Synthesis of tertiary 14C-labelled nonylphenol isomers

The ring-14C-labelled p-nonylphenol (NP) isomers 4(3',5'-dimethyl-3'-heptyl)-phenol (p353NP), 4(3',6'-dimethyl-3'-heptyl)-phenol (p363NP) and 4(2',6'-dimethyl-2'-heptyl)-phenol (p262NP) were synthesized for application in metabolism and sorption studies. Friedel-Crafts alkylation of 14C-labelled phenol and the corresponding tertiary nonylalcohol with BF3 as catalyst was used. After clean-up of p262NP and p363NP by preparative thin-layer chromatography radiochemical yields amounted to 62.8 and 64.6%, specific radioactivities were 332 and 88.2 MBq/mmol, and radiochemical purities 97.6 and 99.0%. For both isomers, a large-scale synthesis with non-labelled phenol was additionally developed, which led to pure products (96 and 99%, respectively) without further purification steps. In the case of p353NP, which was formed as a diastereomeric mixture, the crude synthetic product had a radiochemical purity of 96.9% (radiochemical yield: 76.0%; specific activity: 298 MBq/mmol); thus, purification was not necessary. All products were characterized by means of gas chromatography-mass spectroscopy, 1H- and 13C-NMR, as well as IR.