Decomposition intermediate

The sequence of decomposition intermediates formed varies with the particular preparation of reactant being studied. Gillibrand and Halliwell... 

The kinetics of NaN3 decomposition are sensitive to both pressure and composition of the surrounding atmosphere. The influence of an inert gas in suppressing sublimation of product metal has been mentioned already. The reaction of NaN3 at 623 K was strongly inhibited [711] by NO and by H2. The possible formation of transient decomposition intermediates could not, however, be distinguished from the direct interaction of added gas and azide. 

Accordingly, the present survey is mainly concerned with constant temperature methods, though thermal analysis [730] has been shown to be most valuable in identifying the temperature range of stability and the compositions of decomposition intermediates. 

Chloride is the predominant residual product from reactions at low temperature and in contact with the gaseous products, whereas in vacuum and at high temperature, MgO is formed. It has also been suggested that MgO Mg(C104)2 is a decomposition intermediate [855]. 

A strongly coupled surface complex between a formate ion and adsorbed formic acid is the decomposition intermediate on silver (58). 

Life Substances Decomposition Intermediates Intermediates and Products Typically Found in Nonpolluted Natural Waters... 

Beckett and Hua (2000) investigated the sonolytic decomposition of 1,4-dioxane in aqueous solution at 25 °C at discrete ultrasonic frequencies. They found that the highest first-order decomposition rate occurred at 358 kHz followed by 618, 1,071, and 205 kHz. At 358 kHz, 96% of the initial 1,4-dioxane concentration was decomposed after 2 h and the pH of the solution decreased to 3.75 from 7.50. Major decomposition intermediates were ethylene glycol diformate, methoxyacetic acid, formaldehyde, glycolic acid, and formic acid. 

Pelizzetti, E., Minero, C., Carlin, V, Vincenti, M., Pramauro, E., and Dolci, M. Identification of photocatal34ic degradation pathways of 2-Cl-s-triazine herbicides and detection of their decomposition intermediates, Chemosphere, 24(7) 891-910,1992. 

The thiocyanate is stable toward water for some period of time. However, the alkaline hydrolysis, in analogy with normal thiocyanates (156), causes rapid decomposition. Intermediates CF3SH and HNCO are formed through cleavage of the CF3S—C bond, but whereas the cyanate remains intact, the trifluoromethanethiol hydrolyzes further (85) ... 

Sawkill [114] recently confirmed this observation using an electron microscope and found that silver is evolved as the result of slow reactions. In the early stage of decomposition intermediate compounds, richer in silver than azide, are formed. The pure metal, which is evolved only in the final stage of decomposition has a markedly oriented structure and a grain size of 0.1 x 0.1 x0.05 mfi. 

These thiatriazolines are analogous to the compounds obtained by L abbe and co-workers.64,65 The thermal decomposition intermediates were trapped as shown in Scheme 6, but the presence of the cyclic form has not yet been demonstrated.61... 

From the results it is concluded that the equilibrium depends on the electrolyte composition and has an influence on the surface concentration of the mobile and immobile decomposition intermediates. Hence, the kinetics of the photooxidation of TMPD and the decomposition at illuminated nGaAs photoanodes are dependent on the electrolyte composition. 

The underlying assumption of reactions (37) to (39) is that the first decomposition intermediate and not the free hole h+ constitutes the mobile species involved in the consecutive steps of the dissolution reaction, and hence that the decomposition intermediate Xj is mobile within a two-dimensional surface layer. In other words, a bonding electron can jump from an unbroken surface bond to a neighboring electron-deficient surface bond. Note that here, the only step consuming holes is step (4), so that in an indifferent electrolyte, Eqs. (3) and (5) are expected to hold, with n = 1. 

