A new reaction of bisphenol A and preparation of polysubstituted 9,9-dimethylxanthenes

Article abstract of DOI:10.1021/jo961766d

A new transformation of bisphenol A (1) to polymethylated 9,9-dimethylxanthenes 2-5 in the presence of an exogenous phenol is described. The reaction proceeds with concurrent liberation of phenol, is catalyzed by strong acid, and takes place at synthetically useful rates at temperatures above 100 °C. Materials chemically related to bisphenol A, polycarbonate 16, chroman 11, and tars generated during the manufacture of 1, behave similarly. The product xanthenes are useful as precursors to novel xanthene polyesters such as 33 having high glass transition temperatures relative to analogous materials based on 12 or 13. Catalytic oxidation of xanthenes 2-4 affords highly insoluble diacids that are esterified to the esters 6-8. A mechanistic framework accounting for the appearance of chroman 23 and spiroketal 24 as intermediates is given. Overall, the reaction has the characteristics of a complex series of equilibria in which xanthenes such as 2 are strongly favored.

Full text of DOI:10.1021/jo961766d

1058
J . Org. Chem. 1997, 62, 1058-1063
A New Rea ction of Bisp h en ol A a n d P r ep a r a tion of
P olysu bstitu ted 9,9-Dim eth ylxa n th en es†
Andrew J . Caruso* and J ulia L. Lee
GE Corporate Research and Development Center, Schenectady, New York 12301
Received September 16, 1996X
A new transformation of bisphenol A (1) to polymethylated 9,9-dimethylxanthenes 2-5 in the
presence of an exogenous phenol is described. The reaction proceeds with concurrent liberation of
phenol, is catalyzed by strong acid, and takes place at synthetically useful rates at temperatures
above 100 °C. Materials chemically related to bisphenol A, polycarbonate 10, chroman 11, and
tars generated during the manufacture of 1, behave similarly. The product xanthenes are useful
as precursors to novel xanthene polyesters such as 33 having high glass transition temperatures
relative to analogous materials based on 12 or 13. Catalytic oxidation of xanthenes 2-4 affords
highly insoluble diacids that are esterified to the esters 6-8. A mechanistic framework accounting
for the appearance of chroman 23 and spiroketal 24 as intermediates is given. Overall, the reaction
has the characteristics of a complex series of equilibria in which xanthenes such as 2 are strongly
favored.
In this paper, we describe a useful new transformation
of bisphenol A (1) into polymethylated 9,9-dimethyl-
xanthenes 2-5. The transformation is generally ap-
tion temperatures relative to analogous polyesters based
on dimethyl terephthalate (12) or dimethyl naphthalene-
2,6-dicarboxylate (13).4 Apart from the general felicity
attendant upon the appearance of a new synthetic tool,
the method described here also represents a potential
environmental advance in that it provides a single,
benign outlet for starting materials, byproducts, and post-
consumer debris generated during the manufacture and
use of polycarbonate 10.
One of the principal characteristics of bisphenol A (1)
is its tendency to undergo acid- or base-catalyzed frag-
mentation to phenol (14) and 4-isopropenylphenol (15a ).
plicable to 1 and chemically related materials exemplified
by BPA polycarbonate 10, chroman 11, and acetone, each
of which may serve as the source of the isopropylidiene
group of the product xanthenes. Exposure of 1 to excess
m- or p-cresol or 3,4-dimethylphenol (3,4-DMP) and
methanesulfonic acid (MSA) at moderate temperature
affords one of the aforementioned xanthenes in good yield
and a nearly quantitative yield of liberated phenol.
Mechanistic details of this transformation and experi-
ments illustrating its generality and utility are presented
here. Although xanthene 2 was first described in 1968
by Ourisson,1 direct synthetic approaches to polymethyl-
ated xanthenes were lacking until recently.2 We show
here that polymethylated xanthenes are readily con-
verted to the xanthenedi- and tetracarboxylates 6-9.3
The xanthene dicarboxylates 6-8 have proven useful as
precursors to novel polyesters having high glass transi-
This mode of reactivity has been used to prepare 4-iso-
5
propenylphenol itself
or substituted 4-isopropenyl-
phenols.6
In its p-quinone methide tautomeric form 15b, 4-iso-
propenylphenol is subject to reaction with a variety of
nucleophiles, including hydride,7 cyanide,8 aniline,9 or
(3) Xanthene-4,5-dicarboxylates bearing pendant alkyl groups form
the structural basis of synthetic replicators, molecular compliments
to imides and molecular clefts. Nowick, J . S.; Ballester, P.; Ebmeyer,
F.; Rebek, J ., J r. J . Am. Chem. Soc. 1990, 112, 8902. Park, T. K.;
Schroeder, J .; Rebek, J ., J r. Ibid. 1991, 113, 5125. Park, T. K.; Feng,
Q.; Rebek, J ., J r. Ibid. 1992, 114, 4529.
† This paper is dedicated to Professor Nikolaus H. Fischer.
X Abstract published in Advance ACS Abstracts, February 1, 1997.
(1) Xanthene 2 was produced as a minor byproduct in the condensa-
tion of pulegone with orcinol followed by dehydrogenation-hydro-
genolysis of the intermediate 1-hyrdoxy-3,6,9,9-tetramethyl-5,6,7,8-
(4) Caruso, A. J .; Lee, J . L. US Patent 5,466,777, Nov 14, 1995;
5,504,184, Apr 2, 1996.
(5) Corson, B. B.; Heintzelman, W. J .; Schwartzman, L. H.; Tief-
enthal, H. E.; Lokken, R.J .; Nickels, J . E.; Atwood, G. R.; Pavlik, F. J .
