JP4079584B2 - Selective production of aromatic aldehydes - Google Patents

Description

【００２８】
酸素の非存在下では、ｐ−キシレンから ¹ＡｃｒＨ^+*への光電子移動（ｋ_et）により、その基底状態への逆電子移動（ｋ_b ）と競合して、ｐ−キシレンラジカルカチオンの脱プロトン化が生じ、アクリジニルラジカル（ＡｃｒＨ・）と対となるｐ−キシレニルラジカルが生成し、付加物〔ＡｃｒＨ（ＣＨ₂ Ｃ₆ Ｈ₄ ＣＨ₃ −ｐ）〕が生じる。
【００２９】
酸素の存在下では、ｐ−キシレニルラジカルは、酸素によって迅速に捕捉され、ＡｃｒＨ⁺ の再生成を伴ってＡｃｒＨ・から逆電子移動によってｐ−キシレニルヒドロペルオキシドが得られる（スキーム１を参照）。そのヒドロパーオキシドが分解し、選択的にｐ−トルアルデヒドが生成する。
【００３０】
ｐ−キシレンを１００％選択的に光触媒的に酸素化させることは、以下の蛍光消光試験で示されているように、ｐ−キシレンと酸素化された生成物であるｐ−トルアルデヒドとの反応性の相違によって行なうことができる。
【００３１】
キシレン、トルエンまたはそれに対応するアルデヒドの非存在下および存在下でのＡｃｒＨ⁺ の蛍光（λ_em＝４８８ｎｍ）の寿命（τ）は、時間分解蛍光分光光度計を用いて測定することができる。光電子移動による蛍光消光速度定数ｋ_q （＝Ｋ_q τ^-1）は、消光剤濃度に対するτ₀ ／τ（アセトアルデヒド中、τ₀ ＝３７ｎｓ）の直線状のスターン−ボルマープロット（Stern-Volmer plot)の傾きから測定される。このようにして測定したｋ_q 値を表１に示す。
【００３２】
【表１】

【００３３】
¹ＡｃｒＨ^+*の蛍光は、キシレンから ¹ＡｃｒＨ^+*への電子の移動によって効率よく消光したのに対し、ｐ−トルアルデヒドでは消光が観察されなかった（ｋ_q ＜＜１×１０⁷ Ｍ^-1ｓ^-1）。ｋ_q 値は、ｐ−キシレン＞ο−キシレン＞ｍ−キシレン＞ο−トルアルデヒド＞トルエン＞ｍ−トルアルデヒド＞＞ｐ−トルアルデヒド（観察されず）の順に減少する。この順序は、表１における一酸素化および二酸素化の製造収率と一致する。したがって、光電子移動が速いほど、製造収率が高くなる。
【００３４】
しかしながら、より極性の大きい溶媒であるアセトニトリルにおける製造収率と比較してクロロホルムにおける製造収率がより向上しているのに対し、クロロホルム（４．２×１０⁹ Ｍ^-1ｓ^-1）中で測定したｐ−キシレンに対するｋ_q 値は、表１におけるアセトニトリルの値よりも小さい。溶媒の極性の低下に伴う、電子移動のための再配列エネルギーの減少によってクロロホルムにおける製造収率が向上し、前記スキーム１におけるＡｃｒＨ・からｐ−キシレンラジカルカチオンへの逆電子移動が遅延化する。酸素化生成物を導くｐ−キシレンラジカルカチオンの脱プロトン化が逆電子移動と競合するので、逆電子移動が遅いほど製造収率が高くなる。
【００３５】
再配列エネルギーは、アセトニトリルおよびクロロホルムにおける９−フェニル−１０−メチルアクリジニウムイオン（ＡｃｒＰｈ⁺ ）とその一電子還元体ラジカル（ＡｃｒＰｈ・）との間の電子移動自己交換反応の速度定数を測定することにより、評価することができる。
【００３６】
ＡｃｒＰｈ・ラジカルは、テトラメチルセミキノリンラジカルアニオンによるＡｃｒＰｈ⁺ の電子移動還元によって得られる。ＡｃｒＰｈ・のＥＳＲスペクトルは、脱気したアセトニトリル中で数時間維持した。超微細結合および最大傾斜線幅（ΔＨ_msl ) は、ＥＳＲスペクトルのコンピュータによるシミュレーションによって測定した。このようにして測定したΔＨ_msl 値は、アセトアルデヒド中において、ＡｃｒＰｈ⁺ の濃度の増大に伴って直線的に増大する。
【００３７】
ＥＳＲスペクトルの線幅の変動は、ラジカル種が関与する速度プロセスを調査するのに用いることができる。ＡｃｒＰｈ⁺ とＡｃｒＰｈ・との間の電子移動交換反応の速度定数（ｋ_ex) は、式（Ｉ）：
