Oxidation liquid-phase alcohol

On the oxygen tolerance of noble metal catalysts in liquid phase alcohol oxidations... 

A major problem in noble metal catalyzed liquid phase alcohol oxidations -which is principally an oxidative dehydrogenation- is poisoning of the catalyst by oxygen. The catalytic oxidation requires a proper mutual tuning of oxidation of the substrate, oxygen chemisorption and water formation and desorption. When the overall rate of dehydrogenation of the substrate is lower than the rate of oxidation of adsorbed hydrogen, noble metal surface oxidation and catalyst deactivation occurs. 

The Bashkirov oxidation (liquid-phase oxidation of n-alkanes or cycloalkanes in the presence of boric acid and hydrolysis) yields the corresponding secondary alcohols [16, 17]. The reaction is used industrially for oxidation of C10 to C18 n-alkanes, providing raw materials for detergents and for oxidation of cyclododecane to cyclo-dodecanol as an intermediate for the production of Nylon 12 (Table 1, entry 8). The process is not of much commercial importance in the western world, however. Oxidation in the absence of boric acids usually leads to mixtures of alcohols, ketones, and carboxylic acids (Table 1, entry 9). 

Resin immobilized, stable, spherical CuO nanoparticles prepared in the presence of cyclodextrins (CDs) and NaOH act as catalysts for liquid phase oxidation of various alcohols in air (Table 2.1) A major interest of this process lies with the preparation of this catalytic material under mild conditions, reusability of the catalyst, and the green chemistry approach for liquid phase alcohol. 

Hydrogenations with coppcr-chromium oxide catalyst are usually carried out in the liquid phase in stainless steel autoclaves at pressures up to 5000-6000 lb. per square inch. A solvent is not usually necessary for hydrogenation of an ester at 250° since the original ester and the alcohol or glycol produced serve as the reaction medium. However, when dealing with small quantities and also at temperatures below 200° a solvent is desirable this may be methyl alcohol, ethyi alcohol, dioxan or methylcyc/ohexane. 

Autooxidation. Liquid-phase oxidation of hydrocarbons, alcohols, and aldehydes by oxygen produces chemiluminescence in quantum yields of 10 to 10 ° ein/mol (128—130). Although the efficiency is low, the chemiluminescent reaction is important because it provides an easy tool for study of the kinetics and properties of autooxidation reactions including industrially important processes (128,131). The light is derived from combination of peroxyl radicals (132), which are primarily responsible for the propagation and termination of the autooxidation chain reaction. The chemiluminescent termination step for secondary peroxy radicals is as follows ... 

Isopropyl alcohol can be partially oxidized by a noncatalytic, liquid-phase process at low temperatures and pressure to produce hydrogen peroxide [7722-84-1] and acetone (24—26). 

Direct non-catalytic liquid-phase oxidation of isobutylene to isobutylene oxide gave low yield (28.7%) plus a variety of oxidation products such as acetone, ter-butyl alcohol, and isobutylene glycol ... 

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. 

In earlier work, Bhaumik and Kumar (1995) have reported that the use of two liquid phases in the oxidation of hydrophobic organic substances with aqueous H2O2 using titanium silicate as the catalyst not only enhances the rate of oxidation but also improves selectivity for species like toluene, anisole, and benzyl alcohol. For a single liquid phase acetonitrile was u.sed a solvent. The solid-liquid system gives high ortho selectivity. Thus, in the case of anisole the ratios of o to p for. solid-liquid and solid-liquid-liquid system were 2.22 1 and 0.35 1, respectively. 

The photocatalytic oxidation of alcohols constitutes a novel approach for the synthesis of aldehydes and acid from alcohols. Modification of Ti02 catalyst with Pt and Nafion could block the catalyst active sites for the oxidation of ethanol to CO2. Incorporation of Pt resulted in enhanced selectivity towards formate (HCOO ad)-Blocking of active sites by Nafion resulted in formation of significantly smaller amounts of intermediate species, CO2 and H2O, and accumulation of photogenerated electrons. The IR experimental teclmique has been extended to Attenuated Total Reflectance (ATR), enabling the study of liquid phase photocatalytic systems. 

The aldol condensation of acetone to diacetone alcohol is the first step in a three-step process in the traditional method for the production of methyl isobutyl ketone (MIBK). This reaction is catalysed by aqueous NaOH in the liquid phase. (3) The second step involves the acid catalysed dehydration of diacetone alcohol (DAA) to mesityl oxide (MO) by H2S04 at 373 K. Finally the MO is hydrogenated to MIBK using Cu or Ni catalysts at 288 - 473 K and 3- 10 bar (3). 

One of the exciting results to come out of heterogeneous catalysis research since the early 1980s is the discovery and development of catalysts that employ hydrogen peroxide to selectively oxidize organic compounds at low temperatures in the liquid phase. These catalysts are based on titanium, and the important discovery was a way to isolate titanium in framework locations of the inner cavities of zeolites (molecular sieves). Thus, mild oxidations may be run in water or water-soluble solvents. Practicing organic chemists now have a way to catalytically oxidize benzene to phenols alkanes to alcohols and ketones primary alcohols to aldehydes, acids, esters, and acetals secondary alcohols to ketones primary amines to oximes secondary amines to hydroxyl-amines and tertiary amines to amine oxides. 

Acid Catalysis in Liquid-Phase Oxidation of Hydrocarbons and Alcohols... 

