Oxazolidone formation reaction

A major feature of the chemistry of the oxazolidone formation reaction, emerging from the of epoxy and isocyanate model compound study, was the competition to that reaction provided by the trimerisation of the isocyanate. This process was a complicating factor in the preparation of linear... 

If this mechanism (Reaction 2) is correct the oxazolidone formation... 

Fourthly, the kinetic parameters derived for the oxazolidone forming reaction (Table 7) are not to be regarded as accurate, owing to difficulties in identifying the baseline between Peaks 1 and 2 precisely. However, the greater heat of oxazolidone formation observed for the EMI catalysed reaction, 141.9 kJmole compared with 44 kJmole when the reaction is catalysed by R NBr, is indicative of a more complete reaction. 

DSC Study of Oxazolidone Containing Resins. The DSC results of the PGE/ MDI model reaction, using R NBr or EMI as catalyst, showed that both promoted the trimerisation and the oxazolidone formation, with the latter catalyst being more powerful in respect of each reaction. The gained information suggested that by a careful choice of catalyst, catalyst concentration, and... 

The reaction temperature has a measurable influence on the oxazolidone formation when HEXA is used as catalyst, this point is illustrated in Table 12, oxazolidone concentration increasing with temperature increase. 

M. L. Anthony, E. Holmes, P. C. R. McDowell, T. J. B. Gray, M. Blackmore, J. K. Nicholson, ll NMR Spectroscopic Studies on the Reaction of Haloalkylamines with Bicarbonate Ions Formation of IV-Carbamates and 2-Oxazolidones in Cell Culture Media and Blood Plasma , Chem. Res. Toxicol. 1995, 8, 1046 - 1053. 

Due to these limitations Evans et al. focussed on the exploration of imide-derived enolates (165). They expected these systems to react stereoselective in carbon-carbon bond formation and that the derived imides might be readily hydrolized or reduced under the mild conditions required for the construction of complex products, One of the two chiral 2-oxazolidones (175) chosen for study by Evans et al.179) is derived from (S)-valine and was readily prepared from this inexpensive commercially available a-amino acid having an optical purity exceeding 99 %. The preparation of the related imide-derived enolate (165) is shown in the next scheme. Alkylation reactions employing (175) resulted in excellent diastereoface selection, as summarized in Table 4 179). 

Telomers 422 (n = 2) and other 4-halogeno-l,3-dioxolan-2-ones were shown288 to react readily with ammonia or primary aliphatic amines, with formation of 4-hydroxy-2-oxazolidones (460). The latter, for which the trans arrangement of the hydrogen atoms of the oxazoli-done ring was deduced from H-n.m.r. data, readily underwent replacement of the hydroxyl group by a phenyl group on reaction with... 

The reaction of -NCO isocyanate groups with epoxidic rings, in the presence of special catalysts, leads to the formation of cyclic urethanes (oxazolidones) [1, 3, 12, 13, 23-25] ... 

The disadvantage of hydroxyalkyl urea formation is an intramolecular reaction which leads to an oxazolidone, a cyclic urethane (reaction 20.10) [33]. 

The reaction between the oxazolidone and monoethanolamine (similar to the reaction of any urethane group with an amine) is very favourable, with the formation of a bis (hydroxyethyl) urea (a diol), which is an ideal chain extender in PU chemistry (reaction 20.12) [32, 33]. 

The scission of urethane groups is explained by the following two consecutive reactions (20.13 and 20.14). The first reaction is the addition of alkylene oxide to the active hydrogen of urethane groups (20.13). The resulting hydroxyalkyl urethane, by an intramolecular transesterification, leads to the splitting of the urethane bonds of PU, the PU network is destroyed with the formation of an oxazolidone and a polyether polyol. 

The alkoxylation process is easy to apply to PU foams having a low concentration of urethane and urea groups such as flexible and semiflexible foams, integral skin foams, PU elastomers and so on. Urea groups react in a similar way with urethane groups, with the formation of oxazolidones and amines by an intramolecular alcoholysis of urea groups (reaction 20.15). 

Poly(oxazolidone-urethane-isocyanurates) were prepared from an excess of isocyanate-terminated oxazolidone prepolymers and poly(oxypropylene) glycols of different chain lengths via the formation of NCO-terrainated poly(oxazolidone-urethanes) followed by trimerization of the terminal isocyanate groups as shown in the following reaction scheme ... 

Saturation of an equimolar mixture of aromatic aldehyde cyanohydrins and aromatic aldehydes in absolute ether at 0°C with dry hydrogen chloride results in the formation of 2,5-diaryloxazoles.114 116 The reaction often yields 2,5-diaryl-4-oxazolidones as by-products, and oxazolid-4-ones are the only products or major by-products if either of the starting materials is aliphatic. 

Although several attempts have been made to explain the formation of the oxazoles and oxazolidones from a common intermediate (previously reviewed),1-4 the mechanism of the reaction is not yet completely understood. Further, the synthesis is not unambiguous as it may give a mixture... 

In the conventional curing processes of epoxy resins, the crosslinks developed are of a single strand structure involving ether or amine extension points. The object of this study is the formation of the oxazolidone ring which by reaction of epoxy and isocyanate groups, affords an alternative type of crosslink, which it was anticipated will have a significant influence on the T of the cured epoxy resin. 

An alternative mechanistic explanation for the formation of oxazolidone, derived from the reaction of isocyanate and epoxide, has been given by Gulbins et al. (Reaction 4), Here the oxide anion derived from the epoxy ring attacks the carbonyl (C 0), rather than the imino (C N) double bond as shown in Reaction 2, Ring closure then produces an N-substituted imino-1,3-dioxolane, which isomerises to the 2-oxazolidone. Support for this mechanism was gained from the isomerism of an N-phenyl-2-imino-l,3-dioxolane to the corresponding 2-oxazolidone, using the same reaction conditions. 

Thirdly, EMI is also found to be a very powerful promoter of the formation of oxazolidone as is evidenced by the greater peak areas observed in DSC thermograms for its formation, catalysed by EMI, compared with those catalysed by R NBr. The reduction in Peak 2 temperature for EMI catalysed reactions confirms this conclusion. 

The formation of oxazolidone was followed by DSC using BADGE and MDI and the three catalysts, i.e., EMI, DABCO, and HEXA. By a comparison of thermograms some distinctions between the PGE/MDI and the BADGE/MDI reactions emerged. 

The use of substituted ureas as curing agents for epoxy resins has been the subject of few studies. Ywakura and Izawa [70] analyzed the reactions between phenylglycidyl ether and substituted ureas. In every case, the reaction, carried out under mild conditions (T = 90°C, t = 1 h, mol ratio of epoxy/urea = 1-3, with or without the use of NfCiHs), as catalyst), led to the formation of a 2-oxazolidone and a secondary amine ... 

At 200 °C, the reaction of methyl isothiocyanate and alkylene oxide gives trimethyl isocyanurate. This reaction involves the trimerization of methyl isothiocyanate followed by stepwise replacement of the sulfur by oxygen via spiro compounds. Phenyl isothiocyanate reacts with ethylene oxide to give a mixture of triphenyl isocyanurate and 3-phenyloxazolidine-2-one 90 °. The formation of the oxazolidone is caused by the reaction of the initially formed 2-phenylimino oxathiolene 89 with ethylene oxide in the presence of the catalysts... 

Oxazolidones result from the reaction of epoxides with isocyanates. Oxazolidones have a high thermal stability. A one-component foam system was developed, based on the formation of urethane and oxazolidone from an isocyanate. Mixing an excess of cmde 4,4 -MDl with an aliphatic polyester polyol and an... 

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