CA2246116A1 - Microwave synthesis of quinacridone intermediates - Google Patents

Abstract

This invention relates to a process for preparing 2,5-dianilinotere-phthalic or 2,5-dianilino-3,6-dihydroterephthalic acid, ester, or amide by (a) exposing to microwave radiation a reaction mixture of (i) a succinylsuccinic compound, (ii) about 2 to about 5 moles per mole of succinylsuccinic compound (a)(i) of an aniline, (iii) about 0.01 to about 2.5 equivalents, based on succinylsuccinic compound (a)(i), of an acid catalyst, and (iv) about 0.05 to about 10 parts by weight, per part by weight of succinylsuccinic compound (a)(i), of a solvent, thereby forming a 2,5-dianilino-3,6-dihydroterephthalic compound, (b) optionally, oxidizing the initially formed 2,5-dianilino-3,6-dihydro-terephthalic compound to form a corresponding 2,5-dianilinotere-phthalic compound.

Description

Mo-4716 MICROWAVE SYNTHESIS OF QUINACRIDONE INTERMEDIATES
BACKGROUND OF THE INVENTION
This invention relates to the preparation of optionally substituted 2,5-dianilinoterephthalic and 2,5-dianilino-3,6-dihydroterephthalic acids, esters, and amides, which are useful as intermediates in the preparation of quinacridone pigments, by exposure of appropriate precursors to 5 microwave radiation.
Quinacridone pigments can be prepared by ring fusion of various intermediate 2,5-dianilinoterephthalic acid derivatives in the presence of strong acids such as polyphosphoric acid. The 2,5-dianilinoterephthalic intermediates can themselves be prepared by stepwise reactions of 10 succinylsuccinic acid derivatives (typically diesters) with aniline or derivatives thereof to form 2,5-dianilino-3,6-dihydroterephthalic derivatives that are then oxidized, generally in situ, to form the 2,5-dianilinotere-phthalic intermediates. It is also possible to convert the initialiy formed 2,5-dianilino-3,6-dihydroterephthalic derivatives to 6,13-dihydroquin-15 acridones before oxidization to the corresponding quinacridones. E.g.,S.S. Labana and L.L. Labana, "Quinacridones" in Chemical Review, 67, 1-18 (1967), and U.S. Patents 3,157,659, 3,256,285, 3,257,405, 3,317,539, and 5,367,096, as well as W. Herbst and K. Hunger, Industrial Or~anic Pi~ments (New York: VCH Publishers, Inc., 1993), pages 20 448449, H. Zollinger, Color Chemistry (VCH Verlagsgessellschaft, 1991), pages 239-240, and F. F. Ehrich, "Quinacridone Pigments" in Pi~ment Handbook, Vol. l, edited by P. A. Lewis (John Wiley & Sons, 1988), page 604; see also European Patent Applications 569,823 and 536,083 and Japanese Patent 57/040,562. These reactions, however, typically 25 require elevated temperatures and relatively long reaction times and thus can be attended by undesirable side reactions.

Mo4716 - 2 -Microwave irradiation has been found to be an effective alternative to heating for various organic reactions. E.g., U.S. Patent 5,387,397 and references cited therein; see also Russian Patent 2,045,555, A. K. Bose et al., Res. Chem. Intermed., 20, 1-11 (1994), G. Majetich and R. Hicks, 5 Res. Chem. Intermed., 20, 61-67 (1994), B. K. Banik et al., Bioorganic. &
Medicinal Chemistry Letters, 3, 2363-2368 (1993), B. Rechsteiner et al., Tetrahedron Lett., 34, 5071-5074 (1993), B. K. Banik et al., Tetrahedron Lett., 32, 3603-3606 (1992), and C. Strauss, Chemistry in Australia, 186 (June, 1990). However, the preparation of 2,5-dianilinoterephthalic acids, 10 esters, and amides, such as those prepared according to the present invention for use in the preparation of quinacridone pigments, has not been disclosed.
It has now been found that optionally substituted 2,5-dianilinotere-phthalic acids, esters, and amides can be prepared rapidly and in high 15 yields and purity by exposure of the precursor succinylsuccinic acid derivatives and anilines to microwave radiation. It has also unexpectedly been found that reduced quantities of solvent can also be used.
SUMMARY OF THE INVENTION
This invention relates to a process for preparing a 2,5-dianilino-20 terephthalic compound having the formula (I) ~ R3 or a 2,5-dianilino-3,6-dihydroterephthalic compound having the formula (Il) Mo-4716 - 3 -R1' R2 R4 X--C~NH--~R3 R3~ NH C--X R

