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The olefin metathesis is the other reaction for which rhenium is used as catalyst. Normally Re 2 O 7 on alumina is used for this process. [73] Rhenium catalysts are very resistant to chemical poisoning from nitrogen, sulfur and phosphorus, and so are used in certain kinds of hydrogenation reactions. [23] [74] [75]
The second step then is a concerted SNi reaction breaking a CC bond and forming a new alkylidene-titanium bond; the process then repeats itself with a second monomer: Only much later the polynorbornene was going to be produced through ring opening metathesis polymerisation. The DuPont work was led by Herbert S. Eleuterio.
Rhenium's main oxides are rhenium(IV) oxide and rhenium(VII) oxide. Rhenium(IV) oxide is a gray to black crystalline solid that can be formed by comproportionation. [21] At high temperatures it undergoes disproportionation. It is a laboratory reagent that can be used as a catalyst. It adopts the rutile structure.
Rhenium also forms two iodides, rhenium tetraiodide, which can be reduced from perrhenic acid with hydrogen iodide, and rhenium triiodide, which forms from the decomposition of this. [ 34 ] [ 35 ] Like tungsten and molybdenum , with which it shares chemical similarities, rhenium forms a variety of oxyhalides .
The thiourea hydrogen bonds to the nitro group and stabilizes the incoming negative charge, while the amine acts a specific base to activate the nucleophile. This is an example of bifunctional catalysis. Hydrogen-bond catalysis is a type of organocatalysis that relies on use of hydrogen bonding interactions to accelerate and control organic ...
Rhenium alloys are being used in electronic components, gyroscopes and nuclear reactors. Rhenium finds its most important use as a catalyst. It is used as a catalyst in reactions such as alkylation, dealkylation, hydrogenation and oxidation. However its rarity makes it the most expensive of the refractory metals. [28]
Methylrhenium trioxide is commercially available. It can be prepared by many routes, a typical method is the reaction of rhenium heptoxide and tetramethyltin: [1] Re 2 O 7 + (CH 3) 4 Sn → CH 3 ReO 3 + (CH 3) 3 Sn−O−ReO 3. Analogous alkyl and aryl derivatives are known.
An illustrative example is the effect of catalysts to speed the decomposition of hydrogen peroxide into water and oxygen: . 2 H 2 O 2 → 2 H 2 O + O 2. This reaction proceeds because the reaction products are more stable than the starting compound, but this decomposition is so slow that hydrogen peroxide solutions are commercially available.