GB2096141A - Method for making aromatic bis(ether phthalic acid) or aromatic bis(ether anhydride) - Google Patents

Abstract

A method is provided for converting aromatic bis(ether N- organo substituted phthalimides) to aromatic bis(ether anhydrides) by heating a bisphasic aqueous-organic mixture of aromatic bis(ether N- organo substituted phthalimide), phthalic acid or phthalic anhydride and an exchange catalyst to effect an imide-anhydride exchange producing an aqueous phase containing aromatic bis (ether phthalic acid) and an organic phase containing N-organo substituted phthalimide. A continuous method is also provided by utilizing a heated coiled tube reactor whereby the aqueous phase and the organic phase can then be separated and the aromatic bis (ether phthalic anhydride) recovered from the aqueous phase.

Description

SPECIFICATION Method for making aromatic bis (ether phthalic acid) or aromatic bis (ether anhydride) Prior to the present invention as shown by Heath, et al. U.S. Patent Nos. 3,879,428 and 3,957,862, assigned to the same assignee as the present invention, aromatic bis(ether anhydrides) (hereinafter referred to as "bisanhydrides") of the general formula:

were made by a multi-step procedure involving the base hydrolysis of an aromatic bis(ether N-organo substituted phthalimide) of the formula:

A more specific compound of which is 2,2-bis[4-(3,4-dicarboxy)phenyl]propane bis-N-methylimide which has the formula::

where R is a divalent aromatic radical having from 6-30 carbon atoms and R1 is a monovalent organic radical selected from the class consisting of C(18) alkyl radicals, and organic radicals, having from 620 carbon atoms, for example, aromatic hydrocarbon radicals and halogenated derivatives thereof. This procedure produced a tetra-acid salt which was thereafter acidified to the tetra-acid followed by the dehydration of the tetra-acid to produce the aromatic bis(ethyl anhydride) of formula 1.

Although the procedure of Heath, et al. provides a valuable route to both the aromatic bis(ether phthalic acids) and aromatic bis(ether phthalic anhydrides) it requires the base hydrolysis of the aromatic bis(ether N-organo substituted phthalimide of formula II and the conversion of the resulting salt to the tetra-acid, followed by the dehydration of the tetra-acid. In addition to requiring a variety of steps to convert the bisimide to a bisanhydride, inorganic salts are generated causing disposal problems. Efforts, are, therefore, being directed to providing a more simplified procedure for making the bisanhydride of formula I, or its tetra-acid precursor.

Markezich, et al. U.S. Patent No. 4,128,574 discloses an imide-anhydride exchange reaction resulting in the production of organic polycarboxylic acids, anhydrides thereof, or organic imides. For example, in particular instances, a bisimide of formula IIA, is heated with phthalic anhydride in the presence of water to effect an exchange between the aforementioned bisimide and the phthalic anhydride to provide the corresponding tetra-acid or anhydride thereof.

Although the Markezich, et al. method eliminates many of the disadvantages of the prior art, such as permitting the ready conversion of N-alkyl substituted bisimides, the direct production of cyclic anhydrides, forming inorganic salts or the requirement of a multi-step procedure, Markezich, et al. is essentially a batch method. The recovery of a tetra-acid or bisanhydride at a satisfactory yield, 80% or higher concentration, requires several heating and stripping cycles. it is also difficult to achieve substantial conversion of the bisimide to the tetra-acid or the bisanhydride without resort to the recycling of excessive amounts of phthalic acid or phthalic anhydride.Based on the nature of the exchange between the bisimide and phthalic acid or phthalic anhydride, optimum conversion cannot be realized unless the N-organo phthalimide of the general formula:

where R1 is as previously defined, which is also formed in the reaction, is separated from the mixture.

