Reactions acetaldehyde

Methanol can be hydroformylated with syngas (CO and H2) in the presence of a copper or nickel halide catalyst to give acetaldehyde. Reaction conditions are 350-400°F and 4000-6000 psi. 

The RCO radical produced then adds 02 as expected. For example, for acetaldehyde, reaction (65) is followed by... 

Mechanisms of Aldehyde Oxidation. There must be at least two paths for oxidation of aldehyde to acid, and at least one of these must be temperature dependent. One pathway is the ozone-oxygen oxidation of aldehydes to peracids (14). However, peracid can also serve as an oxidizing agent for aldehyde. In the oxidation of acetaldehyde, Reaction 3 is thought to occur (14). 

The acetaldehyde reaction works well when one drop of dilute sodium hydroxide is added to acetaldehyde. The acetone reaction is best done with insoluble barium hydroxide, Ba(OH)2- Both approaches keep the base concentration low. Without this precaution, the aldol products are not the compounds isolated from the reaction. With more base, further reactions occur, because the aldol products dehydrate rather easily under the reaction conditions to give stable conjugated unsaturated carbonyl compounds. 

The rate-determining step is 3, the transfer of the OH proton to the conjugate base A . For the reverse process, the hydration of acetaldehyde, reaction 4 is rate-determining. For the base-catalyzed reaction the proposed mechanism is very similar ... 

We give a brief discussion of one reaction to illustrate the difference in products between the chain region and the non-chain region. Danby, Buchanan, and Henderson photolyzed acetaldehyde in the temperature range 200-350°C., at acetaldehyde particle densities of 6 X 10 to 10 cm. , and rates of light absorption of 10 to 10 photons/cm. sec. Under these conditions the rate constant for radical-acetaldehyde reactions... 

Aqueous PdCb oxidizes olefins to carbonyl compounds—e.g., ethylene gives acetaldehyde (Reaction 1). 

Acetaldehyde reactions should thus be prevalent provided acetaldehyde is present. As regards direct reaction, it can similarly be expected that formation of F-A+ exceeds that of A+-F and A+-A species at lower pH values. 

Thus, it seems that the major changes induced by micro-oxygenation are due to acetaldehyde reactions (figure 6). In a first stage, acetaldehyde-induced reaction between anthocyanins and flavanols leads to purple ethyl-linked pigments. These intermediate pigments have been shown to be rather unstable... 

Fig. 3. Effect of temperature on the time course of the change in the of rattail tendon produced by O.lOiVf acetaldehyde. Reaction conditions were the same as for Fig. 1.

Experience from fleet tests indicates that at certain points of operation the concentrations of acetic acid can cause odour problems with the type of oxidation catalysts that has been used so far. If we study the possible reaction pathways, we see that acetic acid can be formed directly from ethanol or via acetaldehyde (reactions 4 and 5). The results from the acetaldehyde oxidation experiments give, however, clear evidence that acetic acid is not being formed via the acetaldehyde route (see reaction 5) over these catalysts. 

Detailed Modelling of Acetaldehyde or Propane Oxidation.— The second approach, stated at the outset, attempts to choose a complete kinetic mechanism of a specific system and to proceed to a numerical solution of the detailed mass and energy balance equations via a digital computer. This is the approach chosen by Halstead et al. " who have concentrated on the gas-phase oxidations first of acetaldehyde and latterly of propane. " In the acetaldehyde reaction, Halstead et al. identified peracetic acid as the degenerate branching agent and attributed the self-quenching... 

Nagai, Y., Morooka, S., Matubayasi, N., and Nakahara, M., Mechanisms and kinetics of acetaldehyde reaction in supercritical water Noncatalytic disproportionation, condensation,... 

Finke et 31. found that, with the model Co(C2(DO)(DOH))p in Figure 8.2, the Co—CHjCHCsO) complex was too stable to be an intermediate in the diol to acetaldehyde reaction in their system. The stability of the aldehyde complex is consistent with earlier work of Silverman and Dolphin, who found that the analogous complex decomposed by an acid-catalyzed path with bad = 2.1x1 s" at... 

Notice that the steps in the enol — acetaldehyde reaction are simply the reverse of the acetaldehyde — enol reaction (Fig. 19.15). Note also that in acid, as in base, aldehydes and ketones that have a hydrogens are in equilibrium with their enol forms. We will soon see that although enols are in equilibrium with the related keto forms, it is usually the keto forms that are favored. This equilibrium is called the keto-enol tautomerization.The carbonyl compound and its associated enol are called tautomers. 

More recently Nair et al studied the activity of vanadium oxide catalysts supported on AlgOs, TiOg, and CeOg in the ethanol to acetaldehyde reaction in the oxidative dehydrogenation (ODH) process at 180°C. The acetaldehyde formation rate and product selectivity... 

This observation rules out the formation of vinyl alcohol as a short-lived intermediate that tautomerizes to acetaldehyde (reaction 8.2.2.1). Had vinyl alcohol been formed, its hydroxyl proton would have undergone isotope exchange with D O. It is important to note that with Wacker-type... 

It is well established that the major products of the OH-acetaldehyde reaction are acetyl radical and water, reaction (a). Other possible reaction channels have been proposed ... 

Acetaldehyde Reactions in Water Solution. When calcium hydroxide is added to an aqueous solution containing one mol of acetaldehyde and at least four moU of fonnaldehyde, the tetrahj dric alcohol pentaerythritol (or pentaerythi ite) and calcium formate are produced. This reaction w-as apparently first obseiu ed b> Tollens and Wuegand in 1891. 

---