Dimethyl terephthalate transesterification

Polyester Polyols. Initially polyester polyols were the preferred raw materials for polyurethanes, but in the 1990s the less expensive polyether polyols dominate the polyurethane market. Inexpensive aromatic polyester polyols have been introduced for rigid foam appHcations. These are obtained from residues of terephthaHc acid production or by transesterification of dimethyl terephthalate (DMT) or poly(ethylene terephthalate) (PET) scrap with glycols. 

PBT is produced by the transesterification of dimethyl terephthalate with 1,4-butanediol by means of a catalyzed melt polycondensation (19). PBT is also semicrystalline and is an extremely tough resin. Several commercial resins use a blend of PBT with another resin, such as PET, polycarbonate, or nylon. Typically, composites of PBT contain 20—30 vol % fiber glass. 

Low molecular weight PET and PBT resins are made by melt processes. For higher molecular weight resins, both melt processes or soHd-state polymerization are used. Although terephthaHc acid can be directly esterified, the most common process involves transesterification of dimethyl terephthalate with ethylene glycol or 1,4-butanediol in the presence of trace amounts of metal ion catalysts (67,68). 

On the basis of bulk production (10), poly(ethylene terephthalate) manufacture is the most important ester producing process. This polymer is produced by either the direct esterification of terephthaHc acid and ethylene glycol, or by the transesterification of dimethyl terephthalate with ethylene glycol. In 1990, poly(ethylene terephthalate) manufacture exceeded 3.47 x 10 t/yr (see Polyesters). Dimethyl terephthalate is produced by the direct esterification of terephthaHc acid and methanol. 

PET is the polyester of terephthalic acid and ethylene glycol. Polyesters are prepared by either direct esterification or transesterification reactions. In the direct esterification process, terephthalic acid is reacted with ethylene glycol to produce PET and water as a by-product. Transesterification involves the reaction of dimethyl terephthalate (DMT) with ethylene glycol in the presence of a catalyst (usually a metal carboxylate) to form bis(hydroxyethyl)terephthalate (BHET) and methyl alcohol as a by-product. In the second step of transesterification, BHET... 

These materials are segmented copolyether esters formed by the melt transesterification of dimethyl terephthalate, poly(tetramethylene ether) glycol and 1,4-butane diol. As with the thermoplastic polyurethanes, one can describe a hard segment and a soft segment, the hard segments forming crystalline areas which act as pseudocrosslinks . 

Fig. 1. Biodegradation of dimethyl terephthalate (DMT) by Pasteurella multocida Sa in the presence of ethanol. Ester hydrolysis of DMT involves a transesterification of mono-methyl terephthalate (MMT), and the formation of monoethyl terephthalate (MET).

Transesterification is a crucial step in several industrial processes such as (i) production of higher acrylates from methylmethacrylate (for applications in resins and paints), (ii) polyethene terephthalate (PET) production from dimethyl terephthalate (DMT) and ethene glycol (in polyester manufacturing),... 

The formation of prepolymer can also be achieved by transesterification of dimethyl terephthalate (DMT) with EG, releasing the by-product methanol. High-purity DMT is easily obtained by distillation and in the early years of PET production, all processes were based on this feedstock. During the late 1960s, highly purified TPA was produced for the first time on an industrial scale by re-crystallization. Since then, more and more processes have shifted to TPA as the feedstock and today more than 70 % of global PET production is based on TPA. The TPA-based PET production saves approximately 8 % of total capital investment and 15% of feedstock cost (Figure 2.1). 

PBT is made by reacting 1,4-butanediol (BDO) with terephthalic acid (TPA) or dimethyl terephthalate (DMT) in the presence of a transesterification catalyst. A number of different commercial routes are used for producing the monomers, as discussed below. 

PTT is melt polymerized by either the transesterification of PDO with dimethyl terephthalate (DMT) or by the direct esterification of PDO with purified tereph-thalic acid (PTA). The process is similar to that for PET but with major differences, as follows ... 

