Disproportionate reaction

Zhen-Ming Hu and NakatsujI H 1999 Adsorption and disproportionation reaction of OH on Ag surfaces dipped adcluster model study Surf. Sci. 425 296-312... 

The head element nitrogen does not react. White phosphorus, however, reacts when warmed with a concentrated solution of a strong alkali to form phosphine, a reaction which can be regarded as a disproportionation reaction of phosphorus ... 

With hot water a vigorous but complex reaction occurs, the products including phosphine and phosphoric(V) acid. This disproportionation reaction can be approximately represented as ... 

This is a disproportionation reaction, and is strongly catalysed by light and by a wide variety of materials, including many metals (for example copper and iron) especially if these materials have a large surface area. Some of these can induce explosive decomposition. Pure hydrogen peroxide can be kept in glass vessels in the dark, or in stone jars or in vessels made of pure aluminium with a smooth surface. 

Reaction (11.4) is really a disproportionation reaction of the halate(I) anion 3XO 2X -E XO. ) Reaction (11.3) is favoured by the use of dilute alkali and low temperature, since the halate(I) anions, XO are thermally unstable and readily disproportionate (i.e. reaction (11.4)). The stability of the halate(I) anion, XO , decreases from chlorine to iodine and the iodate(I) ion disproportionates very rapidly even at room temperature. 

This dismutation or disproportionation reaction is known as the Cannizzaro reaction. 

Tlie formation of initiator radicals is not the only process that determines the concentration of free radicals in a polymerization system. Polymer propagation itself does not change the radical concentration it merely changes one radical to another. Termination steps also occur, however, and these remove radicals from the system. We shall discuss combination and disproportionation reactions as modes of termination. 

Table 6 presents a summary of the oxidation—reduction characteristics of actinide ions (12—14,17,20). The disproportionation reactions of UO2, Pu , PUO2, and AmO are very compHcated and have been studied extensively. In the case of plutonium, the situation is especially complex four oxidation states of plutonium [(111), (IV), (V), and (VI) ] can exist together ia aqueous solution ia equiUbrium with each other at appreciable concentrations. 

Reference Electrodes and Liquid Junctions. The electrical cincuit of the pH ceU is completed through a salt bridge that usually consists of a concentrated solution of potassium chloride [7447-40-7]. The solution makes contact at one end with the test solution and at the other with a reference electrode of constant potential. The Hquid junction is formed at the area of contact between the salt bridge and the test solution. The mercury—mercurous chloride electrode, the calomel electrode, provides a highly reproducible potential in the potassium chloride bridge solution and is the most widely used reference electrode. However, mercurous chloride is converted readily into mercuric ion and mercury when in contact with concentrated potassium chloride solutions above 80°C. This disproportionation reaction causes an unstable potential with calomel electrodes. Therefore, the silver—silver chloride electrode and the thallium amalgam—thallous chloride electrode often are preferred for measurements above 80°C. However, because silver chloride is relatively soluble in concentrated solutions of potassium chloride, the solution in the electrode chamber must be saturated with silver chloride. 

Preparations. Magnesium alkyls maybe prepared from a Grignard reagent according to the following disproportionation reaction ... 

As the oxidation state of manganese increases, the basicity declines, eg, from MnO to Mn20y. Oxyanions are more readily formed ia the higher valence states. Another characteristic of higher valence-state manganese chemistry is the abundance of disproportionation reactions. 

Another method for producing petoxycatboxyhc acids is by autoxidation of aldehydes (168). The reaction is a free-radical chain process, initiated by organic peroxides, uv irradiation, o2one, and various metal salts. It is terrninated by free-radical inhibitors (181,183). In certain cases, the petoxycatboxyhc acid forms an adduct with the aldehyde from which the petoxycatboxyhc acid can be hberated by heating or by acid hydrolysis. If the petoxycatboxyhc acid remains in contact with excess aldehyde, a redox disproportionation reaction occurs that forms a catboxyhc acid ... 

Mitsubishi Chemical Industries, Ltd. practiced a Henkel II technology starting with toluene to produce benzoic acid. Reaction of benzoic acid with potassium hydroxide resulted in potassium benzoate, which was subjected to a disproportionation reaction to produce dipotassium terephthalate and benzene. Dipotassium terephthalate reacted with sulfuric acid, and the resulting terephthahc acid was recovered by filtration and drying (65,66). Here, dipotassium sulfate was the by-product. 

Disproportionation reactions of siUcon hydrides occur readily in the presence of a variety of catalysts. For example ... 

Similar disproportionation reactions are catalyzed by organic catalysts, eg, adiponittile, pyridine, and dimethyl acetamide. Methods for the redistribution of methyUiydridosilane mixtures from the direct process have been developed to enhance the yield of dimethylchlorosilane (158). 

The production of sihcon tetrachloride by these methods was abandoned worldwide in the early 1980s. Industrial tetrachlorosilane derives from two processes associated with trichlorosilane, the direct reaction of hydrogen chloride on sihcon primarily produced as an intermediate for fumed sihca production, and as a by-product in the disproportionation reaction of trichlorosilane to silane utilized in microelectronics. Substantial quantities of tetrachlorosilane are produced as a by-product in the production of zirconium tetrachloride, but this source has decreased in the 1990s owing to reduction in demand for zirconium in nuclear facihties (see Nuclearreactors). The price of tetrachlorosilane varies between l/kg and 25/kg, depending on grade and container. 

