Dimethyl terephthalate

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Dimethyl terephthalate
Structural formula of dimethyl terephthalate
Names
Preferred IUPAC name
Dimethyl terephthalate
Systematic IUPAC name
1,4-Dimethyl benzene-1,4-dicarboxylate
Other names
1,4-Benzenedicarboxylic acid dimethyl ester

Dimethyl 4-phthalate
Dimethyl-p-phthalate
Di-Me terephthalate
Methyl 4-carbomethoxybenzoate
Methyl-p-(methoxycarbonyl)benzoate
Methyl terephthalate

Terephthalic acid methyl ester
Identifiers
Abbreviations DMT
1107185
120-61-6 YesY
ChemSpider 13863300 YesY
EC number 204-411-8
Jmol-3D images Image
Image
MeSH Dimethyl+4-phthalate
PubChem 8441
12241382 (2H4)
RTECS number WZ1225000
Properties
C10H10O4
Molar mass 194.18 g·mol−1
Appearance white solid
Density 1.2 g/cm³, ?
Melting point 142 °C (288 °F; 415 K)
Boiling point 288 °C (550 °F; 561 K)
Acidity (pKa) -7.21
Basicity (pKb) -6.60
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY verify (what isYesY/N?)
Infobox references

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.[1]

Production[edit]

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.[1]

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.[2]

1) p-xylene oxidation to p-Toluic acid at 140–180 ⁰C & 500–800 kPa.

P-xylene oxidation to p-toluic acid

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:[1]

Esterification of the resulting acid with methanol

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.

Use[edit]

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.

References[edit]

  1. ^ a b c 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
  2. ^ http://www.gtctech.com/technology-licensing/polyester-technologies/dimethyl-terephthalate-technology/

External links[edit]