THE CORRESPONDING ANHYDRIDES

BACKGROUND

[0001] Aromatic acids, for example aromatic carboxylic acids, are important intermediates for the preparation of linear polymers useful for films, fibers, and the like. Of particular importance are aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, and isophthalic acid for use in the manufacture of synthetic polymers. These intermediates must be exceptionally free of impurities which are colored, which may become colored, or which can act as chain terminators in the polymerization step thereby causing low quality polymers to be obtained. These impurities generally arise during the preparation of the dicarboxylic acid from the starting hydrocarbon (e.g., xylene). Due to the physical and chemical properties of the impurities, known purification and separation processes such as re- crystallization, distillation, and sublimation are generally ineffective for purifying the aromatic acids.

[0002] Alternative methods for purifying the aromatic acids include separating and purifying the phthalic acids by way of the corresponding dimethyl esters. The corresponding dimethyl esters can be obtained with high purity following several recrystallization and/or distillation steps. However, if the free acids are required, the esters must be saponified after the purification. Therefore, while the aforementioned process can provide pure phthalic acids, it is not economical.

[0003] There has been an active interest in overcoming the above-described technical limitations for purifying aromatic carboxylic acids. Accordingly, there remains a need for an improved purification and separation process for the aromatic carboxylic acids.

BRIEF DESCRIPTION

[0004] A method of removing an aromatic carboxy-aldehyde from an aromatic acid or the corresponding anhydride comprises: reacting a hydroxylamine-containing compound with the aromatic carboxy-aldehyde to form a reaction mixture comprising the corresponding nitrone.

[0005] A method for the manufacture of a phenyl dicarboxylic acid comprises:

oxidizing a xylene to provide a stream comprising the phenyl dicarboxylic acid and the corresponding carboxybenzaldehyde and toluic acid contaminants; reacting a hydroxylamine- containing compound with the carboxybenzaldehyde in the stream to form a reaction mixture comprising the corresponding nitrone; and crystallizing the phenyl dicarboxylic acid or the corresponding anhydride from water to provide the purified phenyl dicarboxylic acid or the corresponding anhydride; wherein the phenyl dicarboxylic acid or the corresponding anhydride comprises less than 0.5 wt.% of the carboxybenzaldehyde, preferably less than 0.25 wt.% of the carboxybenzaldehyde, more preferably less than 0.05 wt.% of

carboxybenzaldehyde; and less than 0.2 wt.% of the toluic acid, preferably less than 0.1 wt.% of the toluic acid, more preferably less than 0.05 wt.% of the toluic acid.

[0006] These and other features and characteristics are more particularly described below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The following is a brief description of the drawings wherein like elements are numbered alike and which are presented for the purposes of illustrating the exemplary embodiments disclosed herein and not for the purposes of limiting the same.

[0008] FIG. 1 is a schematic drawing illustrating the method for manufacturing phenyl dicarboxylic acid.

[0009] FIG. 2 is a schematic drawing of a system for manufacturing phenyl dicarboxylic acid.

[0010] FIG. 3 is an illustration of a chemical scheme illustrating the formation of a nitrone from a carboxy-aldehyde impurity and a hydroxy-amine-containing compound.

DETAILED DESCRIPTION

[0011] Described herein is a method for removing an aromatic carboxy-aldehyde from an aromatic acid and a method for the manufacture of a phenyl dicarboxylic acid. A phthalic acid or corresponding anhydride prepared according to the method is also described. It was unexpectedly discovered that a carboxy-aldehyde impurity could be reacted with a hydroxylamine-containing compound to form a corresponding nitrone. The corresponding nitrone can be solubilized in a solvent comprising a C1-C6 alkyl carboxylic acid, and separated from the aromatic acid by filtering, decanting, centrifuging, or the like.

Advantageously, no additional purification steps (e.g., recrystallization, hydrogenation, esterification, and the like) are necessary. The method disclosed herein can provide the aromatic acid at high purity, for example, 90 to 95%. The aromatic acid can also have reduced yellowness index compared to the aromatic acid comprising the aromatic carboxy- aldehyde impurity.

