2- catalysed decomposition

For bromates and iodates, disproportionation to halide and perhalate is not thermodynamically feasible and decomposition occurs either with formation of halide and liberation of O2 (as in the catalysed decomposition of CIOs just considered), or by formation of the oxide ... 

The auto-decomposition of lead tetraacetate in acetic acid, which normally occurs at reflux temperature , can be studied at 50 °C in the presence of sodium acetate The principal products of both the uncatalysed and catalysed decompositions are acetoxyacetic acid and carbon dioxide. The kinetic order of the normal decay of Pb(IV) is complex and evidence was obtained that oxidation of products is significant after the earliest stages. The evidence indicates that slow, simple homolytic breakage of lead tetraacetate to give Pb(OAc)3- and AcO-does not occur but that the solvent plays an integral part, e.g. 

A complex of the type M-H02 is also involved in the rather slower haemin-catalysed decomposition of H202. ... 

A detailed physical examination of the purple complex formed in alkaline solution between Fe(III), ethylenediaminetetraacetic acid (EDTA) and peroxide shows it to have a composition [Fe "(EDTA)02] (togA, 3 c =4.33). This complex catalyses decomposition of peroxide, the rate-pH profile going through a maximum at pH 9-10 . 

A few details have been reported on the slow reductions of 8303 by As(ni) and T1(I) . In the anaerobic reductions by As(III) the reaction is first-order in 820 and although As(III) certainly catalyses decomposition, the dependence of the rate on [As(III)] is small. Aeration leaves the rate of spontaneous decomposition of 820g unaffected, but the As(III)-catalysed route is accelerated by a factor of ten, the kinetic law remaining unchanged. The oxygen effect is interpreted in terms of the chain reaction... 

In another context, Davies et al. have developed the Rh2(-S -DOSP)4-catalysed decomposition of vinyldiazocarbonyl derivatives in the presence of vinyl ethers.The corresponding chiral cyclopentenecarboxylates were formed in high enantioselectivities of up to 99% ee with the full control of the relative stereochemistry at up to three contiguous stereogenic centres, as depicted in Scheme 10.9. 

A very similar rearrangement takes place during the acid-catalysed decomposition of hydroperoxides, RO—OH, where R is a secondary or tertiary carbon atom carrying alkyl or aryl groups. A good example is the decomposition of the hydroperoxide (84) obtained by the air-oxidation of cumene [(l-methylethyl)benzene] this is used on the large scale for the preparation of phenol and acetone ... 

Figure 10.25 Effect of phosphate stabiliser on Fe(m)-catalysed decomposition of hydrogen peroxide in absence of substrate [237]. Initial concentration 2.9 g/l H202, Phosphonate stabiliser 2 g/l, 95 °C, pH 12...

A review of runaway decomposition reactions of DMSO [1], several involving bromides, some alkaline and under vacuum, from temperatures possibly as low as 130°C. A bromide/bromine catalysed decomposition reaction is known [2],... 

The ester is made by adding benzyl alcohol slowly to a preformed solution of phosgene in toluene at 12-16°C, toluene solvent finally being distilled off under vacuum. When discoloured phosgene was used (probably containing iron salts from corrosion of the cylinder), a violent explosion occurred during the distillation phase, presumably involving iron-catalysed decomposition of the chloroformate ester. 

A 6000 m3 aqueous refinery effluent containing sulfides and traces of hydrocarbons was to be treated to remove sulfides before discharge. Aqueous ferric chloride was added, followed by 1800 1 of 50 wt% peroxide added over 40 min, and after a further 30 min an explosion occurred which blew off the lid of the treatment vessel. This was attributed to ignition of the explosive mixture of hydrocarbon vapours and oxygen (from iron-catalysed decomposition of peroxide) formed above the liquid surface. 

In a factory manufacturing organo-iron and organo-manganese catalysts, use of cotton waste to mop up a spill of dilute hydrazine solution led to a spontaneous fire later. The fire was attributed to onset of rapid metal-catalysed decomposition of the hydrazine after sufficient water had evaporated from the waste, the traces of heavy metals originating from dust contamination, etc. 

Another method is that based on the ferrous/ferric thiocyanate determination of hydroperoxides [1]. This exploits the ion-catalysed decomposition as shown by... 

The formation of oligomeric silicon chlorides SixCly from 1 with Si2Cl6 [1] might be due to base -catalysed decomposition of intermediate Me3Si-SiCl3 (a known compound), which would be the product of an anionic trichlorosilylation of the trimethylsilyl group of silylphosphane 1. 

A ring enlargement process was used effectively to access the enantiopure pyrrolo [ 1,4]oxazepine-9a(7//)-carboxylate derivatives 142 and 143. The sequence involved copper (Il)-catalysed decomposition of an a-diazocarbonyl derivative attached to a chiral morpholinone, and a carbenoid, spiro-[5,6]-ammonium ylide, Stevens [1,2] rearrangement sequence. The Stevens and related rearrangements have considerable further potential for novel heterocyclic syntheses <00TA3449>. 

Furthermore, although the intercepts k kiK/k- ) and the slope (kikjK/k-i) are equally influenced by the dimerization constant K in equation 28, this does not imply that they should show the same effect on changing the solvent. According to the dimer mechanism , it could be expected that the base catalysed decomposition of the transition state SB2, measured by Ag, should be more depressed by small additions of protic solvents than the spontaneous decomposition measured by Ag. Indeed, the overwhelming evidence on the classical base catalysis by amines shows that usually Ag is more important in aprotic than in protic solvents1. 

Nevertheless, the results observed for the reactions of o- and p-11 uoronitrobenzenes with propylamines demonstrate that (a) the dichotomy is not only observed when comparing primary with secondary amines (b) the origin is not due to primary steric effects (c) when there is no artho-n. m group the decrease in rate for the bulky amine is greater (d) the diminution in rate is due to an inhibition effect in the base-catalysed decomposition. 

Frimer, A. A., J. Org. Chem., 1977, 42, 3194-3196, footnote 7 A new method of preparation involves interaction of ally lie halides in solvents with 98% hydrogen peroxide in presence of silver ion and base at ambient temperature under argon. The reactions must be run in the dark to prevent precipitation of metallic silver, which will catalyse decomposition of the hydroperoxide or excess hydrogen peroxide. In an experiment not run in the dark, the hydroperoxide from 3-chlorocyclohexene ignited spontaneously after isolation and concentration. 

Available information on the thermal instability of halogenated anilines during vacuum distillation is presented and analysed, and the roles of dehyrohalogenation, polymerisation, salt formastion and dissociation, aerobic oxidation, corrosion and metal-catalysed decomposition are discussed. Experimental work on these topics is presented, and preventive measures proposed. 

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