ｋ_ex＝〔１．５７×１０⁷ （ΔＨ_msl −ΔＨ⁰ _msl ）〕
÷〔（１−Ｐ_i ）〔ＡｃｒＰｈ⁺ 〕〕 （Ｉ）
（式中、ΔＨ⁰ _msl は、ＡｃｒＰｈ⁺ が存在していないときのＥＳＲスペクトルの最大傾斜線幅、Ｐ_i はほぼ０の値をとりうる統計学的な係数を示す）
を用いて決定することができる。
【００３８】
電子移動反応の再編成エネルギー（λ）は、式(II):
〔（ｋ_ex）^-1−（ｋ_diff）^-1〕＝Ｚ^-1ｅｘｐ（λ／４ｋ_B Ｔ） (II)
（式中、Ｚは１０¹¹Ｍ^-1ｓ^-1を示す。ｋ_diffは、アセトアルデヒド中において２．０×１０¹⁰Ｍ^-1ｓ^-1であり、クロロホルム中において１．２×１０¹⁰Ｍ^-1ｓ^-1である。ｋ_B はボルツマン定数を示す）
により、ｋ_ex値から求められる。クロロホルムにおけるλ値は、アセトアルデヒドにおける値（０．３４ｅＶ）よりも小さい０．２７ｅＶであると測定された。
【００３９】
λ値（０．２７，０．３４ｅＶ）は、ＡｃｒＨ・（ＳＣＥによるＥ⁰ _ox＝−０．４３Ｖ）からｐ−キシレンラジカルカチオン（Ｅ⁰ _red ＝１．９３Ｖ）までの逆電子移動の駆動力（−ΔＧ⁰ _et＝２．３６ｅＶ）よりも非常に小さいので、逆電子移動は、マーカスの逆転領域にあり、λ値の減少に伴って低下することが予想される。
【００４０】
溶媒の極性の低下に伴って逆電子移動速度が低下することにより、実験的に観察されるように製造収率が向上する。
【００４１】
ＡｃｒＨ⁺ の代わりにＡｃｒＰｈ⁺ を用いることにより、製造収率がより一層向上することにより、後者よりも前者に対する逆電子移動速度が低下することにもなる。
【００４２】
マーカス(Marcus)逆転領域においては、駆動力の増加に伴って逆電子移動が遅くなる。
【００４３】
ＡｃｒＰｈ・のＥ⁰ _ox値（ＳＣＥによるＥ⁰ _ox＝−０．５５Ｖ）は、ＡｃｒＨ・の値（ＳＣＥによるＥ⁰ _ox＝−０．４３Ｖ）よりも負であるから、ＡｃｒＰｈ・からの逆電子移動の駆動力（２．４８ｅＶ）は、ＡｃｒＨ・からの逆電子移動の駆動力（２．３６ｅＶ）よりも大きい。駆動力が大きくなるにしたがって逆電子移動速度が低下し、製造収率が向上する。
【００４４】
ＡｃｒＨ⁺ よりも光触媒としてＡｃｒＰｈ⁺ の安定性が高められることは、スキーム１における不活性プロセスである、脱プロトン化したラジカルのカップリングがＡｃｒＰｈ・のフェニル基の立体効果により、妨害されることに起因する。
【００４５】
結論として、ＡｃｒＰｈ⁺ をクロロホルム中で光触媒として使用すれば、他の異性体からそれに対応する芳香族アルデヒドに高選択的に光酸素化することができるとともに、ｐ−キシレンからｐ−トルアルデヒドに１００％選択的に光酸素化することができる。
【００４６】
【実施例】
次に、本発明を実施例に基づいてさらに詳細に説明するが、本発明はかかる実施例のみに限定されるものではない。
【００４７】
実施例１
キセノンランプを用いて紫外線カットフィルタ（λ＞３１０ｎｍ）を介してｐ−キシレン３０ｍＭを含む酸素が飽和したアセトニトリル０．６ｍＬ中で１０−メチルアクリジニウム過塩素酸塩（ＡｃｒＨ⁺ ＣｌＯ₄ ^- ：１０ｍＭ）の吸収帯（λ_max ＝３５８ｎｍおよび４１７ｎｍ）の光線を照射したところ、ｐ−キシレンの消失とともに、ｐ−トルアルデヒドの生成が確認された。
【００４８】
２４時間光線を照射したところ、ｐ−トルアルデヒドの収率は、３７％であった。
【００４９】
溶媒として、アセトニトリル０．６ｍＬの代わりに、より極性が小さい溶媒であるクロロホルム−ｄ０．６ｍＬを用い、他の反応条件を同一にして光線を照射したところ、製造収率は、６６％に向上した。
【００５０】
光酸素化反応後には、光触媒であるアクリジニウムイオン（ＡｃｒＨ⁺ ）は、ほとんど変化していなかったが、少量の付加物である９−ｐ−キシレニル−１０−メチル−９，１０−ジヒドロアクリジン〔ＡｃｒＨ（ＣＨ₂ Ｃ₆ Ｈ₄ ＣＨ₃ −ｐ）〕が生成していた。
【００５１】
