 5.6 × 10 ⁻³ mol% is more preferable.

  The oxidation reaction can be carried out by placing the catalyst of the present invention and an aromatic hydrocarbon in a reaction vessel and replacing the inside of the vessel with oxygen. The reaction vessel is not particularly limited as long as it can ensure pressure resistance, hermeticity, safety, etc. and can heat the inside of the vessel, and the scale thereof should be appropriate according to the purpose of an industrial process or the like. Can.

  The oxidation reaction is carried out mainly in the state where the substrate aromatic hydrocarbon is in the liquid phase. The oxidation reaction can be carried out with only the substrate aromatic hydrocarbon without using a solvent. Although a solvent or the like is basically not used, the use of a solvent or an additive is not hindered as long as the effect of the present invention is not impaired.

  As for the conditions of the oxidation reaction, in consideration of the catalyst rotation frequency and the conversion rate, the oxygen pressure is preferably 0.1 MPa or more, and can be performed, for example, in the range of 0.1 to 10 MPa. The upper limit of the oxygen pressure is not particularly limited in terms of reactivity.

  The reaction temperature is not particularly limited, but is preferably 90 to 180 ° C. in consideration of the reaction under mild conditions, more preferably 150 to 180 ° C. in consideration of the catalyst rotation frequency and the conversion, and still more preferably 160 to 180 ° C. When the temperature is raised to 190 ° C. or higher, auto-oxidation is likely to occur, which is not desirable as the reaction condition in that respect.

  The reaction time is not particularly limited, but it is preferably 5 to 40 hours, more preferably 5 to 10 hours, in consideration of the progress of the reaction and the reaction in a short time. When the catalyst of the present invention is used, the reaction proceeds even in such a short time.

  An oxide in which the methyl group in the aromatic hydrocarbon of the substrate is converted to a carboxy group, an oxide converted to an aldehyde group, and an oxidation converted to a hydroxymethyl group by performing an oxidation reaction under the above conditions An object-based product is obtained. When the substrate is toluene, the products of this main component are benzoic acid, benzaldehyde and benzyl alcohol.

  Here, in the present invention, the “main component” means, among the products, an oxide in which the methyl group is converted to a carboxy group, an oxide converted to an aldehyde group, and an oxide converted to a hydroxymethyl group. In any case, it is more than other products such as, for example, an ester obtained by condensation of an oxide in which the methyl group is converted to a carboxy group and an oxide in which the methyl group is converted to a hydroxymethyl group, such as benzyl benzoate. Means

  In one embodiment, an oxide in which the methyl group is converted to a carboxy group, an oxide converted to an aldehyde group, and an oxide converted to a hydroxymethyl group account for at least 90 mol%, at least 95 mol of the product. % Or more, 98 mol% or more, or 99 mol% or more.

  In one aspect, when the methyl group is based on one aromatic hydrocarbon, an oxide in which the methyl group is converted into a carboxy group, an oxide converted into an aldehyde group, and a hydroxymethyl group are converted Among the oxides, the production amount of the oxide in which the methyl group is converted to a carboxy group is the largest. In a typical example, the amount of production is in the order of the oxide in which the methyl group is converted to a carboxy group> the oxide converted to an aldehyde group> the oxide converted to a hydroxymethyl group.

  In the catalytic reaction, the selectivity of the product obtained is important as well as the high activity value and conversion as indicated by the catalyst turnover frequency (TOF). As a product from toluene, a broad reactive substance capable of various developments as an industrial material is useful, and benzoic acid, benzaldehyde and benzyl alcohol are useful substances.

  Benzoic acid is increased in the oxidation reaction of benzaldehyde. Since it is a type of acid-type preservative and has antibacterial and bacteriostatic effects, water-soluble sodium salts and the like are added as preservatives for soft drinks and the like. It has antiseptic properties and is used as a preservative in soy sauce and soft drinks (including carbonated drinks) and for the treatment of cystitis and bronchitis. Industrially it is used as a mordant and academically it is used to standardize alkaline standard solutions. As the main industrial processes to date, it is known to chlorinate toluene to benzotrichloride and then hydrolyze or pass phthalic anhydride over steam heated catalyst. Recently, it is also produced by air oxidation of toluene. In the laboratory, it is obtained by oxidizing toluene with nitric acid or potassium dichromate.

