Pinene oxides, rearrangement

The De Vos s group [142] studied [CUjCbtc) ], anhydrous MOF-199 or HKUST-1 as a selective catalyst exhibiting Lewis acidity in the isomerization reactions of terpene derivatives, pinene oxide rearrangement to campholene aldehyde, and cyclization of citronellal to isopulegol (Reaction 10) ... 

Acid-catalysed rearrangement of epoxides is another widely used reaction in the fine chemicals industry. Here again the use of solid acid catalysts such as zeolites is proving advantageous. Two examples are shown in Fig. 2.25 the isomerization of rsophorone oxide (Elings et al., 1997) and the conversion of a-pinene oxide to campholenic aldehyde (Holderich et al., 1997 Kunkeler etal., 1998). Both products are fragrance intermediates. 

More recently spinning disc reactors have been used by Wilson et alP0) to carry out catalytic reactions using supported zinc triflate catalyst for the rearrangement of a-pinene oxide to yield campholenic aldehyde. The results of this study, presented in Table 20.1, suggest that by using a supported catalyst on a spinning disc reactor it is possible to... 

Rearrangement of a-pinene oxide to campholenic aldehyde Batch Reactor Catalysed SDR... 

Wilson, K., Renson, A. and Clark, J. H. Catalysis Letters 61 (1-2) (1999) 51-55. Novel heterogeneous zinc triflate catalysts for the rearrangement of alpha-pinene oxide. 

Reaction conditions a-pinene 3.97 mL (25 mmol) 1,4-dioxane 40 mL oxidant air (15 mL/min) reaction time = 24h. Conversion and product composition were determined by GC and identified by GC-MS, Minor amounts of rearranged products of a-pinene oxide also formed. 

The catalysts Co-CMS5 and C0-CMS6 have also been tested for the air oxidation of a-pinene. In both the cases air oxidation commences quickly with the formation of a-pinene oxide, verbenol and verbenone as the main products along with other rearranged products as observed in the reactions described above. A conversion of 50.6% and 48.0% are observed for Co-CMSS and C0-CMS6 respectively after 24h (Table 6). 

Campholenic Aldehyde Manufacture. Campholenic aldehyde is readily obtained by the Lewis-acid-catalyzed rearrangement of a-pinene oxide. It has become an important intermediate for the synthesis of a wide range of sandalwood fragrance compounds. Epoxidation of (+)- Ct-pinene (8) also gives the (+)-o -a-pinene epoxide [1686-14-2] (80) and rearrangement with zinc bromide is highly stereospecific and gives (-)-campholenic aldehyde... 

The same author,3 .s and also Ritter and Ruaeel,1448 reported that o-pinene oxide, on the other haud, undergoes a deop-seated skeletal rearrangement under the same conditions, as shown in Eq. <446). 

Vicevic M, Jachuck RJ, Scott K. Process intensification for green chemistry rearrangement of ci-pinene oxide using a catalyzed spinning disc reactor. 4th International Conference on Process Intensification for the Chemical Industry, Brugge, Belgium, Sept. 10, 2001. 

There is a better route. The more likely cation formed on the way to pinene could rearrange to the camphor cation. This is a known chemical reaction and is a simple 1,2-shift of the kind discussed in Chapter 37. However the new cation is formed, addition of water and oxidation would give... 

Figure 3 The rearrangement of a-pinene oxide catalysed by supported zinc triflate...

Alpha-Pinene oxide 9 (Eq. 15.2.5) is known as a reactive molecule which rearranges easily under the influence of an acid catalyst (6, 7). Thereby many products can be formed. For example compounds such as the isomeric campholenic aldehyde 11, trans-carveol 12, trans-sobrerol 13, p-cymene 14 or isopinocamphone 15 are observed as main by-products. At temperatures higher than 200°C more than 200 products can be formed. The industrially most desired compound among these is campholenic aldehyde 10. It is the key molecule for the synthesis of various highly intense sandalwood-like fragrance chemicals (7, 8). 

H. van Bekkum et al. (17) reported that the alpha-pinene oxide 9 can be succesfully converted to campholenic aldehyde 10 (Eq. 15.2.5) in the presence of a BEA-zeolite. Ti-BEA proves to be an excellent catalyst for the rearrangement of a-pinene oxide to campholenic aldehyde in both the liquid and vapor phase. This is mainly attributed to the presence of isolated, well-dispersed titanium sites in a Bronsted-acid-free silica matrix. Furthermore, the unique molecularsized pore structure of the zeolite may enhance selectivity by shape-selectivity. 

For example, rearrangement of a-pinene oxide produces, among the ten or so major products, campholenic aldehyde, the precursor of the sandalwood fragrance santalol. The conventional process employs stoichiometric quantities of zinc chloride but excellent results have been obtained with a variety of solid acid catalysts (see Fig. 2.23), including a modified H-USY [70] and the Lewis acid Ti-Beta [71]. The latter afforded campholenic aldehyde in selectivities up to 89% in the liquid phase and 94% in the vapor phase. 

Japanese authors have made comprehensive investigations of the rearrangements of oxiranes in the presence of solid acids, bases, and salts.The model compounds employed were cyclohexene oxide and 1-methylcyclohexene oxide. The effects of the acidic and basic properties of the catalysts on the selectivity were interpreted on the basis of the products obtained. The main products are carbonyl compounds and allyl alcohol isomers. Rearrangements of limonene oxide over acids and bases were studied on five different types of Al203 similar research has been carried out on 2- and 3-carene oxides, cis- and trans-carvomenthene oxides and a-pinene oxide. ... 

In comparison with the catalytic cationic polymerization of these monomers (14), It Is remarkable that the radiation-induced polymerization gives high conversions at room temperature to a preclpltatable polymer. Although the catalytic polymerizations (14) were carried out in solution between -78 and -130°C under conditions which should minimize the formation of dimer oils and monomer rearrangement products, the highest reported conversion of a-pinene oxide to polymer was only 28%, and In this case the material was described as a viscous oil. Conversions to polymer In the form of a white powder varied from 1 to 20% although 76-100% of the o-pinene oxide... 

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