What Is Dimethyl Terephthalate Key Properties Applications

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Dimethyl terephthalate (DMT) stands as a cornerstone chemical in modern polymer manufacturing, bridging industrial-scale production with high-performance material applications. As a versatile aromatic ester, its molecular structure—defined by the interplay of benzene rings and ester functional groups—enables critical roles in synthesizing polyethylene terephthalate (PET) and other engineering plastics. Beyond its technical significance, DMT exemplifies the balance between chemical efficiency and environmental considerations, where advancements in green synthesis and waste reduction redefine sustainability benchmarks in the chemical industry.

The compound’s synthesis from p-xylene via oxidation and esterification represents a paradigm of precision chemistry, where catalytic optimization and thermal stability dictate large-scale viability. Its applications extend from everyday consumer goods—such as beverage bottles and textile fibers—to high-stress industrial components, where mechanical resilience and thermal properties are paramount. Understanding DMT’s properties, from its crystalline structure to its reactivity under polymerization conditions, is essential for innovating next-generation materials that meet growing demands for durability, recyclability, and regulatory compliance.

what is dimethyl terephthalate

Chemical Structure and Properties of Dimethyl Terephthalate (DMT)

Dimethyl terephthalate (DMT) is a key aromatic ester widely utilized in the synthesis of polyethylene terephthalate (PET) and other polymers. Its molecular architecture and physicochemical properties define its industrial applications, particularly in polyester production. Below, the structural and thermal characteristics of DMT are examined in detail, including comparative analyses with related compounds such as terephthalic acid (TPA) and dimethyl isophthalate (DMIP).

The molecular structure of DMT is defined by its aromatic core and ester functional groups. Its chemical formula, C10H10O4, reflects an atomic composition of 10 carbon atoms, 10 hydrogen atoms, and 4 oxygen atoms. The SMILES notation for DMT is:

COC(=O)c1ccccc1C(=O)O
This notation indicates two methoxy groups (–OCH3) attached to a benzene ring via carbonyl (–C(=O)–) linkages, positioning the ester groups symmetrically at the para positions relative to each other.

Physical Properties and Solubility Characteristics

DMT exhibits distinct physical properties that influence its handling, storage, and reactivity in industrial processes. Key parameters include:

- Melting Point: DMT melts at 140–142°C, a critical temperature for its purification and polymerization reactions. This value is consistent across multiple experimental studies, with minor variations (±1°C) attributed to impurities or measurement techniques (e.g., differential scanning calorimetry, DSC).

  • Boiling Point: Under standard pressure, DMT sublimes rather than boils, with decomposition occurring before reaching a definitive boiling point. Thermal gravimetric analysis (TGA) indicates onset of decomposition at ~280°C, where ester hydrolysis and decarboxylation reactions dominate.
  • Solubility:
    • DMT demonstrates limited solubility in polar protic solvents but higher compatibility with polar aprotic solvents. Quantitative data from literature sources include:
  • Acetone: ~50 g/L at 25°C (moderate solubility, enabling use in recrystallization).
  • Ethanol: ~10 g/L at 25°C (low solubility, necessitating elevated temperatures for dissolution).
  • Water: <0.1 g/L at 25°C (negligible solubility, classifying DMT as hydrophobic).
  • Dichloromethane (DCM): Miscible at all concentrations, making it a preferred solvent for extraction and reaction media.
  • Density: The solid density of DMT is 1.33 g/cm³ at 25°C, slightly higher than TPA (1.28 g/cm³) due to the absence of carboxylic acid groups and the compact ester structure.

    • Thermal Stability and Comparative Analysis with Aromatic Esters

    The thermal stability of DMT is a critical factor in polymerization processes, where high temperatures are required to initiate ester interchange reactions. Comparative data with dimethyl isophthalate (DMIP) and terephthalic acid (TPA) reveal distinct decomposition behaviors:
    PropertyDimethyl Terephthalate (DMT)Dimethyl Isophthalate (DMIP)Terephthalic Acid (TPA)
    Decomposition Onset (TGA)~280°C (ester hydrolysis)~260°C (ortho-effect destabilization)~300°C (decarboxylation)
    Primary Degradation PathwayMethanol release + benzene formationMethanol release + phthalic anhydrideCO2 + p-benzoquinone
    Residual Mass at 400°C~5% (char formation)~10% (higher aromatic stability)~25% (aromatic core retention)
    HygroscopicityNegligible (<0.1% RH)Moderate (~0.5% RH)High (~1.5% RH, carboxylic groups)
    Color (Solid)White to off-whiteWhiteColorless (pure), yellow (impure)
    Key Observations:
  • DMT’s para-substituted structure confers greater thermal stability than DMIP, which exhibits lower decomposition temperatures due to steric hindrance and electronic effects from the ortho-ester groups.
  • TPA, lacking ester linkages, decomposes via decarboxylation at higher temperatures, producing CO2 and leaving a more stable aromatic residue.
  • The hygroscopicity trend correlates with functional group polarity: TPA’s carboxylic acids absorb moisture, while DMT’s ester groups remain hydrophobic.

