A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1948, 28, 63
DOI: 10.15227/orgsyn.028.0063
[2-Fluorenecarboxylic acid, 9-oxo-]
Submitted by George Rieveschl, Jr. and F. E. Ray.
Checked by R. L. Shriner and Arne Langsjoen.
1. Procedure
A 5-l. three-necked round-bottomed flask (Note 1) equipped with a mercury-sealed stirrer, a reflux condenser, and a dropping funnel is set up on a steam bath. In the flask are placed 50 g. (0.24 mole) of 2-acetylfluorene (p. 23) (Note 2) and 650 ml. of glacial acetic acid. After the ketone has been brought into solution by heating and stirring, 450 g. (1.5 moles) of sodium dichromate dihydrate, previously ground to a coarse powder, is added carefully in small portions (about 10 g. each) (Note 3). Heating and stirring are continued throughout the addition, which requires about 45 minutes. The reaction flask is then removed from the steam bath, and the solution is brought to gentle reflux over a flame. During a period of 1.5 hours, 200 ml. of acetic anhydride is added through the dropping funnel. The mixture is refluxed and stirred during this addition and for 8 hours longer (Note 4).
The hot mixture is stirred into 9 l. of hot water in a 5-gal. crock. The suspension is agitated for 15 minutes and is then filtered on a 24-cm. Büchner funnel. The filter cake is washed with four 400-ml. portions of 2% sulfuric acid. The wet filter cake is transferred to a 2-l. beaker containing 700 ml. of a 5% solution of potassium hydroxide (Note 5). The mixture is stirred and heated to about 80°, and the hot solution is filtered. The alkali-insoluble material (Note 6) is washed with 50 ml. of hot 5% potassium hydroxide solution, and the combined alkaline filtrates are placed in a beaker, stirred with 5 g. of decolorizing carbon for 20 minutes, and again filtered. The solution of the potassium salt is heated with vigorous mechanical stirring to 70°, and 200 ml. of 18% hydrochloric acid is added dropwise, the heating being continued so that the temperature rises to about 85°. The fluorenone-2-carboxylic acid separates as a thick yellow mass. It is allowed to digest for 10 minutes with stirring, and the hot mixture is filtered on a 24-cm. Büchner funnel. The acid is washed free of potassium chloride by five or six 200-ml. portions of hot water. The product is pressed as dry as possible and then dried for 3 hours in an oven at 150°. It is a bright canary-yellow, weighs 36–40 g. (67–74%), and melts on an aluminum block at 339–341° (uncor.) with partial sublimation (Note 7).
2. Notes
1. A relatively large flask is used so that the sodium dichromate may be added without the escape of much acetic acid vapor.
2. 2-Acetylfluorene melting at 124–126° has been found to give as good results as the pure compound of melting point 128–129°. The submitters report that the over-all yield from fluorene to fluorenone-2-carboxylic acid can be improved by the use of the crude product of the acylation (m.p. 113–117°) without purification (p. 23).
3. The acetic acid solution of 2-acetylfluorene is conveniently and safely heated to the maximum temperature attainable on the steam bath, and then small portions of sodium dichromate are added as the speed of the reaction permits. To prevent a violent reaction, not more than 10 g. of dichromate is added until the oxidation has begun (as indicated by the appearance of a green color).
4. Small yellow crystals usually appear after the mixture has refluxed for about 7 hours; their quantity does not increase much during the remaining heating period.
5. Sodium hydroxide should not be substituted here because of the lower solubility of the sodium salt.
6. The alkali-insoluble material (3–9 g.) can be washed with water, dried, and recrystallized from 95% ethanol to yield from 1 to 5 g. of pure 2-acetylfluorenone melting at 154–155°. Alternatively, it can be added to the next lot of 2-acetylfluorene if another oxidation is to be carried out.
7. This melting point corresponds to that given in the literature.1,2 The submitters report that the product can be recrystallized from acetic anhydride or Cellosolve.
3. Discussion
The method described is a modification of the method of Dziewonski and Schnayder1 and is described in a patent by the submitters.2 Fluorenone-2-carboxylic acid has also been obtained by the oxidation of 2-fluorenealdehyde3 and by the reaction of 2-acetylfluorene with potassium hypochlorite.4
This preparation is referenced from:

References and Notes
  1. Dziewonski and Schnayder, Bull. intern. acad. polon. sci., 1930A, 529 [C. A., 25, 5416 (1931)].
  2. Rieveschl and Ray, U. S. pat. 2,377,040 [C. A., 39, 3305 (1945)].
  3. Hinkel, Ayling, and Beynon, J. Chem. Soc., 1936, 345.
  4. Schiessler and Eldred, J. Am. Chem. Soc., 70, 3958 (1948).

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

ethanol (64-17-5)

sulfuric acid (7664-93-9)

hydrochloric acid (7647-01-0)

acetic acid (64-19-7)

acetic anhydride (108-24-7)

sodium hydroxide (1310-73-2)

decolorizing carbon (7782-42-5)

potassium hydroxide (1310-58-3)

cellosolve (107-21-1)

sodium dichromate (7789-12-0)

potassium hypochlorite

potassium chloride (7447-40-7)

fluorene (86-73-7)

sodium dichromate dihydrate (10588-01-9)

2-Acetylfluorene (781-73-7)

Fluorenone-2-carboxylic acid,
2-Fluorenecarboxylic acid, 9-oxo- (784-50-9)

2-acetylfluorenone (42136-05-0)

2-fluorenealdehyde (30084-90-3)