Pyrolysis azides

Perhaps one of the most exciting developments in the chemistry of quinoxalines and phenazines in recent years originates from the American University of Beirut in Lebanon, where Haddadin and Issidorides first made the observation that benzofuroxans undergo reaction with a variety of alkenic substrates to produce quinoxaline di-AT-oxides in a one-pot reaction which has subsequently become known as the Beirut reaction . Many new reactions tend to fall by the wayside by virtue of the fact that they are experimentally complex or require starting materials which are inaccessible however, in this instance the experimental conditions are straightforward and the starting benzofuroxans are conveniently prepared by hypochlorite oxidation of the corresponding o-nitroanilines or by pyrolysis of o-nitrophenyl azides. 

Perfluorotetramethylthiadiphosphanorbornadiene and bis(trifluoromethyl) thiadiphosphole can be prepared by thermolysis of an adduct of methanol and hexakis(trifluoromethyl)-l,4-diphosphabarrelene with sulfur [113] (equation 23) Pyrolysis of the adduct of hexafluorinated Dewar benzene and phenyl azide results in ring expansion giving azepine, which photochemically yields an intramolecular 2-1-2 adduct, a good dienophile for the Diels-Alder reaction [114, //5] (equation 24) Thermolysis of fluonnated derivatives of 1,5-diazabicyclo-... 

The most reliable method of preparing benzofuroxans is by decomposition of o-nitrophenyl azides. Decomposition can be achieved by irradiation, or more usually by pyrolysis temperatures between 100° and 1.50° are commonly used. Refluxing in glacial acetic acid is the recommended procedure for 4- or 5-sub-stituted 2-nitrophenyl azides, but with 3- or 6-substituted compounds higher boiling solvents are usually necessary. Quantitative studies on the reaction rate have been made, and a cyclic transition state invoked, an argument which has been used to account for the greater difficulty of decomposition of the 6-substituted 2-nitrophenyl azides. Substituent effects on the reaction rate have also been correlated with Hammett a constants, ... 

Ring fusion seems to occur in the quinoxaline derivative (28), which has been stated to exist in red and blue-black forms. Other derivatives of type 28 are reported. Attempts to prepare 5,6-furo-xanobenzofuroxan by pyrolysis of the azide (29) met with no success. An early example in the literature of such a linear fused structure was shortly afterward revised to the angularly fused type (17). 

Early attempts to prepare 5-amino- and 5-acylaminobenzofuroxans by hypochlorite oxidation of the corresponding o-nitroanilines met with failure. Pyrolysis of the appropriate azide, however, gives 5-dimetliylamino- and 5-acetamidobenzofuroxan, whereas urethans of type (33) are produced by Curtius degradation of the 5-carboxylic acid. Controlled hydrolysis of the acetamido compound and the... 

Interest in the mechanism and product distribution of thermal and photochemical transformations of aryl azides led to the isolation of some nitrogen-containing derivatives of heptafulvalene. Based on elemental analysis and spectroscopic data it has been suggested tentatively that the compound isolated following vapor-phase pyrolysis of azidopentafluoro-... 

Kinetic studies of pyrolysis of azides, giving oxadiazole A-oxides in near-quantitative yields, showed that the 5-azido-6-nitroquinoline pyrolyzed in acetic acid 27.6 times faster than did 5-azidoquinolines, because of the -M effect of the group adjacent to the azide group (85AJC1045). 

Benzofuroxan 79 can be generated from 2-nitrophenyl azide 80 (Scheme 49). Neighboring-group assistance within the pyrolysis leads to a one-step mechanism with an activation barrier of 24.6 kcal/mol at the CCSD(T)/6-31 lG(2d,p) level [99JPC(A)9086]. This value closely resembles the experimental one of 25.5 kcal/mol. Based on the ab initio results for this reaction, rate constants were computed using variational transition state theory. 

Also unexpected is the formation of the 2,2 -(3,4,5,6,7-pentafluoroazepin-2-ylidene) (35) during the flow pyrolysis of perfluorophenyl azide over platinum at 300 C.6°... 

