Backround of the Invention 4,4'-Oxybisphthalic dianhydride (OBPDA) is used for clear, high <BR> <BR> <BR> performance polyimides that exhibit excellent I iV resistance, thermal oxidative stability, chemical resistance and flame retardance with low smoke generation. Applications include composites, foams, adhesives, molded parts, films, microelectronic coatings and fibers. It can also be used as an epoxy curing agent.

Variou,s methods for the preparation of OBPDA have been described in the literature: The oxidation of 3,3',4,4'-tetramethyldiphenyl ethers followed by cyclization [C.S. Marvel et al., J. Am. Chem. Soc., 80, 1197(1958), CA 52: 13707; G.S. Kolesnikov et al., Vysokomol. Soyed, A9(3), 612(1967), CA 67: 22389; Z.N. Lavrova et al., Volokna Sin. Polim, 15 (1970), CA 76: 33912].

Low yields are obtained in the oxidation stage (25%).

The condensation of 4-nitrophthalic anhydride in DMAc, in the presence of benzoic acid, a benzoic acid derivative or a C2-C14-carboxylic acid, or their salts, as catalysts gives OBPDA [US 5,117,002 (1992) Occidental Chem.

Corp., CA 117: 131054].

It was claimed that the reaction of a 4-halophthalic acid or anhydride with an alkali metal hydroxide in a polar aprotic solvent at 125"C yielded OBPDA [JP 80/122,738 (1980), Nlitsui Toatsu Chemicals, Inc., CA 94: 83799], and that heating a mixture of 4-bromophthalic anhydride, 50% aq.

KOH and Cu at >100°C, cooling and neutralizing with 35% HCl gave the corresponding tetra-acid [JP 86/205,232 (1986), Yutaka Kobayashi, CA 106: 32593].

The reaction of 4-halophthalic anhydride, Na2CO3 and NaNO2 in DAISO to give OBPDA in a yield of 87% [JP 80/127,343 (1980) Mitsui Toatsu Chemicals, Inc., CA 94: 191942].

Several other patents assigned to Occidental Chemical Corp. disclose various methods for the preparation of OBPDA. US 4,697,023 (1987, Occidental Chemical Corp., CA 108: 167297) discloses the reaction of a 4- halophthalic anhydride with H20 and an alkali metal compound such as K2CO3, KF, CsF in the presence of a polar aprotic solvent. Thus, the condensation of 4-fluorophthalic anhydride in DNIF or sulfolane gave OBDPA.

US 4,946,985 (1990, Occidental Chemical Corp., CA 114:61915) is the same as US 4,697,023, but with the addition of a copper catalyst. The best results were obtained using a catalyst of cuprous benzoate.

US 4,837,404 (1989, Occidental Chemical Corp., CA 111: 173974) describes the reaction between 4-hydroxyphthalic anhydride and 4- fluorophthalic anhydride and K2C03 or KF in sulfolane or DMF to give OBPDA in yields of 92.6%. then 4-chlorophthalic anhydride was used, the yield was 5.5% OBPDA and when 4-bromophthalic anhydride was used, the yield was 7.0%.

US 4,870,194 (1989) and 5,021,168 (1991, Occidental Chemical Corp., CA 112: 98366) describe the reaction of a 4-halophthalic anhydride with K2CO3 in a specific molar.ratio (>2:1). Best yields of OBPDA are obtained using 4-chlorophthalic anhydride, after 24 hours reaction in 1,2,4- trichlorobenzene (TCB) and in the presence of tetraphenylphosphonium bromide (TPPB) as phase transfer catalyst and methyl polyethylene glycol (MPEG).

The process disclosed in US 4,948,904 (1990, Occidental Chemical Corp., CA 114: 81562) comprises the condensation of 4-hydroxyphthalic anhydride with 4-fluorophthalic anhydride in the presence of KF and red cuprous oxide in anhydrous DMF.

US 5,153,335 (1992, Occidental Chemical Corp., CA 117: 48325), discloses the reaction of a 4-halophthalic anhydride with an alkali metal salt such as Na2CO3 or K2CO3 in the presence of a phase-transfer catalyst, TPPB, using dichlorobenzene as solvent. A co-catalyst of a benzoic acid or benzoic acid derivative is used.

