PROCESS FOR THE RECOVERY OF DIHYDROXYB1ARYL COMPOUNDS
CROSS-REFERENCE TO RELATED APPLICATIONS
This Application is related to the following U.S. Patent Application: U.S. Patent
Application entitled "METHOD FOR PRODUCTION OF BIS(HYDROXYAROMAT1C)
COMPOUNDS" being filed concurrently herewith under Atty Dkt. No.
133063-1, which is hereby incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
This invention relates to the reductive coupling of monohydroxyaryl halide
compounds, and more particularly, to the isolation and recovery of dihydroxybiaryl
compounds formed from such reactions.
Dihydroxybiaryl compounds, including dihydroxybiphenyls, such as 4,4'-
dihydroxybiphenyl (also referred to herein as "biphenol") and 2,2'-dimethyl-4,4'-
dihydroxybiphenyl (also referred to herein as "dimethyl biphenol") have numerous
uses in the chemical industry. For example, biphenol can be used in polymer
preparation, notably in the preparation of polycarbonates, polysulfones, polyimides,
and polyetherimides.
Dihydroxyaryl compounds can be prepared by the reductive coupling of
monohydroxyaryl halides, as described in United States Patent No. 5,177,258.
Briefly, in the synthesis of biphenol, for example, p-bromophenol is contacted with a
reducing agent, such as formic hydrazide or hydrogen, in the presence of an aqueous
base, such as sodium hydroxide, and a platinum group catalyst, preferably palladium,
which may be supported on carbon. The p-bromophenol is supplied to the reaction
with enough base to form the Na-salt, prior to coupling, and after the reaction is
complete, to have the biphenol formed exist as the Na-salt. Isolation of biphenol
requires protonation of the Na-salt with an acid, such as hydrochloric acid. This is
problematic, in part, because introduction of excess acid to the system requires
additional processing for its removal after biphenol is formed. Furthermore, when
HC1 is used for proionation, for example, the Na salt of the acid (NaCl) is formed as a
by-product. When produced on a commercial scale, NaCl is expensive to handle and
to dispose of.
Thus, improved methods for the isolation of dihydroxybiaryl compounds from their
alkali metal salts continue to be sought. In particular, it would be advantageous to
avoid the introduction of a foreign acid, such as HC1, to protonate the salt of the
dihydroxybiaryl compound. Such a process would be more economical because
fewer reagents would need to be purchased and because excess acid would not need to
be removed from the system. Furthermore, isolation of the desired dihydroxybiaryl
compound would be simplified because the need for additional processing operations
to handle the mixture resulting from the use of the foreign acid could be eliminated.
It would also be cost-effective in large scale commercial operations if the base
represented by the Na salt of the dihydroxybiaryl compound in the product mixture
could be recycled in a further reductive coupling reaction of the monohydroxyaryl
halide to form the dihydroxybiaryl compound, instead of being neutralized to form
water, as is the case when HC1 is used.
SUMMARY OF THE INVENTION
The present invention provides a novel and efficient method for preparing
dihydroxybiphenyls from their alkali metal salts. Unlike previous techniques, the
present method unexpectedly avoids the use of a foreign acid to protonate the salt of
the dihydroxybiphenyl, such as the sodium salt of biphenol, by employing the
monohydroxyaryl halide used in the initial reductive coupling reaction. In addition,
the process yields a base, i.e., the alkali metal salt of the monohydroxyaryl halide,
which can be recycled in a further reaction to make the dihydroxybiphenyl.
Therefore, in one aspect, the present invention relates to a method for preparing a
dihydroxybiaryl compound. The method comprises providing an alkali metal salt of
the dihydroxybiaryl compound, followed by contacting the alkali metal salt of
dihydroxybiaryl compound with a corresponding monohydroxyaryl halide compound.
In another aspect, the method of the present invention relates to isolating a
dihydroxybiaryl compound comprising providing an alkali metal salt of the
dihydroxybiaryl compound, followed by contacting the salt with a corresponding
monohydroxyaryl halide compound to form a precipitate in a solution. The
precipitate, which comprises the dihydroxybiaryl compound, is then separated from
the solution.
