Process for the production of fluorenone by catalytic oxidation of fluorene

An improved process for the production of pure fluorenone by oxidation of fluorene with air or oxygen at ambient temperature in the presence of a quaternary salt, the improvement comprising carrying out the reaction in a suspension of fluorene or a fluorene-containing fraction in an aprotic immiscible with water solvent, such as a .alpha.-methyl naphthalene, which contains and is primed with a 30%-60% aqueous alkali metal hydroxide solution, and intimately mixing the organic and aqueous phases during the reaction.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for the production of pure 
fluorenone by oxidation of fluorene fractions with air or oxygen in the 
presence of quaternary salts. 
2. Description of the Prior Art 
According to K. Kinoshita, K. Okada and S. Hashimoto, Nippon Kagaku Zasshi 
80, 206-8 (1959), it has been known to produce fluorenone in the liquid 
phase by air oxidation from fluorene in pyridine as a solvent and sodium 
hydroxide at about 95.degree. C. However, the process requires a 
cumbersome processing (working up) of the alkaline solution by treatment 
with acids and subsequent extraction with ether for obtaining the 
fluorenone. The yield is at most 50%. 
In British Pat. No. 834,590, it has been proposed to oxidize fluorenone by 
oxidation of fluorene in propionic acid in the presence of cobalt bromide 
by passing over oxygen. The yield of fluorenone is given at 75%. 
According to Y. Sprinzak, J. Am. Chem. Soc. 80, 5449-55 (1958), it has been 
known to treat fluorene in a pyridine solution in the presence of Triton B 
as catalyst with oxygen. However, production on an industrial scale would 
be uprofitable because of the required processing of the reaction product 
connected with large quantities of liquid for the isolation of the 
fluorenone as well as because of the consumption of fairly large 
quantities of pyridine. 
German Pat. No. 1,262,268 teaches the production of fluorenone by catalytic 
oxidation of molten fluorene at an elevated temperature of about 
150.degree. C. in the presence of stearates or resinates of manganese, 
cobalt and lead. This process requires special catalysts as well as the 
traditional measure of melting the fluorene. Moreover the yields, which do 
not exceed 50%, are not satisfactory. 
According to T. Soboleva and V. A. Proskuryakow Zh. Prikl. Khm. (Leningrad) 
1970, 43(8), it has furthermore been taught to obtain fluorenone by air 
oxidation of a fluorene emulsion in aqueous alkali at 175.degree. C. under 
pressure. However, this process requires a higher expenditure of power 
than is desirable. 
Finally, it has also been taught in German published application No. 
1,940,051 (priority of Aug. 6, 1969) to oxidize fluoren through the 
oxidation of fluorene in acetic acid in the presence of cobalt and 
manganese acetates as well as potassium bromide by passing over air. In 
this process too, the yields amount to only about 50%. 
It is therefore a primary object of the present invention to provide a 
process for the production of pure fluorenone which is equally 
advantageous from both industrial and economic standpoints. 
SUMMARY OF THE INVENTION 
It has been found that the above object can be attained by an improved 
process for the production of pure fluorenone by oxidation of fluorene 
with air or oxygen at normal or ambient temperature with the use of a 
quaternary salt. The improvement comprises carrying out the reaction in a 
suspension of fluorene or of a fluorene-containing fraction in an aprotic 
organic solvent immiscible with water, which contains and is primed with 
an aqueous alkali metal hydroxide solution containing from 30% to 60% by 
weight of the alkali metal hydroxide, and by intimately mixing the organic 
and aqueous phases during the reaction. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The quaternary salt used is preferably a quaternary ammonium salt such as 
benzyl-trimethyl-ammonium hydroxide which is available commercially as 
Triton B, although other quaternary salts such as the quaternary 
phosphonium salts may be used. 
All of the alkali metal hydroxides can be used. The preferred alkali metal 
hydroxide is sodium hydroxide which is preferably used in a 40% by weight 
aqueous solution. 
Contrary to the previously known processes, the fluorene oxidation 
according to the process of the present invention will succeed with very 
high yields of about 90% with industrially simple means under atmospheric 
pressure. Beyond that, the present process is not comparable with those 
described above since it takes place in a two-phase system. This is also 
the case according to the Soboleva et al. process previously cited, but 
there the use of pressure is required. Hitherto the production was limited 
to processes in which only aprotic solvents miscible with water such as, 
for example, pyridine, could be used. The process of the present invention 
shows that the oxidation is also possible in a suspension of aprotic, 
solvents immiscible with water, such as for example, methyl naphthalene. 
The simultaneous advantage is the saving of solvent which is required in 
the process of the present invention only in an approximate ratio of 1:1 
to the tar component. In the case of the use of pyridine, on the other 
hand, higher portions of solvents are necessary. Thus, Y. Sprinzak, J. Am. 
