A facile synthesis of [¹¹C]acetylene

Acetylene is a versatile synthon organic chemistry. The complexity and difficulty of synthesis of [¹¹C]acetylene has limited its use as a labeling intermediate for PET radiotracers. A new method for production of [¹¹C]acetylene has been developed in our laboratory that simplifies the synthesis procedure allowing for easy automation and implementation. The technique is a modification of Madsen et al. (1981, Phys. Med. Biol. 26(5), 875) that utilized carbon dioxide (¹¹C) and barium. First [ ^11/12C]CO₂ was trapped at room temperature on barium within a quartz reaction tube, then heated to 900°C under hydrogen flow to release [¹¹C]acetylene. Hydrogen gas is apparently oxidized to form water vapor which reacts immediately with the formed carbide to liberate acetylene. Radiochemical yields of 31.4-75.4% and specific activities of 0.11-161 mCi/μmol have been obtained with radiochemical purities greater than 99%. This technique provides a new, efficient and very practical synthesis of [¹¹C]acetylene that can be utilized as synthon for novel PET radiopharmaceuticals.