Benzaldehyde pyrolysis

FIGURE 8.9 The optimized structures of all reactants, intermediates, transition states, and products during benzaldehyde pyrolysis. 

FIGURE 8.11 Energy profile of the stationary points for benzaldehyde pyrolysis reaction. 

TABLE 8.1 The Activation Enthalpy, Activation Entropy, Activation Energy, and Rate Constant of Every Step Dnring Benzoic Acid and Benzaldehyde Pyrolysis... 

S. Phenyldiazomethane (Vacuum pynolyzxa method). In a 200-mL, singlenecked, round-bottomed flask is placed 13.71 g (0.05 mol) of benzaldehyde tosylhydrazone. A 1.0 M solution (51 mL) of sodium methoxide in methanol (0.051 mol) (Note 2) is added via syringe and the mixture is swirled until dissolution is complete (Note 3). The methanol is then removed by rotary evaporator. The last traces of methanol are removed by evacuation of the flask at 0.1 mm for 2 hr. The solid tosylhydrazone salt is broken up with a spatula and the flask is fitted with a vacuum take-off adaptor and a 50-mL receiver flask. The system is evacuated at 0.1 nm and the receiver flask is cooled in a dry ice-acetone bath to about -50°C. The flask containing the salt is immersed in an oil bath and the temperature is raised to 90°C (use a safety shield). At this temperature, red phenyldiazomethane first begins to collect in the receiver flask. The temperature is raised to 220°C over a 1-hr period (Note 4). During this time red phenyldiazomethane collects in the receiver flask (Note 5). The pressure increases to 0.35 mm over the course of the pyrolysis. On completion of the pyrolysis the pressure drops to less than 0.1 mm. 

Phenyldiazomethane, 1, 834. A new method for preparation of this (and other aryl-diazomethanes) involves a vacuum pyrolysis of the sodium salt of benzaldehyde tosylhydrazone, a method introduced for carrying out the Bamford-Stevens reaction. The yield is 80%, the highest yield yet reported. Another advantage is that the reagent is obtained free from solvents. The pyrolysis can also be coitducted in ethylene glycol at 80° with extraction of the aryldiazomethane into hexane.1 Caution All diazo compounds arc highly toxic and potentially explosive. 

A unimolecular elimination involving a semi-polar five-membered cyclic transition state (81) (Scheme 9, R1 = Ph, R2 = R3 = H) appears to account for the formation of benzaldehyde, CO, and H2O on eliminative fragmentation of mandelic acid in the gas phase.44 The same type of transition state has been proposed for gas-phase pyrolysis of ROCH2COOH (R = MeO, EtO, and Ph O) with corresponding formation of ROH, CO, and formaldehyde the rate of reaction is little dependent on R.45... 

Remarkably enough, epoxide 30 was identified among the products of the photolysis of 25 in benzene/benzaldehyde. This seems to be the only reported case where carbene 3c has been intercepted. Pyrolysis of 25 in a nitrogen flow at 400 °C or vacuum pyrolysis at 500 °C led to the same product pattern as the photolysis. Copyrolysis with benzaldehyde or butadiene gave only trapping products of the silene intermediate41. 

The first report about the possible formation of a short-lived 2-silaallene dated back to 1978. Bertrand and coworkers found as products from the pyrolysis of the silaspirocycle 652 in the presence of benzaldehyde, silica and styrene 653 as major products294. They suggested that 2-silaallene 605 is a possible intermediate in this reaction which can account... 

The reaction of BPA in water at 386°C and pr = 0.8 is summarized in Figure 1 and led to benzyl alcohol and benzaldehyde as well as the neat pyrolysis products. BPA conversion was approximately 0.8 after 40 min. Aniline was the major product with a yield of 0.5 after 40 min. Toluene, a primary and major product of neat pyrolysis, had a yield near 0.2. This was roughly equal to the yield of benzyl alcohol, which had a maximum value of 0.15 at 30 min the yield of benzyl alcohol decreased after 30 min. The reduced yield of toluene relative to neat pyrolysis and the presence of benzyl alcohol indicate that water reacted with BPA. 

The reaction of BPA in supercritical methanol at 340°C and pr = 0.5 is summarized in Figure 3 and led to N-methylaniline as a major product. Benzaldehyde and benzyl alcohol were observed in yields less than 0.1. The yield of toluene was 0.56, roughly equivalent to that observed from neat pyrolysis, whereas the aniline yield was approximately 0.1, substantially reduced from that observed in the neat case. The yield of N-methylaniline surpassed that of aniline, as a value of 0.4 was attained after 120 min. Reaction in 13C-labeled methanol showed the label to reside on the methyl group in the N-methylani1ine product, definitively indicating that methanol reacted with BPA. 

Flash vacuum pyrolysis of the dibenzodioxocine 6 was reported to give the 2-(2 -hydroxybenzyl)benzaldehyde 178 (Equation 39), presumably via the intermediate diradical formation <1995JOC8410>. 