[0012] A method of removing an aromatic carboxy-aldehyde from an aromatic acid or the corresponding anhydride can include reacting a hydroxylamine-containing compound with the aromatic carboxy-aldehyde to form a reaction mixture comprising a corresponding nitrone. The initial mixture comprising the aromatic carboxy-aldehyde and the aromatic acid or the corresponding anhydride can be the product of a xylene oxidation, for example, a xylene oxidation conducted on a scale of at least 1 ,000 kilograms per hour. The xylene oxidation can be, for example, a liquid phase oxidation of xylene with air, oxygen, or an oxygen-containing gas. The liquid phase oxidation process can include a solvent, for example acetic acid. The oxidation can take place at a temperature of, for example, 150 to 225°C, and a pressure of, for example, about 2 MegaPascals (MPa). In some embodiments, the xylene oxidation process can include use of a catalyst, for example a catalyst comprising cobalt ions, manganese ions, bromide ions, or a combination comprising at least one of the foregoing.

[0013] The aromatic carboxy-aldehyde can be removed from the aromatic acid or the corresponding anhydride by reacting a hydroxylamine-containing compound with the aromati hydroxylamine-containing compound has the structure

wherein n is 1 to 5 and m is 0 to 4, provided that n+m is not greater than 5. For example, n+m can be 1 , 2, 3, 4, or 5. Each occurrence of R ¹ is independently C6-Cis alkyl, C6-C18 alkylamino, di(C6-Cis aikyl)amino, di(C6-Ci4 alkylamino-Ci-C4 alkylene)amine, C6-C18 alkoxy, C6-C18 alkylamido, C6-C18 alkylthio, or C6-C18 aryl substituted with at least one of the foregoing groups, wherein each R ¹ is optionally substituted with 1 to 3 halogen, cyano, nitro, hydroxyl, thio, C ₁ -C6 alkoxy, C2-C6 acyl, C6-C ₁₀ aryl, C6-C ₁₀ aryloxy, C ₁ -C6 alkoxy, C ₁ -C6 alkylthio, or C2-C6 alkoxycarbonyl groups. Each occurrence of R is independently halogen, cyano, thiocyanato, nitro, C ₁ -C5 alkyl, C ₁ -C5 alkoxy, C ₁ -C5 alkylthio, C3-C5 cycloalkyl, C2-C5 acyl, C6-C ₁ 2 aryl, C ₆ -Ci2 aryloxy, C3-C8 heteroaryl, or carbamoyl. In some embodiments, each occurrence of R ¹ is independently C ₆ -Cig alkyl, Ce-C^ alkoxy, C ₆ -Cig alkylamido, C ₆ - Ci ₈ alkylamino, di(C6-Cis alkyl)amino, or C6-C18 aryl substituted with at least one of the foregoing groups, preferably each occurrence of R ¹ is independently a (2-ethylhexyl)amido group. In some embodiments, n is 1 , m is 0, and R ¹ is a (2-ethylhexyl)amido group. When n is 1 , R can be ortho, meta, or para to the hydroxylamine group, for example, R can be para to the hydroxylamine group. In some embodiments, the hydroxylamine-containing compound can be present in an amount of 0.001 to 10 weight percent, based on the weight of the aromatic carboxy-aldehyde, for example, 0.005 to 5 weight percent, for example, 0.1 to 2 weight percent.

carboxy-aldehyde can have the structure

wherein p is 0 to 4 and y is 1 to 5, provided that p+y is not greater than 5. For example, p+y can be 1, 2, 3, 4, or 5. Each occurrence of R is independently halogen, cyano, thiocyanato, nitro, C ₁ -C5 alkyl, C ₁ -C5 alkoxy, C ₁ -C5 alkylthio, C3-C5 cycloalkyl, C2-C5 acyl, C ₆ -Ci2 aryl, C6-C ₁ 2 aryloxy, C3-C8 heteroaryl, or carbamoyl. In some embodiments, p is 0, and y is 1 to 5, preferably y is 1. For example, the aromatic carboxy-aldehyde can comprise 2- carboxybenzaldehyde, 3-carboxybenzaldehyde, 4-carboxybenzaldehyde, or a combination comprising at least one of the foregoing.

