Pyrolysis mechanisms furan

The general pyrolysis mechanisms of polysaccharides have been determined from model studies on cellulose and involve the splitting of the polysaccharide structure by three basic chemical reaction mechanisms dehydration, retroaldolization, and decarboxylation. Using these basic pyrolysis mechanisms, it is possible to explain the pyrolysis of polysaccharides and evolved pyrolysis products. The hexose degradation pathway for cellulose results in formation of furan- and pyran-type fragments and smaller acyclic aldehyde and ketone fragments. ... 

Due to the existence of five-membered furan rings in low-rank coals [49], the pyrolysis mechanism of furan has become the subject of several experimental studies [50-52]. Recently, some detailed theoretical studies have been carried out to understand the formation processes of CO, C3H4 (propyne and aUene), ketene, acetylene, and so on. 

SimUar [4 + 4] dimers have been reported during the flash vacuum pyrolysis of 2-methyl-3-furylme-thyl benzoate in which 4//,5//,9//,l(iF/-cycloocta[l,2-b 6,5-b difuran (117) is produced in virtually quantative yield.A stepwise mechanism has been forwarded to rationalize the high-yield formation of the corresponding head-to-head [4 + 4] dimer.Other examples of the [4 -h 4] dimerization of 2,3-di-methylene furan and 2,3-dimeAylene thiophene have been reported as well. 

A modified mechanism for the formation of the cycloheptafuranone (83) by pyrolysis of phenyl propiolate (82) has been proposed.The action of copper(I) phenylacetylide on the azulene ester (84) leads to the azuleno[2,l-Zi]furan(85). 2 ... 

The pyrolysis of (5-sultones with two double bonds forms a general synthetic route to substituted furans (equation 73)". De Mayo and his coworkers have shown that photolysis of unsaturated sultones in the presence of nucleophiles100101 produces the corresponding ketosulphonic acid derivatives (equation 74). A general mechanism was... 

Table II presents the quantitative results of those components volatile enough for GC analysis. At low pH the furan compounds predominate when both glucose and xylose are exposed to 300 C. This is not unexpected since all pentoses form 2-furaldehyde(2) in high yield when exposed to aqueous acid solution( ). However, the presence of 2 in the glucose reaction mixture is of interest. The major product obtained from hexoses at elevated temperatures and aqueous acid is 5-hydroxymethyl-2-furaldehyde(1) with minor amounts of 2-(hydroxyacetyl)furan(15). The 2-furaldehyde has been detected after acidic treatment of fructose(1 ), glucose(15,17), and is a major component after the thermolysis of cellulose in distilled water( ). One plausible explanation for the formation of 2 may involve loss of formaldehyde(18) from glucose with consequent pentose formation. It should be noted that the pyrolysis of 1 does produce a small amount of 2( ). However, the reaction conditions are sufficiently different to suggest a different mechanism for hydrothermolysis.

FIGURE 8.4 The formation mechanism of CO via furan pyrolysis proposed by Organ and Mackie. 

FIGURE 8.5 The feasible formation mechanism of CO during furan pyrolysis. 

In the synthesis of methylenecyclobutenones (328 R = H) by pyrolysis of the furan (327 R = H) reported earlier, a likely mechanism was considered to be generation and rearrangement of 2-furylcarbene. This leads to the prediction that the dideu-terio-ester (327 R = D) will give a monodeuterio product, but the dideuterio product... 

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