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Topic: Disproportionation

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	Disproportionation Summary
		Literally, disproportionation is a chemical reaction in which a single metal ion species undergoes an internal redox reaction and forms two different products in stoichiometric quantities.
		Disproportionation is a reaction that is more characteristic of the heavier transition elements and the f-block elements.
		Disproportionation or dismutation is a type of reaction in redox chemistry in which a reactant is both oxidised and reduced in the same chemical reaction forming 2 separate compounds.
	www.bookrags.com /Disproportionation (467 words)

	Olefin metathesis catalyst - Patent 4567159
		By the term "disproportionation" or "metathesis" throughout this specification is meant the conversion of the feed olefinic (or unsaturated) hydrocarbon to a mixture of olefinic (or unsaturated) hydrocarbons having different numbers of carbon atoms than the feed hydrocarbons.
		The disproportionation reaction can be carried out by contacting the olefins to be disproportionated with the catalyst in the liquid phase or the gas phase, depending on structure and molecular weight of the olefins, temperature and pressure.
		The length of time during which the olefinically unsaturated compounds to be disproportionated are contacted with the catalyst depends upon several factors such as the activity of the catalyst, temperature, pressure, and structure of the olefinically unsaturated compound to be disproportionated.
	www.freepatentsonline.com /4567159.html (3672 words)

	Kai Finster: Master Thesis Projects - Microbiology, Biological Sciences, AU (Site not responding. Last check: 2007-10-18)
		The term disproportionation is chosen to distinguish between the transformation of organic and inorganic compounds.
		An analogy to sulfur disproportionation is found by the obligate anaerobic synthrophic methanogenic consortia where juxtapositioning of hydrogen producing and hydrogen consuming bacteria is the key to render thermodynamically unfavorable reactions favorable (Schink 1997).
		Studies of the biochemical pathways of sulfur disproportionation require sufficient cell biomass, which has been difficult to obtain due to the special growth requirements of the culture, such is the presence of metall axides as sulfide scrubs and sufficient buffering capacity to counteract growth ceasing pH fluctuations.
	www.biology.au.dk /kai.finster.projects.htm (2241 words)

	L1. KINETICS AND MECHANISM OF A NEW CLASS OF THE REVERSIBLE TOPOCHEMICAL REACTIONS - DISPROPORTIONATION OF ACIDIC ...
		The observed kinetic particularities of the acidic salts disproportionation are due to a wide variety of the localization forms of this process.
		disproportionation is possibility of it’s proceeding in the damping auto-oscillatory regime.
		The solid state disproportionation is of particular interest, since such process may be considered as an effective way for formation of proton-hydrate sub-lattice which provides the high proton-conductivity of crystals.
	www.cstl.nist.gov /div838/kinet_conf/agenda/l_session/l1/l1.html (968 words)

	[No title] (Site not responding. Last check: 2007-10-18)
		Equilibration disproportionation does not occur at high temperatures but is likely at intermediate temperatures, although slow reaction kinetics at sufficiently low temperatures are such that little or no carbon may form.
		All the surface temperatures of the coils (60 and 90) are higher than the critical CO disproportionation temperature, which is again shown by line 18T in Figure 4 (b).
		To prevent CO from disproportionating, the curves representing the temperature profiles of the heat exchanger walls must be above the line 18T.
	www.wipo.int /cgi-pct/guest/getbykey5?KEY=99/66262.000323&ELEMENT_SET=DECL (7251 words)

	chimie7B : sulfures et Oxydes : recherche
		Isomerization and disproportionation of alkylated derivatives of thiophene, benzothiophene and dibenzothiophene
		However it was also shown that the reactivity of these compounds could be improved significantly by isomerization (displacement of alkyl groups to other positions to the aromatic structure) in the presence of an acidic support.
		The objective is to examine in detail the fundamental aspects of the isomerization and disproportionation of alkylated derivatives of thiophene, benzothiophene and dibenzothiophene over acidic materials which could be used as supports for (or in combination with) hydrotreating catalysts as well as over bifunctional catalysts containing sulfides.
	labo.univ-poitiers.fr /sulfuresetoxydes/uk/recherche/heterocyclic_compounds_reactivity.htm (233 words)

	Isopentane disproportionation - Patent 5489727
		The disproportionation of isopentane(s) in the presence of hydrogen fluoride as the catalyst is improved by adding at least one C.sub.6 -C.sub.18 (preferably C.sub.6 -C.sub.8) isoalkane to the isopentane feed.
		It is an object of this invention to improve the disproportionation of isopentanes (2-methylbutane and/or 2,2-dimethylpropane) to isobutane and C.sub.6 + alkanes.
		In the latter case, the feed rate of the liquid hydrocarbon feed can vary widely depending on the dimensions of the reactor (generally a reactor tube made of a corrosion-resistant metal, optionally equipped with static mixing means), the desired feed throughput and the desired isopentane conversion.
	www.freepatentsonline.com /5489727.html (1762 words)