  Benzaldehyde is increased by the oxidation reaction of toluene or the oxidation reaction of benzyl alcohol. As a main industrial production method to date, the method of producing by hydrolysis of benzal chloride is known. Besides being used as an inexpensive perfume, it has been recognized to have an anti-inflammatory effect.

  Benzyl alcohol is increased by the oxidation reaction of toluene. It is obtained by hydrogenating benzaldehyde in the presence of a catalyst or reducing it with a reducing agent. Excellent solvent, low toxicity, low vapor pressure. Soluble in alcohol and ether, oxidized in air to benzoic acid.

  In the oxygen oxidation reaction of toluene, benzyl benzoate is increased by the condensation reaction of benzaldehyde and benzoic acid, but according to the method using the catalyst of the present invention, benzyl benzoate is hardly generated.

  Each of the oxides of aromatic hydrocarbons obtained by the method of the present invention may be separated and refined into single components by a conventional method and then used according to the purpose.

According to the method and catalyst for producing an oxide of an aromatic hydrocarbon of the present invention, it is possible to industrially carry out an oxidation reaction based on an aromatic hydrocarbon in which a methyl group of primary carbon is bonded to a benzene ring such as toluene. The selectivity of highly useful products can be increased, the catalyst turnover frequency can be increased, and the conversion can be improved in a short time under mild conditions. The catalyst turnover frequency is generally regarded as an indicator of catalyst activity ability, and the conversion rate is important from the viewpoint of implementation considering the cost of metal. According to the method and catalyst for producing an oxide of an aromatic hydrocarbon of the present invention, the catalyst rotation frequency is, for example, 200 atom ^-1 h ^-1 or more, 300 atom ^-1 h ^-1 or more, 400 atom ^-1 h ^-1 or more, further it is 600~1000atom ^-1 h ^-1, the conversion rate of 2% or more as an example, even at 3-6%.

  Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

In FIG. 1 to FIG. 8, the conversion rate (Conversion) of the toluene oxidation reaction is shown by “Product” (product amount: μmol) and “Yield” (yield:%) on the graph vertical axis. The catalyst rotation frequency is indicated by “TOF” (Turnover Frequency: atom ⁻¹ h ⁻¹ ) on the graph vertical axis.
1. Preparation of Catalyst A solution (3. 3) of a fourth generation phenylazomethine dendrimer (TPM-G4) having tetraphenylmethane as its core dissolved in a mixed solvent of chloroform and acetonitrile (chloroform: acetonitrile = 1: 1) under a glove box atmosphere. 10 to 60 equivalents of PtCl ₄ solution (solvent: acetonitrile, 3.0 mM) or 28 equivalents of CuCl ₂ , RhCl ₃ , AuCl ₃ , RuCl ₃ , or 0 μM) depending on the number of elements of the target single element cluster. A solution of [Pd (NCMe) ₄ ] (BF ₄ ) ₂ was added to complex the metal salt. However, for accumulation of the metal salt of Pt ₁₉ , accumulation conditions were examined using a fourth generation phenylazomethine dendrimer (PyTPM-G4) having pyridine as a core.

