Method for the production of phenanthrenequinone

Improvement of the yield and purity of phenanthrenequinone during its production by oxidation of phenanthrene by means of chromic acid in a sulfuric acidic medium is achieved by preparing a dispersion made up of phenanthrene, alkali dichromate and water at 95.degree.-100.degree. C., cooling said dispersion down to 80.degree.-85.degree. C. and carrying out the oxidation reaction under cooling and portion-wise addition of concentrated sulfuric acid in a temperature range between 80.degree. and 85.degree. C.

The invention relates to the production of 9,10-phenanthrenequinone by 
oxidation of phenanthrene with chromic acid in a sulfuric acidic medium. 
This reaction is known from Organic Synthesis, Vol. 34, p. 76 and from 
German Patent No. 12 40 065, which are relied upon herein and incorporated 
by reference. 
In the method described in Organic Synthesis the reaction mixture is heated 
by heat of reaction and the conversion finally takes place under reflux at 
the boiling point of water. The phenanthrenequinone yields vary between 44 
and 48%. 
By contrast, according to German Pat. No. 12 40 065 the oxidation occurs at 
temperatures between 100.degree. and 200.degree. C. under pressure. 
According to this method, a substantial increase in the phenanthrenequinone 
yield is obtained up to 85% of the theoretical yield. However, the 
resultant phenanthrenequinone still contains 12 to 14% unreacted 
phenanthrene, which must be isolated in an additional purifying process. 
Apart from the fact that the method must be carried out under pressure, it 
also has the drawback that the oxidation reaction does not run its full 
course. 
Therefore, it is the primary object of the present invention to provide a 
method for the production of phenanthrenequinone that does not exhibit 
this drawback, that enables the phenanthrene to be completely oxidized 
without the use of pressure, thereby increasing the yield of 
phenanthrenequinone. 
This object is achieved by the method for the production of 
9,10-phenanthrenequinone by oxidation of phenanthrene with the aid of 
chromic acid by dropwise addition of concentrated sulfuric acid to a 
mixture of phenanthrene suspended in water and alkali dichromate, a 
dispersion of phenanthene, alkali dichromate and water being prepared at 
95.degree. to 100.degree. C., then cooling the dispersion down to 
80.degree. to 85.degree. C. and carrying out the oxidation with cooling 
and with controlled addition of concentrated sulfuric acid in a 
temperature range from 80.degree. to 85.degree. C. 
In further detail, the present invention is carried out by adding 0.05 to 
0.5 grams of a wetting agent per mole phenanthrene is added to the 
dispersion containing phenanthrene, alkali dichromate and water. 
In still further detail, the present invention is carried out by preparing 
the dispersion of phenanthrene, alkali dichromate and water by mechanical 
dispersion and maintaining the dispersion during the reaction by 
mechanical dispersion. 
A surprising finding was that the oxidation of phenanthrene occurs readily 
and completely when a dispersion is prepared at 95.degree.-100.degree. C. 
comprising water, alkali dichromate and phenanthrene, cooling this 
dispersion down to 80.degree.-85.degree. C., then starting up the reaction 
by adding concentrated sulfuric acid and maintaining the reaction 
temperature in the 80.degree.-85.degree. C. range during the reaction. 
It was also found that the required quantity of chromate and sulfuric acid 
is smaller than was customary in the past, although the oxidation reaction 
goes farther. 
Other surprising advantages of the method of the present invention reside 
in the fact that the quality of the feedstock is almost irrelevant. The 
method can also be implemented with low-quality phenanthrene without 
producing defective charges which, due to excessive resin formations, can 
no longer be processed. Furthermore, in the method of the invention the 
phenanthrenequinone no longer accumulates in the form of globules or lumps 
that enclose organic and inorganic contaminants, but rather as a finely 
divided crystalline product that can easily be filtered off and washed. 
In practice, the method of the invention is carried out by heating a 
mixture made up of, for example, 1 mole phenanthrene with 1.1 to 2 mole 
sodium dichromate and 300-700 ml water up to 95.degree.-100.degree. C. and 
dispersing it by intensive mixing. Any other convenient alkali dichromate 
may be used for purposes of the invention. 
To stabilize the dispersion, small quantities of a wetting agent may be 
added to the mixture. The addition of a wetting agent permits dispersion 
at relatively low stirring rates and only moderate agitation during the 
reaction which then follows. If no wetting agents are employed, the 
reaction mixture must be held in the dispersed phase during the entire 
reaction through mechanical dispersal either by means of high-speed 
agitators or vibrators or by exposure to ultrasonic waves at high 
frequencies so as to prevent individual particles from settling out by 
gravity. 
Any suitable commercial non-ionic, anionic or cationic auxiliairy agents 
can be used as wetting agents such as, for example, fatty acid esters, 
fatty amines, fatty acid amides, polyamines, polyglycolether, 
carboxylates, fluorinated carboxylates, naphthenates, sulfonates, 
sulfates, phosphates or quaternary ammonium compounds. These wetting 
agents are added to the dispersed mixture or the mixture to be dispersed 
in a quantity from 0.05-0.5 g per mole phenanthrene. Any suitable surface 
active agent may be used as a wetting agent for purposes of the invention 
which is capable of stabilizing the dispersion of the phenanthrene, alkali 
dichromate and water. 
The dispersion produced at 95.degree.-100.degree. C. is cooled down to 
80.degree.-85.degree. C. Only then is the oxidation reaction initiated by 
the addition of concentrated sulfuric acid, the reaction mixture being 
maintained at a temperature of 80.degree.-85.degree. C. by a controlled, 
metered addition of acid and by external cooling. This process step 
usually lasts 2 to 3 hours. This is followed by an afterreaction of the 
strongly acidic reaction mixture lasting approximately one hour at 
80.degree.-85.degree. C. Subsequently, the reaction mixture is cooled to 
50.degree.-70.degree. C., whereupon the phenanthrenequinone is 
precipitated and then filtered off, washed, and dried in a manner known in 
the prior art. The concentration of the sulfuric acid used and the amount 
thereof are known in the art, such as in Organic Synthesis, Vol. 34, p. 
76, and will be apparent to those skilled in the art.

