The Synthesis of Methylacetylene by the Pyrolysis of Propylene. I. The Effect of Pyrolysis Conditions on Product YieldsSakakibara, Yasumasa
doi: 10.1246/bcsj.37.1262pmid: N/A
Propylene has been pyrolyzed in a flow system over a wide range of conditions (temperature, 800∼1400°C; contact time, 4.4×10−4∼2.3 sec.; pressure, 40∼160 mmHg) to find suitable conditions for producing methylacetylene (and allene) and for obtaining data concerning the distribution of pyrolysis products. Under proper conditions, the pyrolysis occurred without any appreciable production of tarry and carbonaceous materials. High temperatures (1200∼1300°C), short contact times (millisecond order; conversions below 30%), and low pressures (below l00 mmHg) were found to required for the good production of methylacetylene-allene. A methylacetylene-allene yield of 38 mol. per 100 mol. of propylene pyrolyzed was realized at 1200°C, 50 mmHg pressure (partial pressure of propylene, 40 mmHg), and 24% conversion (contact time, 1.7 msec.). The other gaseous products were found to be methane, ethylene, hydrogen, acetylene, 1-butene and butadiene, in decreasing order.
The Synthesis of Methylacetylene by the Pyrolysis of Propylene. II. The Mechanism of the PyrolysisSakakibara, Yasumasa
doi: 10.1246/bcsj.37.1268pmid: N/A
A study has been made of the mechanism of the pyrolysis of propylene at high temperatures (800∼1400°C). Of the gaseous products, hydrogen, methane, ethylene, allene, and 1-butene, obtained in the yields of 25, 43, 40, 27, and 9 mol. per 100 mol. of propylene pyrolyzed (3% conversion) respectively, have been found to be the primary products, while methylacetylene, acetylene, and butadiene, obtained in the yields of 9, 4, and 2 mol. respectively, have been found to be the secondary products. In view of the results of the pyrolysis of allene itself, even at a low conversion of 3%, allene appears to undergo considerable secondary reactions, such as isomerization to methylacetylene, addition to propylene and allyl radicals, and decomposition, for example, to acetylene and methane via methylacetylene. On the basis of the observed results, free-radical mechanisms have been proposed for the primary reactions and main secondary reactions. The mechanism for the primary decomposition reaction is a chain process in which the chain is initiated by the reaction C3H6→C3H5· (allyl radical) + H, and is, via the chain-propagating step, terminated by two types of reactions, C3H5·+H→ C3H6 and C3H5· + CH3·→1-C4H8. The formation of allene-methylacetylene has been satisfactorily explained by considering secondary reactions.
Isomerization of cis-Azobenzene in the Solid PhaseTsuda, Morizo; Kuratani, Kenji
doi: 10.1246/bcsj.37.1284pmid: N/A
The thermal and photo-isomerizations of crystalline cis-azobenzene have been studied by infrared spectrophotometry in the temperature range of 36∼58°C, It has been found that the thermal isomerization follows Prout Tompkins’ law, and the values of k3 at 36, 50 and 58°C have been estimated. The Arrhenius plot of K3 is linear, and the activation energy of k3 is 31.3±0.3 kcal./mol. Pre-irradiation with a mercury lamp shortens the induction period, but it does not change the value of k3. On the other hand, the value of k3 is affected by the degree of grinding of azobenzene crystals. In this case, the activation energy is not altered by crystal grinding.The photo-isomerization at 12°C, in contrast to the case of thermal isomerization, has no induction period. However, the trans→cis photo-isomerization does not occur even if the crystal is treated by X-ray or by γ-ray preirradiation.