Pyrolysis, flash products

The first isolated 3//-phosphole, namely 3//-phosphaindene 50, was obtained as a 1 1 mixture with its hydration product 51 by gas-phase pyrolysis (flash vacuum pyrolysis, FVP) over a solid base (Scheme 7) <1999TL5271>. The hindered P=G bond of compound 50 is unreactive. 

Fig. 10. Liquid-fuel production by flash pyrolysis usiag char recycle.

Thermochemical Liquefaction. Most of the research done since 1970 on the direct thermochemical Hquefaction of biomass has been concentrated on the use of various pyrolytic techniques for the production of Hquid fuels and fuel components (96,112,125,166,167). Some of the techniques investigated are entrained-flow pyrolysis, vacuum pyrolysis, rapid and flash pyrolysis, ultrafast pyrolysis in vortex reactors, fluid-bed pyrolysis, low temperature pyrolysis at long reaction times, and updraft fixed-bed pyrolysis. Other research has been done to develop low cost, upgrading methods to convert the complex mixtures formed on pyrolysis of biomass to high quaHty transportation fuels, and to study Hquefaction at high pressures via solvolysis, steam—water treatment, catalytic hydrotreatment, and noncatalytic and catalytic treatment in aqueous systems. 

Table 4. Product Distribution for the Occidental Flash Pyrolysis Process...

The addition of phthalimidylnitrene (374) to simple alkynes affords 1-azirines in yields of 1-15% (Scheme 10). In this reaction, which is of no real preparative value, the symmetrical 2-azirines (375) were suggested as the most plausible intermediates and unequivocal proof of the existence of such species was demonstrated from a series of 1,2,3-triazole pyrolysis reactions <71CC1518). Extrusion of nitrogen from the regioisomeric 4,5-disubstituted 1,2,3-triazoles (376) during flash vacuum pyrolysis furnished identical product mixtures which included both regioisomeric 1-azirines (377). 

The 5-substituted 1,3-dioxolan-4-one 23 is readily deprotonated at the 5 position and can be alkylated with a variety of alkyl halides. The resulting products 24 decompose upon flash vacuum pyrolysis (FVP) at 600°C with loss of acetone... 

The first and to date only synthesis of the parent system 2 uses a flash-vacuum pyrolysis (FVP) of 7,8-diazapentacyclo[4.2.2.02-5.03 9.04 10]dec-7-ene (diazabasketene, 1). After condensation at -196 °C, the pyrolysis product is distilled in vacuum to give pure azocine in ca. 60% yield.12... 

The combination of the flash vacuum pyrolysis (FVP) technique169 with mass spectrometry proved to be particularly useful in identification and characterization of both the fragmentation/rearrangement patterns, intermediates and/or final products formed (see Section IV.E.l). Usually, no structures are indicated in the mass spectra, although ionization and appearance potential can, in principle, provide structural information. 

In the case of flash vacuum pyrolysis, the reaction may be of some synthetic utility. For example, at 700 °C diphenyl sulphoxide produces diphenyl thiosulphonate in 40% yield, however, several other products are also formed. 

In contrast to this behavior stabilized sulfonyl ylides 125 lose PhjP under flash vacuum pyrolysis conditions to give sulfonyl carbenes 127 which evolve to the formation of various products among which the alkenes 129, observed in all the cases (Scheme 35) [129]. 

Barton and co-workers" performed flash vacuum pyrolysis (FVP) on trimethyl-silylvinylmethylchlorosilane (30), resulting in the production of trimethylchlorosi-lane (30%), trimethylvinylsilane (11.5%), and most interestingly, ethynylmethyl-silane (34, 11.9%). A proposed mechanism for the synthesis of 34 (Scheme 10) begins with the lo.ss of trimethylchlorosilane to form silylene 31, which can rearrange either to silaallene 32 or to silirene 33, both of which can lead to the isolated ethynylsilane. 

Starting from 27, cyclo-Cig was prepared in the gas phase by laser flash heating and the neutral product, formed by stepwise elimination of three anthracene molecules in retro-Diels-Alder reactions, was detected by resonant two-photon-ionization time-of-flight mass spectrometry [23]. However, all attempts to prepare macroscopic quantities of the cyclocarbon by flash vacuum pyrolysis using solvent-assisted sublimation [50] only afforded anthracene and polymeric material. 

