Process for preparing hydroperoxides

Abstract: Process for preparing hydroperoxides, comprising oxidizing a hydrocarbon of the formula (I) wherein P and Q, may be the same or different from each other, represent hydrogen or an alkyl group, x is an integer of 1 to 3; and Ar is an aromatic hydrocarbon group, with an oxygen-containing gas in the presence of at least one specific secondary amine compound (IV) that can capture radicals. The present invention can be applied to oxidation of hydrocarbons including arylalkylhydrocarbons such as cumene, m-diisopropylbenzene, p-diisopropylbenzene, 1,3,5-triisopropylbenzene, isopropylnaphthalene, diisopropylnaphthalene, isopropylbiphenyl, diisopropylbiphenyl, etc.

Description: TECHNICAL FIELD The present invention relates to a process for preparing hydroperoxides, which comprises oxidizing hydrocarbon by a gas containing oxygen and converting it selectively to corresponding hydroperoxides. TECHNICAL BACKGROUND The process of oxidizing hydrocarbon by a gas containing oxygen in the absence of a catalyst to prepare corresponding hydroperoxides is known as autoxidation technology. However, in this reaction, it is necessary to raise the reaction temperature to increase the'rate of accumulation of hydroperoxides. Nevertheless, when the reaction temperature is raised to increase the rate of accumulation, the reaction product hydroperoxide is thermally decomposed, resulting in a decline in its selectivity. In other words, since there was such relationship between the rate of accumulation and selectivity that as either one goes up, the other goes down, it was difficult to maintain both of them at high levels. Attempts have been made to oxidize hydrocarbon in the state of gas containing oxygen by a catalyst to produce an effect on the rate of accumulation and/or selectivity in producing corresponding hydroperoxides (Japanese Patent Publication SHO 55-50020, for example). The inventors of the present invention firmly believed that there should be a way to achieve high selectivity, while overcoming the relationship between the rate of accumulation and selectivity and maintaining a commercially viable rate of accumulation at the same time. With this belief, the inventors continued research assiduously. As a result, the inventors successfully made an invention to solve the problem. US 2,734,086 relates to improvements in the production aralkyl hydroperoxides, and more particularly to the production of aralkyl hydroperoxides by the oxidation of aromatic compounds containing an alkyl group which is directly attached to the aromatic nucleus by means of a tertiary carbon atom. The reaction is conducted in the presence of cyclic tertiary amines, especially, quinoline, pyridine and their alkyl substitution products. US 3,160,668 concerns the production of aralkyl hydroperoxides, and more specifically of cumene hydroperoxide, by oxidizing a corresponding aralkyl hydrocarbon with an oxygen-containing gas in the presence of a primary amine having a tertiary alkyl group attached to the amino nitrogen. In the course to the invention, inventors found that a oxidation of a hydrocarbon by a gas containing oxygen in the presence of a specific compound is effective for converting it to the corresponding hydroperoxides. Specifically, the present invention provides a method for oxidizing hydrocarbon by a gas containing oxygen thereby to prepare corresponding hydroperoxides at a high selectivity. DISCLOSURE OF THE INVENTION The process for preparing hydroperoxides by the present invention is based on the attainment of a very high selectivity possible by the use of a compound capable of capturing radicals as a specified compound in the process of oxidizing hydrocarbon by a gas containing oxygen. The present invention is characterized by oxidizing hydrocarbon by a gas containing oxygen in the presence of a compound that can capture radicals and converting it selectively to corresponding hydroperoxides. THE BEST EMBODINMENT OF THE INTENTION The starting material hydrocarbon is a compound of the general formula (I): (wherein P and Q stand for hydrogen or the alkyl group, which may be the same or different from each other; x stands for a whole number of 1 to 3; and Ar stands for the aromatic hydrocarbon group of the x value.) In the general formula (I), it is preferable that at least either of P and Q is the alkyl group, especially preferable that both of them are alkyl groups. Especially the methyl group is preferable as the aforementioned alkyl group. Further, a hydrocarbon group having the x value that can be derived from benzene, naphthalene, biphenyl, diphenyl ether, etc., preferable a hydrocarbon group of the x value that is derived from benzene or naphthalene, may be cited as examples of the aromatic hydrocarbon group. Therefore, in