BACKGROUND

This invention relates to the preparation of diether dianhydrides, and more particularly to improved phase transfer catalyzed methods for such preparation.

Diether dianhydrides are important monomers for the preparation of polyetherimides having exceptionally high temperature performance and excellent solvent resistance. These properties are useful in high performance plastics applications such as advanced composites and electronic circuit materials.

A number of publications describe the preparation of diether dianhydrides, none however, discloses the method of the present invention and its advantages. Such publications include U.S. Pat. Nos. 3,956,320, 3,850,964, 4,868,316, and 6,706,897. Suitable reaction conditions for the reaction between halophthalic anhydrides and aromatic dihydroxy compounds include neat and solvent reactions and the presence of various catalysts, typically phase transfer catalysts such as tetraphenylphosphonium halides, fluorides such as potassium fluoride and cesium fluoride and carboxylic acids and their salts and hydrolysable esters. Many of these reactions suffer from low product yields. Moreover, numerous ambiguities are present in said publications regarding water content of the reaction mixtures and other conditions, making reproducibility questionable.

It is of interest, therefore, to provide a direct method for diether dianhydride preparation which affords high yields and a minimum of by-products, and which is consistently and reproducibly applicable.

BRIEF DESCRIPTION

The present invention provides an improved method for the preparation of diether dianhydrides through the use of substantially anhydrous solvent and at least one thermally stable phase transfer catalyst. In contrast with earlier methods, the method of the present invention consistently affords high yields of the desired product diether dianhydride and is highly reproducible.

In one embodiment the invention is a method for preparing a diether dianhydride which comprises contacting, under reactive and substantially anhydrous conditions, at least one halophthalic anhydride with at least one metal salt of an aromatic dihydroxy compound, in a nonpolar solvent in the presence of a thermally stable phase transfer catalyst.

In a typical embodiment, the invention provides a method for preparing an aromatic diether dianhydride of structure I, [Image Omitted]
wherein Ar is a divalent aromatic radical; R¹is independently at each occurrence a C₁-C₂₀aliphatic radical, C₃-C₂₀cycloaliphatic radical, or a C₂-C₂₀aromatic radical; and n is an integer from 0 to 3 inclusive;

said method comprising contacting under reactive and substantially anhydrous conditions, a mixture comprising:

- (a) at least one halophthalic anhydride of structure II
  wherein R¹is a C₁-C₂₀aliphatic radical, C₃-C₂₀a cycloaliphatic radical, or a C₂-C₂₀aromatic radical; X is selected from the group consisting of chloro, fluoro, bromo, and iodo; and n is an integer ranging from 0 to 3 inclusive;
- (b) at least one salt of an aromatic dihydroxy compound of structure III
  [^âˆ’OArO^âˆ’][M^a+]_(2/a)â€ƒâ€ƒIII
  wherein Ar is a divalent aromatic radical; and M is independently at each occurrence an alkali metal cation, an alkaline earth metal cation, or a mixture thereof; and â€œaâ€ is an integer having a value of 1 or 2;
- (c) at least one aromatic solvent; and
- (d) at least one phase transfer catalyst selected from the group consisting of
  - (i) guanidium salts having structure V
    wherein R³â€”R⁸are independently, at each occurrence a C₁-C₂₀aliphatic radical, a C₃-C₂₀cycloaliphatic radical, or a C₂-C₂₀aromatic radical; and X^âˆ’ is an organic or inorganic anionic species;
  - (ii) aminopyridium salts having structure VI
    wherein R⁹, R¹⁰and R¹¹are independently at each occurrence a C₁-C₂₀aliphatic radical, C₃-C₂₀cycloaliphatic radical, C₂-C₂₀aromatic radical, and wherein said R⁹and R¹⁰may be linked together form a cyclic structure comprising at least one nitrogen atom; and X^âˆ’ is an organic or inorganic anionic species, and
  - (iii) phosphazenium salts havng structure VII
    wherein R¹²and R¹³are independently at each occurrence a C₁-C₂₀aliphatic radical, a C₃-C₂₀cycloaliphatic radical, or a C₂-C₂₀aromatic radical, or R¹²and R¹³may together form a cyclic structure comprising at least one nitrogen atom; and X^âˆ’ is an organic or inorganic anionic species.

