Dimethyl terephthalate

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; Terephthalic acid methyl ester
Identifiers
CAS Number	120-61-6 ;
3D model (JSmol)	Interactive image; Interactive image;
Abbreviations	DMT
Beilstein Reference	1107185
ChEBI	CHEBI:156286;
ChemSpider	13863300 ;
ECHA InfoCard	100.004.011
EC Number	204-411-8;
MeSH	Dimethyl+4-phthalate
PubChem CID	8441; 12241382 (2H4);
RTECS number	WZ1225000;
UNII	IKZ2470UNV ;
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 Key: WOZVHXUHUFLZGK-UHFFFAOYSA-N ; 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). verify (what is ?) 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 (DMT) (Witten Process)

The common 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 a 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 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]

Oxidation of methyl p-toluate followed by esterification also 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 + 2CH₃OH → C₁₀H₁₀O₄ + 2 H₂O

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

Use

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

^ ^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
^ "Dimethyl Terephthalate (DMT)". 2013-05-02.

External links

[Ullmann-1] 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] "Dimethyl Terephthalate (DMT)". 2013-05-02.

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