Ok I am getting some weird data from my team. A reductive ring contraction is being carried out on a heteroaromatic scaffold using various metals In, Sn, Ni, Cu, Fe and Zn in a series of alkanoic solvents AcOH, HCO2H and TFA. Some of the metals behave but I am having problems rationalising the reactivity of Cu which works nicely in AcOH and TFA but does not lead to any ring contraction in formic acid. There obviously must be a rational explanation but it escapes me. Zn behaves OK, working in AcOH and formic acid but not in TFA. Any help on this or simply pointing me into the right direction would be appreciated.
I do not know the answer but did you test these reactions conditions more than once? Did you change the batch of acid, fresh bottle?
Curious to read some comments
Laurent: yes we duplicated the reactions and checked the reagents. It must have to do with the oxidation levels of the copper. We put Cu powder in neat AcOH, TFA and formic acid in the absence of any heterocycle and found the the solutions in AcOH and TFA turned blue (ie Cu2+ is formed) but in formic acid the mixture remained almost colourless (very pale blue). I suspect the formic acid is reducing any Cu2+ formed to Cu+ and that this must be playing some role in preventing the ring contraction. Since there is plenty of metal powder still left in the reaction mixture I wonder whether the surface in the case of formic acid has been coated with some oxide layer which prevents the ring contraction. I really need some input from someone who knows about this kind of heterogenous surface chemistry and is familiar with Cu/H+. Any help would be appreciated!
I guess that you found the main reasons, no the question is WHY? I am sure that there are some organimetallic chemists here...
Laurent: Yes, I have probably picked the wrong Topic headings as am getting little feedback. I will have to repost the query.
- Badges
- Science topic
- Similar topics
- Chemistry
- Electrochemistry