Pyrolysis fragmentation

Figure 12.3 GC/MS (a) and THM GC/MS (b) curves of aged dammar. Peak assignments 2, a cubebene 3, copaene 4, ft bourbonene 8,10 12, cadinane type pyrolysis fragments 14 16, cadinene type pyrolysis fragments 17, calamanene type pyrolysis fragments 18 21, unidentified sesquiterpenoids 22, dammaradienone 23, dammaradienol 24, nor a amyrone 25, 28 nor olean 17 en 3 one 26, dammarenolic acid methyl ester 27, oleanonic acid 28, hydroxydammarenone 29, oleanonic aldehyde 30, ursonic acid methyl ester 31, ursonic aldehyde 32, nor (3 amyrone 34, 20,24 epoxy 25 hydroxy 3,4 seco 4(28) dammaren 3 oic acid methyl ester 35, 20,24 epoxy 25 hydroxy dammaren 3 one 36, dammaradienol...

Thietane compounds could occur in space especially when one considers that sulfine, a commonly observed pyrolysis fragmentation product of thietane oxide, has been detected in the interstellar medium by microwave spectroscopy. Thietane derivatives have been isolated from the plant and animal kingdom, and it seems likely that much still remains untapped. In such plants as Tribus Arctotideae, the thioacetylene structure 13 containing a 3-... 

Gl (MW >5000). Most of the pyrolysis fragments found in this fraction are derived from the three general classes just mentioned. Pyrrole and methylpyrrole originate from proteinaceous material such as polypeptides as well as from single amino acids such as proline and hydroxyproline. A quantitative relationship between amino acid hydrolyzable content and pyrrole abundance was established by Bracewell (20) for some Scottish brown forest soils, and such a correlation probably could be established for water. 

Figure 12. Relative evolution of typical pyrolysis fragments 67 = pyrrole, 94 = phenol, and 82 = 2-cyclopenten l-one.

Thne-of-flight (TOF) mass spectrometric analysis of the pyrolysis fragments of di-t-butyl peroxide suggests t-BuCO as the primary product, followed by decomposition of this radical into CHj.253 Elsewhere, the kinetics of the pyrolysis of dimethyl, diethyl, and di-t-butyl peroxides in a modified adiabatic bomb calorimeter have been investigated.254 The lifetime of acyloxy radicals, generated by the photolysis or thermolysis of acetyl propionyl peroxide, have been studied. Chemical nuclear polarization has been used to determine the rate constant for the decarboxylation of these radical intermediates.255... 

Fig. 5.2(A) presents the pyrolysis mass spectrum for the soil extract. In previous work (ref. 358,359,365) it was shown that complex organic materials like polysaccharides, proteins, lignins, and soil humic fractions have characteristic peaks yielding a typical pattern, which give preliminary information about the composition of the pyrolysis fragments. Thus, characteristic peaks for polysaccharides were observed at 60, 68, 82, 84, 96, 98, 110, 112, and 126 m/z, which were also present in the soil extract. They were shown to be related to acetic acid, furan, methylfuran, hydroxyfuran, furfural, furfuryl alcohol, methylfurfural, methoxy-methylfuran, and a typical pyrolysis fragment of polysaccharides with hexose and/or deoxyhexose units, respectively.

For ail the classes of compounds discussed above, it is possible to trace similarities between pyrolysis fragmentations and mass spectral fragmentations. However, it is not always simple to predict the result of each of the two processes. This adds supplementary complications for the interpretation of the data in the Py-MS analytical technique where the two processes are combined (see Sections 5.4 and 5.5). 

Parent anthocyanin Ring substituent R Ring substituent R Pyrolysis fragment... 

One possibility for understanding the Py-MS results for nucleic acids is to use a parallel between the mass spectral fragmentation and the pyrolysis fragmentation. This can be exemplified for the mass spectra of the silylated 2 -deoxyadenosine-5 -phosphate (deoxy-AMP) and adenosine-5 -phosphate (AMP), which are shown in Figure 13.1.1 and 13.1.2 respectively (El spectra at 70 eV). The interpretation of several fragments in these spectra is given in Table 13.1.1. 

Isothermal (flash pyrolysis). The temperature of the sample is suddenly increased (10-100 ms) to reach the thermal decomposition level (500 - 800°C). This process can be carried out by means of a platinum or platinum-rhodium filament heated by an electrical current directly coupled to the injector port of the GC. Some pyrolysis fragments are obtained in a very short time and can be directly sent to the column and detector. In spite of this short time for the pyrolysis, it is possible to indicate three different phases (a) heating (10 -10 s), (b) stabilization of the maximum temperature, and (c) cooling. However, the main drawback of this technique is the lack of equilibrium between temperatures with the pyrolyzer. 

In a pyrolysis jet, (Chen, et al., 1986 Dunlop, et al., 1988 and 1989) parent molecules are swept quickly through a very high temperature region just before exiting the jet. There is an art to the selection of a parent molecule optimal for production of the desired pyrolysis fragment (Chen, et al., 1986). In a pyrolysis source, the weakest bond breaks first and subsequent reactive collisions are minimized. 

Pyrolysis-gas chromatography EGA Identification of separate pyrolysis fragments usually not made... 

Identification reliable confirmation of the structure of the pyrolysis fragments to enable rational assignment of the origins of the products. 

Mixtures, formulated blends, or copolymers usually provide distinctive pyrolysis fragments that enable qualitative and quantitative analysis of the components to be undertaken, e.g., natural rubber (isoprene, dipentene), butadiene rubber (butadiene, vinylcyclo-hexene), styrene-butadiene rubber (butadiene, vinyl-cyclohexene, styrene). Pyrolyses are performed at a temperature that maximizes the production of a characteristic fragment, perhaps following stepped pyrolysis for unknown samples, and components are quantified by comparison with a calibration graph from pure standards. Different yields of products from mixed homopolymers and from copolymers of similar constitution may be found owing to different thermal stabilities. Appropriate copolymers should thus be used as standards and mass balance should be assessed to allow for nonvolatile additives. The amount of polymer within a matrix (e.g., 0.5%... 

In Table 7 are shown the analysis of pyrolysis fragments obtained from zinc dialkyldithiophosphates containing known alkyl groups. 

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