wherein R1, R2, R3, and R4 are independently hydrogen, C1-C6 alkyl (preferably methyl), C1-C6 alkoxy (preferably methoxy), C5-C7 cycloalkyl, C5-C7 cycloalkoxy, C6-C10 aryl, C6-C10 aryloxy, C7-C16 aralkyl, C7-C16 aralkoxy, hydroxy, halogen (preferably chlorine or fluorine), nitrile, carboxyl or an ester or an amide thereof, or a sulfonyl group (such as an alkyl- or arylsulfonyl group or sulfoxyl or an ester or amide thereof), or any two or more adjacent R1, R2, R3, and R4 (preferably adjacent R1 and R2 or adjacent R2 and R3) together form a fused polyaromatic system (preferably an unsubstituted or ring-substituted a-naphthyl or ,B-naphthyl group), each X is ORa or NRbRC, Ra is hydrogen or C1-C6 alkyl (preferably methyl, ethyl, or butyl and more preferably methyl), and Rb and Rc are independently hydrogen or C1-C6 alkyl, said process comprising (a) exposing to microwave radiation (preferably at a frequency of about 2450 MHz) a reaction mixture comprising (i) a succinylsuccinic compound having the formula (Ill) Mo4716 - 4 -X-C~,~O
(111) O~\C-X
o wherein each X is ORa (wherein Ra is hydrogen or C1-C6 alkyl (preferably methyl, ethyl, or butyl and more preferably methyl)) or NRbRC (wherein Rb and Rc are independently hydrogen or C1-C6 alkyl), (ii) about 2 to about 5 moles (preferably about 2 moles) per mole of succinylsuccinic compound (a)(i) of an aniline having the formula (IV) R3~NH2 (IV) wherein R1, R2, R3, and R4 are defined as above, (iii) about 0.01 to about 2.5 equivalents (preferably 0.03 to 1.6 equivalents), based on succinylsuccinic acid compound (a)(i), of an acid catalyst, and (iv) about 0.05 to about 10 parts by weight, per part by weight of succinylsuccinic compound (a)(i), of a solvent (preferably a lower alkanol or alkanediol), thereby forming a 2,5-dianilino-3,6-dihydroterephthalic compound of formula (Il);
(b) optionally, oxidizing the initially formed 2,5-dianilino-3,6-dihydro-terephthalic compound of formula (Il) to form the corresponding 2,5-dianilinoterephthalic compound of formula (I); and Mo-4716 5 (c) isolating the 2,5-dianilino-3,6-dihydroterephthalic compound (if oxidizing step (b) is omitted) or the 2,5-dianilinoterephthalic compound (if oxidizing step (b) is carried out).
DETAILED DESCRIPTION OF THE INVENTION
As used herein, the term "C1-C6 alkyl" refers to straight or branched chain aliphatic hydrocarbon groups having from 1 to 6 carbon atoms, also referred to as lower alkyl. Examples of C1-C6 alkyl are methyl, ethyl, propyl, butyl, pentyl, hexyl, and the isomeric forms thereof.
The term "C1-C6 alkoxy" refers to straight or branched chain alkyl oxy 10 groups having from 1 to 6 carbon atoms. Examples of C1-C6 alkoxy are methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, and the isomeric forms thereof. The term "C5-C7 cycloalkyl" refers to cycloaliphatic hydro-carbons groups having from 5 to 7 carbon atoms. Examples of C5-C7 cycloalkyl are cyclopentyl, cyclohexyl, and cycloheptyl. The term "C5-C7 15 cycloalkoxy" refers to cycloalkyl oxy groups having from 5 to 7 carbon atoms. Examples of C5-C7 cycloalkoxy are cyclopentyloxy, cyclohexyloxy, and cycloheptyloxy. The term "C6-C10 aryl" refers to phenyl and 1- or 2-naphthyl, as well as to phenyl and naphthyl groups substituted with alkyl, alkoxy, halogen, cyano, as defined herein. The term "C6-C10 aryloxy"
20 refers to phenoxy and 1- or 2-naphthoxy, in which the aryl portion can optionally be substituted as described above for "aryl." The term "C7-C16 aralkyl" refers to C1-C6 alkyl substituted with C6-C10 aryl such that the total number of carbon atoms is from 7 to 16. Examples of C7-C16 aralkyl are benzyl, phenethyl, and naphthylmethyl. The term "C7-C16 aralkoxy"
25 refers to C1-C6 alkoxy substituted with C6-C10 aryl such that the total number of carbon atoms is from 7 to 16. An example of C7-C16 aralkoxy is benzyloxy. Examples of halogen are fluorine, chlorine, bromine, and iodine. As used herein, the term "carboxyl or an ester or amide thereof"
refers to -COOH and corresponding esters -COORi (in which Ri is alkyl, 30 cycloalkyl, aralkyl, or aryl) and amides -COONRiiRiii (in which Rii and R