A convenient conversion of homopiperazine into the 1-methyl derivative involves reductive methylation with formaldehyde and a Raney nickel catalyst.199-199a A small amount of the 1,4-dimethyl derivative is also obtained in this reaction. Use of benzaldehyde with homopiperazine gave 177 which was hydrolyzed to starting materials with hydrochloric acid.199 Pyrolysis of the dihydrobromide of 148 (R = H, R = CH2CH2Br) gave 178, 179, homopiperazine, and piperazine.140... 

Noteworthily, at a contact time of 0.2 seconds, only 5 percent of the furfural decomposes at 660 °C. At such elevated temperatures, furfural decomposes to furan and carbon monoxide, in complete analogy to benzaldehyde which decomposes to benzene and carbon monoxide. The best conditions for the production of furan by pyrolysis of furfural were found to be 725 °C and a contact time of five seconds. Such a process gives a furan yield of 16.5 percent. 

Other variations of the condensation reaction are utilized, such as condensation of a phenol, a substituted benzaldehyde, and formaldehyde. Pyrolysis studies on ion exchange resins are common in literature [21-25]. Depending on the nature of the attached group, as well as on the proportion of the polymer that is derivatized, pyrolysis products originating from these groups can be seen in pyrolysates. 

C. Ruff, K. Hor, B. Weckerle, P. Schreier, T. Konig (2000) H/ H ratio analysis of flavor compounds by on-line gas chromatography pyrolysis isotope ratio mass spectrometry (HRGC-P-IRMS) Benzaldehyde. J. High Resol. Chromatogr. 23, 357-358... 

In contrast, the synthesis of cycloproparenes monosubstituted at Cl by this route failed. For example, pyrolysis of the adduct derived from ll-niethyl-1,6-methano[10]annulene resulted in formation of styrene, while that from the 11-bromo and 11-cyano derivatives gave only polymeric material. Similarly, only benzaldehyde was isolated upon pyrolysis of the adduct 2 of ll-fluoro-l,6-methano[10]annulenc with acetylenedicarboxylate. Benzaldehyde is the expected hydrolysis product of 1-fluorobenzocyclopropene. 

A new preparative synthesis of 2-arylquinazolin-4(3//)-ones, which was reported recently, involved the pyrolysis of Schiff bases derived from 3-amino-l,2,3-benzotriazin-4-one in paraffin oil at 300 C, or in boiling 1-methylnaphthalene. The yields were as high as 86-100% but failed entirely when p-HO-, P-O2N-, and p-Me2N-benzaldehyde, furfural, and pyridine-2-aldehyde were used. The mechanism in Eq. (5) was proposed although the... 

Flash vacuum pyrolysis of 5-phenoxytetrazole (140) took a different course one path leading to 2-aminobenzoxazole (90%) indicates the formation of the imidoylnitrene 141 the other path, giving benzaldehyde in 10% yield, involves the expulsion of two moles of nitrogen. This could occur via phenoxydiazomethane (142) and phenoxycarbene (Scheme 26).187... 

Another attractive feature of the phosphonamide route is that it can be controlled to give cis- and trans-olefins.4 Formation of the adduct is not stereospecific, but the elimination reaction is stereospecific (cis cycloelimination). The synthesis of cis- and trans-1 -phenylpropene is illustrative the former was prepared from the reaction of benzaldehyde with the a-lithio derivative of ethylphosphonic acid bis(dimethyl-amide) to give two diastereoisomeric /3-hydroxyphosphonamides (5) in the ratio of 3.5 1. The major isomer was separated by crystallization and on pyrolysis gave cis-1 -phenylpropene. The isomeric olefin was prepared by reaction of the a-lithio... 

Figure 4.24 Products bearing heteroatoms (N, O, Cl) formed in the ASR pyrolysis at different temperatures 98 propylene nitrile (1), pyridine (2), chlorobenzene (3),phenol (4), benzaldehyde (5), benzonitrile (6), benzeneacetonitrile (7). (Reprinted from J. Anal. Appl. Pyrol., 40-41, R. Rausa and P. Pollesel, page 383. 1997, with permission from Elsevier Science)...

The addition of benzaldehyde to a pyrolysis reaction stream presumably containing tetramethyldisilene gives products believed to be derived from a disiloxetane by a thermal 2 + 2 cleavage to silene and a silanone1 33. 

Cyanopyrazine reacts with cyclopropyllithium to give pyrazinyl cyclopropyl ketone <91JHC1147>. Benzoyl pyrazine is formed by oxidative decyanation of a-pyrazinyl-a-phenylacetonitrile under phase-transfer catalytic conditions <87JHC1061 >. (2-Hydroxy-2-phenylethyl)pyrazines undergo retro-ene reaction on pyrolysis to yield methylpyrazines and benzaldehyde quantitatively <87JOC397i>. 

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