Vanadium compounds addition reactions

In addition to the reactions that produce elemental sulfur, competing reactions also occur that produce undesirable by-products such as sodium thiosulfate. This is detrimental, because the thiosulfate remains in solution, and its concentration can generally be reduced only by bleeding off a portion of the solution inventory. This solution purge waste stream is hazardous, largely because it also contains vanadium compounds. The key to reducing the metal content of the waste stream is to reduce the rate of thiosulfate formation. 

New approaches to the synthesis of SVO cathode material have been reported. In 1995, Takeuchi and Thiebolt patented a new preparation for SVO cathodes prepared via addition of elemental silver to vanadium compounds present in an anhydrous mixture. Oxygen-deficient SVO compounds were found, as well as compounds designed to provide a desired shape in the electrical discharge curve of the cell [59], Following this work in 1996, Takeuchi and Thiebolt patented several methods for the preparation of amorphous SVO prepared by chemical addition reaction at temperatures high enough to melt the mixture, coupled with rapid cooling... 

An example of fortuitous vanadium enolate chemistry is the CO addition reaction to a silylamido vanadium species in which the dimeric metallocycle 32 is transformed into the corresponding cyclic enolate 33, as shown in equation 12. Given silicon s profound oxophilicity, the absence of the Si-O moieties in 33 is surprising. For example, the liquid phase reaction shown in equation 13 is exothermic by ca 420 kJmol , as determined from the enthalpies of formation of tetramethoxymethane and the silicon compounds . 

Oxidative addition reactions for group VA compounds within the context of the discussion found in 5.8.2.9.1 are presented in 10.3.3.1 and 10.3.3.2, including some cases of reactions that may not be true oxidative additions. The discussion on vanadium is separated from its heavier cousins, niobium and tantalum, since the chemistry of V is distinct from that of Nb and Ta. Oxidative additions across metal-metal multiple bonds and involving clusters are not covered. 

With the cydopentadienyl ligand, vanadium forms the simple sandwich compound, "vanadocene , [V( - -C5Hj)2] which is dark violet, paramagnetic (3 unpaired electrons) and extremely air-sensitive. Oxidative addition reactions are possible and provide compounds such as [V()9 -CjH5)2C1 ] (n = 1,2,3) and LV(rj -C5H5)2R2], while it.s reaction with dithioacetic acid produces the dark-brown tetramer [V4(fj -C H5)4( 3-S4), Fig. 22.11. " With four V " atoms, eight electrons are available for six V-V bonds and the implied bond order of 2/3... 

Vanadium Oxytrichloride, VOCl3, commonly known as vanadyl chloride, is the easiest to prepare of all the halogen or oxyhalogen compounds of vanadium. It distils over as a yellow liquid when vanadium pentoxide is strongly heated, or when vanadiun trioxide is gently heated, in a current of chlorine. Addition of charcoal accelerates the reactions 9... 

Detection.—Apart from naturally occurring ores of vanadium, vanadium steels, and ferrovanadium, the commonest compounds of vanadium are those which contain the element in the pentavalent state, viz. the pentoxide and the various vanadates. The analytical reactions usually employed are, therefore, those which apply to vanadates. Most vanadium ores can be prepared for the application of these reactions by digesting with mineral acids or by alkaline fusion with the addition of an oxidising agent. When the silica content is high, preliminary treatment with hydrofluoric acid is recommended. Vanadium steels and bronzes, and ferrovanadium, are decomposed by the methods used for other steels the drillings are, for instance, dissolved in sulphuric acid and any insoluble carbides then taken up in nitric acid, or they are filtered off and submitted to an alkaline fusion. Compounds of lower valency are readily converted into vanadates by oxidation with bromine water, sodium peroxide, or potassium permanganate. 

Arsenic does not combine directly with carbon, silicon or boron. The reaction with metals to form definite arsenides or alloys is described no pp. 57-78. The presence of small quantities of arsenic or of its compounds in certain catalysts has a poisoning effect. The first traces added to the catalyst have the greatest effect thus the activity of 0-35 g. of platinum was reduced linearly by the addition of arsenic up to 0-7 mg., this quantity reducing the catalytic activity to 45 per cent, of its original value the addition of 10 mg. of arsenic, however, depressed the activity only to 26 per cent, of the original value.3 Vanadium catalysts are poisoned by the presence of arsenic, although the action is slow arsenic pentoxide is formed.4... 

Thus, the hydrodesulfurization process is a very complex sequence of reactions due, no doubt, to the complexity of the feedstock. Furthermore, the fact that feedstocks usually contain nitrogen and oxygen compounds (in addition to metal compounds) increases the complexity of the reactions that occur as part of the hydrodesulfurization process. The nitrogen compounds that may be present are typified by pyridine derivatives, quinoline derivatives, carbazole derivatives, indole derivatives, and pyrrole derivatives. Oxygen may be present as phenols (Ar-OH, where Ar is an aromatic moiety) and carboxylic acids (-C02H). The most common metals to occur in petroleum are nickel (Ni) and vanadium (V) (Reynolds, 1997). 

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