DETAILED DESCRIPTION OF THE INVENTION
Dihydroxybiaryl compounds, which can be prepared by the present method, may be
substituted or unsubstituted. Particularly useful dihydroxybiaryl compounds include
4,4'-dihydroxybiphenyl ("biphenol") and 2,2'-dimethyl-4,4' dilhydroxybiphenyl
("dimethyl biphenol"). However, the invention is not limited to the preparation of
these compounds, and other dihydroxybiaryl derivatives may be prepared by the
present method, as would be obvious to one of skill.
Initially, according to the present method, the alkali metal salt of the desired
dihydroxybiaryl compound is provided. There are many known methods for the
production of the alkali metal salt. Conventional synthetic methods include the
reductive coupling of hydroxyaryl halide compounds using a base, such as KOH or
NaOH, a metallic catalyst, such as Pd, Rh, Ru, or Ni, and a reducing agent, such as
hydrogen, sodium formate, paraformaldehyde, glycols, glycerol, methanol, or formic
hydrazide, for example. Typically, the reaction is run at a temperature ranging from
about 20(1 C to about 120" C. A molar ratio of the base to the monohydroxyaryl halide
of at least 1:1 is employed, and the amount of the catalyst needed ranges from about
0.01 and 5% of the weight of the monohydroxyaryl halide. When formic hydrazide is
employed as the reductant, a molar ratio of formic hydrazide to the monohydroxyaryl
halide ranging from about 1:4 to about 1:1 is suitable. Such processes are described
fully in the aforementioned United States Patent No. 5,177,258. Scheme 1 depicts a
conventional process for preparing the sodium salt of biphenol (I) by the reductive
coupling of p-bromophenol (11).
(Figure Removed)
The alkali metal salt of the dihydroxybiaryl compound is then contacted with a
corresponding monohydroxyaryl halide compound, i.e. one which could be used in
the aforementioned reductive coupling reaction to form the alkali metal salt of the
dihydroxybiaryl compound. The corresponding monohydroxyaryl halide compound
protonates the alkali metal salt of the dihydroxybiaryl compound, thereby producing
the desired dihydroxybiaryl product. Typically the protonation reaction occurs at a
temperature ranging from about 20° C to about 120°C. A molar ratio of the
monohydroxyaryl halide to the alkali metal salt of the dihydroxybiaryl compound of
at least 2:1 maximizes the amount of dihydroxybiaryl product.
When the reaction is complete, a precipitate containing the desired dihydroxybiaryl
compound is produced. Generally, the reaction is performed below the melting point
of the dihydroxybiaryl compound and the dihydroxybiaryl compound is substantially
insoluble in the reaction solution matrix. For example, the melting point of biphenol
is 282-284" C. The precipitate can then be separated and removed from the remaining
solution, typically by filtration, to isolate the product. If desired, the solid precipitate
can be washed with water or methanol one or more times. The precipitate can then be
transformed into a purified dihydroxybiaryl compound by recrystallizing the
precipitate in methanol, for example. As used herein, the term "purified" means
having a purity of at least 90 percent, preferably greater than 95 percent, and still
more preferably greater than 98 percent.
In one embodiment, biphenol may be prepared by providing one molar equivalent of
the sodium or potassium salt of 4,4'-dihydroxybiphenyl having formula (I), and
contacting (I) with at least two molar equivalents of p-bromophenol having structure
(11) to form one equivalent of 4,4'-dihydroxybiphenyl (III), which precipitates from
solution, and two molar equivalents of the sodium salt of p-bromophenol (IV)
according to the following Scheme 2:
(Figure Removed)
Alternatively, in the production of biphenol, p-chlorophenol could be substituted for
p-bromophenol (II) in the reaction depicted in Scheme 2. In this case, protonation
using the chloro-compound, which is slightly more acidic than the corresponding
bromo-compound, is at least as effective in acidification compared to the
bromophenol.
