Reactions in the Vapor Phase

Berty, J.M., Process and Equipment for Exothermal Catalytic Reaction in the Vapor Phase, 1969, German Patent Disclosure 1,915,560. 

Chemical vapor deposition may be defined as the deposition of a solid on a heated surface from a chemical reaction in the vapor phase. It belongs to the class of vapor-transfer processes which is atomistic in nature, that is the deposition species are atoms or molecules or a combination ofthese. Beside CVD, they include various physical-vapor-deposition processes (PVD) such as evaporation, sputtering, molecular-beam epitaxy, and ion plating. 

The results here clearly demonstrate some of the important differences between reactions in the vapor phase and those in the aqueous phase. Water solvates the ions that form and thus enhances the heterolytic bond activation processes. This leads to more significant stabilization of the charged transition and product states over the neutral reactant state. The changes that result in the overall energies and the activation barriers of particular elementary steps can also act to alter the reaction selectivity and change the mechanism. 

Model flame studies in hydrogen-oxygen flames show that vaporized Mg, Cr, Mn, Sn or U salts are active as radical recombination catalysts at about 1 ppm (4). It was not determined whether this effect was produced by homogeneous reactions in the vapor phase or by the presence of Gne particles. 

The reaction of perfluoropenta-1,2-diene with cesium fluoride in foramide led to nonafluoropent-2-ene [58]. With anhydrous CsF the reaction in the vapor phase affords perfluoro-2-pentyne with MeOH, the reaction affords l-methoxy-2-per-fluoropentyne and l-methoxy-2H-octafluoro-2-(Z)-pentene [58]. 

It is remarkable that the isotope effects measured for these reactions in the vapor phase are about the same as the solvolysis KIEs measured in aqueous solution. 

In this sequence a radical, possibly a btradical derived from unpairing the electrons of the oxazirane oxygen-nitrogen bond, abstracts the a-hydrogen atom of the A -alkyl group to form (XXI) which subsequently isomerizes to (XXII). Alternatively the formation of (XXII) may take place directly by a concerted, reaction. In either event the iminoaikoxy radical (XXII) carries the chain. The ammonia which is formed presumably comes from aldol-like condensations of the imine (XXIV). The fact that vapor-phase pyrolysis does not take this course simply reflects tbo low probability of a chain reaction in the vapor phase. 

Exercise 4-5 Use the bond-energy table (4-3) to calculate AH° for the following reactions in the vapor phase at 25° ... 

Sabatier and Senderens (59) conducted the first hydrogenation reaction in the vapor phase. In 1903, Normann (60) patented the liquid-phase hydrogenation process for oils. Later, Crossfield and Sons, a British company, purchased the patent. 

The complex Mo205(Me)2-2MeOH was detected (56) as a condensation product of Mo03 vapor with methanol, water, and THF at - 196°C. Such cocondensation reactions in the vapor phase again appear to have considerable potential as a novel synthetic route. 

Mass spectrometry can give valuable information on the structural details of Sn(II) heterometallic derivatives, subject to stability with respect to the disproportionation reaction in the vapor phase. The mass spectral results demonstrate that fast atom bombardment mass spectrometry (FARMS) could find immense applications in the characterization of heterometallic derivatives, particularly of non-volatile, high molecular weight compounds, such as those of tin. 

The different classes of industrial catalytic selective oxidation reactions in the vapor phase (over solid catalysts) are ... 

Removal of heat from the reaction. In the vapor phase catalytic oxidation of naphthalene to phthalic anhydride, the heat of reaction is so great that unless it is rapidly and thoroughly dissipated the temperature of the catalyst mass rises to a point where complete combustion only occurs. Further, there is a tendency for the pentoxide of vanadium to be reduced to lower oxides at the high temperatures used, particularly if the oxygen supply is limited. These lower oxides tend to combine with the phthalic anhydride and subsequently decompose to destroy the anhydride, so that simple limitations of the oxygen supply to prevent further oxidation of the hydrocarbon is not effective. 

The operation takes place in the liquid phase, around 150°C, with palladium nitrate and a selectivity of 72 molar per cent but is accompanied by severe corrosion. It appears preferable to carry out the reaction in the vapor phase, with a catalyst deposited on alumina, promoted by gold and alkaline acetates, to prevent the formation of diphenyl or the direct production of phenol, which ultimately reduces selectivity. Between 180 and 200 0 and at 0.5.106 Pa absolute, the yield is 75 molar per cent, with a once-through -conversion of about 10 per cent... 

When released to the atmosphere, RDX is degraded by reacting with photochemically generated hydroxyl radicals (Atkinson 1987 HSDB 1994). The half-life for this reaction in the vapor phase was estimated to be 1.5 hours (Atkinson 1987 HSDB 1994). No data were located on photolysis of RDX in the atmosphere. However, it is expected that photolysis of RDX is an important fate process in the atmosphere since RDX absorbs ultraviolet wavelengths between 240 and 350 nm (Army 1986e) and it undergoes rapid photolysis in water (Army 1980a). 

Reaction (1) is the analogue in solution of CVD (Chemical Vapor Deposition) reactions in the vapor phase. The method in solution is usually called CBD for Chemical Bath Deposition or CSD for Chemical Solution Deposition. As compared to CVD which is widely used in the semiconductor industry, the development of CBD has remained limited. 

Carrying out the reaction in the vapor phase, within the meshes of a metal packing, with or without other catalyst. 

Isolation of these reactive molecules could not be achieved because of their strong tendency to perform self-condensation. Their existence was proved by carrying out the reaction in the vapor phase [2]. However, their condensation products could be observed by GC-MS methods. Mass-... 

The character of the association is that of a chemical reaction in the vapor phase. Each reaction... 

In this chapter we extend our treatment of mechanisms for metal-catalyzed reactions in the vapor phase to heterogeneous catalytic reactions carried out in aqueous media and electrocatalytic reactions. More specifically, we discuss what is known about the wa-ter/metal interface, its reactivity, and the influence of the aqueous phase on elementary surface processes including adsorption, reaction, diffusion and desorption and sofution-phase kinetic processes. We advance these ideas into the discussion of the mechanisms... 

The main industrial application of P-pinene is the noncatalytic thermal isomerization reaction in the vapor phase to yield P-myrcene (besides limonene and p-menthadiene) as an intermediate for the commercial production of flavor and fragrance chemicals (Figure 3B.6), such as the terpenic alcohols geraniol, nerol and linalool, and synthetic aromas (citral, citronellal, menthol, and myrcenol). ... 

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