Thermolytic cleavage

This approach is compHcated by the fact that the isocyanate is produced via the thermolytic cleavage of the methyl carbamate. Reactions with the unconverted carbamate caimot be prevented. Much effort has been focused on improving the selectivity of the latter step. 

Since the equilibrium lies to the left at higher temperatures, cyclopentadiene can be obtained by thermolytic cleavage of the dimer and distilling the monomer prior to use (cracking distillation). 

Scialdone MA, Shuey SW, Soper P, Hamuro Y, Bums DM. Phosgenated p-nitrophenyl(polystyrene)ketoxime or phoxime resin. A new resin for the solid-phase synthesis of ureas via thermolytic cleavage of oxime-carbamates. J Org Chem 1998 63 4802-4807. 

Thermolytic Cleavage of Allvlic and Benzvlic Ethers and Polvethers. The thermal lability of the types of ethers which are of interest in the context of this study was discovered during a thorough study of the application of certain benzylic carbonates as labile protecting groups for alcohols and phenols [IS]. It was observed that, under acid catalysis, the bis-methylcarbonate derivative of l-(4-hydroxyphenyl)ethanol (4, in Equation 1) was transformed into the benzylic ether (5) which then underwent clean acid-catalyzed thermolysis to the corresponding styrene (6) in very high yield [14]. 

The suitability of ethers derived from 1,4-dihydroxy-1,2,3,4-tetrahydro-naphthalene (DHTN) in the design of polymers susceptible to catalyzed thermolytic cleavage is demonstrated by the behavior of its bis-p-nitrophenyl ether derivative upon treatment by a trace of acid. Figure 2, curve A, shows the H-NMR spectrum of the starting compound, while curve B shows the product which is obtained upon addition of triflic acid. It is readily seen from these spectra that quantitative cleavage into naphthalene and p-nitrophenol is obtained as elimination occurs easily to afford the aromatic product. The driving force in this reaction is the facile aroma-tization which produces naphthalene. 

Prior to the isolation of Arduengo carbenes. many closely related carbene complexes had also been prepared via the thermolytic cleavage of electron-rich alkenes in the presence of various transition metal reagents (Figure 5.6). 

During a synthesis of the protein kinase C inhibitor Balanol. Lampe and co-workers77 found that deprotection of the tert-butyl ester 30.1 [Scheme 6.30] with trifluoroacetic or formic acid was accompanied by substantial quantities of a debenzylated by-product. The same side reaction accompanied thermolytic cleavage of the terf butyl ester in neutral solvents presumably due to add catalysis by the carboxylic acid product 30.2. Thermolysis in quinoline at 205 °C led cleanly to the desired benzophenone carboxylic acid 30.2 in 68% yield. 

Free radicals can be formed by thermolytic cleavage, photolysis (nltravi-olet light photolysis of hydrogen peroxide to form hydroxyl radicals), radiolysis (ionizing radiation of water to form hydroxyl radicals), or by homolytic cleavage with the participation of another molecule (i.e., Fenton reaction). Perkins, J., Radical Chemistry The Eundamentals, Oxford University Press, Oxford, UK, 2000. 

Thermolytic cleavage of species like XIV form sulphenic acid, XV, Reaction (4.48) ... 

Thermolysin is specific for the hydrolysis of peptide linkages which occur adjacent to, but on the imino side of, a hydrophobic amino acid moiety i.e., X-Leu, X-Ileu, X-Phe, X-Val, where X is any other amino acid 185—187). Thus, the specificity of thermolytic cleavage is complementary to that of chymo-tryptic cleavage. 

Photolytic or thermolytic cleavage of the N-0 bond of tetrahydro-1,2-oxazine-3,6-diones (407), followed by decarboxylation, gives intermediate 1,4-diradicals (408) which close to form 3-lactams (409), albeit in poor yields. Diradical intermediates analogous to (408) may be formed in the biosynthesis of isopenicillin N from trlpeptide precursors. In a similar vein, Easton has published full details of the synthesis of 3-lactams by ring contraction of isothiazolidinones, a reaction which may also be relevant to... 

The condensed phase is heated by an ignition source or by thermal feedback of radiant heat from the gas phase oxidation reactions. Thermolytic cleavage of the polymer supplies combustible and noncombustible gaseous products to the gas phase combustion zone. These products react with oxygen and release heat during the production of carbon dioxide, carbon monoxide, water, and soot. 

The symbol Lg derives from latent heat, ie, the recoverable heat in a reversible process. Thermolytic cleavage of primary chemical bonds in the polymer backbone to produce volatile fuel and char is obviously not a reversible process, but the symbol Lg will be used throughout to conform with the literature in the fire sciences. Table 2 illustrates the magnitude of these enthalpic terms for amorphous PMMA, polystyrene (PS), and semicrystalline polyethylene (PE). The stored heat Ahs was obtained by numerical integration of heat capacity versus temperature from ambient to the dissociation temperature as per equation 24. The dissociation... 

When unsaturated fatty acids are subjected to thermolytic cleavage, dimers, polymers and cyclic compounds are produced. The dimers include alicyclic mono-, di-, and triene dehydrodimers, saturated dimers with cyclopentene structures, tetrasubstituted cyclohexanes and bicyclic and tricyclic dimers (Nawar, 1985). Cyclic mononmers exhibit toxicity in experimental animals (Van Gastel et al, 1984), therefore, generation of cyclic monomers at high temperature frying with oils containing polyunsaturated fatty acids should be carefully monitored. 

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