Other embodiments include protonation of the alkali metal salt of dimethyl biphenol
using 2-methyl-4-bromophenol or 2-methyl-4-chlorophenol. 2-Methyl-4-
bromophenol and 2-methyl-4-chlorophenol are monohydroxyaryl halides suitable for
use in the aforementioned reductive coupling reaction to form dimethyl biphenol.
The filtrate, containing the alkali metal salt of the monohydroxyaryl halide, can then
be recycled as one equivalent of the monohydroxyaryl halide and one equivalent of
the base in a further reductive coupling of the monohydroxyaryl halide to form
additional dihydroxybiary) compound, similar to the reaction described in the
previously discussed United States Patent No. 5,177,258 and depicted in Scheme 1.
The filtrate solution, along with an alkali metal hydroxide, such as sodium hydroxide
or potassium hydroxide, is contacted with a metal catalyst, such as palladium, and a
reducing agent, such as hydrogen gas, which may be bubbled into the reaction
mixture or introduced under pressure up to about 100 atm, or formic hydrazide, in
water to produce the alkali metal salt of the desired dihydroxybiaryl compound.
Additional amounts of the monohydroxyaryl halide compound may optionally be
added, but generally, the monohydroxyaryl halide initially added in the precipitation
is used in the subsequent reaction to make the dihydroxybiaryl compound. Scheme 3
depicts the present process of the invention for recycling the sodium salt of pbromophenol
(IV) produced in the protonation process depicted in Scheme 2 in the
reductive coupling of p-bromophenol to form additional amounts of the sodium salt of
biphenol.
(Figure Removed)
Briefly, the metal catalyst, preferably 5% palladium on carbon is initially stirred into a
solution containing NaOH or KOH and the filtrate containing the alkali metal salt of
the hydroxyaryl halide compound. The amount of palladium catalyst used is between
about 0.01 and 5% of the weight of the alkali metal salt of the monohydroxyaryl
halide. To this solution, the reducing agent is added. When formic hydrazide is used,
a molar ratio of formic hydrazide to the alkali metal salt of the hydroxyaryl halide
ranging from about 1:4 to about 1:1 is typical. When hydrogen gas is used as the
reductant, it is generally flowed through the solution at a pressure ranging from about
1 atm to about 100 atm. In one embodiment, hydrogen gas is employed at a pressure
ranging from about 1 atm to about 350 kilopascals, as described in the related U.S.
Patent Application entitled "METHOD FOR PRODUCTION OF B1S(HYDROXYAROMAT1C)
COMPOUNDS" being filed concurrently herewith under Atty Dkt. No.
133063-1 The reaction is typically run at a temperature ranging from about 20°-120°
C, and the alkali metal salt of the dihydroxybiaryl compound is produced again. In
the present process, a molar ratio of the alkali metal hydroxide to the alkali metal salt
of the monohydroxyaryl halide of at least 1:1 maximizes the production of the alkali
metal salt of the dihydroxybiaryl compound. The procedure outlined above for
protonating the alkali metal salt of the dihydroxybiaryl compound with the
monohydroxyaryl halide compound can then be followed again.
In the above Scheme 2, the sodium salt of p-bromophenol (IV) (or the alkali metal salt
of p-chlorophenol, not shown) is formed in the filtrate, which can then be used as one
equivalent of the base and one equivalent of the monohydroxyaryl halide, in the
preparation of biphenol (sodium salt initially) by the reductive coupling of pbromophenol
(or p-chlorophenol), shown in Scheme 3. In other embodiments, the
sodium or potassium salt of 2-methyl-4-bromophenol or 2-methyl-4-chlorophehol
may be formed in the filtrate, each of which could then be used as the base in a
coupling reaction with 2-methyl-4-bromophenol or 2-methyl-4-chlorophenol,
respectively, to form dimethyl biphenol.
The following examples are given by way of illustration and are not intended to be
limitative of the present invention. The reagents, reactants, and catalysts used in the
reactions described herein are readily available materials.
EXAMPLE 1
To a round bottom flask equipped with a magnetic stir bar was charged 1.073.g (5.76
mmol) of biphenol and 0.476 g (11.9 mmol) of NaOH and 9.102 g of water. A clear
yellowish solution containing the sodium salt of biphenol was formed.