Authors have proposed a novel process not to dispose to landfill sites both waste PVC and waste glass but to utilize them to produce fuel and neutralize each other at the same moment. It has been successfully demonstrated that hydrogen chloride produced during flash pyrolysis of PVC was completely neutralized by the fixed glass bed and thus chlorine-lree fuel was produced [1-2]. To carry forward our proposed process we need to know the kinetics of the neutralization process. Also we have to solve the problem of formation of metal chlorides in the product char during pyrolysis of PVC, which is a critical issue for its thermal utilization. Consequently, in the present study the evaluations of neutralization kinetics of glass cullets and the decomposition of CaCl2 in char by steam were conducted. 

A few routes to new silenes, usually involving flash vacuum pyrolysis at high temperatures, have been reported. Silenes were proposed as the result of the thermal expulsion of trimethylmethoxysilane, or a similar volatile fragment, from the starting material but frequently, proof that the silenes proposed to account for the observed products were in fact formed was not provided.116 119 The other thermal route employed was the retro-Diels-Alder regeneration of a silene from an adduct with an aromatic compound—often a 9,10-anthracene or 1,4-naphthalene adduct or, in some cases, a 1,4-benzene adduct, as illustrated in Eq. (19).120... 

Deyerl and co-workers have also studied the photodissociation of the jet-cooled allyl radical produced in a flash pyrolysis source.148,149 The allyl radical is excited near 250 nm and H-atom product is detected by... 

Flash vacuum pyrolysis (FVP) of the 3-(iV-(pyrimidin-2-yl)imino-l-morpholino)propanoate 179 led to pyrimido-pytimidines 182 and 184, as a result of competition between thermal loss of ethanol or morpholine. The ketenimine 181, being unable to undergo cyclization, underwent [l,3]-ethoxy migration to form 183, leading to 184 (Scheme 28). The ratio of the products was studied on variation of the temperature (400, 530, and 600 °C) and the nature of the amino substiuent (NR1R2 = morpholino, pyrrolidino, N(Me)Ph ) <2004AJC577>. 

Pederson and co-workers investigated the thermal behavior of 1,6,6aA4-trithiapentalene and some methyl-substituted derivatives using flash vacuum pyrolysis (FVP). The main products of the fragmentation, following loss of CS and/or CH2=C=S, were shown to be thiophene-3-thiones, or the thiol tautomers <1997J(P2)1261>. 

J. Piskorz, P. Majerski, D. Radlein, A. Vladars-Usas, and D. S. Scott, Flash pyrolysis of cellulose for production of anhydro-oligomers, J. Anal. Appl. Pyrol., 56 (2000) 145-166. 

Methylene cyclopropene (5), the simplest triafulvene, is predicted to be of very low stability. From different MO calculations5 it has been estimated to possess only minor resonance stabilization ranging to 1 j3. Its high index of free valency4 at the exocyclic carbon atom causes an extreme tendency to polymerize, a process favored additionally by release of strain. Thus it is not surprising that only one attempt to prepare this elusive C4H4-hydrocarbon can be found in the literature. Photolysis and flash vacuum pyrolysis of cis-l-methylene-cyclopropene-2,3-dicarboxylic anhydride (58), however, did not yield methylene cyclopropene, but only vinyl acetylene as its (formal) product of isomerization in addition to small amounts of acetylene and methyl acetylene65 ... 

Flash vacuum pyrolysis of methyl imidazol-2-yl carboxylate 290 at 750°C gave 20% yield of 268 via the corresponding ketene 291. Similar pyrolysis of methyl imidazol-l-yl carboxylate 292 gave 20% of a 1 1 2 mixture of compounds 267,268, and 296. This fact can be rationalized by the pathway depicted in Scheme 71. Ketenes 291 and 295 may be intermediates formed from 293 and 294, respectively. They are products of rearrangement of 292. Similar pyrolysis of 4-imidazole carboxylic acid anilide performed at 800°C gave 267 in 20% yield (86JOC306). 

Online coupling of flash-vacuum pyrolysis and mass spectrometry was applied to 3,4-dicyano-l,2,5-oxadiazole-2-oxide (dicyanofuroxan). The 1,2,5-oxadiazole is almost quantitatively pyrolyzed at 500-600 °C. Using collisional activation, the main pyrolysis products were identified as NCCNO and (CN)2 <1997BSB545>. 

S-37 (see above) it is also possible to prepare and to matrix-isolate the silicon species 124, 125, and 126, which again exist in a photoequilibrium. Our first entry to 1-silacyclopropenylidene (124) was the pulsed flash pyrolysis of 2-ethynyl-l,l,l-trimethyldisilane (123).71,72 Even though the structure of educt molecule 123 suggests formation of ethynylsilylene (125), the isolated product was 124. Obviously 125 had already thermally isomerized to the most stable isomer 124 before the products were condensed at 10 K. 

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