Fluorenecarboxylic Acid

Caution Because of the evolution of considerable amounts of hydrogen chloride, this preparation must be conducted in a good hood or the apparatus must be attached to a gas trap. 

A mixture of 45.6 g. (0.2 mole) of benzilic acid (Note 1) in 700 ml. of anhydrous thiophene-free benzene, contained in a 2-1. three-necked flask fitted with a reflux condenser (attached to a calcium chloride drying tube) and a motor-driven sealed stirrer, is cooled in an ice bath until a crystalline mass results. To the stirred mixture is added, in one portion, 80 g. (0.6 mole) of anhydrous aluminum chloride. The stirred mixture is heated until refluxing begins and is maintained at this temperature for 3 hours. During this period much hydrogen chloride is evolved, and the initially yellow solution soon becomes deep red. The solution is cooled and decomposed by the cautious addition of small pieces of ice, and then 400 ml. of water is added cautiously, followed by 200 ml. of concentrated hydrochloric acid. The benzene is removed by steam distillation, and the product is separated by filtration from the hot mixture. The lumps of product are crushed and extracted with 400 ml. of boiling 10% sodium carbonate solution. The mixture is filtered, and the extraction is repeated on the undissolved residue with an additional 200 ml. of hot 10% sodium carbonate solution. The basic filtrates are 

This product can be further purified by stirring it for several minutes with 200 ml. of benzene at 45°. The insoluble portion is collected on a Buchner funnel and washed first with 40 ml. of cold benzene and then with 40 ml. of petroleum ether (b.p. 28-38°). There is thus obtained 30-34 g. (71-81%) of almost colorless 9-fluorenecarboxylic acid melting at 219-222° with some previous sintering (Note 4). 

The Distillation Products Industries grade melting at 150-151° is satisfactory. 

Good results are usually obtained if the temperature during neutralization is not allowed to exceed 15°. 

---

In a related study, Lee-Ruff, Johnston, and co-workers photolyzed 9-hydroxy-9-fluorenecarboxylic acid in hexafluoro-2-propanol (HFIP) and detected a transient (x = ca. 20ps) with = 495nm and strong IR bands at 1575,1600, and 1620cm , which was assigned to zwitterion 20, in excellent agreement with the measured IR... 

Fluorenecarboxylic acid, 33, 37 Formaldehyde, 30, 51 33, 72 a-Formylethyl methyl ketone, 32, 34 Formyl isobutyl ketone, 32, 34 Friedel-Crafts reaction, 30, 1 31, 88 32, 10... 

Favorskil rearrangement of 2-chloro-cyclohexanone, 39, 37 Ferric chloride, 36, 31 37, 77 Ferric nitrate hydrate, 39, 73 Ferrocene, 36, 31, 34 Ferrous chloride solution in tetrahy-drofuran, 36, 31, 34 Fischer indole synthesis, of 1,2-benzo-3,4-dihydrocarbazole, 30, 91 of 1,2,3,4-tetrahydrocarbazole, 30, 90 Flavone, 32, 72 Flavylium chloride, 32, 75 Flow meter, 34, 7 Fluorene, 34, 32 39, 44 Fluorene, 9-methyl-, 39, 43 9-Fluorenecarboxylic acid, 33, 37 o-Fluorobromobenzene, 39, 75... 

An ice-cooled soln. of benzilic acid in dry, thiophene-free benzene treated with anhydrous A1C13, thoroughly shaken, then refluxed 3 hrs. — 9-fluorenecarboxylic acid. Y 82.5%. (R. T. Arnold, W. E. Parham, and R. M. Dodson, Am. Soc. 71, 2439 (1949).)... 

The only case of which we are aware that zwitterionic form 36 has been directly observed is in the transient absorption and TRIR study of the photochemistry of 9-hydroxy-9-fluorenecarboxylic acid (42) in hexfluoro-2-propanol. Lew et al. [144] detected a transient (x = ca. 20 ps) with max=495 nm and strong IR bands at 1575,1600, and 1620 cm , consistent with zwitterion 43 (Scheme 2.20). Because TRIR spectroscopy is perfectly suited to differentiate between forms... 

In 1949 Arnold and Searles [13] reported that allyl, crotyl and 1-methylallyl diphenylacetates, when treated with mesitylmagnesium bromide or sodium hydride, rearrange to the respective a-substituted diphenylacetic acids. Rearrangement of allyl a-ethyl phenyl acetate could also be effected with stronger base like MgBrNEtj, albeit in very low yields (Scheme 5.1.2). The method was further extended to the synthesis of 9-fluorenecarboxylic acid [14] (Scheme 5.1.3). 

Of tricyclic acids belonging to this type, i-acenaphthenecarboxylic acid (XXXII, to be considered as -naphthaleneacetic acid with fixed side-chain) proved to be a highly active compound, whereas 9-fluorenecarboxylic acid (XXXIII) is weakly active only. 

Metalation. Fluorene added to a soln. of the equimolar amount of diphenylcalcium in tetrahydrofuran, allowed to stand 30 hrs. at room temp., then treated with CO2 9-fluorenecarboxylic acid. Y 95%. F. e. s. K. A. Kocheshkov, M. A. Zemlyanichenko, and N. I. Sheverdina, Izvest. 1971, 2617 C. A. 76, 127047 metalation with K-ferf-butoxide/ -C4H9Li/LiBr s. M. Sdilosser and J. Hartmann, Ang. Ch. 85, 544 (1973). 

---