[0015] The aromatic acid can comprise at least 2 carboxylic acid groups. For example, the aromatic acid can comprise 2, 3, 4, or 5 carboxylic acid groups. In some embodiments, the aromatic acid is a dicarboxylic acid, for example phthalic acid, terephthalic acid, isophthalic acid, or a combination comprising at least one of the foregoing. In some embodiments, the aromatic acid is a tricarboxylic acid, for example benzene-1,3,5- tricarboxylic acid.

[0016] The hydroxylamine-containing compound can react with the aromatic carboxy-aldehyde to form a reaction mixture comprising the corresponding nitrone. The nitrone has the structure

wherein n is 1 to 5 and m is 0 to 4, provided that n+m is not greater than 5. For example, n+m can be 1, 2, 3, 4, or 5. Each occurrence of R ¹ is independently C6-C18 alkyl, C6-C18 alkylamino, di(C6-Cis aikyl)amino, di(C6-Ci4 alkylamino-Ci-C4 alkylene)amine, C6-C18 alkoxy, C6-C18 alkylamido, C6-C18 alkylthio, or C6-C18 aryl substituted with at least one of the foregoing groups, wherein each R ¹ is optionally substituted with 1 to 3 halogen, cyano, nitro, hydroxyl, thio, C ₁ -C6 alkoxy, C2-C6 acyl, C6-C ₁₀ aryl, C6-C ₁₀ aryloxy, C ₁ -C6 alkoxy, C ₁ -C6 alkylthio, or C2-C6 alkoxycarbonyl groups. Each occurrence of R ² is independently halogen, cyano, thiocyanato, nitro, C ₁ -C5 alkyl, C ₁ -C5 alkoxy, C ₁ -C5 alkylthio, C3-C5 cycloalkyl, C2-C5 acyl, C6-C ₁ 2 aryl, C6-C ₁ 2 aryloxy, C3-C8 heteroaryl, or carbamoyl. In some embodiments, p is 0 to 4 and y is 1 to 5, provided that p+y is not greater than 5. For example, p+y can be 1, 2, 3, 4, or 5. Each occurrence of R is independently halogen, cyano, thiocyanato, nitro, C ₁ -C5 alkyl, C ₁ -C5 alkoxy, C ₁ -C5 alkylthio, C3-C5 cycloalkyl, C2-C5 acyl, Ce-Cn aryl, C ₆ -Ci2 aryloxy, C3-C8 heteroaryl, or carbamoyl. In some embodiments, each occurrence of R ¹ is independently C6-C18 alkyl, C6-C18 alkoxy, C6-C18 alkylamido, C6-C18 alkylamino, di(C6-Cis alkyl)amino, or C6-C18 aryl substituted with at least one of the foregoing groups, preferably each occurrence of Rj is independently a (2-ethylhexyl)amido group. In some embodiments, n is 1, m is 0, Ri is a (2-ethylhexyl)amido group, y is 1 and p is 0.

[0017] The nitrone formed by the reaction of the hydroxylamine-containing compound and the aromatic carboxy-aldehyde can have a yellowness index at least 5% lower, for example at least 10% lower, for example at least 20% lower than the aromatic carboxy- aldehyde, as determined according to ASTM D1209.

[0018] In some embodiments, the method of removing an aromatic carboxy-aldehyde from an aromatic acid or the corresponding anhydride can further comprise isolating the aromatic acid or corresponding anhydride from the reaction mixture to provide a purified aromatic acid or corresponding anhydride. Isolating the aromatic acid or corresponding anhydride can comprise crystallizing the aromatic acid or the corresponding anhydride from an aqueous solvent, for example, water. Crystallizing the aromatic acid or the corresponding anhydride can further remove a corresponding toluic acid impurity from the aromatic acid or the corresponding anhydride.