DETAILED DESCRIPTION

The present invention may be understood more readily by reference to the following detailed description of preferred embodiments of the invention and the examples included therein. In the following specification and the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings.

The singular forms â€œaâ€ , â€œanâ€ and â€œtheâ€ include plural referents unless the context clearly dictates otherwise.

â€œOptionalâ€ or â€œoptionallyâ€ means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

As used herein the term â€œaliphatic radicalâ€ refers to an organic radical having a valence of at least one consisting of a linear or branched array of atoms which is not cyclic. Aliphatic radicals are defined to comprise at least one carbon atom. The array of atoms comprising the aliphatic radical may include heteroatoms such as nitrogen, sulfur, silicon, selenium and oxygen or may be composed exclusively of carbon and hydrogen. For convenience, the term â€œaliphatic radicalâ€ is defined herein to encompass, as part of the â€œlinear or branched array of atoms which is not cyclicâ€ a wide range of functional groups such as alkyl groups, alkenyl groups, alkynyl groups, halo alkyl groups, conjugated dienyl groups, alcohol groups, ether groups, aldehyde groups, ketone groups, carboxylic acid groups, acyl groups (for example carboxylic acid derivatives such as esters and amides), amine groups, nitro groups and the like. For example, the 4-methylpent-1-yl radical is a C₆aliphatic radical comprising a methyl group, the methyl group being a functional group which is an alkyl group. Similarly, the 4-nitrobut-1-yl group is a C₄aliphatic radical comprising a nitro group, the nitro group being a functional group. An aliphatic radical may be a haloalkyl group which comprises one or more halogen atoms which may be the same or different. Halogen atoms include, for example; fluorine, chlorine, bromine, and iodine. Aliphatic radicals comprising one or more halogen atoms include the alkyl halides trifluoromethyl, bromodifluoromethyl, chlorodifluoromethyl, hexafluoroisopropylidene, chloromethyl; difluorovinylidene; trichloromethyl, bromodichloromethyl, bromoethyl, 2-bromotrimethylene (e.g. â€”CH₂CHBrCH₂â€”), and the like. Further examples of aliphatic radicals include allyl, aminocarbonyl (i.e. â€”CONH₂), carbonyl, dicyanoisopropylidene (i.e. â€”CH₂C(CN)₂CH₂â€”), methyl (i.e. â€”CH₃), methylene (i.e. â€”CH₂â€”), ethyl, ethylene, formyl (i.e. â€”CHO), hexyl, hexamethylene, hydroxymethyl (i.e. â€”CH₂OH), mercaptomethyl (i.e. â€”CH₂SH), methylthio (i.e. â€”SCH₃), methylthiomethyl (i.e. â€”CH₂SCH₃), methoxy, methoxycarbonyl (i.e. CH₃OCOâ€”), nitromethyl (i.e. â€”CH₂NO₂), thiocarbonyl, trimethylsilyl (i.e. (CH₃)₃Siâ€”), t-butyldimethylsilyl, trimethoxysilylpropyl (i.e. (CH₃O)₃SiCH₂CH₂CH₂â€”), vinyl, vinylidene, and the like. By way of further example, a C₁-C₁₀aliphatic radical contains at least one but no more than 10 carbon atoms. A methyl group (i.e. CH₃â€”) is an example of a C₁aliphatic radical. A decyl group (i.e. CH₃(CH₂)₉â€”) is an example of a C₁₀aliphatic radical.

