The Synthesis of (4-Ethenylphenyl)diphenylmethanol

Full text of DOI:10.1021/jo971163h

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928
J . Org. Chem. 1997, 62, 8928-8929
Th e Syn th esis of
4-Eth en ylp h en yl)d ip h en ylm eth a n ol
to detect a product that could be assigned to 1. The main
component is benzophenone. Clearly the polymer is a
(
1
major component of this reaction mixture. The
H
spectrum of the product shows some evidence for the
formation of 1. However, the spectrum also shows strong
evidence for the presence of substantial amounts of a
A. Nzeru, J . R. Ebdon, and S. Rimmer*
The Polymer Centre, Lancaster University, Bailrigg,
Lancaster, Lancs’, UK, LA1 4YA
1
polymer based on styryl repeat units. That is in the H
NMR spectrum (Figure 2, Supporting Information) broad
peaks between 6.8 and 7.4 ppm, which are typical of
phenyl units pendent from a polystyrene derivative, are
observed. The main peaks in the aliphatic region are also
broad and can be assigned to the main chain resonances
of a carbon polymer chain. Resonances are observed at
Received J une 26, 1997
Polymer-immobilized trityl alcohol moieties are im-
portant protecting groups for solid phase peptide syn-
thesis. We also have an interest in polymers function-
alized with this group as precursors to potential stable
free radicals in living free-radical polymerization. The
preparation of these polymers is normally carried out by
lithiation of polystyrene beads followed by quenching of
5
.4 and 5.7 ppm (doublets) which could be assigned to 1
so that some evidence for the production of 1 has been
observed but the major product is polymeric.
Anionic polymerization is known not to occur with
electron rich alkenes. It therefore occurred to us that
styryllithium anion should be sufficiently electron rich
to prevent attack on the vinyl group by nucleophilic
agents. Therefore, if the preparation could be carried out
in such a way that the halostyrene is only present at low
concentration and the rate of lithiation is fast, then
anionic polymerization should be minimized allowing the
styryllithium to be formed without undergoing nucleo-
philic initiation of an anionic polymerization. A simple
way of achieving this would appear to be the reversal of
the mode of addition. So that addition of bromosytene
to tert-butyllithium should give the required result.
Carrying out this procedure in dry diethyl ether solvent
gives the desired styryllithium. After the addition of
benzophenone, the product was subjected again to SEC
analysis. No polymer products were observed, instead a
single low molecular weight sharp peak was observed.
GC-MS of the product gave one GC peak with the highest
weight ion equal to 269 m/z, which corresponds to the
desired product minus OH. No evidence for the presence
of benzophenone could be found. NMR analysis of the
product also confirmed the expected structure (see Fig-
ures 3 and 4, Supporting Information). After purification
this product was produced as a white crystalline powder,
with a melting point of 54-55 °C. This observation is in
conflict with the reported physical form of this material
i.e., a viscous oil.1
1
the lithium salt with benzophenone. It would be ad-
vantageous, however, to synthesize a functional monomer
(4-ethenylphenyl)diphenylmethanol (1)) and then copo-
lymerize this with styrene in a suspension polymeriza-
tion. The advantage of this method is that it allows more
control over the final composition of the product.
(
We considered that lithiation of halostyrenes should
lead to polymerization of any nonlithiated halostyrene.
