Dehydrogenation of isopropanol to acetone

Fig. 3.11 Left molecular orbital diagram of [Pt2(P205H2)4] Right Dehydrogenation of isopropanol to acetone using [Pt2(P205H2)4] as a photocatalyst, based on the description in [6]...

HRhLi, (L = PPh3).82 The reduction of acetophenone and aromatic aldehydes by [Rh(nbd)L2] /NaOPrl In PrlOH decreases with decreasing electron donor ability of L or electron richness of the aldehyde.83 The photolytic dehydrogenation of isopropanol to give acetone and H2 Is catalysed by c1s-fRhCl(C0)(dppm) U In the presence of acetone as photosensitizer.84... 

Acetone is produced by the dehydrogenation of isopropanol according to the following reaction ... 

It is possible that the dehydrogenation of aldehyde to ketene, as in the well known case with acetone, and the subsequent reaction of ketene and aldehyde to give carbon dioxide and an unsaturated hydrocarbon is the explanation.70 The presence of acetic acid might also be accounted for by the interaction of ketene and water. No such reaction would be expected in the case of isopropanol since a temperature of 650° C. is required for the fonnation of ketene from acetone and only traces of carbon dioxide have been reported from this alcohol.81... 

A group of studies in the literature deals with 2-propanol (isopropanol). " According to FTIR studies,no dissociative adsorption can be detected when isopropanol is adsorbed at a Pt surface. The main reaction of isopropanol is its dehydrogenation leading to the formation of acetone. Kinetic studies demonstrate that dehydrogenation of isopropanol is a fast reaction while the oxidation of isopropanol or acetone into CO2 is a relatively slow process. 

Isopropanol was used as a probe molecule to characterize the acidity of heteropolyacid compounds because the product s distribution upon reaction depends on the nature of the surface active sites. Strong Brdnsted (H ) and Lewis acid sites catalyze the dehydration of isopropanol to propylene (di-isopropyl ether over weak Lewis acid sites), and redox/basic sites lead to the dehydrogenation of the alcohol to acetone. 

The most important source of acetone is the Hock process for phenol production. In this process acetone is obtained as stoichiometric coupling product. If acetone needs to be produced deliberately, it can be obtained by oxidative dehydrogenation or dehydrogenation of isopropanol. Oxidative dehydrogenation proceeds at 400-600 °C at silver or copper contacts, direct dehydrogenation is carried out at 300-400 °C using zinc contacts. Alternatively, acetone can also be obtained by a Wacker-Hoechst oxidation of propylene. Acetone is used industrially as solvent. Moreover, the aldol condensate products of acetone (diacetone alcohol) are used as solvents. Acetone is also converted in an add catalyzed reaction with two moles of phenol for the synthesis of bisphenol A. Bisphenol A is an important feedstock for the production of epoxy resins and polycarbonates. 

Most of the world s acetone is now obtained as a coproduct of phenol production by the cumene process. In the cumene-to-phenol process, benzene is alkylated to cumene, which is oxidized to cumene hydroperoxide, and the latter is cleaved to acetone and phenol. Dehydrogenation of isopropanol accounts for most of the acetone that is produced to meet the demand in excess of that supplied by the phenol process. The economics of acetone production are unusual in that the supply depends on the production of phenol, whereas the demand is controlled by the uses of acetone. When the consumption of acetone grows at a slower rate than the growth of demand for phenol, an excess in the supply of acetone occurs. More than 75 % of the world s and about 95 % of the United States acetone production now comes from the cumene-to-phenol process. World production of acetone in 1990 was about three million metric t per year, of which about one-third was made in the United States. It has been predicted that acetone as a coproduct from the cumene-to-phenol process will continue to dominate supply, and production of on-purpose acetone will probably decline as... 

The decomposition of isopropanol proceeds either via (A) dehydration to propene or (B) dehydrogenation to acetone. Both continuous- and pulse-flow measurements have shown that the reactions have similar rates on VI and V8, but (A) is faster than (B) on V8. Reaction (A) requires acid centers these are entirely removed when the soluble vanadium species are removed by isobutanol or NH4OH [28q],... 

