JP2784789B2 - Method for producing 2-alkylanthraquinone - Google Patents

Description

The present invention relates to a method for producing 2-alkylanthraquinone in high yield.
Further, the present invention relates to a method for producing a high purity.

2. Description of the Related Art 2-Alkyl anthraquinone is an industrially important compound used as a catalyst in the production of hydrogen peroxide, a sensitizer for a photosensitive resin, and the like.

The 2-alkylanthraquinone is industrially produced generally by dehydrating and ring-closing 2- (4-alkylbenzoyl) benzoic acid with fuming sulfuric acid as shown in the following formula.

For example, according to J. Chem. Soc., 1945, 181, 2- (4-
t-butylbenzoyl) benzoic acid at 5% by weight 20% or
By reacting for 1.5 hours at 90 ° C. in 25% fuming sulfuric acid, 2-t-butylanthraquinone was obtained in a yield of 75%, and 2- (4-n-butylbenzoyl) benzoic acid was quadrupled in weight. By reacting in a 20% or 25% fuming sulfuric acid in a hot water bath for 1.5 hours, 2-n-butylanthraquinone was obtained in a yield of 72%, respectively.

According to the description of Japanese Patent Publication No. 34-8102, 2-
20% of (4-amylbenzoyl) benzoic acid by 8.1 times weight
By reacting at 95 ° C for 2 hours in fuming sulfuric acid, 2
-T-Amylanthraquinone is obtained in a yield of 78%.

Further, according to U.S. Pat. No. 3,032,560, 2-
(4-mixed aluminum benzoyl) benzoic acid is 7.8 times the weight of 1
By reacting at 85 ° C. for 1.5 hours in 0% fuming sulfuric acid, 2-mixed amyl anthraquinone was obtained in a yield of 69%, and 2- (4-tert-butylbenzoyl) benzoic acid was obtained in a yield of 7.8.
By reacting at 85 ° C. for 3 hours in twice the weight of 10% fuming sulfuric acid, 2-t-butylanthraquinone was obtained in a yield of 75%.
In each, is obtained.

To summarize the above three examples, 2- (4-alkylbenzoyl) benzoic acid was added in 4 to 8 times the weight of 10 to 25% fuming sulfuric acid,
By reacting at a temperature in the range of 85 to 95 ° C for 1.5 to 5 hours, 2-alkylanthraquinone can be obtained in a yield of 69 to 78%.
However, such a yield is still not satisfactory from the viewpoint of industrial production.

Therefore, in order to improve the yield of 2-alkylanthraquinone, U.S. Pat. No. 4,035,396 proposes a method in which a solvent is used in combination with the reaction. According to this method, 2
-(4-Aluminobenzoyl) benzoic acid is dissolved in 6 times by weight of trichlorobenzene, and 5 times by weight of 5% fuming sulfuric acid.
By reacting at 90 ° C. for 4 hours, 2-amylanthraquinone was obtained in a yield of 98%, and 2- (4-t-butylbenzoyl) benzoic acid was dissolved in 6 times by weight of trichlorobenzene, and 4 times By reacting at 90 ° C. for 4 hours in 10.5% by weight of fuming sulfuric acid, 2-t-butylanthraquinone was obtained in a yield of 84%. However, according to this method, obviously, use of a large amount of solvent is indispensable, and there are problems in workability and production efficiency.

On the other hand, attempts have been made to improve the yield of 2-alkylanthraquinone by performing the reaction in a short time using a high reaction temperature of 100 ° C. or higher. For example, according to Japanese Patent Application Laid-Open No. 55-45622, 2- (4-mixed amylbenzoyl) benzoic acid is reacted in 3-fold weight of 100% sulfuric acid at 120 ° C. for 15 minutes to give 2-3.5% pure 93.5% The mixed amyl anthraquinone was obtained in a yield of 60.5%, and 2- (4
-N-butylenebenzoyl) benzoic acid at 3 times the weight of 100
Reaction at 120 ° C for 15 minutes in 2% sulfuric acid to give 92% pure 2-
n-Butylanthraquinone was obtained in a yield of 62.3%, respectively.

