Catalytic liquid phase oxidations with

California Research Corp. under the direction of Toland. Since one-step oxidation of toluene to phenol did not seem feasible, a multistep synthesis was developed. Toluene can be oxidized under various conditions by known methods to benzoic acid. The easiest, most economical method is the catalytic, liquid-phase oxidation with air (27, 30). 

Obtained synthetically by one of the following processes fusion of sodium ben-zenesulphonate with NaOH to give sodium phenate hydrolysis of chlorobenzene by dilute NaOH at 400 C and 300atm. to give sodium phenate (Dow process) catalytic vapour-phase reaction of steam and chlorobenzene at 500°C (Raschig process) direct oxidation of cumene (isopropylbenzene) to the hydroperoxide, followed by acid cleavage lo propanone and phenol catalytic liquid-phase oxidation of toluene to benzoic acid and then phenol. Where the phenate is formed, phenol is liberated by acidification. 

Isobutylene oxide is produced in a way similar to propylene oxide and butylene oxide by a chlorohydrination route followed by reaction with Ca(OH)2. Direct catalytic liquid-phase oxidation using stoichiometric amounts of thallium acetate catalyst in aqueous acetic acid solution has been reported. An isobutylene oxide yield of 82% could be obtained. 

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],... 

The heterogeneous catalyst accelerates hydrocarbon oxidation. The rate of oxidation increases with increasing concentration of the catalyst. However, this increase in the oxidation rate with the catalyst concentration is not unlimited. The oxidation rate reaches a maximum value and does not increase thereafter. Moreover, the cessation of the reaction was observed and very often at a very small increase in the catalyst concentration. Such phenomenon was named critical phenomenon. The basis of critical phenomenon lies in the chain mechanism of oxidation and the dual ability of the catalyst surface to initiate and terminate chains. Numerous observations and studies of critical phenomenon in catalytic liquid-phase oxidations were performed [271 283]. Here are a few examples. 

The catalytic liquid-phase oxidation of aqueous phenol solution, carried out in a variety of reactor systems, demonstrates that phenol can be transformed to nontoxic compounds at milder reaction conditions than used in the thermal processes. The present study indicates that it is advantageous to conduct the reaction in a trickle-bed reactor with partial wetting of catalyst particles, perhaps with cyclic operation, since a direct contact between the catalyst surface and gas-phase increases the concentration of active sites for phenol oxidation. Furthermore, the reaction selectivity in a trickle-bed reactor is higher than that in a slurry reactor. The main drawback of the investigated process is dissolution of metal ions into the liquid-phase, which calls for more stable catalysts. 

A single plant operating in Texas, based on the noncatalytic controlled oxidation of propane-butane hydrocarbons, is reported to consume over 50 million gal annually of these light hydrocarbons together with large volumes of natural gas in the production of over 300 million lb of chemicals per year. Chemical products include formaldehyde purified to resin grade by means of ion-exchaiige resins, acetic acid, methanol, propanol, isobutanol, butanol, acetaldehyde, acetone, methyl ethyl ketone, mixtures of C4-C7 ketones, mixtures of C4-C7 alcohols, and propylene and butylene oxides. Catalytic liquid-phase oxidation of propane and butane is much more specific, and major yields of acetic acid are obtained. 

The largest chemical manufacturing process that utilizes a homogeneous catalytic liquid phase oxidation is the production of purified terephthaiic acid (PTA) (1,4-benzenedicarboxylic acid) from/)-xylene (pX) (1,4-dimethylbenzene) (Eq. (4.1)) [1]. PTA is a commodity chemical with a demand of 51 million tons per year in 2014 [2] and is mainly used in the production of polyethylene tereph-thalate (PET), which is made by polycondensation of PTA with ethylene glycol (Eq. (4.2)). PET is used in numerous applications, ranging from fibers to water bottles. 

On the one hand, hydrocarbon oxidation is a model reaction which enables special features of these catalytic processes to be analyzed. In addition, this resembles, to a considerable extent, enzymatic catalysis it also proceeds at low temperatures with high selectivity and requires small quantities of catalyst [128]. There have been no systematic investigations of catalytic liquid-phase oxidation of paraffins by macromolecular complexes and the scarce data are presented mainly in patents. (Pd complexes bound to ion-exchange resins are highly active in hydrogen oxidation by air (see, for instance [129])). 

The transformation of glycerol by means of catalytic oxidation has been investigated for many years. The selective oxidation of glycerol leads to a broad family of derivatives [100] there is a wide literature on the liquid-phase oxidation with O2, catalyzed by supported Pt/Bi [101-105], and by gold-based catalysts [105b,c, 106]. 

