R.K. Belter / Journal of Fluorine Chemistry 131 (2010) 1302–1307
1307
3. Conclusion
4.3. Example 2 spectra of authentic p-rosolic acid
Trifluoromethoxyaryls (trifluoromethyl aryl ethers) are suscep-
tible to cleavage of the –CF3 group from the phenolic oxygen in HF/
Lewis acid conditions via the formation of a difluoromethyl
oxonium cation. The cleavage is accomplished by Friedel–Crafts
attack on the difluoromethyl oxonium cation by additional
trifluoromethoxyaryls to form rosolic acids as highly colored solid
residues. Electron withdrawing substituents and para-blocking
groups on the aromatic ring have little effect on the rate of
cleavage, though the rosolic acid isomer changes accordingly.
Electron donating groups accelerate alternative reactions.
IR(KBr);
DMSO, 400 MHz):
v
3180,1590, 1449,1349,1290,1161,1020;1HNMR(d6-
6.93(6H,d,J = 8.6 Hz),6.93(6H,d,J = 8.6 Hz);13
d
C
NMR (d6-DMSO, 100 MHz): d 79.8, 114.0, 118.2, 127.2, 128.9, 139.3,
140.8, 155.7, 169.1; 19F NMR (CDCl3, 235 MHz): no peaks.
4.4. Example 3 generation of (tris)-p-hydroxyphenylcarbonium
fluoride (Fig. 3), 23
1.0 g p-rosolic acid was charged to the reactor. The reactor was
evacuated and cooled with ice. 40 g (2.0 mol) anh. hydrogen fluoride
was charged. The solution was heated with stirring to 100 8C for 1 h.
The reactor was vented warm into ice, then put under vacuum and
cooled. The reactor residue consisted of 1.03 g (tris)-p-hydroxy-
phenylcarbonium fluoride, 23, as a green solid.
4. Experimental
IR (KBr);
v
3162, 1589, 1448, 1354, 1293, 1161; 1H NMR (d6-
6.93 (6H, d, J = 7.4 Hz), 6.93 (6H, d, J = 7.4 Hz);
4.1. General
DMSO, 400 MHz):
d
13C NMR (d6-DMSO, 100 MHz):
d 79.8, 114.0, 116.9, 131.3, 139.3,
Anhydrous hydrogen fluoride was Mexichem Fluor S.A.
Authentic p-rosolic acid was from Sigma. Chlorophenols, hydro-
quinone and pyrocatechol were from Aldrich. Dibenzodioxin was
prepared by the method of Rayne et al. [19]. Trifluoromethox-
ybenzenes 5–8 were prepared by the method of Feiring [2,10]. 2-
Phenoxyphenol (20) was prepared via the Ullman coupling of 16
[20]. 97% R-132b and trifluoromethoxybenzenes, 3 and 11, were
from Synquest Labs. Tantalum (V) chloride was NOAH Technolo-
gies 99.99%. Reactions were performed in a Parr 300 mL hastelloy
mini-reactor. 1H and 13C NMR was performed on a Bruker AV-400.
19F MNR was performed on a Bruker DPX-250. MS was performed
on an Agilent 6210 Time-of-Flight spectrometer.
140.8, 155.7, 164.7; 19F NMR (CDCl3, 235 MHz):
d
ꢀ147.7.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
References
[1] R.K. Belter, N.K. Bhamare, J. Fluorine Chem. 127 (2006) 1606.
[2] A. Feiring, US Patent 4,258,225 (1981).
[3] K.C. Malhotra, U.K. Banerjee, S.C. Chaudhry, Transition Met. Chem. 7 (1982) 14.
[4] F. Franczak, Louisiana State University Dept. of Chemistry, Baton Rouge, LA 70803.
[5] D. Pu, Louisiana State University Dept. of Chemistry, Baton Rouge, LA 70803.
[6] Scifinder and SBDS database no. 12337HSP-48-202. These publications offer the
same reference spectra. In d6-DMSO, supposedly the quinone and phenol signals
are differentiated. This phenomenon was not seen with our samples. It is under-
stood that any trace moisture or DMSO itself may set the p-rosolic acid quinone
and phenols into proton exchange equilibria and coalesce the signals. The
literature does not indicate whether low temperature or strict anhydrous con-
ditions were applied. A ‘differentiated quinone’ signal was obtained with the use
of d6-acetone. However, the integration values changed over time to become a
single pair of doublets, indicating deuterium exchange of the phenolic–OH groups
to be in effect rather than differentiation of the quinone signal.
Cautionary note: anhydrous HF causes instantaneous severe
burns to the skin and mucous membranes. HF should be handled
with full PPE protection. An ample supply of HF antidote gel should
be kept on hand before handling HF. See reference for burn
treatment procedures [21].
4.2. Example 1 generation of p-rosolic acid, 2, from
trifluoromethoxybenzene, 1
720 mg (0.002 mol) TaCl5 was charged to the reactor. The
reactor was evacuated and cooled with ice. 50 g (2.5 mol) anh.
hydrogen fluoride was charged. The solution was heated with
stirring to 140 8C for 1 h. The reactor was again cooled with ice.
10.0 g (0.06 mol) trifluoromethoxybenzene was injected and the
reactor was heated to 140 8C for 4 h. The reactor was vented hot
into ice wherein 6.7 g unreacted trifluoromethoxybenzene was
recovered. The reactor was put under vacuum and cooled. The
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chromatographed on silica gel with 15 CH2Cl2/1 MeOH as eluent to
yield p-rosolic acid, 2, as a red solid.
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assigns 15 H’s to the 14
H ‘‘Compound-[2]’’, p-rosolic acid. It also assigns
integration values of 3H and 6H to what should be 4H and 4H phenolic signals.
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Olah, J. Am. Chem. Soc. 109 (1987) 3708.
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(NbCl5, TaCl5).
[13] K.R. Benson, J. Hickey, W.S. Derwin, M.J. Fifolt, S. Mandal, US Patent 6,118,028
(2000) (SbCl5, MoCl5).
[14] A. Feiring, US Patent 4,157,344 (1979) (BF3).
[15] N.N. Yarovenko, A.S. Vasileva, Zh. Obshch. Khim. 28 (1958) 2502 (SbF3/SbCl5).
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[18] W. Treleaven, Louisiana State University Dept. of Chemistry, Baton Rouge, LA
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[19] S. Rayne, R. Sasaki, P. Wan, Photochem. Photobiol. Sci. 4 (2005) 876.
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IR (KBr);
C3HClF2: 290.0943. Found: 291.1038 (M+1).
1H NMR (d6-DMSO, 400 MHz):
6.93 (6H, d, J = 8.6 Hz), 6.93
79.8, 114.0,
v 3180, 1590, 1449, 1349, 1290, 1161; EIMS Calc’d for
d
(6H, d, J = 8.6 Hz); 13C NMR (d6-DMSO, 100 MHz):
d
118.2, 127.2, 128.9, 139.3, 140.8, 155.7, 169.1; 19F NMR (CDCl3,
235 MHz): no peaks.