Reaction of chloral with naphthalene, and the synthesis of α-methoxynaphthylacetic acids from naphthyl(trichloromethyl)carbinols

Abstract

From the Friedel–Crafts reaction of chloral and naphthalene, others have reported the isolation of only 2-naphthyl(trichloromethyl)carbinol. Our reexamination of this reaction has shown that a mixture of 1- and 2-naphthyl(trichloromethyl)carbinols is obtained and that 80 to 90% of the product consists of the 1-naphthyl(trichloromethyl)carbinol. The 1- and 2-naphthyl(trichloromethyl)carbinols, their acetates, and their methyl ethers differ in their nuclear magnetic resonance (n.m.r.) spectra in that the signal of the α-hydrogen of the side chain of the 1-naphthyl isomer always occurs 0.8 p.p.m. downfield compared to the signal of the α-hydrogen of the corresponding 2-naphthyl isomer. This is because the α-hydrogens in the 1-naphthyl series of these compounds are in the region between the 1- and 8-positions of the naphthalene ring and subject to the ring currents of both benzenoid rings.The mixture of crude naphthyl(trichloromethyl)carbinols was converted to the mixture of α-methoxynaphthylacetic acids, and these were separated. A small amount of α,α′-dimethoxy-1,5-naphthalenediacetic acid was also obtained, demonstrating that a certain amount of 1,5-substitution occurred in the Friedel–Crafts reaction of naphthalene and chloral.