Dimethyl terephthalate
Dimethyl terephthalate is an organic compound with the formula. It is the diester formed from terephthalic acid and methanol. It is a white solid that melts to give a distillable colourless liquid. it is an intermediate in some schemes for the recycling of PET, e.g. from plastic bottles.
Production
Dimethyl terephthalate can be prepared via a direct esterification of terephthalic acid with methanol:On a commercial scale, this reaction is usually done at using o-xylene as a solvent. The dimethyl terephthalate that is formed is then purified by distillation. Even terephthalic acid of low purity may be used in this method.
Alternatively, it can be prepared from para-xylene by alternating oxidation and methyl-esterification steps via methyl para-toluate.
Uses
DMT is used in the production of polyesters, including polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate. These polymers are produced by transesterification with a diol. In the production of PET, the transesterification initially produces 2-hydroxyethyl methyl terephthalate.Hydrogenation of DMT affords the diol cyclohexanedimethanol, which is a useful monomer.