SYNTHESIS OF LABELLED PHOSGENE

Phosgene is a versatile reagent for the isotopic labelling of organic molecules and its use for the preparation of a variety of radiopharmaceuticals is well established (see Section 10.8). Given the vast range of organic compounds which can be prepared from 

The CAS registry numbers for isotopically-labelled phosgene are given in Appendix A3. 

Phosgene containing the short-lived radioactive nuclide C has been prepared by zinc reduction of cyclotron-produced ( N(p,a) C) CO j to CO, followed by chlorination to COClj by passage of the gaseous labelled CO over heated PtCl [429,1729,1731], or by 

Alternatively CO, obtained directly by the irradiation of (in the presence of 2% O ) with 15 MeV protons, was mixed with an equal volume of Clj and the mixture exposed over fifteen minutes to u.v. light. The radiochemical yield was about 75% [275]. Since the total time required to obtain COClj for further synthetic use is about thirty minutes, attempts were made to telescope the synthesis by combining the production of the labelled CO and the radiation-induced reaction with Cl, in one step. 

The cyclotron irradiation of a mixture of N j, CO and Cl j gave a yield of COCl j of 25%, but was of relatively low specific activity owing to the presence of carrier amounts of non-radioactive COClj [275]. 

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The development of an efficient synthesis of labelled phosgene was the main determinant in a synthesis of C-2 thymine. ... 

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