Carbon dioxide, thermal with amides

Phenyl-l,3,4-oxathiazol-2-one (370), prepared from primary amides and tri-chloromethanesulfenyl chloride, undergoes a ready thermal elimination of carbon dioxide with the formation of the nitrile sulfide ylide (371). This can be trapped by a wide variety of unsaturated dipolarophiles, and with an alkyne provides a ready route to isothiazoles (372) (see Chapter 4.17). Applications to 1,2,4-thiadiazole synthesis are described in Chapter 4.25. Thermolysis of l,3,4-oxadiazolin-5-ones (500 C/10 mmHg) results in the loss of CO2 and generation of the corresponding nitrilimine (78JOC2037). 

MMA monomer, methanol, and carbon dioxide were detected in the pyrolysis gases. The profiles of rate of evolution against temperature were used to identify the presence of occluded monomer and thermally unstable end groups such as unsaturation. The evolution profiles for MMA and methanol were found to be characteristic for each type of crosslink. Evolution of methanol between 250 °C and 300 "C, and between 300 °C and 350 °C has been attributed to condensation reactions of carboxylic acid and primary amide groups, respectively, with adjacent ester groups. The evolution profiles were used to distinguish between samples from different manufacturers, and to identify material [5]. 

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