552-30-7

Basic information

• Product Name: Trimellitic Anhydride
• Synonyms: 1,2,4-Benzenetricarboxylic acid anhydride;1,2,4-Benzenetricarboxylic acid anhydride-1,2;1,2,4-Benzenetricarboxylic acid, cyclic 1,2-anhydride;1,2,4-benzenetricarboxylicacid,cyclic1,2-anhydride;1,2,4-benzenetricarboxylicacidanhydride;1,3-Dihydro-1,3-dioxo-5-isobenzofurancarboxylic acid;1,3-dihydro-1,3-dioxo-5-Isobenzofurancarboxylicacid;1,3-Dioxo-1,3-dihydro-2-benzofuran-5-carboxylic acid
• CAS NO: 552-30-7
• Molecular Formula: C₉H₄O₅
• Molecular Weight: 192.13
• EINECS: 209-008-0
• Product Categories: Industrial/Fine Chemicals;Fluorenes, etc. (reagent for high-performance polymer research);Functional Materials;Reagent for High-Performance Polymer Research;fine chemicals;Pyridines;pharmaceutical raw material;addictives
• Mol File: 552-30-7.mol

Chemical Properties

• Melting Point: 163-166 °C(lit.)
• Boiling Point: 390 °C
• Flash Point: 227 °C
• Appearance: White to off-white/Flakes
• Density: 1.54
• Vapor Density: 6.6 (vs air)
• Vapor Pressure: <0.01 mm Hg ( 20 °C)
• Refractive Index: 1.4717 (estimate)
• Storage Temp.: Store below +30°C.
• Solubility: 24.4g/l (decomposition)
• PKA: 3.11±0.20(Predicted)
• Explosive Limit: 1-7%(V)
• Water Solubility: DECOMPOSES
• Sensitive: Moisture Sensitive
• Stability: Stable. Moisture sensitive.
• Merck: 14,9703
• BRN: 9394
• CAS DataBase Reference: Trimellitic Anhydride(CAS DataBase Reference)
• NIST Chemistry Reference: Trimellitic Anhydride(552-30-7)
• EPA Substance Registry System: Trimellitic Anhydride(552-30-7)

Safety Data

• Hazard Codes: Xn
• Statements: 37-41-42/43
• Safety Statements: 22-26-36/37/39
• WGK Germany: 1
• RTECS: DC2050000
• F: 10-21
• TSCA: Yes
• Hazardous Substances Data: 552-30-7(Hazardous Substances Data)

Usage

Uses

Used in Plastic Industry:
Trimellitic Anhydride is used as a raw material for polyester resin and polyimide resin, contributing to the production of heatproof, insulating, adhesive, and surfactant materials.
Used in Chemical Industry:
Trimellitic Anhydride is used as a plasticizer for polyvinyl chloride (PVC) and as a curing agent for epoxy-based resins.
Used in Flooring Industry:
Trimellitic Anhydride is used as an embossing agent for vinyl flooring, enhancing the texture and appearance of the material.
Used in Automotive Industry:
Trimellitic Anhydride is used in the production of good heat-proof, weather-proof, and solvent-proof trimellitate plasticizers, such as tri(2-ethylhexyl)trimellitate, which are essential for automotive applications.
Used in Paint and Coating Industry:
Trimellitic Anhydride is used as a curing agent for epoxy resins, which are crucial in the formulation of various surface coatings, adhesives, and polymers.
Used in Dye and Ink Industry:
Trimellitic Anhydride is used as an intermediate for the synthesis of dyes and printing inks, providing a wide range of color options and improved performance.
Used in Pharmaceutical Industry:
Trimellitic Anhydride is used as an intermediate in the synthesis of various pharmaceuticals, contributing to the development of new drugs and therapies.

Air & Water Reactions

Sensitive to moisture. Hydrolyzes slowly. Solutions in water or alcohol may be unstable. Insoluble in water.

Reactivity Profile

1,2,4-Benzenetricarboxylic anhydride reacts exothermically with water. This reaction is expected to be slow, but can become vigorous if local heating accelerates it. Reaction with water is accelerated by acids. Incompatible with acids, strong oxidizing agents, alcohols, amines, and bases. Incompatible with strong oxidizing agents, strong acids or strong bases. .

Hazard

Toxic by inhalation. Respiratory sensitization.

Health Hazard

Trimellitic anhydride (TMAN) causes both respiratory irritation and immunologic respiratory disease.