JP-A-55-64542 and JP-A-55-64543 disclose 2- (4-alkylbenzoyl) benzoic acid.
-Regarding the reaction conditions for producing the alkylanthraquinone, 95% by weight or more, preferably 98% by weight or more of concentrated sulfuric acid, or 1 to 50% by weight, preferably 3 to
30% by weight of fuming sulfuric acid is 2- (4-alkylbenzoyl)
1.5 to 10 times the weight of benzoic acid, preferably 2.5 to 5 times the weight, the reaction temperature is 100 to 180 ° C, preferably 110 to 170 ° C, and the reaction time is 60 minutes or less, preferably 30 minutes or less. However, there is no description of a specific reaction example satisfying these conditions.

Further, Japanese Patent Publication No. 36500/1986 describes a method of adding boric acid to a reaction system. According to this method, 2- (4-mixed amylbenzoyl) benzoic acid is added to 3
B (%) = 0.257A + C (B is the weight percentage of boric acid to the weight of fuming sulfuric acid, A
SO ₃ concentration of fuming sulfuric acid, C is -2 + 2, preferably -
A number in the range of 1.5 to +1.5) In a reaction system to which a certain amount of boric acid is added,
By reacting for 10 minutes, 2 with a purity of 91.4-94.5%
Mixed amyl anthraquinone in a yield of 71.2-81.5%,
Further, 2- (4-t-butylbenzoyl) benzoic acid is converted to 3
In a reaction system in which the same amount of boric acid is added to 25% fuming sulfuric acid of about 4 times the weight, the reaction is carried out at 125 to 145 ° C for 6 to 13 minutes to give 2-t- with a purity of 92.5 to 94.2%. Butyl anthraquinone is obtained in a yield of 76.4-80.2%.

However, according to this method, the combined use of boric acid is indispensable, and not only has a problem in production cost, but also
The purity and yield of the obtained 2-alkylanthraquinone are not always satisfactory. This method also
It has the disadvantage that mass production on a large scale is difficult. In this method, the reaction time must be controlled in a short time, and when it takes a long time to heat or cool,
This is because the system and yield are reduced due to side reactions, and as the reaction scale is increased, the purity and yield are significantly reduced.

As described above, a method capable of producing 2-alkylanthraquinone with high productivity and high purity in high yield has not been found yet.

DISCLOSURE OF THE INVENTION The present inventors have found that a method for producing a 2-alkylanthraquinone by dehydrating and ring-closing 2- (4-alkylbenzoyl) benzoic acid with fuming sulfuric acid has the above-mentioned problems in the conventional method. As a result of diligent research to solve the problem, the dehydration ring-closing reaction is performed continuously at a relatively high reaction temperature and accurately in a short reaction time in a pipe reactor. Further, the inventors have found that high-purity 2-alkylanthraquinone can be produced with high yield and high productivity, and have led to the present invention.

That is, the present invention provides a method for producing a 2-alkylanthraquinone by dehydrating a 2- (4-alkylbenzoyl) benzoic acid with fuming sulfuric acid to produce a 2-alkylanthraquinone.
It is another object of the present invention to provide a method capable of producing high-purity 2-alkylanthraquinone in high yield.

Means for Solving the Problems The present invention provides a compound represented by the general formula (I): (Wherein R represents an alkyl group having 2 to 8 carbon atoms.) 2- (4-alkylbenzoyl) benzoic acid represented by the following formula is dehydrated and closed with a fuming sulfuric acid at a reaction temperature of 150 to 200 ° C. (II) (Wherein, R is the same as described above.) In the method for producing a 2-alkylanthraquinone represented by the formula, 2- (4-alkylbenzoyl) benzoic acid is continuously sent together with fuming sulfuric acid from one end of a pipe reactor. Then, the dehydration ring closure reaction is performed in a pipe reactor within a reaction time of 5 minutes or less, and the reactants are continuously taken out from the other end of the pipe reactor.

According to the method of the present invention, it is possible to heat a reaction product to a predetermined reaction temperature in a short time by using a pipe reactor, and to cool a reaction product after the reaction is completed in a short time. Therefore, side reactions such as sulfonation and carbonization can be suppressed, and as a result, the main reaction, that is, the dehydration ring closure reaction proceeds preferentially. By the way, according to the conventional method using a batch-type reactor, a large amount of reactants must be heated to a predetermined reaction temperature, and after the reaction, it is necessary to cool the reaction. It takes a long time for the subsequent heating and cooling, during which side reactions such as sulfonation and carbonization proceed to lower the yield and purity of the 2-alkylanthraquinone.