J . Org. Chem. 1958, 23, 544. Inoue, K. US Patent 4,594,459, J un 10,
1986. Nagayo, T.; Otsubo, T.; Kuno, S.; Iimuro, S. J P 62,148,441, J ul
2, 1987; Chem. Abstr. 1988, 109, 149054x. Crivello, J . V.; Ramdas, A.
J . J . Mater. Sci. Pure Appl. Chem. 1992, A29(9), 753.
(6) Tashiro, M.; Watanabe, H.; Oe, K. Org. Prep. Proced. Int. 1975,
7, 189.
tetrahydroxanthene1a or in
a phosphorus oxychloride-mediated
condensation reaction between m-cresol and acetone, which gave 2 in
2.5% yield.1b (a) Ourisson, G.; Chazan, J . B. Bull. Soc. Chim. Fr. 1968,
1374. (b) Ibid. 1968, 1384.
(2) Xanthene dianhydrides related to 9 show promise as components
of nearly rodlike polyimides. Trofimenko, S. US Patent 5,051,520, Sept
24, 1991. Auman, B. C.; Trofimenko, S. Macromolecules 1994, 27, 1136.
(7) Olah, G. A.; Kaspi, J .; Meidar, D. Synthesis 1978, 396.
S0022-3263(96)01766-5 CCC: $14.00 © 1997 American Chemical Society

Preparation of Polysubstituted 9,9-Dimethylxanthene
J . Org. Chem., Vol. 62, No. 4, 1997 1059
another phenol.10 Upon heating under neutral condi-
tions, 15a dimerizes in an apparent ene reaction and
undergoes linear trimerization under selected acidic
conditions.11 Upon vigorous treatment with acid neat 1
has been shown to afford indan dimer 16 and spirobi-
indan bisphenol 17 in high yield, presumably via the
intermediate 15a .12
Over the course of several hours, the mixture of
products was transformed into a single major, high-
boiling component that was found to be 3,6,9,9-tetra-
methylxanthene (2).1 We found no evidence for the
formation of spirobiindan 17.14 When carried out on a
50 g scale, 1 was converted cleanly to crude xanthene 2
as a distillable, waxy, off-white solid in 72% yield. The
primary contaminant was 3,9,9-trimethylxanthene (25).
Two of the initially formed products in this reaction were
identified by GCMS and assigned structures 23 and 24,
respectively. Chroman 23 was prepared independently15
by condensation of acetone with m-cresol in the presence
of HCl. Spiroketal 2416 was obtained from the initial
product mixture by column chromatography. When
resubjected to the reaction conditions, each of compounds
23 and 24 afforded tetramethylxanthene 2 in high yield.
A kinetic profile for the reaction of 1 with m-cresol and
MSA is given in Figure 1 below. It illustrates the
intermediacy of compounds 23 and 24 and three other
intermediates (labeled unknowns 1-3).
Given its proclivity to fragmentation to 15a , we were
confident that novel bisphenols 21 could be prepared from
1 upon acid treatment in the presence of excess substi-
tuted phenol. As had been demonstrated earlier by
Mark,10a capture of 15a by an exogenous phenol 18 gives
first a mixed bisphenol 19. A further cycle of fragmenta-
tion and capture affords a new bisphenol 21 via the
substituted isopropenylphenol 20. We anticipated that
materials containing embedded BPA moieties such as
polycarbonate 10 or other phenol-acetone condensation
products,13 isomeric bisphenols, trisphenols, and chro-
mans, generated as byproducts in the manufacture of 1
might behave similarly.
A mechanistic framework that accounts for both the
formation of xanthene derivative 2 from BPA through
the intermediacy of chroman 23 and spiroketal 24 is
given below. Bisphenol A fragments to 15a , the isopro-
penyl group of which is transferred efficiently to the
m-cresol solvent to give 27a 17 via the mixed bisphenol
26. Capture of 27a by excess m-cresol gives the o,o-
bisphenol 28, which undergoes acid-catalyzed dehydra-
tion to give product 3,6,9,9-tetramethylxanthene (2). The
(10) (a) o-Cresol, 2,6-dimethylphenol, p-cresol, 2,3,6-trimethylphenol,
and 2,6-dichlorophenol: Mark, V.; Hedges, C. V. US Patent 4,560808,
Dec 24, 1985. (b) Catechol: Tomioka, A.; Nakanishi, H.; Kuwana, K.;
Kamiya, Y.; Hanabatake, M.; Oi, S. J P 02,172,936, Dec 26, 1988; Chem.
Abstr. 1990, 113, 221391g. (c) 2,6-Diphenylphenol: Wang, Z. Y.; Hay,
A. S. Synthesis 1989, 471. (d) Resorcinol: Ito, M.; Iimuro, S. J P
04,364,147, Oct 8, 1990; Chem. Abstr. 1993, 118, 233643g.
(11) Farnham, A. G. US Patent 3,288,864, Nov 29, 1966.
(12) Curtis, R. F. J . Chem. Soc. 1962, 415. Krimm, H.; Buysch, H.
J . Ger. Offen. 2,645,020, Apr 13, 1978; Chem. Abstr. 1978, 89, 24036e.
Faler, G. R.; Lynch, J . C. US Patent 4,701,566, Oct 20, 1987.
(13) Neumann, F. W.; Smith, W. E. J . Org. Chem. 1966, 31, 4318.
(14) Spirobiindan 17 was found to be stable under the reaction
conditions.
Initially, we observed that 1 upon treatment with
excess m-cresol, 22, containing methanesulfonic acid, was
rapidly transformed at 150 °C into a suite of high-boiling
products and a nearly quantitative yield of liberated
phenol.
(15) Baker, W.; Besly, D. M. J . Chem. Soc. 1940, 1103.
(16) Baker, W.; Besly, D. M. J . Chem. Soc. 1939, 195. Baker, W.;
McOmie, J . F. W.; Wild, J . H. Ibid. 1957, 3060.