Safety Profile

Moderately toxic by ingestion. Has caused pulmonary edema from inhalation. Irritant to lungs and air passages. May be a powerful allergen. Typical attack consists of breathlessness, wheezing, cough, running nose, immunologcal sensitization, and asthma symptoms. When heated to decomposition it emits acrid smoke and irritating fumes. See also ANHYDRIDES.

Synthesis

3-Xylene is carbonylated with carbon monoxide in the presence of boron trifluoride and hydrogen fluoride to form 2,4-dimethylbenzaldehyde. 2,4-Dimethylbenzaldehyde is decomplexed from the acids, purified, and oxidized to trimellitic acid. Trimellitic acid is subjected to normal dehydration and purification steps to obtain high quality trimellitic anhydride.

Potential Exposure

TMA is used to produce trimellitate plasticizers, poly (amide-imide) polymers; in paints, enamels, and coatings; polymers, polyesters; as a curing agent for epoxy and other resins; in vinyl plasticizers; agricultural chemicals; dyes and pigments; pharmaceuticals, surface active agents; modifiers, intermediates, and specialty chemicals.

Carcinogenicity

There are no reports of carcinogenicity associated with TMAN exposure. It was not mutagenic in bacterial assays with or without metabolic activation. No teratogenic effects or developmental toxicity was seen in rats or guinea pigs exposed to 500mg/m3 for 6 hours/day during their period of major organogenesis.

Incompatibilities

Dust can cause an explosion. Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides. Reacts slowly with water, forming trimellitic acid. Compounds of the carboxyl group react with all bases, both inorganic and organic (i.e., amines) releasing substantial heat, water and a salt that may be harmful.

Waste Disposal

Dissolve or mix the material with a combustible solvent and burn in a chemical incinerator equipped with an afterburner and scrubber. All federal, state, and local environmental regulations must be observed.

InChI:InChI=1/C9H4O5/c10-7(11)4-1-2-5-6(3-4)9(13)14-8(5)12/h1-3H,(H,10,11)

Synthetic route

1,2,4-benzene tricarboxylic acid (528-44-9) → trimellitic Anhydride (552-30-7)

benzene-1,2,4-tricarboxylic acid-2-methyl ester (13940-95-9) → trimellitic Anhydride (552-30-7)

Conditions	Yield
at 200℃;

benzene-1,2,4-tricarboxylic acid-1-methyl ester (13912-71-5) → trimellitic Anhydride (552-30-7)

Conditions	Yield
at 200℃;

2,5-dimethylterephthalic acid (6051-66-7) → maleic anhydride (108-31-6) + Pyromellitic dianhydride (89-32-7) + 1,2,4-benzene tricarboxylic acid (528-44-9) + trimellitic Anhydride (552-30-7)

Conditions	Yield
With vanadia at 400℃; Product distribution; effect of temperature on gas-phase oxidation;

2,4-dimethylisophthalic acid (18190-63-1) → Pyromellitic dianhydride (89-32-7) + 1,2,4-benzene tricarboxylic acid (528-44-9) + trimellitic Anhydride (552-30-7)

Conditions	Yield
With vanadia at 400℃; Product distribution; effect of temperature on gas-phase oxidation of methyl-substituted carboxylic acids and anhydrides;

1,2,4-Trimethylbenzene (95-63-6) → trimellitic Anhydride (552-30-7)

Conditions	Yield
Multi-step reaction with 5 steps 2: sulfuric acid 3: aqueous-methanolic KOH-solution 5: 200 °C View Scheme
Multi-step reaction with 5 steps 2: sulfuric acid 3: aqueous-methanolic KOH-solution 5: 200 °C View Scheme
Multi-step reaction with 2 steps 1: KMnO4; water; NaOH-solution / man macht schwefelsauer, behandelt mit SO2, saettigt mit Na2SO4 2: 200 - 220 °C / im Vakuum View Scheme
With 1,1,2,2-tetrabromoethane; cobalt(II) acetate; manganese(II) acetate; acetic acid at 220℃; under 15001.5 - 17251.7 Torr; Reagent/catalyst; Temperature; Pressure; Inert atmosphere; Large scale;	1360 g

1,2-dimethyl 1,2,4-benzenetricarboxylate (54699-35-3) → trimellitic Anhydride (552-30-7)

