Synthesis And Properties Of Azo-calix[4]Arene Derivatives With Morpholine Chelation Group

As the third generation supramolecular host compound after crown ether and cyclodextrin, calixarene has a unique cavity, which is the ideal molecular framework to build new structures and special properties and the important molecular platform to develop ionophores.Many highly selective host molecules can be obtained by functional modification at the upper and lower rim of calixarene. Introducing morpholine group at the lower rim of calixarene can not only enhance coordination with metal ions, but also be considered as a good intermediate to further modify. Diazo-coupling reaction is an important method which is used to functionally modify the upper rim of calixarene. It is possible for introducing azo group into the skeleton of calixarene to make it possess color recognition ability.In this paper, a series of azo-calix[4]arene derivatives with morpholine chelation group were designed and synthesized. The recognition of these compounds upon metal ions were investigated by UV-vis spectrum and fluorescence spectrum. The results are as follows:(1) 5,11,17,23-tetra-t-butyl-25,26,27,28-tetrahydroxycalix[4]arene was synthesi-zed from p-tert-butylphenol and formaldehyde by polymerization reaction and was further used to synthesize 25,26,27,28-tetrahydroxycalix[4]arene with aluminium chloride by reverse Friedel-Crafts alkylation reaction.(2) By selective etherisation,25,26,27,28-tetrahydroxycalix[4]arene reacted with 1,2-dibromoethane to form 25,27-bis(2-bromoethoxy)-26,28-dihydroxycalix[4]arene.(3) 25,27-bis[2-(N-morpholine)ethoxy]-26,28-dihydroxycalix[4]arene was synt-hesized from 25,27-bis(2-bromoethoxy)-26,28-dihydroxycalix[4]arene and morpho-line.(4) 25,27-bis[2-(N-morpholine)ethoxy]-26,28-dihydroxycalix[4]arene reacted with diazonium salts of different aromatic amines to achieve a series of azo-calix[4]arene derivatives:5,17-di(3-methylphenyl)azo-25,27-bis[2-(N-morpholine) ethoxy]-26,28-dihydroxycalix[4]arene; 5,17-di(4-chlorophenyl)azo-25,27-bis[2-(N-morpholine)ethoxy]-26,28-dihydroxycalix[4]arene; 5,17-di(4-bromophenyl)azo-25, 27-bis[2-(N-morpholine)ethoxy]-26,28-dihydroxycalix[4]arene; 5,17-di(4-methoxy phenyl)azo-25,27-bis[2-(N-morpholine)ethoxy]-26,28-dihydroxycalix[4]arene; 5,17-di(2-methoxyformylphenyl)azo-25,27-bis[2-(N-morpholine)ethoxy]-26,28-dihydroxy calix[4]arene; 5-(1-anthraquinone)azo-25,27-bis[2-(N-morpholine)ethoxy]-26,28-di hydroxycalix[4]arene.(5) All the compounds were characterized by 1H NMR and IR and some of them were characterized by ESI-MS and 13C NMR.(6) The yields of 5,17-di(2-methoxyformylphenyl)azo-25,27-bis[2-(N-morpho line)ethoxy]-26,28-dihydroxycalix[4]arene and 5-(1-anthraquinone)azo-25,27-bis[2-(N-morpholine)ethoxy]-26,28-dihydroxycalix[4]arene were improved by the orthogo-nal experiment.(7) The recognition of these azo-calix[4]arene derivatives with morpholine chelation group upon metal ions were investigated by UV-vis spectrum and fluorescence spectrum. The results show that 5,17-di(2-methoxyformylphenyl)azo-25,27-bis[2-(N-morpholine)ethoxy]-26,28-dihydroxycalix[4]arene can recognize La3+, Nd3+, Eu3+, Y3+, In3+ in the UV-vis spectrum and only recognize Eu3+ in the fluorescence spectrum.5-(1-anthraquinone)azo-25,27-bis[2-(N-morpholine)ethoxy]-26,28-dihydroxycalix[4]arene has a good selectivity for rare earth metal ions La3+, Nd3+, Eu3+, Y3+, which leads to obvious color change from light yellow to red detected by naked eyes.