光酸素化による製造収率は、１０−メチルアクリジニウムイオン（ＡｃｒＨ⁺ ）を９−フェニル−１０−メチルアクリジニウムイオン（ＡｃｒＰｈ⁺ ）と置換した場合には、表２に示すように、より一層向上した。
【００５２】
なお、表２には、酸素が飽和したクロロホルム中で２９８Ｋの温度で、ＡｃｒＰｈ⁺ を用い、キシレンおよびトルエンに光線を１０時間照射することにより、光酸素化させたときの結果が示されている。
【００５３】
【表２】

【００５４】
さらに光線の照射を行なったが、二酸化物は存在しなかった。また、光触媒と、ＡｃｒＰｈ⁺ と、ｐ−キシレンとの間では付加物の生成がなかった。
【００５５】
このことから、光触媒としてＡｃｒＰｈ⁺ をクロロホルム中で用いることにより、ｐ−キシレンからｐ−トルアルデヒドに１００％の選択率で光酸素化されていることがわかる。
【００５６】
キセノンランプの代わりに高圧水銀灯を用い、アセトフェノン−メタノールフィルタ（λ＞３００ｎｍ）を介して光線を照射した場合には、ｐ−トルアルデヒド３．０×１０^-2Ｍを１００％の収率で得るための光線の照射時間は、２４時間から１０時間に短縮した。
【００５７】
他の異性体として、ο−キシレンおよびｍ−キシレンを用いたところ、表２に示されるように、それぞれο−トルアルデヒドおよびベンズアルデヒドに変換することができた。
【００５８】
次に、ＡｃｒＰｈ⁺ （１．０×１０^-2Ｍ）を含むキシレン３．０×１０^-2Ｍおよびトルエン３．０×１０^-2Ｍの酸素が飽和したクロロホルム溶液０．６ｍＬに、高圧水銀灯（λ＞３００ｎｍ）を用いて光線を１０時間照射したところ、ο−、ｍ−およびｐ−トルアルデヒドおよびベンズアルデヒドの製造収率は、ｐ−キシレン＞ο−キシレン＞ｍ−キシレン＞トルエンの順に減少した。トルアルデヒドの選択率は、ｐ−キシレン（１００％）＞ｍ−キシレン（９９％）＞ο−キシレン（９４％）の順に減少した。
【００５９】
ｍ−キシレンおよびο−キシレンをさらに酸素化させると、少量のそれに対応するフタルアルデヒドが生成した。ｐ−キシレンの場合、出発物質としてｐ−トルアルデヒドを用いたときには、ｐ−トルアルデヒドの光酸素化が起こらないことが確認された。
【００６０】
【発明の効果】
本発明の製造法によれば、無機酸化剤を使用せずに、環境に優しい酸化剤である酸素を用いて選択性よくアルキルベンゼンから芳香族アルデヒドを製造することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for selective production of aromatic aldehydes. More specifically, the present invention relates to a method capable of producing an aromatic aldehyde useful as an intermediate for producing various drugs such as pharmaceuticals, dyes, insecticides, and fragrances from alkylbenzene.
[0002]
[Prior art]
The reaction of selective partial oxygenation of alkylbenzenes to aromatic aldehydes is a technical field in industrial chemistry for the production of aromatic aldehydes useful as intermediates for the manufacture of various drugs such as pharmaceuticals, dyes, insecticides and fragrances. Is an important chemical reaction.
[0003]
