Process for preparation of 2-(amylbenzoyl)benzoic acid

This invention relates to an improvement in the process for preparation of 2-(amylbenzoyl)benzoic acid containing a high percentage of 2-(t-amylbenzoyl)benzoic acid. More particularly it relates to a process for preparation of 2-(amylbenozyl)benzoic acid wherein said 2-(amylbenzoyl)benzoic acid is prepared by reacting t-amylbenzene with phthalic anhydride in the presence of Lewis acid, characterized by that 2-(amylbenzoyl)benzoic acid containing a high percentage of 2-(t-amylbenzoyl)benzoic acid is produced by suppressing the undesirable isomerization reaction of the amyl radical by applying one of the means selected from the group consisting of the means of introducing an inert gas into the reaction system and the means of reducing the pressure of the reaction system. 2-(Amylbenzoyl)benzoic acid is a compound useful as the starting material of preparation of 2-amylanthraquinone which is an effective organic catalyst in the manufacture of hydrogen peroxide.

BACKGROUND OF THE INVENTION 
Hydrogen peroxide has heretofore been manufactured by the electrolysis of 
ammonium hydrogensulfate solution, but recently a process for its 
manufacture using anthraquinone is being widely adopted. The process for 
manufacturing hydrogen peroxide using anthraquinone is what is called 
"anthraquinone process", in which as the working solution use is made of a 
solution obtained by dissolving an alkylanthraquinone in a suitable 
solvent or a mixture of solvents. In this process hydrogen peroxide is 
obtained in such a way that first hydrogen gas is blown into the working 
solution so as to reduce the alkylanthraquinone in the solution to 
alkylanthrahydroquinone, and then, into the resulting solution is blown an 
oxygen-containing gas to effect oxidation, whereby the 
alkylanthrahydroquinone is again oxidized to regenerate the 
alkylhydroquinone and at the same time hydrogen peroxide is generated. 
While the hydrogen peroxide thus produced is recovered by extraction with 
water from the working solution, the working solution is circulated for 
rense. 
As the alkylanthraquinone used in the above described process there may be 
mentioned 2-ethylanthraquinone, 2-t-butylanthraquinone, 
2-amylanthraquinone, etc., but among them 2-amylanthraquinone (hereinafter 
referred to as "AMQ") is the most useful compound because of its high 
solubility in the working solution. 
Thus, the AMQ now used in the industry is always a mixture of 
2-t-amylanthraquinone (hereinafter referred to as "t-AMQ") and 
2-s-isoamylanthraquinone(hereinafter referred to as "s-AMQ"), and such a 
situation indeed stems from the fact that the 2-(amylbenzoyl)benzoic acid 
itself which is the starting material of preparation of AMQ, is a mixture 
of 2-(t-amylbenzoyl)benzoic acid (hereinafter sometimes referred to as 
"AMB acid") and 2-(s-isoamylbenzoyl)benzoic acid (hereinafter referred to 
as "s-AMB acid"). That is to say, in the process for preparation of AMB 
acid, wherein t-amylbenzene is reacted with phthalic anhydride in the 
presence of Lewis acid, it is impossible to obtain a mixture containing 
more than 55% of t-AMB acid, so that also in the AMQ prepared from such 
AMB acid the content of t-AMQ cannot be more than 55% as a natural 
consequence. This is because when t-amylbenzene and phthalic anhydride 
react in the presence of Lewis acid, portion of the t-amyl radical is 
converted to s-isoamyl radical by isomerization. 
DESCRIPTION OF PRIOR ART 
As described in Japanese Public Disclosure of Patent Application No. 
