Rearrangement of alkyl phenyl ethers to alkylphenols in the presence of cation-exchanged montmorillonite (Mn+-mont)
The rearrangement of alkyl phenyl ethers such as 4-phenoxybutan-2-one 1,1-phenoxybutane 2a, 2-phenoxybutane 2b, 2-methyl-2-phenoxypropane 2c and phenoxycyclohexane 2d have been investigated in the presence of cation-exchanged montmorillonite (Mn+-mont; Mn+= Zr4+, Al3+, Fe3+ and Zn2+). The ether 1 rearranged to 4-(4-hydroxyphenyl)butan-2-one 3(raspberry ketone), the odour source of raspberry, in 16–34% GLC yield, where Zn2+-mont was the most effective catalyst. Similarly, other ethers 2a–d rearranged to the corresponding alkylphenols in up to 75% isolated yield with good product selectivity, Al3+-mont being the catalyst of choice. Al3+-Mont was regenerated and reused in the rearrangement of 2b, 2c and 2d.