As used herein, the term â€œaromatic radicalâ€ refers to an array of atoms having a valence of at least one comprising at least one aromatic group. The array of atoms having a valence of at least one comprising at least one aromatic group may include heteroatoms such as nitrogen, sulfur, selenium, silicon and oxygen, or may be composed exclusively of carbon and hydrogen. As used herein, the term â€œaromatic radicalâ€ includes but is not limited to phenyl, pyridyl, furanyl, thienyl, naphthyl, phenylene, and biphenyl radicals. As noted, the aromatic radical contains at least one aromatic group. The aromatic group is invariably a cyclic structure having 4n+2 â€œdelocalizedâ€ electrons where â€œnâ€ is an integer equal to 1 or greater, as illustrated by phenyl groups (n=1), thienyl groups (n=1), furanyl groups (n=1), naphthyl groups (n=2), azulenyl groups (n=2), anthracenyl groups (n=3) and the like. The aromatic radical may also include nonaromatic components. For example, a benzyl group is an aromatic radical which comprises a phenyl ring (the aromatic group) and a methylene group (the nonaromatic component). Similarly a tetrahydronaphthyl radical is an aromatic radical comprising an aromatic group (C₆H₃) fused to a nonaromatic component â€”(CH₂)₄â€”. For convenience, the term â€œaromatic radicalâ€ is defined herein to encompass a wide range of functional groups such as alkyl groups, alkenyl groups, alkynyl groups, haloalkyl groups, haloaromatic groups, conjugated dienyl groups, alcohol groups, ether groups, aldehyde groups, ketone groups, carboxylic acid groups, acyl groups (for example carboxylic acid derivatives such as esters and amides), amine groups, nitro groups, and the like. For example, the 4-methylphenyl radical is a C₇aromatic radical comprising a methyl group, the methyl group being a functional group which is an alkyl group. Similarly, the 2-nitrophenyl group is a C₆aromatic radical comprising a nitro group, the nitro group being a functional group. Aromatic radicals include halogenated aromatic radicals such as trifluoromethylphenyl, hexafluoroisopropylidenebis(4-phen-1-yloxy) (i.e. â€”OPhC(CF₃)₂PhOâ€”), chloromethylphenyl; 3-trifluorovinyl-2-thienyl; 3-trichloromethylphen-1-yl (i.e. 3-CCl₃Ph-), 4-(3-bromoprop-1-yl)phen-1-yl (i.e. BrCH₂CH₂CH₂Ph-), and the like. Further examples of aromatic radicals include 4-allyloxyphen-1-oxy, 4-aminophen-1-yl (i.e. H₂NPh-), 3-aminocarbonylphen-1-yl (i.e. NH₂COPh-), 4-benzoylphen-1-yl, dicyanoisopropylidenebis(4-phen-1-yloxy) (i.e. â€”OPhC(CN)₂PhOâ€”), 3-methylphen-1-yl, methylenebis(phen-4-yloxy) (i.e. â€”OPhCH₂PhOâ€”), 2-ethylphen-1-yl, phenylethenyl, 3-formyl-2-thienyl, 2-hexyl-5-furanyl; hexamethylene-1,6-bis(phen-4-yloxy) (i.e. â€”OPh(CH₂)₆PhOâ€”); 4-hydroxymethylphen-1-yl (i.e. 4-HOCH₂Ph-), 4-mercaptomethylphen-1-yl (i.e. 4-HSCH₂Ph-), 4-methylthiophen-1-yl (i.e. 4-CH₃SPh-), 3-methoxyphen-1-yl, 2-methoxycarbonylphen-1-yloxy (e.g. methyl salicyl), 2-nitromethylphen-1-yl (i.e. -PhCH₂NO₂), 3-trimethylsilylphen-1-yl, 4-t-butyldimethylsilylphenl-1-yl, 4-vinylphen-1-yl, vinylidenebis(phenyl), and the like. The term â€œa C₃-C₁₀aromatic radicalâ€ includes aromatic radicals containing at least three but no more than 10 carbon atoms. The aromatic radical 1-imidazolyl (C₃H₂N₂â€”) represents a C₃aromatic radical. The benzyl radical (C₇H₈â€”) represents a C₇aromatic radical.

