Compounds with intermediate thermal

Two U.S. patents issued to the Barium Steel Corporation in 1957 claim the formation of the heptacarbonyls M(CO)7 (M = Ti, Zr, Hf) as intermediates for the purification of these metals (9,10). In this described refining process, the finely divided metal is treated with CO at 300-400°C and 4-8 atm. The resulting liquid heptacarbonyl compound is then thermally dissociated to the pure metal and CO. The alleged existence of these binary carbonyls seems highly unlikely without supporting evidence. 

The Friedel-Crafts cyclization of biphenyl-2-sulfonyl chloride to give dibenzothiophene sulfone has been described (55%) ° however, thermal cyclization in octachloronaphthalene at 250°, under nitrogen, is reported to yield dibenzothiophene itself rather than the sulfone (47%). Reaction of biphenyl compounds with oleum (H2SO4 + SO3) to yield derivatives of dibenzothiophene 5,5-dioxide is widely used for the preparation of dyestuff intermediates (Section VI, E, 2). A typical example is shown in Eq. (3), starting from o-tolidine. ... 

Orlov (8a) has compared the dissociative ionization and thermal decomposition of a series of Group IV compounds and discusses the use of the mass spectrometer to study the unstable or nonexistent compounds that are presumably thermolysis intermediates. These include bivalent compounds of Group IV such as silicon(II) derivatives and compounds with multiple bonds. Not only are ions observed important in such correlations, but the mass of the neutral fragment, as confirmed by the decomposition of metastable ions, is of equal importance. 

Reaction of diazo compounds with a variety of transition metal compounds leads to evolution of nitrogen and formation of products of the same general type as those formed by thermal and photochemical decomposition of diazoalkanes. These transition metal-catalyzed reactions in general appear to involve carbenoid intermediates in which the carbene becomes bound to the metal.83 The metals which have been used most frequently in synthesis are copper and rhodium. 

Photochemical or thermal extrusion of molecular nitrogen from ot-diazocarbonyl compounds generates a-carbonylcarbenes. These transient species possess a resonance contribution from a 1,3-dipolar (303, Scheme 8.74) or 1,3-diradical form, depending on their spin state. The three-atom moiety has been trapped in a [3 + 2] cycloaddition fashion, but this reaction is rare because of the predominance of a fast rearrangement of the ketocarbene into a ketene intermediate. There are a steadily increasing number of transition metal catalyzed reactions of diazocarbonyl compounds with carbon-carbon and carbon-heteroatom double bonds, that, instead of affording three-membered rings, furnish hve-membered heterocycles which... 

The reaction of a-diazocarbonyl compounds with nitriles produces 1,3-oxazoles under thermal (362,363) and photochemical (363) conditions. Catalysis by Lewis acids (364,365), or copper salts (366), and rhodium complexes (367) is usually much more effective. This latter transformation can be regarded as a formal [3 + 2] cycloaddition of the ketocarbene dipole across the C=N bond. More than likely, the reaction occurs in a stepwise manner. A nitrilium ylide (319) (Scheme 8.79) that undergoes 1,5-cyclization to form the 1,3-oxazole ring has been proposed as the key intermediate. 

In the oxidation of pentafluoroaniline with performic acid, along with the expected pentafluoronitrosobenzene, a 17% yield of decafluoroazoxy-benzene was isolated. Separate experiments showed that the condensation of the nitrosobenzene with the residual amine did not lead to the clean-cut preparation of the azoxy compound, whereas the thermal degradation of the nitroso compound did afford the azoxy compound. The implications of these observations are that either the azoxy product was formed, at least in part, by direct oxidation of the amine or the thermal history of the reaction permitted its formation from the intermediate nitroso compound [29]. 

The following simplified reaction scheme represents the formation of compound X via the reaction of HCHO with the thermally stabilized entity of the Criegee intermediate CH200 [123] ... 

Catalytic reduction of aromatic nitro compounds to the amines is highly exothermic (AH = —548 12 kJ/mol) and has high potential for hazard in the event of cooling- or other process-failure. The total reaction proceeds via nitroso and hydroxylamino intermediates, both of which are reactive and may undergo undesired condensation or disproportionation reactions, and the thermochemistry of all these possibilities was investigated. The reduction or disproportionation of the hydroxylamino intermediate (which is of low thermal stability) is identified as the fastest and most exothermic step (despite which it can frequently be concentrated or trapped) implications for process safety are considered in detail and verified by experiment with typical compounds and intermediates [1]. A calorimetric study of the hazards inherent in hydrogenation of nitroaromatics was made, using nitrobenzene as model compound [2]. Individual incidents of this type are ... 

The volatiles from cooked meat contain large numbers of aliphatic compounds including aldehydes, alcohols, ketones, hydrocarbons and acids. These are derived from lipids by thermal degradation and oxidation (J7) and many may contribute to desirable flavor. In addition, the aldehydes, unsaturated alcohols and ketones produced in these reactions, as well as the parent unsaturated fatty acids, are reactive species and under cooking conditions could be expected to interact with intermediates of the Maillard reaction to produce other flavor compounds. 

In consideration of conceivable strategies for the more direct construction of these derivatives, nitriles can be regarded as simple starting materials with which the 3+2 cycloaddition of acylcarbenes would, in a formal sense, provide the desired oxazoles. Oxazoles, in fact, have previously been obtained by the reaction of diazocarbonyl compounds with nitriles through the use of boron trifluoride etherate as a Lewis acid promoter. Other methods for attaining oxazoles involve thermal, photochemical, or metal-catalyzed conditions.12 Several recent studies have indicated that many types of rhodium-catalyzed reactions of diazocarbonyl compounds proceed via formation of electrophilic rhodium carbene complexes as key intermediates rather than free carbenes or other types of reactive intermediates.13 If this postulate holds for the reactions described here, then the mechanism outlined in Scheme 2 may be proposed, in which the carbene complex 3 and the adduct 4 are formed as intermediates.14... 

Since then, experiments have been reported which indicate that (1) organocopper compounds will couple with aryl halides (2) arylcopper compounds can be oxidatively and thermally dimerized (3) arylcopper compounds are intermediates in the Ullmann reaction (4) organocopper compounds are intermediates in copper-catalyzed decarboxylations and (5) copper-promoted coupling reactions are not restricted to aromatic halides. The copper(I) oxide-promoted coupling reactions, however, have still to yield firm evidence of a copper intermediate. 

The nitrosamine (121) and especially diazonium salts (122) prepared from it, as well as their alkyl and aryl derivatives, are important synthetic intermediates (b-76MI4i200, p. 325). For conditions that decide between nitrosamine function or diazotization see (73jcS(P1)13S7). At room temperature or in concentrated hydrochloric acid nitrosamines derived from triazoles are unstable, and their decomposition products include chlorotriazoles (63LA(665)144) 5-nitrosamino-3-phenyl-l,2,4-triazole affords the 5-bromo compound with hydrobromic acid at 0 °C and reacts violently with hydroiodic acid (05lA(343)i). Thermal arylation with triazole nitrosamines is possible (73jcs(pi)i357). 

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