Conventionally, for partial oxygenation of alkylbenzene, inorganic oxidizers such as chromium (IV), cobalt (III), manganese (III), cerium (IV), benzeneselenic anhydride, disulfate peroxide / copper ion, etc. (Chem. Br. 1975, 11, 59, Tetrahedron Lett. 1978, 4561, US Patent No. 4,482,438, Electrochem. Sci. Technol. 1976, 11, 143, Tetrahedron Lett. 1985, 28, 3353, Tetrahedron Lett. 1966, 4493, Tetrahedron Lett. 1976, 3331, Tetrahedron Lett. 1981, 22, 2605, etc.).
[0004]
However, when oxygenation of alkylbenzene is carried out using these oxidizing agents, there are disadvantages in that the yield of aromatic aldehydes produced is low and the selectivity is poor. Further, when a stoichiometric amount of an inorganic oxidizing agent is used, there is a disadvantage that a by-product that may cause environmental pollution is generated.
[0005]
In order to avoid the use of stoichiometric and toxic inorganic oxidants, a method for electrochemically recycling these oxidants has been reported (Chem. Int. Ed. Engl. 1986). , 25, 683, J. Org. Chem. 1989, 54, 1526, Tetrahedron Lett. 1986, 42, 553, J. Org. Chem. 1985, 50, 539, J. Synth. Org. Chem., Jpn. 1979 , 37, 914).
[0006]
However, in recent years, development of a method for producing an aromatic aldehyde from alkylbenzene using an oxidizing agent such as oxygen which is an environmentally friendly oxidizing agent without using a conventional inorganic oxidizing agent or the like has been awaited.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above prior art, and without using a conventional inorganic oxidant as an oxidant, using oxygen, which is an environment-friendly oxidant, from alkylbenzene with high selectivity to an aromatic aldehyde. It is an object of the present invention to provide a method capable of selectively producing the above.