Webb, in U.S. Patent No. 4,11 6,980, showed that optimum conversion of the bisimide to the tetra-acid or dianhydride thereof, can be achieved based on the imide-anhydride exchange in the presence of water, as shown by the following: A+B=A'tB', where A and A' are imides and B and B' are anhydrides, if the A' imide is selectively removed from the reaction during the exchange. For example, in the above equation, A can be a bisimide, B can be a phthalic acid, B' can be a bis anhydride or tetra-acid and A' can be an N-organo phthalimide. Webb achieved these results by venting a portion of the vapor phase of the reaction mixture consisting of a liquid phase and a vapor phase during the exchange.The vapor phase consisted essentially of water and N-organo phthalimides with very little phthalic acid so that by continuously venting the vapor phase during the exchange, the reaction is driven to the right. it is, therefore, possible to convert the starting bisimide to the corresponding tetra-acid or bis anhydride without either shutting down the reactor or recycling excessive amounts of phthalic acid.

The present invention is based on the development of a new biphasic imide-anhydride exchange process in which an inert organic solvent solution of an aromatic bis(ether N-organo substituted phthalimide) hereinafter also identified as "Bl" is contacted with an aqueous solution of phthalic acid hereinafter also identified as "PA" and an exchange catalyst at an elevated temperature. Imideanhydride exchange occurs and a major portion of the bis-compound moves from the organic phase to the aqueous phase where it exists as the salt of the aromatic bis(ether phthalic acid) hereinafter also identified as "TA" of the general formula:

where R is as previously defined. This compound is easily converted by conventional means to the aromatic bis(ether phthalic anhydride) hereinafter also identified as "DA" of formula I.The N-organo phthalimide hereinafter also identified as "P 1" formed by the exchange moves out of the aqueous phase and into the organic phase thereby facilitating an increased conversion of the Bl to the TA.

Unreacted (excess) phthalic acid remains in the aqueous phase as a salt.

Before the exchange reaction, all imides (Pl and Bl) exist in the organic phase and all acids and catalysts exist in the aqueous phase. After the exchange reaction, when equilibration is established, the major portion of the BI has moved from the organic phase to the aqueous phase where it exists as a salt of the TA. The phthalic imide, hereinafter also identified as "P 1", formed by the exchange moves into the organic phase along with the unreacted Bl and some aromatic bis(ether N-organo substituted phthalimide ether anhydride) hereinafter identified as "IA" of the general formula:

where R and R' are as previously defined.Therefore, at equilibrium except for a small amount of IA present in both phases, the original condition, with ail imides being present in the organic phase and all acids or salts of the acids being present in the aqueous phase, still exists.

Corrosion problems associated with previous methods can be substantially eliminated by neutralization of all acids by using an amine catalyst and in addition the biphasic exchange process makes possible a clean separation of the N-organo phthalimide from the phthalic acid. The exchange can also be rapidly catalyzed, requires substantiaily less process energy than the previous methods and conserves reactants, solvents and catalyst.

There is provided by the invention a biphasic imide-anhydride exchange process tor making aromatic bis(ether phthalic acid) from aromatic bis(ether phthalimide) which comprises, (A) heating at an elevated temperature, e.g., from 170--2600C, and under superatmospheric pressure, e.g., between 200-500 psi, a mixture comprising:: (i) aromatic bis(ether phthalimide) of formula II, (ii) 2-20 moles of phthalic anhydride or phthalic acid per mole of (i), (iii) a sufficient and effective amount of an exchange catalyst, (iv) 0.01-100 parts of water per part, by weight of (i), (v) 0.01-100 parts of a water-immiscible inert organic solvent per part, by weight, of (i), to produce an equilibrated liquid biphasic reaction mixture, comprising an aqueous phase having selectively dissolved therein, the aromatic bis(ether phthalic acid) formed in the exchange reaction, the exchange catalyst together with any unreacted phthalic acid, and an organic phase having selectively dissolved therein, N-organo substituted phthalimide of formula Ill which was also formed in the exchange reaction, together with any unreacted aromatic bis(ether phthalimide), (B) separating the organic phase from the aqueous phase, and (C) recovering the aromatic bis(ether phthalic acid) from the aqueous phase.

Radicals included by R are for instance,

and divalent organic radicals of the general formula:

where X is a member selected from the class consisting of divalent radicals of the formulas,

-0-, -S-, where m is O or 1 , and y is a whole number from 1 to 5 inclusive.

