Volatile reaction products

With samples that are difficult to dissolve, the first approach is usually to try digesting the sample with an acid or base. Table 7.2 lists the most commonly used acids and bases and summarizes their use. Digestion is commonly carried out in an open container, such as a beaker, using a hot plate as a source of heat. The chief advantage of this approach is its low cost as it requires no special equipment. Volatile reaction products, however, are lost, leading to a determinate error if analyte is included among the volatile substances. 

Incorporation of a chemical compound which decomposes at some stage of the processing operation to yield volatile reaction products. These are known as chemical blowing agents. 

In industrial painting throughput rate is critical and drying equipment will usually be needed. This equipment will control the rate of air movement, to remove solvents and/or volatile reaction products, and is also likely to include devices for raising the temperature of the paint film, or creating free radicals within it. 

As this work progressed, it became convenient for comparative purposes to express the pyrolysis results for a specific pyrolysis experiment in terms of the extent of the observed reaction of the initial organohalogen component content recovered chromatographically. The extent of reaction data as determined by the CGC analysis of the volatile reaction products for the pyrolysis of some representative simple mixtures of DBDPO are summarized in Table II. As illustrated by these data, the results obtained for the DBDPO/Sb203 mixture suggest that, in the absence of a polymer substrate, Sb203 exhibits the same extent of reaction as observed for other inert fillers such as glass beads or alumina. 

As shown by the data for these mixtures also presented in Table II., under the conditions employed here, all of these metals reacted directly with DBDPO. From a mechanistic perspective, that for all three metals the principal DBDPO volatile reaction product was observed to be the octabromodibenzofuran (OBDBF) was considered to be the most important result of these experiments. The observed reactivity of the metal towards the DBDPO decreased in the order Zn° > Sb° > Bi°. Of these data, only the rather large observed difference in the relative reactivities of Sb° (-38% OBDBF) and Bi° (-9% OBDBF) was unexpected based upon the thermodynamics for the formation of their respective halides. 

Similar arguments can be applied for the formation of N2 and its oxides. Enthalpies of decomposition, which are estimated on the basis of the products described above, usually result in a conservative prediction. In practice, decomposition is nearly always incomplete due to the evaporation of volatile reaction products and polymerization or tar formation by heavier molecules. 

Fractional Distillation.—-When several volatile reaction products are to be separated from one another the procedure is not so simple as described above. In proportion as the boiling points of the various constituents approach each other the separation becomes more difficult, and it is not easy with the help of the usual laboratory apparatus to separate with any degree of precision substances which differ in boiling point by 10°. 

The understanding of the SSP process is based on the mechanism of polyester synthesis. Polycondensation in the molten (melt) state (MPPC) is a chemical equilibrium reaction governed by classical kinetic and thermodynamic parameters. Rapid removal of volatile side products as well as the influence of temperature, time and catalysts are of essential importance. In the later stages of polycondensation, the increase in the degree of polymerization (DP) is restricted by the diffusion of volatile reaction products. Additionally, competing reactions such as inter- and intramolecular esterification and transesterification put a limit to the DP (Figure 5.1). 

Bio)chemical reactions may take place prior to or after the continuous separation module and are intended to enhance or facilitate mass transfer, detection or both. The earliest and simplest approach to integrated analytical steps in continuous-flow systems involves a combination of chemical reactions and continuous separations [4,5]. Such is the case with the formation of soluble organic chelates of metal ions in liquid-liquid extractions with the ligand initially dissolved in the organic stream [6], the formation and dissolution of precipitates [7], the formation of volatile reaction products in gas difiusion [8] and that of volatile hydrides in atomic absorption spectro-... 

Fig. 26. Ion-assisted gas-surface chemistry using Ar and XeFj on silicon (Volatile reaction product.).

It is the suspicion of the present author that gas-solid chemical reactions, which happen only in the presence of ion or electron bombardment, are a widely occurring phenomena in a plasma environment. Nevertheless, there are few if any well defined investigations of this topic. This is a consequence of the fact that most reactions of this type (e.g., oxidation or nitridization) produce a thin layer of non-volatile reaction product on the surface and then the reaction stops. A chemical reaction of this type is very difficult to investigate space experimentally. However, when the product is volatile, then the reaction is much easier to study since it continues indefinitely. Therefore, electron-induced chemical reactions will be discussed using an example where the reaction product is volatile. 

The photolysis of 2,5-dimethyl-3,4-dihydro-2//-pyran-2-carbaldehyde highly diluted in hexane gave l,2-dimethylcyclobutane-l,2-dicarbaldehyde (2) in 7% yield (of the volatile reaction products) as a mixture of cis- and p-ans-isomers.43... 