Conditions	Yield
Multi-step reaction with 2 steps 2: 200 °C View Scheme
Multi-step reaction with 2 steps 2: 200 °C View Scheme

benzene-1,2,4-tricarboxylic acid trimethyl ester (2459-10-1) → trimellitic Anhydride (552-30-7)

Conditions	Yield
Multi-step reaction with 3 steps 1: aqueous-methanolic KOH-solution 3: 200 °C View Scheme
Multi-step reaction with 3 steps 1: aqueous-methanolic KOH-solution 3: 200 °C View Scheme

diethyl 4-aminophthalate (22572-84-5) → trimellitic Anhydride (552-30-7)

Conditions	Yield
Multi-step reaction with 3 steps 1: aqueous HCl; aqueous NaNO2 2: aqueous NaOH 3: 180 °C / 0.5 Torr View Scheme

4-cyano-phthalic acid diethyl ester (105903-40-0) → trimellitic Anhydride (552-30-7)

Conditions	Yield
Multi-step reaction with 2 steps 1: aqueous NaOH 2: 180 °C / 0.5 Torr View Scheme

2-amino-5-aminomethyl-4,7-dihydro-5H-thieno[2,3-c]pyran-3-carboxylic acid tert-butyl ester (243968-20-9) + trimellitic Anhydride (552-30-7) → 2-(2-amino-3-tert-butoxycarbonyl-4,7-dihydro-5H-thieno[2,3-c]pyran-5-ylmethyl)-1,3-dioxo-2,3-dihydro-1H-isoindole-5-carboxylic acid (330193-56-1)

Conditions	Yield
In N,N-dimethyl-formamide at 100℃; for 24h;	100%
In N,N-dimethyl-formamide at 100℃; for 24h;	100%
In N,N-dimethyl-formamide at 100℃; for 24h;	100%

4-amino-2,3-dimethyl-1-phenylpyrazolin-5-one (83-07-8) + trimellitic Anhydride (552-30-7) → 2-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)-1,3-dioxo-2,3-dihydro-1H-isoindole-5-carboxylic acid (292870-53-2)

Conditions	Yield
With dmap In N,N-dimethyl-formamide at 20℃; for 72h;	100%
With dmap In N,N-dimethyl-formamide at 110℃; for 12h;	46%

D-tryptophan (153-94-6) + trimellitic Anhydride (552-30-7) → (R)-2-(1-carboxy-2-(1H-indol-3-yl)ethyl)-1,3-dioxoisoindoline-5-carboxylic acid

Conditions	Yield
In diethylene glycol dimethyl ether at 200℃; for 0.166667h; microwave irradiation;	99%

3-(trimethoxysilyl)propan-1-amine (13822-56-5) + trimellitic Anhydride (552-30-7) → C15H21NO8Si (1204776-58-8)

Conditions	Yield
In tetrahydrofuran at -5 - 5℃; for 6h; Inert atmosphere;	99%

3-aminopropyltriethoxysilane (919-30-2) + trimellitic Anhydride (552-30-7) → C18H27NO8Si (1204776-59-9)

Conditions	Yield
In tetrahydrofuran at -5 - 5℃; Inert atmosphere;	99%

5-aminoisophthalic acid (99-31-0) + trimellitic Anhydride (552-30-7) → C17H9NO8 (51222-09-4)

Conditions	Yield
In N,N-dimethyl-formamide for 6h; Heating;	98%

chromium dichloride + diphenyl-phosphinic acid (1707-03-5) + chromium(III) chloride (10025-73-7) + trimellitic Anhydride (552-30-7) → [Cr(OP(CH3)(C6H5)O)2(OOCC6H3C2O3)]x

Conditions	Yield
With trimethylamine In tetrahydrofuran byproducts: (CH3)3NHCl; N2-atmosphere; shaking CrCl3 with trace of CrCl2, refluxing with 2 equiv. of phosphinic acid and 2.5 equiv. NMe3 (1 h), cooling to room temp., addn. of 1 equiv. C9H4O5 and excess NMe3, refluxing (0.5 h); filtration, evapn. to dryness, drying (140°C, several days); elem. anal.;	98%

C53H86N4O15 + trimellitic Anhydride (552-30-7) → C62H90N4O20

Conditions	Yield
In tetrahydrofuran; toluene at 20℃; for 12 - 15h;	98%

4-nitro-aniline (100-01-6) + trimellitic Anhydride (552-30-7) → 2-(4-nitrophenyl)-1,3-dioxo-2,3-dihydro-1H-isoindole-5-carboxylic acid