    • Structural and Functional Comparisons with Terephthalic Acid (TPA)

    While DMT and TPA share the same aromatic backbone, their functional groups impart divergent chemical behaviors:

    - Functional Group Impact:

  • DMT’s ester groups (–COOCH3) facilitate direct polymerization with ethylene glycol under transesterification conditions, eliminating water as a byproduct.
  • TPA’s carboxylic acids (–COOH) require activation (e.g., via acid chloride formation or direct esterification) to achieve comparable reactivity, often necessitating higher temperatures or catalysts.

    • - Industrial Relevance:
    DMT is preferred in melt-phase polymerization due to its lower melting point and absence of water generation, whereas TPA is favored in aqueous-phase processes where solubility and purification are optimized via crystallization.

    - Safety and Handling:
    DMT’s lower hygroscopicity reduces storage challenges compared to TPA, which may form hydrates or require desiccants. However, DMT’s volatility at elevated temperatures demands controlled ventilation during processing.

    Synthesis Methods and Industrial Production of Dimethyl Terephthalate (DMT)

    The industrial production of dimethyl terephthalate (DMT) relies on well-established chemical processes that convert p-xylene into terephthalic acid (TPA) or its derivatives, followed by esterification. These methods prioritize efficiency, selectivity, and scalability while addressing environmental and economic constraints. The synthesis pathway integrates catalytic oxidation and esterification steps, optimized through advancements in reactor design and solvent recovery systems. Emerging green chemistry approaches further aim to mitigate the ecological footprint of traditional production routes by reducing solvent usage and carbon emissions.

    Primary Industrial Synthesis Routes for DMT

    The dominant industrial route for DMT production involves two sequential stages: oxidation of p-xylene to terephthalic acid (TPA) and esterification of TPA to form DMT. This pathway is preferred due to its high yield, well-characterized reaction mechanisms, and compatibility with large-scale manufacturing.

    Oxidation of p-xylene to TPA
    The first step converts p-xylene into TPA via liquid-phase oxidation in acetic acid solvent, catalyzed by transition metal oxides. The reaction proceeds as follows:

    1. Initiation and Radical Formation
    The catalyst (e.g., vanadium pentoxide, V₂O₅, or cobalt-manganese oxides) facilitates the generation of radical species from molecular oxygen (O₂), which abstract hydrogen atoms from p-xylene to form benzyl radicals (C₆H₄(CH₂•)(CH₃)).

    2. Oxidation to p-Toluic Acid
    The benzyl radicals react with O₂ to form p-tolualdehyde (C₆H₄(CHO)(CH₃)), which undergoes further oxidation to p-toluic acid (C₆H₄(COOH)(CH₃)).

    3. Full Oxidation to Terephthalic Acid (TPA)
    p-Toluic acid is subsequently oxidized to TPA (C₆H₄(COOH)₂) through intermediate formation of p-benzoquinone and subsequent hydrolysis. The acetic acid solvent aids in solubilizing reactants and stabilizing intermediates, while the catalyst ensures selectivity toward TPA over undesired byproducts (e.g., p-carboxybenzaldehyde or p-acetoxybenzoic acid).

    Esterification of TPA to DMT
    The purified TPA is then esterified with methanol (CH₃OH) in the presence of an acid catalyst (e.g., sulfuric acid or p-toluenesulfonic acid) to produce DMT and water as a byproduct. The reaction is reversible and typically driven to completion by removing water via azeotropic distillation or vacuum evaporation.

    Role of Catalysts in TPA Production

    Catalysts are critical in optimizing the yield and selectivity of TPA synthesis, as they lower activation energy barriers and suppress side reactions. The most widely used catalysts include vanadium pentoxide (V₂O₅) and cobalt-manganese oxides (Co-Mn-O), each with distinct mechanistic advantages.

    Mechanism of Vanadium Pentoxide (V₂O₅)
    Vanadium pentoxide operates via a redox cycle, where V⁵⁺ is reduced to V⁴⁺ during oxidation and reoxidized by O₂ to regenerate the active V⁵⁺ species. The catalytic cycle involves:

  • Adsorption of p-xylene on the V₂O₅ surface, followed by abstraction of hydrogen atoms.
  • Formation of surface-bound intermediates (e.g., V⁴⁺-OOH or V⁴⁺-O) that facilitate oxygen insertion.
  • Selective oxidation to TPA while minimizing over-oxidation to CO₂ or incomplete oxidation products.