Furthermore, according to the method of the present invention, not only the advantage that the purity and yield of the 2-alkylanthraquinone can be ensured at the time of mass production as at the time of small scale, but also the addition of a solvent such as trichlorobenzene or boric acid There is also an advantage that the yield and purity of 2-alkylanthraquinone equal to or higher than these methods can be realized without using a compound in combination.

 Hereinafter, the method of the present invention will be described in detail.

The amount of fuming sulfuric acid used as a dehydrating ring closure agent is free
It is necessary to use at least 1 mole ratio of SO ( ₃ ) to 2- (4-alkylbenzoyl) benzoic acid. 2-
In the method of producing a 2-alkylanthraquinone by dehydrating and ring-closing (4-alkylbenzoyl) benzoic acid with fuming sulfuric acid, water generated by the progress of the dehydration ring-closing reaction reacts with free SO _{3 in} fuming sulfuric acid. Forms sulfuric acid. Therefore, if the amount of fuming sulfuric acid used is less than 1 mole ratio to 2- (4-alkylbenzoyl) benzoic acid as SO ₃ minutes, fuming sulfuric acid is diluted to 100% sulfuric acid or less during the reaction. Therefore, the amount of by-products of the sulfonate increases. On the other hand, if the amount of fuming sulfuric acid is 1 mol ratio or more, there is no particular upper limit, but in consideration of economy and operability, 1.
It is preferred to use them in a molar ratio of 2 to 3.0.

In the method of the present invention, the concentration of fuming sulfuric acid is 5-35.
% Is preferably used. Although fuming sulfuric acid having a concentration of 5% or less can be used, a large amount of fuming sulfuric acid is used in order to make the free SO ₃ minute 1 mol ratio or more based on 2- (4-alkylbenzoyl) benzoic acid. It is necessary to reduce productivity. On the other hand, fuming sulfuric acid of 35% or more can be used.
Since it is preferable to use 1% by weight or more of (4-alkylbenzoyl) benzoic acid, there is no economic advantage by using fuming sulfuric acid of 35% or more.

In the method of the present invention, the reaction temperature is from 150 to 200C, preferably from 160 to 180C. Reaction temperature is 150 ℃
If it is lower, the rate of the dehydration ring-closure reaction becomes slow,
The reaction requires a long time to complete, resulting in an increase in the amount of by-products such as carbides or sulfonates,
The yield and purity of the alkylanthraquinone decrease. On the other hand, when the reaction temperature is higher than 200 ° C., the yield and purity of the 2-alkylanthraquinone decrease because the amount of generated carbide increases.

Furthermore, in the method of the present invention, the reaction time is within 5 minutes, and if it is longer than 5 minutes, the yield of by-products such as carbides or sulfonates increases, so that the yield of 2-alkylanthraquinone is increased. And the purity is reduced.

In the method of the present invention, a pipe reactor is used as the reactor. Here, the pipe reactor has a heating device capable of controlling the temperature and is a device for a continuous reaction formed by a straight or curved pipe, and a raw material solution or each raw material is supplied from one end of the pipe. The reactant that has been constantly fed under pressure and has completed the reaction is pushed out from the other end.

As the material of the pipe reactor, stainless steel, glass lining, ceramics, heat-resistant glass, etc., which are resistant to fuming sulfuric acid to be used, are used.

The length of the pipe reactor depends on the pipe diameter, feed rate of raw materials,
It is determined by various conditions such as reaction time and production amount, but is not particularly limited as long as it is within a range in which the pressure loss in the pipe with respect to the capacity of the pump used for feeding the raw material is taken into consideration.

The diameter of the pipe reactor is preferably 4 inches or less, particularly preferably 2 inches or less, since the rate of heat transfer during heating and cooling during the reaction depends on the control of the reaction temperature and reaction time of the present invention. When the pipe is thicker than 4 inches, the heat transfer area with respect to the feed amount of the raw material becomes insufficient unless the length of the pipe is made extremely long, so that the temperature control of heating and cooling and the control of the reaction time tend to be insufficient. There is.

The reactants in the pipe reactor are desirably agitated to obtain a uniform reaction temperature. A mechanical stirrer is also used to stir the reactants, but if the pipe length is long,
A turbulent filler such as a static mixer is preferably used.

