Glycols reactions

Chemical Properties. Neopentyl glycol can undergo typical glycol reactions such as esterification (qv), etherification, condensation, and oxidation. When basic kinetic studies of the esterification rate were carried out for neopentyl glycol, the absolute esterification rate of neopentyl glycol with / -butyric acid was approximately 20 times that of ethylene glycol with / -butyric acid (7). 

Chemical Properties. The chemistry of 1,4-cyclohexanedimethanol is characteristic of general glycol reactions however, its two primary hydroxyl groups give very rapid reaction rates, especially in polyester synthesis. 

Other possible chemical synthesis routes for lactic acid include base-cataly2ed degradation of sugars oxidation of propylene glycol reaction of acetaldehyde, carbon monoxide, and water at elevated temperatures and pressures hydrolysis of chloropropionic acid (prepared by chlorination of propionic acid) nitric acid oxidation of propylene etc. None of these routes has led to a technically and economically viable process (6). 

Fig. 6. Effect of temperature on rhodium-catalyzed CO hydrogenation ( ) methanol ( ) ethylene glycol. Reaction conditions 75 ml y-butyrolactone solvent, 3 mmol Rh, 10.5 mmol 2-hydroxypyridine, 0.5 mmol cesium 2-pyridinolate, 544 atm, H2/CO = 1, 4 hr (88).

In competition, the C(6)-yl and C(5)-yl radicals may disproportionate, possibly via an adduct [reactions (80) and (81)]. This yields the hydrate via an enol [reaction (83)]. The other product is the glycol [reaction (82)]. In the original paper (Al-Sheikhly and von Sonntag 1983), it has been proposed that it maybe formed in an ET reaction. Due the considerable rearrangement energies involved in ET reactions as compared to radical recombination reactions, it is now considered that this ET reaction might occur via an addition/elimination process [reactions (80) and (81)] such as has also been found for other systems. 

Table 9.1 Analytical technology utilized for glycolization reaction/crystallization and drying during scale-up experiment. Adapted from David etal. (2004)30 ...

Course of the reaction. In Table I, data are presented from two typical experiments which show the relative rates of formation of ammonia and carbon dioxide. These data serve to indicate a possible course of the urea-ethylene glycol reaction. Clearly, the synthesis of ethyleneurea did not proceed through simple elimination of two moles of water from an equimolar mixture of reactants for there was no evidence that water per se was obtained from the reaction. Indeed, it did not appear to be even a primary product since, if it had been and if it had reacted with urea, then the quantity of carbon dioxide relative to ammonia would have been much higher in the early stages of the reaction. From the very large quantity of ammonia evolved it appeared that the primary product was a carbamate. This carbamic acid ester of ethylene glycol subsequently lost carbon dioxide with formation of the desired C—N bond as indicated by the following equations ... 

Elimination of a water molecule takes place with various types of radicals and is catalysed by acids and bases. This has been observed with the radicals from ethylene glycol [reaction (64)] (von Sonntag and Thoms, 1970 Burchill and Perron, 1971) and other glycols, and... 

Figure 6. Esterification of terephthalic acid with ethylene glycol reaction temperature 473 K, reaction time 90 min.

The reaction between 65/35-TDI (65% 2,4-isomer, 35% 2,6-isomer) and a poly(oxypropylene)glycol, in the presence of small amounts of water, was studied by Aleksandrova and Lakosina [196]. The reaction rates were followed by disappearance of NCO, representing the combination of the two reactions, and by the rate of CO2 evolution as a measure of the NCO/water reaction. Tertiary amines were found to catalyse the reaction with water about the same as that with the glycol. Dibutyltin dilaurate catalysed the TDI/glycol reaction about 1.5 times as strongly as the TDI/water reaction. 

On the other hand, thallic ion oxidizes olefins to a mixture of glycols and carbonyl compounds—e.g., ethylene gives acetaldehyde and ethylene glycol (Reaction 2). 

An important feature of the reactions of epoxides is the formation of compounds that contain rno functional groups. Thus, reaction with water yields a glycol reaction with an alcohol yields a compound that is both ether and alcohol. 

We may recall the well-known reactions of these two oxidants on vicinal glycols, reactions (5.16) and (5.17). 

The direct polyesterification reaction of diacids with glycols is the most important industrial synthetic route to polyester polyols. The second most important synthetic route is the transesterification reaction between dimethyl esters of dicarboxylic or dibasic acids (dimethyl adipate, dimethyl terephthalate, dimethyl carbonate or even polyethylene terephthalate) and glycols (reaction 8.2) [1, 3-8]. 

The esters of phosphorus acid are obtained by condensation of triphenylphosphites or trialkylphosphites with various polyols, such as dipropylene glycol (reaction 18.10) [5,... 

Glycolysis of a PU polymer is similar to a transesterification reaction, in fact a reaction between a carbamic ester (urethane) and a glycol (reaction 20.5). 

Poly(vinyl chloride) is a less useful polymer than poly(ethylene glycol). Reactions of Poly(mcthyl methacrylate)... 

In the second stage, the temperature is raised and vacuum is applied to remove the free glycol. Reaction continues to produce polsmier and glycol, which is removed, and the two reactants approach exact balance and high molecular wei t is achieved. ... 

The reaction of olefins with peracids involves firstly the formation of an epoxide, reaction (5.1) in acidic media the epoxide may suffer ring-opening to yield the mono-ester of a glycol, reaction (5.2). ... 

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