After stirring for 90 minutes, reduction was performed with a methanol solution (ca. 530 mM) to which 60 equivalents of NaBH ₄ of the total number of metal equivalents was added. The reaction solution was mixed with ketjen black (Ketjenblack: KB) dispersed with methanol, and the dendrimer complex was accumulated and supported on KB. The catalyst supported on KB was filtered through a membrane filter, washed with methanol and then vacuum dried.
2. Oxygen oxidation reaction of toluene and catalytic activity evaluation 2-1. Reaction conditions In an autoclave, the prepared catalyst (for platinum, for example, supported amount: 0.47 wt% 10 mg) and toluene (2 mL) were added. Thereafter, the inside of the vessel was purged with oxygen for replacement, and heating reaction was performed at the reaction temperature, oxygen pressure, and reaction time described below. After heating, a portion of the solution is collected, and the obtained toluene oxide is measured by ¹ H NMR and GC-MS spectra, and the conversion and catalyst for each type of product are measured using the observed signal intensity. The rotation frequency was calculated.
2-2. Examination of the number of platinum elements (Figure 1)
The molar ratio of platinum to toluene (Pt / Toluene) 0.0012 mol%, reaction temperature 160 ° C., oxygen pressure 1 MPa, O ₂ atmosphere, reaction time 5 hours, changing the number of platinum elements to 10 to 60 products And the conversion rate from toluene and the catalyst turnover frequency were measured. The results are shown in FIG. The products of the oxidation reaction were mostly benzoic acid, benzaldehyde and benzyl alcohol, and the formation of the ester compound benzyl benzoate was hardly observed. Among the main products benzoic acid, benzaldehyde and benzyl alcohol, benzoic acid is the most abundant, and the amount of production is generally in the order of benzoic acid, benzaldehyde and benzyl alcohol. The catalytic activity tends to be the same as in the case of electrochemical oxygen reduction reaction or in the case of indane oxidation (Non-Patent Document 1), and a platinum element number 19 cluster carrier Pt ₁₉ @ TPM-G4 / KB was used The catalytic activity (yield 6.34%, TOF 1038 atom ⁻¹ h ⁻¹ ) in the case was the highest. The catalyst rotation frequency was generally higher than in the case of using nanoparticles such as non-patent documents 2 and 4 as a catalyst. To TOF is carrier clusters of platinum element number 28,60 in the range of about any 400atom ^-1 h ^-1, even TOF is either the carrier of the platinum element number 19 or less of the cluster 800atom ^-1 h ^-1 It is the above, and the tendency which increases with platinum element number 19 or less was seen.
2-3. Examination of the amount of Pt supported on ketjen black (Fig. 2)
The supported amount of platinum supported on ketjen black was examined using a supported body of a platinum element number 12 (Pt ₁₂ ) and a supported amount of a platinum element number 28 (Pt ₂₈ ). The conditions were a reaction temperature of 160 ° C., an oxygen pressure of 1 MPa, a reaction time of 5 hours, and a supported amount of 0.47 wt%. The results are shown in FIG. Product selectivity did not vary significantly with platinum loading. In both cases of Pt ₁₂ and Pt _28, the amount of reaction product increased due to the increase in the loading amount, and at the loading amount of 0.47 wt%, the increase in the conversion rate and the catalyst rotation frequency became remarkable. When the loading amount was further increased, the conversion gradually increased, and the catalyst turnover frequency tended to gradually decrease.
2-4. Oxygen pressure and dependence on oxygen concentration (Figure 3)
The dependence of the reaction on the oxygen pressure and the oxygen concentration was examined using a support of platinum element number 19 (Pt ₁₉ ) and a platinum element number 13 cluster (Pt ₁₃ ). The conditions were a reaction temperature of 160 ° C., a reaction time of 5 hours, and a loading of 0.47 wt%. The results are shown in FIG. In the figure, the horizontal axis of the graph indicates oxygen pressure (MPa). Product selectivity did not vary significantly with oxygen pressure and oxygen concentration. Pt ₁₃ and indicates one oxygen pressure 0.1~1MPa the same catalytic activity in the case of the _{Pt 19,} was found to proceed sufficiently even under mild reaction conditions 0.1 MPa. Since no catalytic activity is observed in the reaction in air, an oxygen atmosphere is essential in this reaction.
2-5. Influence of reaction temperature (Fig. 4, Fig. 5)
The reaction temperature was varied from 130 ° C. to 180 ° C. at every 10 ° C. using a support of platinum ₁₉ carbon (Pt ₁₉ ) and a support of platinum 13 carbon (Pt ₁₃ ) . The conditions were an oxygen pressure of 1 MPa, a reaction time of 5 hours, and a supported amount of 0.47 wt%. The results are shown in FIG. 4 and FIG. Product selectivity did not vary significantly with reaction temperature. The reaction proceeded efficiently at a reaction temperature of 150 to 180 ° C., and in particular, 160 to 180 ° C. was favorable in terms of the conversion rate and the catalyst rotation frequency. At a reaction temperature of 130 ° C. and 140 ° C., the catalyst activity decreased. When the temperature is raised to 190 ° C. or higher, auto-oxidation tends to occur, which is not desirable as a reaction condition.
2-6. Influence of reaction time (Figure 6)
Using a support of platinum element number 19 cluster (Pt ₁₉ ) and a platinum element number 13 cluster (Pt ₁₃ ), reaction temperature 160 ° C., oxygen pressure 1 MPa, reaction time 5 to 40 hours Change over time was confirmed. The results are shown in FIG. Nearly 100% of the reaction had proceeded with Pt ₁₃ and reaction time 5-10 hours For both _{Pt 19.} The TOF has been decreasing since then, but deviations from the support of clustered platinum nanoparticles, decomposition of platinum sub-nanoparticles, etc. are considered.
2-7. Catalytic activity of toluene with single noble metal and Cu (Figure 7, Figure 8)
In addition to Pt (platinum), investigations were conducted on Au (gold), Ru (ruthenium), Rh (rhodium), Pd (palladium) as a single precious metal, and Cu (copper) as a base metal. The conditions were Pt (platinum), the optimum reaction temperature of 160 ° C., the oxygen pressure of 1 MPa, the reaction time of 5 hours, the supported amount of 0.47 wt%, and the number of metal elements was 28. The results are shown in FIG. In addition, Cu (copper), Pt (platinum), and Au (gold) were examined under the same conditions as the number 60 of metal elements. The results are shown in FIG. The amount of substance is not the same because the loading amount is standardized by weight percentage. Therefore, in the case of light elements (metals) having a small atomic weight, the conversion ratio tends to be high, and the catalyst rotation frequency tends to be low. In addition, in the case of the catalyst rotation frequency, as described in the preceding paragraph, there is a possibility that the catalyst rotation frequency may be lowered due to the deviation from the support of clustered nanoparticles, the decomposition of sub-nanoparticles, and the like. From FIG. 7, although the conversion rate and the catalyst rotation frequency increase or decrease compared to Pt (platinum), the catalytic activity was confirmed for any of the metals. The same tendency was observed in the case of the number 60 of metal elements in FIG. The selectivity of the resulting product did not vary significantly with the metal species and the number of metal elements.

