Propane-1,3-diols transesterification

The PTT is aromatic polyester prepared by the melt polycondensation of 1,3-propanediol (1,3-PDO) with either TPA or dimethyl terephthalate (DMT). The PTT is synthesized by the transesterification of propanediol with dimethylene terephthalate or by the esterification of propane diol with TPA. The reaction is carried out in the presence of hot catalyst like titanimn butoxide (Ti(OBu) ) and dibutyl tin oxide (DBTO) at a temperature of 260°C. The important by-products of this reaction include acrolien and allyl alcohol (Chuah, 2001). Direct esterification of propane diol and TPA is considered as the least economic and industrial method. The reaction is carried out in the presence of a heel imder a pressure of 70-150 kPa at a temperature of 260°C. The heel is usually referred to the added PTT oligomers which act as a reaction mediiun and increase the solubility of TPA (Chuah, 2001). Recent studies by different groups show that the selection of the catalyst plays a major role on the reaction rate and PTT properties. Commonly used catalysts like titanium (Doerr et al., 1994), tin (Kurian and Liang, 2001 Fritz et al., 1969) and antimony (Karayannidis et al., 2003 Fitz et al., 2000) compounds have their own limitations. Titanimn-based catalysts are active but the PTT is discolored, antimony-based catalysts are toxic and only active in polycondensation while tin-based compounds have lower catalytic activity. Karayannidis and co-workers (2003) reported the use of stannous oetoate ([CHj(CH2)3CH(C2Hj)COO]jSn) as the catalyst for PTT synthesis but its catalytic activity is poor, resulting in a low molecular weight PTT which was confirmed... 

It was found that the transesterification of dimethyl H-phosphonate with 1,2-propane-diol yields 4-methyl-2-hydro-2-oxo-l,3,2-dioxaphospholane [56]. Obviously, the first stage of the reaction furnished methyl-2-hydroxypropyl H-phosphonate. Subsequent intramolecular transesterification of the methyl-2-hydroxypropyl phosphonate yielded 4-methyl-2-hydro-2-oxo-l,3,2-dioxaphospholane. The specific reactivity of these esters of H-phosphonic acid is determined by the presence of a P-hydroxyl gronp. The role of the P-hydroxyl gronp may be regarded as an intramolecular catalysis. The reactivity enhancement of P-hydroxylethyl esters of H-phosphonic acid probably can be explained through hydrogen bonding, which favors the intramolecular transesterification reaction. 

Alkylene CCs have been prepared through the transesterification of appropriate glycols with dialkyl carbonates (usually diethyl or dimethyl carbonate) in the presence of a suitable catalyst. One of the first such examples was the synthesis of six-membered CCs by the transesterification of propane-1,3-diols with DEC catalyzed by sodium ethanolate (Equation 7.31) [289], The reaction was carried out at temperatures between 293 and 333 K, and a conversion yield of 40% was obtained. 

A similar method has been reported by Albertsson et al. [290], in which equimolar amounts of propane-1,3-diol and DEC were used, with stannous 2-ethylhexanoate as the transesterification catalyst, affording a yield of 53%. 

In applying this method to carbohydrate 1,3-diols, a British groups preferred to liberate carbohydrate 1,3-diols firom their boronates by transesterification with propane-1,3-diol rather than with ethylene glycol. The boronate was treated in acetone with propane-1,3-diol and the solution evaporated to dryness. Extraction with petroluem ether removed the exchanged boronate and crystallization of the residue afforded the carbohydrate component. 

The synthesis of six-membered cyclic carbonates by transesterification of propane-1,3-diols (PPDs) with diethyl carbonate catalyzed with sodium ethanolate described by Carothers and Van Natta gives a yield of 40%. Also Pohoryles and... 

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