	Elemental Sulfur and Thiosulfate Disproportionation by Desulfocapsa sulfoexigens sp. nov., a New Anaerobic Bacterium ...
		Thiosulfate and elemental sulfur disproportionation were affected by the presence of molybdate.
		Disproportionation of inorganic sulfur compounds by the sulfate-reducing bacterium Desulfocapsa thiozymogenes gen. nov., sp.
		Bacterial disproportionation of elemental sulfur coupled to chemical reduction of iron or manganese.
	aem.asm.org /cgi/content/full/64/1/119 (4750 words)

	Abstract Mix (Site not responding. Last check: 2007-10-18)
		From a quantitative determination of the disilane products as a function of the reactant ratio, a value for the branching ratio of cross-disproportionation of di- and trimethylsilyl radicals relative to the branching ratio for the disproportionation of dimethylsilyl radicals can be extracted.
		Our results provide strong evidence that the ratio of the rate constants for hydrogen abstraction from di- and trimethylsilane by H atoms is larger than absolute rate measurements suggest.
		Disproportionation reactions yielding silaethenes occur to a minor extent, and are responsible for the formation of six trisilanes.
	wwwuser.gwdg.de /~ilein/a_mix.htm (201 words)

	Publikationen Prof. Dr. Gerhard Roewer
		The Lewis-base catalyzed disproportionation mechanism is discussed and seems to involve donor stabilized silylenes as key intermediates in the polymer formation process.
		Catalyst for the disproportionation of aryl- or alkylhalodisilanes to aryl- or alkylhalomonosilanes and aryl- or alkylhalopolysilanes.
		Silica-supported phosphine oxide catalyst for the disproportionation of aryl- or alkylhalodisilanes to aryl- or alkylhalomono- and polysilanes.
	www.chem.tu-freiberg.de /ano/publ_roewer.html (10954 words)

	The Function of the Trimethylsilyl Substituent in the Syntheses of Low-valent Phosphorus and Arsenic Containing ...
		Summary: The heterogeneous disproportionation of 1,1,2,2-tetrachlorodimethyldisilane to chloromethylsilanes and oligo(chloromethylsilane)s is catalyzed by Lewis bases like bis(dimethylamid)phosphoryl compounds and N-heterocycles.
		One interesting polysilane synthesis has been developed based on the disproportionation of chloromethyldisilanes, that are by-products of the industrial chloromethylsilane production (Müller-Rochow-Synthesis) [1].
		The heterogeneous catalytic disproportionation offers the access to a poly(chloromethylsilane) free of catalyst, due to a perfect phase separation between the catalyst, the starting chloromethyldisilane and the reaction products [1].
	www.chem.tu-freiberg.de /ano/agsi/material/poli/thl/THL1.htm (896 words)

	Famar.pl (Site not responding. Last check: 2007-10-18)
		Catalytic activity of our catalyst is determined in the disproportionation test in the following way: 100 grams of rosin and 2 grams of Catalyst J-30 M-2 are mixed together in a three-neck flask of capacity 250 ml and equipped with a mechanical agitator, thermometer and on inlet of nitrogen or carbon dioxide.
		Catalyst J-30 M-2 was used for fifteen years for disproportionation of gum rosin, tall oil rosin as well as distilled tall oil.
		Gum rosin is disproportionated in the continuously operated plant with the working catalyst concentration of about 1,5 %.
	www.famar.pl /Catalyst.htm (284 words)

	U (Site not responding. Last check: 2007-10-18)
		R.A. Kemp and D.M. Hamilton, "Disproportionation of Olefins", USP 4754099.
		D.M. Hamilton and R.A. Kemp, "Concurrent Isomerization and Disproportionation of Olefins", USP 4996386.
		R.A. Kemp and D.M. Hamilton, "Concurrent Isomerization and Disproportionation of Olefins", USP 5120896.
	www.unm.edu /chemistry/faculty/research/kemp/kempat.htm (677 words)

	esp@cenet Vue de la description
		Disproportionation of the higher oxidation state of the catalyst was reduced in United States Patent No. 6,624, 262 by an addition of excess ligands to modify the catalyst environment.
		In certain embodiments, the suitable catalyst may be at least partially soluble in the reaction media, possess a low redox potential, stability towards ionic species, low propensity to disproportionation, and sufficient conditional metal-radically transferable atom or group phylicity to act as a catalyst in the reaction media.
		Disproportionation of the transition metal complex is another parameter that has to be considered when determining the suitability of a particular catalyst in a certain environment, for example, the reaction of Cul containing species to give a Cull species and
	v3.espacenet.com /textdes?DB=EPODOC&IDX=WO2004096872&CY=ep&LG=fr&QPN=WO2004096872 (14011 words)