the present invention, preferable examples of the arylalkyl hydrocarbon include,but not limited to, diisopropylbenzenes such as cumene, cymene, m-diisopropylbenzene and p-di-isopropyl benzene, triisopropylbenzenes such as 1,3,5-tri-isopropylbenzene, ethylbenzene, sec-butylbenzene, sec-butylethylbenzene, isopropylnaphthalenes, diisopropylnaphthalene such as 2,6-diisopropyl naphthalene, isopropyl diphenyls, diisopropylbiphenyls such as 4,4'-diisopropylbiphenyl, and mixtures of not less than two of these. Cumen is most preferable. The compound of the present invention that can capture radicals refers to a compound having the ability to capture radicals, and it does not matter whether the compound itself possesses such ability or such ability is given to the compound under reaction conditions. In the preparation of the present invention, either those radicals which are stable at room temperature or those compounds which form radicals under reaction conditions may be used. In the reaction of oxidizing hydrocarbon by a gas containing oxygen, various by-products are formed. In the case of the example of the autoxidation of cumene, dimethylphenylcarbinol, acetophenone and dicumylperoxide may be cited as examples of such by-products. It is presumed that there are alkyl radicals such as cumyl radical and cumenehydroperoxy radical, hydroxy radical, etc. present in the process of reaction. It is presumed in the present invention that the compound that can capture radicals acts on these radicals in some respects, such as capturing the radicals inducing the reaction of the formation of such by-products, and consequently the selectivity of the hydroperoxide corresponding to the raw material hydrocarbon is improved. In selecting the compound that can capture radicals in the present invention, it is possible to use the difference in the SOMO (single occupied molecular orbit) energy level (Δε (SOMO)) between the radical of or derived from said compound that can capture radicals, and the radicals to be captured. The SOMO energy level is calculated by the method as described below. It is desirable to select such compound capable of capturing radicals that the difference in the SOMO energy level, Δ ε (SOMO), is normally 0 - 964,9 KJ/moℓ (0 to 10eV), preferably 0 - 386.0 KJ/moℓ (0 to 4eV), more preferably 0 - 96.5 KJ/moℓ (0 to 1eV). For example, it is desirable to select such compound capable of capturing radicals in the present invention that its relationship with the radical (formula I-2 below) corresponding to the hydrocarbon to be oxidized is as follows: Δ ε (SOMO) = | ε a (SOMO) - εb (SOMO)| = 0 - 964.9 KJ/moℓ (0 to 10eV) wherein εa (SOMO) stands for the SOMO energy level of the compound cable of capturing radicals or the radical formed therefrom, and εb (SOMO) stands for the SOMO energy level of the radical corresponding to the hydrocarbon to be oxidized. (wherein P and Q, standing for hydrogen or the alkyl group, may be the same or different from each other; x stands for a whole number of 1 to 3; and Ar stands for the aromatic hydrocarbon group of the x value.) ε (SOMO) Calculation Method: The structural calculation of a radical is made by a semiempirical molecular orbit method (MNDO-PM3 method: MOPAC program) to calculate ε (SOMO). The ε (SOMO) of those which are not a radical is determined by the structural calculation of the corresponding radical. As the aforementioned Δε (SOMO) becomes lower, the hydrocarbon radical is easier to capture. The Δε (SOMO) is normally in the range of 0 - 964.9 KJ/moℓ (0 to 10eV), preferably 0 - 386.0 KJ/moℓ (0 to 4eV), more preferably 0 - 96.5 KJ/moℓ (0 to 1eV). The use of a compound having a proper value of Δ ε (SOMO) has the characteristic that in comparison with the case of adding no such compound, the selectivity goes up over the selectivity of hydroperoxide in other reaction at the same rate of accumulation. Because of this, the use of such compound enables hydrocarbon to be converted at high selectivity and at a high concentration. The compound that can capture radicals is at least one secondary amine compound that can capture radicals selected from (a) the general formula (IV) wherein m is an integer of 0-3, and A, B, X 1 , X 2 , R 1 , R 2 , R 3 , and R 4 each separately represent hydrogen, a cyano group, an isothiocyanic acid group or a substituent comprising an element selected from hydrogen, carbon, oxygen and halogen; and wherein each carbon atom ring member may form a double bond between adjoining atoms, and (b) compounds, wherein two or more structures of formula (IV) are crosslinked through any of the groups selected from X 1 and X 2 . The substituent mentioned in the definition of the general formula (IV) may be hydrogen, hydrocarbon group, heterocyclic compound residue, or an oxygen-containing group, or a