Several conclusions may be drawn from the results discussed in this section. Firstly, it appears that in almost all cases studied, the stabilization reaction involves decomposition intermediates instead of free holes. We will not comment on this point here (for a discussion, see ref. [52]). Similarly, we will not enlarge on the observation that in certain cases, Xj and in other cases X2 intermediates are involved, as these problems are beyond the scope of the present paper, which essentially pertains to anodic dissolution and etching. As far as this subject is concerned, two important points emerge, i. e., the fact that, due to the interconnection between stabilization and dissolution, the latter reaction tends to dominate at sufficiently high current densities, and the fact that, depending on the semiconductor and on the circumstances, dissolution either occurs by the DH or by the DX mechanism. In what follows, independent information on the latter point will be gathered, and the factors which determine the dissolution mechanism will be investigated. 

A shift in the band edge position also explains the observed dependence of the hole injection rate on the electrode polarization. Fig. 11 exempliHes this by the total current-potential behavior of a (111) n-GaP electrode in alpine Fe(CN) solutions (pH = 13), together with the partial current due to the injection of holes (revealed by rotating ring-disk experiments, see ref. [73]). Also at p-GaP, it was shown that the hole injection rate is lower with anodic polarization than with cathodic polarization. The potential-dependent position of the band edges is ascribed to a potential-dependent accumulation of positive charges (holes, surface decomposition intermediates,. ..) at the semiconductor surface [62, 73]. 

As in the case of anodic etching, electron injection by Xj (reaction (51)) is considered to occur parallel to reaction (46). Further oxidation of X2 to the final products proceeds analogously. The fact that the decomposition intermediates of the chemical etching process are essentially the same as those of the anodic etching process leads to mixed chemical-anodic etching of the p-GaP anode in acidic Br2 solutions the competitive chemical and anodic reactions are linked via the radical intermediates. This explains why at sufficiently high anodic polarization, the etching of p-GaP consumes neither 3 Br2 molecules per GaP siu face entity nor 6 holes, but 1 Br2 molecule and 4 holes. 

The technical/commercial importance of the arsine thermolysis mechanisms is the role of decomposition intermediates in the deleterious incorporation of carbon into the growth of MOCVD-produced GaAs. Wendt and Speckman in their investigations into the thermal decomposition of arsines show the crucial importance of the production of AsHj radicals in the formation of low-carbon GaAs. 

CHARACTERIZATION OF REACTANTS, DECOMPOSITION INTERMEDIATES AND PRODUCTS, AND THE FORMULATION OF MECHANISMS... 

The discussion here will emphasize the problems involved in obtaining information about solids from NMR measurements. NMR has also been used to identify solvent-extracted decomposition intermediates [23], but allowance has to be made for possible solvent-intermediate interactions. 

Hemic. Organic soil material of intermediate stage of decomposition. Intermediate fiber content (U.S. system). 

An examination of the behavior of peroxides in the course of their rapid thermal decanposition, provides some insight into the nature of the decomposition intermediates and/or products. NMR spectra taken during the thermolysis of various peroxides and per-oxyesters in solution at temperatures where they have short half lives, e.g. benzoyl peroxide and t-butyl peroxypivalate at 110 C, contain emission peaks and/or enhanced absorption peaks. These peaks are presumed to be those of the reaction products resulting from interactions involving the transient decomposition products, e.g. interactions between pairs of caged radicals or from radical pair encounters. The NMR spectra are indicative of the occurrence of chemically induced dynamic nuclear polarization (CIDNP). 

Based on results of XPS, it is found surface carbon species can be removed from catalysts through the reaction with N2O decomposition intermediate products, for example, adsorbed O or N. Since no N Is photoelectron was detected by XPS, the depletion of surface carbon can be described by the following two reactions [10] ... 

The temperature increase would also favour the dissociation of the water decomposition intermediates which require thermal activation of the dissociation. For example the dissociation HO2 —H + O2 is characterised by =17.5 kJ and A Z =27.3 kJ. To cite yet another circumstance, it is known from electrochemistry that the temperature increase by one degree would decrease the overvoltage in oxygen and l drogen release by 3 to 4 mV. For example, the temperature rise in the electrolyser from room temperature to 70-80 C would lead to a 40% decrease in overvoltage. 

---