Isophorone isomerization

Fig. 3. Relationship between the rate constant K) for isophorone isomerization and the number of sites for CO2 adsorption on calcined hydrotalcites with various compositions (107).

Isomerization of jS-isophorone to a-isophorone has been represented as a model reaction for the characterization of solid bases 106,107). The reaction involves the loss of a hydrogen atom from the position a to the carbonyl group, giving an allylic carbanion stabilized by conjugation, which can isomerize to a species corresponding to the carbanion of a-isophorone (Scheme 9). In this reaction, zero-order kinetics has been observed at 308 K for many bases, and consequently the initial rate of the reaction is equal to the rate constant. The rate of isomerization has been used to measure the total number of active sites on a series of solid bases. Figueras et al. (106,107) showed that the number of basic sites determined by CO2 adsorption on various calcined double-layered hydroxides was proportional to the rate constants for S-isophorone isomerization (Fig. 3), confirming that the reaction can be used as a useful tool for the determination of acid-base characteristics of oxide catalysts. 

Figure 9.1 Rate constant for isophorone isomerization at 308 K as a function of the number of sites determined by C02 adsorption for a series of basic solids ( ) KF ( ) Mg(La)0 (a) Mg(Al)0 and ( ) Ba(Al)0. Reprinted from Journal of Catalysis, vol. 211, Figueras et al., Isophorone isomerization as model reaction for the characterization of solid bases application to the determination of the number of sites, pp. 144-149, Copyright (2002), with permission from Elsevier...

Figucras, F Lopez. J Sanchez-Valente. J Vu, TTH Clacens. J-M Palomeque. J. Isophorone isomerization as model reaction for the characterization of solid bases application to the determination of the number of sites. Journal of Catalysis 2002 211, 144-149. 

Isomerized wood rosin, 32, 2 Isonicotinic acid, 37, 7 2-Isonitrosocyclohexanone, 32, 38 Isophorone, 37, 58 ISOPHORONE OXIDE, 37, 58 Isopropyl alcohol, 31, 112 Isopropyl iodide, 30, 34 31, 33 -Isopropylphenylacetamide, 32, 94 Ji-Isopropylphenyldichlorophosphine, 31,89 ISOTHIOCYANIC ACID, 1 -NAPHTHYL ESTER,... 

Terpene epoxides are very reactive compounds. Some products formed by isomerization of such epoxides are valuable raw materials for perfumes, synthetic flavourings and pharmaceuticals, and also provide useful intermediates in organic syntheses. The isomerization of isophorone oxide 23 (Eq. 15.2.9) was originally investigated by H.O. House and R.L. Wasson using boron trifluoride etherate as a homogeneous catalyst (24). 

Table 15.2 Conversion and selectivities obtained with used zeolites in the liquid phase isomerization of isophorone oxide 23...

In conclusion, the use of zeolites as catalysts in the isomerization of isophorone oxide 23, yields up to 86% keto aldehyde 24. The formation of 26 by... 

Comparison of empirical formulas indicates that compounds II and III are isomeric, and correspond to an apparent trimer of isophorone I minus two molecules of water. This circumstance suggests that the carbonyl group of I is a center of C-C bond formation by way of aldol condensation followed by elimination of the resulting alcohol. Predictably, enone I should be prone to polymerize under alkaline conditions due to its two electrophilic carbons and three potential carbanionic centers (see Scheme 55.1). 

In polyurethane 33, the azobenzene moieties are separated from each other along the polymer backbone by isophorone units and have the free volume necessary for isomerization and molecular reorientation. This polymer s azobenzene moieties can be photoisomerized readily in mixed LBK films, as demonstrated by measuring the optically induced birefringence that originates from the photoreorientation of the chromophore upon polarized irradiation see Section 6.5.2). 

Roederer et a/. ° investigated an isomeric reaction (alpha- and beta-isophorone) at 388, 423 and 493 K. They experimented in a stirred batch reactor in the form of... 

Preliminary experiments revealed that the selectivity of titania-silica aerogel in the epoxidation of P-isophorone was moderate. The selectivity related to the olefin converted was below 90 % at low temperature, and dropped rapidly at 80 °C or above. The most important side reactions were the formation of 3,5,5-trimethyl-2-cyclohexene-4-hydroxy-l-one (2) by ring opening of the epoxide (1), and the isomerization of P- to a-isophorone (3), as shown in Scheme 2. Epoxidation of 2 and 3, and the oxidation at the OH group of 2 to a dicarbonyl compound were slow and the amounts of these by-products were usually aroimd 1 % or less. 

The importance of the acid-catalyzed side reactions are illustrated in Table 3 by the product distribution obtained using either TBHP or cumene hydroperoxide (CHP) as oxidant. The epoxidation with TBHP is faster and considerably more selective. When using CHP, about 20 mol% of the coproduct 2-phenyl-2-propanol was dehydrated to a-methylstyrene. It is likely that the simultaneously formed water increases the (Brpnsted) acidity of the aerogel and thus accelerates the ring opening and - to a smaller extent - the isomerization reactions. No oxidation products were formed in the absence of peroxide, as expected. Slow isomerization from p- to a-isophorone catalyzed by titania-silica was the only reaction observed. The data in Table 3 indicate that the simultaneous presence of peroxide and catalyst in the reaction mixture markedly accelerates the acid-catalyzed isomerization reaction. 

Thermal and metal-catalyzed cyclizations of silyloxy-substituted hexatrienes have been report-ecj io9. i io Silylation of the enolate derived from phorone 70 affords the (Z)-silyl ether 71. It was concluded that ZjE isomerization must occur at elevated temperatures, since a 53% yield of isophorone 72 is obtained upon thermolysis of a xylene solution of 71 at 220 °C (36 h) followed by acidic hydrolysis of the enol ether products. 

Terpene epoxides are very reactive compounds. Some are prepared conventionally by isomerization using homogeneous catalysts such as Bp3.Et20 [35,36]. The rearrangement of isophorone oxide (Figure 6) yields the keto aldehyde (13), which is an intermediate for fragrance chemicals. If the reaction is performed in the presence of zeolites the keto aldehyde (13) and the keto-enol form of the a-diketone... 

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