(8) Morgan, T. A. US Patent 4,806,673, Feb 21, 1989.
(9) Krimm, H.; Ruppert, H.; Schnell, H. US Patent 3,418,371, Dec
24, 1968. Hefner, R. E., J r. US Patent 4,683,276, J ul 28, 1987.
(17) Divakar, K. J .; Rao, A. S. Synth. Commun. 1976, 6, 423.

1060 J . Org. Chem., Vol. 62, No. 4, 1997
Caruso and Lee
appearance of chroman 23 and spiroketal 24 as inter-
mediates is consistent with a complex series of equilibria
in which tetramethylxanthene 2 is strongly favored.
Chroman 23 is thought to be the product of a Diels-Alder
reaction of 27a with its tautomer 27b. Loss of m-cresol
from 23 affords the presumed intermediate, chromene
29, which suffers a second Diels-Alder reaction with 27b
to give spiroketal 24.
F igu r e 1. Kinetic profile of the reaction of BPA with m-cresol
containing methanesulfonic acid at 150 °C.
Ta ble 1. Con ver sion of BP A to Xa n th en es 2-5.
Su bstr a tes, Ca ta lyst Loa d in g, Rea ction Con d ition s,
P r od u cts, a n d P r od u ct Yield s
mole
ratio
BPA/cat. (°C) (h)
yield
time phenol
product
yield(s)
(%)
T
entry
RPhOH
m-cresol
(%)
prod
1
2
3
4
5
6
7
8
9
29
125 17
79
95
96
92
81
95
0
92
100
c
2
2
2
2
2
2
2
2
3
5
5
12.5
42
60.4
79.5
2
72
0b
57
48
57d
c
m-cresol
m-cresol
m-cresol
m-cresol
m-cresol
m-cresol
m-cresol
p-cresol
1.1
1.1
1.1
55a
1.1
150
150
1
3
150 23
145 17
150 50
No Cat. 150 41
A significant side reaction in xanthene formation from
bisphenol A involves capture of 2-isopropenyl-5-methyl-
phenol (27a ) by phenol to give the o,o-bisphenol 30, which
upon dehydration affords the known1 trimethylated
product 25.
2.2
2.2
2.1
2.1
3.1
100 71.5
150 15
100 40
100 71
150 12
135 45
140 52
10 3,4-DMP
11 3,4-DMP
12 2,4-DMP
100
68
0
13 m-,p-cresol (1:1) 3.9
90 2, 3, 4e 62
14 o-cresol
2.0
96
0
a
Catalyst was Nafion fluorinated sulfonic acid resin. Other-
b
wise, the catalyst was CH3SO3H. In the absence of catalyst
recovery of BPA was quantitative. c Yield of product (phenol or
d
xanthene) was substantial but was not made quantitative. Yield
of crude product. e As a 1.9:1:4.8 mixture of tetramethylxanthenes
2, 3, and 4.
10-12:1. Excess m-cresol can be recovered by distillation
and reused. Liberated phenol may be recovered from the
m-cresol using a known extractive distillation proce-
dure.20
In range-finding studies various alkylated phenols,
catalyst loadings, reaction times, and temperatures were
examined. Substrates, reaction conditions, products, and
yields are gathered in Table 1. Xanthene formation
works well for both m- and p-cresol as well as 3,4-
dimethylphenol, which afford tetramethylxanthenes 2
and 3 and hexamethylxanthene 5, respectively. Best
yields of 3,6,9,9-tetramethylxanthene (2) are obtained at
150 °C when substantial amounts of methanesulfonic
acid catalyst are used and as the reaction time ap-
proaches 24 h (Table 1, entries 1-4). The reaction does
not occur in the absence of a catalyst, in which case BPA
is recovered unchanged (Table 1, entry 7). BPA itself is
highly sensitive to other acidic catalysts under these
conditions (Table 1, entry 5). In all cases, the trimethyl-
ated product 25 or its equivalent was present as a
An attempt at continuous removal of phenol from the
reaction mixture during the preparation of tetramethyl-
xanthene 3 from 1 and p-cresol led to the formation of
the known unsubstituted xanthene 3118 (mp 165-167 °C
(lit.18 mp 165 °C)) as a major byproduct whose structure
was confirmed by its transformation to xanthone diacid
32.19 Compound 31 appears to result from oxidation of
p-cresol followed by methylene group transfer to excess
p-cresol and dehydration under the reaction conditions.
The formation of trimethylxanthenes such as 25 could
be suppressed using more dilute reaction conditions.
Typically, we used 1.0 L of m-cresol per 50 g of BPA
employed. Under these conditions, we obtained product
polymethylated xanthenes 2 and 25 in a ratio of about
(18) Reilly, J ; Drumm, P. J .; Barrett, H. S. B. J . Chem. Soc. 1927,
67.
(20) Wust, A.; Hammerstroem, K. US Patent 4,325,789, Apr 20,
1982.
(19) Pfeifer, J .; Duthaler, R. US Patent 4,714,669, Dec 22, 1987.

Preparation of Polysubstituted 9,9-Dimethylxanthene
J . Org. Chem., Vol. 62, No. 4, 1997 1061
significant (5-10%) impurity in the product xanthene.
The reaction fails unaccountably when either 2,4-di-
methylphenol or o-cresol is employed (Table 1, entries
12 and 14). Although 1 is converted quantitatively to
phenol in the presence of acid and excess o-cresol little
or no polymethylated xanthene product is observed
(Table 1, entry 14).