As used herein the term â€œcycloaliphatic radicalâ€ refers to a radical having a valence of at least one, and comprising an array of atoms which is cyclic but which is not aromatic. As defined herein a â€œcycloaliphatic radicalâ€ does not contain an aromatic group. A â€œcycloaliphatic radicalâ€ may comprise one or more noncyclic components. For example, a cyclohexylmethyl group (C₆H₁₁CH₂â€”) is an cycloaliphatic radical which comprises a cyclohexyl ring (the array of atoms which is cyclic but which is not aromatic) and a methylene group (the noncyclic component). The cycloaliphatic radical may include heteroatoms such as nitrogen, sulfur, selenium, silicon and oxygen, or may be composed exclusively of carbon and hydrogen. For convenience, the term â€œcycloaliphatic radicalâ€ is defined herein to encompass a wide range of functional groups such as alkyl groups, alkenyl groups, alkynyl groups, halo alkyl groups, conjugated dienyl groups, alcohol groups, ether groups, aldehyde groups, ketone groups, carboxylic acid groups, acyl groups (for example carboxylic acid derivatives such as esters and amides), amine groups, nitro groups and the like. For example, the 4-methylcyclopent-1-yl radical is a C₆cycloaliphatic radical comprising a methyl group, the methyl group being a functional group which is an alkyl group. Similarly, the 2-nitrocyclobut-1-yl radical is a C₄cycloaliphatic radical comprising a nitro group, the nitro group being a functional group. A cycloaliphatic radical may comprise one or more halogen atoms which may be the same or different. Halogen atoms include, for example; fluorine, chlorine, bromine, and iodine. Cycloaliphatic radicals comprising one or more halogen atoms include 2-trifluoromethylcyclohex-1-yl, 4-bromodifluoromethylcyclooct-1-yl, 2-chlorodifluoromethylcyclohex-1-yl, hexafluoroisopropylidene2,2-bis (cyclohex-4-yl) (i.e. â€”C₆H₁₀C(CF₃)₂C₆H₁₀â€”), 2-chloromethylcyclohex- 1 -yl; 3-difluoromethylenecyclohex-1-yl; 4-trichloromethylcyclohex-1-yloxy, 4-bromodichloromethylcyclohex-1-ylthio, 2-bromoethylcyclopent-1-yl, 2-bromopropylcyclohex-1-yloxy (e.g. CH₃CHBrCH₂C₆H₁₀â€”), and the like. Further examples of cycloaliphatic radicals include 4-allyloxycyclohex-1-yl, 4-aminocyclohex-1-yl (i.e. H₂NC₆H₁₀â€”), 4-aminocarbonylcyclopent-1-yl (i.e. NH₂COC₅H₈â€”), 4-acetyloxycyclohex-1-yl, 2,2-dicyanoisopropylidenebis(cyclohex-4-yloxy) (i.e. â€”OC₆H₁₀C(CN)₂C₆H₁₀Oâ€”), 3-methylcyclohex-1-yl, methylenebis(cyclohex-4-yloxy) (i.e. â€”OC₆H₁₀CH₂C₆H₁₀Oâ€”), 1-ethylcyclobut-1-yl, cyclopropylethenyl, 3-formyl-2-terahydrofuranyl, 2-hexyl-5-tetrahydrofuranyl; hexamethylene-1,6-bis(cyclohex-4-yloxy) (i.e. â€”OC₆H₁₀(CH₂)₆C₆H₁₀Oâ€”); 4-hydroxymethylcyclohex-1-yl (i.e. 4-HOCH₂C₆H₁₀â€”), 4-mercaptomethylcyclohex-1-yl (i.e. 4-HSCH₂C₆H₁₀â€”), 4-methylthiocyclohex-1-yl (i.e. 4-CH₃SC₆H₁₀â€”), 4-methoxycyclohex-1-yl, 2-methoxycarbonylcyclohex-1-yloxy (2-CH₃OCOC₆H₁₀Oâ€”), 4-nitromethylcyclohex-1-yl (i.e. NO₂CH₂C₆H₁₀â€”), 3-trimethylsilylcyclohex-1-yl, 2-butyldimethylsilylcyclopent-1-yl, 4-trimethoxysilylethylcyclohex-1-yl (e.g. (CH₃O)₃SiCH₂CH₂C₆H₁₀â€”), 4-vinylcyclohexen-1-yl, vinylidenebis(cyclohexyl), and the like. The term â€œa C₃-C₁₀cycloaliphatic radicalâ€ includes cycloaliphatic radicals containing at least three but no more than 10 carbon atoms. The cycloaliphatic radical 2-tetrahydrofuranyl (C₄H₇Oâ€”) represents a C₄cycloaliphatic radical. The cyclohexylmethyl radical (C₆H₁₁CH₂â€”) represents a C₇cycloaliphatic radical.