The feed rate of the reaction solution varies depending on the volume of the pipe reactor, but the reactants in the reactor take a predetermined reaction time, namely,
Set to be the residence time.

Supply of the raw material to the pipe reactor may be a raw material solution prepared by dissolving and mixing the alkylbenzoyl benzoic acid and fuming sulfuric acid that are the raw materials in the previous step, or may be sent to the pipe reactor,
Alternatively, both raw materials may be constantly fed into a pipe melting device of a reactor in which a pipe melting device and a pipe reactor are connected.
Furthermore, both materials may be mixed and dissolved directly in a pipe reactor.

When the raw material solution is prepared in the preceding step, the dissolution temperature is preferably 50 ° C. or lower, particularly preferably 30 ° C. or lower, in order to prevent the dehydration ring closure reaction from proceeding due to the heat of dissolution generated during dissolution.

When the raw material melting step is also performed continuously with the reaction step, a reaction apparatus in which a pipe melting device with or without a heating device is connected to a pipe reactor is used, and is continuously and simultaneously parallel to the pipe melting device. And feed both raw materials. In this case, the 2- (4-alkylbenzoyl) benzoic acid to be fed may be in powder or molten form. Also,
As in the case of preparing the raw material solution in the previous step, it is not necessary to maintain the temperature at the time of melting at 50 ° C. or lower, and by preheating the raw material or heating from the outside, the internal temperature of the melting part is 80 to
Dissolution while maintaining the temperature at around 150 ° C. has the advantage that the dissolution time can be reduced.

Alternatively, 2- (4-alkylenebenzoyl) benzoic acid heated to 80 to 150 ° C. and fuming sulfuric acid heated to 80 to 150 ° C. may be directly fed into the pipe reactor simultaneously and constantly.

As a heating method of the pipe reactor, a heating method using a heating medium or the like is preferably used, but since the fuming sulfuric acid has a polarity, a method of directly heating the reactant by a dielectric heating method using a microwave is also preferable. Available to

The dielectric heating method is, as used in microwave ovens, by irradiating microwaves (high frequency).
The reactant itself is vibrated to generate heat, and the energy transfer is more effective and quicker than in a heating method in which a heat medium or the like is used to transfer heat through an external temperature gradient.
Therefore, by utilizing the dielectric heating method for the reaction in the pipe reactor, the reaction temperature can be controlled accurately and promptly, so that the method of the present invention can be performed more advantageously.

In particular, as the pipe diameter of the pipe reactor increases, the advantage of the dielectric heating method becomes more remarkable. The microwave used is effective in the range of 30 to 300,000 MHz. However, industrially available microwaves are restricted by law to certain frequency bands, which include 0-50, 896, 915 and 2450 MHz.
In order to adopt the dielectric heating method, the pipe reactor needs to be made of a material such as glass and ceramics that can transmit microwaves.

After a predetermined reaction time, the reactant is cooled in a cooling pipe connected to a pipe reactor, and then discharged into water or ice water. By treating the precipitate by a conventional purification method, the desired high-purity 2-alkylanthraquinone can be obtained in a high yield.

Effects of the Invention As described above, according to the present invention, 2- (4-alkylbenzoyl) benzoic acid is reacted with fuming sulfuric acid at a reaction temperature of 150-2.
In a method for producing a 2-alkylanthraquinone by dehydration and ring closure at 00 ° C., a relatively high reaction temperature and accurately controlling the reaction time to a short time in a pipe reactor, By performing the dehydration ring-closure reaction, high-purity 2-alkylanthraquinone can be produced with high yield and high productivity.

EXAMPLES Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

Example 1 (Production of 2-ethylanthraquinone) Powdered 2- (4-ethylbenzoyl) benzoic acid (purity 9) was added to 452.7 g of 28% fuming sulfuric acid while stirring at 25 to 30 ° C.
(4.0%) 150.9 g was gradually added and dissolved to prepare a raw material solution. The volume of this raw material solution at 25 ° C. was 366 ml.

This raw material solution was provided with an external heating jacket, loaded with a stainless steel static mixer, having an inner diameter of 8 mm and a length of 7 mm.
The solution was fed into a linear glass pipe reactor having an effective volume of 27.8 ml at a rate of 13.9 ml / min using a ceramics metering pump. A heat medium is introduced into the outer jacket in the same direction as the traveling direction of the raw material solution.
C., set at 158.degree. C. at the outlet.