ring formed by not less than two of these being connected to each other. Specific examples of the hydrocarbon group include straight-chain or branched alkyl groups having 1 to 30, preferably 1 to 20, carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, neopentyl and n-hexyl; straight-chain or branched alkenyl groups having 2 to 30, preferably 2 to 20, carbon atoms, such as vinyl, aryl and isopropenyl; straight-chain or branched alkinyl group having 2 to 30, preferably 2 to 20 carbon atoms, such as ethynyl and propargyl; cyclic saturated hydrocarbon groups having 3 to 30, preferably 3 to 20, carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and adamantyl; cyclic unsaturated hydrocarbon group having 5 to 30 carbonn atoms such as cyclopentadienyl, indenyl and fruorenyl and aryl groups having 6 to 30, preferably 6 to 20, carbon atoms, such as phenyl, benzyl, naphtyl, biphenyl, terphenyl, phenanthryl and anthracenyl. Hydrogen atom in the aforementioned hydrocarbon group may be substituted by halogen atom. Examples of such hydrocarbon group include halogenated hydrocarbon groups having 1 to 30, preferably 1 to 20, carbon atoms, such as trifluoromethyl, pentafluorophenyl and chlorophenyl. Furthermore, the aforementioned hydrocarbon group may be substituted by other hydrocarbon groups mentioned above. Examples of such hydrocarbon group include aryl-group-substituted alkyl groups such as benzyl and cumyl; alkyl-group-substituted aryl groups such as tolyl, isopropylphenyl, t-butylphenyl, dimethylphenyl and di-t-butylphenyl; and substituted aryl groups in which an aryl group is substituted by alkoxy group, aryl group or aryloxy group. Moreover, the aforementioned hydrocarbon groups may contain the heterocyclic compound residue or oxygen-containing group mentioned below. Out of them, especially preferable hydrocarbon groups are particularly straight-chain or branched alkyl groups having 1 to 30, preferably 1 to 20, carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, neopentyl and n-hexyl; aryl groups having 6 to 30, preferably 6 to 20, carbon atoms, such as phenyl, naphtyl, biphenyl, terphenyl, phenanthryl and anthracenyl; and substituted aryl groups having 1 to 5 of substituents such as alkyl group or alkoxy group having 1 to 30, preferably 1 to 20 carbon atoms, and aryl group or aryloxy group having 6 to 30, preferably 6 to 20 carbon atoms. Examples of the heterocyclic compound residue include residues of oxygen-containing compounds such as furan and pyrane; and groups having these heterocyclic compound residues further substituted by substitutional groups such as the alkyl group and alkoxy group having 1 to 30, preferably 1 to 20 carbon atoms. Examples of the oxygen-containing group include the alkoxy group, aryloxy group, ester group, acyl group, carboxyl group, carbonate group, hydroxy group, peroxy group and carboxylic acid anhydride group. Examples of the alkoxy group, out of these, include the alkoxy group having 1 to 30 carbon atoms, specifically, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy and tert-butoxy. Examples of the aryloxy group include the aryloxy group having 6 to 30 carbon atoms, specifically, phenoxy, 2,6-dimethylphenoxy and 2,4,6-trimethylphenoxy. Examples of the ester group include the ester group having 1 to 30 carbon atoms, specifically, acetyloxy, benzoyloxy, methoxycarbonyl, phenoxycarbonyl and p-chlorophenoxycarbonyl. Examples of the acyl group include the acyl group having 1 to 30 carbon atoms, specifically, the formyl group, acetyl group, benzoyl group, p-chlorobenzoyl group and p-methoxybenzoyl group. Preferable examples of the hydrogen or other substitutional groups of the general formula (IV) are hydrogen, alkyl group, aryl group, halogen, cyano group, isothiocyanic acid group, -COORa (wherein Ra stands for hydrogen, alkyl group and aryl group), hydroxyl group, hydroxyalkyl group, alkoxy group, arylalkoxy group, or oxo group (= O). The examples of the aforementioned secondary amine may incude a compound having a structure in which two or more structures of the general formula (IV) are crosslinked through any of the radicals of X 1 and X 2 . In the general formula (IV), the preferable compounds are that all of R 1 , R 2 , R 3 and R 4 are groups selected from the alkyl group. For example, they include 2,2,6,6-tetraalkyl piperidine, 2,2,6,6-tetraalkyl-4-piperidinol, bis-(2,2,6,6-tetraalkyl piperidyl)-sebacate or 2,2,5,5-tetraalkyl pyrrolidine, or the said compound substituted by the aforementioned group. Specific examples of the secondary amine include, but are not limited to, the following: In this invention, the oxidation of hydrocarbon is conducted in the presence of at least one compound that can capture radicals. Two or more compounds that can capture radicals can be used. Supposing the