[0008]
[Means for Solving the Problems]
Gist of the present invention, the presence of acridinium ion derivatives as a photocatalyst, oxygen used as the oxidant, is irradiated with light to alkylbenzene, a selective process for the preparation of Kaoru aromatic aldehyde Ru is oxygenated alkyl benzene, the The present invention relates to a method for selectively producing an aromatic aldehyde in which the acridinium ion derivative is 9-phenyl-10-methylacridinium perchlorate and the alkylbenzene is partially oxygenated in chloroform .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
According to the production method of the present invention, as described above, in the presence of an acridinium ion derivative as a photocatalyst, oxygen is used as an oxidizing agent, light is irradiated to the alkylbenzene, and the alkylbenzene is partially oxygenated. Corresponding aromatic aldehydes can be selectively produced.
[0010]
The present invention has one major feature in that an acridinium ion derivative is used as a photocatalyst. Thus, when an acridinium ion derivative is used, an aromatic aldehyde can be produced from alkylbenzene with high selectivity. Moreover, since an acridinium ion derivative hardly deactivates during reaction, there exists an advantage that it can be repeatedly used by collect | recovering after completion | finish of reaction.
[0011]
Representative examples of acridinium ion derivatives include 9-phenyl-10-methylacridinium perchlorate, 9-alkyl-10-alkylacridinium perchlorate, and the like. Among these, 9-phenyl-10-methylacridinium perchlorate has a merit that the selectivity of the resulting aromatic aldehyde can be increased, and thus can be suitably used.
[0012]
The amount of the acridinium ion derivative is 1 to 100 parts by weight, preferably 10 to 20 parts by weight, with respect to 100 parts by weight of alkylbenzene, from the viewpoint of light absorption efficiency and catalyst efficiency.
[0013]
In the present invention, oxygen is used as the oxidizing agent. As described above, since oxygen is used, there is no possibility of causing a problem related to environmental pollution unlike a conventionally used inorganic oxidizing agent.
[0014]
In order to perform oxygenation of alkylbenzene efficiently, oxygenation of alkylbenzene is preferably performed in a solvent.
[0015]
Examples of the solvent include chloroform, acetonitrile, methanol, ethanol and the like. Among these, chloroform can be preferably used because it improves the selectivity of the resulting aromatic aldehyde.
[0016]
The amount of the solvent is not particularly limited, but is 100 to 10,000 parts by weight, preferably 100 to 1000 parts by weight with respect to 100 parts by weight of alkylbenzene, from the viewpoint of controlling the polarity of the reaction solution and improving the efficiency of product separation. It is desirable that
[0017]
The amount of oxygen for oxygenating the alkylbenzene is preferably as large as possible in order to efficiently oxygenate the alkylbenzene. When the oxygenation of the alkylbenzene is performed in a solvent, the amount of oxygen is usually preferably a saturated amount in the solvent from the viewpoint of efficiently performing the oxygenation of the alkylbenzene.
[0018]
The alkylbenzene used as a starting material is not particularly limited. Representative examples of alkylbenzene include, for example, o-xylene, m-xylene, p-xylene, toluene, ethylbenzene and the like. Among these, p-xylene can be preferably used from the viewpoint of selectivity.
[0019]
The amount of alkylbenzene is usually 1 to 100 parts by weight, preferably 1 to 10 parts by weight with respect to 100 parts by weight of the solvent, from the viewpoint of reaction efficiency and efficiency of product separation.
[0020]
Oxygenation of alkylbenzene can be easily performed, for example, by dissolving alkylbenzene and an acridinium ion derivative in a solvent in which oxygen is dissolved, and irradiating it with light.
[0021]
As the light beam, a light beam having a wavelength of 300 to 450 nm, preferably 350 to 420 nm can be used. Examples of the irradiation source of light include a xenon lamp provided with an ultraviolet cut filter and a high-pressure mercury lamp provided with an acetophenone-methanol filter.
[0022]
The irradiation time of the light varies depending on the kind of alkylbenzene, the amount used, and so on, so it cannot be determined unconditionally. Usually, such irradiation time may be until the alkylbenzene is converted into the corresponding aromatic aldehyde.
