Acetone formation

Although acetone was a major product, it was not observed by infrared spectroscopy. Flowing helium/acetone over the catalyst at room temperature gave a prominent carbonyl band at 1723 cm 1 (not show here). In this study, a DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) cell was placed in front of a fixed reactor DRIFTS only monitored the adsorbed and gaseous species in the front end of the catalyst bed. The absence of acetone s carbonyl IR band in Figure 3 and its presence in the reactor effluent suggest the following possibilities (i) acetone formation from partial oxidation is slower than epoxidation to form PO and/or (ii) acetone is produced from a secondary reaction of PO. 

Table 2 Results from the decomposition reaction of isopropanol on (MPMol2)b and (MPMol2)b series at 150°C conversion, rate for propene formation (rp) and rate for acetone formation (ra).

Yeast alcohol dehydrogenase (YADH), catalysis of reduction by NADH of acetone formate dehydrogenase (FDH), oxidation by NAD of formate horse-liver alcohol dehydrogenase (HLAD), catalysis of reduction by NADH of cyclohexanone With label in NADH, the secondary KIE is 1.38 for reduction of acetone (YADH) with label in NAD, the secondary KIE is 1.22 for oxidation of formate (FDH) with label in NADH, the secondary KIE is 1.50 for reduction of cyclohexanone (HLAD). The exalted secondary isotope effects were suggested to originate in reaction-coordinate motion of the secondary center. 

The reaction of propane in CaY appears to be an authentic thermal Frei oxidation [55], Propane is, itself, inert in CaY but slowly oxidizes at 21°C with complete selectivity for formation of acetone. In contrast, propane oxidation in BaY did not commence until the temperature was raised to 55°C, but even at this elevated temperature, the high regioselectivity for acetone formation argues for a thermal Frei oxidation mechanism,... 

The selectivity of acetone formation on a V205-Ti02 catalyst active in the transformation of propylene to acetic acid could be enhanced by adding water vapor to... 

The oxyhydration of propene to acetone occurs at a much lower temperature than the allylic oxidation and demands, in principle, the presence of excess steam. The reaction is initiated by addition of a proton from the catalyst surface and the acetone formation involves oxygen originating from water. 

The combination Sn02— Mo03 may also produce acrolein with reasonable selectivity. However, recent studies mainly concern acetone formation, which is favoured under appropriate conditions (excess of water and relatively low temperatures) (see Sect. 2.2.4). 

The characteristic reaction conditions and the special role of acidic sites in acetone formation accord very well with what is known about the mechanism. The first step in this process is the reversible uptake of a proton by the propene molecule, as evidenced by the D20 experiments carried out with a Sn02—Mo03 catalyst by Buiten [63,64], viz. 

We have also studied the change in regioselectivity and the selectivity of acetone formation as functions of the dispersion. Table 2 shows both sets of data. It is seen that the regioselectivity does not depend on the dispersion on all catalysts, the sterically less hindered bond breaks. In other words, the regioselectivity is not affected by the variation in the metal structure. This observation correlates well with our former results the different regio-selectivities are due to the different types of mechanism, and these mechanisms are governed by the different affinities of the metals for oxygen (refs 3,4). 

Regioselectivity data for the transformation of methyloxirane and the selectivity of acetone formation. 

Regioselectivity = TOFAc+TOF2P /TOFAc+ OF2P+TC,riP Selectivity of acetone formation = T0FAc/T0FAc+TDF2p-... 

The regioselectivity of the transformation of methyloxirane is independent of the catalyst structure, but it depends on the nature of the metal. The selectivity of acetone formation exhibitsa curve with a slight minimum character as a function of dispersion, since this selectivity is determined by the hydrogen availability on the surface. 

The peroxyl radical anion formed in reaction (10) has an immeasurably short ( 10 6 s ) lifetime, i.e ku is much larger than k 0 x [H20], and even at high [OH ] the rate of acetone formation is essentially given by kw x [OH ] (Bothe et al. 1977). The situation is similar for other a-hydroxyalkylperoxyl radical anions (Rabani et al. 1974 Ilan et al. 1976 Bothe et al. 1983) with the exception... 

Propionic aldehyde and acetone formation can be represented by the two mechanisms shown in Figures 7.14 and 7.15. As follows from these mechanisms of the catalytic act, with... 

Acetone is the important product of the mimic s monooxygenase activity. It is synthesized at high temperature, 220 °C or higher. The yield of acetone noticeably increases with contact time and temperature, reaching 15 wt.%. In this case, two ways of acetone formation (catalytic isomerization of epoxide and direct synthesis from C3H6) are also probable. 

A study of the intermediate products from the ozonolysis of iso-proplymercuric chloride shows that the rate of build-up of isopropyl alcohol adequately accounts for the rate of acetone formation. The reaction sequence therefore appears to be one of carbon-mercury cleavage, followed by oxidation by ozone. 

FIGURE 10.13 Major channel of acetone formation from OH-oj-pinene reactions. 

From the excited-state oxirane, mainly propanal is formed by hydrogen abstraction via a biradical. With the increase of pressure, the excited state is quenched and, at the same time, there is a rise in the quantity of acetone. The two products are therefore not formed from the same intermediate. Acetone formation is conceived... 

Since both the radicals CH3CO and CH3COCO rapidly decompose, the experimental methods available at present are not adequate to decide between initiation steps (2) and (2 ). Reactions (3), or (3 ), (4) and (6) necessarily follow step (2), or (2 ), if chains are to occur. Since acetone is produced in about 10-15 % yield of the biacetyl decomposed, reaction (5) has to be assumed. Other alternatives for acetone formation, as for instance the recombination of CH3 and CH3CO radicals or the addition of CH3 to ketene, are not able to explain the high acetone yield around 500 The mechanism of reaction (5) is uncertain (see Section 7 in Part II). 

A mechanism for acetone formation which involves only the alkylperoxy species requires a rather unlikely intramolecular H atom transfer (51), as follows ... 

Aromatic or a,p-unsaturated acid chlorides were found to undergo nqnd oxidative addition with these palladium complexes, and the subsequent acylation of an organotin proceeded smoothly in HMPA (1-60 min) or in acetone. Formation of simple aliphatic acylpalladium(II) complexes proceeds at markedly reduced rates and the acylation of organotins is slower but still use l (10-24 h). 

Tetracarbonylalkyl derivatives of cobalt(I) have low stability. As early as 1964 it had been noted that ketones are formed in the thermal decomposition of CoR(CO)4 (R = Me, Et) presumably involving a binuclear intermediate or an intermolecular mechanism. The mechanism of acetone formation was studied for other cobalt systems that are more easily handled, namely, Co(>/ -C5H5)Me2(PMe3) and Co2(ti -CsH )2Me2(fi2-CO)2 . Upon carbonylation, in the former case, the transient carbonyl derivative Co()j -C5H5)Me2(CO) was observed spectroscopically, whereupon it underwent carbon monoxide insertion to give an acetyl-methyl complex, followed by reductive elimination of acetone ... 

In their study of isopropanol oxidation over copper(ii) oxide, Volta e/a/. found that their kinetic data agreed with an earlier reaction scheme where dis-sociatively adsorbed oxygen is involved in the rate-determining step. The rate of acetone formation (Fac) fitted equation (25) ... 

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