SYNTHESIS AND STABILITY OF ISOTOPICALLY LABELED P-CHLORO-M-XYLENOL (PCMX)

The synthesis, reaction kinetics, and pH stability of isotopically lab eled p-chloro-m-xylenol (PCMX) were evaluated. While base catalysis wa s more rapid than acid catalysis, the latter allowed the use of a coso lvent for deuterium and tritium labeling using as little as 250 muL la beled water. Both acid and base catalysis were markedly more rapid tha n that reported previously for the deuteration of PCMX and related phe nols. Isotopic labeling occurred only at the 2 and 6 ring positions, o rtho to the phenolic group of PCMX. No deuterium loss was observed aft er storage for 21 days at 37-degrees-C over a pH range of 2-14. Isotop ic loss was observed only below pH 2. The prepared H-3-labeled PCMX ha d a specific activity of 1.18 mCi/mmol, a radiochemical purity of 99.0 %, and a chemical purity exceeding 99.0%, with a high stability during prolonged cold storage.