[0023]
Moreover, although there is no limitation in particular in the temperature at the time of irradiating a light ray (when using a solvent, the temperature of a solvent), such temperature should just be about 10-30 degreeC normally.
[0024]
Thus, an aromatic aldehyde can be efficiently produced using alkylbenzene as a starting material.
[0025]
After completion of the reaction, the acridinium ion derivative can be recovered and used repeatedly. Therefore, the method of the present invention is a highly practical method excellent in economic efficiency.
[0026]
By the way, the present inventor shows that oxygenation from an aromatic compound in which a hydrogen atom of a benzene ring is substituted with a methyl group to an aromatic aldehyde is shown in the following scheme 1 taking p-xylene as an example. Thus, it has been reported that it proceeds via photoelectron transfer from toluene to a singlet excited state of 10-methylacridinium ion ( ¹ AcrH ^{+ *} ).
[0027]
[Chemical 1]

[0028]
In the absence of oxygen, the photoelectron transfer from p-xylene to ¹ AcrH ^{+ *} (k _et ) competes with its reverse electron transfer to its ground state (k _b ), deprotonation of the p-xylene radical cation. As a result, a p-xylenyl radical paired with an acridinyl radical (AcrH.) Is generated, and an adduct [AcrH (CH ₂ C ₆ H ₄ CH ₃ -p)] is generated.
[0029]
In the presence of oxygen, the p-xylenyl radical is rapidly trapped by oxygen and p-xylenyl hydroperoxide is obtained by reverse electron transfer from AcrH. With regeneration of AcrH ⁺ (see Scheme 1 reference). The hydroperoxide decomposes to selectively produce p-tolualdehyde.
[0030]
The photocatalytic oxygenation of p-xylene selectively 100% is the reaction of p-xylene with the oxygenated product p-tolualdehyde, as shown in the fluorescence quenching test below. This can be done by gender differences.
[0031]
The lifetime (τ) of fluorescence (λ _em = 488 nm) of AcrH ⁺ in the absence and presence of xylene, toluene or the corresponding aldehyde can be measured using a time-resolved fluorescence spectrophotometer. The fluorescence quenching rate constant k _q (= K _q τ ⁻¹ ) due to photoelectron transfer is a linear Stern-Volmer plot of τ ₀ / τ (in acetaldehyde, τ ₀ = 37 ns) against the quencher concentration. ) Measured from the slope. Table 1 shows the k _q values measured in this way.
[0032]
[Table 1]

[0033]
¹ AcrH ^{+ *} is a fluorescent, whereas the efficiently quenched by electron transfer from xylene ¹ to AcrH ^{+ *,} p- quenching with tolualdehyde was observed ^{_{(k q << 1 × 10 7}} M - ¹ s ^-1 ). The k _q value decreases in the order of p-xylene>o-xylene>m-xylene>o-tolualdehyde>toluene> m-tolualdehyde >> p-tolualdehyde (not observed). This order is consistent with the monooxygenation and dioxygenation production yields in Table 1. Therefore, the faster the photoelectron transfer, the higher the production yield.
[0034]
However, compared with the production yield in acetonitrile, which is a more polar solvent, the production yield in chloroform is improved, whereas in chloroform (4.2 × 10 ⁹ M ⁻¹ s ⁻¹ ) The measured k _q value for p-xylene is smaller than the value of acetonitrile in Table 1. The reduction in the rearrangement energy for electron transfer accompanying the decrease in the polarity of the solvent improves the production yield in chloroform, and the reverse electron transfer from AcrH. To the p-xylene radical cation in Scheme 1 is delayed. Since the deprotonation of the p-xylene radical cation leading to the oxygenated product competes with reverse electron transfer, the slower the reverse electron transfer, the higher the production yield.
[0035]
Rearrangement energy measures the rate constant of the electron transfer self-exchange reaction between 9-phenyl-10-methylacridinium ion (AcrPh ⁺ ) and its one-electron reductant radical (AcrPh.) In acetonitrile and chloroform Can be evaluated.
