The formation of 4,4′-difluorobenzophenone from 4,4′-dinitrodiphenylmethane

Article abstract of DOI:10.1016/S0022-1139(98)00274-7

The novel one pot oxidation/fluorodenitration of 4,4′-dinitrodiphenylmethane to form 4,4′-difluorobenzophenone has been achieved using tetramethylammonium fluoride in N,N-dimethylacetamide.

Full text of DOI:10.1016/S0022-1139(98)00274-7

Journal of Fluorine Chemistry 92 (1998) 127±129
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The formation of 4,4 -di¯uorobenzophenone from
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4
,4 -dinitrodiphenylmethane
*
Dave J. Adams, James H. Clark , Heather McFarland
Department of Chemistry, University of York, Heslington, York YO1 5DD, UK
Received 1 July 1998; accepted 4 August 1998
Abstract
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The novel one pot oxidation/¯uorodenitration of 4,4 -dinitrodiphenylmethane to form 4,4 -di¯uorobenzophenone has been achieved
using tetramethylammonium ¯uoride in N,N-dimethylacetamide. # 1998 Elsevier Science S.A. All rights reserved.
Keywords: Fluoroaromatics; Fluoride; PEEK
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1
. Introduction
4-nitro-4 -¯uorobenzophenone were also detected. Inclusion
of an oxygen feed increased the yield of BDF to a modest
28%. Many by-products could be detected, including the
expected ethers (formed via hydrolysis of the ¯uoroaromatic
or by reattack of the displaced nitrite ion [11]) and tetra(4-
nitrophenyl)ethene, previously identi®ed in the attempted
oxidation of DNDPM [12]. It is known that DMSO can be
deprotonated by strong bases [13] and indications that
reactions involving such anions are occurring was given
by the detection of DMSO related products in similar
systems [14]. An increase in yield was obtained when the
reaction was carried out in N,N-dimethylacetamide
(DMAc), Table 1.
PEEK (poly(etheretherketone)) is a high temperature
thermoplastic which can be compression moulded and
extracted [1] and has many uses, with applications in the
automotive, oil and aerospace industries [2]. PEEK is
usually prepared via a high temperature condensation of
0
4
,4 -di¯uorobenzophenone (BDF) with hydroquinone [3].
While hydroquinone is readily available, BDF is expensive
and contributes greatly to the overall cost of PEEK. Numer-
ous methods exist in the literature for the formation of BDF
[
4,5]. However, these routes tend to involve hazardous
reagents and result in the formation of toxic by-products.
The basic properties of ¯uoride ion are well-known [6].
The base-catalysed oxidation of diphenylmethanes is also
well-documented [7,8] and there are reports in the literature
of the use of ¯uoride ion for such reactions [9]. Fluoro-
denitration has also been used to form a ¯uorinated benzo-
phenone [10].
0
Quantitative oxidation of DNDPM to 4,4 -dinitrobenzo-
phenone (DNB) was found to be possible at room tempera-
ture in DMAc in the presence of small quantities of ¯uoride.
In the absence of ¯uoride, no reaction occurs. After reaction,
the only detectable tetramethylammonium salt is TMAF,
indicating that the oxidation is catalytic.
We have found that it is possible to make use of both the
basic and nucleophilic properties of ¯uoride ion in one pot
for the novel synthesis of BDF from 4,4 -dinitrodiphenyl-
methane (DNDPM), Scheme 1.
In line with the above results, the ¯uorodenitration of
DNB was found to be solvent dependent. A 70% yield of
BDF was obtained after 1 h in DMAc at 1008C. A compar-
able yield was obtained in sulfolane, but the reaction was
slower, taking 2 h to reach completion. In both cases, the
only detectable by-products were oligomeric ethers. A low
yield of 28% of BDF was obtained in DMSO after 20 min,
but, in re¯uxing acetonitrile, complete conversion to non-
volatile products was obtained in this time. Both DMSO and
acetonitrile contain relatively abstractable hydrogens, and
Christe et al. [15] have reported that it is possible to
deprotonate acetonitrile with anhydrous TMAF. In our
reaction, IR analysis of the product mixture formed in
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2
. Results and discussion
Reaction of excess dried tetramethylammonium ¯uoride
(TMAF) with DNDPM in DMSO at 1008C resulted in a low
yield (20%) of BDF being obtained after 60 min. Traces of
*
Corresponding author. Tel.: +44-1904-432-559; fax: +44-1904-432-
5
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16; e-mail: jhcl@york.ac.uk
022-1139/98/$ ± see front matter # 1998 Elsevier Science S.A. All rights reserved.
P I I : S 0 0 2 2 - 1 1 3 9 ( 9 8 ) 0 0 2 7 4 - 7