compound that can capture radicals has captured a radical, the enthalpy (ΔH) to break the bond between the compound and the radical can be determined by calculation by the method as described below. The appropriate range of ΔH depends on the type of the radical to be captured, and the value may be used to select the compound that can capture radicals of the present invention. Satisfactory results can be obtained by selecting as the compound of the present invention that can capture radicals such compound that the value of enthalpy (ΔH) is -30 to 50KJ/moℓ when calculated on the basis of the assumption that the radical to be captured is the radical corresponding to the hydrocarbon to be oxidized (formula I-2). The value of the enthalpy (ΔH) is preferably -25 to 50KJ/moℓ, more preferably -20 to 50KJ/moℓ. Using the compound that can capture those radicals whose ΔH is within such appropriate range produces satisfactory results as intended by the present invention. H (heat of formation) calculation method: H was calculated by conducting structural optimization for the structure showing the smallest amount of energy (most stable structure) by semiempirical molecular orbital method( AM1 method: MOPAC program) after carrying out conformation search by the molecular force field method (CHARMm force field: QUANTA program). The selection of the compound that can capture radicals has the figures within the appropriate range of Δε (SOMO) aforementioned and the value of the enthalpy(ΔH) is most preferable in this invention. Next, given below is an explanation of the reaction conditions of the present invention. The usage of the compound that can capture radicals or the compound that turns into the compound that can capture radicals in the reaction system in the present invention is normally in the range of 0.00001 to 5.0 parts by weight, preferably in the range of 0.0001 to 0.1 parts by weight, per 100 parts by weight of the starting material hydrocarbon. As the oxygen-containing gas as the oxidizing agent, air is normally used, but oxygen or any mixed gas of oxygen and nitrogen may also be used. The reaction may normally be conducted at atmospheric pressure, but it may also be conducted under elevated pressure. The reaction temperature is normally in the range of 40 to 120°C, preferably in the range of 50 to 100°C. Furthermore, this reaction may be conducted in the presence of a basic compound in the state of a solid or an aqueous solution. Examples of the basic compounds include sodium carbonate, sodium hydrogencarbonate, sodium hydroxide, potassium carbonate, potassium hydrogencarbonate, potassium hydroxide, barium oxide and magnesium oxide. The amount of the basic compound used in the reaction is normally 0.0001 to 10.0 parts by weight, preferably 0.001 to 5.0 parts by weight, per 100 parts by weight of the starting material hydrocarbon. The reaction in the present invention may be conducted by either batch or continuous method. In the case of conducting the reaction by the batch method, if the starting material hydrocarbon is a liquid at the reaction temperature, the aforementioned compound that can capture radicals or the aforementioned compound that turns into the compound that can capture radicals in the reaction system is added to the starting material and normally made to undergo oxidation reaction by blowing air into the material with heating and agitation. If required, an inactive organic solvent may be used as the reaction solvent in the reaction. On the other hand, if the starting material arylalkyl hydrocarbon is a solid at the reaction temperature, it is made to be dissolved in an inactive organic solvent to form a solution, and the aforementioned compound that can capture radicals or the aforementioned compound that turns into the compound that can capture radicals in the reaction system may be added to the solution and made to undergo oxidation reaction by blowing air into the material with heating and agitation. Further, in the present invention, a small amount of hydroperoxide which corresponds to the hydrocarbon may be present, as required, as the initiator in the hydrocarbon at the time of the start of the reaction. A catalyst such as a transition metal complex may also be used additionally as required. Such catalyst may be formed as a fixed bed, and the starting material hydrocarbon or its solution and air may be caused to pass through the fixed bed, while being mixed. According to the method of the present invention, the formed hydroperoxide can be easily recovered from the reaction mixture by distillation or any other conventional means after the completion of the reaction and after filtering out the catalyst as required . Examples Given below is a specific description of examples of preparing organic hydroperoxides from arylalkyl hydrocarbon. However, the present invention is not limited in any way by the following examples: Example 1 50 mg of 2,2,6,6-tetramethyl-4-piperidinol were added to a mixture of 126 g of cumene and 54 g of cumenehydroperoxide, and all of them were dissolved. 