[0019] In some embodiments, the isolating can further comprise adding a solvent to the reaction mixture in an amount and under conditions effective to solubilize the nitrone but not the aromatic acid or the corresponding anhydride, and separating the solubilized nitrone from the non-solubilized aromatic acid. For example, the solvent can be added to the reaction mixture in a solvent:reaction mixture volumetric ratio of 1 : 100 to 100: 1, for example 1 :50 to 50:1, for example 1:20 to 20: 1, for example 1: 10 to 10: 1, for example 1 :5 to 5: 1, for example 1 :2 to 2: 1, for example 1: 1 to solubilize the nitrone but not the aromatic acid or the corresponding anhydride. For example, the solvent can be added to the reaction mixture at a temperature of 0 to 150°C, for example 10 to 100°C, for example 20 to 75°C, for example 20 to 50°C. In some embodiments, the solvent can be a C ₁ -C6 alkyl carboxylic acid, optionally substituted with a hydroxyl, cyano, nitro, or halogen. For example, the solvent can comprise acetic acid, propionic acid, butyric acid, or a combination comprising at least one of the foregoing. Separating the solubilized nitrone from the non-solubilized aromatic acid can be by, for example, filtering, decanting, centrifuging, and the like. In some embodiments, following separation, the isolated aromatic acid or the corresponding anhydride can be crystallized to remove the corresponding toluic acid.

[0020] The separated aromatic acid or the corresponding anhydride can have a purity of 90 to 99.9%, for example, 90 to 99%, for example, 90 to 95%. For example, in some embodiments, the separated aromatic acid or the corresponding anhydride can have less than 2 weight percent (wt.%) of the aromatic carboxy-aldehyde, for example less than 1 wt.% of the aromatic carboxy-aldehyde, for example less than 0.5 wt.% of the carboxy aldehyde.

[0021] The crystallized aromatic acid or the corresponding anhydride can have less than 2 wt.% of the corresponding toluic acid, for example, less than 1 wt.% of the corresponding toluic acid, for example less than 0.5 wt.% of the corresponding toluic acid.

[0022] After the reacting to form the nitrone, or after isolating the purified aromatic acid or corresponding anhydride, the aromatic acid or corresponding anhydride can have a yellowness index at least 5% lower, for example at least 10% lower, for example, at least 20% lower than the aromatic acid or corresponding anhydride before the reacting to form the nitrone, as determined according to ASTM D1209. In some embodiments, after the reacting to form the nitrone, or after isolating the purified aromatic acid or corresponding anhydride, the aromatic acid or corresponding anhydride can have a delta Y value at least 5% lower, for example at least 10% lower, for example, at least 20% lower than the aromatic acid or corresponding anhydride before the reacting to form the nitrone, as determined according to ASTM D1209. In some embodiments, the color properties (e.g., yellowness index) of the purified aromatic acid or corresponding anhydride can be evaluated using a tristimulus colorimeter.

[0023] Also described herein is a method for the manufacture of a phenyl dicarboxylic acid. The method can include oxidizing a xylene to provide a stream comprising the phenyl dicarboxylic acid and the corresponding carboxybenzaldehyde and toluic acid contaminants; reacting a hydroxylamine-containing compound with the carboxybenzaldehyde in the stream to form a reaction mixture comprising the corresponding nitrone; and crystallizing the phenyl dicarboxylic acid or the corresponding anhydride from water to provide the purified phenyl dicarboxylic acid or the corresponding anhydride. The xylene can be ortho-xylene, meta-xylene, para-xylene, or a combination comprising at least one of the foregoing xylenes. In some embodiments, the xylene is a combination of at least two of the foregoing xylenes. The hydroxylamine-containing compound can be as described above. For example, the hydroxylamine-containing compound can have the above-described structure, wherein each occurrence of Rj is independently a (2-ethylhexyl)amido group. In some embodiments, n is 1, m is 0, and Rj is a (2-ethylhexyl)amido group.

[0024] The phenyl dicarboxylic acid or the corresponding anhydride can comprise less than 0.5 wt.% of the carboxybenzaldehyde, for example, less than 0.25 wt.% of the carboxybenzaldehyde, for example, less than 0.05 wt.% of carboxybenzaldehyde; and less than 0.2 wt.% of the toluic acid, for example, less than 0.1 wt.% of the toluic acid, for example, less than 0.05 wt.% of the toluic acid.

[0025] In some embodiments, the method advantageously excludes an additional purification step, for example a hydrogenation reaction. For example, the method for manufacturing a phenyl dicarboxylic acid can exclude the catalytic hydrogenation of the aromatic carboxy-aldehyde, for example using a palladium hydrogenation catalyst.