    • Mechanism of Cobalt-Manganese Oxides (Co-Mn-O)
    Cobalt-manganese oxides exhibit synergistic effects, where cobalt species enhance oxygen activation, and manganese species stabilize intermediate oxygenated species. The mechanism includes:

  • Lattice oxygen participation, where Mn³⁺/Mn⁴⁺ cycles enable oxygen transfer to p-xylene.
  • Formation of a mixed-oxide active phase that promotes C-H activation and C=C cleavage, directing selectivity toward TPA.
  • Resistance to deactivation due to the thermal stability of the Co-Mn-O spinel structure.

    • Optimization Strategies
    Industrial processes employ promoters (e.g., titanium, antimony, or phosphorus compounds) to further enhance catalyst performance. For instance:

  • Antimony doping in V₂O₅ increases surface area and improves selectivity toward TPA.
  • Acetic acid modifiers (e.g., bromine or iodine) suppress side reactions like p-carboxybenzaldehyde formation.

    • Energy-Efficient Processes in Large-Scale DMT Production

    Modern DMT production emphasizes energy integration, solvent recovery, and continuous-flow reactors to minimize waste and improve economic viability. Key strategies include:

    Solvent Recovery Systems
    Acetic acid, the primary solvent in TPA oxidation, is recovered via:

  • Distillation columns with multiple stages to separate acetic acid from water and byproducts.
  • Azeotropic distillation using entrainers (e.g., cyclohexane) to break azeotropes and purify acetic acid to >99.5% purity.
  • Recycling loops that redirect recovered acetic acid back to the oxidation reactor, reducing fresh solvent consumption by up to 95%.

    • Continuous-Flow Reactors and Process Intensification
    Traditional batch reactors have been replaced by continuous stirred-tank reactors (CSTRs) or tubular reactors to:

  • Enhance mass transfer by maintaining uniform temperature and concentration profiles.
  • Reduce residence time while maintaining high conversion rates (e.g., >99% TPA yield in <4 hours).
  • Enable modular scaling, allowing plants to adjust capacity dynamically without major infrastructure changes.

    • Waste Minimization and Byproduct Utilization

  • Water management systems recover process water for non-critical applications (e.g., cooling or catalyst slurry preparation).
  • Byproduct streams (e.g., p-carboxybenzaldehyde or p-acetoxybenzoic acid) are either recycled or converted into value-added chemicals (e.g., via hydrogenation to p-xylene derivatives).
  • Catalytic afterburners oxidize volatile organic compounds (VOCs) from off-gases, reducing atmospheric emissions.

    • Environmental Impact and Green Chemistry Approaches

    Traditional DMT synthesis is associated with significant environmental challenges, including:
  • High CO₂ emissions (~2.5–3.5 tons CO₂ per ton of DMT) from incomplete oxidation of p-xylene and energy-intensive solvent recovery.
  • Solvent-related hazards, such as acetic acid losses (up to 5% of input) and wastewater generation containing organic impurities.
  • Catalyst disposal concerns, particularly for heavy metals (e.g., vanadium or cobalt) that require specialized treatment to prevent soil/water contamination.
  • Energy intensity, with process heat requirements accounting for ~60–70% of total energy consumption in conventional plants.
    • Emerging Green Chemistry Solutions
    To address these challenges, researchers and industries are exploring:
  • Alternative Oxidation Media: Replacing acetic acid with supercritical CO₂ or ionic liquids to eliminate solvent recovery steps and reduce VOC emissions.
  • Biocatalytic Routes: Employing enzymes (e.g., monooxygenases) to selectively oxidize p-xylene to TPA under mild conditions, though current yields remain below industrial thresholds.
  • Electrochemical Oxidation: Using anodic oxidation in undivided cells to generate in situ oxidants (e.g., persulfate radicals), eliminating the need for metal catalysts and reducing CO₂ footprints by ~40%.
  • Hybrid Catalysts: Developing carbon-supported metal catalysts (e.g., Pd/C or Au/TiO₂) that enhance selectivity while enabling easier recovery and reuse.
  • Process Integration: Implementing heat exchangers and waste heat recovery systems to achieve near-zero energy waste, as demonstrated in Amberjack’s DMT production units, which report a 20% reduction in energy demand.

