Liquid-phase oxidation with oxygen

Acetaldehyde to Acetic Acid. The formation of acetic acid furnishes an excellent example of liquid-phase oxidation with molecular oxygen. Acetic acid may be obtained by the direct oxidation of ethanol, but the concentrated acid is generally obtained by oxidation methods from acetaldehyde that may have been formed by the hydration of acetylene or the oxidation of ethanol. The oxidation usually occurs in acetic acid solution in the presence of a catalyst and at atmospheric or elevated pressures. Temperatures may range up to lOO C, depending upon conditions, but are usually lower. 

Through study of the mechanism by which the catalyzed liquid-phase oxidation of acetaldehyde to acetic proceeds, it has been found, that at temperatures below 15 C and in suitable solvents the acetaldehyde forms an unstable compound, acetaldehyde monoperacetate. At controlled low temperatures this compound can be made to yield peracetic acid and acetaldehyde. Salts of the metals cobalt, copper, and iron catalyze the first-stage reaction, in a manner used in acetic acid manufacture. 

This process is significant in that it is now in pilot-plant operation, and commercial production of peracetic acid is being planned. Previously, in situ use of this peracetic oxidation of unsaturated natural fatty acids to epoxy derivatives has been demonstrated. It is to be eiq)ected that the commercial availability of low-cost peracetic acid will open many new areas of epoxidation reaction since almost any olefinic double bond is capable of 

Apparatus for batch liquid-phase oxidation of acetaldehyde to acetic acid. 

Oxidation of fatty oils by peracetic acid results in products which are epoxidized, hydroxylated, and acetylated and have properties of value for use in vinyl plasticizers and greases.  

---

Other examples of nitroxyl radicals such as TEMPO [3Id, j] have been used successfully in several examples of environmentally friendly liquid-phase oxidations with. oxygen. Sheldon et al. have reported on the use of N-hydroxysaccharin as an alternative to NHPI in the oxidation of cycloalkanes to dicarboxylic acids [31h]. Other examples include the aerobial oxidation in the presence of NHPI, o-phenanthroline and bromine, in an acetonitrile/CCU solvent and in the absence of metals, at 100 °C. The selectivity was 75% to AA and 22% to cyclohexanone, at 48% cyclohexane conversion [31i]. 

In the 1980 s zeolites attracted a renewed attention. They were shown to be rather promising catalysts if, instead of O2, a chemically pre-modified oxygen entering the oxygen-containing molecules is used. The most known example is an excellent catalytic performance of titanium silicalites in the liquid phase oxidations with H2O2 [5]. A gas phase oxidation with nitrous oxide is another approach in this field being intensively developed in the last years [2],... 

Typical examples of liquid-phase oxidation with molecular oxygen catalyzed by heteropoly compounds are listed in Table XXVI. Introduction of Vs + or... 

Liquid-Phase Oxidations with Hydrogen Peroxide and Molecular Oxygen Catalyzed by Polyoxometalate-Based Compounds... 

Laboratory-scale liquid phase oxidation with heterogeneous catalysis is generally performed under mild conditions by bubbling air or oxygen at 20-50 C and atmospheric pressure in the presence of Pd, Pt, Au, or derived bimetallic catalysts [4]. 

It is recovered by redistillation of the fluorene oil fraction, which boils between 290 and 305 °C (or from the distillation fore-runnings in anthracene production), followed by recrystallization, for example, from solvent naphtha. Technical fluorene, 95% pure, is commonly used to produce fluorenone by liquid-phase oxidation with air/oxygen at around 100 °C. Fluorenone can principally be used as a mild oxidant for Oppenauer oxidation, particularly in steroid chemistry. 

Oxidation. Acetaldehyde is readily oxidised with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid and derivatives). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the Hquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is beheved to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21 -0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or osone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directiy by Hquid-phase oxidation at 5—50°C with a cobalt salt catalyst (37) (see Peroxides and peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of /)-xylene to terephthaHc acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

---