	[No title] (Site not responding. Last check: 2007-10-18)
		Within a zeolite pore, hydrocarbon conversion reactions, such as paraffin isomerization, olefin skeletal or double bond isomerization, oligomerization and aromatic disproportionation, alkylation or transalkylation reactions are governed by constraints imposed by the channel size.
		Disproportionation Catalyst In one aspect of the present invention, the first stage acidic catalyst can be a selectivated catalyst treated in situ or ex situ with
		When the desired coke deposition has been effected, the alkylaromatic feed is continued in contact with the coke-containing catalyst under conditions of temperature and hydrogen concentration conducive to disproportionation, with a greatly reduced coking rate.
	www.wipo.int /cgi-pct/guest/getbykey5?KEY=01/09067.010208&ELEMENT_SET=DECL (7060 words)

	session9 (Site not responding. Last check: 2007-10-18)
		Hydrogen is well known for modifying the physical and mechanical properties of materials (particularly the magnetic behavior of intermetallics and the embrittlement of steels), but it is less well known in terms of its influence on their microstructure.
		As the name indicates, the materials is disproportionated by reacting with hydrogen at elevated temperatures and then recombined by the subsequent removal of hydrogen under a vacuum.
		The hydrogenation disproportionation desorption and recombination (HDDR) process can be used to produce highly coercive NdFeB- and SmFe- type powders, for the former material also in a magnetically anisotropic form [1,2].
	www.ifw-dresden.de /imw/ismanam/session9.htm (976 words)

	Metal Ion Catalysis of Natural Products Transformations. Novel Aldopentose Disproportionation Reactions Catalyzed by ... (Site not responding. Last check: 2007-10-18)
		The overall process is a catalytic disproportionation reaction, in which two aldopentose molecules are transformed into the corresponding alditol and aldonolactone, both with an unchanged configuration around carbon atoms 2, 3, and 4.
		The mechanism of this reaction is suggested to involve coordination of a hydrated and an unhydrated substrate molecule through their carbon-1 bound oxygen atoms followed by a hydride shift from the hydrated to the unhydrated substrate.
		This disproportionation process is subsequently followed by aquation of the reaction product to give the free alditol and a mixture of the aldonic acid and the corresponding aldonolactone.
	pubs.acs.org /cgi-bin/abstract.cgi/inocaj/2005/44/i06/abs/ic0400989.html (202 words)

	LaNi5-xMx Alloys for Ni/Metal Hydride Electrochemical Cells
		This increase in diffusion increases the La content at the surface, where the La is readily oxidized to form a thick hydroxide layer in one of the disproportionation reactions.
		Preliminary support for this approach has been found through an analysis of cyclic lifetimes for various solutes as reported in the literature; the analysis reveals a close relationship between cyclic lifetime and the heat of formation of the solute with lanthanum (see figure).
		The finding of this relationship motivated the hypothesis that the rates disproportionation and/or degradation could be reduced by adding solutes that bond strongly with lanthanum.
	www.nasatech.com /Briefs/May99/NPO20107.html (604 words)

	Food Colloids Gallery (Site not responding. Last check: 2007-10-18)
		Disproportionation is an important type of instability in foams, whereby large bubbles grow in size at the expense of smaller ones due to the Laplace pressure difference.
		A single bubble may shrink due to disproportionation between the bubble and the planar air/water interface.
		In this research, light microscopy combined with image analysis has been used to study disproportionation of protein-stabilized air bubbles at a planar air-water interface, by monitoring time-dependent changes in bubble radii.
	www.foodcolloids.com /gallery (415 words)

	Alkyl Halides to Aldehydes and Ketones using 2-Nitropropane/NaOH - [www.rhodium.ws]
		The reactions appear to proceed by formation of aminobenzyl 2-propanenitronates which disproportionate into acetoxime and benzamides, thus establishing a relationship with the reaction of halides with sodium 2-propanenitronate to form esters with subsequent disproportionation.
		The unexpected formation of acetoxime and dimethylbenzamide is explicable only if the two result from the disproportionation of the ester, α-dimethylaminobenzyl 2-propanenitronate, arising from oxygen alkylation of 2-propanenitronic acid by the cation.
		The preparation of dimethylbenzamide in aqueous alcohol suggested that the more general reaction, converting halides to carbonyl compounds, might not necessarily require metallic sodium and anhydrous alcohol, and might be a preparative reaction for aliphatic carbonyl compounds under milder conditions.
	www.erowid.org /archive/rhodium/chemistry/halide.carbonyl.html (2112 words)