Radicals included by R1 are for example, phenyl tolyl, xylyl, naphthyl, chlorophenol, bromonaphthyl, etc. and alkyl radicals, such as methyl, ethyl, propyl, etc.

The bisimides of formula II and a method for making them, are more particularly described in the aforementioned patent 3,879,428, Wirth et al., which is based on the initial formation of N-organo substituted phthalimide of the formula:

where X is a radical selected from the class consisting of nitro, halo, e.g. chloro, fluoro, bromo, etc., and R' is as previously defined. The phthalimide of formula VI can be formed by effecting a reaction between X-substituted phthalic anhydride and an organic amine, such as aniline, toluidine, methyl amine, ethyl amine, etc.

Included by the phthalimides of formula VI are, fdr example, N-methyl-4-nitrophthalimide, N phenyl-3-nitrophthalimide, N-phenyl-4-nitrophthalmide, N-methyl-3-nitrophthalimide, N-butyl-4 nitrophthalimide, etc. As further shown in U.S. Patent No. 3,879,428, the aromatic bis(ether phthalimide)s of formula Il can be made by effecting reaction between phthalimides of formula Vi and an alkali diphenoxide of the general formula: M--OO--RR-O-M (Vll) where R is as previously defined, and M is a metal ion of an alkali metal for example, sodium, potassium, lithium, etc.

Included by the alkali diphenoxides of formula VII, are sodium and potassium salts of the following dihydric phenols.

2,2-bis(2-hydroxyphenyl)propane; 2,4'-dihydroxydiphenyl methane; bis-(2-hydroxyphenyl)methane; 2,2-bis-(4-hydroxyphenyl)propa ne hereinafter identified as "Bisphenol-A" or "BPA"; 1,1 -bis-(4-hydroxyphenyl)ethane; 1,1 -bis-(4-hydroxyphenyl)propane; 2,2-bis-(4-hydroxyphenyl)pentane; 3,3-bis-(4-hydroxyphenyl)pentane; 4,4'-dihydroxybiphenyl; 4,4'-dihydroxy-3,3,5,5'-tetramethylbiphenyl; 2,4'-dihydroxybenzophenone; 4,4'-dihydroxydiphenylsulfone; 2,4'-dihydroxydiphenylsulfone; 4,4'-dihydroxydiphenyl sulfoxide; 2,4'-dihydroxydiphenylsulfoxide; 4,4'-dihydroxydiphenyl sulfide; hydroquinone; resorcinol; 3,4'-dihydroxydiphenylmethane; 4,4'-dihydroxybenzophenone; 4,4'-dihydroxydiphenylether, etc.

Exchange catalysts which can be employed in the invention are; acids such as sulfuric, phosphoric, hydrochloric, methanesulfonic, fluoroboric, toluenesulfonic, acetic butyric, trifluoroacetic acids, etc.; metal salts, such as FeCI3, ZnCI2, SnCI4, AICI3 and their bromides; trialkyl amines hereinafter also identified as "R3 N", such as trimethylamine, triethylamine, tripropylamine, tributylamine, etc. with the preferred catalysts being triethylamine and trimethylamine.

Organic solvents which can be used in the invention are inert, water immiscible solvents which selectively dissolve any imide compounds present initially or formed during the exchange reaction for example, toluene, benzene, xylene, chlorobenzene and orthodichlorobenzene.

The following broad and preferred parameters have been determined for the biphasic imideanhydride process: 1. Temperature Range 170C2600C Preferred 1850--2250C 2. Pressure Determined by temperature Range 200-500 psi 3. PAto Bl Mole Ratio Range 2:1 to 20:1 Preferred 4-6:1 4. Catalyst to PA Mole Range 1:1 to 3:1 Ratio Preferred 2:1 5. Organicsolventto Range 0:1 to 10:1 water weight ratio Preferred ""4:1 6. Solids Content Range 1% to 70% Preferred 10-15% A more complete understanding of the practice of the present invention, by way of example only, can be obtained by reference to the drawing.