75558/1973, in the case where hydrogen peroxide is manufactured by the use 
of a mixture of t-AMQ and s-AMQ, if s-AMQ is predominant in the mixture 
ratio, the solubility of amylanthrahydroquinone in the working solution 
decreases, so that not only does the yield of hydrogen peroxide per a 
definite quantity of working solution decrease, but also portion of AMQ 
suffers decomposition to form oxyanthrone, tetrahydroanthrone, anthrone, 
etc. which render the regeneration of AMQ impossible, at the same time 
causing a considerable difficulty in the pufication of hydrogen peroxide 
due to these impurities. Such being the case, in order to prepare AMQ 
containing a high percentage of t-AMQ a number of investigations have been 
attempted. For instance, there have been proposed (1) a process wherein 
t-AMQ is separated from the conventional mixture of t-AMQ and s-AMQ 
(Japanese Public Disclosure of Patent Application No. 75558/1973), (2) a 
process wherein t-amylmagnesium parahalide obtained by reacting 
p-halo-t-amylbenzene with magnesium is condensed with phthalic anhydride 
to give 2-(4'-t-amylbenzoyl)benzoic acid and then this is converted to 
t-AMQ by cyclization (Japanese Patent Publication No. 32517/1972 
corresponding to French Patent No. 6917283), and (3) a process wherein AMB 
acid containing a high percentage of t-AMB acid is prepared by the use of 
both Lewis acid and phthalic anhydride in large excess to t-amylbenzene, 
and then this is converted to AMQ containing a high percentage of t-AMQ by 
cyclization (Japanese Public Disclosure of Patent Application No. 
75558/1973). But, in the process of (1) the yield of t-AMQ decreases 
inevitably, and in the processes of (2) and (3) the adoption of Grignard 
process and the use of Lewis acid and phthalic anhydride in large excess 
add to the cost, and so on, so that it is the present situation that such 
deficiencies are hampering the industrial practice in any of these 
processes. 
SUMMARY OF THE INVENTION 
In view of such a situation the present inventors have made an elaborate 
investigation in order to obtain the AMB acid containing a high percentage 
of t-AMB acid which may be used as the starting material for the 
preparation of the AMQ containing a high percentage of t-AMQ. As a result 
it was discovered that when t-amylbenzene reacts with phthalic anhydride 
in the presence of Lewis acid, the AMB acid containing a high percentage 
of t-AMB acid can be obtained with extreme ease merely by applying one of 
the means selected from the group consisting of the means of introducing 
an inert gas or an inert low boiling liquid gasifiable at the reaction 
temperature into the reaction system and the means of reducing the 
pressure of the reaction system, and thus the present invention was 
achieved. 
That is to say, in accordance with this invention the AMB acid containing a 
high percentage of t-AMB acid can be obtained by applying either the means 
of introducing an inert gas or an inert low boiling liquid gasifiable at 
the reaction temperature into the reaction system or the means of reducing 
the pressure of the reaction system under otherwise the same conditions as 
the conventional process, and using the AMB acid thus obtained as the 
starting material, the AMQ containing a high percentage of t-AMQ can be 
obtained by the conventional process. 
The reason why the application of such means enables us to obtain the AMB 
acid containing a high percentage of t-AMB acid is not yet clear and now 
under investigation, but it may probably be attributable to the fact that 
the expulsion of the hydrogen halide formed as by-product during the 
reaction, resulting from the introduction of an inert gas or reduction of 
pressure, causes the concentration of said hydrogen halide within the 
reaction system to decrease, so that the isomerization of from t-amyl 
radical to s-amyl radical is hampered. 
Either of the means of suppressing the isomerization, which are the 
indispensable requirement in the process of this invention, may achieve 
almost the same effect. 
The process of this invention will be explained more fully below. The first 
means comprises an introduction of an inert gas or an inert low boiling 
liquid gasifiable at the reaction temperature into the reaction system 
while t-amyl benzene and phthalic anhydride are reacting. 
As the inert gas use can be made of a variety of prior-known gases, such 
as, for instance, air, nitrogen, oxygen hydrogen, nitrogen oxide, sulfur 
dioxide, carbon monoxide, carbon dioxide, freon gas, sulfur hexafluoride, 
rare gases, e.g., helium, neon, argon, etc., and gaseous saturated 
hydrocarbons, e.g., methane, ethane, propane, etc. Among them the most 
preferable are air, oxygen, nitrogen, carbon dioxide, etc. As the inert 
low boiling liquid gasifiable at the reaction temperature use can be made 
of low boiling liquids such as, for instance, carbon disulfide, carbon 
tetrachloride, when the reaction is carried out at a temperature above the 
gasification temperature of said liquids. 
