Pyrolysis equations

Cowley and coworkers have reported two other reactions. One is the reaction of the silylphosphide 11a with dichloroborane, which afforded the diphosphadiboratane, resulting in the formation of the phosphaborene by flash-vacuum pyrolysis (equation 101)135. The other is the reaction of the silylphosphide 11a with ( j5-C5H4Me)2WCl2, which gave compounds 14 and 15 (equation 102)136. A phosphinidene tungsten complex was assumed to be a reactive intermediate. 

The reaction proceeds via the normal six-membered transition state mechanism of ester elimination. The intermediate chlorobutyric acid yielded butyrolactone through participation of the COOH group under the reaction conditions. The pure chlorobutyric acid was pyrolyzed and gave butyrolactone in quantitative yield. The mechanism is similar to that of bromobutyric acid pyrolysis (equation 76). The data are shown in Table 23. 

Simple 5(4//)-oxazolones are stable at moderate temperatures. The diphenyl derivative (183) yields the acylimine (184) on flash vacuum pyrolysis (equation 23) (80AG(E)564). The presence of acyl substituents at C(4) destabilizes the ring such compounds rearrange at 180 °C to oxazoles by a process akin to that described in Section 4.18.3.1.2(i) (equation... 

The favored reaction mechanism is that which yields methylsilene and ethylene upon pyrolysis (equation 37). 

Mass and energy balances are obtained from stoichiometric reaction equations. For the preparation of the pyrolysis equation, the product spectrum must be known experimentally. The same is true for gasification, except for very high temperatures, where thermodynamic equilibrium is attained. 

The following examples of pyrolysis equations are oversimplified, but show the essentials. The simplified formula C3(H 0)2 (MW 72) represents the dahf-composition of the organic part in wood, straw or any other lignocellulosic biomass. 

The pyrolysis equations above are based on an assumed which is not generally known from condensed phase considerations alone. To proceed further and obtain a solution for mass flux requires information about the conductive heat feedback to the surface from the gas phase qc which must be supplied by the gas... 

The silanorbornenes 51A and 51B produced the corresponding silenes upon flash vacuum pyrolysis (equation 92). These were not configurationally stable at 400-650 °C... 

Unfortunately, lifetimes of the catalysts are so severely limited that they are of no commercial value.(l) In the 1980 s, however, two groups reported that by conducting the reaction in the presence of alcohols, especially methanol, they greatly improved catalyst lifetime.(2-11) The product, a carbamate (equation 2), could be converted into the isocyanate by pyrolysis, equation 3. 

Manufacture. For the commercial production of DPXN (di-/)-xylylene) (3), two principal synthetic routes have been used the direct pyrolysis of -xylene (4, X = Y = H) and the 1,6-Hofmaim elimination of ammonium (HNR3 ) from a quaternary ammonium hydroxide (4, X = H, Y = NR3 ). Most of the routes to DPX share a common strategy PX is generated at a controlled rate in a dilute medium, so that its conversion to dimer is favored over the conversion to polymer. The polymer by-product is of no value because it can neither be recycled nor processed into a commercially useful form. Its formation is minimised by careful attention to process engineering. The chemistry of the direct pyrolysis route is shown in equation 1 ... 

In TBP extraction, the yeUowcake is dissolved ia nitric acid and extracted with tributyl phosphate ia a kerosene or hexane diluent. The uranyl ion forms the mixed complex U02(N02)2(TBP)2 which is extracted iato the diluent. The purified uranium is then back-extracted iato nitric acid or water, and concentrated. The uranyl nitrate solution is evaporated to uranyl nitrate hexahydrate [13520-83-7], U02(N02)2 6H20. The uranyl nitrate hexahydrate is dehydrated and denitrated duting a pyrolysis step to form uranium trioxide [1344-58-7], UO, as shown ia equation 10. The pyrolysis is most often carried out ia either a batch reactor (Fig. 2) or a fluidized-bed denitrator (Fig. 3). The UO is reduced with hydrogen to uranium dioxide [1344-57-6], UO2 (eq. 11), and converted to uranium tetrafluoride [10049-14-6], UF, with HF at elevated temperatures (eq. 12). The UF can be either reduced to uranium metal or fluotinated to uranium hexafluoride [7783-81-5], UF, for isotope enrichment. The chemistry and operating conditions of the TBP refining process, and conversion to UO, UO2, and ultimately UF have been discussed ia detail (40). 

Ethylene Dichloride Pyrolysis to Vinyl Chloride. Thermal pyrolysis or cracking of EDC to vinyl chloride and HCl occurs as a homogenous, first-order, free-radical chain reaction. The accepted general mechanism involves the four steps shown in equations 10—13 ... 

Synthesis. Iminoboranes, thermodynamically unstable with respect to oligomerization can be isolated under laboratory conditions by making the oligomerization kineticaHy unfavorable. This is faciUtated by bulky substituents, high dilution, and low temperatures. The vacuum gas-phase pyrolysis of (trimethylsilylarnino)(aLkyl)haloboranes has been utilized as an effective method of generating iminoboranes RB=NR as shown in equation 19 for X = F,... 

Iminoboianes have been suggested as intermediates in the formation of compounds derived from the pyrolysis of azidoboranes (77). The intermediate is presumed to be a boryl-substituted nitrene, RR BN, which then rearranges to the amino iminoborane, neither of which has been isolated (78). Another approach to the synthesis of amino iminoboranes involves the dehydrohalogenation of mono- and bis(amino)halobotanes as shown in equation 21. Bulky alkah-metal amides, MNR, have been utilized successfully as the strong base,, in such a reaction scheme. Use of hthium-/i /f-butyl(ttimethylsilyl)amide yields an amine, DH, which is relatively volatile (76,79). 

The unit of the veloeity eonstant k is see Many reaetions follow first order kineties or pseudo-first order kineties over eertain ranges of experimental eonditions. Examples are the eraeking of butane, many pyrolysis reaetions, the deeomposition of nitrogen pentoxide (NjOj), and the radioaetive disintegration of unstable nuelei. Instead of the veloeity eonstant, a quantity referred to as the half-life iyj is often used. The half-life is the time required for the eoneentration of the reaetant to drop to one-half of its initial value. Substitution of the appropriate numerieal values into Equation 3-33 gives... 

Sulfenyl chlondes react with allyl alcohols to yield allyl sulfenates, whtch are in equihbnum with the allyl sulfoxides [12] (equation 9a) These products can be oxidized to the corresponding sulfones (equation 9b) Pyrolysis of the sulfoxides gives sulfines or evidence for the presence of sulfmes Pyrolysis of sulfones leads to unsamrated compounds by extrusion of sulfur dioxide [12] (equation 9c)... 

Tnvalent phosphorus species containmg organofluonne groups have been prepared by pyrolysis at 830 C and 0 01 torr of pentafluoroethyltnfluoromethyl-tnmethylstannylphosphanes 138] (equation 38)... 

Fluorinated alkynes are readily prepared by treatment of the mtermediate formed by acylation with a second equivalent of ylide followed by pyrolysis [63. 64, 65] (equation 57)... 

Hexafluorabenzene may also add to methylene Lnphenylphosphorane to form a new pentafluorophenyl-bearing yhde Treatment of tins ylide with an acid fluonde or acid anhydride followed by pyrolysis (shown in equation 58) forms the corresponding pentafluorophenylacetylene [66] (equation 58). 

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 pyrolysis of sodium chlorodinuoroacetate is still a widely used, classical method for generating difluorocarbene, especially with enol and allyl acetates [48, 49, 50, 51] (equation 21) A convenient alternative that avoids the hygroscopic salt uses methyl chlorodifluoroacetate with 2 equivalents of a lithium chlonde-hexa-methylphosphoric triamide complex at 75-80 °C in triglyme [52], Yields are excellent with electron-rich olefins but are less satisfactory with moderately nucleophilic alkenes (4-5% yields for 2-bulenes)... 

The six-membered nng in polyfluoropyndazmes is much more stable, and pyrolysis at 680-725 °C is needed to eliminate mirogen, resulting m various fluonnated acetylene compounds in 80-90% yield [77](equation 46)... 

Similarly, low-temperature photolysis of 4,5,6-fluorosubstituted 1,2,3-tna zines results in the elimination of nitrogen, but the product composition depends on the substituents When the substituents are fluonne atoms, the intermediate product IS a four-membered, mtrogen-contaming ring that quickly dimenzes When all the substituents are perfluoroalkyl groups, the pyrolysis results in a mixture perfluoroalkyl acetylenes and perfluoroalkyl cyanides [79] (equations 48 and 49). 

The pyrolysis of perfluoro carboxylic salts can result both in mono and bimolecular products At 210-220 °C, silver salts give mostly the coupled products, at 160-165 °C in A -methylpyrrolidinone, the corresponding copper salts also give the simple decarboxylated compounds in nearly equal amounts The decomposition of the copper salts m the presence of lodobenzene at 105-125 °C results m a phenyl derivative, in addition to the olefin and coupled product [94] (equations 60-62)... 

The high temperature pyrolysis of sulfonyl fluonde results in the elimination of sulfur dioxide, although secondary reactions also occur, depending on the residence tune With perfluorooctanesulfonyl fluonde, long residence times result in perfluoro(Cg-Cig) compounds, and shorter residence times lead to perfluoro-hexadecane [98] (equation 65)... 

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-... 

In addition to the pyrolysis of chlorodifluoromethane [9], another commercially important synthesis of TFE is based on tnfluoromethane [/O] (equation 1). 

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