Solid rare earth chlorides (CeClj, NdClj, SmClj,EuClj, or YbClj) were reacted with NH4-Y (H-Y) with 05/0 1 ratios of 2.6,12.5 and 28 [83]. The activity of the exchanged materials for catalytic liquid-phase oxidation of cyclohexane depended on the nsi/n i ratio, type of cation (Ce=Yb>Sm>Eu>Nd) and the reaction temperature. 

Figure 31 shows that among metal oxide supports, TOF markedly changes depending on not only the kind of metal oxides but also on their size [98]. Especially, fine particles of Ce02 with mean diameter of 5 nm present the highest catalytic activity. On the other hand, Prati and her coworkers [31] reported that gold NPs supported on activated carbons are very active and selective in the liquid phase oxidation of various alcohols. 

Metals and metal oxides, as a rule, accelerate the liquid-phase oxidation of hydrocarbons. This acceleration is produced by the initiation of free radicals via catalytic decomposition of hydroperoxides or catalysis of the reaction of RH with dioxygen (see Chapter 10). In addition to the catalytic action, a solid powder of different compounds gives evidence of the inhibiting action [1-3]. Here are a few examples. The following metals in the form of a powder retard the autoxidation of a hydrocarbon mixture (fuel T-6, at T= 398 K) Mg, Mo, Ni, Nb V, W, and Zn [4,5]. The retarding action of the following compounds was described in the literature. 

The chapter by C. J. Swan and D. L. Trimm, which also emphasizes the effect on catalytic activity of the precise form of a metal complex, shows too that, depending on the metal with which it is associated, the same ligand can act either as a catalyst or inhibitor. The model reaction studied was the liquid-phase oxidation of ethanethiol in alkaline solution, catalyzed by various metal complexes. The rate-determining step appears to be the transfer of electrons from the thiyl anion to the metal cation, and it is shown that some kind of coordination between the metal and the thiol must occur as a prerequisite to the electron transfer reaction (8, 9). In systems where thiyl entities replace the original ligands, quantitative yields of disulfide are obtained. Where no such displacement occurs, however, the oxidation rates vary widely for different metal complexes, and the reaction results in the production not only of disulfide but also of overoxidation and hydrolysis products of the disulfide. 

The catalytic activities of all samples were tested for the liquid phase oxidation of 2,6-DTBP to quinone using H20, as an oxidant. Reactions were carried out under vigorous stirring in a two-neck glass flask equipped with a condenser and a thermometer. The oxidation of 2.6 DTBP was conducted using 10 mmol of substrate, 100 mg of catalyst, 10 g acetone as a solvent, and 30 mmol of 35 wt% H,02. The reaction was performed at 333 K for 2 h. The products were analyzed using a GC equipped with a HP-5 capillary column and a FID. 

Table 2 reports the catalytic activities of the catalysts prepared for 2.6-DTBP oxidation. All the titanium grafted materials were active as catalysts for liquid phase oxidation of 2.6-DTBP, and catalytic activity decreased in the order of MCM-48 (24.5% conversion) > HMS (22.8%) > KIT-1 (16.0%) > MCM-41 (14.3%) > SBA-1 (5%). Apparently. 3 dimensional channel system of MCM —48, and HMS with small particle size and textual mesoporosity proved to be useful in liquid phase reaction [1,2,3], Chemical analysis of the titanium-grafted SBA-1 by EDX showed far less titanium at the surface than the others it seems surface nature of SBA-1 synthesized in acidic medium is different from the rest. All Ti-grafted samples suffered from titanium leaching during the liquid phase oxidation HMS host resulted in over 4 % loss in metal content while the rest showed 2%. 

The catalytic capability of Au in liquid-phase oxidation can be tuned to a wider scope by choosing the support, size of Au, alkaline(with or without) and solvents. The products changed dramatically, depending on the solvents reactant alone without solvent, water, nonpolar and polar organic solvents. 

Though precious metal catalysts can be eliminated from the liquid-phase oxidation of sec-butanol [109], nevertheless, the process parameters (23.5% MEK yield and 79.4% selectivity) are lower compared with catalytic processes. Moreover, at 115-130 °C process implementation requires application of 9-20 atm pressure and, to reduce the induction period, the use of initiating additives. 

In this context, works [20, 21] should be mentioned, in which 0 2 ion-radicals were ESR detected in all samples of solution quickly frozen after initiation of H202 catalytic dissociation on metals and oxides (applied on A1203). The ion-radicals mentioned occur on the surface and desorb to the liquid phase, where, with high probability, they induce free radical processes. These results conform to the Weiss mechanism (6.3) of H202 dissociation on heterogeneous catalysts. 

The most straightforward immobilization method for catalytically active redox elements for liquid phase oxidation reactions consists of isomorphic substitution. Well-known systems with very peculiar properties that will not be treated in further detail are ... 

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