There is no particular limitation to the method of introducing the above 
described gases or liquids. For instance, they may be either blown into 
the reaction mixture through a pipe, or blown against the surface of the 
reaction mixture under agitation, and so on. In such a case, however, it 
is preferable that the gas is introduced continuously or intermittently 
throughout the whole period of the reaction or in the initial stage of the 
reaction. The quantity of the gas introduced is not critical, but usually 
about 5-1500 cc per ml of reaction liquid will suffice. 
The second method comprises reducing the pressure of the reaction system 
during the reaction. Since the reaction is usually conducted under the 
ordinary pressure, it will suffice to reduce the pressure of the reaction 
system somewhat below about 500 mm Hg. Although the extent of reduction of 
the pressure is not limitative, there is found a tendency that the larger 
the extent of reduction the more effect of this invention can be 
exhibited. Thus, it is usually preferable to carry out the reaction below 
330 mm Hg. Even under a high vacuum as low as less than 10 mm Hg the 
process of this invention is of course feasible, but as the reaction 
solvent becomes more liable to volatilize it is economically undesirable. 
In this invention, therefore, it is most desirable to carry out the 
reaction under a pressure reduced to about 50-250 mm Hg. In the practice 
of this invention, there is no need of reducing the pressure of the 
reaction system throughout the whole period of the reaction, and by 
reducing the pressure of the reaction system only in the initial stage of 
the reaction the AMB acid containing a high percentage of t-AMB acid can 
be produced. The method of reducing the pressure of the reaction system is 
not critical, and use can be made of any usual pressure-reducing 
apparatuses such as a vacuum pump, an aspirator, etc. as they are. 
The relative quantities of phthalic anhydride and t-amyl-benzene used in 
this invention are not particularly limitative, and the relative 
quantities within the range as used in the conventional process can always 
produce almost the same effect. Heretofore, it is also reported that by 
the use of an excess quantity of phthalic anhydride against the quantity 
of t-amyl-benzene the AMB acid containing a higher percentage of t-AMB 
acid can be prepared, but it is a quite surprising fact that when the 
process of this invention employs jointly this condition the percentage of 
t-AMB acid can be remarkably increased. 
As the Lewis acid use can be made of a variety of prior-known compounds, 
such as aluminum chloride, aluminum bromide, ferric chloride, zinc 
chloride, boron trifluoride, etc., among which aluminum chloride is most 
preferable. The Lewis acid need not be used in large excess, so that as in 
the conventional process about 2 moles or excess (usually 2-2.2 moles) per 
mole of phthalic anhydride will suffice. 
The solvents used in this invention include a variety of solvents usually 
used in Friedel-Crafts reaction, such as, for instance, chlorobenzene, 
dichlorobenzene, trichlorobenzene, tetrachloroethane, etc. The reaction 
temperature employed is usually 0.degree.-100.degree. C, or preferably 
15.degree.-60.degree. C, and the reaction time is usually on the order of 
2-15 hours. 
The AMB acid prepared in the above described way is separated and purified 
by the prior-known conventional means such as recrystallization, etc. 
The AMB acid containing a high percentage of t-AMB acid obtained in 
accordance with this invention can be readily converted to the AMQ 
containing a high percentage of t-AMQ.

DETAILED DESCRIPTION OF THE INVENTION 
In order to make this invention more understandable Examples and 
comparative Examples will be shown below. 
EXAMPLE 1 
One mole of phthalic anhydride, 1.0 mole of t-amylbenzene, and 2.1 moles of 
aluminum chloride are reacted for 4 hours at 40.degree. C in 6.0 moles of 
chlorobenzene under a reduced pressure of 250 mm Hg. Then the reaction 
liquid is discharged into dilute sulfuric acid so as to decompose the 
reaction product, and the solvent layer is separated and thoroughly washed 
with hot water. After unreacted phthalic acid has bee removed, the AMB 
acid formed is extracted from the solvent layer with a dilute aqueous 
solution of sodium hydroxide. The extract obtained by the aqueous solution 
of sodium hydroxide is acidified with dilute sulfuric acid to deposit the 
AMB acid, which is filtered, thoroughly washed with water, and then dried 
to give a yield of 93 mole % as AMB acid. By the analysis of the AMB acid 
obtained based on NMR spectrum the ratio of the amyl radical isomers was 
found to be t-AMB acid : s-AMB acid = 65.3 : 34.7. 
