Propene from pyrolysis

Subsequently, Chickos examined the pyrolysis of cis-anti- and trans-1,2-dimethyl-cw-3,4-dideuteriocyclobutane at 510°C in a flow system. The cis-anti-cis isomer undergoes fragmentation to cis- and ra/z -propene-Ji in a 1.5 1 ratio, while the ratio of the trans- to cw-propenes from the trans-cis isomer is 1 1 at conversions of 26 and 56 %, respectively (Scheme 5.24). The Principle of Conservation of Orbital Symmetry predicts that the retro 2 + 2 reaction should proceed in a + a fashion if it were a concerted process. If this were the case, then the propylene formed from the cis-anti-cis isomer should have been exactly a 1 1 mixture of deuterium isomers. The fact that it is not a 1 1 mixture rules out concert as the sole reaction pathway initiated by cleavage of the more substituted bond. 

The kinetics of the thermal decomposition of 1,1,1-trifluoroacetone have been studied, both in the presence and absence of foreign gases (e.g., nitric oxide, propene, perfluoropropene). The following reactions were written to account for the predominant products from pyrolysis of the ketone alone at 547 °C and initial pressure 106 mmHg ... 

Above 300°C. the effective reaction of an alkyl radical with oxygen may be Reaction 3 rather than 2 because of the reversibility of Reaction 2. If it is assumed that Reaction 3 is important at about 450°C., its rate can be estimated from the competition between pyrolysis and oxidation of alkyl radicals. Falconer and Knox (21) observed that the ratio of (pro-pene)/(ethylene) from the oxidation of propane between 435° and 475°C. increased with oxygen concentration and decreased with temperature—the apparent activation energy difference for the two reactions forming the olefins being 27 =t 5 kcal. per mole. They interpreted this result in terms of a competition between Reactions 1 and 3. The observed ratio (propene)/(ethylene) was 3.5 at 435°C. and 10 mm. of Hg pressure. If log ki(propyl) = 13.2 — 30,000/2.30RT, the value for the n-propyl radical (34), then log k3 = 8.0. If the A factor is 109-3, we derive the Arrhenius equation... 

The list of pyrolysis products of cottonwood shown in Table VII (llj reflects the summation of the pyrolysis products of its three major components. The higher yields of acetone, propenal, methanol, acetic acid, CO, water and char from cottonwood, as compared to those obtained from cellulose and xylan, are likely attributed to lignin pyrolysis. Other results are similar to those obtained from the pyrolysis of cell-wall polysaccharides. This further verifies that there is no significant interaction among the three major components during the thermal degradation of wood. 

In connection with the methoxy participation, the gas-phase pyrolytic elimination of 4-chloro-1 -butanol was investigated177. The products are tetrahydrofuran, propene, formaldehyde and HCl. It is implied that the OH group provides anchimeric assistance from the fact that, besides formation of the normal unstable dehydrochlorinated intermediate 3-buten-l-ol, a ring-closed product, tetrahydrofuran, was also obtained. The higher rate of chlorobutanol pyrolysis with respect to chlorethanol and ethyl chloride (Table 27) confirmed the participation of the OH group through a five-membered ring in the transition state. 

Acetonitrile oxide was generated from 3,4-dimethylfuroxan oxide by flash vacuum pyrolysis and trapped at -40 °C where its and 13C NMR spectra were examined. Warming to room temperature in the presence of propene produced 3,5-dimethyl-2-isoxazoline (Scheme 108) (79TL2443). The oxide could also be generated by photolysis of furoxan (68CC977). 

The procedure described is essentially the same as that of Buck-ley and Scaife.3 The yield has been increased from 55.5% up to 72% by using 1.3 mol eq of phthalic anhydride and by carefully controlling the pressure and cooling the receiving flask. Although 2-nitropropene has previously been prepared by pyrolysis of 2-nitro-1-propyl benzoate in 72% overall yield from 2-nitro-l-propanol,4 the present method is preferred for its preparation since the procedure is much simpler and the product is directly obtainable from 2-nitro-l-propanol without first preparing its ester. It is also applicable to the preparation of 1-nitro-l-propene (58%),5-6 2-nitro-1 -butene (82%),7 and 2-nitro-2-butene (60%).6,7 In general, aliphatic nitroolefins have the tendency to polymerize readily with alkali. 

From the molecular beam MS of the pyrolysis products of the P/N fractions, a number of phenolic compounds were detected guaiacol (2-methoxyphenol) (m/z 124), catechols (m/z 110), isomers of substituted 2-methoxyphenols with alkyl groups such as methyl (m/z 138), vinyl (m/z 150), 3-hydroxy-propen(l)-yl (m/z 180), allyl (m/z 164), hydroxyethyl (m/z 168), and ethyl (152), most likely in the para position. In addition, a few carbohydrate-derived components are also present in this fraction such as furfuryl alcohol and other furfural derivatives. 

Biacetyl has often been used for sensitizing the pyrolysis of organic compounds" . Radicals, resulting from the thermal decomposition of biacetyl, initiate the chain decomposition of such substances. However, NO causes no inhibition of notable significance in such systems . Nevertheless, this cannot be considered as an evidence against the occurrence of chains, since the sensitized decompositions are definitely inhibited by, for instance, propene . 

Pyrolysis of the formed polysilazane at 750° C generates several alkylsilanes such as dimethylsilane, trimethylsilane, ethyldimethylsilane, tetramethyidisiloxane, pentamethyidisiloxane, methylenebisdimethylsilane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, etc. The presence of the cyclic compounds similar to those from poly(dimethylsiloxane) was an indication that some polysiloxane sequences may be present in the polymer. Thermal degradation studied between 350° C and 650° C showed the formation of some hydrogen, methane, ethane, and propene. 

Coming back to the a(C-C)/(3(C-H) primary split ratio (Table 3), it would be valuable to compare these values with that obtained either in the thermal pyrolysis of propene or in chemical activated systems. For example, in shock tube experiments (1650-2300 K), the dominant bimolecular initiation reaction leads to the C-C bond rupture, although a possible contribution of the 3(C-H) bond rupture cannot be excluded (50). This is also observed in the decomposition of hot propene formed from ethylcarbene f(E)(C3H ) s 414 kJ/mol] a(C-C)/ P(C-H) = 22 (51). Conversely, hot propene formed by the addition of singlet methylene to ethylene [(EXCsH ) s 464—492 kJ/mol) gives rise to C-H bond... 

From mixed plastics, the formation of ethene, methane and hydrogen increase with temperature but the formation of propene and higher hydrocarbons decreases. Whether the isolation of olefins can compete economically with the oil cracking process remains to be seen, but the total hydrocarbon pyrolysate is similar to naphtha, the feedstock for petrochemicals production. It should be noted that because pyrolysis is primarily a non-oxidative process carried out under carefully controlled conditions, the possibility of dioxin formation is much reduced. In 1995 about 100 kT of mixed plastics wastes were converted into chemical feedstocks in Europe by pyrolysis, and this is expected to increase at the expense of incineration over the next ten years. 

Although crotonic acid, or 2-pentenoic acid from HV comonomer, is the main decomposition product from the biopolymers at low temperature, other degradation products appear under high-temperature pyrolysis conditions. For PHB homopolymer these include propene and carbon dioxide from the breakdown of crotonic acid itself, isocrotonic acid from the obvious reorganization reaction and /3-butyrolactone as a short-lived intermediate that spontaneously decomposes by 0-alkyl scission to propene and carbon dioxide or by O-acyl scission to acetaldehyde and ketene. Similar reactions can be proposed for the comonomer decomposition and some pyrolysis experiments have already been reported. ... 

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