Dimethyl terephthalate

Description

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.

Chemical Properties

The empirical formula of dimethyl terephthalate (DMT) is C10H10O4. Its structural formula is 1,4-(COOCH3)2C6H4. At room temperature, exists as colorless crystals. DMT is soluble in ether and chloroform, slightly soluble in ethanol, and fairly insoluble in water (<1 g/L at 13℃).

Uses

Dimethyl terephthalate is used widely as an industrial intermediate to manufacture polyethylene terephthalate (PET) and dioctyl terephthalate (OECD, 2001).It is used in the Polyester Film (Audio/Video Tape,X-ray Film,Photo Film), Polyester Fiber, Pet Bottle, Polyester Adhesive, Engineering Plastics. DMT is volatile, it is an intermediate in some schemes for the recycling of PET.

Uses

Dimethyl terephthalate is used in the production of polyesters, including polyethylene terephthalate (PET) and poly trimethylene terephthalate. It consists of benzene substituted with carboxy methyl groups (CO₂CH₃) at the 1 and 4 positions. Because DMT is volatile, it is an intermediate in some schemes for the recyclic of PET, e.g. from plastic bottles.
Hydrogenation of DMT affords the diol cyclohexanedimethanol, which is a useful monomer.

Application

Dimethyl terephthalate undergoes enzymatic polycondensation with 1,8-diaminooctane to yield oligo(octamethylene terephthalamide).
Dimethyl terephthalate was used to synthesize silicone aromatic polyesters by the transesterification reaction with α,ω-bis(hydroxyalkyl)-terminated poly(dimethylsiloxane) in toluene. It was used in the synthesis of multiblock copolymers consisting of polyiso-butylene, dimethyl terephthalate and 1,4-butanediol.

Preparation

Several processes have been developed for the preparation of dimethyl terephthalate from p-xylene, but the most important proceeds as follows:

The oxidation steps are carried out in the liquid phase at about 170??C and 1.5 MPa (15 atmospheres) in the presence of a cobalt acetate or naphthenate catalyst whilst the esterifications are conducted at about 150??C. Dimethyl terephthalate may also be produced by esterification of terephthalic acid.

Production Methods

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.

Definition

ChEBI: Dimethyl terephthalate is a diester resulting from the formal condensation of the carboxy groups of terephthalic acid with methanol. It is a primary ingredient widely used in the manufacture of polyesters and industrial plastics. It is a methyl ester, a diester and a phthalate ester. It derives from a terephthalic acid.

Synthesis Reference(s)

Chemistry Letters, 15, p. 851, 1986
Journal of the American Chemical Society, 111, p. 8742, 1989 DOI: 10.1021/ja00205a039
Tetrahedron Letters, 17, p. 3299, 1976

General Description

Dimethyl terephthalate appears as white solid or heated colorless liquid. Has no odor. Liquid solidifies in cool water. Solid and liquid sink in water. (USCG, 1999)

Air & Water Reactions

When mixed with air, the vapor or dust forms very hazardous and highly reactive mixtures. . Insoluble in water.

Reactivity Profile

DIMETHYL TEREPHTHALATE is an ester. Esters react with acids to liberate heat along with alcohols and acids. Strong oxidizing acids may cause a vigorous reaction that is sufficiently exothermic to ignite the reaction products. Heat is also generated by the interaction of esters with caustic solutions. Flammable hydrogen is generated by mixing esters with alkali metals and hydrides. Can generate electrostatic charges. [Handling Chemicals Safely 1980. p. 250]. DIMETHYL TEREPHTHALATE is sensitive to heat. The molten material reacts with water due to the temperature. DIMETHYL TEREPHTHALATE is incompatible with strong oxidizers, strong acids and strong bases.

Hazard

H317 (56.25%): May cause an allergic skin reaction [Warning Sensitization, Skin]
H319 (14.06%): Causes serious eye irritation [Warning Serious eye damage/eye irritation]
H412 (29.69%): Harmful to aquatic life with long lasting effects [Hazardous to the aquatic environment, long-term hazard]

Health Hazard

Molten DMT will cause severe burns of skin on contact.

Fire Hazard

DIMETHYL TEREPHTHALATE is combustible.

Safety Profile

Moderately toxic by intraperitoneal route. Mdly toxic by ingestion. An eye irritant. Mutation data reported. When heated to decomposition it emits acrid smoke and irritating fumes

Potential Exposure

Tumorigen,Mutagen. Primary Irritant. Essentially all DMT is consumedin the production of polyethylene terephthalate, the polymerfor polyester fibers and polyester films. Less than 2% ofproduction is used to make polybutylene terephthalateresins and other specialty products

First aid

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medical attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit.

Carcinogenicity

In a study conducted by the NCI, DMT was not considered to be carcinogenic in rats or mice ingesting 2500 or 5000 ppm in the diet for 103 weeks.

Source

Dimethyl terephthalate is a natural product found in Hypotrachyna nepalensis, Uncaria elliptica, and other organisms with data available.

storage

Color Code—Blue: Health Hazard/Poison: Storein a secure poison location. Prior to working with DMT youshould be trained on its proper handling and storage. Storein tightly closed containers in a cool, well-ventilated areaaway from oxidizers, nitrates, acids,Wear protective gloves andclothing to prevent any reasonable probability of skin contact. Safety equipment suppliers/manufacturers can providerecommendations on the most protective glove/clothingmaterial for your operation. All protective clothing (suits,gloves, footwear, headgear) should be clean, available eachday, and put on before work. Contact lenses should not beworn when working with this chemical. Wear dust-proofchemical goggles and face shield unless full face-piecerespiratory protection is worn. Employees should washimmediately with soap when skin is wet or contaminated.Provide emergency showers and eyewash. and sources of ignition.A regulated, marked area should be established where thischemical is handled, used, or stored in compliance withOSHA Standard 1910.1045.

Shipping

Wear protective gloves andclothing to prevent any reasonable probability of skin contact. Safety equipment suppliers/manufacturers can providerecommendations on the most protective glove/clothingmaterial for your operation. All protective clothing (suits,gloves, footwear, headgear) should be clean, available eachday, and put on before work. Contact lenses should not beworn when working with this chemical. Wear dust-proofchemical goggles and face shield unless full face-piecerespiratory protection is worn. Employees should washimmediately with soap when skin is wet or contaminated.Provide emergency showers and eyewash.

Purification Methods

Purify it by recrystallisation from aqueous EtOH, MeOH or CCl4; or by zone melting. [Beilstein 6 H 843, 6 III 4250, 6 IV 3303.] .

Incompatibilities

Incompatible with strong acids, nitrates,strong oxidizers.