Pyrolytic Methods

Natural black (human hair, bovine eyes) and synthetic tyrosine-, dopa-, dopamine-melanins were investigated by Curie point pyrolysis- 

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A novel pyrolytic method of generating nitrile ylides in situ was reported by Burger [44] (equation 45) Such nitrile ylides react with various dipolarophiles alkynes [44] (equation 46), nitriles [45] (equation 47), dimethyl azodicarboxylate [45], aldehydes [45], and nitroso compounds [46]... 

R. F. C. Brown, Pyrolytic Methods in Organic Chemistry, Academic Press, New York, 1980. 

For a summary of methods of radical formation, see Giese, B. Radicals in Organic Synthesis Formation of Carbon-Carbon Bonds Pergamon Elmsford, NY, 1986, p. 267. For a review on formation of free radicals by thermal cleavage, see Brown, R.F.C. Pyrolytic Methods in Organic Chemistry Academic Press NY, 1980, p. 44. 

Khan [181] has described a method for determining Paraquat and Diquat in soils involving catalytic dehydrogenation of the herbicide followed by gas chromatography and also a pyrolytic method [182]. 

The pyrolytic method was first used to establish the chirality at sulfur in steroidal sulfoxide derivatives of 5a-cholestane (199). It was found that behavior of the diastereomeric sulfoxides 190, derivatives of 4/3-phenylsulfinyl-5a-cholestane having opposite configurations at sulfur, is quite different when the compounds are heated in boiling benzene. One of them, 190a, undergoes complete decomposition, affording 5a-cholest-3-ene 191, but the second diastereomer is quite inert under these conditions. 

The propene split-off route to generate intermediates is well-established, cf. Brown, R.F.C. "Pyrolytic Methods in Organic Chemistry" Academic Press New York 1980. It has been applied by our group to prepare e.g. silatoluene (Bock, H. Bowling, R.A. Solouki, B. Barton, T.J. Burns, G.T. J. 7 m. Chem. Soc. 1980, 102, 429), silabenzene (Solouki, B. Rosmus, P. Bock, H. Maier, G. Angew. Chem. 1980, 2, 56 Angew. Chem. Int. Ed. 

A few pyrolytic methods of synthesis are known, leading directly to the formation of pyridine rings by formation of the /3, y-bond. Alkylpyridines are obtained when unsaturated imines (116) or (117) are passed over heated zeolites (80IZV655) or alumina (72IZV2263). More dehydrogenation is achieved by the use of nickel or alumina, as in the synthesis of tetrahydroquinolines (118) or octahydrophenanthridine (119) (78IZV1446). 

R.F.C. Brown, Pyrolyt. Methods Org. Chem., Organic Chemistry a series of monographs, Bd. 41, Aca-... 

For reviews of the reverse Diels-Alder reaction, see Iehihara Synthesis 1987, 207-222 Lasne Ripoll Synthesis 1985, 121-143 Ripoll Rouessac Rouessac Tetrahedron 1978, 34, 19-40 Brown Pyrolytic Methods in Organic Chemistry-, Academic Press. New York, 1980, pp. 259-281 Kwart King Chem. Rev. 1968, 68, 415-447. 

The usefulness of this pyrolytic method is emphasized by the synthesis of i>i-[3410][7]metacyclophane [400]. 

The best way to make carbon suboxide is a pyrolytic method, starting with tartaric acid. The latter is converted into diacetyltanaric anhydride and then pyrolyzed at 625-65(TC (either in an empty tube or in a keiene lamp) into acetic acid and carbon suboxtde. the latter in 35-5(15 yields,... 

Silenes are formed by rearrangement of silylcarbenes. If polysilylated diazomethanes 298-300 are employed, a selective migration of a silyl group to the carbene centre occurs and silenes 301, 92 and 302 are formed (equations 74-76)164. The outcome of trapping reactions is independent of the mode of silene generation photochemical and pyrolytic methods give the same results. 

Pyrolytic methods involve the use of dithiolane S, S -dioxides as starting materials which, upon heating, afford reactive thioaldehydes, such as trifluorothioacetaldehyde, trapped as the Diels-Alder adduct369,370 (equation 82). In equation 80 an enethiolate was formed, and this feature has been employed also in the cleavage of the oxathiolane 78. The silver vinylthiolate 79 thus obtained was applied in the preparation of new antibacterial cephem derivatives371. 

R. F. C. Brown (1980). Pyrolytic methods in organic chemistry , in Organic Chemistry A Series of Monographs. Ed. H. H. Wasserman, Vol. 41. New York Academic Press. 

Since early 1980, degradation methods have been used in DOM research with the aim to produce identifiable subcompounds that can be related to components of the macromolecular structure often referred as building blocks. Oxidative, hydrolytic, and pyrolytic methods were used as degradation reactions in combination with... 

Several pyrolytic methods of preparation have been reported. The thermal decomposition of 1-benzylbenzotriazole in the presence of copper at 350-400° gives phenanthridine in low yield,189 together with some jV-benzylaniline.190 The pyrolysis of 11-phenyldibenzo-thiazepine (166) (R1 = R2 = H) in diethyl phthalate in the presence of copper bronze provides 6-phenylphenanthridine in 94% yield,191... 

Branched cydodextrins are also used to increase the solubility of complexes. Two methods are used to make branched cydodextrins, an enzymic method and a pyrolytic method. In the enzymic method, a starch debranching enzyme, such as pul-lulanase, is added to a solution of cyclodextrin and a large excess of D-glucose or maltose to force the reaction to proceed in the reverse direction, i.e. to add rather than remove a branch.69 Since the equilibrium favors the debranching reaction, yields are low and the product typically contains —15% branched cyclodextrin and —85% glucose or maltose. Purification is difficult because of the high solubility of both the glucose or maltose and the branched cyclodextrin, but much of the unreacted cyclodextrin can be removed by crystallization. 

In parallel with the arc method in gaseous phase and the pyrolytic method for synthesis of carbon nanostructures, since 2000 year the present group of researchers has been investigating and developing the method for arc synthesis in liquid phase. This method has a number of advantages over those used at present. 

The experiments have shown that with the pyrolytic method of synthesis, in spite of the high duration (1-104 s) of technological process, CNTs are formed at the first moments of interaction and only after that they change their morphology and geometric dimensions. In this case it is of interest to consider the time of nanostructure formation and to know is it limiting at the arc synthesis or these structures are formed much more faster. 

The thermal, unsensitized infrared laser, and SiF4 laser sensitized decomposition of 1,2-dichloropropane were described by Tsang and coworkers96. The dichloro substrate yielded via four reaction channels 3-chloropropene, cw-l-chloropropene, trans- 1-chloro-propene and 2-chloropropene. These products have also been observed in thermal and laser-induced processes. Comparative data of the dichloropropane decomposition between the laser-induced experiment and the other pyrolytic methods indicated the former to be associated with complex phenomena with infrared multiphoton-induced decomposition. Consequently, a wide range of processes appeared to occur and the unimolecular rate parameters can be unambigously interpreted only at definite high pressure. 

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