EXAMPLE 2
To the solution containing the sodium salt of biphenol from Example 1, 2.09 g (12.08
mmol) of p-bromophenol were added, and a precipitate formed. The solution
containing the precipitate was then filtered, and the solid was recovered. HPLC
analysis of the solid indicated that it contained 94.2% biphenol. Approximately,
0.8603 g were recovered, representing a 76% overall recovery.
EXAMPLE 3
The procedure of Example 2 was followed, except that prior to filtering, 9.91 g of
water and 1.29 g of methanol were added to the solution to assist in preventing phase
separation, and a fraction of the resulting solution (5,68 g) was filtered to separate the
solid. An excess of 37% HC1 (0.5695 g, molar amount needed to neutralize base was
0.2824 g) was added to the filtrate to neutralize all the base present, and the pH was
measured to be around 0. The resulting solution had a small amount of solid present,
and 8.245 g of methanol were added to achieve complete dissolution. This solution
was then analyzed by HPLC for biphenol and p-bromophenol. The analysis showed
the ratio of p-bromophenol to biphenol to be around 20:1 (3.41% to 0.17%) by
weight, compared with the expected number of about 2:1 (2.09:1.073=1.94:1) if
protonation had not occurred. The expected p-bromophenol concentration was
3.42%. The expected composition of biphenol if it were all still present would be
1.75%. This indicates that the majority of the biphenol present was eliminated by the
precipitation process (90% precipitation of biphenol).
EXAMPLE 4
A coupling reaction to produce biphenol is performed by charging a round bottom
flask equipped with a magnetic stir bar with 0.6 part of palladium catalyst (5% by
weight on carbon), 2.5 parts of the sodium salt of 4-bromophenol produced in the
filtrate of Example 2, and 2.5 parts NaOH. After stirring for five minutes, 3 parts of
formic hydrazide is added, and the mixture is stirred for 10 minutes. While stirring,
the mixture is heated to 85° C, and the temperature is maintained for 30 minutes. Two
and 1/2parts (2.5) parts 4-bromophenol is then added, and a precipitate containing
biphenol forms. The precipitate is filtered from the solution and washed with
methanol. Purified biphenol having a purity of at least 90% is then obtained by
recrystallizing the precipitate in methanol.
While typical embodiments have been set forth for the purpose of illustration, the
foregoing descriptions and examples should not be deemed to be a limitation on the
scope of the invention. Accordingly, various modifications, adaptations, and
alternatives may occur to one skilled in the an without departing from the spirit and
scope of the present invention.

What is claimed is:
1. A method for preparing a dihydroxybiaryl compound comprising:
(a) providing an alkali metal salt of said dihydroxybiaryl compound; and
(b) contacting said alkali metal salt of said dihydroxybiaryl compound with a
corresponding monohydroxyaryl halide compound.
2. The method of claim 1, wherein said dihydroxybiaryl compound is 4,4'-
dihydroxybiphenyl.
3. The method of claim 2, wherein said corresponding monohydroxyaryl halide
compound is p-bromophenol or p-chlorophenol.
4. The method of claim 2, wherein said alkali metal salt of said dihydroxybiaryl
compound is the sodium salt of 4,4'-dihydroxybiphenyl or the potassium salt of 4,4'-
dihydroxybiphenyl.
5. The method of claim 1, wherein said dihydroxybiaryl compound is 2,2'-
dimethyl-4,4'-dihydroxybiphenyl.
6. The method of claim 5, wherein said corresponding monohydroxyaryl halide
compound is 2-methyl-4-bromophenol or 2-methyl-4-chlorophenol.
7. The method of claim 5, wherein said alkali metal salt of said dihydroxybiaryl
compound is the sodium salt of 2,2'-dimethyl-4,4'-dihydroxybiphenyl or the
potassium salt of 2,2'-dimethyl-4,4'-dihydroxybiphenyl.
8. The method of claim 1, wherein a temperature ranging from about 20° C to
about 120° C is employed.
