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Topic: How do you hydrolyse dicyanoethene?  (Read 5520 times)

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Offline joyb

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How do you hydrolyse dicyanoethene?
« on: February 19, 2013, 08:46:27 AM »
The question asks to identify the products and mechanism of the following reaction:
CH3CH=C(CN)2 + H2O → C2H4O + C3H2N2
The problem is on a sheet about addition to a C=C bond. I can't work out how you get two products with those molecular formulae. If anyone could help it would be much appreciated!
« Last Edit: February 19, 2013, 09:04:17 AM by amberbarton »

Offline sjb

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Re: How do you hydrolyse dicyanoethene?
« Reply #1 on: February 19, 2013, 08:54:23 AM »
The question asks to identify the products and mechanism of the following reaction:
CH₃CH=C(CN)₂ + H₂O → C₂H₄O + C₃H₂N₂
The problem is on a sheet about addition to a C=C bond. I can't work out how you get two products with those molecular formulae. If anyone could help it would be much appreciated!

Can you format the numbers using [sub][/sub] tags (they're barely readable)? In any event, where are your nucleophiles / electrophiles? Is the first compound CC=C(C#N)C#N?

Offline joyb

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Re: How do you hydrolyse dicyanoethene?
« Reply #2 on: February 19, 2013, 09:06:08 AM »
Yes, that is the reactant. I imagine that as the nitrile groups are electron withdrawing the dicyanoethene is the electrophile and water the nucleophile.

Offline orgopete

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Re: How do you hydrolyse dicyanoethene?
« Reply #3 on: February 19, 2013, 09:48:55 AM »
Hint, what structure is C3H2N2?
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Offline joyb

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Re: How do you hydrolyse dicyanoethene?
« Reply #4 on: February 19, 2013, 10:02:03 AM »
I would guess NCCH2CN but really I don't know.

Offline Dan

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Re: How do you hydrolyse dicyanoethene?
« Reply #5 on: February 19, 2013, 10:19:05 AM »
Good guess...

Have a look at your starting malononitrile. Is it a nucleophile/electrophile/acid/base?

What kind of reagent is water - nucleophile/electrophile/acid/base?
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Offline joyb

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Re: How do you hydrolyse dicyanoethene?
« Reply #6 on: February 19, 2013, 03:26:30 PM »
My original thought was that water would act as a nucleophile and that conjugate addition would occur due to the electron withdrawing nature of the CN groups. That doesn't give me the correct molecular formulae though, which is why I'm stuck.

Offline Dan

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Re: How do you hydrolyse dicyanoethene?
« Reply #7 on: February 19, 2013, 03:53:10 PM »
My original thought was that water would act as a nucleophile and that conjugate addition would occur due to the electron withdrawing nature of the CN groups.

Good. Half way there.

Hint: The pKa of H2(CN)2 is around 11
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Offline joyb

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Re: How do you hydrolyse dicyanoethene?
« Reply #8 on: February 19, 2013, 06:57:51 PM »
I don't really understand how you get from the reactants to the products.

Offline Dan

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Re: How do you hydrolyse dicyanoethene?
« Reply #9 on: February 20, 2013, 02:55:53 AM »
I don't really understand how you get from the reactants to the products.

I know that.

You are almost there, what you have suggested so far is correct, you just need to finish it.

You know you have this intermediate so far:
CC(O)C(C#N)(C#N)

You know CH2(CN)2 (malononitrile) is one of the final products. Draw a circle around the part of the intermediate that corresponds to malononitrile. Which bond needs to break to make malononitrile?
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Offline joyb

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Re: How do you hydrolyse dicyanoethene?
« Reply #10 on: February 20, 2013, 04:20:46 AM »
The C-C bond needs to break... I'm not sure how lysis could occur without another reactant though.
« Last Edit: February 20, 2013, 05:02:29 AM by amberbarton »

Offline Dan

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Re: How do you hydrolyse dicyanoethene?
« Reply #11 on: February 20, 2013, 05:50:13 AM »
Hint: Why is this compound unstable?

CC(O)(O)C
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Offline joyb

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Re: How do you hydrolyse dicyanoethene?
« Reply #12 on: February 20, 2013, 06:03:02 AM »
I honestly don't know. If anything I would guess repulsion between the areas of high electron density surrounding each of the oxygens.

Offline Dan

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Re: How do you hydrolyse dicyanoethene?
« Reply #13 on: February 20, 2013, 06:11:04 AM »
Ok, google carbonyl hydration, and/or think about the instability of this one:

CC(O)(Cl)C
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Offline joyb

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Re: How do you hydrolyse dicyanoethene?
« Reply #14 on: February 20, 2013, 07:06:00 AM »
I think I'm going to have to give up on this one...

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