A tetramethylxanthene 4 having its benzylic methyl
groups arrayed along the “long axis” of the molecule may
be obtained as the principle component in a mixture with
xanthenes 2 and 3 by reaction of BPA with a 1:1 mixture
of m- and p-cresol (Table 1, entry 13).
materials will be described in detail elsewhere.26 For the
present, we note that xanthene polyesters based on
diesters 6-8 range from amorphous to crystalline ma-
terials and show significantly higher glass transition
temperatures than the corresponding dimethyl tere-
phthalate 12 or naphthalene-2,6-dicarboxylate 13-based
polymers. Thus, poly(ethylenexanthene-3,6-dioate) (33)
gave a tough transparent film when molded on a Carver
press, was amorphous, and displayed a glass transition
temperature of 164 °C.27
The conversion of bisphenol A to polymethylated xan-
thenes with liberation of phenol holds potential for
recovery of material values from debris generated in the
manufacture of bisphenol A polycarbonate. For example,
mixtures of condensation products of phenol with acetone
(BPA tars)21 consisting primarily of mixtures of bisphenol
A(1) with its o,p-isomer and chroman 11 are converted to
substantially pure tetramethylxanthene 2 with con-
comitant liberation of phenol (see the Experimental
Section).22 Pure chroman 11 is also converted to xan-
thene 2 and phenol though somewhat less efficiently than
BPA under typical reaction conditions. We have found
as well that a variety of BPA polycarbonate-containing
materials can serve as latent sources of BPA for the
xanthene-forming reaction, and an example of this
process is given in the Experimental Section.
Although one can envision a host of uses for poly-
methylated 9,9-dimethyl xanthenes 2-5, compounds that
are stable at high temperature and have an agreeable
odor relative to the malodorous parent 9,9-dimethyl-
xanthene,23 we focused on their utility as precursors to
the corresponding dicarboxylic acids for use in polymer
synthesis. Benzylic oxidation of tetramethylxanthenes
2-4 using a variant of the Mid-Century process24 fol-
lowed by Fischer esterification afforded new 9,9-di-
methylxanthene dicarboxylic esters 6-8. Efforts to
oxidize hexamethylxanthene 5 catalytically were ham-
pered by the complexity of the product mixtures obtained.
Tetraester 9 was obtained upon treatment of hexa-
methylxanthene 5 with a stoichiometric amount of
Na2Cr2O7 in water at 250 °C under autogenous pressure
of 595 psi followed by esterification.25
In conclusion, a new and useful reaction of bisphenol
A (1) with substituted phenols in the presence of meth-
anesulfonic acid has been evaluated. The method allows
the efficient large-scale preparation of product poly-
methylated 9,9-dimethylxanthenes, which we have shown
to be readily converted to xanthene di- and tetracarbox-
ylic esters. The diesters can be converted to novel
polyesters having markedly higher glass transition tem-
peratures than analogous materials based upon conven-
tional diesters 12 and 13. The synthetic methodology
developed offers a unique opportunity to create poten-
tially useful new materials such as polyester 33 from
waste materials generated during the manufacture and
use of BPA polycarbonate 10.
Exp er im en ta l Section
The di- and tetraacid intermediates are highly in-
soluble and are conveniently isolated in pure form from
the reaction mixture by filtration. In the case of tetra-
methylxanthene 4, obtained initially as a 2:1:4.7 mixture
of xanthenes 2, 3, and 4, respectively, catalytic oxidation
affords the corresponding mixture of diacids. The in-
solubility of the diacids plays an important role in the
removal of undesired monoacids derived from trimeth-
ylated products such as 25, which are found in all
xanthenes prepared from BPA or a BPA-like material
capable of releasing phenol under acidic conditions.
The esters 6-9 are soluble and are readily converted
into novel polyesters4 using standard melt polymerization
techniques. The preparation and properties of these new
Gen er a l Meth od s. Melting points are uncorrected. 1H
and 13C NMR were measured in CDCl3 on a GE-QE 300
instrument unless otherwise indicated. Chemical shifts are
reported in ppm relative to tetramethylsilane (0 ppm). Reac-
tion progress was followed by GC and/or TLC. In nonprepara-
tive experiments, yields were determined by GC using an
internal standard, biphenyl or tetradecane, together with an
independently derived calibration table. Small-scale reactions
were carried out in 20 mL screw cap vials equipped with
magnetic fleas. Bisphenol A tar and chroman 11 starting
materials were obtained from GE Plastics, Mt. Vernon, IN.
Glass transition temperatures (Tg’s) and some melting points
were determined by differential scanning calorimetry (DSC).
P r epa r a tion of 3,6,9,9-Tetr a m eth ylxa n th en e (2).1 Gen -
er a l Meth od . The following procedure is generally applicable
to the preparation of xanthenes 2-5 from bisphenol 1, poly-
carbonate 10, chromans 11 and 23, spiroketal 24, BPA tars,
and acetone. Following the progress of the reaction by GC is
recommended in order to assure complete conversion of
(21) Carnahan, J . C. US Patent 4,277,628, J ul 7, 1981.
(22) Caruso, A. J .; Lee, J . L. US Patent 5,430,199, J ul 4, 1995.
(23) Zaugg, H. E.; Michaels, R. J . J . Org. Chem. 1974, 39, 351.
Mesiters, A.; Mole, T. Aust. J . Chem. 1974, 27, 1655.
(24) Ebner, J .; Reily, D. In Active Oxygen in Chemistry; Foote, C.
S., Silverstone-Valentine, J ., Greenberg, A., Liebman, J . F., Eds.;
Chapman & Hall: Glasgow, 1995. Oxidations of this type are con-
veniently carried out as described in: Wheeler, T. N.; Craig, T. A.;
Morland, R. B.; Ray, J . A. Synthesis 1987, 883.
(26) Caruso, A. J .; Lee, J . L. manuscript in preparation.