	Biogeochemical cycling of iodine and silicon (Site not responding. Last check: 2007-10-18)
		Research has been performed in three quite different areas: the rate of disproportionation of hypoiodous acid, the general distribution of iodine in the oceans, with particular emphasis on Shelf Seas of the UK, e.g., the Irish Sea, and the effect of phytoplanktonic algae upon the iodate and iodide in seawater.
		In disproportionation iodine in a given oxidation state produces compounds with both higher and lower oxidation states.
		Effect of Iodide Concentration upon the Kinetics of Disproportionation of Hypoiodous Acid in borate buffer.
	www.brookes.ac.uk /bms/research/truesdale.html (1087 words)

	American Chemical Society: Chemical & Engineering Safety Letters
		Chem., 57, 3751 (1992)], we warned that, in the absence of substrate and under an inert atmosphere, HSi(OCH2CH3)3 is disproportionated by Ti(OCH(CH3)2)4 to form SiH4, a pyrophoric gas.
		Such disproportionations, catalyzed by many metal complexes, have been reported in the literature [Adv.
		It has come to our attention that silane production may occur with our catalyst system even in the presence of substrate, especially if the reaction is run on a large scale or a large excess of silane is used.
	pubs.acs.org /cen/safety/19930329.html (353 words)

	Free Radical Polymerisation: Theoretical Evaluation
		The new solution for chain-length distributions (at least numerically) coincides with our earlier results (analytical solution [1] as well as data computed by use of numerical models) which were obtained by starting with strict coupling of time and degree of polymerization followed by an a posteriori Poisson broadening.
		For the case of a (pseudostationary) laser-pulse initiated polymerization process a closed solution could be derived for the pseudostationary radical concentration and for the chain-length distribution of dead polymer terminated by disproportionation or stabilized by chain-transfer to monomer or solvent.
		The methods available are strongly dependent on the type of mean of the length of the two reacting radicals; generally valid relationships between kinetic properties may be deduced for an arbitrary function; propagation probabilities (which are the key values for further investigations), however, are numerically accessible only.
	www.univie.ac.at /mmphc/pp_num.html (3744 words)

	Multiple sulfur isotope fractionations in biological systems: A case study with sulfate reducers and sulfur ...
		This concentration is still large enough not to effect the fractionation produced by the organisms (Habicht and others, 2002).
		Frederiksen T. M., and Finster, K., 2003, Sulfite-oxido-reductase is involved in the oxidation of sulfite in Desulfocapsa sulfoexigens during the disproportionation of thiosulfate and elemental sulfur: Biodegredation, v.
		Thamdrup B., Finster, K., Hansen, J. W., and Bak, F., 1993, Bacterial disproportionation of elemental sulfur coupled to chemical-reduction of iron or manganese: Applied and Environmental Microbiology, v.
	www.ajsonline.org /cgi/content/full/305/6-8/645 (5246 words)

	Some new observations on an old reaction: disproportionation and the formation of P-O-P intermediates in the ... (Site not responding. Last check: 2007-10-18)
		C in a sealed tube) led to the isolation of the unexpected dimethyldiphenoxyphosphonium bromide 3 (18% yield), together with diphenyl methylphosphonate, triphenyl phosphate, and bromobenzene (Scheme 3).
		This result was reminiscent of the disproportionations reported by Nesterov who found that thermal decomposition of the methyl iodide adducts of diphenyl phenylphosphonite and phenyl diphenylphosphinite above 200
		In part it may result from disproportionation (Scheme 11) although the absence of equivalent quantities of the corresponding dimethyl substituted disproportionation products 21 suggests that it is also an oxidation product resulting from the interaction of triaryl phosphite, produced by dissociation (Scheme 9), with adventitious oxygen.
	www.arkat-usa.org /ark/journal/2004/I09_Yuan/CY-1133L/CY-1133L.asp (3341 words)

	Untitled Document (Site not responding. Last check: 2007-10-18)
		Gutfleisch, M. Kubis, A. Handstein, K.-H. Müller, L. Schultz: “Hydrogenation disproportionation desorption recombination in Sm-Co alloys by means of reactive milling”, Appl.
		Gutfleisch, M. Kubis, A. Handstein, K.-H. Müller and L. Schultz: “Hydrogenation disproportionation desorption recombination processes applied to NdFeB-, SmFe- and SmCo-type alloys”, MRS Symp.
		In this way the international community was familiarized with all partners involved in MAG-NET, with the aims and objectives as well as the work plan of the thematic network.
	mag-net.ee.umist.ac.uk /pubs/p3.html (1328 words)

	dismutation \| English \| Dictionary & Translation by Babylon
		Disproportionation or dismutation disproportionation is any chemical reaction of the type A + A → A' + A", where A, A' and A" are different chemical species.
		For example: 2 ArH+ → ArH + ArH2+ The reverse of disproportionation is called comproportionation.
		This definition comes from IUPAC ([1]) While the most common type is a redox reaction, other types are possible.
	www.babylon.com /definition/dismutation (90 words)

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