Acetone decomposition mechanism

The following mechanism has been proposed for the thermal decomposition of acetone. 

For the photolysis of ferf-butyl nitrite a possible reaction mechanism (Scheme 6) consists of the production of ferf-butoxy radicals (equation 3), followed by their decomposition to give acetone and methyl radicals (equation 4). The latter are trapped by the nitric oxide liberated in the first step (equation 5). However, the absence of ethane production in the actual experiments suggested that an intramolecular formation of nitrosomethane is unlikely ". ... 

The slow combustion reactions of acetone, methyl ethyl ketone, and diethyl ketone possess most of the features of hydrocarbon oxidation, but their mechanisms are simpler since the confusing effects of olefin formation are unimportant. Specifically, the low temperature combustion of acetone is simpler than that of propane, and the intermediate responsible for degenerate chain branching is methyl hydroperoxide. The Arrhenius parameters for its unimolecular decomposition can be derived by the theory previously developed by Knox. Analytical studies of the slow combustion of methyl ethyl ketone and diethyl ketone show many similarities to that of acetone. The reactions of methyl radicals with oxygen are considered in relation to their thermochemistry. Competition between them provides a simple explanation of the negative temperature coefficient and of cool flames. 

The complex /rara-PtH(02CH)[PEt3]2 catalyzes the decomposition of formic acid in the presence of sodium formate. A mechanism based on the equilibria described in Scheme 2 has been proposed by Paonessa and Trogler (60). The role of formate ion is to promote catalysis by reaction with the platinum dimer (10) or the solvated complex [frans-PtH(S)L2]+, where S = acetone, to reform the catalytically active monomeric species 11 and 12. 

As an alternative method of procedure, the following may be substituted for Steps 4 to 7 inclusive of the above process. After distilling the benzol, the tarry mass may be stirred directly with 2000 mL of hot 0.3 N NaOH with a mechanical stirrer. The suspension is chilled and the supernatant Liquid poured or siphoned off. Repetition of the extraction two or three times is advisable. The alkaline aqueous solution is then extracted five or six times with 400 mL portions of sulfuric ether, thus transferring the hormone to ether solution. After distillation of the ether the residue is steam distilled as long as a distillate other than water is obtained. The condensed water is removed by vacuum distillation and the small amount of dark tarry residue leached 5 times with 50 mL of hot 0.3 N NaOH. This solution is filtered and the filtrate extracted with sulfuric ether (100 mL, 6 times). The ether solution is distilled and the residue leached with cold 0.3 N NaOH using 20 mL five times. This alkaline solution is filtered and extracted with 50 mL of sulfuric ether five times. Upon distillation of the ether and solution of the residue in a small quantity of hot ethyl alcohol, the hormone separates in semi-crystalline balls which may be filtered off. A further quantity is obtained by adding 3 volumes of water to the alcoholic solution. It may be recrystallized from 25% aqueous ethyl alcohol or from 25% aqueous acetone or from any of the following chloroform, benzol, ethyl acetate, ethyl ether or petroleum ether. The final product consists of colorless crystals which, when crystallized from dilute alcohol, possess a distinct rhomboid outline. The crystals melt at 242-243°C (248-249°C corrected) with some decomposition. 

Photodecomposition. Since the last review of photochemistry of HFA (61), there has been a great deal of effort expended in the study of the primary processes and decomposition modes of HFA. The photodecomposition products observed appear to be carbon monoxide and hexafluoroethane exclusively. The trifluoroacetyl radical, CF3CO, must be very unstable. As in acetone, it has been proposed that the decomposition processes must overcome an energy barrier, as temperature-dependent quantum yields were observed (252). A detailed mechanism that takes into account a vibrational deactivation cascade has been proposed by several authors (34,35,97,252). 

Whereas acetone shows little tendency to undergo chain decomposition in photolysis or pyrolysis, acetaldehyde has been found to decompose by a chain mechanism which tends to quite sizable chain lengths as the temperature is raised. As a consequence of this behavior, the dec(3mposition has been found to be remarkably sensitive to the presence of small amounts of substances that can form free radicals more readily than pure acetaldehyde does. A further result of this sensitivity is that the data on the pyrolysis obtained under different conditions or in different laboratories show quite important discrepancies. In compensation for these difficulties the stoichiometry of the pyrolysis seems to be quite simple, the products being CO + CH4, together with very small amounts of C2H6 and also some II2 at temperatures near 500°C. These can be represented by ... 

---