Phase mechanism

Vapor-Phase Mechanisms. Phosphoms flame retardants can also exert vapor-phase flame-retardant action. Trimethyl phosphate [512-56-1] C H O P, retards the velocity of a methane—oxygen flame with about the same molar efficiency as antimony trichloride (30,31). Both physical and chemical vapor-phase mechanisms have been proposed for the flame-retardant action of certain phosphoms compounds. Physical (endothermic) modes of action have been shown to be of dominant importance in the flame-retardant action of a wide range of non-phosphoms-containing volatile compounds (32). 

Vapor-Phase Mechanisms. Phosphorus flame retardants can also exert vapor-phase llamc-rctardam acliun. Both physical and chemical vapor-phase mechanisms have been proposed lor the flamc-reuirdatit action of certain phosphorus compounds, such as triphenvl phosphate. 

Figure 8.3 Proposed reaction mechanism for methanol synthesis on Pd and comparison with gas-phase mechanism surface intermediates are speculative and associated energies are estimates

BAC-MP4 method Coupled-cluster calculations Gas-phase thermochemistry Equilibrium Gas-phase mechanisms 

The question as to whether a flame retardant operates mainly by a condensed-phase mechanism or mainly by a vapor-phase mechanism is especially comphcated in the case of the haloalkyl phosphoms esters. A number of these compounds can volatilize undecomposed or undergo some thermal degradation to release volatile halogenated hydrocarbons (37). The intact compounds or these halogenated hydrocarbons are plausible flame inhibitors. At the same time, thek phosphoms content may remain at least in part as relatively nonvolatile phosphoms acids which are plausible condensed-phase flame retardants (38). There is no evidence for the occasionally postulated formation of phosphoms haUdes. Some evidence has been presented that the endothermic vaporization and heat capacity of the intact chloroalkyl phosphates may be a main part of thek action (39,40). 

Mitosis is only initiated when the DNA has been completely rephcated during S phase. Mechanisms must exist that register completion of S phase and couple this to entry into M phase. 

HILIC is a variant of normal-phase chromatography that employs polar stationary phases and RPLC-type mobile phases. Because HILIC separations occur by a normal-phase mechanism, the organic component of the mobile phase 

Fire retardants are generally considered to operate by one of two modes, referred to as vapor phase and solid phase mechanisms. Vapor phase fire 

Alkyl diphenyl phosphate plasticizers can exert flame-retardant action in vinyl plastics by a condensed-phase mechanism, which is probably some sort of phosphoms acid coating on the char. Triaryl phosphates appear to have a vapor-phase action (29). 

Because the oxidants for S02 are generated in the VOC-NO. system discussed in Chapter 6, the overall gas-phase mechanism for the oxidation of S02 to h2so4 is quite complex. The reader is referred to the mechanism in the RADM model (Regional zlcid Deposition Model) for a treatment of the VOC-NO -S02 chemistry (Stockwell et al., 1990 Gao et al., 1996). It should be noted that an earlier version of this mechanism is given in some of the examples included with the OZIPR model discussed in Chapter 16 and whose applications are included with this book. 

A comparison is made between the gas phase and solution phase reaction pathways for a wide range of organic reactions. Examples are presented in which the gas phase and solution phase mechanisms are the same for a given set of reactants in which they differ, but attachment of the first molecule of solvent to the bare gas phase ionic reactant results in the solution phase products and in which the bare, monosolvated, and bulk-solvated reactions proceed by three different pathways for the same reactants. The various tools available to the gas phase ion chemist are discussed, and examples of their use in the probing of ionic structures and mechanisms are reported. 

The oxidation of the methyl radicals formed by DMTC pyrolysis is well understood compared with the tin chemistry. Gas-phase mechanisms describing this chemistry are readily available [61-63]. These reactions lead to the formation of other reactive species that can attack DMTC, including H, O, OH, and HO2. The OH radical in particiflar is a very efficient H-abstractor, and will therefore quickly react with DMTC  

It is our intention to point out clues, mostly from the literature, some from our own work, which suggest approaches to new flame retardant systems with greatly increased efficiency. Both vapor phase and condensed phase mechanisms will be considered. 

Ferguson et al. [18] reported on the application of a mixed-mode HPLC separation, coupled with ESI-MS for the comprehensive analysis of NPEOs and nonylphenol (NP) concentrations and distributions in sediment and sewage samples. The mixed-mode separation, which operates with both size-exclusion and reversed-phase mechanisms, allows the resolution of NPEO ethoxymers prior to introduction to 

As noted above, it should be realized that understanding the activity on a surface is not the only issue needed to fully characterize the catalytic system. There must be an understanding of how the surface reactions produce intermediates that can desorb and initiate gas phase reactions close to the surface. To that extent, the author is developing a catalytic shock tube technique to probe the interface of the catalyst surface and the immediate gas phase layer, bridging the gap between surface mechanisms and gas phase mechanisms. 

Triphenylphosphine oxide [791-28-6], C gH OP, and triphenyl phosphate [115-86-6], C gH O P, as model phosphoms flame retardants were shown by mass spectroscopy to break down in a flame to give small molecular species such as PO, HPO2, and P2 (33—35). The rate-controlling hydrogen atom concentration in the flame was shown spectroscopically to be reduced when these phosphoms species were present, indicating the existence of a vapor-phase mechanism. 

The extraction system which was measured by the HSS method for the first time was the extraction kinetics of Ni(II) and Zn(II) with -alkyl substituted dithizone (HL) [14]. The observed extraction rate constants linearly depended on both concentrations of the metal ion [M j and the dissociated form of the ligand [L j. This seemed to suggest that the rate determining reaction was the aqueous phase complexation which formed a 1 1 complex. However, the observed extraction rate constant k was not decreased with the distribution constant Kj of the ligands as expected from the aqueous phase mechanism. 

We can, however, form alkoxide ions that are monosolvated by a single alcohol group, via the Riveros reaction [Equation (7)]. When the monosolvated methoxide is reacted with acrylonitrile, the addition process reaction (8a), is the major pathway, because there is a molecule of solvent available to carry off the excess energy. The proton transfer pathway, reaction (8b), becomes endothermic, because the methoxide-methanol hydrogen bond, at about 29 kcal/mol, must be broken in order to yield the products. Thus, one can observe either the unique gas phase mechanism in the gas phase, reaction (6b), or the solution phase mechanism in the gas phase, reaction (8a), and the only difference is in the presence of the first molecule of solvent. 

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