CA 02246116 l99X-08-28 Mo-4716 - 6 -are independently hydrogen, alkyl, cycloalkyl, aralkyl, or aryl). As used herein, the term "sulfonyl group" refers to -SO2-RiV groups, such as alkylsulfonyl (in which RiV is alkyl; for example, methylsulfonyl or ethane-sulfonyl), arylsulfonyl (in which RiV is aryl; for example, phenylsulfonyl, 1-5 or 2-naphthylsulfonyl, and substituted forms such as toluenesulfonyl), sulfoxyl and corresponding esters (in which RiV is OH, alkoxy, cyclo-alkoxy, aralkoxy, aryloxy), and sulfonamides (in which RiV is -NRVRvi, wherein Rv and RVi are independently hydrogen, alkyl, cycloalkyl, aralkyl, or aryl).
Succinylsuccinic compounds of formula (Ill) can be prepared by methods known in the art. E.g., W. Herbst and K. Hunger, Industrial Or~anic Pi~ments (New York: VCH Publishers, Inc., 1993), page 448;
H. Zollinger, Color Chemistry (VCH Verlagsgessellschaft, 1991), page 239; F. F. Ehrich, "Quinacridone Pigments" in Piqment Handbook, Vol. l, edited by P. A. Lewis (John Wiley & Sons, 1988), page 604; and U.S.
Patent 5,367,096. For example, the preferred dialkyl succinylsuccinates of formula (Illa) RaOOC~O
(Illa) O/~\COORa wherein Ra is C1-C6 alkyl, can be prepared by cyclization of the corre-sponding dialkyl succinates. Dimethyl and diethyl succinylsuccinates (especially dimethyl succinylsuccinate) are particularly suitable and are commercially available, for example, from Hoechst AG, DSM Chemie Linz, and Aldrich Chemical. Succinylsuccinic acid (as the free acid or metal salts) and amides thereof are generally less preferred.
Anilines of formula (IV) can be prepared by known methods but are also often commercially available. The selection of R1, R2, R3, and Mo-4716 - 7 -R4 depends, of course, on the particular quinacridone that is ultimately to be prepared from the intermediates of formula (I) and (Il). For example, unsubstituted quinacridone would ultimately be derived from unsubstituted aniline (in which R1, R2, R3, and R4 are hydrogen) and 2,9-disubstituted 5 quinacridones would be derived from para-substituted anilines (preferably those in which only R2 is a specified substituent and R1, R3, and R4 are all hydrogen, such as 4-methylaniline (i.e., p-toluidine), 4-methoxyaniline, and 4-chloroaniline), whereas the less preferred 4,11-disubstituted quin-acridones would be derived from ortho-substituted anilines (preferably 10 those in which only R4 is a specified substituent and R1, R2, and R3 are all hydrogen).
Although generally less preferred, it is also possible to use polyaromatic derivatives of aniline in which any two or more adjacent R1, R2, R3, and R4 together form one or more fused polyaromatic hydro-15 carbon groups, such as naphthyl, anthryl, phenanthr,vl, and the like. Eachof the fused ring systems can, of course, be ring-substituted with C1-C6 alkyl, C1-C6 alkoxy, C5-C7 cycloalkyl, C5-C7 cycloalkoxy, C6-C10 aryl, 6 10 ar,vloxy, C7-C16 aralkyl, C7-C16 aralkoxy, hydroxy, halogen nitrile, carboxyl or an ester or an amide thereof, or a sulfonyl group.
20 Preferred polyaromatic amines are a-naphthylamine and ,~-naphthylamine (in which adjacent R1 and R2 and adjacent R2 and R3, respectively, form fused-on benzene rings), each of which can be substituted as described above.
Acid catalysts (a)(iii) include known organic or mineral acids.
25 Examples of suitable organic acids include carboxylic acids (for example, acetic and formic acids) and sulfonic acids (for example, alkylsulfonic acids such as methylsulfonic and ethanesulfonic acids and arylsulfonic acids such as phenylsulfonic, naphthylsulfonic, and toluenesulfonic acids) Suitable mineral acids include sulfuric acid, hydrochloric acid, and 30 phosphoric acid (including mono and dialkyl esters of phosphoric acid).