9. The method of claim 1, wherein a molar ratio of said corresponding
monohydroxyaryl halide compound to said alkali metal salt of said dihydroxybiaryl
compound of at least 2:1 is employed.
The method of claim 1, further comprising after step (b), the steps of:
(c) removing a precipitate formed by said contacting step from a solution formed by
said contacting step, wherein said precipitate comprises said dihydroxybiaryl
compound; and
(d) recycling the remaining solution comprising an alkali metal salt of said
monohydroxyaryl halide compound to form additional said alkali metal salt of said
dihydroxybiaryl compound by contacting said remaining solution with a metal
catalyst, an alkali metal hydroxide, and a reducing agent.
10. The method of claim 10, wherein said metal catalyst is palladium, and said
reducing agent is formic hydrazide.
11. The method of claim 10, wherein said metal catalyst is palladium, and said
reducing agent is hydrogen gas.
12. The method of claim 12, wherein said hydrogen gas is employed at a pressure
ranging from about 1 atm to about 350 kilopascals.
13. The method of claim 10, wherein said alkali metal hydroxide is potassium
hydroxide or sodium hydroxide.
14. The method of claim 10, wherein a temperature ranging from about 20° C to
about 120°C is employed.
15. The method of claim 10, wherein said dihydroxybiaryl compound is 4,4'-
dihydroxybiphenyl, said corresponding monohydroxyaryl halide compound is pbromophenol
or p-chlorophenol, and said alkali metal salt of said dihydroxybiaryl
compound is the sodium salt of 4,4'-dihydroxybiphenyl or the potassium salt of 4,4'-
dihydroxybiphenyl.
16. The method of claim 10, wherein said dihydroxybiaryl compound is 2,2'-
dimethyl-4,4'-dihydroxybiphenyl, said corresponding monohydroxyaryl halide
compound is 2-methyl-4-bromophenol or 2-methyl-4-chlorophenol, and said alkali
metal salt of said dihydroxybiaryl compound is the sodium salt of 2,2'-dimethyl-4-4'-
dihydroxybiphenyl or the potassium salt of 2,2'-dimethyl-4,4'-dihydroxybiphenyl.
17. The method of claim 10, wherein a molar ratio of said alkali metal hydroxide
to said alkali metal sail of said monohydroxyaryl halide compound of at least 1:1 is
employed.
18. A method for isolating a dihydroxybiaryl compound comprising:
(a) providing an alkali metal salt of said dihydroxybiaryl compound;
(b) contacting said alkali metal salt of said dihydroxybiaryl compound with a
corresponding monohydroxyary] halide compound to form a precipitate in a solution;
and
(c) separating said precipitate from said solution, wherein said precipitate comprises
said dihydroxybiaryl compound.
19. The method of claim 19, wherein said dihydroxybiaryl compound is 4,4'-
dihydroxybiphenyl, wherein said corresponding monohydroxyaryl halide compound
is p-bromophenol or p-chlorophenol, and wherein said alkali metal salt of said
dihydroxybiaryl compound is the sodium salt of 4,4'-dihydroxybiphenyl or the
potassium salt of 4,4'-dihydroxybiphenyl.
20. The method of claim 19, wherein said dihydroxybiaryl compound is 2,2'-
dimethyl-4,4'-dihydroxybiphenyl, wherein said corresponding monohydroxyaryl
halide compound is 2-methyl-4-bromophenol or 2-methyl-4-chlorophenol, and
wherein said alkali metal salt of said dihydroxybiaryl compound is the sodium salt of
2,2'-dimethyl-4,4'-dihydroxybiphenyl or the potassium salt of 2,2'-dimethyl-4,4'-
dihydroxybiphenyl.
21. The method of claim 19, wherein a molar ratio of said corresponding
monohydroxyaryl halide compound to said alkali metal salt of said dihydroxybiaryl
compound of at least 2:1 is employed.
22. The method of claim 19, further comprising the step of washing said separated
precipitate with water or methanol at least one time.
23. The method of claim 23, further comprising the step of recrystallizing said
washed precipitate to provide a purified dihydroxybiaryl compound having a purity of
at least 90 %.