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28
D.J. Adams et al. / Journal of Fluorine Chemistry 92 (1998) 127±129
2
54 MHz for 19F. Reactions were carried out in conven-
tional glassware. Analysis by GC±MS used a Finnigan MAT
Magnum system ®tted with a DB5 capillary column (50 m)
and ion trap system. Further mass spectrometry was carried
out on a VG Analytical Autospec instrument. All chemicals
used except TMAF were purchased from Aldrich and used
without further puri®cation. TMAF was purchased from
Apollo as the tetrahydrate. This was dried for three days at
608C on a Schlenk line. Karl Fischer analysis of the dried
TMAF gave 19.4 w/w% water.
Scheme 1. The formation of BDF from DNDPM.
Table 1
Reaction of DNDPM with TMAF to give BDF
a
Solvent
Reaction time (min)
Yield (%)
DMSO
DMAc
60
60
60
28
45
71(59)
b
0
DMAc
3.1. 4,4 -Dinitrodiphenylmethane
a
Yields calculated by GC area, corrected by the presence of an internal
standard. The figure in parentheses indicates the isolated yield
Diphenylmethane (12.8 g, 76.2 mmol) was placed in a
round bottomed ¯ask and cooled in an ice bath. Nitric acid
(40 ml) and sulphuric acid (10 ml) were added and the
mixture gently heated to 508C. After 2 h, solid precipitated.
Water (150 ml) was added and the solution was stirred for
30 min. The solid was then collected by ®ltration and
washed well with ether. After boiling in ethanol, the solid
(
unoptimised).
b
Room temperature oxidation (10 mol% TMAF), followed by fluoro-
denitration at 1008C after further addition of TMAF (290 mol%).
acetonitrile revealed CꢀN stretching bands, even after
exhaustive drying under vacuum.
Surprisingly, water was found to have very little effect on
the reaction. Oxidation at room temperature followed by
0
was recrystallised from toluene to give 4,4 -dinitrodi-
phenylmethane (3.95 g 21% yield).
0
‡
¯
uorodenitration resulted in a 71% conversion to BDF. This
4,4 -Dinitrodiphenylmethane: MS (m/z, %) M 258:
165 (100), 258 (59), 212 (37), 241 (14), 63 (13), 89 (11),
system contains the added mole equivalent of water formed
during oxidation. While added water is expected to lead to
side products via the hydrolysis of the ¯uorinated product,
this yield is comparable with that obtained from the ¯uoro-
denitration of pre-formed DNB (72%). The use of anhy-
drous TMAF (formed via the method of Christe et al. [15])
resulted in a slightly lower yield of BDF (67%), again
indicating that the success of the ¯uorodenitration reaction
is not particularly sensitive to the water content.
We also attempted to extend this oxidation/¯uorination to
another class of compounds, the substituted ethylbenzenes,
Table 2. However, only in one case was the desired ¯uoro-
acetophenone formed in measurable quantities. Many side
products were formed, with aldol products being identi®ed
in the reaction mixture, indicating that the ¯uoride might be
1
77 (8); H-NMR (CDCl ) ꢀ 8.17 (d), 7.57 (d) ppm, m.p.
3
1828C.
3.2. Typical simultaneous reaction
DNDPM (0.062 g, 0.24 mmol) was placed in a round
bottomed ¯ask under an argon atmosphere, along with
biphenyl (0.025 g, 0.16 mmol), the internal standard. The
solvent (10 ml) was then added and the reaction heated to
the required temperature. After removal of a sample, TMAF
(0.086 g, 0.72 mmol) was added and the reaction regularly
sampled. Samples were removed, DCM added and washed
once with 1 M HCl and twice with water. After drying, the
samples were analysed by GC. The identity of the products
was con®rmed by comparison of GC retention time, GC±
MS, H- and 19F-NMR spectroscopy with authentic sam-
ples.
attacking the ±CH moiety.
3
1
In conclusion, we have managed to make use of both the
basic and nucleophilic properties of ¯uoride as a means of
forming BDF from DNDPM in one pot.
0
‡
4,4 -Di¯uorobenzophenone: MS (m/z, %) M 218: 123
(
100), 95 (62), 75 (43), 218 (37); 19F-NMR (CDCl ) ꢀ -
3
3
. Experimental
106 ppm.
-Nitro-4 -¯uorobenzophenone: MS (m/z, %) M 245:
123 (100), 245 (56), 95 (36), 150 (23), 75 (14), 104 (9), 170
0
‡
4
1H-NMR and 19F-NMR spectra were recorded on a JEOL
1
(7); 19F-NMR (CDCl ) ꢀ-105 ppm.
EX 270 spectrometer operating at 270 MHz for H and
3
Table 2
Reaction of ethylbenzenes with TMAF in DMAc at 1008C
a
Substrate
Product
Reaction time (min)
Yield (%)
4
2
4
-Nitroethylbenzene
-Nitroethylbenzene
-Chloroethylbenzene
4-Fluoroacetophenone
2-Nitroacetophenone
No reaction
60
120
180
15
13
±
a
Yield based on GC area, corrected by the presence of an internal standard.