5.6 g of purified water were added to it, and this mixture was heated under 6 K pressure to 105°C. The cumene was oxidized by continuous reaction at a residence time of 1 hour while blowing air into it at a rate of 400 ml/min with vigorous agitation. The rate of accumulation of cumenehydroperoxide after 4, 5 and 6 hours from the start of the reaction was determined and averaged by iodometry and gas chromatography to be 3.7 wt%/hr. Furthermore, the selectivity of the cumenehydroperoxide which was formed in the reaction was determined and averaged by high performance liquid chromatography to be 92 mol%. Example 2 The reaction was conducted in the same manner as Example 5 except that 36 mg of bis-(2,2,6,6-tetramehyl-4-piperidyl)-sebacate was added in place of 2,2,6,6-tetra-methyl-4-piperidinol. The rate of accumulation of cumenehydroperoxide after 4, 5, and 6 hours from the start of the reaction was determined and averaged by iodometry and gas chromatography to be 3.8 wt%/hr. Furthermore, the selectivity of the cumenehydroperoxide which was formed in the reaction was determined and averaged by high performance liquid chromatography to be 90 mol%. Comparative Example 1 The reaction was conducted in the same manner as Example 1 except that 2, 2, 6, 6-tetramethyl-4-piperidinol was not used. The rate of accumulation of cumenehydroperoxide during 3 hours from the start of the reaction was determined and averaged by iodometry and gas chromatography to be 5.5 wt%/hr. Furthermore, the selectivity of the cumenehydroperoxide which was formed in the reaction was determined and averaged by high performance liquid chromatography to be 86 mol%. Comparative Example 2 The reaction was conducted in the same manner as Comparative Example 1 except that the reaction temperature was set at 100°C. The rate of accumulation of cumenehydroperoxide during 4, 5 and 6 hours from the start of the reaction was determined and averaged by iodometry and gas chromatography to be 3.9 wt%/hr. Furthermore, the selectivity of the cumenehydroperoxide which was formed in the reaction was determined and averaged by high performance liquid chromatography to be 89 mol%.

Claims: Process for preparing hydroperoxides, comprising oxidizing a hydrocarbon of the following formula (I): wherein P and Q, which may be the same or different from each other, represent hydrogen or an alkyl group, x is an integer of 1-3; and Ar is an aromatic hydrocarbon group, with an oxygen-containing gas in the presence of at least one secondary amine compound that can capture radicals selected from (a) the general formula (IV) wherein m is an integer of 0-3, and A, B, X 1 , X 2 , R 1 , R 2 , R 3 , and R 4 each separately represent hydrogen, a cyano group, an isothiocyanic acid group or a substituent comprising an element selected from hydrogen, carbon, oxygen and halogen; and wherein each carbon atom ring member may form a double bond between adjoining atoms, and (b) compounds, wherein two or more structures of formula (IV) are crosslinked through any of the groups selected from X 1 and X 2 . Process of Claim 1, wherein the arylalkyl hydrocarbon of formula (I) is cumene, cymene, m-diisopropylbenzene, p-diisopropylbenzene, 1,3,5-triisopropylbenzene, isopropylnaphthalene, diisopropylnaphthalene, isopropylbiphenyl, diisopropylbiphenyl or a mixture of two or more thereof. Process according to Claim 2, wherein the arylalkyl hydrocarbon is cumene. Process of Claim 1, wherein in the compound of formula (IV) two or more structures of formula (IV) are crosslinked through any of the groups selected from X 1 and X 2 . Process of Claim 1, wherein A and B, X 1 X 2 , R 1 , R 2 , R 3 , and R 4 in formula (IV) each separately represent hydrogen, an alkyl, aryl, halogen, -COOR a (wherein R a represents hydrogen, alkyl or aryl), or a hydroxyl, hydroxyalkyl, alkoxy, arylalkoxy or oxo group (=O). Process of Claim 1, wherein R 1 , R 2 , R 3 and R 4 in formula (IV) represent an alkyl group. Process of Claim 6, wherein the compound of formula (IV) is 2,2,6,6-tetraalkylpiperidine, 2,2,6,6-tetraalkyl-4-piperidinol, bis-(2,2,6,6-tetraalkylpiperidyl)-sebacate or 2,2,5,5-tetraalkylpyrrolidine.

Inventors: FUJITA TERUNORI, HIROKANE NOBUYA, KAMIMURA MAKOTO, KATO KOJI, KURODA HIROSHI, MAKIO HARUYUKI, MATSUI SHIGEKAZU, TAKAI TOSHIHIRO, FUJITA, TERUNORI, HIROKANE, NOBUYA, KAMIMURA, MAKOTO, KATO, KOJI, KURODA, HIROSHI, MAKIO, HARUYUKI, MATSUI, SHIGEKAZU, TAKAI, TOSHIHIRO
Applicants: MITSUI CHEMICALS INC, MITSUI CHEMICALS, INC.
Application year: 1998
Main classification: C07C409
IPC codes: C07C409