As noted, the present invention provides a method for the preparation of diether dianhydrides of the formula I: [Image Omitted]
wherein Ar is a divalent aromatic radical; R¹is independently at each occurrence a C₁-C₂₀aliphatic radical, C₃-C₂₀cycloaliphatic radical, or a C₂-C₂₀aromatic radical; and n is an integer from 0 to 3 inclusive; said method comprising contacting, under reactive and substantially anhydrous conditions:

- (a) at least one halophthalic anhydride of the formula II:
  wherein R¹is a C₁-C₂₀aliphatic radical, a C₃-C₂₀cycloaliphatic radical, or a C₂-C₂₀aromatic radical; n is an integer from 0 to 3 inclusive; and X is a leaving group selected from the group consisting of fluoro, chloro, bromo, and iodo;
- (b) at least one metal salt of an aromatic dihydroxy group of the formula III
  [^âˆ’OArO^âˆ’][M^a+]_(2/a)â€ƒâ€ƒIII
  wherein Ar is a divalent aromatic radical; and M is independently at each occurrence an alkali metal cation, an alkaline earth metal cation, or a mixture thereof; and â€œaâ€ is an integer having a value of 1 or 2;
- (c) at least one aromatic solvent; and
- (d) at least one thermally stable phase transfer catalyst.

Diether dianhydrides having structure I are exemplified by 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (CAS Registry No. 38103-06-9); 2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride; 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]butane dianhydride; 1,1-bis[4-(3,4-dicarboxyphenoxy)phenyl]cyclohexane dianhydride; 1,1-bis[4-(3,4-dicarboxyphenoxy)phenyl]-3,3,5-trimethylcyclohexane dianhydride; 5,5â€²-[[1,1â€²-biphenyl]-4,4â€²-diylbis(oxy)]bis-1,3-isobenzofurandione (CAS Registry No. 26177-82-2).

Exemplary halophthalic anhydrides, as represented by formula II, include 3-chlorophthalic anhydride, 4-chlorophthalic anhydride, 3-fluorophthalic anhydride, 4-fluorophthalic anhydride, and combinations thereof.

The method of the present invention typically employs a salt of an aromatic dihydroxy compound, said salt having formula III
[^âˆ’OArO^âˆ’][M^a+]_(2/a)â€ƒâ€ƒIII
wherein Ar is a divalent aromatic radical, and M is independently at each occurrence an alkali metal cation, an alkaline earth metal cation, or a mixture thereof, and â€œaâ€ is an integer having a value of 1 or 2. Salts having structure III are exemplified by hydroquinone disodium salt, resorcinol disoldium salt, bisphenol A disodium salt, bisphenol A dipotassium salt, 4,4â€²-biphenol disodium salt, and the like.

The salt of the aromatic dihydroxy compound is typically derived from an aromatic dihydroxy compound having structure IV [Image Omitted]
wherein R²is independently at each occurrence a halogen atom, a nitro group, a cyano group, a C₁-C₁₂aliphatic radical, C₃-C₁₂cycloaliphatic radical, or a C₃-C₁₂aromatic radical; q is independently at each occurrence an integer from 0 to 4 inclusive; and W is a bond, O, S, SO, SO₂, Se, a C₁-C₂₀aliphatic radical, C₃-C₂₀cycloaliphatic radical, or a C₃-C₂₀aromatic radical.

Dihydroxy aromatic compounds IV are exemplified by 3,4â€²-dihydroxydiphenylmethane; 4,4â€²-dihydroxybenzophenone; 4,4â€²-dihydroxydiphenylether; 2,2-bis(2-hydroxyphenyl)propane; bis-(2-hydroxyphenyl)methane; 2,2-bis(4-hydroxyphenyl)propane; 4,4â€²-dihydroxybiphenyl; 2,2-bis(4-hydroxy 2,6-dibromophenyl)propane, 2,4â€²-dihydroxybenzophenone; 4,4â€²-dihydroxydiphenylsulfone; 4,4â€²-dihydroxydiphenyl sulfoxide; 4,4â€²-dihydroxydiphenyl sulfide; and the like. Preferred aromatic dihydroxy compounds are bisphenol A (CAS Number: 80-05-7) and biphenol (CAS Number: 92-88-6).