Further, when this AMB acid was cyclized with 2% fuming sulfuric acid 
according to the conventional process, AMQ could be readily obtained. By 
the analysis of this AMQ based on NMR spectrum the ratio of the isomers 
was found to be t-AMQ : s-AMQ = 68.5 : 31.5. 
COMATIVE EXAMPLE 1 
When Example 1 was repeated except that the reaction in Example 1 was 
carried out under the ordinary pressure, AMB acid was obtained in a yield 
of 90 mole %. Further, by its cyclization AMQ was obtained. The ratios of 
the isomers in the respective products were as follows: 
t-AMB acid : s-AMB acid = 45.6 : 54.4, 
t-AMQ : s-AMQ = 48.5 : 51.5. 
EXAMPLE 2 
By repeating Example 1 except that the reaction in Example 1 was carried 
out under a reduced pressure of 250 mm Hg for 2 hours after the initiation 
of the reaction, and after the pressure of the reaction system has been 
returned to the ordinary pressure the reaction was further continued for 2 
hours, AMB was obtained (yield 90%). Further, by its cyclization AMQ was 
obtained. The ratios of the isomers in the respective products were as 
follows: 
t-AMB acid : s-AMB acid = 63.8 : 36.2, 
t-AMQ : s-AMQ = 66.5 : 33.5. 
EXAMPLE 3 
By repeating Example 1 except that the reaction in Example 1 was carried 
out first by reducing the pressure within the reactor to about 50 mm Hg at 
the time of charging starting materials and then by maintaining the 
pressure at about 100 mm Hg., AMB was obtained (yield 95 mole %). By its 
cyclization AMQ was obtained. The ratios of the isomers in the respective 
products were as follows: 
t-AMB acid : s-AMB acid = 71.3 : 28.7 
t-AMQ : s-AMQ = 74.1 : 25.9 
EXAMPLE 4 
By repeating Example 1 except that chlorobenzene used in Example 1 was 
replaced by dichlorobenzene and the reaction was carried out at 50.degree. 
C, there was obtained AMB acid, from which AMQ was obtained by 
cyclization. The ratios of the isomers in the respective products were as 
follows: 
t-AMB acid : s-AMB acid = 71.6 : 28.4 
t-AMQ : s-AMQ = 73.6 : 26.4 
EXAMPLE 5 
While blowing dry air into 6 moles of chlorobenzene liquid 1.0 mole of 
phthalic anhydride, 1.0 mole of t-amylbenzene, and 2.1 moles of aluminum 
chloride are added to the liquid. Continuing the blowing of dry air 
reaction is carried out for 4 hours at 40.degree. C. Then the reaction 
liquid is poured in dilute sulfuric acid so as to decompose the reaction 
product, and the solvent layer is separated and, thoroughly washed with 
hot water. After removal of unreacted phthalic acid the AMB acid formed is 
extracted from said solvent layer with a dilute aqueous solution of sodium 
hydroxide. The extract obtained by the aqueous solution of sodium 
hydroxide is acidified with dilute sulfuric acid to deposit AMB acid, 
which is filtered, thoroughly washed with water, and then dried (yield 87 
mole %). By the analysis of the AMB acid thus obtained based on NMR 
spectrum the ratio of the amyl radical isomers was found to be t-AMB acid 
: s-AMB acid = 77.6 : 22.4. Further, with respect to the AMQ which was 
obtained by cyclizing this AMB acid with fuming sulfuric acid, the 
analysis based on NMR spectrum showed t-AMQ : s-AMQ = 79.0 : 21.0 in the 
ratio of the isomers. 
EXAMPLE 6 
By repeating Example 5 except that dry air was blown against the surface of 
the reaction liquid instead of blowing dry air into the reaction liquid in 
Example 5, there was obtained AMB acid (yield 88 mole %), which was 
cyclized to give AMQ. The ratios of the isomers in the respective products 
were as follows: 
t-AMB acid : s-AMB acid = 70.8 : 29.2 
t-AMQ : s-AMQ = 73.7 : 26.3 
EXAMPLE 7 
By repeating Example 5 except that nitrogen was used in place of air and 
reaction was carried out for 2 hours at 55.degree. C in Example 5, there 
was obtained AMB acid (yield 91 mole %), which was cyclized to give AMQ. 