[0026] The method for manufacturing the phenyl dicarboxylic acid as described above is further illustrated in Figure 1. Xylene 10 is oxidized 12 to provide a crude phenyl dicarboxylic acid product 14 comprising the phenyl dicarboxylic acid and the corresponding carboxybenzaldehyde and toluic acid contaminants. The crude product 14 is purified 16, for example by reacting a hydroxylamine-containing compound with the carboxybenzaldehyde to form the corresponding nitrone. A purified phenyl dicarboxylic acid product 18 is obtained by crystallizing the phenyl dicarboxylic acid or the corresponding anhydride from water to provide the purified phenyl dicarboxylic acid or the corresponding anhydride 18.

[0027] As illustrated in Figure 2, a system 20 for the manufacture of a phenyl dicarboxylic acid according to the above-described method represents another aspect of the present disclosure. The system 20 can comprise a feed stream 22 comprising xylene, an organic acid (e.g., acetic acid), and an oxygen source (e.g., air), entering into a first reactor 24 for oxidizing a xylene to provide a stream 26 comprising the phenyl dicarboxylic acid and the corresponding carboxybenzaldehyde and toluic acid contaminants, and a second reactor 28 for reacting a hydroxylamine-containing compound with the carboxybenzaldehyde in the stream 26 to form a reaction mixture 30 comprising the corresponding nitrone. The first reactor can generally be any reactor for carrying out a liquid phase oxidation of xylene. For example, the first reactor can be a continuous or semi-continuous stirred tank reactor, a batch reactor, a tower reactor, a tubular reactor, or a multitubular reactor. Any of the

aforementioned reactors can be employed in series or in parallel. In some embodiments, reacting a hydroxylamine-containing compound with the carboxybenzaldehyde can be carried out in a second reactor different from the first reactor. In some embodiments, reacting a hydroxylamine-containing compound with the carboxybenzaldehyde can be carried out in the same reactor as used for oxidizing the xylene (i.e., the first and second reactors can be the same or different reactors).

[0028] The following example is merely illustrative of the method disclosed herein and are not intended to limit the scope hereof.

EXAMPLE

[0029] An aromatic carboxy-aldehyde impurity was removed from a phenyl carboxylic acid according to the above described method, and as shown in the chemical scheme of Figure 3.

[0030] Following the oxidation of xylene, N,N-dihexyl-4-(hydroxyarnino)benzamide (shown as compound 2 in Figure 3) was added to the reactor in a molar amount equivalent to the molar amount of carboxy-aldehyde impurity (shown as compound 1 in Figure 3). After the addition of compound 2, the reaction mixture was stirred for 1 hour at a temperature of about 20 to about 50°C. After 1 hour, the reaction mixture was filtered to remove the nitrone formed by reaction of the N,N-dihexyl-4-(hydroxyamino)benzamide and the carboxybenzaldehyde (shown as compound 3 in Figure 3). Following the separation, purified phenyl carboxylic acid was obtained.

[0031] The method disclosed herein includes at least the following embodiments.

[0032] Embodiment 1 : A method of removing an aromatic carboxy-aldehyde from an aromatic acid or the corresponding anhydride, comprising: reacting a hydroxylamine- containing compound with the aromatic carboxy-aldehyde to form a reaction mixture comprising the corresponding nitrone.

[0033] Embodiment 2: The method of Embodiment 1, further comprising isolating the aromatic acid or corresponding anhydride from the reaction mixture to provide a purified aromatic acid or corresponding anhydride.

[0034] Embodiment 3: The method of Embodiment 1 or Embodiment 2, wherein after the reacting to form the nitrone or the isolating, the aromatic acid or corresponding anhydride has a yellowness index of at least 5% lower, at least 10% lower, or at least 20% lower than the aromatic acid or corresponding anhydride before the reacting, as determined according to ASTM D1209. [0035] Embodiment 4: The method of Embodiment 1 or Embodiment 2, wherein after the reacting to form the nitrone or the isolating, the aromatic acid or corresponding anhydride has a delta- Y value at least 5% lower, at least 10% lower, or at least 20% lower than the aromatic acid or corresponding anhydride before the reacting, as determined according to ASTM D1209.

