Organic compounds -- part of the class 532-570 series – Organic compounds – Sulfur containing
Reexamination Certificate
2002-10-10
2004-03-02
Parsa, J. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Sulfur containing
C568S028000, C568S032000
Reexamination Certificate
active
06700020
ABSTRACT:
The present invention relates to an improved semicontinuous process for the preparation of 4,4′-dihydroxydiphenyl sulfone, comprising the following steps:
(a) reaction of phenol with a sulfonating agent,
(b) suspension of the resulting crude product in water heated to at least 40° C., which is free of inert organic solvents and can contain residual amounts of unreacted phenol, and filtration of the product, and
(c) recycling of the resulting educt-containing and/or product-containing waste streams into the preparative process.
4,4′-Dihydroxydiphenyl sulfone (“4,4′-bisphenol S”) is of great economic value inter alia as an auxiliary substance for electroplating, as a raw material for the manufacture of condensation resins, for example to be used as leather tanning agents, and for the manufacture of fibers and especially plastics such as polyether sulfones. As the properties of polymers prepared from 4,4′-dihydroxydiphenyl sulfone are highly dependent on the degree of purity and the isomer ratio of the monomers used, it is desirable to have selective processes for the synthesis of 4,4′-dihydroxydiphenyl sulfone. It is also desirable, for economic and ecological reasons, to have synthetic processes with minimal waste streams or none at all.
Synthetic processes which make use of combustible inert organic solvents, such as methanol, ethanol, o-dichlorobenzene or toluene, in the isolation of 4,4′-dihydroxydiphenyl sulfone from the reaction mixture, for example the processes described in JP-A 50/106 937, CN-A 87/100 796, EP-A 220 004 or WO 92/02493, are likewise unacceptable for ecological and safety reasons.
U.S. Pat. No. 3,297,766 has disclosed a semicontinuous process for the preparation of 4,4′-dihydroxydiphenyl sulfone wherein sulfuric acid is reacted with phenol at 180-188° C. with continuous distillation of the water of reaction, the reaction mixture is then cooled to 55-75° C. and the solid which has precipitated out is filtered off and washed with water to give a mixture of 4,4′-and 2,4′-dihydroxydiphenyl sulfone. The waste streams from the filtration and rinsing, and the phenol discharged during distillation of the water of reaction, are fed back into the next cycle of the preparative process.
JP-A 50/106 936 describes the preparation of 4,4′-dihydroxydiphenyl sulfone by reacting phenol with a sulfonating agent, such as sulfuric acid, at 180-200° C. and crystallizing out and separating off the 4,4′-dihydroxydiphenyl sulfone. The latter is isolated by dissolving or dispersing the crude reaction product in 3 to 8% by weight aqueous phenol solution and crystallizing out and separating off the 4,4′-dihydroxydiphenyl sulfone with or without cooling. If there is still a relatively large amount of unreacted phenol in the reaction product, it is only possible to work with the addition of pure water. 1 to 5 parts by weight of aqueous phenol solution are used per part by weight of reaction product. The solution separated off, which contains phenol and water, can be re-used in a subsequent reaction cycle. According to the Example in JP-A 50/106 936, treatment of the reaction product with 8% by weight aqueous phenol solution at 75° C., cooling to 40° C. and centrifugation of the 4,4′-dihydroxydiphenyl sulfone which has precipitated out gives an isomeric purity of 98.7%.
Although the process of JP-A 50/106 936 provides the desired product in high isomeric purity, it has the disadvantage of working with large amounts of aqueous treatment solution for isolation from the reaction mixture. These amounts on the one hand require sizeable and hence expensive apparatuses and on the other hand reduce the yield. Furthermore, the presence of large amounts of phenol in the isolation of the product has the disadvantage that the phenol can easily remain stuck to the product as an impurity by forming adduct complexes therewith.
It is known that sulfonation reactions of phenol with sulfuric acid involve reversible equilibria which, with further phenol, proceed via phenol-2-sulfonic acid and phenol-4-sulfonic acid to give 2,4′- and 4,4′-dihydroxydiphenyl sulfone. The isomerization equilibrium which exists between 2,4′- and 4,4′-dihydroxydiphenyl sulfone favors the thermodynamically more stable 4,4′ isomer. However, the isomerization is kinetically inhibited and a catalyst, for example phenol-4-sulfonic acid, is usually necessary for the equilibrium to be reached within a period acceptable in terms of process engineering. The isomerization equilibrium can also be shifted in favor of the 4,4′ isomer by selectively withdrawing it. Furthermore, if the phenol is present in less than the stoichiometric amount, trimers, such as 2,4′,4″-trihydroxytriphenyl disulfone, and higher phenolsulfonic acid oligomers can be formed.
It is an object of the present invention to provide a preparative process for 4,4′-dihydroxydiphenyl sulfone which is free of inert organic solvents in the steps involving the reaction and the isolation of the product from the reaction mixture, in which the waste streams can be recycled into the preparative process, which yields the desired product in high isomeric purity and high yield, even without downstream purification operations, and which, in the isolation of the product from the reaction mixture, involves the smallest possible amounts of treatment solution, the latter being substantially free of unreacted phenol.
We have found that this object is achieved by the semicontinuous process for the preparation of 4,4′-dihydroxydiphenyl sulfone defined at the outset, wherein, in carrying out step (b), the crude product and water are used in a weight ratio of 85:15 to 55:45, preferably 75:25 to 60:40.
The hot water used to suspend the reaction mixture is free of inert organic solvents, especially water-miscible solvents such as methanol, ethanol, isopropanol or acetone, or, if appropriate, halogenated hydrocarbons such as toluene, chlorobenzene or dichlorobenzenes. The residual amounts of unreacted phenol which can be dissolved out of the reaction mixture in the suspension step, or which may already be present to a small extent in the water used, if the latter originates from the previous cycle of the preparative process and has been produced by distillation of the mother liquor from step (b) of said cycle, can be up to a maximum of 2.5% by weight, particularly 0.05 to 1.5% by weight and very particularly 0.1 to 1.0% by weight, based in each case on the amount of water used.
In one preferred embodiment, the water added for treating the reaction mixture in step (b) is at a temperature of 80° C. to 100° C. Particularly good results are achieved with water at 90° C. to 100° C. In principle, it is also possible to work at temperatures above 100° C., for example at 100° C. to 130° C., if the treatment with water is carried out in a closed apparatus under superatmospheric pressure. The treatment water can also be added in the form of steam. The duration of the treatment with water is not critical and as a rule is 5 minutes to 5 hours. The treatment with water is normally accompanied by thorough mechanical mixing, for example by stirring.
In another preferred embodiment, the suspension of the crude product in water and the filtration of the product, in step (b), are carried out at approximately the same temperature. Approximately the same temperature conventionally means working in a temperature range of approx. 10° C., especially approx. 5° C. This embodiment avoids cooling of the suspension, which would result in the crystallization of dissolved constituents.
The suspension (“slurrying”) and the filtration can be carried out by the techniques and with the apparatuses conventionally used for this purpose, for example with stirred tanks, mixers or kneaders for the suspension, and with suction filters or centrifuges for the filtration.
In another preferred embodiment, the product filtered off in step (b) is rinsed with water heated to at least 40° C., preferably 80°
Kast Jürgen
Pabst Gunther
BASF - Aktiengesellschaft
Keil & Weinkauf
Parsa J.
LandOfFree
Semi-continuous method for producing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semi-continuous method for producing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semi-continuous method for producing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3209635