A highly selective synthesis of 1,1 '-bi-2-naphthol by oxidative coupling of naphthol on mesoporous Fe,Cu/MCM-41 aluminosilicates

The oxidative coupling of 2-naphtol to 2,2'-dihydroxy-1,1'-binaphthyl (bina phthol) by air or oxygen has been carried out in the presence of Cu2+- and Fe3+-doped MCM-41 aluminosilicate as catalyst. Fe-exchanged MCM-41 was foun d to be a very efficient catalyst; excellent mass balances (>95%) with almo st total conversion and selectivity to binaphthol were achieved. The same r eaction has also been carried out on Cu2+- and Fe3+-Y zeolites. Taking into account the relative dimensions of binaphthol and the catalyst pores, mole cular modeling predicts that binaphthol can be accommodated inside the zeol ite Y supercages (1.3 nm), but it cannot diffuse outside the zeolite caviti es through the smaller pore apertures (0.74 nm). This prediction has been c onfirmed by dissolving a Y zeolite after the reaction, whereby unextractabl e binaphthol entrapped within the cavities was recovered. Variable amounts of two secondary by-products have also been detected, and their structure a ssigned to (2,8'); (8,2')-dioxo-1,1'-binaphthyl and bisnaphthofuran based o n analytical and spectroscopic data. Their percentage is particularly high when alumina-supported CuSO4 is used as the catalyst.