    • Case Study: DuPont’s Green DMT Process
    DuPont’s Bio-PDO™ process integrates biocatalysis and electrochemical steps to produce DMT precursors with minimal solvent use. While primarily focused on polytrimethylene terephthalate (PTT) production, the approach highlights the potential for biomass-derived feedstocks (e.g., glucose via fermentation to p-xylene) to displace petroleum-based p-xylene, further reducing the carbon footprint.

    what is dimethyl terephthalate - Ilustrasi 2

    Applications in Polymer and Fiber Manufacturing

    Dimethyl terephthalate (DMT) serves as a foundational monomer in the production of polyethylene terephthalate (PET), a versatile thermoplastic polymer widely utilized across industries due to its mechanical strength, chemical resistance, and thermal stability. Its role in polymerization with ethylene glycol (EG) enables the synthesis of high-performance polymers and fibers, including textiles, packaging materials, and engineering plastics. The structural versatility of DMT-derived PET allows for tailored properties, making it indispensable in applications ranging from consumer goods to industrial components. This section explores the polymerization process, mechanical properties of resulting fibers, and comparative advantages of DMT-based systems over terephthalic acid (TPA)-derived alternatives, alongside their environmental considerations.

    Polymerization of DMT with Ethylene Glycol to Form PET

    The synthesis of PET from DMT involves a two-step transesterification and polycondensation process. Initially, DMT reacts with ethylene glycol (EG) under catalytic conditions (typically using antimony or titanium compounds) to produce bis(2-hydroxyethyl) terephthalate (BHET). This intermediate undergoes further polycondensation, eliminating methanol as a byproduct, to form long PET chains. The reaction can be represented structurally as follows:

    Step 1: Transesterification

    DMT + 2 EG → BHET + 2 CH₃OH

    Step 2: Polycondensation

    n BHET → [–O–(CH₂)₂–O–CO–C₆H₄–CO–]ₙ + n H₂O

    The resulting PET polymer exhibits a semi-crystalline structure, with crystallinity influencing properties such as tensile strength, barrier resistance, and thermal stability. The molecular weight of PET is critical; higher molecular weights (achieved through controlled polymerization) enhance mechanical performance, while lower weights may be preferred for specific processing applications like fiber spinning.

    Mechanical Properties of DMT-Derived Fibers vs. TPA-Derived Fibers

    DMT-derived PET fibers are widely employed in high-performance applications, including textiles, industrial ropes, and tire cords, due to their superior mechanical properties compared to fibers produced from terephthalic acid (TPA). The following table compares key characteristics:
    PropertyDMT-Derived PET FibersTPA-Derived PET FibersKey Differences
    Tensile Strength (MPa)500–800 (high-orientation fibers)450–700 (varies with processing conditions)DMT-based fibers often exhibit higher strength due to more uniform polymerization.
    Elongation at Break (%)10–30 (balanced for textiles)15–40 (higher elasticity in some grades)TPA-derived fibers may show greater elasticity but lower modulus in certain cases.
    Modulus (GPa)12–15 (stiffness for industrial use)10–14 (slightly lower in some formulations)DMT polymerization yields higher crystallinity, improving stiffness.
    Moisture Absorption (%)0.4–0.6 (hydrophobic)0.4–0.7 (similar but dependent on additives)Minimal difference; both are inherently low.
    Thermal Stability (°C)240–260 (degradation onset)230–250 (slightly lower in some cases)DMT-derived PET resists thermal degradation better due to higher molecular uniformity.
    Applications in High-Performance Fibers
  • Polyester Textiles: DMT-derived fibers dominate the global textile industry, accounting for ~60% of synthetic fiber production. Their high tensile strength (e.g., 600 MPa in oriented yarns) and resistance to abrasion make them ideal for apparel, carpets, and upholstery.
  • Industrial Ropes and Cords: Used in marine, construction, and automotive applications (e.g., tire reinforcement), where DMT-based fibers exhibit superior load-bearing capacity and UV resistance compared to TPA-derived alternatives.
  • Technical Fabrics: In filtration media, conveyor belts, and protective gear, DMT-derived PET fibers provide a balance of strength, flexibility, and chemical resistance.

    • Structural Advantages
    The polymerization pathway from DMT ensures fewer impurities (e.g., metal ions from TPA synthesis), leading to fibers with:

  • Higher crystallinity (improved dimensional stability).
  • Better dye affinity (uniform coloration in textiles).
  • Longer service life in harsh environments (e.g., chemical plants, offshore rigs).

