Trimethylcyclohexanone, selectivity

With other less-rigid cyclohexanones, the stereochemical course of the reduction is less easy to predict. In general, a mixture of products is obtained in which, with comparatively unhindered ketones, the more stable equatorial alcohol predominates with hindered ketones, the axial alcohol is often the main product. Thus, reduction of 4-tert-butylcyclohexanone 84 with lithium aluminium hydride gives predominantly the equatorial trans-4-/ crt-butylcyclohexanol, whereas the hindered 3,3,5-trimethylcyclohexanone 85 gives a mixture containing mainly the axial alcohol 86 (7.69,7.70). The latter is almost the only product when a more hindered and hence more selective reducing agent such as L-selectride [LiBH( Bu)3] or lithium hydrido-tri-tert-butoxyaluminate [LiAlH(0 Bu)3] is employed. 

Table 1 Catalyst screening results for the selective hydrogenation of isophorone to trimethylcyclohexanone (TMCH).

The copolymer (Fig. 14.4) is prepared from l,l-bis(4-hydroxyphenyl)-3,3, 5-trimethylcyclohexane (1) and bisphenol A. The cyclohexane containing bisphenol (1) is prepared by the condensation of phenol with 3,3,5-trimethylcyclohexanone and an acidic catalyst. The cyclohexanone can be prepared by the selective hydrogenation of isophorone [113, 114]. The Tg of the copolymers can be varied from 150°C (e.g., BPAhomopolymer) to 240°C [e.g., homopolymer of l,l-bis(4-hydroxyphenyl)-3,3,5-trimethylcydohexane]. And the resins can be prepared by either melt or interfacial processes. For increased ductility, terpolymers have been reported with a sUoxane block [115]. For applications requiring low moisture absorption, the bisphenol (1) has been polymerized with bisphenol M (see the section New Copolymers for Optical Storage Media ). 

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