in Fig. 1, there is shown a continuous three step imide-anhydride exchange process incorporating the method of the present invention which produces 2,2-bis 4-(3,4-dicarboxyphenoxy)phenyl propane of at least 97 mole percent purity by effecting the imide-anhydride exchange between PA and BI in the presence of an organic solvent which selectively absorbs the imide, separating and removing the organic phase, then repeating the equilibration-separation two more times with organic solvent to produce TA in the aqueous phase. The organic phase is used in the third, second then first equilibration-separation steps after which it is distilled to remove the imides and returned to the third equilibration step and recycled.Of the imides removed during the distillation Pl is recovered and can be nitrated and used to produce more BI, while the remaining Bl and IA are recycled. After recovery of the TA from the aqueous phase by distillation of H20, R3N and unreacted PA these materials are recycled to the first equilibration step.

More particularly, there is shown at 10, the first equilibration vessel, in which an aqueous solution of excess PA and two moles of R3N catalyst per mole of PA is heated together with a toluene solution of BI. Phthalic acid (PA) or phthalic anhydride is fed to 10 via line 3 from a PA reservoir 2 along with recycled water, R3N and any unreacted PA from the previous cycle via line 12. Toluene is recycled from step 2 of the previous cycle via line 1 3. BI feed stock is fed from reservoir 1 via line 11 to the first equilibration vessel 10 along with unreacted BI and partially reacted IA which are separated from the toluene in stills 4 and 6 and transferred via lines 5 and 8.The two phases are heated together at approximately 2000C and 300-500 Ibs. per square inch pressure, depending upon the exact temperature, for 1 to 2 hours to produce a mixture which is chemically equilibrated.

At this time, the mixture is pumped from equilibration vessel 10 via line 14 to the first step phase separator or decantor 20. While still hot, the mixture is allowed to settle and separate, the toluene phase is drawn off and pumped via line 22 to a first distillation unit 4 in which the toluene is stripped off and condensed for subsequent recycling. The still bottoms from 4, containing BI, IA and Pl are pumped via line 5 to a second still 5 where Pl is distilled off for possible subsequent production of BI.

The still bottoms from 6 containing Bl and IA are recycled via line 8 to the first equilibration vessel 10.

The aqueous phase from the first step phase separator 20 is pumped via line 21 to a second equilibration vessel 30 where it is mixed with toluene decanted from the third step phase separator 60.

When equilibration is achieved in the second equilibration vessel 30, the mixture is pumped via line 31 to the second step phase separator 40 where, after settling, the toluene layer is returned to the first equilibration vessel 10 via line 13 and the aqueous phase is pumped via line 41 to the third equilibration vessel 50. Toluene from still 4 is pumped via line 52 to the third equilibration vessel 50 and the mixture is equilibrated once more and pumped to the final phase separator or decantor 60.

After stealing, the toluene layer from 60 is returned via line 32 to the second equilibration vessel 30, and the aqueous phase is fed via line 61 to a third still 70 in which PA, H2O and R3N are distilled off, condensed and returned via line 12 to the first equilibration vessel 10. The still bottoms from 70 are drained off to yield DA.

In order that those skilled in the art will be better able to understand the practice of the invention, the following examples are given by way of illustration and not by way of limitation.

Each of the 9 equilibrations were carried out batchwise as described below. The toluene phases were manipulated as indicated in Figure II which is self explanatory.

Example I A one liter autoclave was charged with 35.7g (0.24 mol) phthalic anhydride, 21 .84g (0.04 mol) of the bis imide of formula IIA, hereinafter also identified as "BPA-BI", 67 ml (0.48 mol) triethylamine, 80 ml water, and 320 ml toluene. The autoclave was flushed with N2, sealed and heated to 2000C for 2 hours. The autoclave was then cooled and opened. The organic and aqueous phases were separated and samples were taken of each. The aqueous phase was returned to the autoclave together with the next appropriate portion of toluene according to Figure II. The autoclave was again flushed with N2, sealed and reheated to 2000C for 2 hours. The work-up described for the first equilibration was repeated.

