Pyrolysis reverse reaction

The hydroxyl derivative of X-CN is cyanic acid HO-CN it cannot be prepared pure due to rapid decomposition but it is probably present to the extent of about 3% when its tautomer, isocyanic acid (HNCO) is prepared from sodium cyanate and HCI. HNCO rapidly trimerizes to cyanuric acid (Fig. 8.25) from which it can be regenerated by pyrolysis. It is a fairly strong acid (Ka 1.2 x 10 at 0°) freezing at —86.8° and boiling at 23.5°C. Thermolysis of urea is an alternative route to HNCO and (HNCO)3 the reverse reaction, involving the isomerization of ammonium cyanate, is the clas.sic synthesis of urea by F. Wohler (1828) ... 

A method for the stereospecific synthesis of thiolane oxides involves the pyrolysis of derivatives of 5-t-butylsulfinylpentene (310), and is based on the thermal decomposition of dialkyl sulfoxides to alkenes and alkanesulfenic acids299 (equation 113). This reversible reaction proceeds by a concerted syn-intramolecular mechanism246,300 and thus facilitates the desired stereospecific synthesis301. The stereoelectronic requirements preclude the formation of the other possible isomer or the six-membered ring thiane oxide (equation 114). Bicyclic thiolane oxides can be prepared similarly from a cyclic alkene301. 

For temperatures above 400°C. it might be argued that because Reaction 2 is highly reversed, Reaction 8 could not compete effectively with Reaction 1, and that Reaction 3 is required to explain why any reaction with oxygen occurs above about 400°C. The rate of radical pyrolysis relative to Reaction 8 when Reaction 2 is in equilibrium and... 

Diels-Alder reactions are, of course, reversible, and the pathway followed for the reverse reaction (2,3 arrows) can sometimes be as telling as the pathway for the forward reaction. The direction in which any pericyclic reaction takes place is determined by thermodynamics, with cycloadditions, like the Diels-Alder reaction, usually taking place to form a ring because two n-bonds on the left are replaced by two Diels-Alder reaction can be made to take place in reverse when the products do not react with each other rapidly, as in the pyrolysis of cyclohexene 2.3 at 600°. It helps if either the diene or the dienophile has some special stabilization not present in the starting material, as in the formation of the aromatic ring in anthracene 2.15 in the synthesis of diimide 2.16 from the adduct 2,14, and in... 

Very little work has been reported on the gas-phase pyrolysis of acid halides and two excellent reviews are available4,185. Acetyl chloride was decomposed in a static system at 242-491 °C186. The reversible reaction (equation 97) occurs at 242-350 °C, where the equilibrium lies to the left. The equilibrium constant, Kp, was found to be invariable with initial pressure, and temperature-dependent according to the van t Hoff equation 8.314 In Kp (-100.3 2.0) 103/T + (132.9 3.2). Addition of HC1 reduced the extent of the reaction but did not alter the value of Kp. However, at 270-329 °C the reaction is found to be homogeneous, molecular, and to obey a first-order rate law. The rate coefficients were given by... 

Two main types of terminations take place in free radical reactions during pyrolysis, namely combination and disproportionation. The radical-radical combination takes place with almost zero activation energy E. The reaction rate already discussed as the reverse reaction of scission has a typical rate constant k 10 -10 ° s. ... 

These reactions increase the heating value of the gas product, since methane has a high heat of combustion. However, these reactions are very slow except under high pressure and in the presence of a catalyst. Another source of the methane in the syngas is the pyrolysis process. Reaction R-4.11 is the reverse steam methane reforming reaction. All reactions that produce methane are exothermic reactions. 

Vapor phase thermolysis of [6]paracydophane (la) (Structures 1) yielded spiro triene 77 (Structures 10) as the major product via homolytic cleavage of one of the benzylic bonds [5b, 10]. FVP of [5.2.2]propelladiene (21a) (Structures 3) afforded spiro compound 78 (Structures 10) by similar homolysis of intermediate [5]paracyclophane (2a) (Structures 1) [61]. In contrast, the reverse reaction, FVP of spiro trienes, was successfully used for the preparation of [n]paracy-clophanes with n = 7 and 8 [62]. Pyrolysis of spiro tetraene 79, however, did not give [7]paracycloph-3-ene (80) (Structures 10) [63]. Evidently, [7]paracy-clophane is the borderline case with regard to the thermodynamic stabilities between the bridged aromatic compound and the spiro triene isomer. 

As reported, the thermal decomposition behaviour of amino trimethylene phosphonic acid (ATMP) and l-hydro)yethylidene-l,l-diphosphonic acid (HEDP) have been studied and a comparison of the experimental results from thermal decomposition by TGA-FTIR and pyrolysis GC-MS, together with modelling of the formation reactions, showed the usefulness of the latter method in predicting the possible decomposition products. Thus, pyrolysis GC-MS was used to determine the gaseous decomposition products of ATMP and HEDP at temperatures corresponding to the main decomposition steps detected by TGA-FTIR spectroscopy and, from a comparison of the experimental results with theoretical modelling, it was established that the decomposition process should follow the formation mechanism, i.e. the thermal decomposition can be understood as the reverse reaction of phosphonic acids. 

Hexafluoropropylene oxide (HFPO), which decomposes reversibly to di-fluorocarbene and trifluoroacetyl fluonde with a half-life of about 6 h at 165 °C [30], is a versatile reagent. Its pyrolysis with olefins is normally carried out at 180-2(X) °C, and yields are usually good with either electron-nch or electron-poor olefins [31, 32, 33, 34, 35, 36, 37] (Table 2). The high reaction temperatures allow the eyclopropanation of very electron poor double bonds [58] (equation 10) but can result in rearranged products [39, 40, 41] (equations 11-13)... 

The quality and quantity of sites which are capable of reversible lithium accommodation depend in a complex manner on the crystallinity, the texture, the (mi-cro)structure, and the (micro)morphology of the carbonaceous host material [7, 19, 22, 40-57]. The type of carbon determines the current/potential characteristics of the electrochemical intercalation reaction and also potential side-reactions. Carbonaceous materials suitable for lithium intercalation are commercially available in many types and qualities [19, 43, 58-61], Many exotic carbons have been specially synthesized on a laboratory scale by pyrolysis of various precursors, e.g., carbons with a remarkably high lithium storage capacity (see Secs. 

The molybdenum and tunsten diphenylacetylene compounds have been chemically useful primarily as precursors to the quadruple metal-metal bonded dimers [M(Por)]2, formed by solid-state vacuum pyrolysis reactions. However. Mo(TTP)()/"-PhC CPh) is also a useful substrate in atom-transfer reactions, reacting with Sx or Cp2TiS i to form Mo(TTP)=S. The reaction can be reversed by treatment of Mo(TTP)=S with PPh (which removes sulfur as PhxP=S) and PhC CPh. The order of preference for ligand binding to molybdenum 11) has been established to be PPh < PhC CPh < 4-picoline. ... 

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