Volatile acids kinetics

Volatile Acids Kinetics. In evaluating the methane fermentation kinetics of the three volatile acids chosen for study, it was necessary to consider the process biochemistry and stoichiometry. According to Barker (19), acetic acid is fermented to methane and carbon dioxide in a single step while both propionic and butyric acids are fermented in two steps. In the first step these acids are fermented to acetic acid and methane by species of methanogenic bacteria. The resulting acetic acid is then fermented by different methanogenic species to methane and carbon dioxide. The stoichiometry of these fermentations is shown by the following equations (19). 

Marina Bely for her work on fermentation kinetics (Section 3.4) and the production of volatile acidity (Sections 2.3.4 and 14.2.5)... 

Until now we have been discussing the kinetics of catalyzed reactions. Losses due to volatility and side reactions also raise questions as to the validity of assuming a constant concentration of catalyst. Of course, one way of avoiding this issue is to omit an outside catalyst reactions involving carboxylic acids can be catalyzed by these compounds themselves. Experiments conducted under these conditions are informative in their own right and not merely as means of eliminating errors in the catalyzed case. As noted in connection with the discussion of reaction (5.G), the intermediate is stabilized by coordination with a proton from the catalyst. In the case of autoprotolysis by the carboxylic acid reactant, the rate-determining step is probably the slow reaction of intermediate [1] ... 

There have been relatively few detailed kinetic studies of the decompositions of metal acetates, which usually react to yield [1046] either metal oxide and acetone or metal and acetic acid (+C02 + H2 + C). Copper(II) acetate resembles the formate in producing a volatile intermediate [copper(I) acetate] [152,1046,1047]. 

Pyrolyses of formates, oxalates and mellitates yield CO and C02 (H2, H20 etc.) as the predominant volatile products and metal or oxide as residue. It is sometimes possible to predict the initial compositions from thermodynamic considerations [94], though secondary reactions, perhaps catalyzed by the solids present, may result in a final product mixture that is very different. The complex mixtures of products (hydrocarbons, aldehydes, ketones, acids and acid anhydrides) given [1109] by reactants containing larger organic groupings makes the collection of meaningful kinetic data more difficult, and this is one reason why there are relatively few rate studies available for the decompositions of these substances. 

A second method of solving the kinetics dilemna consists of driving a polymerization reaction to completion by removing a volatile coproduct as in the case of uranyl dicarboxylate polymers from uranyl acetate and the dicarboxylic acid (5) ... 

Applications involving ring transfer or loss. The kinetic lability, volatility, and Lewis acidity of heavy alkaline earth metallocenes have been the properties most important to their applications. The gas-phase decomposition of volatile metallocenes is useful in the preparation of thin films of alkaline earth-containing materials and in doping semiconductors. Reviews are available on the use of group 2 organometallic compounds as precursors for chemical-vapour deposition (CVD).2 3... 

The observed ambient organic aerosol formation rates are also consistent with those estimated by extrapolation of smog-chamber kinetic data. Other heavy unsaturates, such as styrene and indene, are present in the atmosphere and may contribute, in part, to the formation of benzoic acid and homophthalic acid, respectively. Diesel exhaust and industrial emission are possible sources of such heavy unsaturates. Diolefins of C6+ are not present in gasolines and exhaust gases and have not been found in the atmosphere, and their possible role as precursors of the Cs-7 difiinctional acidic compounds is seriously challenged. Lower diolefins are emitted in automobile exhaust. Examination of vapor-pressure data indicates that the bulk of their expected photooxidation products remains in the gas phase, including most of the less volatile C3-4 dicarboxylic acids. 

ARO reaction with phenols and alcohols as nucleophiles is a logical extension of HKR of epoxides to synthesize libraries of stereochemically defined ring-opened products in high optical purity. To this effect Annis and Jacobsen [69] used their polymer-supported Co(salen) complex 36 as catalyst for kinetic resolution of epoxides with phenols to give l-aiyloxy-2-alcohols in high yield, purity and ee (Scheme 17). Conducting the same reaction in the presence of tris(trifluoromethyl)methanol, a volatile, nonnucleophilic protic acid additive accelerates KR reaction with no compromise with enantioselectivity and yield. Presumably the additive helped in maintaining the Co(III) oxidation state of the catalyst. 

Fig. 14.10 Reaction path diagram [149] illustrating major steps in volatile-N conversion in flames for different nitrogen species hydrogen cyanide (HCN), ammonia (NH3), cya-nuric acid (HNCO), acetonitrile (CH3CN), and pyridine (C5H5N). The diagram is based on chemical kinetic modeling at moderate fuel-N concentrations. Solid lines denote elementary reaction pathways, while dashed arrows denote routes that involve intermediates and reactions not shown.

Volatile organic compounds (VOCs), especially trihalomethanes, are frequently found in drinking water due to the chlorination of humic acids. When UV irradiation is applied to the pre-ozonation of humic acids, the decomposition of VOC precursors increases (Hayashi et al., 1993). The ozonation rates of compounds such as trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane, 1,2-dichloroethane, and 1,2-dichloropropane were found to be dependent on UV intensity and ozone concentration in the aqueous phase by Kusakabe et al. (1991), who reported a linear relationship between the logarithmic value of [C]/[C0] and [03]f for 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene. The other two organochlorines followed the same first-order kinetics with and without UV irradiation (Kusakabe et al., 1991). Thus, the decomposition rate can be expressed as ... 

Amadori compounds (N-substituted-l-amino-l-deoxy-2-ketoses) are potential precursors to the formation of many of these heterocyclic volatile products. The secondary nitrogen in most Amadori compounds is weakly basic and is therefore a likely site for rapid nitrosation reactions via normal reactions with nitrous acid, under mildly acidic conditions. However, purified Amadori compounds are usually obtained only after tedious isolation procedures are invoked to separate them from the complex mixtures of typical Maillard browning systems. Takeoka et al. ( 5) reported high performance liquid chromatographic (HPLC) procedures to separate Amadori compounds in highly purified form on a wide variety of columns, both of hydrophilic and hydrophobic nature. They were able to thus demonstrate that reaction products could be followed for kinetic measurements as well as to ensure purity of isolated products. 

A manometric technique was used to measure the rate of pressure rise which in turn is a measure of the rate of formation of volatile products produced during the thermal decomposition of hydrazinium monoperchlorate and hydrazinium diperchlorate. Kinetic expressions were developed, temperature coefficients were determined, and an attempt was made to interpret these in terms of current theories of reaction kinetics. The common rate-controlling step in each case appears to be the decomposition of perchloric acid into active oxidizing species. The reaction rate is proportional to the amount of free perchloric acid or its decomposition products which are present. In addition the temperature coefficients are similar for each oxidizer and are equivalent to that of anhydrous perchloric acid. 

Instead of using volatile organic solvents, it would be beneficial, for compatibility with fuel cells and the environment, to use just water as the solvent. The solubility of AB in water is high, 25 wt.% [14]. Aqueous AB solutions are also relatively stable if kept under an inert gas atmosphere [10, 111]. In air the solution possesses a much lower stability which is believed to result from an increase in acidity in the solution due to the dissolution of CO2 [111]. The stability of the aqueous AB solution is obviously kinetically controlled since the decomposition is thermodynamically favored due to the formation of strong B—O bonds according to ... 

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