In addition, in order to keep the residence time of the reactant constant by discharging the gas generated during the reaction before the reactant during the liquid sending, the liquid was sent at an angle of about 20 ° in the direction in which the outlet became higher. After the completion, the outlet was inclined at an angle of about 30 ° so that the outlet was lowered in order to completely discharge the reactants.

The residence time of the reactants in the reactor was about 2 minutes and the temperature at the reactor outlet was 165 ° C. In addition, it took about 28 minutes for all the raw material solutions to pass through the reactor. The reaction product extruded from the reactor was continuously discharged and diluted in ice water 1 with stirring. Extract the precipitate with 500 ml of toluene, warm water,
After washing sequentially with 5% aqueous sodium hydroxide solution and warm water, filtering,
The toluene was distilled off to obtain 121.0 g (90.7% yield) of 2-ethylanthraquinone having a purity of 98.8% as yellow-orange crystals.

Example 2 (Production of 2-t-butylanthraquinone) Powdered 2- (4-t-butylbenzoyl) benzoic acid (purity 95.6%) was added to 282.3 g of 28% fuming sulfuric acid while stirring at 25 to 30 ° C. ) 141.2 g was gradually added and dissolved to prepare a raw material solution. The volume of this raw material solution at 25 ° C. was 270 ml.

This raw material solution was placed in the same reactor as in Example 1 at 13.9 ml /
The liquid was sent at a speed of minutes. The temperature of the heating medium was set at 170 ° C. at the inlet and 157 ° C. at the outlet. The residence time of the reactants in the reactor was about 2 minutes and the temperature at the outlet of the reactor was 160 ° C. Also,
It took about 22 minutes for the entire feed solution to finish passing through the reactor. The reaction product extruded from the reactor was treated in the same manner as in Example 1 to give 97.5% pure 2-t-butylanthraquinone.
120.0 g (92.6% yield) were obtained as yellow-orange crystals.

Example 3 (Production of 2-mixed amyl anthraquino) 12.5% fuming sulfuric acid 444.6 g was stirred at 25 to 30 ° C.
Powdered 2- (4-mixed amylbenzoyl) benzoic acid (95.0% order, t-amyl form / isosec-amyl form = 51.6 /
48.4) 148.2 g was gradually added and dissolved to prepare a raw material solution. The volume of this raw material solution at 25 ° C. was 367 ml.

This raw material solution was placed in the same reactor as in Example 1 at 16.7 ml /
The liquid was sent at a speed of minutes. The temperature of the heating medium was set at 180 ° C. at the inlet and 166 ° C. at the outlet. The residence time of the reactants in the reactor was 1 minute and 40 seconds, and the temperature at the reactor outlet was 167 ° C. Also, it took about 23 minutes for all the raw material solutions to pass through the reactor. The reaction product extruded from the reactor was treated in the same manner as in Example 1 to give a 2-mixed amyl anthraquinone 117 having a purity of 97.9% (t-amyl form / isosec-amyl form = 52.8 / 47.2).
g (86.6% yield) was obtained as a yellow-orange viscous liquid.

Example 4 (Production of 2-mixed amyl anthraquinone) 14.4% fuming sulfuric acid was added to 444.6 g while stirring at 25 to 30 ° C.
Powdered 2- (4-mixed amylbenzoyl) benzoic acid (purity 95.8%, t-amyl form / isosec-amyl form = 82.6 /
17.4) 148.2 g was gradually added and dissolved to prepare a raw material solution. The volume of this raw material solution at 25 ° C. was 366 ml.

This raw material solution was placed in the same reactor as in Example 1 at 11.1 ml /
The liquid was sent at a speed of minutes. The temperature of the heating medium was set at 170 ° C. at the inlet and 158 ° C. at the outlet. The residence time of the reactants in the reactor was 2 minutes and 30 seconds, and the temperature at the reactor outlet was 158 ° C. In addition, it took about 35 minutes for all the raw material solutions to pass through the reactor. The reaction product extruded from the reactor was treated in the same manner as in Example 1 to give 2-mixed amylanthraquinone 12 having a purity of 97.1% (t-amyl form / isosec-amyl form = 83.8 / 16.2).
2.3 (89.1% yield) was obtained as a yellow-orange viscous liquid.