D.J. Adams et al. / Journal of Fluorine Chemistry 92 (1998) 127±129
129
0
3
.3. 4,4 -Dinitrobenzophenone
Acknowledgements
0
4
,4 -Dinitrodiphenylmethane (0.9852 g, 3.82 mmol) was
We would like to thank Victrex plc for ®nancial support to
(DA and HM) and the Royal Academy of Engineering/
EPSRC for a Clean Technology Fellowship (to JHC). We
would also like to thank Keith Martin for the Karl±Fischer
analysis.
placed in a round bottomed ¯ask with DMAc (50 ml).
TMAF (0.090 g, 0.75 mmol) was then added and the system
sealed under a positive pressure of oxygen. After stirring
overnight, the solution was poured into cold water (300 ml)
and the solid collected by ®ltration to give 4,4 -Dinitro-
benzophenone, which was recrystallised from toluene
0
(
0.901 g, 87% yield).
0
References
‡
4,4 -Dinitrobenzophenone: MS (m/z, %) M 272: 150
100), 272 (77), 104 (32), 92 (21), 76 (20), 84 (7), 120
6); 1H-NMR (DMSO) d 8.40 (d), 8.01 (d) ppm, m.p.
(
(
[1] O.B. Searle, R.H. Pfeiffer, Poly. Eng. Sci. 25 (1985) 474.
[2] A.M. Thayer, Chem. Eng. News 68 (1990) 37.
[
[
3] J.B. Rose, P.A. Staniland, USP 4 320 224 (1978).
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868C.
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3
.4. Tetra(4-nitrophenyl)ethylene
[
[
[
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Chem. Ser. 75 (1968) 174.
An authentic sample was prepared by the nitration of
tetraphenylethylene with nitric acid at 508C, MS (m/z, %):
5
[
1
12 (100), 408 (6), 326 (12), 313 (9), 300 (6), H-NMR
(
CDCl ) d 7.19 (8H, d), 8.08 (8H, d) ppm. IR (KBr disc) ꢁ
3
[9] J.H. Clark, S.J. Barlow, B.W. Trenbrith, A.J. Butterworth, J. Chem.
Res. (S), (1994) 102.
�
1
max (cm ) 1598, 1522, 1345; m.p. 3048C. Analysis: Calc.
for C H N O requires: C, 60.9%; H, 3.1%; N, 10.9%.
Found: C, 61.19%; H, 3.09%; N, 10.9%.
[
10] J.H. Clark, D. Wails, C.W. Jomes, H. Smith, N. Boechat, L.U.
Mayer, J.S. Mendonca, J. Chem. Res. (S), (1994) 478.
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14] D.J. Adams, J.H. Clark, H. McFarland, D.J. Nightingale, J. Fluorine
Chem., submitted for publication.
2
6 12 4 8
[
[
[
[
3
.5. Reactions of substituted ethylbenzenes
Reactions were carried out as above for DNDPM.
‡
[15] K.O. Christe, W.W. Wilson, R.O. Wilson, R. Bau, J. Feng, J. Am.
Chem. Soc. 112 (199) 7619.
4
-Fluoroacetophenone: MS (m/z, %) M 139: 123(100),
19
1
39(18), 76(15), 63(5); F-NMR (CDCl ) d-105 ppm.
3