The samples of both phases from each cycle were stripped of solvent under vacuum (""25 mm) and 2000C, and analyzed by liquid chromatography (Waters Associates LC, corisol-l column 1/8"x2', solvent=40% CH2CI2, 59.5% CHCI3 and 0.5% Et2O; flow rate=2 ml/min, detector=UV, A254). The results are given in the following tables, where the compositions of the ingredients in the aqueous phase are given in mole percent.

Table I Composition of the Amide-Anhydride Exchange Product (Mole Percent) Cycle I Equilibration Bl IA TA 1 .02 1 5.2 84.8 2 .02 1.8 98.2 3 .02 0.6 99.4 Cycle II Equilibration Bl IA TA 1 .02 6.0 84.0 2 .02 2.4 97.6 3 .02 0.4 99.6 Cycle Ill Equilibration Bl IA TA 1 .02 11.2 88.8 2 .02 2.4 97.6 3 .02 0.5 99.5 The above results show that a biphasic exchange reaction is capable of providing a product having at least 85 mole percent TA after only 1 equilibration step. Two and three steps resulted in ""98 and ""99.5 mole percent products, respectively.

The third equilibration in all three cycles produced~18 grams (0.035 mol) of > 99 mole percent TA which corresponds to an 86% overall conversion of the BI of formula II to TA of Formula IV which would be readily dehydrated to the DA of formula I.

There is also included in this invention the development of a continuous biphasic imide anhydride exchange process in which the inert organic solvent solution of an aromatic bis(ether N-organo substituted phthalimide) hereinafter also identified as "Bl" is contacted with the aqueous solution of phthalic acid hereinafter also identified as "PA" and an exchange catalyst at an elevated temperature in a heated coiled tube reactor. Imide-anhydride exchange occurs and a major portion of the biscompound moves from the organic phase to the aqueous phase where it exists as the salt of the aromatic bis(ether phthalic acid) hereinafter also identified as "TA" of the general formula:

The elevated temperature and pressure requirements for the imide-anhydride exchange reaction are easily accommodated in the laboratory by simple autoclaves.However, on an industrial scale such heavy walled pressure equipment becomes very expensive. In addition, agitation of the contents of the autoclaves which would facilitate shorter reaction times becomes very difficult since this type of equipment with moving parts and high pressure seals around rotating shafts is very expensive and difficult to maintain. Mixing is a prime concern in attaining equilibrium with the biphasic system of the present invention. Mixing can be obtained by passing the biphasic mixture through a coil of tubing held in a horizontal position. Due to density differences the organic phase rises through the aqueous phase on the ascending side of the coil and the aqueous phase falls through the organic phase on the descending side of the coil.The process continues along the length of the coil and gives good contact between the two phases and consequently accelerates the equilibration process.

There is thus provided a continuous biphasic imide-anhydride exchange process for making aromatic bis(ether phthalic acid) from aromatic bis(ether phthalimide) which comprises, (A) passing through a heated coiled tube reactor at an elevated temperature, e.g., from 1 70- 26O0C, and under superatmospheric pressure, e.g., from between 200-700 psi, a mixing comprising:: (i) aromatic bis(ether phthalimide) of formula II, (ii) 2-20 moles of phthalic anhydride or phthalic acid per mole of (i), (iii) a sufficient and effective amount of an exchange catalyst, (iv) 0.01-100 parts of water per part, by weight, of (i), (v) 0.01-100 parts of a water-immiscible inert organic solvent per part, by weight, of (i), to produce an equilibrated liquid biphasic reaction mixture, comprising an aqueous phase having selectively dissolved therein, the aromatic bis(ether phthaiic acid) formed in the exchange reaction, the exchange catalyst together with any unreacted phthalic acid, and an organic phase having selectively dissolved therein, N-organo substituted phthalimide of formula Ill which was also formed in the exchange reaction, together with any unreacted aromatic bis(ether phthalimide), (B) separating the organic phase from the aqueous phase, and (C) recovering the aromatic bis(ether phthalic acid) from the aqueous phase.