Example 5 (Production of 2-mixed amylanthraquinone) 14.4% fuming sulfuric acid was added to 444.6 g while stirring at 25 to 30 ° C.
Powdered 2- (4-mixed amylbenzoyl) benzoic acid (purity 95.8%, t-amyl form / isosec-amyl form = 82.6 /
17.4) 148.2 g was gradually added and dissolved to prepare a raw material solution. The volume of this raw material solution at 25 ° C. was 366 ml.

On the other hand, the ends of a U-shaped glass pipe with an inner diameter of 8 mm, a length of 55 cm and an effective volume of 27.6 ml
Two stainless steel pipes with an outer diameter of 5 mm and an inner diameter of 3 mm welded to penetrate the wall of a commercially available microwave oven (high frequency output: 500 W, oscillation frequency: 2450 MHz, power supply: AC 100 V) with a Teflon pipe so as to have an inclination angle of ゜Connected to make a microwave heated pipe reactor. One beaker containing 100 ml of water was placed at each of the four corners of the microwave oven equipped with the glass pipe in order to adjust the high frequency output.
While heating the previously prepared raw material solution at a high frequency output of 500 W,
In the microwave heated pipe reactor, from the lower inlet,
The solution was fed at a rate of 22.1 ml / min using a ceramics metering pump. The temperature of the reaction was 165 ° C. as measured at the outlet of the reactor using a thermistor. After the completion of the liquid feeding, the microwave oven was tilted so that the inlet of the reactor was high in order to completely discharge the reactants.

The residence time of the reactants in the reactor was 1 minute and 15 seconds, and it took about 18 minutes for the entire feed solution to pass through the reactor. The reaction product extruded from the reactor was treated in the same manner as in Example 1 to have a purity of 96.8% (t-amyl form / isosec-amyl form = 84.
1 / 15.9) 2-mixed amyl anthraquinone 122.8 (yield 8
9.1%) as a yellow-orange viscous liquid.

Example 6 (Production of 2-ethylanthraquinone) The reaction was carried out using a continuous reaction apparatus as shown in FIG.

A glass pipe melting unit 11 having an inner jacket with a thermal insulator 8 and having a 1.5 cm inner diameter, a length of 25 cm and an effective volume of 26.5 ml equipped with a forced stirrer 9 and a stainless steel staticer having an outer jacket 8 mm inside diameter loaded with mixer 10,
Glass pipe reactor 12 with a length of 76 cm and an effective volume of 27.8 ml
Was connected to produce a continuous reaction apparatus.

The dissolving unit 11 was provided with a degassing tool 3, and in order to check the reaction temperature, thermistors 7 were disposed at the inlet and the outlet of the heating medium as described later. In such a dissolver, fuming sulfuric acid is continuously fed from the supply port 1 and molten 2- (4-alkylbenzoyl) benzoic acid is continuously fed from the supply port 2 to the dissolver. The reactor 12 is also provided with a gas vent 14.

A heat medium was introduced into the outer jacket of the dissolver in a direction opposite to the direction in which the raw materials proceeded, and the temperature of the heat medium was set at 90 ° C. at the inlet 4 and at 85 ° C. at the outlet 5. In this dissolver 11, 2- (ethylbenzoyl) benzoic acid heated to 150 ° C. and melted (purity 94.0
%) Is equivalent to 9.0 ml / min (about 9.8 g / min). ), At the same time, 28% fuming sulfuric acid 15.5ml / min (about 29g
/ Min. The liquid was continuously fed at the speed of (1).

A heat medium was introduced into the outer jacket of the reactor 12 in the same direction as the reaction product. 175 at inlet 4
C. and at outlet 5 at 169.degree. The temperature of the reactants at reactor outlet 6 was 169 ° C. The residence time of the reactants in the dissolver and reactor was a total of 2 minutes and 12 seconds. This reaction operation was continued for about 15 minutes. During this time 2- (4-ethylbenzoyl) benzoic acid passed through the reactor
147 g, 28% fuming sulfuric acid weighed 435 g.

The reaction product extruded from the reactor was treated in the same manner as in Example 1,
Drained into ice water 13 and treated to give 116.6 g (88.2% yield) of 2-ethylanthraquinone with 97.1% purity as yellow-orange crystals.

Comparative Example 1 (Production of 2-ethylanthraquinone) 282.7% fuming sulfuric acid in a 500 ml four-necked flask 452.7
g at a temperature of 25 to 30 ° C. with stirring to obtain powdery 2- (4-
150.9 g of ethylbenzoylbenzoic acid (purity 94.0%) was gradually added and dissolved.

