Cyclopentanones, from decomposition

Carbenes are known intermediates in the thermolytic or photolytic decomposition of the lithium or sodium salts of tosylhydrazones, which, for endocyclic carbenes, results in ring contraction when the elimination of / - or y-hydrogens is impeded. Simple cyclobutanes generally cannot be prepared by this route from monocyclic cyclopentanone tosylhydrazones. However, the lithium salt of bicyclo[2.2.1]heptan-7-one tosylhydrazone gave bicyclo[3.2.0]hept-l-ene (4) as the major product (74%) by vacuum pyrolysis at 185 JC/20 Torr, together with bicyclo[2.2.1]heptane (14%) and tricyclo[2.2.1.02,7]heptane (12%) in 80% overall yield.67... 

This type of fragmentation has been observed for a number of compounds, most of them having an exocyclic double bond. The decomposition of cyclopentanone (3) into ethene and carbon monoxide was described as a typical example in Section II. Cleavage of y-thiobutyrolactone (54) into carbon monoxide, ethene, and thioformaldehyde [93JCS(P2)1249] was mentioned in Section V.E. Another typical example is the formation of atomic carbon from 5-diazotetrazole (89JA8784). 

Very few details of these experiments have been published. In view of the insensitivity of the total quantum yield for the decomposition of cyclopentanone, as determined from the products, to the presence of a variety of gases including oxygen (33), this claim needs to be confirmed. 

The kinetics of the decomposition of cyclopentanone are complex and definitely differ from those of cyclobutanone as well as from those of other ketones. In spite of the uncertain mechanism, it may be stated that this reaction is, in many respects, similar to the pyrolysis of cyclopentane. In both cases, dehydrogenation and rupture of the ring take place as simultaneous processes. 

The main conclusion to be drawn from the application of the benzene photosensitization method to the decomposition of cyclobutanone is that the Cj-hydrocarbons originate from the low-lying triplet state of the ketone. However, use of this method in the investigation of cyclopentanone decomposition indicated that reactions I, II and III (if it is a separate primary process) occur from the first excited state of the ketone. This conclusion was based on the quantitative agreement found between the pressure dependence of the decarbonylation-product formation and the fluorescence quenching by cyclopentanone. 

Further reaction of Aese species with carbonyl compounds and hydrolysis of the resulting alkoxide leads to p-oxidoalkyl selenoxides which have been transformed into allyl alcohols on thermal decomposition (Schemes 51, 52 and 54, entry a see Section 2.6.4.4) or reduced to p-hydroxyalkyl selenides or to alkenes (Scheme 53). P-Oxidoalkyl selenoxides derived from cyclobutanones react in a different way since Aey rearrange to cyclopentanones upon heating (Scheme 54, b. Schemes 120 and 121 and Section 2.6.4.5.3). 

By competitive methods Ishikawa and Noyes (226) (sensitized biacetyl phosphorescence) and Cundall and Davies (159) (butene-2 isomerization) both estimated the triplet lifetime to be of the order of 10 ys. In a reexamination of the butene-2 system, Lee (227) estimated a value of 100 ys, a finding confirmed by Cundall and Dunnicliff (105). An examination of the kinetics of the benzene photosensitized composition of cyclopentanone decomposition allowed a value of longer than 3 ys to be deduced. This type of experiment is far from satisfactory since photochemical processes can Intervene at low pressures, and impurities and the quenching effects of photoproducts can affect the results. These problems can only be overcome by some form of direct measurement. Parmenter and Ring (228) used a flash method in which 20 torrs of benzene and 0.01 torr of biacetyl were submitted to a 20 J,... 

This result contrasts with that from cyclopentanone tosylhydrazone, which yielded cyclopentane (94%) as the major product,and with the cationic decomposition of the sodium salt of cyclobutanone tosylhydrazone in ethylene glycol which gave an 86% yield of a mixture of bicyclo[1.1.0]butane 41 (60%), cyclobutene (12%) and methylenecyclopropane (6%). Likewise, deamination of cyclobutylamine hydrochloride with amyl nitrite leads in low yield (13%) to methylenecyclopropane (56%) along with cyclobutene (40%). ... 

Using chemical ionization, it is difficult to use the unimolecular decomposition spectra of the MH" ion to distinguish cyclohexanone from its isomers, 2-methyl- and 3-methyl-cyclopentanone, since they lead uniquely to the elimination of a molecule of... 

The reaction of NO with the double bonds of enamines also produces compounds containing the diazeniumdiolate functional group bound to carbon, and some of the compounds prepared in this way have the potential to serve as spontaneous NO donors [43]. The compounds chosen for study were enamines 1-4 derived from condensation of cyclopentanone or cyclohexanone with morpholine or pyrrolidine. When these enamines were dissolved in acetonitrile and treated with NO gas (5-atm pressure) at room temperature, a vigorous exothermic reaction resulted, accompanied by high uptake of NO and formation of a brown precipitate. Attempts to isolate the solid precipitates often resulted in rapid decomposition, with the release of large volumes of gaseous NO. At -78 °C in diethyl ether, the reaction of 4-(l-cyclohexen-l-yl) morpholine (IX) afforded a good yield of crystalline NO addition product (X) ... 

Di Pasquale and co-workers [15] applied TGA and on-line flash Py-GC-MS to a study of thermal decomposition processes in glass hardened polyamides. The thermal decomposition of each polymer was found to begin at about 350 °C and proceeded with a weight loss of 100% for the non-glass fibre-reinforced polymers, under a nitrogen atmosphere. The analysis of the pyrolysate compounds showed that from polyamide-6,6 the most common volatile product at degradation temperatures was cyclopentanone, while from polyamide-6 there was a significant yield of e-caprolactam. 

The fast pyrolysis decomposition of cellulose starts at temperatures as low as 150°C. Pyrolysis of cellulose below 300°C results in the formation of carboxyl, carbonyl, and hydro peroxide groups, elimination of water and production of carbon monoxide and carbon dioxide as well as char residue (Evans and Milne, 1987). Therefore low pyrolysis temperatures will produce low yields of organic liquid yields. Fast pyrolysis of cellulose, above 300°C, results in liquid yields up to 80 wt.%. Cellulose initially decomposes to form activated cellulose (Bradbury et al., 1979). Activated cellulose has two parallel reaction pathways, depolymerization and fragmentation (ring scission). The main products from each reaction pathway are rather different as ring scission produces hydroxyacetaldehyde, linear carbonyls, linear alcohols, esters, and other related products (Bradbury et al., 1979 Zhu and Lu, 2010 Lin et al., 2009) and depolymerization produces monomeric anhydrosugars, furans, cyclopentanones, and pyrans and other related products (Bradbury et al., 1979 Zhu and Lu, 2010 Lin et al., 2009). Each reaction pathway is independent and is influenced by pyrolysis temperature and residence time (Bradbury et al., 1979). 

---