[0036]
The AcrPh. Radical is obtained by electron transfer reduction of AcrPh ^{+ with} a tetramethylsemiquinoline radical anion. The ESR spectrum of AcrPh. Was maintained for several hours in degassed acetonitrile. _Hyperfine coupling and maximum tilt linewidth (ΔH _msl ) were measured by computer simulation of ESR spectra. The ΔH _msl value measured in this way increases linearly with increasing concentration of AcrPh ^{+ in} acetaldehyde.
[0037]
Variations in the line width of the ESR spectrum can be used to investigate rate processes involving radical species. The rate constant (k _ex ) of the electron transfer exchange reaction between AcrPh ⁺ and AcrPh · is given by the formula (I):
k _ex = [1.57 × 10 ⁷ (ΔH _{msl −ΔH} ⁰ _msl )]
÷ [(1-P _i ) [AcrPh ⁺ ]] (I)
(In the formula, ΔH ⁰ _msl is the maximum slope line width of the ESR spectrum when AcrPh ⁺ is not present, and P _i is a statistical coefficient that can take a value of almost 0)
Can be determined.
[0038]
The reorganization energy (λ) of the electron transfer reaction is given by the formula (II):
[(K _ex ) ⁻¹ − (k _diff ) ⁻¹ ] = Z ⁻¹ exp (λ / 4 k _B T) (II)
(In the formula, Z represents 10 ¹¹ M ⁻¹ s ⁻¹ . K _diff is 2.0 × 10 ¹⁰ M ⁻¹ s ⁻¹ in acetaldehyde and 1.2 × 10 ¹⁰ M ⁻ in chloroform. ¹ s ⁻¹ , k _B represents Boltzmann constant)
_Is obtained from the k _ex value. The λ value in chloroform was measured to be 0.27 eV, which is smaller than the value in acetaldehyde (0.34 eV).
[0039]
The λ value (0.27, 0.34 eV) is the driving force of reverse electron transfer from AcrH · (E ⁰ _ox = −0.43 V by SCE) to p-xylene radical cation (E ⁰ _red = 1.93 V). Since it is much smaller than (−ΔG ⁰ _et = 2.36 eV), the reverse electron transfer is in the Marcus inversion region, and is expected to decrease as the λ value decreases.
[0040]
The decrease in reverse electron transfer rate with decreasing solvent polarity increases the production yield as observed experimentally.
[0041]
By using AcrH ⁺ of AcrPh instead ^+, by the production yield is further improved, reverse electron transfer rate for the former than the latter also decreases.
[0042]
In the Marcus reversal region, the reverse electron movement becomes slower as the driving force increases.
[0043]
Since the E ⁰ _ox value of AcrPh · (E ⁰ _ox = −0.55 V by SCE) is more negative than the value of AcrH · (E ⁰ _ox = −0.43 V by SCE), the reverse electron from AcrPh · The driving force (2.48 eV) for movement is larger than the driving force (2.36 eV) for reverse electron movement from AcrH. As the driving force increases, the reverse electron transfer speed decreases and the production yield improves.
[0044]
AcrH ⁺ the AcrPh ⁺ stability is enhanced as a photocatalyst than are inert process in Scheme 1, the steric effect of the phenyl group of the coupling of the deprotonated radical AcrPh ·, to be disturbed to cause.
[0045]
In conclusion, if AcrPh ⁺ is used as a photocatalyst in chloroform, it can be photooxygenated with high selectivity from other isomers to the corresponding aromatic aldehydes, and from 100 to 100 p-tolualdehyde. % Can be photooxygenated selectively.
[0046]
【Example】
Next, the present invention will be described in more detail based on examples, but the present invention is not limited to such examples.