(27) Tg’s for the corresponding polyesters based on ethylene glycol
and dimethyl terephthalate (PET) and ethylene glycol and dimethyl
naphthalene-2,6-dioate (PEN) are 81 and 125 °C, respectively. Yoon,
K. H.; Lee, S. C.; Park, O. O. Polymer J . 1994, 26, 816.
(25) Friedman, L. Org. Synth. 1963, 43, 80.

1062 J . Org. Chem., Vol. 62, No. 4, 1997
Caruso and Lee
intermediates to the product xanthenes. Bisphenol A (1)
(50.00 g, 0.219 mol), m-cresol (1.0 L, 9.56 mol), and methane-
sulfonic acid (19.00g, 0.198 mol) were charged to a 2 L flask
equipped with a reflux condenser, nitrogen inlet, and magnetic
stir bar. The flask was then heated to 130-150 °C for 24 h.
After cooling, the reaction vessel was fitted with a distillation
head and most of the m-cresol and liberated phenol were
distilled away at ∼1 Torr. A 95% yield of phenol was obtained
in the distillate as judged by quantitative GC using biphenyl
as an internal standard. The residue was dissolved in toluene
(500 mL), washed with 5% NaOH, and water, dried over
MgSO4, concentrated under reduced pressure, and distilled
through a Vigreux column at 1 Torr to give a fraction boiling
at 160-178 °C as a 10:1 mixture of tetramethylxanthene 2
and trimethylxanthene 25 (41.35 g, 91% purity, 0.158 mol, 72%
yield) as a waxy white solid. Recrystallization from MeOH
afforded an analytical sample of 2: mp 59-60 °C (lit.1b mp
6.76 (d, d, J ) 2, 8 Hz; 2H), 6.50 (br d, J ≈ 2 Hz, 2H), 1.98 (s,
6H), 2.08 (d, J ) 14 Hz, 2H), 1.95 (d, J ) 14 Hz, 2H), 1.60 (s,
12H) ppm; 13C-NMR 150.2, 136.8, 128.4, 126.1, 122.4, 118.0,
97.7, 46.7, 32.5, 32.3, 30.5, 20.9 ppm; IR 2968, 2936, 1625,
1581, 1512, 1144, 1030, 889, 812 cm-1; HRMS calcd for
C23H28O2 336.2089, found 336.2084.
Xa n th en e 2 fr om Sp ir ok eta l 24. Spiroketal 24 (54 mg,
purity ) 97%, 0.155 mmol) was heated at 145-150 °C for 22
h with a stock solution of m-cresol containing methanesulfonic
acid (MSA) (2.0 mL, [MSA] ) 19 mg/mL). After cooling, the
reaction mixture was assayed quantitatively by GC for tetra-
methylxanthene 2 (101.5 mg, 0.43 mmol, 92%).
Con ver sion of Ch r om a n 23 to Tetr a m eth ylxa n th en e
2. Chroman 2315 (100 mg, 0.34 mmol), m-cresol (2.0 mL),
methanesulfonic acid (23.9 mg, 0.25 mmol), and tetradecane
(100.7 mg) were heated at 150 °C for 21.5 h, at which time
quantitative gas chromatography indicated complete conver-
sion to 2 (151.7 mg, 0.64 mmol, 94%).
1
61-62 °C); H-NMR 7.27 (d, J ) 8 Hz, 2H), 6.86 (br m, 4H),
2.32 (s, 6H), 1.56 (s, 6H); 13C-NMR 21.0, 32.7, 33.4, 116.7,
123.8, 123.9, 126.0, 127.1, 150.2 ppm; IR 3035, 2969, 2920,
1634, 1615, 1590, 1566, 1498, 1411, 1306, 1264, 1170, 878, 812
cm-1; HRMS calcd for C17H18O 238.1358, found 238.1359.
Xanthene 2 was further characterized by its conversion to
diester 6 (see below).
Xa n th en e 2 a n d P h en ol fr om P ost-Con su m er P olyca r -
bon a te. Flakes of post-consumer, crushed polycarbonate milk
jug (100 mg, ∼0.39 equiv of BPA), m-cresol (2.0 mL, 19.1
mmol), and methanesulfonic acid (22 mg, 0.23 mmol) afforded
after 20.5 h at 150 °C phenol (72 mg, 0.77 mmol, 98%) and
tetramethylxanthene 2 (83.9 mg, 0.35 mmol, 90%).
Xa n th en e 2 a n d P h en ol fr om BP A Ta r . A mixture of
BPA tar (10.46 g) consisting of (wt %) 30% BPA 1, 40% o,p-
BPA; 10% chroman 11, and a suite of other phenol-acetone
condensation products13 (20%); m-cresol (150 mL, 1.435 mol);
and methanesulfonic acid (1.482 g, 15.4 mmol) gave after 4.5
h at 150-155 °C and distillation recovered m-cresol containing
phenol (7.40 g, 78.72 mmol). On the basis of a molar ratio of
residual phenol- and acetone-derived components of from 1.5-
2.0 in the BPA tar we estimate the yield of phenol to be 86-
92%. The pot residue gave upon workup a 41:8:1(HPLC)
mixture (9.30 g) of tetramethylxanthene 2, trimethylxanthene
25, and the parent 9,9-dimethylxanthene. A portion of this
material was vacuum distilled to give a fraction boiling at
160-190 °C (1 Torr) as a 6.8:1 mixture of xanthenes 2 and 25
(7.435 g). A portion of this material (5.00 g, 18.44 mmol of 2)
was converted via catalytic oxidation (see general method
below) to 9,9-dimethylxanthene-3,6-dicarboxylic acid (3.574 g,
11.99 mmol, 65%) as a highly insoluble white powder: mp >
326 °C; 1H-NMR(DMSO-d6) 13.03 (br s, 2H), 7.68 (s, 4H), 7.56
(s, 2H), 1.61 (s 6H) ppm; 13C-NMR 166.6, 149.3, 134.2, 130.6,
127.3, 124.4, 116.8, 34.4, 31.9 ppm; IR 2969, 2677, 2568, 1689,
1419, 1300 cm-1; HRMS calcd for C17H14O5 298.0840, found
298.0841.