Conditions	Yield
With acetic acid at 130℃; for 16h; Condensation;	97%
In acetic acid for 20h; Reflux;	95%

3,4,5-Trimethoxyaniline (24313-88-0) + trimellitic Anhydride (552-30-7) → [2-(3,4,5-trimethoxy)phenyl]-1,3-dioxo-2,3-dihydro-1H-isoindole-5-carboxylic acid

Conditions	Yield
With acetic acid at 130℃; for 16h; Condensation;	97%

2-methyl-8-quinolinol (826-81-3) + trimellitic Anhydride (552-30-7) → C19H11NO5

Conditions	Yield
In nitrobenzene at 175 - 180℃; for 3h;	97%

2-(4'-hydroxyphenyl)-2-(4'-aminophenyl)-propane (837-11-6) + trimellitic Anhydride (552-30-7) → N-{4-[2-(4-hydroxyphenyl)isopropyl]phenyl}trimellitimide

Conditions	Yield
Stage #1: 2-(4'-hydroxyphenyl)-2-(4'-aminophenyl)-propane; trimellitic Anhydride In 1-methyl-pyrrolidin-2-one at 20℃; for 6h; Inert atmosphere; Stage #2: In 1-methyl-pyrrolidin-2-one; toluene at 120℃; for 10h; Dean-Stark;	97%

α,ω-Diisocyanato-polybutadiene, isocyanate group conc. 719 mmol/g, Mw/Mn = 1.3, structure units 1,2- : 1,4-trans : 1,4-cis = 60 : 25 : 15 + trimellitic Anhydride (552-30-7) → Poly(α,ω-diisocyanato-polybutadiene-co-trimellitic anhydride), LBD-3000 content 42 wt percent

Conditions	Yield
With 1-methyl-pyrrolidin-2-one at 70 - 180℃; for 9h; Polymerization;	96%

bis(4-aminophenyl)diphenylsilane (3454-24-8) + trimellitic Anhydride (552-30-7) → 2-(4-((4-(5-carboxy-1,3-dioxoisoindolin-2-yl)phenyl)diphenylsilyl)phenyl)-1,3-dioxoisoindoline-5-carboxylic acid (1357585-01-3)

Conditions	Yield
With acetic acid at 20℃; for 15h; Reflux;	96%

O-(4-methoxybenzyl)-hydroxylamine HCl + trimellitic Anhydride (552-30-7) → 2-(4-methoxybenzyloxy)-1,3-dioxoisoindoline-5-carboxylic acid (863990-91-4)

Conditions	Yield
With pyridine at 90℃; for 24h;	95%

trimellitic Anhydride (552-30-7) → 1,4-dihydroxy-phthalazine-6-carboxylic acid (42972-13-4)

Conditions	Yield
Stage #1: trimellitic Anhydride With hydrazine In isopropyl alcohol for 5h; Heating / reflux; Stage #2: With hydrogenchloride; water In isopropyl alcohol at 20℃; for 1h;	95%

2,6-diamino-4-trifluoromethyl-40-phenoxydiphenyl ether (1374879-15-8) + trimellitic Anhydride (552-30-7) → 2,6-bis(N-trimellitimido)-4-trifluoromethyl-40-phenoxydiphenyl ether (1374879-16-9)

Conditions	Yield
With acetic acid for 15h; Inert atmosphere; Reflux;	95%

m-Hydroxyaniline (591-27-5) + trimellitic Anhydride (552-30-7) → N-(3-hydroxyphenyl)trimellitimide (82811-05-0)

Conditions	Yield
Stage #1: m-Hydroxyaniline; trimellitic Anhydride In 1-methyl-pyrrolidin-2-one at 20℃; for 6h; Inert atmosphere; Stage #2: In 1-methyl-pyrrolidin-2-one; toluene at 120℃; for 10h; Dean-Stark;	95%

5-amino-1-naphthol (83-55-6) + trimellitic Anhydride (552-30-7) → N-(5-hydroxynaphthyl)trimellitimide

Conditions	Yield
Stage #1: 5-amino-1-naphthol; trimellitic Anhydride In 1-methyl-pyrrolidin-2-one at 20℃; for 6h; Inert atmosphere; Stage #2: In 1-methyl-pyrrolidin-2-one; toluene at 120℃; for 10h; Dean-Stark;	95%

di(4-isocyanatophenyl)methane (101-68-8) + trimellitic Anhydride (552-30-7) → Poly(4,4\-methylenedi(phenylisocyanate)-trimellitic anhydride)