Diazidonaphthalene. Pale yel crysts, mp 95—100° with decompn prepd by the bis-diazotation of 1,8-diajninonaphthalene followed by treatment with Na azide (Ref 5). It has been patented as a photosens ingredient in a photocopying process (Ref 6) 2,3-Diazidonaphthalene. Needles from petr eth (bp 40—60°), mp 63—4° prepd in five steps starting with 3-amino-2-naphthoic acid. Its pyrolysis in a Pyrex tube at 400° gave... 

Pyrolysis of diethyl aluminum azide [(C2H5)2A1N3] at 450-870°C). 

The pyrolysis of aluminum-nitrogen organic complexes, such as diethyl aluminum azide [(C2H5)2A1N3], is also used successfully at low deposition temperatures (450-870°C).0 l Another metallo-organic, hexakis(dimethylamido)dialuminum, reacting with ammonia allows deposition at 200-250°C at atmospheric pressure. 1... 

The Curtius rearrangement involves the pyrolysis of acyl azides to yield isocy-anates. " The reaction gives good yields of isocyanates, since no water is present to... 

Two other results will now be pointed out which presumably also require reinterpretation in the light of the reaction behavior of iminooxophosphoranes. Thus the gas phase pyrolysis of diphenylphosphoryl azide is reported to give monomeric 92 50) and the dehydrohalogenation of phenylphosphoric adamantylamidic chloride with methylhydrazine the heterocumulene 93 51), which is even considered resistant to water. Since partly correct analytical values are available, 92 and 93 may well be oligomers. 

The vapour-phase pyrolysis of benzenesulphonyl azide at 625 °C gave a 17.5% yield of azobenzene 71>, and a trace of the latter was also reported when the azide was heated in boiling cyclohexanone >. 

Rice, F. O. et al., J. Amer. Chem. Soc., 1957, 79, 1880-1881 This blue solid (a cyclic dimer of diazene, 93.3% of nitrogen), obtained by freezing out at — 195°C the pyrolysis products of hydrogen azide, is extremely explosive above this temperature. An explosion at — 125°C destroyed the apparatus. 

The endothermic nitride is susceptible to explosive decomposition on friction, shock or heating above 100°C [1], Explosion is violent if initiated by a detonator [2], Sensitivity toward heat and shock increases with purity. Preparative precautions have been detailed [3], and further improvements in safety procedures and handling described [4], An improved plasma pyrolysis procedure to produce poly (sulfur nitride) films has been described [5], Light crushing of a small sample of impure material (m.p. below 160°C, supposedly of relatively low sensitivity) prior to purification by sublimation led to a violent explosion [6] and a restatement of the need [4] for adequate precautions. Explosive sensitivity tests have shown it to be more sensitive to impact and friction than is lead azide, used in detonators. Spark-sensitivity is, however, relatively low [7],... 

Raasch, and Schaumann and co-workers, have studied the reactions of bis (trifluoromethyl)thioketene (83 R1 = CF3) with alkenes, with thioketones, and with carbodiimides or Schiff-base imines. The products were, respectively, thietans, 1,3-dithietans (84 R1 = CF3), and 1,3-thiazetidines (85 R1 = CF3) (from the carbodiimide).114,115 With phenyl azide the 1,2,3,4-thiatriazoline (86 R = CF3) is formed subsequent pyrolysis yields2,l-benzisothiazole.114... 

Internal nitrenes normally react at the adjacent position. Reduction of 2-(2-nitrophenyl)furan by ethyl phosphite yields furoindole derivatives in fair yield (34%) only, whereas much better results attend the pyrolysis of 2-(2-azidophenyl)furan.280 Furopyrazoles are obtained similarly.281 Azidofurans yield nitrenes that insert into adjacent CH links to form furo-pyrroles.282 Quite different results attend either the pyrolysis or the photolysis of azide 107a for the expected insertion into the side chain occurs giving the related indole but it is accompanied by the surprising replacement of furan oxygen by nitrogen producing 107b and similar products.283... 

The well known pyrolysis of azides and the reaction of IV-chlor-amines with soda lime are regarded as rearrangements of a nitrogen diradical ... 

Banks and co-workers found that gas-phase pyrolysis of pentafluorophenyl azide yields a diazaheptafulvalene (Scheme 16).50 The formation of the product was viewed as dimerization of the perfluoro analogue of 4b, although it is possible that it could, instead, have been formed by dimerization of the corresponding cyclic ketenimine. 

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