The ratios of the isomers in the respective products were as follows: 
t-AMB acid : s-AMB acid = 68.2 : 31.8 
t-AMQ : s-AMQ = 71.7 : 28.3 
EXAMPLE 8 
By repeating Example 5 except that helium was used in place of air in 
Example 5, there was obtained AMB acid (yield 88 mole %). In this example, 
however, the helium was circulated for reuse. After the hydrogen chloride 
gas mixed in the gaseous effluent from the reaction system has been 
removed by the use of sodium hydroxide the gaseous effluent was again 
blown into the reaction mixture for reuse. The AMB acid was cyclized to 
give AMQ. The ratios of the isomers in the respective products were as 
follows: 
t-AMB acid : s-AMB acid = 74.4 : 25.6 
t-AMQ : s-AMQ = 75.9 : 24.1 
EXAMPLE 9 
By repeating Example 5 except that ordinary air as it was used in place of 
dry air in Example 5, there was obtained AMB acid (yield 72 mole %). In 
this example, however, air was allowed to enter the reaction system 
through an air introducing tube in such a way that placing one end of said 
air introducing tube outside the reaction system and the other end within 
the reaction liquid, the pressure of the reaction system is weakly 
reduced. The AMB acid was cyclized to give AMQ. The ratios of the isomers 
in the respective products were as follows: 
t-AMB acid : s-AMB acid = 68.3 : 31.7, 
t-AMQ : s-AMQ = 70.5 : 29.5. 
EXAMPLE 10 
By repeating Example 5 except that using 2.0 moles of aluminum chloride in 
Example 5 reaction was carried out for 10 hours at 30.degree. C, there was 
obtained AMB acid (yield 85 mole %), which was cyclized to give AMQ. The 
ratios of the isomers in the respective products were as follows: 
t-AMB acid : s-AMB acid = 85.1 : 14.9, 
t-AMQ : s-AMQ = 87.3 : 12.7 
EXAMPLE 11 
By repeating Example 5 except that orthodichlorobenzene was used in place 
of chlorobenzene in Example 5 and reaction was carried out for 4 hours at 
45.degree. C, there was obtained AMB acid (yield 86 mole %), which was 
cyclized to give AMQ. The ratios of the isomers in the respective products 
were as follows: 
t-AMB acid : s-AMB acid = 68.4 : 31.6, 
t-AMQ : s-AMQ = 70.9 : 29.1 
EXAMPLE 12 
By repeating Example 5 except that the time of blowing dry air was limited 
to 2 hours after the initiation of the reaction, and thereafter, without 
blowing air, the reaction was further carried out for 2 hours, there was 
obtained AMB acid (yield 90 mole %), which was cyclized to give AMQ. The 
ratios of the isomers in the respective products were as follows: 
t-AMB acid : s-AMB acid = 71.2 : 28.8, 
t-AMQ : s-AMQ = 73.5 : 26.5. 
EXAMPLE 13 
While blowing dry air at a rate of 100 liters/hour into 12 moles of 
chlorobenzene liquid 2.0 moles of phthalic anhydride, 1.0 mole of 
t-amylbenzene, and 3.0 moles of aluminum chloride are added to the liquid. 
Continuing the blowing of dry air reaction is carried out for 2.0 hours at 
40.degree. C, and after stopping the blowing of air, the reaction is 
further continued for 2.0 hours at 40.degree. C. Then the reaction liquid 
is poured in dilute sulfuric acid so as to decompose the reaction product. 
The resulting solution is allowed to stand overnight (several hours), and 
the crystals of phthalic acid deposited are removed by filtration. The 
solvent layer is separated from the filtrate and thoroughly washed with 
hot water to remove the remaining unreacted phthalic acid. Then AMB acid 
is extracted from the solvent layer with an aqueous solution of sodium 
hydroxide, and the extract obtained by the aqueous solution of sodium 
hydroxide is acidified with dilute sulfuric acid so as to deposit the AMB 
acid. The AMB acid thus deposited is recovered by filtration, thoroughly 
washed with water, and dried (yield 85 mole %). By the analysis of the AMB 
acid thus obtained based on NMR spectrum the ratio of the isomers of amyl 
radical was found to be t-AMB acid : s-AMB acid = 87.1 : 12.9. Further, 
with respect to the AMQ which was obtained by cyclizing this AMB acid with 
fuming sulfuric acid, the analysis based on NMR spectrum showed t-AMQ : 
s-AMQ = 89.0 : 11.0 in the ratio of the isomers. 