Conditions	Yield
With 1-methyl-pyrrolidin-2-one at 70 - 180℃; for 9h; Polymerization;	94%

O-allylhydroxylamine hydrochloride (38945-21-0) + trimellitic Anhydride (552-30-7) → 2-(allyloxy)-1,3-dioxoisoindoline-5-carboxylic acid (863990-92-5)

Conditions	Yield
With pyridine at 90℃; for 24h;	94%

4-amino-phenol (123-30-8) + trimellitic Anhydride (552-30-7) → 2-(4-hydroxyphenyl)-1,3-dioxo-2,3-dihydro-1H-isoindole-5-carboxylic acid (22005-25-0)

Conditions	Yield
Stage #1: 4-amino-phenol; trimellitic Anhydride In 1-methyl-pyrrolidin-2-one at 20℃; for 6h; Inert atmosphere; Stage #2: In 1-methyl-pyrrolidin-2-one; toluene at 120℃; for 10h; Dean-Stark;	93%
With acetic acid at 130℃; for 16h; Condensation;	85%

2-Ethylhexyl alcohol (104-76-7) + trimellitic Anhydride (552-30-7) → Hatcol 200 (3319-31-1)

Conditions	Yield
With methanesulfonic acid In water at 180 - 208℃; for 3h; Reagent/catalyst; Temperature; Inert atmosphere;	93%

α,ω-Diisocyanato-polybutadiene, isocyanate group conc. 719 mmol/g, Mw/Mn = 1.3, structure units 1,2- : 1,4-trans : 1,4-cis = 60 : 25 : 15 + trimellitic Anhydride (552-30-7) → Poly(α,ω-diisocyanato-polybutadiene-co-trimellitic anhydride), LBD-3000 content 94 wt percent

Conditions	Yield
With 1-methyl-pyrrolidin-2-one at 70 - 180℃; for 9h; Polymerization;	92%

4-chloro-aniline (106-47-8) + trimellitic Anhydride (552-30-7) → 2-(4-chlorophenyl)-1,3-dioxo-2,3-dihydro-1H-isoindole-5-carboxylic acid

Conditions	Yield
With acetic acid at 130℃; for 16h; Condensation;	92%
With acetic acid In diethyl ether Reflux;

N-phenylphenylene-1,4-diamine (101-54-2) + trimellitic Anhydride (552-30-7) → C21H14N2O4 (330217-26-0)

Conditions	Yield
In acetic acid for 10h; Inert atmosphere; Reflux;	92%

1,4-(4-amino-2-trifluoromethylphenoxy)-2-(3'-trifluoromethylphenyl)benzene + trimellitic Anhydride (552-30-7) → 2,2'-(4,4'-(3'-(trifluoromethyl)biphenyl-2,5-diyl)bis(oxy)bis(3-(trifluoromethyl)-4,1-phenylene))bis(1,3-dioxoisoindoline-5-carboxylic acid)

Conditions	Yield
With acetic acid at 120℃; for 13h;	92%

α,ω-Diisocyanato-polybutadiene, isocyanate group conc. 719 mmol/g, Mw/Mn = 1.3, structure units 1,2- : 1,4-trans : 1,4-cis = 60 : 25 : 15 + trimellitic Anhydride (552-30-7) → Poly(α,ω-diisocyanato-polybutadiene-co-trimellitic anhydride), LBD-3000 content 16 wt percent

Conditions	Yield
With 1-methyl-pyrrolidin-2-one at 70 - 180℃; for 9h; Polymerization;	91%

3-chloro-aniline (108-42-9) + trimellitic Anhydride (552-30-7) → 2-(3-chlorophenyl)-1,3-dioxo-2,3-dihydro-1H-isoindole-5-carboxylic acid

Conditions	Yield
With acetic acid at 130℃; for 16h; Condensation;	91%

m,p-dichloroaniline (95-76-1) + trimellitic Anhydride (552-30-7) → [2-(3,4-dichloro)phenyl]-1,3-dioxo-2,3-dihydro-1H-isoindole-5-carboxylic acid

Conditions	Yield
With acetic acid at 130℃; for 16h; Condensation;	91%
With acetic acid In diethyl ether Reflux;