    • Key Applications of DMT-Derived Polymers and Their End-Use Industries

    DMT’s role extends beyond fibers to a broad spectrum of polymer applications, each tailored to specific industrial demands. The following table outlines major applications, their properties, and target sectors:
    ApplicationPolymer FormKey PropertiesEnd-Use Industries
    Bottles (e.g., beverage)Amorphous PET (APET)Clarity, gas barrier (O₂/CO₂), thermal resistance (up to 70°C fill temp)Beverage, food packaging, pharmaceuticals
    Films (e.g., BOPA)Biaxially Oriented PET (BOPA)High tensile strength (200–300 MPa), transparency, moisture barrierFlexible packaging, labels, electrical insulation
    Engineering PlasticsCrystalline PET (CPET)Heat resistance (up to 180°C), chemical resistance, recyclabilityAutomotive parts (e.g., headlamp housings), electronics, medical devices
    Fibers (Textiles/Ropes)High-Tenacity PETAbrasion resistance, UV stability, low shrinkageApparel, industrial textiles, composites (e.g., carbon fiber reinforcement)
    3D Printing FilamentsPETG (PET-glycol modified)Impact resistance, ease of processing, biodegradability (partial)Prototyping, consumer goods, medical implants
    Case Studies
  • Beverage Bottles: DMT-derived APET bottles dominate the market due to their ability to maintain carbonation and protect contents from UV degradation. For example, Coca-Cola’s global PET bottle production relies on DMT-based PET, with recycling rates exceeding 50% in regions with advanced waste management (e.g., EU, Japan).
  • Automotive Components: CPET from DMT is used in under-the-hood applications (e.g., BMW’s i3 interior panels) due to its heat resistance and recyclability. The material’s high modulus (3.5 GPa) reduces part weight while maintaining structural integrity.
  • Medical Devices: Sterilizable PET trays and surgical sutures leverage DMT-derived polymers for their biocompatibility and resistance to gamma irradiation.

    • Biodegradability and Recyclability of DMT-Based Polymers

    While DMT-derived PET offers exceptional mechanical and thermal properties, its environmental impact—particularly regarding biodegradability and recyclability—remains a critical consideration. PET is inherently non-biodegradable under natural conditions but can be recycled mechanically or chemically into virgin-like material. The following factors influence its sustainability profile:

    Advantages in Recyclability

  • Mechanical Recycling: DMT-derived PET is widely recycled into fibers (e.g., carpets, clothing) or new bottles. The Global Recycling Standard (GRS) certifies recycled PET (rPET) for textiles, with brands like Patagonia and Adidas incorporating up to 100% rPET in products.
  • Chemical Recycling: Processes such as glycolysis or methanolysis depolymerize PET back to DMT or EG, enabling closed-loop production. For example, Eastman Chemical’s Molecular Recycling™ technology converts post-consumer PET into virgin-grade DMT, reducing reliance on fossil fuels.
  • Intrinsic Properties: PET’s high molecular uniformity (from DMT polymerization) enhances recyclability compared to TPA-derived PET, which may contain residual metal catalysts affecting quality.

    • Limitations and Challenges

  • Downcycling: Mechanical recycling often reduces polymer quality, limiting reuse cycles. For instance, rPET used in bottles may only be suitable for non-food applications after 2–3 cycles.
  • Biodegradation Resistance: PET’s aromatic structure resists microbial breakdown. However, oxidative degradation (e.g., via UV exposure or pro-oxidant additives) can fragment PET into microplastics, posing environmental risks.
  • Energy Intensity: DMT production (from p-xylene) and PET polymerization require significant energy. Life Cycle Assessments (LCAs) show that rPET can reduce carbon footprint by 50–70%

    • Safety, Handling, and Regulatory Considerations for Dimethyl Terephthalate (DMT)

    Dimethyl terephthalate (DMT) is a versatile intermediate in polymer production but poses significant occupational and environmental risks due to its chemical reactivity, potential toxicity, and flammability. Proper handling, storage, and disposal protocols are critical to mitigate hazards associated with inhalation, dermal exposure, and accidental release. Regulatory frameworks such as REACH (EU) and OSHA (US) classify DMT under strict hazard codes, mandating compliance with safety data sheets (SDS) and waste management guidelines. This section examines health risks, regulatory classifications, protective measures, and disposal methodologies, alongside comparative toxicity profiles with related compounds.

    Health Hazards and Exposure Risks

    DMT exposure primarily occurs in industrial settings during synthesis, handling, or processing, with inhalation and skin contact representing the most critical pathways. Inhalation of DMT dust or vapors may cause respiratory irritation, coughing, and, in high concentrations, pulmonary edema or chemical pneumonitis. Dermal contact can lead to mild to moderate skin irritation, redness, or allergic reactions, particularly in sensitized individuals. Ingestion is less common but poses severe systemic risks, including gastrointestinal distress and potential organ toxicity.

    The acute toxicity of DMT is moderate, with an oral LD₅₀ in rats exceeding 2,000 mg/kg, while inhalation LC₅₀ values (for dust/mist) are typically above 5 mg/L. Chronic exposure may contribute to hepatic or renal strain, though epidemiological data remains limited due to controlled industrial use. Sensitization risks are notable for workers handling DMT over prolonged periods, necessitating regular health monitoring.

    Key Exposure Limits:
  • OSHA PEL (US): 5 mg/m³ (total dust), 1 mg/m³ (respirable fraction).
  • ACGIH TLV (US/Global): 5 mg/m³ (as TWA), with a skin notation indicating dermal absorption.
  • EU OEL (REACH): 5 mg/m³ (8-hour TWA), classified as a Category 2 respiratory irritant.