Qualitatively similar results were obtained for reaction and desorption of normal and iso-propanol on the 011 [-faceted TiO2(001) surface. In the case of normal propanol, almost half of the molecules initially adsorbed desorbed as the parent molecule at 370 K, while half of the remaining surface species reacted to form propanol at 580 K. The ratio of propene to propionaldehyde generated at 580 K was 10 1. Desorption of isopropanol quantitatively mirrored the desorption of normal propanol in two desorption states at 365 and 512 K. Isopropanol did not generate any dehydrogenation products (e.g., acetone), and the surface did not generate any bimolecular coupling products for any of the probe alcohol molecules. The absence of ether formation on the (Oil [-faceted surface is consistent with the need for double-coordination vacancies to facilitate that reaction, and the absence of such sites on this surface of titanium dioxide [80]. 

The decomposition of isopropanol can lead to the formation of propene and/or isopropyl ether (depending on the reaction temperature) if the catalyst possesses acidic sites [8], The dehydrogenation process towards acetone requires the catalyst to possess redox properties [15]. 

Figure 20 shows the diffusivities of isopropanol, acetone and propene under the conditions of single-component adsorption on zeolite Na-X [170]. All three compounds are involved in a well-established test reaction to discriminate between acid and basic zeolites [171,172] Isopropanol is dehydrated to propene on acid catalysts, while it is dehydrogenated to acetone on basic catalysts. Figure 20 shows that the diffusivity of propene, i.e. of the product of the acid-catalyzed reaction is more than one order of magnitude larger than the diffusivities of the reactant (isopropanol) and of the product (acetone) of the base-catalyzed reaction. Hence, if the acid- and base-catalyzed reactions both were to occur in parallel, the difference in... 

The isopropanol can be dehydrogenated to acetone per the referenced patents. The reaction is highly endothermic and at 90% conversion does result in coking of the catalyst, which requires a one-week regeneration burnout every two months. At 80% conversion, the catalyst run length can be extended to six months. Expected catalyst life is four regenerations after which the catalyst must be replaced at 6/lb. 

Usually Fe203 is regarded to be weakly acidic and basic. It catalyzes the dehydrogenation of ethanol, but only dehydration has been reported for 2-butanoP and isopropanol.It has been reported that 7-Fe203 which had been partially reduced was very active for the isomerization of 1-butene via a cationic allyl intermediate. IR study of adsorption and desorption of NH3 showed the presence of strong Lewis acid sites, but formation of nitrogen oxides from adsorbed NH3 was observed at higher temperatures. Interaction of the surface with acetic acid produced acetone. ... 

Alcohols will serve as hydrogen donors for the reduction of ketones and imi-nium salts, but not imines. Isopropanol is frequently used, and during the process is oxidized into acetone. The reaction is reversible and the products are in equilibrium with the starting materials. To enhance formation of the product, isopropanol is used in large excess and conveniently becomes the solvent. Initially, the reaction is controlled kinetically and the selectivity is high. As the concentration of the product and acetone increase, the rate of the reverse reaction also increases, and the ratio of enantiomers comes under thermodynamic control, with the result that the optical purity of the product falls. The rhodium and iridium CATHy catalysts are more active than the ruthenium arenes not only in the forward transfer hydrogenation but also in the reverse dehydrogenation. As a consequence, the optical purity of the product can fall faster with the... 

Although metals have generally been considered to exert only a dehydrogenating action in the reactions involved in the pyrolysis of the alcohols, it is possible for them to act toward dehydration in certain instances. By passing isopropanol over reduced copper at 320° C. it is possible to obtain acetone and propene, and by using ethanol, to obtain acetaldehyde and ethylene. By treating menthol in the same way menthene is formed. A determination of the water formed in each of these cases suggests that the catalytic action of the metal is one of direct dehydration.44... 

The Shvo catalyst 1 can participate in the transfer of hydrogen from one molecule to another. Such hydrogen transfer reactions are useful in synthetic organic chemistry for the reduction of ketones (aldehydes) and imines, and for the oxidation of alcohols and amines. In the former case (transfer hydrogenation), a hydrogen donor such as isopropanol or formic acid is used, which reduces the carbonyl compound or imine to alcohol or amine, respectively. In the oxidation of alcohols and amines (transfer dehydrogenation), a hydrogen acceptor such as acetone or a quinone is used. 

The measurement of the activity in a specific catalytic reaction, such as isopropanol decomposition or butene isomerization is also often used in the field. Catalysts may, for example, be characterized by their ability to dehydrate isopropanol molecules into propene, or to dehydrogenate them in acetone. The former reaction tests their acidity and the latter their basicity (Ai, 1977 Cunningham et al., 1981 Nollery and Ritter, 1984 Tanabe et al., 1989 Gervasini and Auroux, 1991). 

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