[0047]
Example 1
10-Methylacridinium perchlorate (AcrH ⁺ ClO ₄ ⁻ : 10 mM) in 0.6 mL of acetonitrile saturated with oxygen containing 30 mM of p-xylene through an ultraviolet cut filter (λ> 310 nm) using a xenon lamp ) Was irradiated with light in the absorption band (λ _max = 358 nm and 417 nm), and formation of p-tolualdehyde was confirmed as p-xylene disappeared.
[0048]
When irradiated with light for 24 hours, the yield of p-tolualdehyde was 37%.
[0049]
As a solvent, chloroform-d 0.6 mL, which is a solvent having a smaller polarity, was used instead of acetonitrile 0.6 mL, and irradiation with light was performed under the same other reaction conditions. The production yield was improved to 66%. .
[0050]
After the photooxygenation reaction, the photocatalyst acridinium ion (AcrH ⁺ ) was hardly changed, but a small amount of adduct, 9-p-xylenyl-10-methyl-9,10-dihydroacridine [ _{AcrH (CH 2 C 6 H 4} CH 3 -p) ] was produced.
[0051]
When manufacturing yield by light oxygenation, substituting for the 10-methyl acridinium ions (AcrH ⁺⁾ of 9-phenyl-10-methyl-acridinium ions (AcrPh ^+), as shown in Table 2, more Improved.
[0052]
Table 2 shows the results when photooxygenation was performed by irradiating xylene and toluene with light for 10 hours using AcrPh ⁺ at a temperature of 298 K in chloroform saturated with oxygen. .
[0053]
[Table 2]

[0054]
Further irradiation with light was performed, but no dioxide was present. Further, no adduct was formed between the photocatalyst, AcrPh ⁺ and p-xylene.
[0055]
From this, it can be seen that by using AcrPh ⁺ as a photocatalyst in chloroform, the photo-oxygenation is performed from p-xylene to p-tolualdehyde with a selectivity of 100%.
[0056]
When a high-pressure mercury lamp is used instead of a xenon lamp and irradiated with light through an acetophenone-methanol filter (λ> 300 nm), p-tolualdehyde 3.0 × 10 ⁻² M is obtained with a yield of 100%. Therefore, the irradiation time of the light beam was shortened from 24 hours to 10 hours.
[0057]
When ο-xylene and m-xylene were used as other isomers, as shown in Table 2, they could be converted into ο-tolualdehyde and benzaldehyde, respectively.
[0058]
Next, 0.6 mL of chloroform solution saturated with oxygen of 3.0 × 10 ⁻² M of xylene and 3.0 × 10 ⁻² M of toluene containing AcrPh ⁺ (1.0 × 10 ⁻² M) was added to a high pressure mercury lamp. (Λ> 300 nm) when irradiated with light for 10 hours, the production yields of ο-, m-, and p-tolualdehyde and benzaldehyde decreased in the order of p-xylene>ο-xylene>m-xylene> toluene. did. The selectivity for tolualdehyde decreased in the order of p-xylene (100%)> m-xylene (99%)> ο-xylene (94%).
[0059]
Further oxygenation of m-xylene and o-xylene produced a small amount of the corresponding phthalaldehyde. In the case of p-xylene, it was confirmed that no photo-oxygenation of p-tolualdehyde occurred when p-tolualdehyde was used as a starting material.
[0060]
【The invention's effect】
According to the production method of the present invention, an aromatic aldehyde can be produced from alkylbenzene with high selectivity using oxygen, which is an environmentally friendly oxidant, without using an inorganic oxidant.

Claims (2)

Presence acridinium ion derivatives as a photocatalyst, oxygen used as the oxidant, is irradiated with light to alkylbenzene, a selective process for the preparation of alkylbenzene Fang aromatic aldehyde Ru is oxygenated, the acridinium ions derivative 9 A selective method for producing an aromatic aldehyde, which is phenyl-10-methylacridinium perchlorate, wherein the alkylbenzene is partially oxygenated in chloroform . Alkylbenzenes method according to claim 1 Symbol mounting a p- xylene.