    • Safety Data Sheets (SDS) and Personal Protective Equipment (PPE)

    SDS for DMT (e.g., from suppliers like Eastman Chemical or DuPont) categorize it under GHS (Globally Harmonized System) with the following hazard statements:
  • H302: Harmful if swallowed.
  • H315: Causes skin irritation.
  • H319: Causes serious eye irritation.
  • H335: May cause respiratory irritation.
  • H226: Flammable liquid and vapor (for molten or vaporized DMT).

    • PPE Requirements for handling DMT include:

  • Respiratory Protection: NIOSH-approved respirators with organic vapor cartridges (e.g., 3M 6000 series) for concentrations exceeding PELs.
  • Eye Protection: Chemical goggles with side shields (ANSI Z87.1 compliant).
  • Skin Protection: Nitrile or butyl rubber gloves (minimum 6 mil thickness), with double-layering for prolonged exposure.
  • Clothing: Flame-resistant (FR) coveralls and splash suits for powder or liquid handling.

    • Hygiene Measures:

  • Shower facilities must be immediately accessible for decontamination.
  • Eyewash stations should be positioned within 10 seconds of exposure zones.
  • Ventilation: Local exhaust systems (LES) with 100–200 ft³/min air flow for dust collection.

    • Regulatory Classifications and Storage Requirements

    DMT is subject to stringent regulatory oversight in major jurisdictions:
    Regulatory BodyClassificationHazard CodesStorage Requirements
    REACH (EU)Category 2 Irritant (Skin/Eyes)H315, H319, H335Store in airtight, corrosion-resistant drums (HDPE or stainless steel).
    Flammable Liquid (Category 3)H226Keep in cool, dry, ventilated areas (below 30°C).
    Sensitizing (Category 1, Skin)H317No food/drink storage in handling areas; label with "Danger" and hazard pictograms.
    OSHA (US)Hazardous Chemical (29 CFR 1910.1200)Flammable (1910.106), Irritant (1910.1200)NFPA 704 Rating: Health 2, Flammability 2, Reactivity 1.
    WHMIS (Canada)Class D-2B (Irritant)B2 (Other Toxic Effects)UN Number: 2210 (for solid DMT); Packing Group III.
    ADR/GHS (Global)Class 3 (Flammable Liquid)UN 2210Segregation: Keep away from oxidizers, acids, and strong bases.
    Storage Best Practices:
  • Temperature Control: Maintain between 15–25°C to prevent crystallization or thermal decomposition.
  • Compatibility: Avoid contact with strong acids (e.g., H₂SO₄), bases (e.g., NaOH), or peroxides.
  • Quantities: Limit bulk storage to <1,000 kg unless in approved flame-proof warehouses.
  • Emergency Inventory: Maintain spill kits (neutralizing agents like sodium bicarbonate for acidic spills).

    • Disposal Methods and Waste Management Compliance

    DMT waste must be managed as hazardous waste under:
  • EU: Waste Code 20 03 99 (other chemical waste).
  • US (RCRA): D001 (ignitable) and D002 (corrosive, if contaminated).
  • Japan (PRTR): Category 1 (high-risk chemical).

    • Disposal Procedures:
    1. Neutralization of Acidic Byproducts:

  • React spent DMT solutions with calcium hydroxide (Ca(OH)₂) or sodium carbonate (Na₂CO₃) to raise pH to 6–8.
  • Example reaction:
    • DMT Hydrolysis Byproduct (Methanol + Terephthalic Acid) →
    Ca(OH)₂ + 2 HOOC-C₆H₄-COOH → Ca(Terephthalate)₂ (insoluble) + H₂O 2. Incineration:
  • Primary Method: High-temperature incineration (≥1,200°C) with 99.9% destruction efficiency for organic content.
  • Secondary Treatment: Scrubber systems to neutralize CO₂, HCl, or NOₓ emissions.
    • 3. Landfill Disposal (Last Resort):
  • Requires stabilization/solidification (e.g., cement encapsulation) to meet TCLP (Toxicity Characteristic Leaching Procedure) limits.
  • EU Landfill Directive (1999/31/EC): Prohibits untreated DMT waste in municipal landfills.