The coiled tube reactor of this embodiment may be constructed of any tubing which will withstand the temperatures and pressure of the reaction and will not be attacked by the biphasic process reaction mixture. Examples of tubing which can be used are 316 stainless steel, 347 stainless steel, glass, etc.

The length of the tubing (I), cross sectional area of the tubing (a), and flow rate (r), effect the rate of the exchange reaction and consequently the residence time (t) required to approach equilibration.

These parameters are related by I/a/r=t. Kinetic studies indicated that a residence time of ""2 hours was needed.

The coiled tube reactor is heated, for example, by an oil filled heating jacket or other conventional means.

The following broad and preferred parameters have been determined for the bi-phasic imide anhydride continuous hot tube reactor process: 1. Temperature Range 1700--2600 Preferred 185-2250C 2. Pressure Determined by temperature Range 200-700 psi 3. PAto BI Mole Ratio Range 2:1 to 20:1 Preferred 4-6:1 4. Catalyst to PA Mole Range 1:1 to 3:1 Ratio Preferred ""2:1 5. Organicsolventto Range 0:1 to 10:1 water weight ratio Preferred ""4:1 6. Solids Content Range 1% to 60% Preferred ""10-1 5% 7. PA Concentration in Range 0.2-6 mole/liter aqueous phase Preferred ""3 mole/liter 8.BI Concentration in Range 0.02-1 mole/liter Organic Phase Preferred ""0.2 mole/liter In the practice of the continuous process an aqueous solution containing PA and an exchange catalyst and an organic solution containing the BI are combined and fed into the coiled tube reactor under pressure. Heating of both reactant phases is generally required to maintain higher concentration reactant solutions. After passage through the reactor the phases are separated by conventional means and the solvents, reactants and catalysts are distilled off for optional recycling. The Pl recovered from the organic phase can be nitrated and used to produce more Bl. The TA product in the aqueous phase yields the DA product after dehydration.

Example II The hot tube reactor was 24 feet of 10.9 mm l.D. 347 stainless steel tubing with a volume of 640 cc, formed into a multiturn 1 6 cm diameter coil oriented in a horizontal position with respect to the coil axis. The reactor coil was enclosed in a copper jacket and heated to 2000C with flowing hot oil. The pressure in the reactor was maintained at 500 psi to prevent boiling of the contents.

An aqueous solution of 2.98 mole/liter PA and 4.5 mole/liter triethylamine catalyst was heated to 650C to prevent crystallization and pumped to the coiled hot tube reactor at a rate of 3 ml/min.

A toluene solution of 0.22 mole liter BI was heated to 800C and pumped to the hot tube reactor at 7 ml/min. These flow rates result in a PA to Bl mole ratio of 5.75:1.

The total running time was ""6 hrs. with a total flow rate of 10 ml/min and samples were taken every 6 minutes after the calculated residence time.

The reactor was initially filled with aqueous PA solution.

The samples of both phases were stripped of solvent under vacuum (""25 mm) and 2000 C, and analyzed by liquid chromatography (Waters Associates LC, corisol-l column 1/8"x2', solvent=40%, CH2CI2, 59.5% CHCI3 and 0.5% Et2O; flow rate=2 ml/min, detector=UV, 254).

The results are given in Table II, where the concentration of bis-compounds (BI+IA+TA) is given in grams per liter and the concentration of TA in the bis-compounds is given in mole %.

The data shows a steady state or equilibrium was reached at ""120 min. and thereafter no additional mass was transferred from the organic phase and the mole % TA remained unchanged at ""75%.

Table Il Composition of the imide-anhydride exchange product from the coiled hot tube reactor Bis-compounds* Mole % TA in Time (MinutesJ liter bis-compounds 39 8.99 43 50 33.33 70 60 87.66 83 72 119.33 81 81 146.33 79 93 163.33 76 105 170.66 75 120 182.00 75 135 184.03 77 152 186.60 74 170 188.00 74 189 186.66 74 205 183.30 75 *bis-compounds=Bl+IA+TA The above results show that a continuous biphasic exchange reaction carried out in a coiled hot tube reactor is capable of providing a product having at least ""75 mole percent TA after one pass through the reactor. The product from the first pass was sent back through the reactor under the same conditions except the toluene contained no BI.This resulted in a product having ""95 mole % TA. A third pass, again with toluene only in the organic phase, gives a product with at least 97 mole % TA.

