Functional groups, thermal decomposition

Correlations of the oxygen balance of a parent energetic compound and its impact sensitivity (a thermal decomposition phenomenon) are well known 11-31. Hammett correlations with the explosive sensitivity in arylammonium perchlorate salts have been uncovered [4]. Relationships between the composition [5] and decomposition [6,7] of explosives and their detonation velocity are known. Extensive studies have been made relating molecular structure to the kinetics and thermolysis trends for aliphatic nitro compounds [8J, azides [9,10], and nitramines [11]. Correlations of the melting point with burn-rate [12], functional group with decomposition temperature [13], and various structural parameters with stability [14] have been proposed. 

However, certain additives can decrease the rate of thermal decomposition [28]. These additives include cyclic sulfates, sulfones, sultones, aliphatic and aromatic anhydrides, and polymers with pendant carboxylic acid functional groups. Most of these materials are latent acids, which decompose on heating in the presence of moisture to form a strong acid, as shown for cyclic sulfate, 9, in Eq. 5. 

In both compounds there are type (I) azo functions surrounded by alkyl groups and one cyano group. Upon heating, tertiary alkyl radicals and cyano alkyl radicals are formed. These radicals are relatively stable due to hyper conjugation and, in the case of cyano substituted alkyl radicals, to resonance. Therefore, azo groups (I) have a high proneness to thermal decomposition. 

Reduction by diimide can be advantageous when compounds contain functional groups that would be reduced by other methods or when they are unstable to hydrogenation catalysts. There are several methods for generation of diimide and they are illustrated in Scheme 5.4. The method in Entry 1 is probably the one used most frequently in synthetic work and involves the generation and spontaneous decarboxylation of azodicarboxylic acid. Entry 2, which illustrates another convenient method, thermal decomposition of p-toluenesulfonylhydrazide, is interesting in that it... 

The Nazarov cyclization of vinyl aryl ketones involves a disruption of the aromaticity, and therefore, the activation barrier is significantly higher than that of the divinyl ketones. Not surprisingly, the Lewis acid-catalyzed protocols [30] resulted only in decomposition to the enone derived from 46,47, and CO. Pleasingly, however, photolysis [31] readily delivered the desired annulation product 48 in 60 % yield. The photo-Nazarov cyclization reaction of aryl vinyl ketones was first reported by Smith and Agosta. Subsequent mechanistic studies by Leitich and Schaffner revealed the reaction mechanism to be a thermal electrocyclization induced by photolytic enone isomerization. The mildness of these reaction conditions and the selective activation of the enone functional group were key to the success of this reaction. 

Information about the thermal stability of materials and mixtures can be obtained with little effort. It is known that when certain functional groups are present an increased probability of exothermic decomposition needs to be accounted for. A list of special compounds and materials are given in the Appendix (section G 1). 

Aromatic acyl halides containing a nitro group adjacent to the halide function show a tendency towards violent thermal decomposition. The few individually indexed compounds are ... 

Thermal decomposition of peroxides generates a variety of radical groups which can covalently react with CNTs. This strategy has been employed in particular by Peng and co-workers who functionalized sidewalls with benzoyl, lauroyl and carboxyalkyl derivatives [38]. 

An important route to the carbazoles is the thermal or photolytic decomposition of orf/zo-azidobiphenyls. Of the two procedures, thermolysis proceeds in higher yields. One advantage of photolysis is that it proceeds at room temperature and would therefore be compatible with thermally labile functional groups. 

Quantitative analysis of copolymers is relatively simple if one of the comonomers contains a readily determinable element or functional group. However, C,H elemental analyses are only of value when the difference between the carbon or hydrogen content of the two comonomers is sufficiently large. If the composition cannot be determined by elemental analysis or chemical means, the problem can be solved usually either by spectroscopic methods, for example, by UV measurements (e.g., styrene copolymers), by IR measurements (e.g., olefin copolymers), and by NMR measurements, or by gas chromatographic methods combined with mass spectroscopy after thermal or chemical decomposition of the samples. 

In cycloaddition reactions the [6,6] double bonds of Cjq exhibit a dienophilic character. A large variety of cycloadditions have carried out with Cjq and the complete characterization of the products, mainly monoadducts, has greatly increased our knowledge of fullerene chemistry. These chemical transformations also provide a powerful tool for the functionalization of the fullerene sphere. Almost any functional group can be covalently linked to Cjq by the cycloaddition of suitable addends. Some types of cycloadducts exhibit a remarkable stability for example, they can be thermally treated up to 400 °C without decomposition. This is an important requirement for further side-chain chemistry as well as for possible applications of the new fullerene derivatives, which may be of interest due to their biological activity or as new materials. 

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