[0036] Embodiment 5: The method of Embodiment 2 or Embodiment 3, wherein the isolating further comprises crystallizing the aromatic acid or the corresponding anhydride from an aqueous solvent.

[0037] Embodiment 6: The method of Embodiment 5, wherein the aqueous solvent is water.

[0038] Embodiment 7: The method of Embodiment 5 or Embodiment 6, wherein the crystallizing further removes the corresponding toluic acid from the aromatic acid or the corresponding anhydride.

[0039] Embodiment 8: The method of Embodiment 2 or Embodiment 3, wherein the isolating further comprises adding a solvent to the reaction mixture, in an amount and under conditions effective to solubilize the nitrone but not the aromatic acid or the corresponding anhydride; and separating the solubilized nitrone from the non-solubilized aromatic acid.

[0040] Embodiment 9: The method of Embodiment 8, wherein the solvent comprises a Q-C6 alkyl carboxylic acid optionally substituted with a hydroxyl, cyano, nitro, or halogen, preferably wherein the solvent comprises acetic acid, propionic acid, or a combination comprising at least one of the foregoing.

[0041] Embodiment 10: The method of Embodiment 8, wherein the separating is by filtering, decanting, or centrifuging the reaction mixture to separate the aromatic acid or corresponding anhydride from the solvent comprising the solubilized nitrone.

[0042] Embodiment 11 : The method of Embodiment 10, further comprising crystallizing the separated aromatic acid or the corresponding anhydride to remove the corresponding toluic acid.

[0043] Embodiment 12: The method of any of Embodiments 1 to 11, wherein the separated aromatic acid or corresponding anhydride has a purity of 90-99%.

[0044] Embodiment 13: The method of any of Embodiments 5 to 7 or 11, wherein the crystallized aromatic acid or corresponding anhydride has less than 2 wt.% of the corresponding toluic acid, preferably less than 1 wt. % of the corresponding toluic acid, more preferably less than 0.5 wt.% of the corresponding toluic acid. [0045] Embodiment 14: The method of any of Embodiments 1 to 13, wherein the mixture comprising an aromatic carboxy-aldehyde and an aromatic acid or the corresponding anhydride is the product of a xylene oxidation.

[0046] Embodiment 15: The method of Embodiment 14, wherein the xylene oxidation is conducted on a scale of at least 1,000 kilograms per hour.

[0047] Embodiment 16: The method of any of Embodiments 1 to 15, wherein the hydro nd has the structure

wherein n is 1 to 5 and m is 0 to 4, provided that n+m = 1, 2, 3, 4, or 5; each occurrence of R is independently C6-Cis alkyl, C6-C18 alkylamino, di(C6-Cis aikyl)amino, di(C6-Ci4 alkylamino-Ci-C4 alkylene)amine, C6-C18 alkoxy, C6-C18 alkylamido, C6-C18 alkylthio, or C ₆ - Ci ₈ aryl substituted with at least one of the foregoing groups, wherein each R ¹ is optionally substituted with 1 to 3 halogen, cyano, nitro, hydroxyl, thio, C ₁ -C6 alkoxy, C2-C6 acyl, C6-C ₁₀ aryl, C6-C ₁₀ aryloxy, C ₁ -C6 alkoxy, C ₁ -C6 alkylthio, or C2-C6 alkoxycarbonyl groups; and each occurrence of R is independently halogen, cyano, thiocyanato, nitro, C ₁ -C5 alkyl, C ₁ -C5 alkoxy, C ₁ -C5 alkylthio, C3-C5 cycloalkyl, C2-C5 acyl, ^- n aryl, ^- n aryloxy, C3-C8 heteroaryl, or carbamoyl.

[0048] Embodiment 17: The method of Embodiment 16, wherein each occurrence of R ¹ is independently C6-C18 alkyl, C6-C18 alkoxy, C6-C18 alkylamido, C6-C18 alkylamino, di(C6-Ci ₈ alkyl)amino, or C6-C18 aryl substituted with at least one of the foregoing groups, preferably wherein each occurrence of Rj is independently a (2-ethylhexyl)amido group.

