Syntheses of Dibenzo and Dicyclohexano-18-Crown

More recently, Dale and Daasvatn have shown that the product composition can be influenced by adding a templating cation (see Sect. Addition of copper 

It should probably also be noted before closing this section that 18-crown-6 and some of its aliphatic relatives have been found to form quite a variety of complexes or solvates with neutral molecules. We have noted the formation of an acetonitrile sol-vate . Although the other complexes are generally beyond the scope of the present work, we wish to call attention to their existence so that the worker attempting to improve purification procedures will check the literature for his particular method. This is especially important since a number of the solvates are found, to our knowledge, only in the patent literature. 

Two of the most widely used crown ethers have been dibenzo-18-crown-6 and dicyclo-hexano-18-crown-6.(In older literature, the latter is often referred to as dicyclohexyl-18-crown-6 .) A major reason for this is that Pedersen reported complete details of the preparation of both compounds in Organic Syntheses in 1972. As a result, both compounds were readily prepared and available. 

Pedersen s preparation of dibenzo-18-crown-6 involves catechol and bis(2-chloroethyl) ether. In this procedure, sodium hydroxide is used as base and M-butanol as solvent. The reactants are heated overnight and the crude crown is obtained by precipitation from acetone in which it is almost completely insoluble. The yield range specified is 39—48% and is readily realized. The overall preparation is illustrated in Eq. (3.11). 

The procedure described above is what Pedersen characterized as a synthesis by method Pedersen s alphabetical designations (see Sect. 3.1) are rarely used, but 

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