Example Ill The initial conditions and concentrations were the same as in Example-l, however, the flow rate for the aqueous phase and the organic phase were both 5 ml/min. This results in a PA to Bl mole ratio of 13.42;1.

The results are given below in Table-Ill.

Table-Ill Coiled Hot Tube Reactor Product Composition Bis-compound Mole % TA in Time (min.) Concentration bis-compounds liter 56 67.6 88 68 94.9 88 81 100.0 88 93 102.0 88 105 104.0 88 116 100.6 88 128 100.3 88 141 101.1 88 These data show that a steady state is established after~81 min. and yields a product having ""88 mole % TA. The shorter time to reach equilibrium, 81 min. vs. 120 min. in Example II, and the higher mole % TA, 88% vs. 77% in Example II, are due to higher PA or BI mole ratio 13.42:1 vs. 5.75:1 in Example II.

Claims (21)

Claims

1. A biphasic imide-anhydride exchange process for making aromatic bis(ether phthalic acid) of the formula:

or the anhydride thereof which comprises: (A) heating a mixture comprising: i) aromatic bis(ether phthalimide) of the formula:

(ii) phthalic anhydride or phthalic acid.

(iii) an exchange catalyst.

(iv) water.

(v) a water-immiscible inert organic solvent to produce an equilibrated liquid biphasic reaction mixture, comprising an aqueous phase having selectively dissolved therein the aromatic bis(ether phthalic acid) formed in the exchange reaction, the catalyst, along with any excess phthalic acid, and an organic phase having selectively dissolved therein, N-organo substituted phthalimide of the formula:

which was also formed inshhe exchange reaction, together with any unreacted aromatic bis(ether phthalimide), (B) separating the organic phase from the aqueous phase.

(C) recovering the aromatic bis(ether phthalic acid) from the aqueous phase, and optionally dehydrating it to form the dianhydride, where R is a divalent aromatic radical having from 6-30 carbon atoms and R1 is a monovalent organo radical selected from the class consisting of C(18) alkyl radicals, and organic radicals having from 6-20 carbon atoms selected from the class consisting of aromatic hydrocarbon radicals and halogenated derivatives thereof.

2. A process as claimed in claim 1, wherein the reaction temperature is between 1 700C-2600C and the reaction pressure is between 200 psi-500 psi.

3. A process as claimed in claim 1 or claim 2, wherein the phthalic acid is present in an amount of between 2-20 moles of the anhydride per mole of aromatic bis(etherphthalimide).

4. A process as claimed in any one of the preceding claims, wherein the exchange catalyst is a trialkyl amine.

5. A process as claimed in claim 4 wherein the exchange catalyst is triethyl amine.

6. A process as claimed in any one of the preceding claims, wherein the catalyst is present in a mole ratio of from 1 to 3 moles of catalyst per mole bis(imide).

7. A process as claimed in any one of the preceding claims wherein, on a weight basis, between 0.01 and 100 parts of water per part bis(imide) are used.

8. A process as claimed in any one of the preceding claims wherein the organic solvent is toluene.

9. A process as claimed in any one of the preceding claims wherein, on a weight basis, between 0.01 and 100 parts of solvent per part bis(imide) are used.

10. A process as claimed in any one of the preceding claims, wherein R1 is methyl.

11. A process as claimed in any one of the preceding claims, wherein the aromatic bis(ether phthalic acid) is 2,2-bis[4-(3,4-dicarboxyphenoxy) phenylipropane.

1 2. A process as claimed in any one of the preceding claims, wherein the bis(ether N-organo substituted phthalimide) is 2,2-bis[4-(3,4-dicarboxy phenoxy)phenyl]propane bis-N-methylimide.

