[Messi]

So you added the salt to the thioketene.

I made a mistake earlier when I said what I did. I did indeed add my thioketene to the salt

By the way, random question: I made a an amine that was on my triple bond (heptyne), and I did the reaction to trap the thioketene with my amine to create the thioamide but it didn't work. Usually these cyclization reactions with a ketene (C=C=O) are done at temperatures of ~60°C, however to create a thioketene and to react it with an amine it must be done at -78°C. Could this be a reason why when I try to cyclize and create a thioamide it isn't working?

[discodermolide]

It could be.
Question, why does the thioketene generation have to be done at -78°C, do you know this for fact? Have you tried it at a higher temperature? I would find out exactly what temperature you can use for this thioketene generation and trapping with an amine.

[Messi]

It could be.
Question, why does the thioketene generation have to be done at -78°C, do you know this for fact? Have you tried it at a higher temperature? I would find out exactly what temperature you can use for this thioketene generation and trapping with an amine.

I have tried it at -78°C and have had best results with it (better yield, less side reactions, cleaner). I also tried it at 0°C and the reaction did work, but with a much lower yield. A paper I found, said to do the reaction at -78°C. I guess I should try the reaction tomorrow at 50°C with the hope that it doesn't work so my "hypothesis" is correct? 

I believe ΔG=ΔH-TΔS has something to do it, no?

[discodermolide]

I hope you mean -50°C. Also try at -25°C, -10°C.
You need to find the highest temperature that gives you the best yield and cleanest product.

[Messi]

I hope you mean -50°C. Also try at -25°C, -10°C.
You need to find the highest temperature that gives you the best yield and cleanest product.

Agreed of course!

Well, do you think my rationale of using ΔG=ΔH-TΔS as an argument is valid as to why I am not seeing a reaction? Come to think about it... I'm not sure if it is a valid argument or not.

When we do cyclization reactions, how come we always see heat (Δ) as one of the necessities, and we rarely see cyclization reactions under cold temperatures?

[discodermolide]

Usually you need to heat it to overcome any ring strain energy that may be a barrier to cyclisation.
There are plenty of cyclisations that go at lower temperatures.
Have a look here for some guidelines.
http://en.wikipedia.org/wiki/Baldwin's_rules

[Messi]

Have a look here for some guidelines.
http://en.wikipedia.org/wiki/Baldwin's_rules

Thanks! I just had a read, interesting.

Usually you need to heat it to overcome any ring strain energy that may be a barrier to cyclisation.

Hopefully in my case, the reason my reaction is not working because temperature isn't high enough What do you think, am I right? Is it logical? I am going to bring it up to my supervisor tomorrow and see what he says...

[discodermolide]

Sure ask him his opinion.

[Messi]

Sure ask him his opinion.

For the reaction below to take place, would heat be a necessity?

[discodermolide]

Probably not. Heat it and you will end up with a series of many polymeric amines. It may not even give much cyclic product.

[Messi]

Probably not. Heat it and you will end up with a series of many polymeric amines. It may not even give much cyclic product.

So my earlier rationale regarding cyclization of the thiolactam shown below is false? I don't need heat to induce cyclization?

[discodermolide]

You cannot compare an alkyl halide and a thioketene in reactivity. The thioketene should be more reactive towards nucleophiles.

[Messi]

You cannot compare an alkyl halide and a thioketene in reactivity. The thioketene should be more reactive towards nucleophiles.

So you are saying it most likely does not need heat to cyclize? Heat was my basis of argument at to why cyclization was not occurring. Am I wrong!?

[discodermolide]

You are doing the reaction at -75°C, if I remember correctly. Let it warm to 0°C and see what happens, that's heating the reaction!

[Messi]

You are doing the reaction at -75°C, if I remember correctly. Let it warm to 0°C and see what happens, that's heating the reaction!

I did do this, and the reaction didn't work! No cyclization.

Does it make sense that it isn't working though? My whole paper is based on the argument that heat is needed for the reaction to take place. Am I actually wrong? Is my argument weak? I want an honest answer