|Preferred IUPAC name
|Systematic IUPAC name
1,4-Benzenedicarboxylic acid dimethyl ester
|Molar mass||194.18 g·mol−1|
|Density||1.2 g/cm³, ?|
|Melting point||142 °C (288 °F; 415 K)|
|Boiling point||288 °C (550 °F; 561 K)|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Dimethyl terephthalate (DMT) is an organic compound with the formula C6H4(CO2CH3)2. It is the diester formed from terephthalic acid and methanol. It is a white solid that melts to give a distillable colourless liquid.
Dimethyl terephthalate (DMT) has been produced in a number of ways. Conventionally and still of commercial value is the direct esterification of terephthalic acid. Alternatively, it can be prepared by alternating oxidation and methyl-esterification steps from p-xylene via methylp-toluate.
Dimethyl Terephthalate (DMT) (Witten Process)
The common method for the production of DMT from para-xylene (PX) and methanol consists of four major steps: oxidation, esterification, distillation, and crystallization. A mixture of p-xylene (PX) and p-Toluic ester (PT) is oxidized with air in the presence of a heavy metal catalyst (Co/Mn). The acid mixture resulting from the oxidation is esterified with methanol (MeOH, CH3OH) to produce a mixture of esters. The crude ester mixture is distilled to remove all the heavy boilers and residue produced; the lighter esters are recycled to the oxidation section. The raw DMT is then sent to the crystallization section to remove DMT isomers, residual acids and aromatic aldehydes.
1) p-xylene oxidation to p-Toluic acid at 140–180 ⁰C & 500–800 kPa.
2) Esterification of the resulting acid with methanol results in Methyl p-toluate at 250⁰C and 2500 kPa and subsequent oxidation and esterification of Methyl p-toluate yields Dimethyl terephthalate (DMT) as shown in the below reaction:
Dimethyl Terephthalate (DMT) production through Direct Esterification
If highly impure Terephthalic acid is available, DMT can be made in a separate process by esterification with methanol to dimethyl terephthalate which is then purified by distillation:
- C8H6O4 (TPA) + 2CH3OH (Methanol) → C10H10O4 (DMT) + 2 H2O
at presence of o-xylene at 250–300 ⁰C.
DMT is used in the production of polyesters, including polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), and polybutylene terephthalate (PBT). It consists of benzene substituted with carboxymethyl groups (CO2CH3) at the 1 and 4 positions. Because DMT is volatile, it is an intermediate in some schemes for the recycling of PET, e.g. from plastic bottles.
Hydrogenation of DMT affords the diol cyclohexanedimethanol, which is a useful monomer.
- Richard J. Sheehan "Terephthalic Acid, Dimethyl Terephthalate, and Isophthalic Acid" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.doi:10.1002/14356007.a26_193
- Supplier:Teijin Limited http://www.teijin.com/products/chemicals/dmt/
- International Chemical Safety Card 0262
- U.S. National Library of Medicine: Hazardous Substances Databank – Dimethyl+terephthalate
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