Chem. Soc. 80, 5449-55 (1958) prescribes (page 5453) that 10 ml. of 
pyridine are required per 0.01 mole of fluorene. 
As a result of the two-phase system used in the present invention, it is 
possible after completion of the oxidation process to separate the 
homogeneous organic phase from the inorganic aqueous phase, that is to 
say, from the alkali metal hydroxide solution. Since the solvents such as 
methyl-naphthalene do not dissolve in water, a mixing of the two phases 
will be avoided. The ratio of organic phase to alkali solution phase is 
not critical and may generally be from 2:1 to 10:1. 
It is therefore possible within the scope of the process of the present 
invention to distill the fluorenone off directly without further 
processing of the reaction mixture after the separation of the phases. 
With the distillation as the final step, there is the advantage that it is 
not absolutely necessary to use pure fluorene for the oxidation, but that 
one may oxidize corresponding fluorene cuts as obtained in the case of tar 
processing (cf. Example 6). 
The concentration of the alkali metal hydroxide solution should only be 
such so as to assure that the concentration which is reduced during the 
reaction is not substantially below 30% by weight at the end of the 
reaction. In Example 1 to follow, in which a 40% sodium hydroxide solution 
was used, the decanted sodium hydroxide solution had a content of about 
34% of alkali and after concentration may be used for a new oxidation 
batch. The methyl naphthalene distilled off may likewise be used for a new 
oxidation batch. The process also permits the use of fluorene fractions 
with a fluorene content of 50%-75% fluorene.

The following non-limiting examples will illustrate the possibilities of 
the use of various starting products for carrying out the oxidation 
process of the invention. 
EXAMPLE 1 
In a vessel with a stirrer mechanism, 1 kg. of pure fluorene (95-97%) was 
suspended in 1 kg. .alpha.-methyl naphthalene, primed with 300 g. of a 40% 
sodium hydroxide solution. Then 1 g. of Triton B 
(benzyl-trimethyl-ammonium hydroxide) was added and air was conducted 
through the suspension at 20.degree.-30.degree. C. while stirring 
vigorously. After each 10 hours another gram of Triton B was added. After 
a reaction time of 48 hours, the stirrer mechanism was stopped. The 
product was allowed to settle and then the homogeneous, organic phase was 
separated from the inorganic phase. From the organic phase, the methyl 
naphthalene was first distilled over by helm distillation and subsequently 
the fluorenone (95%) was distilled over at standard pressure or under 
vacuum through a short Vigreux column. The yield of fluorenone (95%) 
amounted to 986 g.=91% of theory. 
EXAMPLE 2 
The operation was conducted under the same conditions and with the same 
quantitative ratios as stated in Example 1; however, the .alpha.-methyl 
naphthalene was replaced by a commercial methyl naphthalene fraction which 
had a content of 15-30% .alpha.-methyl naphthalene, 45-60% .beta.-methyl 
naphthalene as well as a residue of quinoline bases and boiling attendant. 
The yield of fluorenone (95%) amounted to 960 g.=88% of theory. 
EXAMPLE 3 
The operation was conducted under the same conditions and with the same 
quantitative ratios as stated in Example 1; however, the .alpha.-methyl 
naphthalene was replaced by a de-based commercial methyl naphthalene 
fraction. The yield of fluorenone (95%) amounted to 972 g.=90% of theory. 
EXAMPLE 4 
The operation was conducted under the same conditions and with the same 
quantitative ratios as stated in Example 1 with the exceptions that 
instead of pure fluorene, a commercial fluorene fraction with a fluorene 
content of at least 50% was used and that the .alpha.-methyl naphthalene 
was replaced by pure quinoline. The yield of fluorenone (95%) amounted to 
1.035 g.=96% of theory. 
EXAMPLE 5 
Again, the operation was conducted under the same conditions and with the 
same quantitative ratios as stated in Example 1 with the exceptions that 
instead of pure fluorene, a commercial fluorene fraction with a fluorene 
content of at least 50% was used and that the .alpha.-methyl naphthalene 
was replaced by a raw quinoline fraction. The yield of fluorenone (95%) 
amounted to 1.016 kg.=94% of theory. 
EXAMPLE 6 
The operation was conducted under the same conditions and with the same 
quantitative ratios as stated in Example 1, with the exceptions that 
instead of pure fluorene, a commercial fluorene fraction with a fluorene 
content of 72% was used and as a suspension agent, .alpha.-methyl 
naphthalene was used. The distillation was conducted with the aid of a 
28-tray column under vacuum at a pressure of 150 or 50 mm of mercury. The 
yield of fluorenone (95%) amounted to 652 g.=85% of theory.