The invention will be further understood by reference of the following 
examples. 
EXAMPLE 1 
178 g (86%) phenanthrene are mixed with 500 g Na.sub.2 Cr.sub.2 O.sub.7. 
2H.sub.2 O and 400 g water. 
The mixture was reacted with 0.1 g tetraethylammoniumfluoroctane sulfonate 
and heated up to 100.degree. C. with agitation (180 rpm), then cooled down 
to 80.degree. C. 
Under further agitation, 950 g concentrated sulfuric acid is added within 2 
hours and the temperature of the reaction mixture is maintained in a 
temperature range of 80.degree.-85.degree. C. by external cooling. 
Post-agitation is carried out for 1 hour at 85.degree. C., then the mixture 
is cooled down to 50.degree. C. The precipitated 9,10-phenanthrenequinone 
is isolated from the sulfuric acidic mother liquor and washed with water 
until the wash water runs through almost neutral. 
After drying, 175.5 g finely divided, crystalline phenanthrenequinone with 
92% purity is obtained and a yield 90% of the theoretical yield relative 
to the phenanthrene charged. The product is free of unreacted 
phenanthrene. 
EXAMPLES 2-6 
As in Example 1, phenanthrene is oxidized into phenanthrenequinone with 
changes in the individual conditions. The following list shows these 
changes and the yields of phenanthrenequinone obtained in the individual 
examples. 
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Example 
Change Yield/Content 
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2 Reaction at 100.degree. C. (without 
86%/80% 
cooling to 80.degree. C.) 
3 As in Example 2, no wetting 
85%/80% 
agent 
4 0.2 g diisobutylnaphthalene 
89%/92% 
sulfonate as wetting agent 
5 Charging of 82% phenanthrene 
88%/89% 
6 Preparation and maintenance of 
90%/92% 
the dispersion by exposure to 
ultrasonic waves, no wetting 
agent 
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Further variations and modifications of the invention will be apparent to 
those skilled in the art from the foregoing.