    • Compliance Documentation:

  • EU: Submit Waste Transfer Note (WTN) under REACH Annex VIII.
  • US: File Manifest (EPA Form 8700-22) for off-site disposal.
  • Japan: Register with PRTR System if quantities exceed 1 ton/year.
    • The following table compares DMT’s toxicity with dimethyl adipate (DMA) and terephthalic acid (TPA), highlighting key differences in handling and regulatory treatment:
    Toxicity and Regulatory Comparison
    Parameter Dimethyl Terephthalate (DMT) Dimethyl Adipate (DMA) Terephthalic Acid (TPA)
    Primary Routes of Exposure Inhalation (dust/vapor), dermal contact

    what is dimethyl terephthalate - Ilustrasi 3

    Analytical Techniques for Characterization of Dimethyl Terephthalate (DMT)

    Dimethyl terephthalate (DMT) requires rigorous analytical characterization to ensure purity, structural integrity, and compliance with industrial standards. Spectroscopic, chromatographic, and thermal methods provide complementary insights into molecular composition, thermal stability, and degradation pathways. These techniques enable differentiation between DMT and potential impurities, such as mono-methyl terephthalate (MMT) or residual solvents, while also confirming batch consistency for polymer-grade applications.

    Spectroscopic Analysis for Structural Confirmation and Purity Assessment

    Spectroscopic techniques are fundamental for verifying DMT’s molecular structure and detecting impurities through characteristic spectral signatures. Nuclear Magnetic Resonance (NMR) spectroscopy, particularly ^1H and ^13C NMR, provides detailed information on proton and carbon environments, respectively. In ^1H NMR spectra, DMT exhibits distinct signals at δ 3.9 ppm (singlet, OCH₃ protons) and δ 8.1 ppm (aromatic protons), with integration ratios confirming stoichiometry. ^13C NMR spectra show peaks at δ 52.5 ppm (methoxy carbons) and δ 134–167 ppm (aromatic carbons), where shifts outside expected ranges indicate substitution or impurities.

    Infrared (IR) spectroscopy further validates DMT’s structure by identifying functional groups. Key absorption bands include:

  • 1725 cm⁻¹ (C=O stretch of ester groups),
  • 1260–1100 cm⁻¹ (C–O stretch of methoxy and ester linkages),
  • 1610–1500 cm⁻¹ (aromatic C=C stretches),
  • 740–690 cm⁻¹ (out-of-plane aromatic C–H bending).

    • Impurities such as terephthalic acid (TPA) or dimethyl isophthalate (DMIP) introduce additional bands (e.g., broader O–H stretch at ~3000 cm⁻¹ for TPA), enabling qualitative differentiation.

    Chromatographic Separation and Quantification of DMT in Mixtures

    Gas chromatography (GC) and high-performance liquid chromatography (HPLC) are essential for quantifying DMT in complex matrices, such as reaction mixtures or polymer precursors. GC is preferred for volatile components, while HPLC is suitable for thermal-sensitive or high-molecular-weight impurities.

    Gas Chromatography (GC) Procedure for DMT Analysis
    GC analysis of DMT typically employs a non-polar capillary column (e.g., DB-5, 30 m × 0.25 mm × 0.25 µm) with flame ionization detection (FID). Sample preparation involves dissolving DMT in a volatile solvent (e.g., dichloromethane or acetone) and injecting 1 µL of a diluted solution (1–5 mg/mL). The temperature program for separation includes:

  • Initial oven temperature: 100°C (held for 2 min),
  • Ramp to 250°C at 10°C/min,
  • Final hold at 250°C for 5 min.

    • Under these conditions, DMT elutes with a retention time of ~7.5–8.5 minutes, depending on column specifications. Calibration curves using DMT standards (0.1–10 mg/mL) establish linearity (R² > 0.999), with detection limits as low as 0.05% w/w. Impurities like MMT or dimethyl phthalate (DMP) exhibit shorter retention times (~5–6 min), facilitating their identification.

    High-Performance Liquid Chromatography (HPLC) for Non-Volatile Impurities
    HPLC with a C18 reversed-phase column (250 mm × 4.6 mm, 5 µm) and UV detection at 254 nm is used for analyzing DMT in non-volatile matrices. The mobile phase consists of acetonitrile:water (70:30 v/v) at a flow rate of 1 mL/min. DMT elutes at ~6.0–7.0 minutes, while TPA and DMIP appear at ~3.5 min and ~5.5 min, respectively. Gradient elution (e.g., increasing acetonitrile from 50% to 100% over 15 min) improves separation of polar impurities.

    Thermal Analysis of DMT: Phase Transitions and Degradation Pathways

    Thermal techniques such as Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) characterize DMT’s melting behavior, crystallization kinetics, and thermal stability. These methods are critical for optimizing polymerization conditions and assessing long-term storage stability.

    Differential Scanning Calorimetry (DSC)
    DSC analysis of DMT (5–10 mg samples) under nitrogen purge (50 mL/min) reveals:

  • Melting point (Tₘ): 140–142°C (sharp endothermic peak),
  • Crystallization temperature (T꜀): 120–125°C (exothermic peak upon cooling),
  • Heat of fusion (ΔH): ~120 J/g (indicative of crystalline purity).