This raw material solution was heated and heated in an oil bath set at 160 ° C., and it took 25 minutes to bring the internal temperature to 165 ° C. After maintaining the internal temperature at 165 ° C. for further 2 minutes, the reaction solution was discharged into ice water 1 for dilution. The precipitate was treated in the same manner as in Example 1 to obtain 91.7 g (yield: 65.4%) of 2-ethylanthraquinone having a purity of 93.2% as orange crystals.

Comparative Example 2 (Production of 2-mixed amyl anthraquinone) 11.8% fuming sulfuric acid 44 in a 500 ml four-neck flask
4.6 g of the powdered 2- (4
148.2 g of mixed amylbenzoylbenzoic acid (purity 95.0%, t-amyl form / isosec-amyl form = 51.6 / 48.4) was gradually added and dissolved.

The raw material solution was heated and heated in an oil bath set at 162 ° C., and it took 26 minutes to reach an internal temperature of 167 ° C. In addition, one minute 40
After maintaining the internal temperature at 167 ° C. for 2 seconds, the reaction solution was discharged into ice water 1 for dilution.

The precipitated Harz-like substance was treated in the same manner as in Example 1,
73.7 g of 2-mixed amyl anthraquinone (t-amyl form / isosec-amyl form = 54.1 / 45.9) having a purity of 92.7% (yield 52.9)
%) As an orange viscous liquid.

Comparative Example 3 (Production of 2-t-butylanthraquinone) In Example 2, the feed rate of the raw material solution was 0.5 ml / min, the residence time of the reactant in the reactor was 56 minutes, and the temperature of the heating medium was jacketed. The reaction was carried out in the same manner as in Example 2 except that the temperature was set at 120 ° C. at the inlet and 111 ° C. at the outlet. In this case, the temperature of the reactants at the reactor outlet is 110 ° C.,
102.6 g (76.9% yield) of 2-t-butylanthraquinone having a purity of 94.7% was obtained as yellow-orange crystals.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an example of a reaction apparatus that can be suitably used in the present invention. 1 ... fuming sulfuric acid supply port, 2 ... molten 2- (4-alkylbenzoyl) benzoic acid supply port, 3 ... degassing tip,
4 ... heat medium inlet, 5 ... heat medium outlet, 6 ... reactant outlet,
7 ... Thermistor, 8 ... Insulation material, 9 ... Stirring rod, 10 ...
… Static mixer, 11… Dissolver, 12… Reactor, 13… Ice water, 14… Gas vent.

Claims (5)

(57) [Claims] 1. The compound of the general formula (I) (Wherein R represents an alkyl group having 2 to 8 carbon atoms.) 2- (4-alkylbenzoyl) benzoic acid represented by the following formula is dehydrated and closed with a fuming sulfuric acid at a reaction temperature of 150 to 200 ° C. (II) (Wherein, R is the same as described above.) In the method for producing a 2-alkylanthraquinone represented by the formula, 2- (4-alkylbenzoyl) benzoic acid is continuously sent together with fuming sulfuric acid from one end of a pipe reactor. And performing a dehydration ring closure reaction in a pipe reactor within a reaction time of 5 minutes or less, and continuously removing a reactant from the other end of the pipe reactor. 2. The method according to claim 1, wherein a raw material solution obtained by dissolving 2- (4-alkylbenzoyl) benzoic acid in fuming sulfuric acid at 50 ° C. or lower is continuously supplied into a pipe reactor. A method for producing a 2-alkylanthraquinone. 3. A reaction apparatus comprising a pipe reactor and a pipe reactor connected with or without a heating device, wherein 2- (4-alkylbenzoyl) benzoic acid and fuming sulfuric acid are added to the pipe melter. 2. The method for producing a 2-alkylanthraquinone according to claim 1, wherein. 4. A method in which 2- (4-alkylbenzoyl) benzoic acid heated to 80 to 150 ° C. and fuming sulfuric acid heated to 80 to 150 ° C. are simultaneously and continuously fed into a pipe reactor. The method for producing a 2-alkylanthraquinone according to claim 1, wherein 5. The method for producing a 2-alkylanthraquinone according to claim 1, wherein microwave heating is used as the heating method.