Vapor-phase hydrolysis

In the typical flame or vapor-phase hydrolysis process, which uses SiCfy as the precursor, sihcon tetrachloride vapor is fed into a flame using an oxygen carrier gas. Fine (<50 nm), amorphous sihca particles form in the flame (57). 

Broido, A. The Vapor Phase Hydrolysis of the Trichlorides of Lanthanum,... 

Phenol has been obtained by distillation from petroleum and synthesis by oxidation of cumene or toluene, and by vapor-phase hydrolysis of chlorobenzene (USITC 1987). In 1995, 95% of U.S. phenol production was based on oxidation of cumene except at one company that used toluene oxidation and a few companies that distilled phenol from petroleum (CMR 1996). In 1995 the total annual capacity of phenol production approached 4.5 billion pounds (CMR 1996). 

The hexafluoride is a very powerful oxidizing agent reacting violently with most oxidizable substances. Reaction with liquid water is violent forming HF, oxygen, lower fluorides of platinum, and other products. In vapor phase hydrolysis occurs more smoothly. 

Transparent vitreous sihca is made by electric melting of natural quartz minerals such as sand in vacuum. It also may be made by fusing quartz in flame or by vapor phase hydrolysis or oxidation of pure silicon compounds by heating electrically or using a flame or plasma. Translucent form is made by fusion of high purity quartz sand crystals. 

LB Gilman, C Woodward. An evaluation of microwave heating for the vapor phase hydrolysis of proteins. I. Comparison to vapor phase hydrolysis for 24 hours. In Current Research in Protein Chemistry. San Diego Academic Press, 1990, pp 23-36. 

Keil, R., and Kirchman, D. (1991b) Dissolved combined amino acids in marine waters as determined by vapor-phase hydrolysis method. Mar. Chem. 33, 243-259. 

Silicon Dioxide occurs as an amorphous substance that shows a noncrystalline pattern when examined by X-ray diffraction. It is produced synthetically, either by a vapor-phase hydrolysis process, yielding fumed silica, or by a wet process, yielding precipitated silica, silica gel, colloidal silica, or hydrous silica. Fumed silica is produced in an essentially anhydrous state, whereas the wet-process products are obtained as hydrates or contain surface-adsorbed water. 

Amino Acid Analysis. Vapor phase hydrolysis with HCl containing 0.1% sodium sulfite and amino acid analysis were performed as previously described (3). 

Fumed silica is traditionally produced by vapor phase hydrolysis of silicon tetrachloride in a hydrogen-oxygen flame [83]. Figure 7.16 shows the reaction sequence for this process. 

Vapor phase hydrolysis of chlorotoluenes appears to be accompanied by a much smaller degree of isomerization than liquid phase hydrolysis, and accordingly, the Hooker-Raschig process is considered more attractive than the original Dow process. The process, however, is much less attractive than the sulfonation and alkylation processes. The chemistry of the process is as follows ... 

OPF2H can be isolated among the products from the vapor phase hydrolysis of PF3, and is also obtained by treating halogenodifluoro-phosphines PF2X with MesSnOH (50). 

To perform AAA, a peptide must first be hydrolyzed in order to liberate the individual amino acids. To enhance the reliability of the results, each peptide. sample should be analyzed in triplicate. Hydrolysis is accomplished under either vapor-phase or liquid-phase conditions, through use of 6 N HCl. For vapor-phase hydrolysis, a specially designed screw-capped reaction vessel that is fitted with an inert slide valve is utilized (supplied by vendors such as Pierce and Waters). The desalted, dry peptide is placed in an acid-washed glass tube (e.g., 6 X 50 mm). One or more of these tubes is then inserted into the reaction vessel. After addition of approximately 250 /aL of 6 N HCl to the bottom of the reaction vessel, each vessel is purged with... 

This could indicate a slightly endothermic reaction. A small heat of reaction, hoWver, would indicate that the entropy factor T AS), although small, plays a paH, in determining the equilibrium position. A calculation from the free energies of formation of the gases at 25°C gives AF° = 1.1 kg-cal per mole for the vapor-phase hydrolysis. 

The superior approach to tryptophan analysis involves the addition of dodecanethiol to HCl, especially when combined with automatic vapor-phase hydrolysis. Alternative hydrolysis agents such as methane sulfonic acid, mercap-toethanesulfonic acid, or thioglycolic acid can produce 90% or greater yields. Acid hydrolysis additives and alkaline hydrolysis using 4.2 M NaOH are also used with varying results. 

Fumed silica, or fumed silicon dioxide, is produced by the vapor phase hydrolysis of silicon tetrachloride in an H2/O2 flame. The reactions are shovm in Chapter 19. Hydrophilic fumed silica bearing hydroxyl groups on its surface is produced by this process. Hydrophobic fumed silica is made by processing fumed hydrophilic silica through in-line hydrophobic treatments such as with silanes, siloxanes, silazanes, and so on [1]. Examples of different types of hydrophobic fumed silica coatings include DMDS (dimethyldichlorosilane), TMOS (trimethoxyoctylsilane), HMDS (hexamethyldisilazane). 

Aerosils or pyrogenic silica. Powders made by condensing silica from the vapor phase at elevated temperature. The silica vapor is produced by a) direct volatilization of SiOj, (6) reduction of SiOj to volatile SiO which is reoxidized, (c) oxidation of volatile silicon compounds such as chloride or esters, or (d) vapor phase hydrolysis of SiF. ... 

Fumed silica is produced from the vapor-phase hydrolysis of silicon tetrachloride as shown in Figure 8.7. 

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