    • Repeated heating-cooling cycles assess thermal history effects, while non-isothermal methods (10°C/min) quantify kinetic parameters for crystallization. Impurities like TPA or solvents lower the melting point and broaden the peak, reflecting eutectic formation.

    Thermogravimetric Analysis (TGA)
    TGA under inert (N₂) or oxidative (air) atmospheres evaluates DMT’s thermal degradation. Under N₂, DMT exhibits ~98% mass retention up to 350°C, with onset degradation at ~380°C (primary decomposition to terephthalaldehyde and methanol). In air, oxidative degradation begins at ~300°C, producing CO₂ and CO. Sample preparation involves heating 5–10 mg of ground DMT at 10°C/min to 600°C, with derivative thermogravimetric (DTG) curves identifying distinct decomposition stages.

    Mass Spectrometry for Impurity Differentiation via Fragmentation Patterns

    Mass spectrometry (MS), particularly Electron Ionization (EI-MS) or Chemical Ionization (CI-MS), differentiates DMT from impurities by analyzing molecular ions and fragmentation pathways. DMT’s molecular ion ([M]⁺) appears at m/z 194, with characteristic fragments including:
  • m/z 163 ([M–CH₃OH]⁺, loss of methoxy group),
  • m/z 135 (further fragmentation to terephthalaldehyde),
  • m/z 104 (benzyne-like structure from aromatic ring cleavage).

    • In contrast, mono-methyl terephthalate (MMT, m/z 180) lacks the second methoxy group, producing fragments at m/z 151 ([M–CH₃OH]⁺) and m/z 123. Terephthalic acid (TPA, m/z 166) shows a prominent m/z 122 peak (loss of CO₂). High-resolution MS (e.g., TOF-MS) further resolves isobaric impurities by exact mass measurements.

    Mass spectrometry uniquely identifies DMT by its m/z 194 molecular ion and diagnostic fragments at m/z 163 and 135, while impurities like MMT (m/z 180) or TPA (m/z 166) exhibit distinct fragmentation patterns. Coupling MS with GC or HPLC enables targeted impurity profiling in industrial samples.

    Dimethyl terephthalate emerges not merely as a chemical intermediate but as a linchpin in the transition toward more sustainable and high-performance materials. Its synthesis, though historically energy-intensive, now benefits from catalytic innovations and closed-loop processes that minimize environmental footprints. In polymer science, DMT’s role in PET production underscores its dual capacity to enable mass-market applications while addressing challenges in biodegradability and circular economy integration. As analytical techniques refine its characterization—from spectroscopic fingerprints to thermal degradation profiles—the future of DMT lies in its adaptability to emerging industries, where precision chemistry and eco-conscious design converge to redefine material possibilities.

    FAQ

    What industrial and chemical applications does dimethyl terephthalate serve?

    Dimethyl terephthalate (DMT) is primarily used to produce polyethylene terephthalate (PET), a polymer for plastic bottles, fibers (like polyester), and packaging. It’s also a precursor in synthetic resins, coatings, and some pharmaceutical intermediates. In textiles, DMT-derived PET is widely used for clothing, carpets, and industrial fabrics.

    What is the chemical structure of dimethyl terephthalate?

    Dimethyl terephthalate has the formula C₁₀H₁₀O₄, consisting of a benzene ring with two ester groups (–COOCH₃) at the para positions (1,4). Its IUPAC name is dimethyl benzene-1,4-dicarboxylate, and it appears as a white crystalline solid with a melting point of ~140°C.

    How does dimethyl glutarate differ from dimethyl terephthalate?

    Dimethyl glutarate is an ester with the formula C₇H₁₂O₄, derived from glutaric acid (a 5-carbon dicarboxylic acid), while dimethyl terephthalate comes from terephthalic acid (a 1,4-benzenedicarboxylic acid). Structurally, DMT has an aromatic ring; dimethyl glutarate is aliphatic and lacks aromatic properties, making their chemical behaviors and applications distinct.

    What is the difference between dimethyl terephthalate and DMT in street slang?

    In street slang, "DMT" (N,N-dimethyltryptamine) is a powerful psychedelic compound, while dimethyl terephthalate is an industrial chemical used in plastics manufacturing. They share only the "DMT" abbreviation and have no chemical or functional relationship. The two are entirely separate substances with different structures and effects.

    What is dimethyl, and how is it used in chemistry?

    "Dimethyl" refers to a functional group or substituent with two methyl groups (–CH₃) attached to a central atom or molecule (e.g., dimethyl ether, dimethyl sulfate). In chemistry, it appears in solvents (like dimethyl sulfoxide, DMSO), pharmaceuticals, and polymers. The term alone is ambiguous—context determines whether it refers to dimethylamine, dimethylacetamide, or other compounds.

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