Accelerator acetaldehyde

Whereas, at 800 K, small amounts of added O2 (up to 10 %) greatly accelerate acetaldehyde decomposition, at 1030 K little eflFect is observed. The changing influence of O2 may be explained by the relative importance of the two competing initiation reactions, (30) and (la). 

Ozone accelerates the autoxidation of acetaldehyde to peracetic acid at below 15°G. Acetaldehyde hemiacetal peracetate, an intermediate product, is... 

Another approach is to use an easily oxidized substance such as acetaldehyde or methylethyl ketone, which, under the reaction conditions, forms a hydroperoxide. These will accelerate the oxidation of the second methyl group. The DMT process encompasses four major processing steps oxidation, esterification, distillation, and crystallization. Figure 10-16 shows a typical p-xylene oxidation process to produce terephthalic acid or dimethyl terephthalate. The main use of TPA and DMT is to produce polyesters for synthetic fiber and film. 

Not shown in Fig 13 is the effect of added water, which was found to greatly accelerate decompn at both 140° and 171°. Addition of 5 x 10"4 moles of acetaldehyde did not alter the initial decompn rate at 163°. However, addition of larger amounts (1.5 x ltT3 moles) produced explns. In a separate series of expts, it was found that about 0.5 mole of N02 was formed for every mole of PETN decompd, and this ratio decreased rapidly in the middle stages of decompn and then increased again in the final stages... 

Vinyl acetate is normally inhibited with hydroquinone to prevent polymerisation. A combination of too low a level of inhibitor and warm, moist storage conditions may lead to spontaneous polymerisation. This process involves autoxidation of acetaldehyde (a normal impurity produced by hy droly sis of the monomer) to a peroxide which initiates exothermic polymerisation as it decomposes. In bulk, this may accelerate to a dangerous extent. Other peroxides or radical sources will initiate the exothermic polymerisation. 

Reaction of guanine nucleosides and nucleotides with acetaldehyde yields the tricyclic pyrimidopurines (Equation 160), this reaction being accelerated by the addition of a basic amino acid such as arginine or lysine at pH 8 <2002TL6701>. 

Liang Q, Carlson EC, Borgerding AJ, Epstein PN. A transgenic model of acetaldehyde overproduction accelerates alcohol cardiomyopathy. J Pharmacol Exp Ther 1999 291 766-772. 

Selective oxidation of ethylene to acetaldehyde was carried out over carbon-supported Pd and Pt membrane catalysts.1322 The concept of supported liquid-phase catalysis was also successfully applied in the Wacker oxidation.1323 The Wacker reaction can be performed in alcohol-supercritical C02.1324 C02 as cosolvent accelerates reaction rates and remarkably affects the selectivity towards methyl ketone in the presence of an alcohol. 

The cyclic sequence of Reactions 5 and 6 can be accelerated by adding a species which promotes the formation of Co(III) from Co(II). In the oxidation of alkylaromatic hydrocarbons ozone (7), acetaldehyde (8), and methyl ethyl ketone (4) act as promoters in this way. 

Recently, researchers at Catalytica proposed a new technology for ethylene oxidation (368). Typical compositions are aqueous ca. O.l mM Pd2+, 5-25 mM Cl , and ca. 0.30 M NavH(3+ -v)PVxMoi2 04o (preferably x = 2-3). The Pd2+ and chloride concentrations are only 1/100 those in the oridinary Wacker system. The solutions at pHO-l result in high reaction rates and stability of Pd2+, as shown in Fig. 65. The stability of Pd2+ is further improved by the presence of chloride ion in a concentration of about 0.01 M. In this system, the phosphomolybdate serves two functions in the Pd° reoxidation (l) It solubilizes high concentrations of Vs + in aqueous solution and (2) it accelerates the reoxidation of V4+ by dioxygen. Kinetics (the reaction is first-order in Pd2+ and in ethylene concentrations and zero-order in Vs + concentration) shows that the oxidation of ethylene to produce acetaldehyde is rate-determining. 

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