Synthesis of styryl organometallics with protection of the
vinyl group as the 2-phenylethyl bromide has been
2
reported for this reason. Grignard reactions have also
been used.3
-6
However, the normal procedure in Grig-
nard reactions is to add the alkyl halide to magnesium
so that the Grignard reagent has little chance to react
with the halostyrene. We were therefore surprised to
7
find a report on the synthesis and polymerization of 1
by addition of tert-butyllithium to bromostyrene followed
by reaction of the supposed styryllithium with benzophe-
none. Since this procedure must initially produce sty-
ryllithium (an anionic initiator) in the presence of
bromostyrene (a monomer that is capable of undergoing
8
anionic polymerization ), anionic polymerization should
ensue. Therefore we have attempted to repeat this
preparation. The product was as reported earlier as a
7
viscous yellow oil. In our hands the material produced
from this procedure had a highly viscous nature. Size
exclusion chromatography (SEC) analysis of this oil
showed it to be polymeric in nature. The SEC chromato-
gram is shown in Figure 1 (Supporting Information). The
number average molecular weight (against polystyrene
In the previous work no attempt to polymerize the
monomer to give an easily characterized linear polymer
was made. We considered that the compound 1 might
have a tendency to undergo hydrogen abstraction during
radical poymerization as shown in Scheme 1. This
reaction would effectively terminate polymerization. We
therefore polymerized the monomer with styrene under
radical conditions (as shown in Scheme 2). This yielded
a polymer with a Gaussian distribution of molecular
-
1
standards) of the polymeric product was 105 kg mol
Also shown in this plot is the low molecular weight peak
of the unreacted benzophenone. SEC can be used in a
semiquantitative manner to assay the fraction of polymer
in the oil. Assuming that the refractive index response
factors are similar for each component, then the fraction
of polymer in the product is approximately 0.5 mol %.
The product was also subjected to GC-MS which failed
-
1
weights (M
n
) 13 kg mol , M
w n
/M ) 1.9). The 5 h
reaction period yielded a conversion of approximately
0%. H NMR confirmed the presence of both monomer
1
1
*
To whom correspondence should be addressed. Fax +44 (1524)-
44037, e-mail s.rimmer@lancaster.ac.uk
1) Functionalized polymers and their applications; Akelah, A., Moet,
A., Eds.; Chapman and Hall: New York, 1990; p 75.
units in the main chain. The spectrum is shown in
Figure 5, Supporting Information.
8
(
In conclusion we have shown that the reported proce-
dure for the synthesis of 1 produces mainly polymer
rather than the target compound. The procedure can be
improved by reversing the mode of addition of bromosty-
rene and tert-butyllithium. Thus by adding 4-bromo-
stryene to tert-butyllithium it is possible to minimize the
rate of nucleophilic attack on the vinyl group of 4-bro-
mostyrene. Future reports will present the copolymer-
(
(
(
(
2) Saunders, J .; Williams, R. A. J . Am. Chem. Soc. 1957, 79, 3712.
3) Leebrick, J . R.; Ramsden, H. E. J . Org. Chem. 1958, 23, 935.
4) Sewar, A. N.; Wirth, J .; Neville, R. J . Org. Chem. 1960, 25, 807.
5) Letsinger, R. L.; Kornet, M. J .; Mahadevan, V.; J erina, D. M. J .
Am. Chem. Soc. 1964, 86, 5163.
(
6) Rabinowitz, R.; Marcus, R. J . Org. Chem. 1961, 26, 4157.
(7) Borhan, B.; Wilson , J . A.; Gasch, M. J .; Ying, K.; Kurth, D. M.;
Kurth, M. J . J . Org. Chem. 1995, 60, 7375.
8) Konigsberg, I.; J agurgrodzinski, J . J . Polym. Sci. A-Polym. Chem.
983, 21, 2649.
(
1
S0022-3263(97)01163-8 CCC: $14.00 © 1997 American Chemical Society

Notes
Sch em e 1. P ossible In h ibition Rea ction of
J . Org. Chem., Vol. 62, No. 25, 1997 8929
Rep ea t P r ep a r a tion of (4-eth en ylp h en yl)d ip h en ylm eth -
a n ol Usin g P r eviou sly Rep or ted Meth od . 4-Bromostyrene
20.0 g, 0.105 mol) was dissolved in dry diethyl ether (500 mL).
Com p ou n d 1 d u r in g Ra d ica l Cop olym er iza tion
(
This solution was then cooled under nitrogen to -78 °C. tert-
Butyllithium (1.7 M, 0.231 mol) was then added. Benzophenone
(19.6 g, 0.110 mol) was then dissolved in ether (30 mL) and
added dropwise to the reaction mixture. The reaction was then
allowed to warm to room temperature and stirred for a further
4
H
h. The reaction mixture was worked-up by washing with 1%
SO and saturated NaCl. The solvent was then removed to
2
4
yield a highly viscous oil.
