Organic reactions utilizing shape-selective microporous solids

• Main Author: Butters, M.
• Published: Swansea University 1986
• Subjects: 547.6
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636191

Chapters one, two and three provide some introductory information including a detailed review of supported reagents (from 1978 to mid-1986). Chapter four describes the electrophilic activation of a series of different chlorine-containing compounds by the presence of silica gel, these include <i>tert</i>-butylhypochlorite, N, N-dichloramine-T, N, N-dichlorourethane and calcium hypochlorite. Their ability to chlorinate toluene in the ring is comparable to more traditional reagents (like Cl<SUB>2</SUB> in acetic acid). Optimal results are obtained with silica which is significantly acidic and which has been dried at 120<SUP>o</SUP>C. The application of such reagents extends from anisole to more deactivated substrates like biphenyl. Chapter five involves the utilization of a variety of aluminosilicate (zeolite) supports. Thus by careful consideration of structural parameters (Al/Si ratio, counter cations, pore and cavity size/shape, and conditions of activation) it is shown that <i>tert</i>-butylhypochlorite in the presence of H<SUP>+</SUP>, Na<SUP>+</SUP> Faujasite X produces highly <i>para</i>-selective monochlorinations (> 90% para) of monosubstituted benzenes. For example, chlorobenzene in acetonitrile (at 40<SUP>o</SUP>C) produces dichlorobenzene (92% isolated yield) with an isomer ratio of 97% para/3% ortho. Similarly, toluene is chlorinated at 25<SUP>o</SUP>C in dichloromethane/diethyl ether (1/3) to give monochlorotoluenes quantitatively with a p:o ratio of 91:9. Proton-exchanged forms of Faujasite with a low aluminium content (Si/Al > 2.4) give by-products resulting from Friedel-Crafts type alkylation reactions. Presence of the stronger acid sites responsible for this reaction change is confirmed by ammonia-temperature programmed desorption experiments. Chapter six deals with the evaluation of different N-chlorodialkylamines in the presence of silica gel as <i>ortho</i>-selective chlorinating reagents for phenols. For example, N-chloro bis (2-chloroethyl) amine in the presence of silica gel in tetrachloromethane solvent gives good mono- to di-chlorination ratios with high selectivity for the <i>ortho</i>- position in phenol (o/p ~ atop = 12.75). Chapter seven outlines some preliminary attempts to control the exo-endo isomer ratio in the 4π + 2π cycloaddition reaction between cyclopentadiene and acrylonitrile.