High-pressure disproportionation

Ceo = Fullerene SWNTs = Single-walled carbon nanotubes MWNTs = Multiwalled carbon nanotubes DWNTs = Double-walled carbon nanotubes CNTs = carbon nanotubes TEM = Transmission electron microscopy HRTEM = High-resolution transmission electron microscopy SEM = Scanning electron microscopy AFM = Atomic force microscopy Ch = Chiral vector CVD = Chemical vapor deposition HiPco process = High-pressure disproportionation of CO RBM = Radical breathing vibration modes DOS = Electronic density of states. 

The coordination chemistry of NO is often compared to that of CO but, whereas carbonyls are frequently prepared by reactions involving CO at high pressures and temperatures, this route is less viable for nitrosyls because of the thermodynamic instability of NO and its propensity to disproportionate or decompose under such conditions (p. 446). Nitrosyl complexes can sometimes be made by transformations involving pre-existing NO complexes, e.g. by ligand replacement, oxidative addition, reductive elimination or condensation reactions (reductive, thermal or photolytic). Typical examples are ... 

For /-butyl peresters there is also a variation in efficiency in the series where R is primary secondary>tertiary. The efficiency of /-butyl peroxypentanoate in initiating high pressure ethylene polymerization is >90%, that of /-butyl peroxy-2-ethylhexanoate ca 60% and that of/-butyl peroxypivalate ca 40%.196 Inefficiency is due to cage reaction and the main cage process in the case where R is secondary or tertiary is disproportionation with /-butoxy radicals to form /-butanol and an olefin.196... 

High-pressure in-situ NMR spectroscopy have been reported about reactions of carbon monoxide with cobalt complexes of the type, [Co(CO)3L]2. For L=P(n-C4H9)3, high pressures of carbon monoxide cause CO addition and disproportionation of the catalyst to produce a catalytically inactive cobalt(I) salt with the composition [Co(CO)3L2]+[Co(CO)4] . Salt formation is favoured by polar solvents [13],... 

The imstable seven-membered ring molecule disproportionates rapidly to form eight-membered SCjSj and a few minor components. The SejSj was characterized by chemical analysis, molecular weight determination, high-pressure liquid chromatography (HPLC), X-ray crystallography, and Raman spectroscopy and was shown to contain mainly the isomer 1,2,3-Se3S5 (see also 3.2-3.4). 

Fe(OH)2 is thermodynamically unstable with respect to magnetite (eq. (8.2) and (8.3)) and other Fe " compounds. It can, however, exist as a mestable phase for limited periods. Wustite, FeO, is only stable at temperatures greater than 570 °C. At lower temperatures it disproportionates to Fe° and Fe304. Figure 8.1 shows the stability domains for wustite, iron and magnetite as a function of temperature and oxygen content. The phase boundaries of wustite at high pressures have been estab-... 

Toluene disproportionation was carried out in a high-pressure continuous flow micro reactor. Granular catalyst (32-64 mesh, 2.5 cm ) was loaded into a stainless steel tube reactor. Toluene was fed at a rate of 10 cm h (liquid) in the flow of H2S(0.2vol.%)/H2 mixture gas (200 cm min b at 623K and 6MPa. The effluent was analyzed by gas chromatography (Shimadzu, GC-9A) by a flame ionization detector (FID). 

The hexanes undergo side reactions even more readily than do the pentanes. Although disproportionation and cracking can be suppressed to some extent by the addition of cyclic hydrocarbons, this treatment is not effective enough to ensure satisfactory catalyst life, and hydrogen at relatively high pressure must be used as the inhibitor. 

The study of pyridine-piperidine reactions under high pressure conditions has given much information concerning the kinetics of HDN, but these results are however complicated by alkyl transfer (disproportionation) reactions, and thus the possibility of using such reactions as an easy test for determination of mechanism and as a catalyst probe is partly excluded. The study of polycyclic amines (quinoline, etc.) for the same purpose is limited by the complexity and the number of different possible routes, but is a very interesting test reaction for an overall study of catalytic activity or selectivity toward HDN in industrial conditions. Because no disproportionation occurs and the numbers of products and routes are reasonable, the studies of pyridine-piperidine and alkylpyridine-alkylpiperidine HDN under normal H2 pressure and low amine pressure (< lOTorr) are very powerful test reactions both for mechanism determination and catalyst study, although these conditions are far removed from those of industrial practice. 

The monophosphides REP (RE = La, Ce, Pr, Nd, Sm, Gd, Tb, Tm, Yb) crystallize in the NaCl-type structure at ambient pressure. All of them undergo phase transitions, some into a tetragonally distorted CsCl related structure (Ea, Pr, Nd) and the others into a more complicated unknown high-pressure phase (Sm, Gd, Tb, Tm, Yb) at pressures from 35 to 51 GPa, respectively. It might be that a disproportionation occurs, similar to that in Eu2As2. ... 

Disproportionation of toluene occurs via benzenium [10] or benzylic [19] cations. Formation of a benzylic type of carbocation is limited by high pressure of hydrogen and omitted in Figure 2. The presence of strong acid sites at high reaction temperatures (873 K) results in the reaching of the near-equilibrium products concentrations of the products in the disproportionation of toluene. ... 

The micropore space can work as the high pressure field, as suggested in section 3. If this assumption is correct, we can observe a macroscopic high pressure effect in the micropore. The disproportionation reaction of (NO)2 given by Eq. (16) ... 

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