The nonsaturated esters with tt-C=C bonds and without activated a-C—H bonds (esters of acrylic acid (CH2=CHCOOR) and esters of vinyl alcohols (RC(0)0CH=CH2)) are oxidized by the chain mechanism with chain propagation via the addition of peroxyl radicals to the double bond. Oligomeric peroxides are formed as primary products of this chain reaction. The kinetic scheme includes the following steps in the presence of initiator I and at p02 sufficient to support [02] > 10 4 mol L-1 in the liquid phase [49]. 

ACID CATALYSIS IN LIQUID-PHASE OXIDATION OF HYDROCARBONS AND ALCOHOLS... 

Heterogeneous catalysis is widely used in technology for gas-phase oxidation of hydrocarbons to alcohols, aldehydes, epoxides, anhydrides, etc. Homogeneous catalysis predominates in the liquid-phase oxidation technology. Nevertheless, a series of experimental studies was devoted in the 1970s to 1990s to heterogeneous catalysis. The main objects of study were metal oxides and metals as catalysts. 

The rise in this ratio with the increasing number of tertiary C—H bonds in the molecule is explained by the increased probability of peroxyl radical undergoing isomerization. The experiments indicate that oxidized PP contains mainly block hydroperoxyl groups [12,88]. Hydrocarbons with tertiary C—H bonds (for example, isobutane, isopentane, and cumene) are oxidized in the liquid phase to stable molecular products, mainly hydroperoxides and A[02] = [ROOH], The recombination of tertiary peroxyl radicals gives rise to small amounts of dialkyl peroxide and alcohol (see Chapter 2). 

Vardanyan [65,66] discovered the phenomenon of CL in the reaction of peroxyl radicals with the aminyl radical. In the process of liquid-phase oxidation, CL results from the disproportionation reactions of primary and secondary peroxyl radicals, giving rise to trip-let-excited carbonyl compounds (see Chapter 2). The addition of an inhibitor reduces the concentration of peroxyl radicals and, hence, the rate of R02 disproportionation and the intensity of CL. As the inhibitor is consumed in the oxidized hydrocarbon the initial level of CL is recovered. On the other hand, the addition of primary and secondary aromatic amines to chlorobenzene containing some amounts of alcohols, esters, ethers, or water enhances the CL by 1.5 to 7 times [66]. This effect is probably due to the reaction of peroxyl radicals with the aminyl radical, since the addition of phenol to the reaction mixture under these conditions must extinguish CL. Indeed, the fast exchange reaction... 

Skeletal catalysts are usually employed in slurry-phase reactors or fixed-bed reactors. Hydrogenation of cottonseed oil, oxidative dehydrogenation of alcohols, and several other reactions are performed in sluny phase, where the catalysts are charged into the liquid and optionally stirred (often by action of the gases involved) to achieve intimate mixing. Fixed-bed designs suit methanol synthesis from syngas and catalysis of the water gas shift reaction, and are usually preferred because they obviate the need to separate product from catalyst and are simple in terms of a continuous process. 

Several examples have been reported of the use of palladium-mediated oxidation reactions of alcohols and alkyl halides. Palladium(II) acetate in the presence of iodobenzene converts primary and secondary alcohols into carbonyl compounds under solid-liquid two-phase conditions [20], However, other than there being no further oxidation to carboxylic acids, the procedure has little to commend it over other methods. It is relatively slow with reaction times in the order of 2 days needed to achieve yields of 55-100%. 

The activity of elemental carbon as a metal-free catalyst is well established for a couple of reactions, however, most literature still deals with the support properties of this material. The discovery of nanostructured carbons in most cases led to an increased performance for the abovementioned reasons, thus these systems attracted remarkable research interest within the last years. The most prominent reaction is the oxidative dehydrogenation (ODH) of ethylbenzene and other hydrocarbons in the gas phase, which will be introduced in a separate chapter. The conversion of alcohols as well as the catalytic properties of graphene oxide for liquid phase selective oxidations will also be discussed in more detail. The third section reviews individually reported catalytic effects of nanocarbons in organic reactions, as well as selected inorganic reactions. 

Oxidation of ethyl alcohol was one of the two important commercial routes to acetaldehyde until the 1950s, The other, much older route was the hydration of acetylene. The chemical industry was always after a replacement of acetylene chemistry, not just for acetaldehyde production, but all its many applications. Acetylene was expensive to produce, and with its reactive, explosive nature, it was difficult to handle. In the 1950s, acetylene chemistry and the ethyl alcohol oxidation route were largely phased out by the introduction of the liquid phase direct oxidation of ethylene. Almost all the acetaldehyde produced uses the newer process. 

T. R. Felthouse. P. B. Fraundorf, R. M. Friedman, C. L. Schosser, Expanded Lattiee Ruthenium Pyroehlore Oxide Catalysts. I. Liquid Phase Oxidations of Vicinal Diols, Primary alcohols, and related Substrates with Molecular Oxygen, J. Catal. 127 (1991)... 

K. Ebitani, K. Motokura, T. Mizugaki, K. Kaneda, Heterotrimetallic RuMnMn Species on a Hydrotalcite Surface as Highly Efficient Heterogeneous Catalysts for Liquid-phase Oxidation of Alcohols with Molecular Oxygen, Angew. Chem. 44 (2005) 3423-3426. 

Dinitrogen tetroxide reacts with simple alcohols in the gas and liquid phase to yield the corresponding nitrite ester as the major product together with trace amounts of oxidation products (Equation 3.4). This is the case for neat reactions and those conducted in methylene chloride between subambient and ambient temperatures. 

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