BHET formation is conducted at temperatures of 200 to 250 °C to achieve reasonable reaction rates. The activation energies of the two reactions are of the order of 25 000-30 000 cal/mol [4, 5], The BHET formation is usually conducted under pressure to keep the ethylene glycol in the liquid state. Terephthalic acid is slurried with ethylene glycol for the esterification reaction. Dimethyl terephthalate is dissolved in ethylene glycol and BHET for a liquid-phase transesterification reaction. The synthesis of BHET is driven to this material by the removal of water or methanol. The reactions are reversible at reasonable rates if the concentrations of water or methanol reactants are held high. 

In the case of the esterification of the diacid, the reaction is self-catalyzed as the terephthalic acid acts as its own acid catalyst. The reverse reaction, the formation of TPA and EG from BHET is catalytic with regard to the usual metal oxides used to make PET, but is enhanced by either the presence of hydroxyl groups or protons. In the case of transesterification of dimethyl terephthalate with ethylene glycol, the reaction is catalytic, with a metal oxide needed to bring the reaction rate to commercial potential. The catalysts used to produce BHET are the same as those needed to depolymerize both the polymer to BHET and BHET to its simpler esters. Typically, titanium, manganese and zinc oxides are used for catalysts. 

Methyl benzoate, [93-58-3], CTfCOOCI Ig, bp, 198—200°C at 101.3 kPa d [ , 1.094 n], 1.5205. Insoluble in water, this is a colorless, transparent liquid solidifying at about 15°C. Methyl benzoate is prepared by the direct esterification of benzoic acid and methanol. It is used in the fragrance industry and in the production of other benzoate esters (via transesterification). A technical-grade methyl benzoate is available as a by-product in the manufacture of dimethyl terephthalate [120-61 -6]. 

Polycondensation Reaction. Transesterification was carried out in the conventional manner (4) with 97 grams (0.50 mole) of dimethyl terephthalate (DMT) and 69 grams (1.10 moles) of ethylene glycol in the presence of 0.088 gram of Ca(OAc)2 H20 and 0.044 gram of Sb203 at 160°-230°C. After completing the transesterification, 0.080... 

On 5-10 000 ton pilot-plant level, chemical and now also biological 1,3-PPD have been incorporated into PPT fibers. The fiber product, Sorona , is synthesized in a continuous process via transesterification from dimethyl terephthalate ( T ) and 1,3-propanediol ( 3-G ) with the help of a catalyst to the polymer ( 3-GT ), finished under vacuum, and pelletized. Figure 20.12 summarizes the process. 

Dimethyl terephthalate was transesterified with ethylene glycol in the presence of the modifiers taken at different concentrations. The alcohol distillate (Table 1) obtained from conducting the process with diethyl phosphite as modifier revealed the increased presence of water, acetaldehyde and acetal as compared with the alcohol distillate from the transesterification of dimethyl terephthalate with ethylene glycol -.1,2). These observations were in support of the conclusion that diethyl phosphite is unsuitable as a modifier for polyethyleneterephthalate. 

The studies carried out on the alcohol distillate obtained from the co-transesterification of dimethyl terephthalate with ethylene glycol in the presence of the sodium salt of diethyl phosphite or the di-sodium salt of 1,2-dicarbomethoxyethylphosphonic acid in various concentrations showed (Table I) that the side reactions were markedly suppressed. 

The concept of transesterifications was used for polymerization reactions by Hedrick and colleagues [76]. Various biodegradable polyesters were synthesized with the l,3-dimethylimidazol-2-ylidene carbene in THF at 25 °C. Polymers such as poly(e-caprolactone) were obtained with no need of organometallic catalysts, as in classical methods. Poly(ethylene terephthalate) (PET) 97 was synthesized in the ionic liquid 98, which functions as the reaction medium and, at the same time, as a precatalyst that is activated (99) with KOt-Bu. Dimethyl terephthalate (DMT) 100 was condensed with an excess of ethylene glycol 101 to generate 102. The melt condensation of 102 was performed under vacuum using a heating ramp to 280 °C. 