The salt of the aromatic dihydroxy compound may be formed by contacting the aromatic dihydroxy represented by structure IV with at least one metal salt, such as a metal hydroxide, in a substantially anhydrous solvent. Typically, the at least one metal salt is employed such that the total amount of the at least one metal salt corresponds to at least one molar equivalent with respect to the number of hydroxyl groups present in the aromatic dihydroxy compound. When more than one metal salt is employed the metal salt of aromatic dihydroxy compound may comprise two or more different metal cations. It will be understood by those in the art that when the valency of the metal cation is greater than 1, one metal cation moiety may be bound to more than one oxygen in structure III. The salt of the aromatic dihydroxy compounds may be produced separately and added to the reaction mixture to make the diether dianhydride. In an alternate embodiment, the salt of the aromatic dihydroxy compound may be produced in situ in the reaction vessel used to make the diether dianhydride. Typically, the salt of the aromatic dihydroxy compound is prepared by contacting a metal hydroxide with a an aromatic dihydroxy compound. Suitble metal hydroxides include sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide, magnesium hydroxide, calcium hydroxide, aluminum hydroxide, combinations thereof, and the like.

The reaction to produce diether dianhydrides may be performed in the absence or in the presence of at least one solvent. In various embodiments it is preferred that the reaction be conducted in a solvent. While dipolar aprotic solvents may be used, their use is generally not advisable since they can promote side reactions and the formation of colored by-products. In various embodiments suitable solvents have a boiling point above about 120Â° C., preferably above about 150Â° C. and more preferably above about 180Â° C. Suitable solvents include, but are not limited to, ortho-dichlorobenzene (hereinafter â€œo-dichlorobenzeneâ€ ), para-dichlorobenzene (hereinafter â€œp-dichlorobenzeneâ€ ), 2,4-dichlorotoluene, 1,2,4-trichlorobenzene, diphenyl sulfone, phenetole, anisole, veratrole, and mixtures thereof. It is more preferred that chlorinated aromatic liquids be employed as solvents, examples of which include, but are not limited to, o-dichlorobenzene, 2,4-dichlorotoluene and 1,2,4-trichlorobenzene. o-Dichlorobenzene is often preferred since it is a high boiling liquid and thus, permits for the reaction to be run at higher temperatures and/or at superatmospheric pressures. The choice of o-dichlorobenzene as a solvent also allows for the use of a greater proportion of phase transfer catalyst in the reaction mixture. Such reaction conditions result in desirably higher reaction rates.

The reaction mixture should be substantially anhydrous, the term â€œsubstantially anhydrousâ€ denoting a total water content of less than about 50 ppm, preferably less than about 20 ppm and most preferably less than about 10 ppm by weight. Any water present above this amount can inhibit the reaction, irrespective of its source. Traces of water may be present in either of the reagents, and they should be carefully removed by drying before beginning the reaction. Drying can be achieved by methods known in the art. Liquid reagents and solvents can be dried by distillation and/or by contact with molecular sieves, and solid materials by heating in an oven, most often under vacuum.