The main problem with the processes described in the aforementioned US patents nos. 4,697,023, 4,946,985, 4,837,404, 4,870,194, 5,021,168, and 5,153,335 is the evolution of CO2 (due to the use of K2CO3 in said processes) during the feeding in of the reagents at a high temperature, leading to technical problems and to long reaction times. The presence of water is required to be limited to precise trace amounts, something which is very difficult to implement in practice. The presence of more than trace amounts of water significantly reduces the yield of OBPDA. These disadvantages make said process less attractive for industrial implementation. Also, the best yields are obtained therein by using 4- fluorophthalic anhydride, an expensive starting material.

It is therefore an object of the invention to provide an industrial process for the preparation of OBPDA which is simple and efficient, which includes simple reaction steps and work-up procedure, and which gives OBPDA in high yields and high purity.

It is another object of the invention to provide a process for the preparation of OBPDA in which no CO2 is evolved during the feeding in of the reagents, leading to a less problematic feeding stage.

It is yet another object of the invention to provide a process which does not use a bromobenzoic acid co-catalyst or copper catalyst, leading to a simpler work-up procedure and fewer reaction side-products.

It is still another object of the invention to provide a process for the preparation of OBPDA in which no water, and therefore no source of water, is required in the stage of the process in which the OBPDA is formed.

It is another object of the invention to provide a very simple reaction procedure to obtain OBPDA, whereby all the reactants are introduced together into either an autoclave, or a reaction vessel at atmospheric pressure, and heated, and which procedure dispenses with the necessity for expensive pumps and equipment for feeding in the reaction materials at high temperatures, as required in the prior art.

It is another object of the invention to provide novel compounds which may be used in the process of the invention.

Other objects and advantages of the invention will become apparent as the description proceeds.

Summary of the Invention The process according to the invention comprises two steps. In the first step, in which the reagent for the main, second step is prepared, a 4- halophthalic anhydride (HPAn), wherein halo is chosen from among bromo-, chloro- or fluoro- (BPAn, CPAn, and FPAn, respectively), is reacted with an alkali metal hydroxide chosen from among aqueous KOH, aqueous NaOH, or a mixture thereof, to produce the corresponding dialkali-4-halophthalate, specifically dipotassium- or disodium-4- halophthalate (DPHP or DSHP, respectively), or a mixture thereof. After the completion of this reaction, i.e. when the pH of the solution reaches 7.5, the water is evaporated and the dipotassium- or disodium-4- halophthalate obtained is dried to a water content of <0.2%, since the presence of water in the subsequent step drastically reduces the yield of OBPDA.

In the second step, dipotassium- or disodium-4-halophthalate (DPHP or DSHP), or mixture thereof, is reacted with 4-halophthalic anhydride (HPAn), using a suitable haloaromatic solvent such as dichlorobenzene (DCB) or trichlorobenzene (TCB) and a phase transfer catalyst, such as tetraphenylphosphonium bromide (TPPB), to yield OBPDA. The halogen in the HPAn is not necessarily the same halogen as in the DPHP or DSHP. The reaction can be carried out in an autoclave, or at atmospheric pressure. The reaction is monitored by titration for halide (to determine the conversion of the reactants) and by gas chromatographic analysis.

Upon completion of the reaction to yield OBPDA, the reaction mixture is diluted with hot solvent and filtered hot to remove inorganic salts and unreacted phthalate from the reaction mixture. The solution is then cooled and filtered to obtain the crystallised OBPDA in a purity of 99%.

Unreacted 4-halophthalic anhydride remains in the mother liquor. The solvent and unreacted 4-halophthalic anhydride are distilled in order to separate them; the separated 4-halophthalic anhydride and solvent can then be recycled. The OBPDA obtained after filtration is recrystallized to give OBPDA in a purity of above 99.5%.

The invention also comprises, as new compositions of matter, the compounds dipotassium-4-bromophthalate, disodium-4-bromophthalate, and disodium-4-fluorophthalate.

Detailed Description of Preferred Embodiments As stated, the process according to the invention comprises two steps: 1. The preparation of dipotassium-4-halophthalate and/or disodium-4- halophthalate by the reaction between HPAn (BPAn, CPAn or FPAn) and KOH and/or NaOH.

2. The reaction of halophthaiic anhydride (BPAn, CPiln or FPAn) with the dry (<0.2% water) dipotassium-4-halophthalate and/or disodium-4- halophthalate to form OBPDA.

Stage 1: Preparation of dipotassium-4-haiophthalate or diodium- 4-halophthalate Dipotassium-4-halophthalate or disodium-4-halophthalate (where halo is bromo-, chloro- or fluoro), or a mixture thereof, is prepared by the reaction between the appropriate 4-halophthalic anhydride (HPAn) and KOH or NaOH respectively; or a mixture thereof.