2,7,9,9-Tetr a m eth ylxa n th en e (3). BPA (103.10 g, 0.452
mol), methanesulfonic acid (20.28 g, 0.21 mol), and p-cresol
(2.0 L) afforded after workup crude xanthene 3 (147.7 g) as a
dark oily solid. Vacuum distillation (∼1 Torr) gave a fraction
boiling at 138-140 °C shown by GCMS to be a 10:1 mixture
(15.37 g) of xanthene 3 (13.99 g, 58.8 mmol, 13%) and 2,9,9-
trimethylxanthene. Recrystallization (MeOH) afforded an
1
analytical sample: mp 95-96 °C; H-NMR 7.16 (br d, J ≈ 2
Hz, 2H), 6.95 (d, d, J ) 2, 8 Hz, 2H), 6.90 (d, J ) 8 Hz, 2H),
2.30 (s, 6H), 1.59 (s, 6H) ppm; 13C-NMR 21.1, 32.6, 34.0, 116.2,
126.6, 128.1, 129.8, 132.1, 148.5 ppm; IR 2972, 2926, 1488,
1297, 1258, 816 cm-1; HRMS calcd for C17H18O 238.1358, found
238.1364. This material was further characterized by its
conversion to diester 7.
Tetr a m eth ylxa n th en e 3 fr om Aceton e a n d p-Cr esol.
Acetone (397 mg, 6.84 mmol), p-cresol (10.34 g, 95.6 mmol),
and MSA (122 mg, 1.27 mmol) were heated at 135 °C for 90 h.
The reaction mixture was diluted with toluene (50 mL),
washed with 10% NaOH solution (3 × 100 mL) and water,
dried (MgSO4), and concentrated under reduced pressure to
afford crude xanthene 3 (1.122 g) as a dark oil that crystallized
upon exposure to a trace of crystalline 3. Recrystallization
(MeOH) gave pure 3 (583 mg, 2.45 mmol, 36%), mp 95-96
°C.
2,6,9,9-Tetr a m eth ylxa n th en e (4) (a s a Mixtu r e w ith
Xa n th en es 2 a n d 3). Bisphenol A (27.36 g, 0.12 mol),
m-cresol (150 mL, 1.43 mol), p-cresol (150 mL, 1.43 mol), and
methanesulfonic acid (2.96 g, 30.9 mmol) gave an oily melange
of tetramethylxanthenes 2, 3, and 4 (21.89 g). A portion of
this material (19.89 g) was distilled (∼1 Torr) to give a fraction
boiling at 160-175 °C, which was shown by GCMS to consist
of a 1.9:1:4.8 mixture of xanthenes 2, 3, and 4 (17.742 g, 75.4
mmol, 62%), respectively, containing 3,9,9-trimethylxanthene
(25) and 2,9,9-trimethylxanthene as the principal impurities.
The identity of xanthene 4 in this mixture was confirmed by
its conversion to pure diester 8 (see below).
2,3,6,7,9,9-Hexa m eth ylxa n th en e (5). BPA (100.0 mg,
0.439 mmol), 3,4-dimethylphenol (2.000 g, 16.39 mmol), and
MSA (20 mg, 0.21 mmol) were heated at 100 °C for 40 h. The
product mixture was diluted with toluene, washed with 10%
NaOH and water, dried over MgSO4, and concentrated under
reduced pressure to give 52 (67.3 mg, 0.25 mmol, 57%) as a
brown solid: 1H-NMR 7.12 (s, 2H), 6.81 (s, 2H), 2.23 (s, 6H),
2.22 (s, 6H), 1.59 (s, 6H) ppm.
Hexa m eth ylxa n th en e 5 fr om Aceton e. A mixture of 3,4-
dimethylphenol (1.50 kg, 12.2 mol), acetone (47.30 g, 0.815
mol), and methanesulfonic acid (9.45 g, 98.3 mmol) was heated
at 100-120 °C for 120 h and then at 150 °C for 7 h. Removal
of excess 3,4-dimethylphenol by distillation (∼1 Torr) and
workup gave a dark waxy solid that was placed on a fritted
funnel and washed with MeOH to afford a 4.8:1 mixture
(100.99 g) of hexamethylxanthene 52 and 4,4,4′,4′6,7,6′,7′-
octamethylspirobichroman (34).16 This product mixture was
used to prepare tetraester 9 (see below). The mixture (10.00
g) was slurried in boiling methanol (300 mL) and filtered on a
fritted funnel. The filtrate was set aside and afforded grayish
Xa n th en e 2 a n d P h en ol fr om Ch r om a n 11. Chroman
11 (100.0 mg, 0.373 mmol), m-cresol (2.0 mL, 19.1 mmol), and
methanesulfonic acid (19 mg, 0.20 mmol) gave after 39 h at
150 °C phenol (38.5 mg, 0.41 mmol, 55%) and 3,6,9,9-tetra-
methylxanthene 2 (34.2 mg, 0.14 mmol, 19%).