Purification of the Organoselenium Compounds. After the oxidation of 2-butene with selenium dioxide was completed, the acetic acid solvent and the volatile reaction products were distilled at reduced pressure (10 mm. HgA). The residue, a yellow oil, was purified by adsorption chromatography in a column packed with silica gel. n-Hexane and ethyl ether were used as eluents. The same procedure was applied to the fractionation and purification of the organoselenium compounds obtained from the oxidation of bis(l-methyl-2-acetoxypropyl) selenide with peracetic acid. 

The simplest work-up procedure for non-volatile reaction products and products which are obtained in the form of alkali metal salts is to allow the ammonia to evaporate overnight through the guard-tube into a vented fume... 

Condensation of volatile reaction products on the sample support system of a TA can give rise to anomalous weight changes. 

The translational temperature Tt plays an important kinetic role. At high temperatures chemical reactions are fast, and — in view of the decreasing rate of surface recombination of atoms — the energy exchange of the system with the environment becomes slower. Consequently, the theoretical model can be applied to such systems (for comparison see Table 1 in43)). The actual equilibrium concentration of the volatile reaction products — CN in the present case - may be reduced by dissociative de-excitation of electronically excited species (cf. also the system C/H2). 

The extruder is a continuous high-temperature short-time reactor. Ingredients, moisture, temperature, pressure, and shear can interactively produce many Mail lard-type flavor compounds. As the extrudate exits the extruder, many of the volatile reaction products may be lost with steam since the extrudate passes from a zone of relatively high pressure within the extruder to atmospheric pressure. By controlling formulation variables, the extruder can serve as a useful tool to thermally produce volatile and nonvolatile compounds which make significant contributions to overall flavor. 

Chemical methods are generally based on the reaction of surface hydroxyl groups with a selectively reacting compound to form a covalently bonded surface species of well known composition. As reactive compounds, diborane,4,5 boron trichloride,6,7 diazomethane,8 organosilanes,3,6,9,10,11,12,13,14 and organometallic compounds15 have been employed. a0H is then derived from the amount of the chemisorbed species as well as the amount of volatile reaction products. 

The products of reduction of salt anions are typically inorganic compounds like LiF, LiCl, Li20, which precipitate on the electrode surface. Reduction of solvents results, apart from the formation of volatile reaction products like ethylene, propylene, hydrogen, carbon dioxide, etc., in the formation of both insoluble (or partially soluble) components like Li2C03, semicarbonates, oligomers, and polymers.281 283 359 A combination of a variety of advanced surface (and bulk) analytical tools (both ex situ and in situ) is used286-321 332 344 352 353 360-377 to gain a comprehensive characterization... 

S. M. Monti, R. G. Bailey, and J. M. Ames, The influence of pH on the non-volatile reaction products of aqueous Maillard model systems by HPLC with diode array detection, Food Chem., 1998, 62, 369-375. 

When the fluorination has been completed, stopcocks BS and RS are closed, and the entire manifold is evacuated and rinsed with dry air ten times and then retained under diminished pressure.7 The condenser of the fractionating column B is precooled to the boiling temperature of the most volatile reaction product. This is achieved by manually closing relay RP of an electronic control circuit. The control leads of this circuit are connected to manometer MS in such a way as to be actuated at the pressure desired for distillation. 

The deposition process is illustrated in the left part of Fig. 5. The precursor gases are sprayed on the surface by the nozzle , where they are adsorbed. In a second step, the incoming ion beam decomposes the adsorbed precursor gases. Then the volatile reaction products desorb from the surface and are removed through the vacuum system, while the desired reaction products remain fixed on the surface as a thin film. The deposited material is not fully pure however, because organic contaminants as well as Ga ions (from the ion beam) are inevitably included in the deposited film [23],... 

A similar experiment was reported by RJ. Dougan et al. [90], A set-up called Qn-line Separation and Condensation AppaRatus (OSCAR) was installed at the LBNL 88-Inch Cyclotron. Nuclear reaction products were collected with a KQ aerosol gas-jet and were transported from the target chamber to the OSCAR set-up where 02 was added. The aerosol particles were destroyed on a hot quartz wool plug and the formation of tetroxides occurred at a temperature of 650°C. Non volatile reaction products were retained on the quartz wool plug whereas the volatile tetroxides were swept by the carrier gas flow to a condensation chamber, where they were deposited on a Ag disk, which was cooled with liquid N2. An annular Si... 

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