The thermally stable phase transfer catalysts (hereinafter referred to as â€œPTCsâ€ ) are known in the art; reference is made, for example, to U.S. Pat. No. 5,081,298. By â€œthermally stableâ€ , it is meant that the phase transfer catalyst is of greater stability under the reaction conditions employed, than a tetraalkyl ammonium phase transfer catalyst such as tetrabutyl ammonium bromide. The thermally stable phase transfer cataylts used according to the method of the present invention are believed to possess greater stability with respect to olefin-forming elimination reactions (Sayseff and Hoffman type eliminations) and dealkylation than are the phase transfer catalysts comprising tetraalkyl ammonium moieties. Typical catalysts used according to the method of the present invention include hexaalkylguanidinium salts, pyridinium salts, phosphazenium salts and the like. Representative hexaalkylguanidinium salts are shown in formula V. [Image Omitted]
wherein R³â€”R⁸are independently, at each occurrence a C₁-C₂₀aliphatic radical, a C₃-C₂₀cycloaliphatic radical, or a C₂-C₂₀aromatic radical; and X^âˆ’ is an organic or inorganic anionic species. Representative pyridnium salts suitable for use as phase transfer catalysts are shown in formula VI [Image Omitted]
wherein R⁹, R¹⁰and R¹¹are independently at each occurrence a C₁-C₂₀aliphatic radical, C₃-C₂₀cycloaliphatic radical, C₂-C₂₀aromatic radical, and wherein said R⁹and R¹⁰may be linked together form a cyclic structure comprising at least one nitrogen atom; and X^âˆ’ is an organic or inorganic anionic species. Representative phosphazenium catalysts are shown in formula VII [Image Omitted]
wherein R¹²and R¹³are independently at each occurrence a C₁-C₂₀aliphatic radical, a C₃-C₂₀cycloaliphatic radical, or a C₂-C₂₀aromatic radical, or R¹²and R¹³may together form a cyclic structure comprising at least one nitrogen atom; and X^âˆ’ is an organic or inorganic anionic species. Suitable phase transfer catalysts are illustrated by 1-neopentyl-4-(N,N-dibutylamino)-pyridinium chloride, 1-neopentyl-4-piperidin-1-ylpyridinium chloride, 1-neopentyl-4-piperidin-1-ylpyridinium mesylate, 1-3-methylheptyl-4-(4-methyl)-piperidin-1-ylpyridinium chloride, hexaethylguanidinium chloride, dodecamethyl phosphazenium chloride, and the like.

The molar ratio of the two reactants, the halophthalic anhydride and the metal salt of an aromatic dihydroxy compound, is typically at least 2:1. In one embodiment the molar ratio of the two reactants, the halophthalic anhydride and the metal salt of an aromatic dihydroxy compound, is in the range of from about 2.1:1 to about 3.1:1. By way of illustration, a molar ratio of the two reactants, the halophthalic anhydride and the metal salt of an aromatic dihydroxy compound having a value of 2:1 refers to 2 moles of halophthalic anhydride per mole of the metal salt of an aromatic dihydroxy compound.

The amount of PTC used may be in the range of from about 0.2 mole percent to about 10 mole percent, with respect to the salt of the aromatic dihydroxy compound, more preferably in the range of from about 0.5 mole percent to about 2 mole percent.

When the reaction between the halophthalic anhydride and the metal salt of an aromatic dihydroxy compound is complete, the product diether dianhydride may be isolated by conventional techniques that are well known to those of ordinary skill in the art.

Without further elaboration, it is believed that one skilled in the art can, using the description herein, utilize the present invention to its fullest extent. The following examples are included to provide additional guidance to those skilled in the art in practicing the claimed invention. The examples provided are merely representative of the work that contributes to the teaching of the present application. Accordingly, these examples are not intended to limit the invention, as defined in the appended claims, in any manner.

EXAMPLES

All parts and percentages are by weight unless otherwise designated. Chemicals and solvents were reagent grade, and were carefully dried. Solvents were dried over activated 3 â„« molecular sieves before use. Analysis was performed by contacting the reaction mixture with n-butylamine and acetic acid for at least 30 minutes to convert anhydrides to the corresponding N-(n-butyl)imides, followed by high pressure liquid chromatography using a tetrahydrofuran-water mixture as the eluting solvent.

Example 1

A dry 25 mL flask was charged with 403 mg (1.482 mmol) of the disodium salt of bisphenol A, 500 mg (3.012 mmol) of 4-fluorophthalic anhydride, 46 mg (0.148 mmol) of 4-(N,N-dibutylamino)-N-neopentylpyridinium chloride, 8.5 g (10% solids) of dry o-dichlorobenzene and 55 mg of o-terphenyl (internal standard). The flask was immersed in an oil bath maintained at 180Â° C. and the mixture was stirred magnetically. The temperature within the reaction flask was about 175Â° C. Samples (Ëœ0.1 mL) were withdrawn periodically dissolved in 6 mL of acetic acid and approximately. 0.5 mL of methylamine (40% aqueous soln.) and heated at 125-130Â° C. for 1.5 hours. These samples were analyzed for the bis N-methyl imide of bisphenol A dianhydride by liquid chromatography. By following the diether dianhydride formation in this manner it was determined that the yield of product bisphenol A dianhydride (BPADA) had reached 82% after one hour.