The behavior of oligosiloxanediols in the presence of strong bases is different. The contribution to the overall process of the disproportionation reaction, involving a migration of the ultimate siloxane unit between siloxane molecules, is much greater and may even completely dominate the polycondensation reaction (80). The reactivity enhancement of the siloxane bond adjacent to the sHanolate anion can be understood in terms of n(0) (7 (SiO) conjugation. 

Several side reactions or post-cuting reactions are possible. Disproportionation reactions involving terminal hydride groups have been reported (169). Excess SiH may undergo hydrolysis and further reaction between silanols can occur (170—172). Isomerization of a terminal olefin to a less reactive internal olefin has been noted (169). Viaylsilane/hydride interchange reactions have been observed (165). 

The transalkylation reaction is essentiaHyisothermal and is reversible. A high ratio of benzene to polyethylbenzene favors the transalkylation reaction to the right and retards the disproportionation reaction to the left. Although alkylation and transalkylation can be carried out in the same reactor, as has been practiced in some processes, higher ethylbenzene yield and purity are achieved with a separate alkylator and transalkylator, operating under different conditions optimized for the respective reactions. 

This decomposition is thermodynamically favored by decreasing temperature and increasing pressure (28). Decomposition is extremely slow below 673 K in the absence of a catalyst however, between 673—873 K many surfaces, particularly iron (29), cobalt, and nickel (30), promote the disproportionation reaction. 

The chain is broken by a combination or disproportionation reaction between the two radicals. 

For further examples of acyl-alkyl diradical disproportionation reactions, see ref. 2 and 91. 

Defluorination occurs even with sodium fluoride at 530 °C when tetra-fluorothiolene is converted to 2,5-difluQrothiophene [63], Dehydrofluonnation would be expected at such high temperature, but defluonnation is favored. The product composition also excludes a disproportionation reaction mechanism (equation 32). 

It is noteworthy that only in the case of dehydroquinolizidine derivatives does monomethylation produce the N-alkylated product. The formation of dialkylated products can be explained by a disproportionation reaction of the monoalkylated immonium salt caused by either the basicity of the starting enamine or some base added to the reaction mixture (most often potassium carbonate) and subsequent alkylation of the monoalkylated enamine. Reinecke and Kray 113) try to explain the different behavior of zJ -dehydroquinolizidine and zJ -dehydroquinolizidine derivatives by the difference in energies of N- and C-alkylation transition states because of the presence of I strain. 

The disproportionation reaction of isoquinolinium salts to 1,2-dihydro-isoquinolines and isocarbostyril derivatives (Scheme 16) was used by Brown and Dyke for the synthesis of berberine and 8-oxoberberine derivatives (277-279). 

Under alkaline conditions disproportionation reactions predominate. Thus with Na20 the dioxonitrate(II) first formed, disproportion-ates into the corresponding nitrite(III) and dioxodinitrate(iV-iV)(I) ... 

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... 

No 3,4-dihydroquinolmes of type 29 have ever been isolated, or even detected by any spectroscopic method however, their intermediacy was postulated for the disproportionation reaction of 1,2-dihydroquinolines (85CJC412) and for flash-vacuum thermolysis of triazoles (98JOC5779). 

Aldehydes 1 that have no a-hydrogen give the Cannizzaro reaction upon treatment with a strong base, e.g. an alkali hydroxide.In this disproportionation reaction one molecule is reduced to the corresponding alcohol 2, while a second one is oxidized to the carboxylic acid 3. With aldehydes that do have a-hydrogens, the aldol reaction takes place preferentially. 

Destruction of macroradicals—scission of kinetic chains. A disproportionation reaction is most common at this stage ... 

Olefins could he catalytically converted into shorter and longer-chain olefins through a catalytic disproportionation reaction. For example, propylene could he disproportionated over different catalysts, yielding ethylene and butylenes. Approximate reaction conditions are 400°C and 8 atmospheres ... 

Table 8-5 indicates the wide variety of catalysts that can effect this type of disproportionation reaction, and Figure 8-7 is a flow diagram for the Phillips Co. triolefm process for the metathesis of propylene to produce 2-butene and ethylene. Anderson and Brown have discussed in depth this type of reaction and its general utilization. The utility with respect to propylene is to convert excess propylene to olefins of greater economic value. More discussion regarding olefin metathesis is noted in Chapter 9. 

Typical conditions for the disproportionation reaction are 450-530°C and 20 atmospheres. A mixture of C0O-M0O3 on aluminosilicates/alumina catalysts can he used. Conversions of approximately 40% are normally used to avoid more side reactions and faster catalyst deactivation. The equilihrium constants for this reaction are not significantly changed hy shifting from liquid to vapor phase or hy large temperature changes. 

Terephthalic acid is an important monomer for producing polyesters. The main route for obtaining the acid is the catalyzed oxidation of paraxylene. It can also be produced from benzoic acid by a disproportionation reaction of potassium benzoate in the presence of carbon dioxide. Benzene is the coproduct ... 

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