Synthesis of ascorbic-6-14C acid

L‐ascorbic‐6‐14C acid with a specific activity of 3.25 μCi/mg was prepared from D‐glucose‐1‐14C in an overall yield of 10 %. Synthetic steps were : glucose to sorbitol, sorbose, diisopropylidene sorbose, potassium diisopropylidene 2‐ketogulonate, 2‐ketogulonic acid and ascorbic acid. In a similar manner L‐ascorbic‐5‐14C acid was prepared from D‐glucose‐2‐14C. Conversion of 2‐keto‐L‐gulonic acid to ascorbic acid was done in 0.5 M trifluoroacetic acid solution at 115°C with 2 % acetone as a decomposition inhibitor. The reaction probably proceeds via an enediol intermediate.