Pyrolytic reactions

Essential Oils. Essential oils are produced by distillation of flowers, leaves, stems, wood, herbs, roots, etc. Distillations can be done directly or with steam. The technique used depends mosdy on the desired constituents of the starting material. Particular care must be taken in such operations so that undesired odors are not introduced as a result of pyrolytic reactions. This is a unique aspect of distillation processing in the flavor and fragrance industry. In some cases, essential oils are obtained by direct expression of certain fmits, particular of the citms family. These materials maybe used as such or as distillation fractions from them (see Oils, essential). 

Another example of this is the loss of acetic acid when delphinine is heated in hydrogen at 200-215°. Just as aconitine is so converted into pyraconitine so delphinine yields pyrodelphinine, C3 H4 0,N, m.p. 208-212°, and similarly a-oxodelphinine, C33H430j qN, under like treatment loses acetic acid and yields pyro-a-oxodelphinine, C3 H3gOgN, which crystallises from methyl alcohol in needles, m.p. 248-250°, after sintering at 238°. This, on hydrogenation, forms a hexahydro-derivative, m.p. 183-5°, presumably by saturation of the benzoyl radical, which therefore leaves unexplained the mechanism by which acetic acid is lost in this pyrolytic reaction (c/. pyropseudaconitine, p. 683). 

Elimination reactions of fluorine compounds are not limited to the removal of simple molecules Frequently, large molecules or combination of smaller ones are formed as by-products, especially in pyrolytic reactions For example perhalo genated acid chlorides lose not only carbon monoxide but also chlorine fluoride [106, 107] (equations 74 and 75)... 

Methane is unique among hydrocarbons in being thermodynamically stable with respect to its elements. It follows that pyrolytic reactions to convert it to other hydrocarbons are energetically unfavourable and will be strongly equilibrium-limited. This is in marked contrast to the boranes where mild thermolysis of B2H6 or B4H10, for example, readily yields mixtures of the higher boranes (p. 164). Vast natural reserves of CH4 gas exist but much is wasted... 

Pyrolytic elimination from isoindoline A -oxides also affords iso-indoles, but yields were found to be generally lower than those obtained by Kreher and Seubert s procedure. The considerable amount of polymeric material formed in the pyrolytic reaction makes isolation of the isoindole difficult, but a convenient method for separation of the product was found utilizing complex formation with 1,3,5 -trin i tro benzene. 

The preparation of 2,3,7,8-tetrachlorodibenzo-p-dioxin by chlorination of 2,7-dichlorodibenzo-p-dioxin yields a product containing significant quantities of trichloro- and pentachlorodibenzo-p-dioxins (11). Such mixtures are not amenable to separation on a preparative scale. Although 2,3,7,8-tetrachlorodibenzo-p-dioxin has been prepared by the pyrolytic condensation of sodium 2,4,5-trichlorophenate, this method is undesirable for preparation of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the gram scale (2, 12). The pyrolytic reaction is difficult to control and the potential danger is enhanced by the product s toxicity. The salt was dissolved in bEEE [bis(2-ethoxyethyl) ether, bp 189°-190°C] and refluxed for 15 hours with the Ullmann catalyst. The desired product was obtained in 39% yield by condensation of potassium 2,4,5-trichlorophenate (Reaction 3). 

One of the reasons for the slow development of selenophene chemistry was the lack of convenient procedures for obtaining selenophene, its homologs, and derivatives. However, Gronowitz et al.42 have reported a semilarge-scale synthesis of selenophene (10), which gives about 150-200 g ( 58% yield) of selenophene per day. The procedure is a pyrolytic reaction... 

The more active cobalt catalyst for pyrolytic reactions was prepared by microwave calcination of cobalt nitrate which was converted to cobalt oxide by rapid microwave heating [7]. 

Bell, J., and R. I. Reed Isotopic Tracer Studies of Pyrolytic Reactions. 

Both 1st- and 2nd-order rate expressions gave statistically good fits for the control samples, while the treated samples were statistically best analyzed by 2nd-order kinetics. The rate constants, lst-order activation parameters, and char/residue yields for the untreated samples were related to cellulose crystallinity. In addition, AS+ values for the control samples suggested that the pyrolytic reaction proceeds through an ordered transition state. The mass loss rates and activation parameters for the phosphoric acid-treated samples implied that the mass loss mechanism was different from that for the control untreated samples. The higher rates of mass loss and... 

Synthesis of (Z)-(lR)-tranH-Norchrysanthemic Acid by Pyrolytic Reaction of Chrysanthemum Dicaroboxylic Acid Monomethyl Ester with a New Catalyst... 

In the absence of air and moisture, the polyimide degrades through a pyrolytic reaction. Since radical-initiated oxidation can be catalyzed by the presence of transition metals, the nature of the substrate will have a profound effect on the thermal life of the film in air. 

As expected the weight loss in N2 is much less than in air. This is consistant with the expectation that the pyrolytic reaction of polyimide should have a much higher activation energy than the radical-initiated oxidation. It is noted that the loss on wafer at 500°C in air appear to be much more than those of thick films obtained previously. 

Recently, evidence in support of the likely existence of diradicals in the aforementioned pyrolytic reactions has been provided by the thermal transformation of the isotopically and stere-ochemically labeled [jp -7-2H3]methyl-a-pinene (28) at 256.7 °C. The resulting hydrogen transfer product 30 and the cycloreversion product 31 are both obtained, presumably via the geometrically defined intermediate diradical 29.110... 

The presence of a considerable proportion of methylated bodies in low temperature tar and its origin must be explained. The fact that the yield of methane remains largely the same even when tar formation is completely inhibited would indicate that the methyl groups of coal possibly do not participate in forming the methylated bodies in tar. It is not unlikely, therefore, that such methylated bodies in tar are synthesized during pyrolytic reaction of the hydroaromatic structure (via methylenes). 

Knox, Norrish, and Porter (38, 56), using their technique of flash photolysis/ whereby a substance is suddenly raised to high temperature by a very intense light flash and the resulting pyrolytic reactions observed spectroscopically, clearly observed acetylene as an intermediate in the formation of carbon by flash photolysis and pyrolysis of ketene. MacCormac and Townend (47) found acetylene in cool flames of ether and oxygen, with 50 mole % ether and temperatures in the range of 320° to 395° C. 

The pyrolytic reactions of pentafluorophenyl and heptafluoro-2-naphthyl propargyl ethers give product mixtures containing benzo- and naphtho[6]furan derivatives, resulting from initial Claisen rearrangement followed by further intra- and intermolecular reactions.31 34... 

Polyfluoroparafins, fluorocarbons, and other perfluoro denvatives show remarkable heat stability They are usually stable at temperatures below 300 °C Thermal decomposition at 500-800 °C, however, causes all possible splits in the molecules and produces complex mixtures that are difficult to separate For preparative purposes, only pyrolyses that do not yield complicated mixtures of products are of interest [7] The pyrolytic reactions of polyfluoro and perfluoro derivatives, when carried out at 500-1100 °C, represent the most useful route to preparative generation of perfluoroolefins on the laboratory scale [7]... 

Although the majority of studies in this area involve five-membered ring cyclic anhydrides, a few pyrolytic reactions involving acyclic anhydrides have been reported. Thus, for example, FVP of 278 gives the alkylideneketene 279 with loss of trifluoroacetic acid142, while at 650 °C 280 loses both trifluoroacetic acid and cyclopentadiene to afford the indenylideneketene 281, which cyclizes by way of 282 to give 283143. FVP of... 

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