Sch em e 2. Ra d ica l Cop olym er iza tion of
Com p ou n d 1
Syn th esis of (4-Eth en ylp h en yl)d ip h en ylm eth a n ol (1).
tert-Butyllithium (1.7 M, 0.0578 mol) was dissolved in dry diethyl
ether (125 mL). The solution was cooled to -78 °C and put
under nitrogen. 4-Bromostyrene (5.0 g, 0.0263 mol) was then
fed dropwise into the vessel with stirring. Transmetalation was
instantaneous and gave a red-colored solution of 4-styryllithium.
Benzophenone (4.9 g, 0.0275 g) dissolved in dry diethyl ether
(7.5 mL) was then added dropwise. On complete addition the
cooling bath was removed, and the reaction was allowed to warm
to room temperature. After 4 h the reaction was washed with
1
% H
2
SO
4
(75 mL) and saturated NaCl solution (75 mL). The
SO and recrystalized from 40-60
ization reactivity ratios and also procedures for the
preparation of gellike and macroreticular polymer sup-
ports functionalized with trityl alcohol.
product was dried with Na
petroleum ether. Yield 60%; M (- OH) ) 269, FTIR, 3300-
3
2
4
+
600, 3000-3100, 2000-1800, 1625, 1575, 1550, 1500, 1450,
400, 1300, 1200, 1150, 1140, 1000, 900, 850, 775, 675, 650 cm ;
H NMR (400 MHz, CDCl ) 2.82 (1H), 5.25 (1H, d), 5.77 (1H,
3
-1
1
1
Exp er im en ta l Section
d), 6.75 (1H, t), 7.2-7.4 (14H, m). 13C NMR (100 MHz, CDCl3)
8
1
6
1.8, 114, 125.7, 127.2, 127.8, 127.9, 128.1, 136.3, 136.4, 146.4,
46.7. Anal. C 87.8%, H 6.5%, O 5.6% (expected C 88.4%, H
.3% O 5.6%). Mp ) 54-55 °C.
An a lysis. GC-MS was carried out on a Perkin-Elmer 8420
gas chromatograph fitted to a Perkin-Elmer ITD. The column
Alltech (UK)) was 30 m long with an internal diameter of 0.2
(
Cop olym er iza t ion of 1 w it h St yr en e. Distilled styrene
mm and a capillary film thickness of 0.25 µm and was a BP1
type coating. The sample was injected from dichloromethane
solution at 350 °C. The heating ramp was 50-320 °C at 25 °C
(0.4160 g, 4.00 mmol) was mixed with 1 (0.1250 g 0.43 mmol)
and toluene (4.5 mL). Azobis(isobutyronitrile) (0.005 g 0.03
mmol) was then added. This solution was then added to an
ampule and degassed using the usual freeze/thaw cycling
method. Four cycles were performed before the ampule was
sealed off. The ampule was placed in a water bath at 60 °C for
5 h. After this time the ampule was opened, and the solution
precipitated into methanol. The resultant polymer was isolated,
redissolved in toluene, and reprecipitated into methanol.
-
1
min with a helium pressure of 10 psi. SEC measurements
where carried out with Styragel 5 mm mixed gel columns,
calibrated against polystyrene standards, (Polymer Laboratories)
and a refractive index detector system. Tetrahydrofuran was
3
-1
used as the eluent at a flow rate of 1.0 cm min
.
Sample
-
3
concentrations were approximately 0.2 g 100 cm . The NMR
spectra were recorded at 400 MHz ( H) and 100 MHz ( C);
tetramethylsilane was used as the internal standard.
1
13
Ma ter ia ls. Diethyl ether was dried by first refluxing in a
mixture of a dispersion of sodium in oil and benzophenone. Once
the characterstic purple coloration of the dry sodium-benzophe-
none complex was observed, the dry ether was distilled onto dry
Su p p or tin g In for m a tion Ava ila ble: Figures 1-5 referred
to in the text (5 pages). This material is contained in libraries
on microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
4
A molecular sieves and used immediately. THF was SEC grade
Fisher) and used as supplied. Petroleum ether 40-60 (Aldrich)
was used as supplied. Toluene (Aldrich) was distilled before use.
(
J O971163H