Platinum reactivity

As mentioned, cyclopentanes can be formed with monofunctional catalysts, and so even with dual function catalysts, one would expect some of the cyclopentanes to form via mechanisms associated with the platinum reactivity part of the dual functionality. 

Bromine has a lower electron affinity and electrode potential than chlorine but is still a very reactive element. It combines violently with alkali metals and reacts spontaneously with phosphorus, arsenic and antimony. When heated it reacts with many other elements, including gold, but it does not attack platinum, and silver forms a protective film of silver bromide. Because of the strong oxidising properties, bromine, like fluorine and chlorine, tends to form compounds with the electropositive element in a high oxidation state. 

Other elements have atoms that can have different ratios of protons to neutrons. Indeed, hydrogen actually consists of three types of atoms. All hydrogen atoms have the same number of protons (one for hydrogen), giving each a mass of 1 Dalton, but some atoms of hydrogen also contain one neutron in the nucleus as well as the proton (mass of 2 Da), while yet others have two neutrons with each proton (mass of 3 Da). Thus hydrogen has three naturally occurring isotopes of mass 1, 2, and 3 Da. Chemically, there are only small differences between the reactivities of the different isotopes for any one element. Thus isotopes of palladium aU react in the same way but react differently from all isotopes of platinum. 

Common catalyst compositions contain oxides or ionic forms of platinum, nickel, copper, cobalt, or palladium which are often present as mixtures of more than one metal. Metal hydrides, such as lithium aluminum hydride [16853-85-3] or sodium borohydride [16940-66-2] can also be used to reduce aldehydes. Depending on additional functionahties that may be present in the aldehyde molecule, specialized reducing reagents such as trimethoxyalurninum hydride or alkylboranes (less reactive and more selective) may be used. Other less industrially significant reduction procedures such as the Clemmensen reduction or the modified Wolff-Kishner reduction exist as well. 

Dry chlorine reacts with most metals combustively depending on temperature alurninum, arsenic, gold, mercury, selenium, teUerium, and tin react with dry CI2 in gaseous or Hquid form at ordinary temperatures carbon steel ignites at about 250°C depending on the physical shape and titanium reacts violendy with dry chlorine. Wet chlorine is very reactive because of the hydrochloric acid and hypochlorous acid (see eq. 37). Metals stable to wet chlorine include platinum, silver, tantalum, and titanium. Tantalum is the most stable to both dry and wet chlorine. 

Catalytic dewaxiag (32) is a hydrocrackiag process operated at elevated temperatures (280—400°C) and pressures, 2,070—10,350 kPa (300—1500 psi). However, the conditions for a specific dewaxiag operatioa depead oa the aature of the feedstock and the product pour poiat required. The catalyst employed for the process is a mordenite-type catalyst that has the correct pore stmcture to be selective for normal paraffin cracking. Platinum on the catalyst serves to hydrogenate the reactive iatermediates so that further paraffin degradation is limited to the initial thermal reactions. 

Several types of nitrogen substituents occur in known dye stmetures. The most useful are the acid-substituted alkyl N-substituents such as sulfopropyl, which provide desirable solubiUty and adsorption characteristics for practical cyanine and merocyanine sensitizers. Patents in this area are numerous. Other types of substituents include N-aryl groups, heterocycHc substituents, and complexes of dye bases with metal ions (iridium, platinum, zinc, copper, nickel). Heteroatom substituents directly bonded to nitrogen (N—O, N—NR2, N—OR) provide photochemically reactive dyes. 

Reactive halogens in various series have been removed by catalytic hydrogenation with either platinum or palladium catalysts, and other nucleophiles which have been used in chloride displacements include hydroxide ion, alkoxides, hydrosulflde, hydrazine and toluene-p-sulfonylhydrazine, and trimethyl phosphite. 

F1 NMR of chemisorbed hydrogen can also be used for the study of alloys. For example, in mixed Pt-Pd nanoparticles in NaY zeolite comparaison of the results of hydrogen chemisorption and F1 NMR with the formation energy of the alloy indicates that the alloy with platinum concentration of 40% has the most stable metal-metal bonds. The highest stability of the particles and a lowest reactivity of the metal surface are due to a strong alloying effect. 

Ac-Imidazole, PtCl2(C2H4), 23°, 0.5-144 h, 51-87% yield. Platinum(II) acts as a template to catalyze the acetylation of the pyridinyl alcohol, C5H4N(CH2) CH20H. Normally acylimidazoles are not very reactive acy-lating agents with alcohols. 

Differences are also observed in the reactivity of platinum(II) complexes of [82X2] and [802X2] towards halogens. In the former case oxidative addition to give platinum(IV) complexes occurs, with retention... 

The octahedral hexafluorides are obtained directly from the elements and both are volatile, extremely reactive and corrosive solids, RhFg being the least stable of the platinum metal hexafluorides and reacting with glass even when carefully dried. They are thermally unstable and must be frozen out from the hot gaseous reaction mixtures, otherwise they dissociate. 

Passivity is the loss of chemical reactivity of certain metals and alloys under specific environmental conditions. In other words, certain metals (e.g., iron, nickel, chromium, titanium, etc.) become relatively inert and act as noble metals (e.g., gold and platinum). Figure 4-420 shows the behavior of a metal immersed in an air-free acid solution with an oxidizing power corresponding to point A... 

The benzylic position of an alkylbcnzene can be brominated by reaction with jV-bromosuccinimide, and the entire side chain can be degraded to a carboxyl group by oxidation with aqueous KMnCfy Although aromatic rings are less reactive than isolated alkene double bonds, they can be reduced to cyclohexanes by hydrogenation over a platinum or rhodium catalyst. In addition, aryl alkyl ketones are reduced to alkylbenzenes by hydrogenation over a platinum catalyst. 

The platinum black by reduction of the oxide may sometimes be used a second, third or even more times in the reduction of certain compounds merely by reactivating (Note 8) with air or oxygen. A spent catalyst must be reworked (Note 9)... 

Thermolysis of m-PtH(CH2CMe3)(cy2PC2H2Pcy2) at 45-80°C yields a bent platinum(0) complex (Figure 3.13) that is intensely reactive to a whole range of unactivated C—H bonds in saturated and unsaturated hydrocarbons. 

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