P r ep a r a tion of Sp ir ok eta l 24. A three-neck, 2.0 L flask
equipped as in the general example above was charged with
bisphenol A (1) (105.30 g, 0.461 mol), m-cresol (1020.68 g, 9.438
mol) and tetradecane (61.32 g, 0.309 mol, GC ISTD). The
mixture was warmed to 100 °C, and methanesulfonic acid (1.53
g, 0.016 mol) was added. The mixture was then heated at 150
°C for 10 h. At this point, gas chromatography of the reaction
mixture revealed a 3.4:1 mixture of tetramethylxanthene 2 and
spiroketal 24. Excess m-cresol was distilled off at 1 Torr. The
pot residue was dissolved in toluene, washed with 10% NaOH
solution, water, and brine, dried over MgSO4, and concentrated
under reduced pressure to give the crude product as a dark
brown oil (76.43 g). A portion of this material (3.10 g) was
subjected to column chromatography on silica gel (152 g) in
hexane-toluene (6:1) to give spiroketal 24 (502 mg, 1.49 mmol,
24% contained yield). Recrystallization (MeOH) gave an
analytical sample: mp 125-131 °C (lit.1b mp 125.5-127.5 °C;
132-133 °C, dimorphic solid); 1H-NMR 7.20 (d, J ) 8 Hz, 2H),
crystals (5.02 g) of
a
7:1 mixture of hexamethyl-
xanthene and 34. The methanol-insoluble solid was
5

Preparation of Polysubstituted 9,9-Dimethylxanthene
J . Org. Chem., Vol. 62, No. 4, 1997 1063
again slurried in boiling MeOH, filtered, and air dried to give
(d, J ) 8 Hz, 1H), 7.09 (d, J ) 8.5 Hz, 1H), 3.93 (s, 3H), 3.92
(s, 3H) 1.68 (s, 6H) ppm; IR 2975, 2950, 1730, 1720, 1615, 1605,
1575, 1442, 1435, 1417, 1275, 1208, 1122, 1078, 1000, 940, 922,
892, 829, 763, 728 cm-1; UV (MeOH) λ ) 245 nm (log ꢀ ) 4.35),
272 nm (log ꢀ ) 4.26); HRMS calcd for C19H18O5 326.1154,
found: 326.1138.
pure 34 (330 mg, 0.91 mmol) as a snow white solid: mp 197-
1
199 °C (lit.16 mp 199-200 °C); H-NMR 7.04 (s, 2H), 6.48 (s,
2H), 2.18 (s, 6H), 2.09 (s, 6H), 2.05 (d, J ) 13.8 Hz, 2H), 1.92
(d, J ) 13.8 Hz, 2H), 1.59 (s, 6H), 1.33 (s, 6H) ppm; HRMS
calcd for C25H32O2 364.2402, found 364.2428.
Gen er a l P r oced u r e for Oxid a tion a n d Ester ifica tion
of Xa n th en es 2-5. Dim eth yl 9,9-d im eth ylxa n th en e-3,6-
d ica r boxyla te (6). Tetramethylxanthene 2 (11.88 g, 90%
purity, 44.9 mmol), Co(OAc)2(H2O)4 (127 mg, 0.51 mmol),
Mn(OAc)2‚(H2O)4 (128 mg, 0.52 mmol), di-tert-butyl peroxide
(248 mg, 1.70 mmol), 48% HBr (248 mg), and acetic acid (125
mL) were charged to a 500 mL autoclave equipped for stirring
and pressurized to 300 psi with oxygen. The stirred mixture
was maintained at 130-170 °C for 4 h. The reaction is
sufficiently exothermic to generate an internal temperature
of 160-170 °C once it initiates at about 130 °C. Additional
O2 was added to maintain an internal pressure of 250-300
psi. After cooling, the vessel was vented and the product
collected on a fritted funnel and washed with water to give
after air drying 9,9-dimethylxanthene-3,6-dicarboxylic acid
(10.456 g, 35.1 mmol, 78%) as a white solid, mp > 326 °C. The
diacid (8.870 g, 29.7 mmol), methanol (225 mL), and concen-
trated H2SO4 (1.5 mL) were heated to reflux for 8 h. The
reaction mixture was cooled in an ice bath, and the orange
crystalline solid was collected by filtration, washed with water,
and air dried to afford ester 6 (8.62 g, 26.4 mmol, 90%).
Recrystallization (i-PrOH) afforded an analytical sample: mp
Tet r a m et h yl 9,9-Dim et h ylxa n t h en e-2,3,6,7-t et r a ca r -
boxyla te (9). To a high-pressure bomb equipped for stirring
.
was added Na2Cr2O7 2H2O (188 g, 630 mmol), water (200 mL),
and a 4.8:1 mixture of hexamethylxanthene 5 and 34 (44.80 g
total, 34.85 g, 130.8 mmol of 5). The reactor was sealed and
heated to 250 °C under autogenous pressure at ∼600 psi for
19 h. Upon cooling, the reaction mixture was filtered to give
recovered starting material (23.2 g as a 4.2:1 mixture of
xanthene 5 and 34) and a homogeneous aqueous filtrate that
was acidified with 10% HCl to afford pure 9,9-dimethyl-
xanthene-2,3,6,7-tetracarboxylic acid as a cream-colored solid
(21.2 g, 54.9 mmol, 42%): 1H-NMR(DMSO-d6) 8.20 (s, 2H), 7.64
(s, 2H), 1.68 (s, 6H). Esterification of a portion (15.25 g, 39.5
mmol) of this material afforded tetraester 9 (8.26 g, 18.7 mmol,
1
47%) as a light green solid: mp (DSC) 152 °C; H-NMR 7.89
(s, 2H), 7.35 (s, 2H), 3.93 (s, 6H), 3.92 (s, 6H), 1.68 (s, 6H)
ppm; IR 1719, 1549, 1431, 1398, 1286,1116, 782 cm-1 13C-
;
NMR 167.3, 166.7, 151.3, 132.9, 131.4, 128.2, 126.2, 117.0,
52.6, 52,.5, 34.2, 32.3 ppm; HRMS calcd for C23H22O9 442.1264,
found 442.1268.