A solution of aqueous KOH and/or NaOH is prepared, which is then heated to about 70°C. HPAn is slowly added with constant stirring, until the molar ratio of the total amount of HPAn added to the base initially present is 1:2. The reaction is exothermic and the temperature rises. The reaction is monitored by measuring the pH; when the pH reaches 7.5, the reaction is complete. The water is then evaporated and the dipotassium-4- halophthalate or disodium-4-halophthalate obtained is dried at 1700 C, under vacuum, to a water content of '0.2% w/w. The phthalate is then used in the second stage of the process.

Stage 2: Preparation of OBPDA In this stage, the dipotassium-4-halophthalate and/or disodium-4- halophthalate obtained in stage 1 is reacted with a halophthalic anhydride in a suitable haloaromatic solvent, such as dichloro- or trichlorobenzene, in the presence of a phase transfer catalyst, to form OBPDA. The reaction can be performed at atmospheric pressure, or in an autoclave. The HPAn used in this stage may be the same or different from the HPAn used in the preparation of DPHP or DSHP in the first stage of the process of the invention.

Starlinz materials for Stage 2 The dipotassium-4-halophthalate or disodium-4-halophthalate for the process is prepared, and dried to a water content of '0.2%, as described above in Stage 1. The HPAn may be prepared, for example, by acidification, thermal ring closure and fractional distillation of the corresponding sodium-4-halophthalate, or obtained from commercial sources. The feed materials for stage 2, i.e. DPHP or DSHP, HPAn and solvent, must not contain more than 0.2% water. The solvent used is preferably 1,2-dichlorobenzene (DCB). Preferably, the phase transfer catalyst used is tetraphenylphosphonium bromide (TPPB).

Reactant quantities for Stave 2 The molar ratio of the total amount of dipotassium-4-halophthalate and disodium-4-halophthalate to HPAn is 0.8-1.1, preferably about 0.9. It is preferable to use a small excess of HPAn to phthalate, since any unreacted HPAn is recovered and can be recycled. The solvent, preferably DCB, is used in the relatively small amount of 50-150 wt.% of the HPAn, preferably 100 wt.%. The phase transfer catalyst, preferably TPPB, is used in an amount of 1.0-3.0 wt.% of the HPAn, preferably 2 wt.%.

TemPerature for Stave 2 reaction The reaction is carried out in an autoclave or at atmospheric pressure at 210-230"C, preferably 220"C. NVhen the reaction is carried out in an autoclave, the pressure is autogenous. WRen the reaction is carried out at atmospheric pressure, the temperature (210-230"C) is achieved by adjusting the ratio of HPAn to solvent, since this ratio determines the vapour pressure. In one embodiment of the invention, equal amounts by weight of DCB and HPAn are used and the reaction temperature is 220"C.

Work-up of Stage 2 Upon completion of the reaction, the reaction mixture is cooled to 150- 1600C, diluted with DCB, and the whole diluted reaction mixture heated to 180"C. The diluted reaction mixture is maintained at this temperature for 30 mins. with stirring to ensure complete dissolution of the OBPDA, and then filtered hot through a heated funnel to remove (a) organic and inorganic salts formed during the reaction, and (b) unreacted dipotassium- 4-halophthalate or disodium-4-halophthalate. The solution is cooled, causing crystallisation of OBPDA, and the product (OBPDA) is filtered and dried. The unreacted HPAn remains in the mother liquor, and this may be recovered by (a) removal of remaining solvent from the mother liquor by evaporation, follo+>red by (b) separation of the unreacted HPAn from the residue of the evaporation by fractional distillation. The recovered, unreacted HPAn can be recycled. The solvent is also recycled.

OBPDA is obtained in a purity of 99%. A simple recrystallization from DCB, TCB or other suitable solvent produces OBPDA in a purity of >99.5%.

One of the advantages of this invention is the simplicity of the reaction procedure, whereby all the reactants are introduced together into either an autoclave, or a reaction vessel at atmospheric pressure, and heated.

This procedure dispenses with the necessity for expensive pumps and equipment for feeding in the reaction materials at high temperatures.

Another advantage of this invention is the simple work-up procedure which produces the OBPDA directly in a purity of 99%. OBPDA, in a purity of >99.5%, can be obtained by a simple recrystallization from DCB.

The foregoing characteristics and advantages of the present invention will be better understood through the following illustrative and non-limitative examples.

