S. Stavber et al. / Tetrahedron 56 (2000) 1929–1936
1935
preparative TLC (SiO2, n-C6H14:CH2Cl22:5) and crystal-
Determination of second-order rate constants for fluo-
rination of alkenes with NFTh
lisation from n-C6H14, while their structure and purity was
verified by NMR, mass spectrometry and combustion
analysis. The yields listed below refer to pure compounds.
Various amounts (0.3, 0.45, 0.6, 0.9, 1.2 mmol) of substrate
(1,1-diphenylethene (1), triphenylethene (2), acenaphthy-
lene (7), 9-benzylidenefluorene (10a) and substituted
9-benzylidenefluorene (10b–10f)) were dissolved in a
thermostatted mixture of 35 mL of acetonitrile and 5 mL
of methanol (or 5 mL of water for 1 and 7), while
0.3 mmol of tetraphenylethene (3), due to its low solubility,
was dissolved in a mixture of 45 mL of acetonitrile and
5 mL of methanol, then 20 mL of a thermostatted aceto-
nitrile solution of NFTh (0.6 mmol) was added and the re-
action mixture further stirred at 24ЊC. The progress of
NFTh consumption was monitored by iodometric
titration and at various times, 10 mL aliquots of reaction
mixture were mixed with 20 mL of ice cold 0.02 M KI and
the liberated iodine was titrated with 0.05 M Na2S2O3.
Second-order rate constants were calculated from the
equation:
9-Methoxy-9-[1-fluoro-1-methylphenyl]fluorene (11a). 135
mg (44%); mp 95.0–95.6ЊC (mp lit.395.9–96.9ЊC); NMR
2
(CDCl3): dH 2.9 (s, 3H), 5.6 (d, JHF46 Hz, 1H), 5.7–8.8
2
(m, 13H); dF Ϫ185.0 (d, JFH46 Hz, 1F).
9-Methoxy-9-[1-fluoro-1-(p-methylphenyl)methyl]fluorene
(11b). 106 mg (33%); mp 142.3–142.4ЊC; NMR (CDCl3):
dH 2.2 (s, 3H), 2.9 (s, 3H), 5.8 (d, 2JHF46 Hz, 1H), 6.7–7.8
2
(m, 12H); dF Ϫ185.0 (d, JFH46 Hz, 1F); MS: m/z 318
(Mϩ, 0.1%), 196 (25), 195 (100), 180 (37), 152 (19), 123
(6); HRMS calcd for C22H19OF m/z 318.1420, found m/z
318.1419; elem. anal. calcd for C22H19OF: C 82.98%, H
6.03%, found C 83.50%, H 5.88%.
9-Methoxy-9-[1-fluoro-1-(m-methylphenyl)methyl]-
fluorene (11c). 156 mg (48%); mp 116.5–117.7ЊC; NMR
2
(CDCl3): dH 2.1 (s, 3H), 2.9 (s, 3H), 5.7 (d, JHF46 Hz,
1=ꢀcA0 Ϫ cB0 × ln ꢀcB0 × cA=ln ꢀcA0 × cB k2 × t
ꢀ2
2
1H), 6.4–7.8 (m, 12H); dF Ϫ184.7 (d, JFH46 Hz, 1F);
MS: m/z 318 (Mϩ, Ͻ0.1%), 196 (29), 195 (100), 180
(33), 152 (18), 123 (9); HRMS calcd for C22H19OF m/z
318.1420, found m/z 318.1429; elem. anal. calcd for
C22H19OF: C 82.98%, H 6.03%, found C 83.43%, H
5.99%.
and are presented in Fig. 1 for fluorinations in the presence
of methanol as nucleophile, but for fluorination in the
presence of water their values are k26.7×10Ϫ3 MϪ1 sϪ1
for the fluorination of 1 and k22.8×10Ϫ3 MϪ1 sϪ1 for fluori-
nation of 7.