[0049] Embodiment 18: The method of any of Embodiments 1 to 17, wherein the hydroxylamine-containing compound is reacted with the aromatic carboxy-aldehyde in an amount of 0.001 to 10 weight percent, based on the weight of the aromatic carboxy-aldehyde.

[0050] Embodiment 19: The method of any of Embodiments 1 to 18, wherein the aromati the structure

wherein p is 0 to 4 and y is 1 to 5, provided that p+y = 1, 2, 3, 4, or 5; and each occurrence of R is independently halogen, cyano, thiocyanato, nitro, C ₁ -C5 alkyl, C ₁ -C5 alkoxy, C ₁ -C5 alkylthio, C3-C5 cycloalkyl, C2-C5 acyl, C - n aryl, C - n aryloxy, C3-C8 heteroaryl, or carbamoyl.

[0051] Embodiment 20: The method of Embodiment 19, wherein the aromatic carboxy-aldehyde comprises 2-carboxybenzaldehyde, 3-carboxybenzaldehyde,

4-carboxybenzaldehyde, or a combination comprising at least one of the foregoing.

[0052] Embodiment 21 : The method of any of Embodiments 1 to 20, wherein the aromatic acid comprises 2, 3, 4, or 5 carboxylic acid groups.

[0053] Embodiment 22: The method of any of Embodiments 1 to 21, wherein the aromatic acid is an aromatic diacid, preferably phthalic acid, terephthalic acid, isophthalic acid, or a combination comprising at least one of the foregoing.

[0054] Embodiment 23: The method of any of Embodiments 1 to 22, wherein the nitrone has a yellowness index of at least 5% lower, at least 10% lower, or at least 20% lower than the aromatic carboxy-aldehyde as determined according to ASTM D1209.

[0055] Embodiment 24: The method of any of Embodiments 1 to 23, wherein the nitrone

1 2 3

wherein R , R , n and m are as defined in Embodiment 16; and R , p and y are as defined in Embodiment 19.

[0056] Embodiment 25: A phthalic acid or corresponding anhydride prepared according to the method of any of Embodiments 1 to 24.

[0057] Embodiment 26: A method for the manufacture of a phenyl dicarboxylic acid, comprising: oxidizing a xylene to provide a stream comprising the phenyl dicarboxylic acid and the corresponding carboxybenzaldehyde and toluic acid contaminants; reacting a hydroxylamine-containing compound with the carboxybenzaldehyde in the stream to form a reaction mixture comprising the corresponding nitrone; and crystallizing the phenyl dicarboxylic acid or the corresponding anhydride from water to provide the purified phenyl dicarboxylic acid or the corresponding anhydride.

[0058] Embodiment 27: The method of Embodiment 26, wherein the phenyl dicarboxylic acid or the corresponding anhydride comprises: less than 0.5 wt.% of the carboxybenzaldehyde, preferably less than 0.25 wt.% of the carboxybenzaldehyde, more preferably less than 0.05 wt.% of carboxybenzaldehyde; and less than 0.2 wt.% of the toluic acid, preferably less than 0.1 wt.% of the toluic acid, more preferably less than 0.05 wt.% of the toluic acid.

[0059] Embodiment 28: A phenyl dicarboxylic acid prepared according to the method of Embodiments 26 or 27.

[0060] Embodiment 29: A system for the manufacture of a phenyl dicarboxylic acid according to the method of any of Embodiments 26 to 28, comprising: a first reactor for oxidizing a xylene to provide a stream comprising the phenyl dicarboxylic acid and the corresponding carboxybenzaldehyde and toluic acid contaminants; and a second reactor for reacting a hydroxylamine-containing compound with the carboxybenzaldehyde in the stream to form a reaction mixture comprising the corresponding nitrone.

[0061] In general, the invention may alternately comprise, consist of, or consist essentially of, any appropriate components herein disclosed. The invention may additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any components, materials, ingredients, adjuvants or species used in the prior art compositions or that are otherwise not necessary to the achievement of the function and/or objectives of the present invention.

[0062] Unless otherwise specified herein, any reference to standards, testing methods and the like, such as ASTM D1209, ASTM D1003, ASTM D3359, ASTM D3363, refer to the standard, or method that is in force at the time of filing of the present application.