COMATIVE EXAMPLE 2 
By repeating Example 13 except that dry air is not blown in Example 13, AMB 
acid was obtained (yield 86 mole %). t-AMB acid : s-AMB acid = 61.0 : 
39.0. The ratio of the isomers in the AMQ which was obtained by cyclizing 
this AMB acid according to the procedure in Example 13 was as follows: 
t-AMQ : s-AMQ = 62.3 : 37.7. 
EXAMPLE 14 
By repeating Example 13 except that the reaction was carried out using the 
molar ratio of chlorobenzene: phthalic anhydride : t-amylbenzene : 
aluminum chloride = 6.0 : 1.0 : 1.0 : 2.0, there was obtained AMB acid 
(yield 87 mole %). t-AMB acid : s-AMB acid = 74.5 : 25.5; t-AMQ : s-AMQ = 
75.8 : 24.2. 
EXAMPLE 15 
By repeating Example 13 except that the reaction was carried out using the 
molar ratio of chlorobenzene: phthalic anhydride : t-amylbenzene : 
aluminum chloride = 6.0 : 2.0 : 1.0 : 2.1, there was obtained AMB acid 
(yield 82 mole %). t-AMB acid : s-AMB acid = 89.2 : 10.8; t-AMQ : s-AMQ = 
91.0 : 9.0. 
When the reaction was carried out without air blowing the following result 
was obtained (yield of AMB acid 83 mole %). t-AMB acid : s-AMB acid = 63.8 
: 36.2; t-AMQ : s-AMQ = 65.7 : 34.3. 
EXAMPLE 16 
By repeating Example 13 except that the reaction was carried out using the 
molar ratio of chlorobenzene : phthalic anhydride : t-amylbenzene : 
aluminum chloride = 6.0 : 1.5 : 1.0 : 2.1 and instead of blowing air the 
pressure of the reaction system was reduced to 100 mm Hg for the same 
period of time, there was obtained AMB acid (yield 84 mole %). t-AMB acid 
: s-AMB acid = 85.2 : 14.8; t-AMQ : s-AMQ = 86.6 : 13.4. 
When the reaction was carried out under no reduction of pressure the 
following result was obtained (yield of AMB acid 82 mole %). t-AMB acid : 
s-AMB acid = 61.5 : 38.5; t-AMQ : s-AMQ = 65.7 : 34.3. 
EXAMPLE 17 
By repeating Example 13 except that the reaction was carried out at 
30.degree. C for 10 hours using the molar ratio of chlorobenzene : 
phthalic anhydride : t-amylbenzene : aluminum chloride = 6.0 : 2.5 : 1.0 : 
2.1, while blowing nitrogen gas, there was obtained AMB acid (yield 51 
mole %). t-AMB acid : s-AMB acid = 90.4 : 9.6; t-AMQ : s-AMQ = 92.3 : 7.6. 
When the reaction was carried out without nitrogen gas blowing the 
following result was obtained (yield of AMB acid 49 mole %). t-AMB acid : 
s-AMB acid = 72.1 : 27.9; t-AMQ : s-AMQ = 73.8 : 26.2. 
EXAMPLE 18 
By repeating Example 13 except that the reaction was carried out using 
orthodichlorobenzene in place of chlorobenzene and in the molar ratio of 
orthodichlorobenzene : phthalic anhydride : t-amylbenzene : aluminum 
chloride = 20.0 : 5.0 : 1.0 : 6.6, there was obtained AMB acid (yield 84 
mole %). t-AMB acid : s-AMB acid = 89.8 : 10.2; t-AMQ : s-AMQ = 91.5 : 
8.5. 
When the reaction was carried out without air blowing the following result 
was obtained (yield of AMB acid 86 mole %). t-AMB acid : s-AMB acid = 69.2 
: 30.8; t-AMQ : s-AMQ = 70.1 : 29.9.