Polyesterification. High molecular weight linear polyester resins, such as poly(ethylene terephthalate) (PET), poly(propylene terephthalate) (PPT), and poly(butylene terephthalate) (PBT), can be produced by either transesterification of dimethyl terephthalate (DMT) with an excess of the corresponding diol or by direct esterification of terephthalic acid (TPA). Tetraalkyl titanates, such as TYZOR TPT or —TYZOR TBT, have been found to be excellent catalysts for either of these reactions. However, in the case of PET, the residual titanate catalyst reacts with trace quantities of aldehydic impurities produced in the polymerization process to generate a yellow discoloration of the polymer (468,469). In the case of PPT and PBT, where the color of polymer is not as critical, organic titanates are the catalyst of choice because of their greater reactivity than antimony or tin (470). Numerous processing variations have been described in the literature to minimize formation of tetrahydrofuran in the PBT process (471—472). 

As far as quantitative chemical derivatization GC analysis is concerned, it is necessary to mention especially the work of Gehrke and his collaborators, who specified the fundamental concepts of quantitative GC analysis combined with the chemical derivatization of sample compounds and applied them to the accurate determination of the twenty natural protein amino acids and other non-protein amino acids as their N-TFA-n-butyl esters [5 ], the urinary excretion level of methylated nucleic acid bases as their TMS derivatives [6], TMS nucleosides [7] and other investigations. Further examples include a computer program for processing the quantitative GC data obtained for seventeen triglyceride fatty acids after their transesterification by 2 NKOH in n-butanol [8], a study of the kinetics of the transesterification reactions of dimethyl terephthalate with ethylene glycol [9] and the GC-MS determination of chlorophenols in spent bleach liquors after isolation of the chlorophenols by a multi-step extraction, purification of the final extract by HPLC and derivatization with diazoethane [10]. 

Synthesis of the 2G-based copolymer can be somewhat more difficult than synthesis of the analogous 4G-based copolymer. If the ethylene glycol and dimethyl terephthalate monomers are prereacted to form bis (2-hydroxy ethyl) terephthalate, and this product is then copolymerized with poly(tetramethylene ether) glycol to form the block copolymer using tetrabutyl titanate as the transesterification catalyst, the reaction proceeds readily and copolymer of high inherent viscosity is easily obtained. If the ethylene glycol monomer is not prereacted and tetrabutyl titanate is again used as the transesterification catalyst, the copolymerization proceeds more slowly and a block copolymer of lower inherent viscosity is usually obtained. 

All these plastics are essentially the same compound, composed of terephthalic acid (para-phthalic acid) esterified with ethylene glycol. This polyester is made by a base-catalyzed transesterification of dimethyl terephthalate with ethylene glycol at a temperature around 150 °C. At this temperature, methanol escapes as a gas, driving the reaction to completion. We will study polyesters and other polymers in more detail in Chapter 26. 

Kodef polyester is formed by transesterification of dimethyl terephthalate with 1,4-di(hydroxy methyficyclohexane. Draw the structure of Kodel . 

The first step in the reaction of dimethyl-terephthalate and ethylene glycol is transesterification to form b i s(p-hy droxyethy 1) terephthalate (bis-HET) and eliminate methanol. 

Polyethylene terephthalate) in short PET is a polyester. It is mainly used in the garment industry with or without natural cotton and has trade names such as Terylene , Dacron , etc. As the name indicates, it is a polymer between terephthalic acid (PT) and ethylene glycol. Both terephthalic acid and dimethyl terephthalate (DMT) can be used to make the polymer. A majority of the modem plants tend to use PT as the starting material because of the availability of high-purity PT on a large scale. Both PT and DMT are first converted to bis(hydroxy ethyl) terephthalate 8.17 (see reaction 8.26). For PT this is effected by a straightforward esterification reaction. For DMT a transesterification reaction catalyzed by zinc and manganese acetate is used. 

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