[0063] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. "Combination" is inclusive of blends, mixtures, alloys, reaction products, and the like. Furthermore, the terms "first," "second," and the like, herein do not denote any order, quantity, or importance, but rather are used to denote one element from another. The terms "a" and "an" and "the" herein do not denote a limitation of quantity, and are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. "Or" means "and/or." The suffix "(s)" as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term. Reference throughout the specification to "one embodiment", "another embodiment", "an embodiment", and so forth, means that a particular element described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other

embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments. [0064] The modifier "about" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). The notation "+ 10%" means that the indicated measurement can be from an amount that is minus 10% to an amount that is plus 10% of the stated value.

[0065] As used herein, the term "hydrocarbyl" and "hydrocarbon" refers broadly to a substituent comprising carbon and hydrogen, optionally with 1 to 3 heteroatoms, for example, oxygen, nitrogen, halogen, silicon, sulfur, or a combination thereof; "alkyl" refers to a straight or branched chain, saturated monovalent hydrocarbon group; "alkylene" refers to a straight or branched chain, saturated, divalent hydrocarbon group; "alkylidene" refers to a straight or branched chain, saturated divalent hydrocarbon group, with both valences on a single common carbon atom; "alkenyl" refers to a straight or branched chain monovalent hydrocarbon group having at least two carbons joined by a carbon-carbon double bond; "cycloalkyl" refers to a non-aromatic monovalent monocyclic or multicylic hydrocarbon group having at least three carbon atoms, "cycloalkenyl" refers to a non-aromatic cyclic divalent hydrocarbon group having at least three carbon atoms, with at least one degree of unsaturation; "aryl" refers to an aromatic monovalent group containing only carbon in the aromatic ring or rings; "arylene" refers to an aromatic divalent group containing only carbon in the aromatic ring or rings; "alkylaryl" refers to an aryl group that has been substituted with an alkyl group as defined above, with 4-methylphenyl being an exemplary alkylaryl group; "arylalkyl" refers to an alkyl group that has been substituted with an aryl group as defined above, with benzyl being an exemplary arylalkyl group; "acyl" refers to an alkyl group as defined above with the indicated number of carbon atoms attached through a carbonyl carbon bridge (-C(=0)-); "alkoxy" refers to an alkyl group as defined above with the indicated number of carbon atoms attached through an oxygen bridge (-0-); and "aryloxy" refers to an aryl group as defined above with the indicated number of carbon atoms attached through an oxygen bridge (-0-).

[0066] Unless otherwise indicated, each of the foregoing groups can be unsubstituted or substituted, provided that the substitution does not significantly adversely affect synthesis, stability, or use of the compound. The term "substituted" as used herein means that at least one hydrogen on the designated atom or group is replaced with another group, provided that the designated atom's normal valence is not exceeded. When the substituent is oxo (i.e., =0), then two hydrogens on the atom are replaced. Combinations of substituents and/or variables are permissible provided that the substitutions do not significantly adversely affect synthesis or use of the compound. Exemplary groups that can be present on a "substituted" position include, but are not limited to, cyano; hydroxyl; nitro; azido; alkanoyl (such as a C2-6 alkanoyl group such as acyl); carboxamido; Ci-6 or C ₁ -3 alkyl, cycloalkyl, alkenyl, and alkynyl (including groups having at least one unsaturated linkages and from 2 to 8, or 2 to 6 carbon atoms); Ci_6 or Ci_3 alkoxyl; C -w aryloxy such as phenoxy; Ci_6 alkylthio; Ci_6 or Ci_3 alkylsulfinyl; Ci_6 or Ci_3 alkylsulfonyl; aminodi(Ci_6 or Ci_3)alkyl; C -12 aryl having at least one aromatic rings (e.g., phenyl, biphenyl, naphthyl, or the like, each ring either substituted or unsubstituted aromatic); C -i9 arylalkyl having 1 to 3 separate or fused rings and from 6 to 18 ring carbon atoms; or arylalkoxy having 1 to 3 separate or fused rings and from 6 to 18 ring carbon atoms, with benzyloxy being an exemplary arylalkoxy.

[0067] While particular embodiments have been described, alternatives,

modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.

[0068] I/we claim: