Thermal disproportionation

The formation of antimony trichloride from antimony oxychloride has been described by two different mechanisms. One asserts that formation is via a thermal disproportionation as described in equations 3—6 (12). 

Naphthalenedicarboxylic acid has been prepared by fusing dipotassium 2,6-naphthalenedisulfonate with potassium cyanide to give the corresponding dinitrile, which is hydrolyzed by oxidation of 2-methyl-6-acetylnaphthalene with dilute nitric acid at 200 by the thermal disproportionation of potassium a- or /3-naphthoate to dipotassium 2,6-naphthalenedicarboxylate and naphthalene and by the present method. The present method is much more convenient than earlier methods, if a suitable autoclave is available. 

The present method for preparing aromatic dicarboxylic acids has been used to convert phthalic or isophthalic acid to tereph-thalic acid (90-95%) 2,2 -biphenyldicarboxylic acid to 4,4 -biphenyldicarboxylic acid 3,4-pyrroledicarboxylic acid to 2,5-pyr-roledicarboxylic acid and 2,3-pyridinedicarboxylic acid to 2,5-pyridinedicarboxylic acid. A closely related method for preparing aromatic dicarboxylic acids is the thermal disproportionation of the potassium salt of an aromatic monocarboxylic acid to an equimolar mixture of the corresponding aromatic hydrocarbon and the dipotassium salt of an aromatic dicarboxylic acid. The disproportionation method has been used to convert benzoic acid to terephthalic acid (90-95%) pyridine-carboxylic acids to 2,5-pyridinedicarboxylic acid (30-50%) 2-furoic acid to 2,5-furandicarboxylic acid 2-thiophenecar-boxylic acid to 2,5-thiophenedicarboxylic acid and 2-quinoline-carboxylic acid to 2,4-quinolinedicarboxylic acid. One or the other of these two methods is often the best way to make otherwise inaccessible aromatic dicarboxylic acids. The two methods were recently reviewed. ... 

The product is the dihydrogen orthoperiodate N33H2I06, which is a convenient starting point for many further preparations (see Scheme on next page). Paraperiodates of the alkaline earth metals can be made by the thermal disproportionation of the corresponding iodates, e g. ... 

This dimeric formulation also accounts for the thermal disproportionation of the compound into a mixture of 2-methyl-l,2,3,4-tetrahydro-jS-carbohne and 2-methyl-jS-carboline anhydro-base. Normal pseudobase formation (453 R = CHs ) takes place in the case of 9-methyl-3,4-dihydro-j3-carbohne methiodide (452 R = CHg). Neither the dimeric anhydro-base nor the -methyl pseudo-base undergo a base-catalyzed disproportionation reaction to give the 1,2,3,4-tetrahydro-and the l-oxo-l,2,3,4-tetrahydro-jS-carboline in a manner analogous... 

Dithiazolyl radical 228 photochemically and thermally disproportionates to afford the 1,2,5-thiadiazole 229 and the unstable 1,2,3-trithiole 230 (Equation 54) <2000JCD3365>. Thermolysis of perfluoro-l,3A4(i2,2,4-benzodithiadia-zine 231 affords complex mixtures of heterocycles including perfluoro-2,l,3-benzothiadiazole 232 and 7,8-difluoro-benzo[l,2- 3,4-f ]bis[l,2,5]thiadiazole 233 (Equation 55) <2005EJI4099>. 

The crystalline monoadduct 8 has been reported to undergo a regiospecific thermal disproportionation into a solid 1 1 mixture of Cgo and the trans-l bisadduct isomer 9a (Scheme 6) [36]. However,bisadducts 9 obtained under the HSVM conditions were a mixture of positional isomers [35]. 

Scheme 6 Thermal disproportionation reaction of Cgo-anthracene adduct 8 in crystal...

Although the noncatalytic thermal disproportionation of alkenes is symmetry-for-bidden, the formation of metal complex 1 with the four-centered cyclic intermediate makes the reaction symmetry-allowed.61... 

Whereas most disproportionation reactions among the haloalkanes take place catalytically, the emphasis is on thermal disproportionation in the case of the haloalkenes and perhalogenated aromatics. 

In two patents40 41 the thermal disproportionation of chlorofluorobenzenes is claimed. The data given show that the additives used have an influence on the conversion of the disproportionation of l,3,5-trichloro-2,4,6-trifiuorobcnzcnc and 1,3-dichloro-2,4,5,6-tetrafiuoroben-zene. The additives are aluminum trifluoride (prepared by thermal decomposition of NH4-A1F4), cesium fluoride, and aluminum trifluoride on magnesium fluoride. 

There is only a small number of reactions known whereby a perfluorinated aromatic compound is formed by thermal disproportionation perfluorotoluene is disproportionated at temperatures above 500 C to form perfluorobenzene and perfluoroxylcnc.42 44 The perfluoroxylene itself can be dismutated at 550°C to yield perfluorotoluene and 1,2.4- and 1,3,5-perfluoro-... 

An anomalous X-ray scattering study of (+(-tubocurarine dibromide (73 4MeOH) confirmed the structure and absolute configuration earlier assigned. The N-N distance is 10.66 A (47,48). A purified sample of (+(-tubocurarine chloride (73a), prepared by selective quatemization of (+(-tubocurine (74) (Section V,B,1), gave the anomalous MS behavior previously ascribed to thermal disproportionation or the presence of impurities. In particular, the MS has mle 594 [17%, (M - 15)+, loss of Me] but also 608 (3.7%) and 622 (0.5%). The higher peaks seem to be due to a thermal Hofmann elimination followed by recombination with methyl radicals. Similar behavior is observed with the tertiary bases (—)-curine (75) and (+(-tubocurine (74), and may be general for alkaloids of this skeletal type (49). 

Thermal disproportionation in the absence of added base takes place when 1,1,2,2-tetramethoxydimethyldisilane is heated at 185° C for 40 hours, giving methyltrimethoxysilane, tris(methyldimethoxysilyl)methylsilane and a viscous nonvolatile polysilane residue (4). 

For R = C2H5 and X = C1, the values of the equilibrium constants were Kt = 5.3 and K2 = 1.5. For R = w-C4H9 and X = Cl, Kx = 5.3 and /with boron trifluoride etherate (176). The reaction of Eq. (76) has been utilized as a general method for the preparation of various alkylhaloboranes. Thermal disproportionation studies of these products have been reported (168). 

SiF2 is also formed on thermal disproportionation of Si2F6549). Another disproportionation553) occurs under the catalytic influence of triethylamine, forming a brown powder (SiF0.9i) which ignites spontaneously in air. 

In the case of brominated additives the process is less studied, for decabromodiphenyl oxide, a widely used brominated fire-retardant additive, Sb8OnBr2 is the dominant oxybromide, whereas Sb405Br2 was not detected in measurable amounts. It was assumed that, if this last is formed by bromination of Sb8OnBr2, it eliminates SbBr3 relatively rapidly either by thermal disproportionation or by chemical reaction with decabromodiphenyl oxide.42... 

Vanadium(II) chloride is formed when a mixture of vanadium (IV) chloride and hydrogen is passed through a hot tube1 and by the reduction of vanadium(III) chloride with hydrogen.2 It is also produced by the thermal disproportionation of vanadium(III) chloride3,4 into the nonvolatile dichloride and the volatile tetrachloride. 

Secondary phosphine oxides thermally disproportionate into secondary phosphines and phosphinic acids (3). The phosphine can be reoxidized to the phosphine oxide and continue this cycle. 

Dicyclohexylphosphine oxide would thermally disproportionate into dicyclohexylphosphinic acid and dicyclohexylphosphine. We found that both the phosphine oxide, m.p. 72°-75°C., at 15%, and the phosphinic acid, m.p. 144°-145°C., at 5%, in polyethylene are flame retardants. 

Previously we described the high thermal stability of phosphine oxides and phosphonic acids and indicated that this stability may allow a shielding of the polymer from the flame (19). The thermal disproportionation of secondary phosphine oxides into secondary phosphines and phosphinic acids (1) was also reviewed. 

Independent experiments show that the alkyl alkyne undergoes alkyl migration to carbon monoxide at — 100°C where the acyl can be trapped with phosphine, phosphite, or free carbon monoxide. Although the alkyl alkyne is converted to the acyl derivative by scavenging CO under the photolytic reaction conditions, these same alkyl derivatives can be isolated following thermal disproportionation of the acyl for a few minutes in refluxing toluene. Evidently thermal loss of CO from CpW(CO)-(HC=CH)[C(0)Me] promotes alkyl migration from the acyl back to the... 

Reaction of P-hydridocyclophosphazenes (e.g., 30) with CC14 results in the replacement of hydrogen by chlorine (383-385). Metalation of the hydridocyclophosphazene (30) and subsequent treatment with the chlorocyclophosphazene (31) leads to the formation of the two-ring assembly phosphazene (32), which can also be prepared by the direct reduction of 31 with potassium or by thermal disproportionation of the phosphinocyclophosphazene (33) (385). 

Periodates are best obtained by oxidizing iodate (or even I" or I2) electrolytically or with Cl2 in strongly basic solution to give Na3H2IC>6, or by thermal disproportionation of an iodate ... 

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