P oly(eth ylen e 9,9-d im eth ylxa n th en e-3,6-d ioa te) (33).
Diester 6 (2.0002 g, 6.13 mmol), ethylene glycol (571.5 mg, 9.21
mmol), and tetraethyl hexyltitanate (4.9 µL) were charged to
a 25 mL two-necked round-bottom flask equipped with a
mechanical stirrer, short-path distillation head, receiving flask,
and nitrogen inlet. The reaction vessel was purged with
nitrogen and then lowered into a salt bath preheated to 180
°C. Methanol began to distill over slowly. After 45 min at
180 °C, the bath temperature was raised to 250-280 °C and
held there for 0.5 h. After 45 min, the apparatus was attached
to the house vacuum (P ) 40-100 Torr). The reaction mixture
was visibly more viscous as the remaining excess ethylene
glycol distilled into the receiver. After 30 min at the slightly
reduced pressure (P ) 40-100 Torr), the apparatus was
evacuated (P ) 1 Torr). The contents of the reaction vessel
became very viscous, and after 45 min at 1 Torr as much of
the polymer as possible was pulled using a spatula from the
hot reaction vessel under a plume of nitrogen. The strands of
product removed were immediately immersed in water and
subsequently air dried to give polyester 33 (1.48 g, 74% of
theory, slightly yellow glass), which gave upon compression
at 280 °C on a Carver press a tough, clear film: Tg ) 163.7
°C; GPC gave Mn ) 77 970; Mw ) 241 700. The product was
soluble in chloroform: 1H-NMR 7.76 (d, d, J ) 2, 8 Hz, 2H),
7.73 (br s, 2H), 7.45 (d, J ) 8 Hz, 2H), 4.66 (s, 4H), 1.62 (s,
6H) ppm; 13C-NMR 32.0, 34.7, 62.9, 117.9, 124.5, 126.3, 129.4,
134.7, 150.1, 165.6 ppm.
1
154-155 °C; H-NMR 1.65 (s, 6H), 3.93 (s, 6H), 7.47 (d, J )
8Hz, 2H), 7.73 (br s, 2H), 7.75 (d, d, J ) 2, 8 Hz, 2H) ppm;
13C-NMR 31.9, 34.7, 52.2, 117.8, 124.4, 126.2, 129.7, 134.5,
150.1, 166.4 ppm; IR 2975, 2955, 1712, 1105, 1005, 932, 768
cm-1; HRMS calcd for C19H20O5 326.1154, found 326.1150.
Concentration of the filtrate afforded additional diester 6 (0.47
g) of lower purity (81.2% pure by HPLC).
Dim eth yl 9,9-Dim eth ylxa n th en e-2,7-d ioa te (7). Tetra-
methylxanthene 3 (14.36 g, 91.5% purity, 55.2 mmol) gave 9,9-
dimethylxanthene-2,7-dicarboxylic acid (15.22 g, 51.0 mmol,
92%) as a white solid that was fully characterized as its
dimethyl ester 7. The diacid (10.00 g, 33.5 mmol) gave diester
7 (5.72 g, 17.5 mmol, 52%) as an off-white crystalline solid:
mp 150-151 °C; 1H-NMR 8.15 (d, J ) 2 Hz, 2H), 7.91 (d, d, J
) 2, 8 Hz, 2H), 7.09 (d, J ) 8 Hz, 2H), 3.92 (s, 6H), 1.69 (s,
6H) ppm 13C-NMR 32.8, 34.1, 52.1, 116.6, 125.5, 128.7, 129.3,
129.6, 153.2, 166.5 ppm; IR 2978, 1715, 1609, 1578, 1447, 1259,
1130, 1112, 912, 843 cm-1; HRMS calcd for C19H18O5 326.1154,
found 326.1180. The filtrates afforded additional diester 7
(2.87 g, 8.8 mmol, 26%).
Dim eth yl 9,9-Dim eth ylxa n th en e-2,6-d ioa te (8). A 1.8:
1.0:4.8 mixture of xanthenes 2, 3, and 4 of 90% purity (14.50
g, 54.8 mmol) was oxidized to afford a mixture of the corre-
sponding acids, 9,9-dimethylxanthene-3,6-dicarboxylic acid,
9,9-dimethylxanthene-2,7-dicarboxylic acid, and 9,9-dimethyl-
xanthene-2,6-dicarboxylic acid, as a cream-colored solid (12.28
g, 41.2 mmol, 75%) having a mp >300 °C. A portion of this
material (4.137 g, 13.87 mmol) was esterified in MeOH to
afford the product diesters (4.05 g) as a 1:4.2:1.2 mixture of
dimethyl 9,9-dimethylxanthene-2,7-dicarboxylate (7), dimethyl
9,9-dimethylxanthene-2,6-dicarboxylate (8), and dimethyl 9,9-
dimethylxanthene-3,6-dicarboxylate (6) as a cream-colored
solid. The crude product was recrystallized twice from metha-
nol to afford pure dimethyl 9,9-dimethylxanthene-2,6-dicar-
1
Su p p or tin g In for m a tion Ava ila ble: Copies of H-NMR
data for compounds 2, 3, 5-9, 24, 33, and 34 and 13C data for
24 and 9,9-dimethylxanthene-3,6-dicarboxylic acid (17 pages).
This material is contained in libraries on microfiche, im-
mediately 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. This material can
also be requested directly from the author.
1
boxylate (8) (465 mg, 1.42 mmol, 10%): mp 145-147 °C; H-
NMR 8.14 (d, J ) 2 Hz, 1H), 7.91 (d, d, J ) 2, 8.5 Hz, 1H),
7.78 (d, d, J ) 1.8, 8.1 Hz, 1H), 7.74 (br d, J ≈ 2 Hz, 1H), 7.49
J O961766D