Calix-4-hydroquinone

Calixquinones can be easily reduced to the corresponding calixhydroquinones (Zn/HCl or Na2S204) . The calix[8]hydroquinone 57b, however, was prepared from the octabenzyl ether 57a obtained by one-pot condensation in a mixture with the analogous calix[6]- and -[7]arene. Oxidation of 57b to the respective octaquinone was not reported, but the ewrfo-ether 57c was obtained by exhaustive 0-propylation prior to the cleavage of the benzyl ether groups . Inherently chiral derivatives of a calix[4]arene monoquinone have been obtained by 1,4-addition of various nucleophiles to the quinoid system. 

L = p-benzyl-calix[5]arene)2]-8 toluene. HBpt = 3,5-bis(pyridine-2-yl)-l,2,4-triazole. H2Q = 1,4-hydroquinone. 

Hydrazine can be stabilized by formation of an inclusion compound with hydroquinone.58 Uncomplexed anhydrous hydrazine can be explosive. Highly toxic dimethyl sulfate can be handled more easily as an inclusion compound with toxic 18-crown-6. Both of these toxic compounds could be avoided through the use of dimethyl carbonate (as described in Chap. 2). Reactive intermediates, such as benzyne, have been stabilized by generating them inside hosts.59 Even the noble gas xenon can be trapped reversibly by hosts such as a cryptophane, 4-ferf-butyl-calix[4]arene or a-cyclodextrin.60... 

In fact, the large number of fascinating molecular architectures (Figure 5) formed from cucurbiturils lead to the concept of self-assembling capsules. These self-assembling capsules are receptors with enclosed cavities that are formed by the reversible noncovalent interaction of two or more, not necessarily identical, subunits. As would be in a subsequent section, the self-assembly of isolated calix[4]hydroquinone molecules leads to well-defined honeycomb architectures [64,65]. One of the advantages of these self-assembling capsules is that they can... 

Fig. 34.13. Top and side views of a silver nanowire inside a calix[4]quinone-hydroquinone (CQHQ) nanotubes (right figures), and the band structures of an isolated silver nanowire (left—first on the left figure), a silver nanowire encapsulated in a CQHQ nanotube (second), a CQHQ nanotube (third), and a calix[4]hydroquinone (CHQ) nanotube (last). (Reproduced with permission from American Physical Society [156].)...

Solvent molecules of water and acetone trapped in calix[4]hydroquinone supramolecular nanotubes have been studied by solid state and fast MAS NMR and DFT calculations. It has been shown that both water and acetone molecules occupy well-defined average positions, but undergo fast reorientation motions during which their protons interchange their positions. 

Fig. 11.2 Calix [4] hydroquinone neinotubes showing the longitudined one-dimensional H-bond arrays. Each tube has four thin threads of infinitely long one dimensioned hydogen bond relays, and the diameter of each is 8 A (Reproduced from Ref. [2] with kind permission of The American Chemical Society)...

Lee et al. show a self-assembly method to form nanolenses made of calix[4]hydroquinone (CHQ). This compound is composed of four p-hydroquinone subunits with eight hydroxyl groups [10]. Dissolving the CHQ monomers in 1 1 water-acetone solution leads to the formation of needle-like CHQ nanotube crystals with infinitely long hydrogen-bonded arrays. When the crystals are heated at 40°C in aqueous environments, CHQ molecules released from the crystals can re-assemble into nanospheres. 

Some years ago, a simple and convenient route to selectively functionalize the calix[8]arene exo rim was introduced [34]. The easily accessible 1,5-xylylene-bridged derivatives 26a-b, can be easily deprotected by hydrogenolysis to give 27a-b which can be selectively functionalized at the free phenolic rings because of their higher reactivity with respect to the (9-alkylated ones. In this way, the first examples of caUx[8]arenes partially substituted with p-nitro,p-amino, quinone, and hydroquinone functionalities have been obtained (Scheme 7.2) [34, 64]. 

Fig. 3.17 The assembly of calix[4]hydroquinone 36 to nanotubes based on ID infinite hydrogen bonding ehains [74]...

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