Claims (6)

The following equation (I):
(Wherein, at least one of R is a primary carbon methyl group, and n Rs are each independently the methyl group or a phenyl group. N is an integer of 1 to 6.) Using the aromatic hydrocarbon having the methyl group as a substituent as a substrate, a single-element cluster of groups 8 to 11 having an element number of 4 to 60 is supported on a support under an oxygen atmosphere. A product comprising an oxide in which the methyl group is converted to a carboxy group by an oxidation reaction in the presence of a catalyst, an oxide converted to an aldehyde group, and an oxide converted to a hydroxymethyl group. A process for the production of oxides of aromatic hydrocarbons,   The method for producing an oxide of an aromatic hydrocarbon according to claim 1, wherein the aromatic hydrocarbon is toluene, and the oxide of the main component is benzoic acid, benzaldehyde, and benzyl alcohol.   The method for producing an oxide of an aromatic hydrocarbon according to claim 1 or 2, wherein the single element cluster is a noble metal or a cluster of copper.   The method for producing an oxide of an aromatic hydrocarbon according to any one of claims 1 to 3, wherein the single element cluster is a reduced product of a dendrimer in which the metal salt of the single element is accumulated.   The method for producing an oxide of an aromatic hydrocarbon according to any one of claims 1 to 4, wherein the oxidation reaction is performed at a temperature of 90 to 180 ° C and an oxygen pressure of 0.1 MPa or more. The following equation (I):
(Wherein, at least one of R is a primary carbon methyl group, and n Rs are each independently the methyl group or a phenyl group. N is an integer of 1 to 6.) An oxide in which the methyl group is converted to a carboxy group, an oxidation in which the methyl group is converted to an aldehyde group by performing an oxidation reaction in an oxygen atmosphere using an aromatic hydrocarbon having the methyl group as a substituent as a substrate And a catalyst for obtaining a product containing an oxide converted to a hydroxymethyl group as a main component, the single-element cluster of groups 8 to 11 having 4 to 60 elements Catalyst supported on a carrier.