Upstream product

• 105903-40-0 4-cyano-phthalic acid diethyl ester 
• 22572-84-5 diethyl 4-aminophthalate 
• 2459-10-1 benzene-1,2,4-tricarboxylic acid trimethyl ester 
• 54699-35-3 1,2-dimethyl 1,2,4-benzenetricarboxylate 
• 95-63-6 1,2,4-Trimethylbenzene 
• 18190-63-1 2,4-dimethylisophthalic acid 
• 6051-66-7 2,5-dimethylterephthalic acid 
• 13912-71-5 benzene-1,2,4-tricarboxylic acid-1-methyl ester 
• 13940-95-9 benzene-1,2,4-tricarboxylic acid-2-methyl ester 
• 528-44-9 1,2,4-benzene tricarboxylic acid 

Downstream Products

• 20262-55-9 11,3-dioxoisoindoline-5-carboxylic acid 
• 439586-66-0 4,4'-trimellitimido-3'',4''-dimethyltriphenylamine 
• 868622-72-4 2-(2-benzyl-1,3-dioxo-2,3-dihydro-1H-isoindol-5-ylmethyl)-malonic acid dimethyl ester 
• 868622-66-6 1,3-dioxo-2-phenethyl-2,3-dihydro-1H-isoindole-5-carboxylic acid tert-butoxy-amide 
• 868622-65-5 2-benzyl-1,3-dioxo-2,3-dihydro-1H-isoindole-5-carboxylic acid tert-butoxy-amide 
• 868622-73-5 3-(2-benzyl-1,3-dioxo-2,3-dihydro-1H-isoindol-5-yl)-propionic acid 
• 868622-64-4 1,3-dioxo-2-phenyl-2,3-dihydro-1H-isoindole-5-carboxylic acid tert-butoxy-amide 
• 868622-71-3 2-benzyl-5-bromomethyl-isoindole-1,3-dione 
• 868622-70-2 2-benzyl-5-hydroxymethyl-isoindole-1,3-dione 
• 170433-63-3 dimethyl 4-hydroxymethylphthalate 
• 67822-79-1 2-benzylisoindolin-1,3-dione-5-carboxylic acid chloride 

Relevant articles and documents

Preparation method and application of trimellitic acid or trimesic acid

The invention belongs to the technical field of organic synthesis processes, and particularly relates to a preparation method and application of trimellitic acid or trimesic acid. According to the characteristics of the oxidation reaction process of 1,2,4-trimethylbenzene or mesitylene, two stages of reactors are connected in series, different oxidation reaction process conditions are respectively adopted, particularly, a second-stage reactor adopts a reaction strengthening technology, and an oxygen-enriched oxidation mode is adopted to strengthen the oxidation reaction process and increase the yield of the trimellitic acid or the trimesic acid.

METHOD FOR PRODUCING CARBOXYLIC ACID ANHYDRIDE, METHOD FOR PRODUCING CARBOXYLIC IMIDE, AND METHOD FOR MANUFACTURING ELECTROPHOTOGRAPHIC PHOTOSENSITIVE MEMBER

A method for producing a carboxylic acid anhydride includes heating a composition containing a specific compound in a solvent to yield the carboxylic acid anhydride. The solvent is an aprotic polar solvent having a boiling point of 50° C. or more.

PHYSICOCHEMICAL STUDY OF SEPARATION AND INTERACTION OF TRIMELLITIC ANHYDRIDE AND TRIMELLITIC ACID.

The objective of this work is to study the physicochemical characteristics of TMAc (Trimellitic Acid) and TMAn (Trimellitic Anhydride) to select and develop a method for purification of technical TMAn obtained by dehydration of TMAc, and to investigate the phase diagram of the system TMAc-TMAn, obtained during production of technical TMAn. It is shown by the method of controlled sublimation for purification of crude TMAn that the purest fraction contains 99. 95 plus or minus 0. 03 mole % of TMAn; the purity of the sublimed product, determined cryoscopically, was 99. 95 plus or minus 0. 03 mole %. The experimental value of the cryoscopic constant of TMAn, 1. 45 plus or minus 0. 09 mole %/deg at P equals 0. 95, is in good agreement with the calculated value of 1. 53 mole %/deg. The enthalpy of fusion of TMAn was determined, and found to be 5. 20 plus or minus 0. 02 kcal/mole. Thermal analysis of the binary system TMAn-TMAc showed the existence of a eutectic, melting at 166 plus or minus 0. 5 degree and containing 3. 5 plus or minus 0. 5 mole % of TMAc.