Mo~716 - 8 -The quantity of acid catalyst is generally not critical but should be an amount sufficient to catalyze the desired reaction but not so large that significant amounts of undesirable by-products and degradation products are formed. Typical quantities of the acid catalyst range from about 0.01 to about 2.5 equivalents (preferably 0.03 to 1.6 equivalents), relative to the succinylsuccinic compound (a)(i).
Suitable solvents (a)(iv) include polar organic liquids that are capable of dissolving or suspending the components of the reaction mixture and efficiently absorb microwave radiation without boiling or 10 significantly decomposing or otherwise reacting during step (a) or optional oxidation step (b). Examples of suitable solvents include monofunctional alcohols, particularly lower alkanols (such as methanol, ethanol, butanol, pentanol, hexanol, and isomeric forms thereofl, and higher functionality alcohols, particularly alkanediols (such as ethylene glycol, propylene 15 glycol, 1,4-butanediol, and the like). Other organic solvents can, of course, also often be used, but it is generally advisable to avoid solvents that can react with the reactive components. Generally unsuitable reactive solvents of this type include ketones and carboxylic esters, which can react with anilines of formula (IV). Lower alkanols and diols are 20 particularly suitable solvents. The quantity of solvent is generally not critical but should be an amount sufficient to dissolve or suspend the components of the reaction mixture but not so large as to require removal of excessive amounts after the reaction is complete. Typical quantities of solvent range from about 0.05 to about 10 parts by weight (preferably 1 25 to 6 parts by weight) relative to the succinylsuccinic compound (a)(i).
The reaction mixture used in step (a) is exposed to microwave radiation by any conventional method using a conventional microwave source but is preferably carried out by methods described by A. K. Bose et al., Res. Chem. Intermed., 20, 1-11 (1994), G. Majetich and R. Hicks, 30 Res. Chem. Intermed., 20, 61-67 (1994), B. K. Banik et al., Bior~anic. &

Mo-4716 - 9 -Medicinal Chemistry Letters, 3, 2363-2368 (1993), B. Rechsteiner et al., Tetrahedron Lett., 34, 5071-5074 (1993), B. K. Banik et al., Tetrahedron Lett., 32, 3603-3606 (1992), and C. Strauss, ChemistrY in Australia, 186 (June, 1990). Microwave frequencies ranging from about 2450 MHz to 5 about 20 GHz (i.e., 20,000 MHz) are generally suitable, but a frequency of about 2450 MHz is typical of commercial microwave ovens and is preferred. The peak power levels available in commercial microwave ovens are typically between about 80 and 1000 watts, but somewhat lower power levels (or reduced power-on cycle times) can be used as 10 long as the desired reaction occurs and somewhat higher power levels (and increased power-on cycle times) can be used as long as the purity and yield of products are not adversely affected. The temperatures produced during microwave irradiation are generally not critical (within the iimitations discussed above). For safety reasons, power levels and cycle 15 times should generally be selected to provide temperatures well below the boiling point of the reaction medium. It is possible to use either batchwise or continuous microwave irradiation.
The initially formed product of step (a) is a 2,5-dianilino-3,6-dihydroterephthalic compound of formula (Il). Oxidation of the initially 20 formed product is required to form the corresponding 2,5-dianilinotere-phthalic compounds of formula (I). Oxidation step (b) can be carried out by known methods, for example, by using aromatic nitro compounds (such as sodium m-nitrobenzenesulfonate), chloroanil, anthraquinone-2-sulfonic acid or a salt thereof, anthraquinone-2,7-disulfonic acid or a salt 25 thereof, air or other oxygen-containing gases, halogens, or electrolytic oxidation. E.g., U.S. Patents 3,285,952, 4,981,997, 5,367,096, and 5,616,779, Canadian Patent 1,071,208, French Patent 1,496,960, and Japanese Patents 51/059,830 and 51/108,029.
Oxidation step (b) is often carried out under basic conditions. For 30 example, oxidation with sodium m-nitrobenzenesulfonate is typically Mo-4716 - 10-carried out in the presence of alkali metal hydroxide. Under these conditions, ester groups (i.e., where Ra is alkyl) are hydrolyzed to the free acid (i.e., where Ra is hydrogen). Consequently, even if a dialkyl succinylsuccinate is used as the starting material, the ultimate product will be a 2,5-dianilinoterephthalic acid rather than an ester.
The reaction product from step (a) or optional oxidation step (b) is then isolated in step (c) using methods known in the art, such as filtration, and then dried if desired. Other collection methods known in the art, such as centrifugation, microrillldlion, or even simple decantation, are 10 also suitable.
The 2,5-dianilinoterephthalic compounds of formula (I) and 2,5-dianilino-3,6-dihydroterephthalic compounds of formula (Il) that are prepared according to the present invention can be used as inter-mediates in the preparation of quinacridone pigments of formula (V) R2~" N~ J~R

R3~ ~ '~\N~R2 in which R1, R2, R3, and R4 have the definitions given above for formulas (I) and (Il). It is, of course, also possible to prepare the corresponding 6,13-dihydroquinacridones, which can, if desired, be oxidized to the corresponding quinacridones of formula (V).
Particularly preferred 2,5-dianilinoterephthalic and 2,5-dianilino-3,6-dihydroterephthalic compounds are dialkyl esters having the formulas (la) and (lla), respectively, Mo-4716 -11 -R4 RaOOC ~NH~ R3 R3 ~NH COORa R

R R

and \ ~
R4 RaOOC NH ~R3 R3 ~NH COORa R

wherein R1, R2, R3, and R4 are defined as above and each Ra is C1-c6 5 alkyl (preferably methyl, ethyl, or butyl, but especially methyl).
Selection of aniline starting materials having appropriate R1, R2, R3, and R4 groups will determine the particular quinacridone (V) that iS
formed. For example, unsubstituted aniline will ultimately yield unsubsti-tuted quinacridone and para-substituted anilines, Such as p-toluidine (i.e., 10 4-methylaniline), 4-methoxyaniline, and 4-chloroaniline, Will yield 2,9-disubstituted quinacridones, whereas ortho-substituted anilines Will yield the generally less preferred 4,11-disubstituted quinacridones. Particularly preferred quinacridones include 2,9-dimethylquinacridone, 2,9-dimethoxy-quinacridone, and 2,9-dichloroquinacridone, as well as solid solutions 15 thereof. Although ring-fused quinacridones are generally also less preferred, it iS possible to use a-naphthylamine and ~-naphthylamine to prepare "dibenzoquinacridones" in Which benzene rings are fused at the 3,4- and 10,1 1-positions and at the 2,3- and 9,1 0-positions, respectively.

Mo4716 - 12 -The following examples further illustrate details for the process of this invention. The invention, which is set forth in the foregoing disclo-sure, is not to be limited either in spirit or scope by these examples.
Those skilled in the art will readily understand that known variations of 5 the conditions of the following procedures can be used. Unless otherwise noted, all temperatures are degrees Celsius and all percentages are percentages by weight.
EXAMPLES
Microwave irradiation for the following examples was provided by a 10 GE model JES 1030TW microwave oven operating at about 2450 MHz and 800 watts.
Purity of each intermediate was determined by HPLC using reverse-phase high-pressure liquid chromatography with a Waters 712 WISP system equipped with a Waters Nova C-18 cartridge using 15 tetrahydrofuran/water as eluant.
Examples 1-2 (comparison) Examples 1 and 2 are comparison examples in which the quinacridone intermediates were prepared by conventional heating methods instead of microwave irradiation.
20 Example 1 (comparison method) CH300C ~NH~

~NH COOCH3 To 160 9 of methanol solvent were added 20.75 9 (215 mmol) of dimethyl succinylsuccinate ("DMSS"), 48 9 (515 mmol) of aniline, and 18 9 (300 mmol) of acetic acid. The mixture was heated at 102-105~C for 25 three hours. After cooling the mixture to room temperature, the solid Mo-4716 - 13-component was collected by filtration and washed with methanol. The wet presscake was dried overnight in an oven at 60~C to give 77.0 g of 2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester (94.6% yield).
Example 2 (comparison method) CH300C~NH~CI

CI~NH COOCH3 To 160 g of methanol solvent were added 49 g (90.9 mmol) of DMSS, 25.5 g (200 mmol) of p-chloroaniline, and 12 g (200 mmol) of acetic acid. The mixture was heated at 95-100~C for five hours. After cooling the mixture to room temperature, the solid component was collected by filtration and washed with methanol. The wet presscake was dried overnight in an oven at 60~C to give 38.0 g of 2,5-bis(4-chloro-anilino)-3,6-dihydroterephthalic acid dimethyl ester (93.4% yield).
Examples 3-9 Examples 3-9 illustrate the preparation of quinacridone inter-mediates using microwave irradiation instead of conventional heating methods.
Example 3 CH300C ~C~NH~

~NH COOCH3 To 12.5 g of butanol solvent were added 12.5 g (54.8 mmol) of DMSS, 12.5 g (134.2 mmol) of aniline, and 4.90 g (81.6 mmol) of glacial acetic acid. The reaction mixture was irradiated in the microwave oven Mo-4716 - 14~
for 3.5 minutes. The reaction mixture was cooled to room temperature and diluted with a total of 250 mL of methanol. The solid component was collected by filtration and washed with 50 mL of acetone. The presscake was dried overnight in an oven at 60~C to give 19.8 g of 2,5-dianilino-3,6-5 dihydroterephthalate dimethyl ester (95.5% yield), an intermediate in thepreparation of unsubstituted quinacridone. HPLC analysis indicated 97.5% 2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester (above formula) and 1.1% 2-anilino-5-hydroxy-3,6-dihydroterephthalic acid dimethyl ester.
10 Examples 4-9 Examples 4-9 were carried out as described in Example 3 except for varying the arylamine starting material, solvent, acid, and reaction times as shown in the following Table. Yields of each intermediate are also given in the Table.

Table Preparation of 2,5-Dianilino-3,6-dihydroterephthalic Acid Dimethyl Esters of Examples 4-9 R1 .

CH300C~3'NH~R3 :

R3 < ~NH COOCH3 Example Arylamine R1 R3 Solvent Acid Reaction Yield O
catalysttime (min.) (%) r 4 Aniline H H Pentanol Acetic 4.0 94 ,_ Aniline H H Pentanol Sulfuric (96%) 4.0 95 6 p-Toluidine H CH3 Butanol Acetic 2.5 97 o 7 o-Toluidine CH3 H Butanol Acetic 2.5 100 8 4-Chloroaniline H Cl Butanol Acetic 2.5 99 9 4-Fluoroaniline H F Butanol Acetic 2.2 97 Mo4716 - 16-Example 10 HOOC ~NH~3 ~NH COOH

Example 10 illustrates the preparation of 2,5-dianilinoterephthalic acid by microwave-induced oxidation and hydrolysis of 2,5-dianilino-3,6-5 dihydroterephthalic acid dimethyl ester prepared according to Example 3of the invention.
To 200.0 9 of propylene glycol were added with stirring 30.0 9 (79.3 mmol) of 2,5-dianilino-3,6-dihydroterephthalic acid dimethyl ester, 50.0 9 of aqueous sodium hydroxide, and 18.0 9 of sodium m-nitro-10 benzenesulfonate (as the oxidizing agent). The reaction mixture was irradiated in the microwave oven for 1.75 minutes. The reaction mixture was allowed to cooled to room temperature. A portion of the reaction mixture was then diluted with 1000 mL of water and stirred for 15 minutes. Insoluble particles were removed by filtration and the pH of the 15 filtrate was adjusted to 4.8 with acetic acid to precipitate the product.
HPLC analysis of the precipitate indicated 97.9% 2,5-dianilinoterephthalic acid (above formula) and 1.3% 2-anilino-5-hydroxyterephthalic acid.

Claims (12)

1. A process for preparing a 2,5-dianilinoterephthalic compound having the formula or a 2,5-dianilino-3,6-dihydroterephthalic compound having the formula wherein R1, R2, R3, and R4 are independently hydrogen, C1-C6 alkyl, C1-C6 alkoxy, C5-C7 cycloalkyl, C5-C7 cycloalkoxy, C6-C10 aryl, C6-C10 aryloxy, C7-C16 aralkyl, C7-C16 aralkoxy, hydroxy, halogen, nitrile, carboxyl or an ester or an amide thereof, or a sulfonyl group, or any two or more adjacent R1, R2, R3, and R4 together form a fused polyaromatic system, each X is OR a or NR b R c, R a is hydrogen or C1-C6 alkyl, and R b and R c are independently hydrogen or C1-C6 alkyl, said process comprising (a) exposing to microwave radiation a reaction mixture comprising (i) a succinylsuccinic compound having the formula wherein each X is OR a or NR b R c, R a is hydrogen or C1-C6 alkyl, and R b and R c are independently hydrogen or C1-C6 alkyl, (ii) about 2 to about 5 moles per mole of succinylsuccinic compound (a)(i) of an aniline having the formula wherein R1, R2, R3, and R4 are defined as above, (iii) about 0.01 to about 2.5 equivalents, based on succinylsuccinic acid compound (a)(i), of an acid catalyst, and (iv) about 0.05 to about 10 parts by weight, per part by weight of succinylsuccinic compound (a)(i), of a solvent, thereby forming a 2,5-dianilino-3,6-dihydroterephthalic compound;
(b) optionally, oxidizing the initially formed 2,5-dianilino-3,6-dihydro-terephthalic compound to form the corresponding

2,5-dianilinoterephthalic compound; and (c) isolating the 2,5-dianilino-3,6-dihydroterephthalic compound or the 2,5-dianilinoterephthalic compound.
2. A process according to Claim 1 wherein the microwave radiation has a frequency of about 2450 MHz.

3. A process according to Claim 1 wherein R1, R3, and R4 are each hydrogen and R2 is C1-C6 alkyl, C1-C6 alkoxy, or halogen.

4. A process according to Claim 1 wherein succinylsuccinic compound (a)(i) is a dialkyl succinylsuccinate having the formula wherein each R a is C1-C6 alkyl.

5. A process according to Claim 4 wherein each R a is methyl.

6. A process according to Claim 1 wherein about 2 moles of the aniline per mole of succinylsuccinic compound (a)(i) are used.

7. A process according to Claim 1 wherein 0.03 to 1.6 equivalents of acid catalyst (a)(iii) is used.

8. A process according to Claim 1 wherein solvent (a)(iv) is a lower alkanol or alkanediol.

9. A process according to Claim 1 wherein oxidation step (b) is carried out under basic conditions.

10. A process according to Claim 1 for preparing a 2,5-dianilino-3,6-dihydroterephthalic ester having the formula wherein each R a is methyl, ethyl, or butyl, R1, R3, and R4 are each hydrogen, and R is C1-C6 alkyl, C1-C6 alkoxy, or halogen, said process comprising (a) exposing to microwave radiation, at a frequency of about 2450 MHz, a reaction mixture comprising (i) a dialkyl succinylsuccinate having the formula wherein each R a is methyl, ethyl, or butyl, (ii) about 2 to about 5 moles per mole of dialkyl succinyl-succinate (a)(i) of an aniline having the formula wherein R1, R3, and R4 are hydrogen and R2 is C1-C6 alkyl, C1-C6 alkoxy, or halogen, (iii) about 0.03 to 1.6 equivalents, based on dialkyl succinyl-succinate (a)(i), of an acid catalyst, and (iv) about 0.05 to about 10 parts by weight, per part by weight of dialkyl succinylsuccinate (a)(i), of a lower alkanol or alkanediol as solvent; and (b) isolating the 2,5-dianilino-3,6-dihydroterephthalic ester.

11. A process according to Claim 1 for preparing a 2,5-dianilino-terephthalic acid or ester having the formula wherein each R a is hydrogen, methyl, ethyl, or butyl, R1, R3, and R4 are each hydrogen, and R2 is C1-C6 alkyl, C1-C6 alkoxy, or halogen, said process comprising (a) exposing to microwave radiation, at a frequency of about 2450 MHz, a reaction mixture comprising (i) a succinylsuccinic compound having the formula wherein each R a is hydrogen, methyl, ethyl, or butyl, (ii) about 2 to about 5 moles per mole of succinylsuccinic compound (a)(i) of an aniline having the formula wherein R1, R3, and R4 are hydrogen and R2 is C1-C6 alkyl, C1-C6 alkoxy, or halogen, (iii) about 0.03 to 1.6 equivalents, based on succinylsuccinic compound (a)(i), of an acid catalyst, and (iv) about 0.05 to about 10 parts by weight, per part by weight of succinylsuccinic compound (a)(ii), of a lower alkanol or alkanediol as solvent, thereby forming a 2,5-dianilino-3,6-dihydroterephthalic acid or ester;
(b) oxidizing the 2,5-dianilino-3,6-dihydroterephthalic acid or ester to form the corresponding 2,5-dianilinoterephthalic acid or ester; and (c) isolating the 2,5-dianilinoterephthalic acid or ester.

12. A process according to Claim 1 for preparing a 2,5-dianilino-terephthalic acid having the formula wherein each R a is hydrogen, R1, R3, and R4 are each hydrogen, and R is C1-C6 alkyl, C1-C6 alkoxy, or halogen, said process comprising (a) exposing to microwave radiation, at a frequency of about 2450 MHz, a reaction mixture comprising (i) a dialkyl succinylsuccinate having the formula wherein each R a is methyl, ethyl, or butyl, (ii) about 2 to about 5 moles per mole of dialkyl succinyl-succinate (a)(i) of an aniline having the formula wherein R1, R3, and R4 are hydrogen and R2 is C1-C6 alkyl, C1-C6 alkoxy, or halogen, (iii) about 0.03 to 1.6 equivalents, based on dialkyl succinyl-succinate (a)(i), of an acid catalyst, and (iv) about 0.05 to about 10 parts by weight, per part by weight of dialkyl succinylsuccinate (a)(ii), of a lower alkanol or alkanediol as solvent, thereby forming a 2,5-dianilino-3,6-dihydroterephthalic ester;
(b) oxidizing the 2,5-dianilino-3,6-dihydroterephthalic ester under basic conditions to form the corresponding 2,5-dianilinoterephthalic acid;
and (c) isolating the 2,5-dianilinoterephthalic acid.