1 3. A bisphasic imidide-anhydride exchange process for making aromatic bis(ether phthalic acid) of the formula:

or the anhydride thereof from aromatic bis(ether phthalimide) which comprises: (A) heating at a temperature of 1 70-2600C and a pressure of 200-500 psi, a mixture comprising: (i) aromatic bis(ether phthalimide) of the formula:

(ii) 2-20 moles phthalic anhydride or phthalic acid per mole of (i).

(iii) 1-3 moles of a trialkylamine exchange catalyst per mole of (i).

(iv) 0.01-100 parts of water per part by weight of (i).

(v) 0.01-100 parts of a water immiscible organic solvent per part by weight of (i) to produce an equilibrated liquid biphasic reaction mixture, comprising an aqueous phase having selectively dissolved therein the aromatic bis(ether phthalic acid) formed in the exchange reaction, the trialkylamine catalyst, along with any excess phthalic acid, and an organic phase having selectively dissolved therein, N-organo substituted phthalimide of the formula:

which was also formed in the exchange reaction, together with any unreacted aromatic bis(ether phthalimide).

(B) separating the organic phase from the aqueous phase, (C) recovering the aromatic bis(ether phthalic acid) from the aqueous phase, where R is a divalent aromatic radical having from 6-30 carbon atoms and R' is a monovalent organo radical selected from the class consisting of C(a alkyl radicals, and organic radicals having from 6-20 carbon atoms selected from the class consisisting of aromatic hydrocarbon radicals and halogenated derivatives thereof where X is a radical selected from the class consisting of nitro, halo, fluoro, bromo, etc., and R1 is as previously defined.

14. A process as claimed in any one of the preceding claims, further comprising a plurality of equilibration and phase separation steps.

1 5. A process as claimed in any one of the preceding claims, wherein the reactants catalysts and solvents are recycled and conserved in a continuous manner.

1 6. A process as claimed in any one of the preceding claims, which is made continuous by passing the mixture of (A) through a heated coiled tube reactor.

1 7. A process as claimed in claim 1 6 wherein the reaction temperature is between 1700-- 2600C and the reaction pressure is between 200 psi-700 psi.

1 8. A process as claimed in claim 16, for making aromatic bis(ether phthalic acid) of the formula:

or the anhydride thereof from aromatic bis(ether phthalamide), which comprises: (A) passing a mixture comprising: (i) aromatic bis(ether phthalimide) of the formula:

(ii) 2-20 moles phthalic anhydride or phthalic acid per mole of (i).

(iii) 1-3 moles of a trialkylamine exchange catalyst per mole of (i).

(iv) 0.01-100 parts of water per part by weight of (i).

(v) 0.01100 parts of a water immiscible organic solvent per part by weight of (i) through a coiled tube reactor at 1 700C-2600C and a pressure of 200-700 psi to produce an equilibrated liquid biphasic reaction mixture, comprising an aqueous phase having selectively dissolved therein the aromatic bis(ether phthalic acid) formed in the exchange reaction, the trialkylamine catalyst, along with any excess phthalic acid, and an organic phase having selectively dissolved therein, N-organo substituted phthalimide of the formula::

which was also formed in the exchange reaction, together with any unreacted aromatic bis(ether phthalimide), (B) separating the organic phase from the aqueous phase, (C) recovering the aromatic bis(ether phthalic acid) from the aqueous phase, where R is a diva lent aromatic radical having from 6-30 carbon atoms, R1 is a monovalent organo radical selected from the class consisting of C(18 alkyl radicals, and organic radicals having from 620 carbon atoms selected from the class consisting of aromatic hydrocarbon radicals and halogenated derivatives thereof and X is a radical selected from the class consisting of the nitro group and halogen.

1 9. A process as claimed in claim 18, wherein the reactants, catalysts and solvents are recycled in a continuous manner.

20. A process as claimed in claim 1, substantially as hereinbefore described in any one of the Examples.

21. Aromatic bis(ether phthalic acid) when produced by a process as claimed in any one of the preceding claims.