Question

Can alkenes react with potassium dichromate?

Answer 1

tip: other way to word the question: "Can alkenes be oxidised?"

Answer 2

Hmm...I'm not sure but what I've learnt is no, it cannot. Alkenes can react with acidified potassium permanganate to form diol... but not potassium dichromate..

Answer 3

No, the alkene will not react as potassium dichromate isn't strong enough but it will react with acidified potassium manganate which is a stronger oxidising agent. In this case you'll end up with a 1,2 diol and I think this reaction is on the A level syllabus.

Answer 4

I'm revising for Units 1&2 in Edexcel (Nuffield) Chemistry and I'm having trouble remembering when when Potassium manganate(VII) is used and when sodium dichromate is used in reactions.

I know acidified potassium manganate is an oxidising agent which is why it can be used to oxidise an alkene to a diol, but isn't sodium dichromate an oxidising agent too? Why can't that be used instead? And does anyone have a way to remember which of these chemicals you use in different reactions? I keep getting mixed up. (Sorry for the poor chemistry pun).

One other thing... Why do potassium manganate and sodium dichromate always seem to be mixed with sulphuric acid? Aren't they all just oxidising agents doing the same thing?

Help much appreciated.

Answer 5

1.acidified sodium dichromate is also an oxidising agent, as Cr2O7^(2-) is reduced to Cr^(3+)

2. As @ichigoflavour has mentioned, it can't be used in this case because dichromate ion is not strong enough to oxidise alkenes in this case (I think)

3. I use tables/diagrams to remember it, like the one in the attachment.

4. They are not doing the same thing.... For instance, MnO4- in acidic medium will be reduced to Mn2+, while in neutral / alkaline medium, it will be reduced to MnO2...

Answer 6

Thank you everyone! :)