Examples 1-3: Preparation of dipotassium-4-halophthalate The reaction was carried out between halophthalic anhydride (BPAn, CPAn, or FPAn), and KOH in a molar ratio of 1:2, at 70-100°C. The 4- chlorophthalic anhydride (CPAn) used for the process was prepared from sodium-4-chlorophthalate obtained from Aldrich, by acidification, thermal ring closure and fractional distillation. The 4-fluorophthalic anhydride (FPAn) used was purchased from OxyChem. The 4-bromophthalic anhydride (BPAn) used was manufactured at Bromine Compounds Ltd.

A solution of aq. KOH was prepared at 70°C. The HPAn was then slowly added with constant stirring. The reaction was monitored by measuring the pH. At completion, the pH was 7.5. The water was then evaporated and the dipotassium halophthalate obtained was dried at 170°C, under vacuum, to a water content of #0.2%. The results are presented in Table I: Table I Ex. Weight of reagents, g pH of Dry product no. H20 85% FPAn CPAn BPAn aq. salt Wt, g % H2O KOH 1 145.5 105.6 133 - - 7.5 206.0 0.1 2 34.2 1 26.4 37 - 7.5 53.7 0.1 3 179.1 269.7 474 7.4 648.5 0.l Examples 4-6: Preparation of the disodium-4-halophthalate Examples 1-3 were repeated using NaOH instead of KOH. The results are presented in Table II: Table II Ex. Weight of reagents, g a pH of D roduct no. H20 NaOH FPAn CPAn BPAn aq. salt Wt, g % H2O 4 164 64 133 - - 7.4 178.0 0.1 5 45 1 6 37 7.4 48.5 0.2 6 224 64 1 - 183 7.4 231.Q 0.2 Example 7: Preparation of OBPDA at atmospheric Pressure Into a flask placed in an oil bath and equipped with a mechanical stirrer, a thermocouple and a condenser, were placed BPAn (56.8 g, 0.25 mole), dipotassium-4-bromophthalate (64.2 g, 0.2 mole), TPPB (1 g) and DCB (29 g). The reaction mixture was heated to reflux (215-2250C) and the contents stirred for 6 hrs. The conversion of dipotassium-4- bromophthalate (82.3%) was determined by titration of Br- (329 mmols) and by GC of the reaction mixture.

The reaction mixture was cooled to 1600C and diluted with 500 g DCB.

The contents were then stirred and refluxed (180"C) for 30 mins., then filtered through a sinter funnel with a heated jacket at 1600C. The cake was rinsed with 150 g hot DCB.

The filtrate was cooled, with stirring, under a dry, inert atmosphere, and the resulting crystals filtered through a sinter. The solid was washed with 100 g cold DCB.

The solid product was dried in a vacuum oven at 1900C for 15 hi. OBPDA (40.9 g) was obtained in a purity of~99.0%, as determined by differential scanning calorimetry (DSC) and GC, and in a yield of 66% based on dipotassium-4-bromophthalate. Fractional distillation of the mother liquor produced DCB (710 g) and BPAn (14 g); as stated, these can be recycled.

Example 8: Preparation of OBPDA in an autoclave Into an autoclave were placed BPAn (90.8 g, 0.4 mole), dipotassium-4- bromophthalate (115.6 g, 0.36 mole), TPPB (2 g) and DCB (103 g). The autoclave was closed and heated to 225"C for 5.5 hrs. The conversion of dipotassium-4-bromophthalate (83.3%) was determined by titration of Br- (600 mmol) and GC of the reaction mixture.

The autoclave was cooled to 1800 C, opened, and the contents transferred to a flask and diluted with 850 g DCB. The contents were stirred and refluxed (180"C) for 30 mins., then filtered through a sinter funnel with a heated jacket at 1600C. The cake was rinsed with 200 g hot DCB.

The filtrate was cooled, with stirring, under a dry, inert atmosphere, then the precipitate filtered through a sinter. The solid was washed with 120 g cold DCB.

The solid product was dried in a vacuum oven at 1900C for 15 hr. OBPDA (76.5 g) was obtained in a purity of 99.0% (DSC and GC) and a yield of 68.6%. Fractional distillation of the mother liquor produced DCB (1150 g) and BPAn (23 g), which can be recycled.

