Checked by Carol M. Taylor and Amos B. Smith, III.
1. Procedure
A.
9-Phenyl-9-fluorenol. A
flame-dried, 3-L, three-necked, round-bottomed flask equipped with an
overhead stirrer,
rubber septum, and
glass stopper, under a
nitrogen atmosphere, is charged with
bromobenzene (158 mL, 1.5 mol, (Note
2)) and
ethyl ether (800 mL, (Note
2)). The solution is cooled in an
ice bath and stirred at 0°C. A
flame-dried, 1-L, graduated cylinder fitted with a rubber septum is filled with
767 mL of a 1.5 M solution of butyllithium in hexane (1.15 mol, (Note 3)) under a
nitrogen atmosphere. The
butyllithium solution is then added to the 0°C
ether solution over 30 min via a Teflon cannula with a positive
nitrogen pressure. After the addition is complete, the solution is stirred for 20 min at 0°C and a solution of
fluorenone (180 g, 1 mol, (Note 4)) in tetrahydrofuran (THF) (300 mL, (Note 5)) is added over 25 min via a Teflon cannula using positive
nitrogen pressure. The ice bath is removed, the mixture is allowed to reach room temperature (24°C), and stirred for 2 hr. During this time,
lithium bromide precipitates out of the reaction mixture. Water (250 mL) is added to dissolve the precipitate, the layers are separated, and the organic layer is washed with 800 mL of water and
800 mL of brine. The
brine wash is discarded, and the other aqueous layers are combined and extracted with
ethyl ether (2 × 200 mL). The combined organic layers are evaporated on a
rotary evaporator at an initial bath temperature of 30–35°C and, when most of the volatile material has been removed, at a bath temperature of 70–75°C until a yellow solid is obtained (Note
6).
2. Notes
1. A pamphlet describing techniques for the handling of air-sensitive solutions can be ordered from Aldrich Chemical Company, Inc.
4.
Fluorenone was obtained from Chemical Dynamics Corporation or Fluka Chemical Corporation and recrystallized from absolute
ethanol to remove fluorene.
6. The physical properties of
9-phenyl-9-fluorenol, which was recrystallized from
isooctane to give pale yellow, translucent needles, are as follows:
13C NMR (Nicolet, 200 MHz) δ: 83.5, 120.0, 124.7, 125.3, 127.1, 128.1, 128.4, 129.0, 139.5, 143.1, 150.3; mp
107–108°C (lit. mp
85°C,
2 107°C3). The checkers observed mp
85–86°C. Anal. Calcd for C
19H
14O: C, 88.34; H, 5.46. Found: C, 88.39; H, 5.60.
8. Use of a Morton flask and an overhead stirrer allows for better mixing of the two-phase system and gives conversion to product faster than does use of a standard round-bottomed flask with an overhead stirrer.
9. Aqueous
hydrobromic acid (HBr) (48%) was obtained from the J. T. Baker Chemical Company.
10. The relative amounts of
9-phenyl-9-fluorenol and
9-bromo-9-phenyl-fluorene were determined as follows: A
13C NMR spectrum (CDCl
3 solution, Bruker 400 MHz) of an authentic sample of
9-bromo-9-phenylfluorene was recorded and then doped in 1% increments with authentic
9-phenyl-9-fluorenol. A
13C NMR spectrum (CDCl
3 solution, Bruker 400 MHz) was recorded after each doping, and the heights of the peaks at 120.3 ppm (bromide) and 120.0 ppm (alcohol) were monitored. These spectra were compared with a
13C NMR spectrum (CDCl
3 solution, Bruker 400 MHz) of the sample in question. Application of this technique to an evaporated aliquot of the reaction mixture in Step B, indicated >97% conversion of alcohol to bromide after 24 hr.
11.
9-Bromo-9-phenylfluorene is greater than 99% pure as shown by
13C NMR, (determined by the procedure in (Note
10)); mp
99°C (lit.
4 mp
99°C).
12. The physical properties of
9-bromo-9-phenylfluorene, which was recrystallized from
isooctane to give light-yellow, lustrous flakes, are as follows:
13C NMR δ: 67.5, 120.3, 126.1, 127.4, 128.0, 128.3, 128.5, 129.0, 138.1, 141.1, 149.6; mp
99°C (lit.
4 mp
99°C); IR (CHCl
3) cm
−1: 3060 (m), 3000 (m), 1600 (w), 1485 (m), 1445 (s), 1150 (m), 830 (w), 690 (m), 620 (m); UV (EtOH) λ, nm, (ε): 310 (8,000), 276 (29,000), 238 (59,000), 230 (70,000), 213 (78,000). Anal. Calcd. for C
19H
13Br: C, 71.04; H, 4.08; Br, 24.88. Found: C, 71.11; H, 4.13; Br, 25.07.
13. The submitters report that
9-bromo-9-phenylfluorene of poorer quality can also be prepared on an identical scale in a lower yield using
phenyllithium (obtained from Aldrich Chemical Company, Inc.) following the procedure given in Step A with minor modifications: A black solution of
phenyllithium (632 mL, 1.14 mol, (Note 14)) was added to a 0°C solution of
fluorenone (180.2 g, 1 mol, (Note 4)) in THF (1360 mL, (Note 5)) over 30 min, and the solution was stirred for 2 hr at room temperature (24°C). Isolation as described in Step A and conversion to the bromide as described in Step B, afforded
234 g (
72.8%) of
9-bromo-9-phenylfluorene as an orange/yellow solid (mp
98°C, lit.
4 mp
99°C); >99% pure [
13C NMR (Note
10)] that was contaminated with approximately 20 g of a black solid; mp 91–94.5°C. This alternative procedure was not checked by the checkers.
14.
Phenyllithium ("2.0 M" in
cyclohexane/ether, 70/30, found to be 1.8 M by titration as described in (Note
3)) was obtained from the Aldrich Chemical Company, Inc., as a black solution and was added to the solution of
fluorenone via Teflon cannula under positive
nitrogen pressure.
All toxic materials were disposed of in accordance with "Prudent Practices in the Laboratory"; National Academy Press; Washington, DC, 1995.
3. Discussion
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