Dimethyl terephthalate

Names
Preferred IUPAC name Dimethyl benzene-1,4-dicarboxylate
Other names Dimethyl terephthalate 1,4-Benzenedicarboxylic acid dimethyl ester Dimethyl 4-phthalate Dimethyl p-phthalate Di-Me terephthalate Methyl 4-carbomethoxybenzoate Methyl-p-(methoxycarbonyl)benzoate Methyl terephthalate, di- Terephthalic acid dimethyl ester (2:1)
Identifiers
CAS Number	120-61-6 Y
3D model (JSmol)	Interactive image Interactive image
Abbreviations	DMT
Beilstein Reference	1107185
ChEBI	CHEBI:156286
ChemSpider	13863300 Y
ECHA InfoCard	100.004.011
EC Number	204-411-8
MeSH	Dimethyl+4-phthalate
PubChem CID	8441 12241382 (2H4)
RTECS number	WZ1225000
UNII	IKZ2470UNV Y
CompTox Dashboard (EPA)	DTXSID0020498
InChI InChI=1S/C10H10O4/c1-13-9(11)7-3-5-8(6-4-7)10(12)14-2/h3-6H,1-2H3 Y Key: WOZVHXUHUFLZGK-UHFFFAOYSA-N Y InChI=1/C10H10O4/c1-13-9(11)7-3-5-8(6-4-7)10(12)14-2/h3-6H,1-2H3 Key: WOZVHXUHUFLZGK-UHFFFAOYSA-N
SMILES COC(=O)C1=CC=C(C=C1)C(=O)OC O=C(OC)c1ccc(cc1)C(=O)OC
Properties
Chemical formula	C10H10O4
Molar mass	194.186 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 otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Dimethyl terephthalate (DMT) is an organic compound with the formula C₆H₄(COOCH₃)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

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 methyl p-toluate (PT).^[1]

Dimethyl terephthalate by the Witten process

The method for the production of DMT from p-xylene (PX) and methanol consists of a multistep process involving both oxidation and esterification. A mixture of p-xylene (PX) and methyl p-toluate is oxidized with air in the presence of cobalt and manganese catalysts. The acid mixture resulting from the oxidation is esterified with methanol to produce a mixture of esters. The crude ester mixture is then distilled to remove all the heavy boilers and residue that are produced; lighter esters such as monomethyl terephthalate 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]

Oxidation of methyl p-toluate followed by esterification also yields dimethyl terephthalate (DMT) as shown in the below reaction:^[1]

Dimethyl terephthalate by direct esterification

DMT can also be made by a different route, namely direct esterification of terephthalic acid with methanol. The dimethyl terephthalate that is formed is then purified by distillation. Even terephthalic acid of low purity may be used in this method.

C₈H₆O₄ + 2CH₃OH → C₁₀H₁₀O₄ + 2 H₂O

in the presence of o-xylene at 250–300 °C.

Uses

DMT is used in the production of polyesters, including polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), and polybutylene terephthalate (PBT). Structurally, DMT consists of a benzene ring substituted at the 1 and 4 positions with methyl carboxylate (-CO₂CH₃) groups. 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.