9-Methoxy-9-[1-fluoro-1-(p-chlorophenyl)methyl]-
For the Hammett correlation plot relative rate factors for
substituted benzylidenefluorenes (10a–10f) were calculated
from k2 values and are presented in Fig. 3.
fluorene (11d). 154 mg (45%); mp 131.4–132.0ЊC; NMR
2
(CDCl3): dH 2.9 (s, 3H), 5.8 (d, JHF46 Hz, 1H), 6.6–7.7
2
(m, 12H); dF Ϫ184.0 (d, JFH46 Hz, 1F); MS: m/z: 338
(Mϩ, 0.3%), 196 (24), 195 (100), 180 (36), 152 (19), 143
(9); elem. anal. calcd for C21H16OFCl: C 74.44%, H 4.77%,
found: C 74.81%, H 5.05%.
Influence of solvent polarity on second-order rate
constant in fluorination of 1,1-diphenylethene (1) and
acenaphthylene (7) with NFTh
9-Methoxy-9-[1-fluoro-1-(m-trifluoromethylphenyl)methyl]-
fluorene (11e). 215 mg (58%); mp 76.9–78.2ЊC; NMR
2
1.2 mmol of 1,1-diphenylethene (1) or acenapthylene (7)
was dissolved in 40 mL of acetonitrile–water mixture
(acetonitrile–water 34ϩ6; 28ϩ12; 16ϩ24 and 4ϩ36 only
for 1, 7 precipitated from a 40% acetonitrile–60% water
mixture) and thermostatted at 24ЊC for 1 and at 30ЊC for
7, 20 mL of a thermostatted acetonitrile solution containing
0.6 mmol NFTh was added and stirred. The progress of
NFTh consumption was monitored by iodometric titration.
The results are presented in Table 2 and Fig. 2.
(CDCl3): dH 2.9 (s, 3H), 5.9 (d, JHF46 Hz, 1H), 6.9–7.8
2
(m, 12H); dF Ϫ64.2 (s, 3F), Ϫ184.0 (d, JFH46 Hz, 1F);
MS: m/z: 372 (Mϩ, 1%), 196 (24), 195 (100), 180 (36), 177
(8), 152 (17); elem. anal. calcd for C22H16OF4: C 70.95%, H
4.34%, found: 71.47%C, 4.53%H.
The crude reaction mixture obtained after fluorination of
p-methoxy substituted derivative of 9-benzylidenefluorene
10a showed two signals in the 19F NMR spectra: at dF
2
Ϫ180.5 (d, JFH45 Hz) for 9-methoxy-9-[1-fluoro-1-(p-
methoxyphenyl)methyl]fluorene (11f) and at dF Ϫ165.7 (d,
3JFH14 Hz) for 9-fluoro-9-[1-methoxy-1-(p-methoxyphe-
nyl)methyl]fluorene (12f) in the ratio 4:1. The crude reaction
mixture was crystallised from n-C6H14 and analysed by
mass spectroscopy, where fragmentation of both regio-
isomers were present: MS m/z: 334(Mϩ, 6%), 314 (10),
239 (20), 196 (100), 195 (88), 180 (88), 165 (27), 152
(82), 151 (66), 139 (98), 96 (46); HRMS calcd for
C22H19O2F m/z 334.1369, found m/z 334.1375. After several
crystallisations of the crude reaction mixture from n-C6H14
9-methoxy-9-[1-fluoro-1-(p-methoxyphenyl)methyl]fluorene
(11f) was isolated as a white crystalline product (mp 135.5–
137.3ЊC, elem. anal. calcd for C22H19O2F C 79.01%, H
5.74%, found C 79.36%, H 5.59%).
Determination of thermodynamic parameters for fluo-
rination of 1,1-diphenylethene (1) and acenaphthylene
(7) with NFTh in the presence of methanol or water
1.2 mmol of 1,1-diphenylethene (1) or acenapthylene (7)
was dissolved in a mixture of 35 mL of acetonitrile and
5 mL of methanol or water, solutions were thermostatted
at three different temperatures (24, 30 and 38ЊC) and
20 mL of a thermostatted acetonitrile solution of NFTh
(0.6 mmol) was added. The reaction mixture was stirred
and the progress of NFTh consumption was monitored by
iodometric titration. A linear correlation between the k2 and
temperature was observed and activation parameters were