Examples 9-14: Preparation of OBPDA using different 4- halophthalic anhydrides and phthalates Example 8 was repeated using different halophthalic anhydrides and dipotassium- and disodium-4-halophthalates. Each reaction lasted 6 hours. The results are summarised in Tables III-V: Table III: Preparation of OBPDA from BPAn and dipotassium- or disodium- 4-bromonhthalate Ex. Starting materials, Solvent Catalyst Conv. OBPDA no. a (mols) * DCB TPPB by Br Yield ** BPAn DPBP ! DSBP 9 a 9 113.5 144.5 - 129 2.6 93 110.2 74.8 (0.5) ( 0.45) 10 68.1 - 78.0 73 1.6 25 8.0 9.1 (0.3) (0.27) * DPBP = dipotassium-4-bromophthalate, DSBP = disodium-4-bromophthalate ** The OBPDA yield is calculated by calibrated GC and is based on total bromophthalic moieties Table IV: Preparation of OBPDA from CPAn and dip otassium- or dis odium-4-chloro phthalate Ex. Starting materials, Solvent Catalyst Conv. OBPDA no. g (mols) * DCB TPPB by CF Yield ** CPAn DPCP DSCP g g % 11 35.2 47.0 - 42 1.0 74.4 33.2 59.5 (0.19) (0.17) 12 35.2 41.6 39 1.0 35.0 10.1 18.1 (0.19) (0.17) * DPCP = dipotassium-4-chlorophthaiate, DSCP = disodium-4-chlorophthalate * * The OBPDA yield is calculated by calibrated GC and is based on total chlorophthalic moieties Table V: Preparation of OBPDA from FPAn and dipotassium- or disodium4fluorophthalate Ex. Starting materials, Solvent Catalyst Conv. OBPDA no. r (mols) * DCB TPPB by F Yield ** FPAn DPFP DSFP g % g % no. 13 49.8 70.2 - 60 1.4 89.5 61.6 69.7 (0.3) (0.27) 14 49.8 - 61.6 56 1.4 54.8 29.2 33.0 (0.3) (0.27) * DPFP = dipotassium-4-fluorophtlialate, DSFP = disodium-4-fluorophthalate ** The OBPDA yield is calculated by calibrated GC and is based on total fluorophthalic moieties Examples 15-20 Comparative examples using dipotassium- and disodium phthalate Example 8 was repeated for purposes of comparison using the three different halophthalic anhydrides with dipotassium- and disodium phthalate. The reaction lasted 6 hours. The results are summarised in Tables VI-VIII: Table VI: Preparation of OBPDA from BPAn Starting materials, g (mols) Solvent Catalyst Conv OBPDA no. * DCB TPPB by Br Yield ** BPAn DPP DSP g g a 15 90.8 4{4-70l.l7l 36.5 58.9 (0.4) (0.2) 16 90.8 42.0 166 1.1 24 5.3 8.5 (0.4) (0.2) * DPP = dipotassium phthalate, DSP = disodium phthalate The OBPDA yield is calculated by calibrated GC and is based on total bromophthalic moieties Table VII: Preparation of OBPDA from CPAn Ex. Starting materials, Solvent Catalyst Conv OBPDA no. g (mols) * DCB TPPB by Cl Yield ** CPAn DPP DSP g g % g % 17 54.7 36.3 T 43 0.8 62.4 14.9 32.0 0.3) (0.15) 18 54.7 - 31.5 32 0.8 13.0 4.6 9.9 (0.3) (0.15) * DPP = dipotassium phthalate, DSP = disodium phthalate ** The OBPDA yield is calculated by calibrated GC and is based on total chlorophthalic moieties Table VIII: Preparation of OBPDA from FPAn Ex. Starting materials, Solvent - Catalyst Conv. OBPDA no. g g (mols) * DCB TPPB by F Yield ** FPAn DPP I DSP e e g 19 66.4 48.2 - 57 1.1 68.7 31.5 50.8 (0.4) (0.2) i 20 66.4 - 42.0 54 1.1 69.3 29.4 j 47.4 (0.4) (0.2) * DPP = dipotassiumphthalate, DSP = disodiumphthalate ** The OBPDA yield is calculated by calibrated GC and is based on total fluorophthalic moieties The foregoing examples have been provided to illustrate the invention without involving any limitation. It will be appreciated by skilled practitioners of the art that many modifications and variations, such as e.g. reaction time, reaction temperature and pressure, molar ratios of the reactants, use of dipotassium or disodium salts of other suitable difunctional acids, solvents used, and so forth, may be employed in carrying out the invention, all without departing from its spirit or exceeding the scope of the claims.