Example 2

The reaction of Example was was carried out on a slightly larger scale (6.09 mmol scale based on disodium salt of bisphenol A). The product isolated as follows. The hot reaction mixture (after one hour at approximately 175Â° C.) was filtered through Celite and the filtrate was steam distilled to remove o-dichlorobenzene and hydrolyze the anhydride moieties. The resulting aqueous suspension was made basic by addition of sodium carbonate, treated with activated charcoal and filtered through Celite. The filtrate was acidified by addition to cold hydrochloric acid and the product was extracted into ether. Evaporation of the ether extracts afforded 3.01 g (88.9%) of the tetracid as a white solid.

Example 3

A dry 100 mL flask was charged with 1.69 g (7.3 mmol) of the disodium salt of biphenol, 2.44 g, (146 mmol) of 4-fluorophthalic anhydride, 2 mL (14 mmol) of hexaethylguanidinium chloride as a 15 weight % solution in o-dichlorobenzene, and 44 g of dry o-dichlorobenzene. The flask was immersed in an oil bath maintained at 180Â° C. and the mixture was stirred magnetically. After 15 minutes, the reaction mixture was filtered hot to remove the sodium fluoride by-product. The filtrate was allowed to cool to room temperature and the product dianhydride crystallized from the solvent as a cream colored solid which was isolated by filtration (3.1 g, 90% yield).

Example 4

A dry 100 mL flask was charged with 2.0 g (7.3 mmol) of the disodium salt of bisphenol A, 2.67 g (14.6 mmol) of 4-chlorophthalic anhydride, 4 mL (14 mmol) of hexaethylguanidinium chloride as a 15 weight % solution in o-dichlorobenzene, 48 g of dry o-dichlorobenzene, and 100 mg of o-terphenyl (internal standard). The flask was immersed in an oil bath maintained at 180Â° C. and the mixture was stirred magnetically. The reaction was followed as in Example 1. The yield of biphenol dianhydride had reached 25% after 5 hours.

Example 5

A dry 100 mL flask was charged with 2.0 g (7.3 mmol) of the disodium bisphenol A, 2.67 g (14.6 mmol) of 3-chlorophthalic anhydride, 4 mL (14 mmol) of hexaethylguanidinium chloride as a 15 weight % solution in o-dichlorobenzene, 48 g of dry o-dichlorobenzene, and 100 mg of o-terphenyl (internal standard). The flask was immersed in an oil bath maintained at 180Â° C. and the mixture was stirred magnetically. The reaction was followed as in Example 1. The yield of bisphenol A dianhydride had reached 40 % after 2 hour.

Table 1 shows the effect of the catalyst used, catalyst concentration and the % solids content in the reaction mixture on the final yield of the product dianhydride.

TABLE 1MetalConc.Conc.Exp.counterTimeTemp.(%CatalystYieldNo.ion(h)(Â° C.)solid)Catayst*(mole %)(%)1Na2.017510none022Na2.017510Bu₄NBr1023Na0.3175109a10904Na4.0175109a0.5855Na1.0175107a5826Na0.5175107a10887Na0.5175307a10608Na0.5175407a10559Na1.0175107b107510Na1.0175107c107511Na1.0175108108212K2.517597a53813K2.517597b53714K5.5175107a1075
*Bu₄NBr: Tetrabutyl ammonium bromide

7a: 1-neopentyl-4-(N,N-dibutylamino)-pyridinium chloride

7b: 1-neopentyl-4-piperidin-1-ylpyridinium chloride

7c: 1-neopentyl-4-piperidin-1-ylpyridinium mesylate

8: 1-3-methylheptyl-4-(4-methyl)-piperidin-1-ylpyridinium chloride

9a: Hexaethylguanidinium chloride

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.