Pyrolysis product identity

A good pyrolysis instrument must be able to heat a sample reproducibly, to a preset temperature at a known rate for a specific amount of time. Inability to control any of these variables will result in a pyrogram that cannot be reproduced. If required, the separated pyrolysis products can each be fed into a mass spectrometer to obtain detailed information on pyrolysis product identity (PGC-MS (Section 3.8)) or into an NMR spectrometer (PGC-NMR spectroscopy) or into a FT-IR spectrometer (Section 3.9). 

The addition of phthalimidylnitrene (374) to simple alkynes affords 1-azirines in yields of 1-15% (Scheme 10). In this reaction, which is of no real preparative value, the symmetrical 2-azirines (375) were suggested as the most plausible intermediates and unequivocal proof of the existence of such species was demonstrated from a series of 1,2,3-triazole pyrolysis reactions <71CC1518). Extrusion of nitrogen from the regioisomeric 4,5-disubstituted 1,2,3-triazoles (376) during flash vacuum pyrolysis furnished identical product mixtures which included both regioisomeric 1-azirines (377). 

A typical ethane cracker has several identical pyrolysis furnaces in which fresh ethane feed and recycled ethane are cracked with steam as a diluent. Figure 3-12 is a block diagram for ethylene from ethane. The outlet temperature is usually in the 800°C range. The furnace effluent is quenched in a heat exchanger and further cooled by direct contact in a water quench tower where steam is condensed and recycled to the pyrolysis furnace. After the cracked gas is treated to remove acid gases, hydrogen and methane are separated from the pyrolysis products in the demethanizer. The effluent is then treated to remove acetylene, and ethylene is separated from ethane and heavier in the ethylene fractionator. The bottom fraction is separated in the deethanizer into ethane and fraction. Ethane is then recycled to the pyrolysis furnace. 

In some instances, subtle changes in the precursor architecture can change the composition and microstructure of the final pyrolysis product. For example, pyrolysis of —[MeHSiNH] — leads to amorphous, silicon carbide nitride (SiCN) solid solutions at >1000°C (see SiCN section). At ca 1500 °C, these material transform to SisN SiC nanocomposites, of interest because they undergo superplastic deformation20. In contrast, chemically identical but isostructural — [F SiNMe] — transforms to Si3N4/carbon nanocomposites on heating, as discussed in more detail below21. 

The questions raised by these products led to a study of the pyrolysis products of thiophene itself. Thiophene, 0-4 mole, pyrolyzed alone under the identical conditions as with phthalic anhydride, gave 0-76 g of product (thiophene-free) that analyzed (relative intensities in the low-voltage mass spectrum) ... 

Direct pyrolysis of the DKPs corresponding to Pro-Val or Val-Pro was proven to generate the same types of compounds shown in Table 12.2.2. This is a proof that DKPs are the main primary pyrolysis products of these dipeptides. However, the pyrolysis of the dipeptides and their corresponding DKP does not generate identical pyrograms (chromatographic profiles of the pyrolysates). Therefore, some other processes may take place during the pyrolysis of each compound. 

From the similarity of the pyrolysis products of the copolymer with that of polyethylene, it can be inferred that the pyrolysis process takes place by a free radical mechanism. The cleavage of the polyethylene segments generates the portion of the pyrolysate identical to that of the polyethylene homopolymer. Similar reactions take place for the poly(methacrylic acid) segments. From a free radical ending with a methacrylic acid unit, the formation of 2-methyl-2-propenoic acid by p-cleavage to the atom bearing the unpaired electrons is shown below. 

The pyrolysis products of synthetic c/s-polyisoprene in an oxidative pyrolysis are very likely identical with those shown in Table 7.1.5. 

On treatment with iV-bromoacetamide followed by alkali the olefin (46), a pyrolysis product of yV-isobutyrylcyclobuxidine F, afforded the corresponding 1/3,10/3-epoxide.The latter was readily transformed into (47) which was found to be identical with A -isobutyrylbuxaline F, an alkaloid from Buxus balearica. p-Nitroperbenzoic acid converted (48) into the la,10a-epoxide (49). Successive treatment of (49) with triphenylphosphine and sodium methoxide afforded the novel cyclopropane derivative (50). 

Figure 7 shows a number of pyrolysis products which were identified with PPIGCMS. The identity and molecular ions of a number of major peaks in the TIC have been marked in the chromatogram. The guaiacol (m/z=124), hydroxystyrene (m/z=120) and methoxyhydroxystyrene (m/z=150) are the pyrolysis products of a monocotyledon lignin... 

We secured about 250 mg of the crystalline and naturally occurring enantiomer (—)-79, and examined its pyrolysis. GC-MS analysis of (—)-79 at the column temperature of 180 °C gave a product with a mass spectrum identical to that reported for Persoons periplanone-A. Having been encouraged by the preliminary GC-MS experiment, about 80 mg of (—)-79 was subjected to thermal decomposition at 220 °C on a 3% OV-17 column, which had been employed by Persoons for his purification experiment. After TLC purification of the thermolysis product, we obtained an oil in 71% yield based on (—)-79, whose IR and H-NMR spectra were identical with those reported for Persoons periplanone-A. It was therefore the pyrolysis product of (—)-79, although its structure was still unknown. 

The pyrolysis products identified in this work are quite different from those observed by other investigators. The principal difference is that in our experiments the volatile products are flushed away rapidly by the carrier gas. This condition perhaps better simulates the state at the surface of a burning polymer. In any event, it is important in any study of the effect of flame retardants that identical techniques and experimental conditions be used in the study of polymer with and without the additives. 

An effective interpretation of data cannot be made without a knowledge of the identity of the pyrolysis products, and hence with good fortune, a diagnosis of the composition of the original polymer can be made. Therefore, every effort should be made to identify and interpret the significance of at least the major products by... 

The identification of pyrolysis products and their sources in intact organisms was not widespread in pyrolysis studies until the last decade. Classification and differentiation of organisms were often based on the relative peak heights of one or more peaks at a given retention time in the pyrogram. This simplistic approach can lead to erroneous conclusions when the chemical identities of pyrolysis products and their origin are unknown. 

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