8 replies to this topic

[PYRODUDE!!!]

Hey guys, I'm trying to work out the equation and mechanism equations for synthesis of 1-Bromobutane. (From butan-1-ol, hydrobromich acid and sulphuric acid)

I think the general equation is something like:

R-CH2-OH + H+ <--> R-CH2-+OH2 <--> (Br-) R-CH2-Br + H2O

No idea about the mechanisms though.

Regards

PYRODUDE!!!

[Steve]

Crap, I've been out of Uni for a year with RSI, let's see if I can remember this...

Basic SN2 reaction

A lone pair from the oxygen in the alcohol group donates an electron to an H+ ion (acid solution) (Technically it'll be a H30+ ion that decomposes to give a water molecule as well) to form a dative bond and results in the -OH2+ group, which is a good leaving group.

Next the Bromine ion (Br-) donates an electron into the carbon atom which is joined to the -OH2+ group to form the SN2 intermediate. (The Br ion will have to go in via a Lewis acid like Aluminium tribromide for example.)

Next / simultaneously, an electron from the carbon - Oxygen bond jumps over onto the carbon to release a neutral H20 Molecule and the bromobutane.

I think both the butane chemicals will be liquid at room temp & pressure, so no problems there.
And you'll need the Lewis acid catalyst or you'll be going nowhere fast.

I think that sums it all up, but feel free to ask if some parts don't make sense.

What do you want bromobutane for anyway? Other than a precursor for that whatnot-something addition reaction.

[lord_dranack]

Next the Bromine ion (Br-) donates an electron into the carbon atom which is joined to the -OH2+ group to form the SN2 intermediate. (The Br ion will have to go in via a Lewis acid like Aluminium tribromide for example.)

Just one thing, in Sn2 there is no intermediate formed- it uses a transition state - a minor point, but just the sort of thing that loses a mark in an exam!

[PYRODUDE!!!]

Crap, I've been out of Uni for a year with RSI, let's see if I can remember this...

Basic SN2 reaction

A lone pair from the oxygen in the alcohol group donates an electron to an H+ ion (acid solution) (Technically it'll be a H30+ ion that decomposes to give a water molecule as well) to form a dative bond and results in the -OH2+ group, which is a good leaving group.

Next the Bromine ion (Br-) donates an electron into the carbon atom which is joined to the -OH2+ group to form the SN2 intermediate. (The Br ion will have to go in via a Lewis acid like Aluminium tribromide for example.)

Next / simultaneously, an electron from the carbon - Oxygen bond jumps over onto the carbon to release a neutral H20 Molecule and the bromobutane.

I think both the butane chemicals will be liquid at room temp & pressure, so no problems there.
And you'll need the Lewis acid catalyst or you'll be going nowhere fast.

I think that sums it all up, but feel free to ask if some parts don't make sense.

What do you want bromobutane for anyway? Other than a precursor for that whatnot-something addition reaction.

Thanks, my uncle explained most of it to me. Cheers, I just wanted to know.

[PYRODUDE!!!]

Ok I lied, I do need it for something and have another question:

Ok, synthesis of 1-Ethoxybutane with sodium metal, ethanol and 1-Bromobutane (this is what I needed it for from the first reaction).

Its Sn2 again isn't it.


Synthesis of Dibenzalacetone via aldol reaction with ethanol, benzaldehyde, acetone, water and sodium hydroxide. I have the overall equation for this, but it has phenol rings and stuff so its a bit hard to write in a post.. Need the mechanism again, which I think is pretty long..

Help would be very much appreciated.

Regards

[adamw]

With all these people helping you, are you going to explain what you need the info for? It would be nice...

[Richard H]

Sounds like A-level Chemistry to me...

[PYRODUDE!!!]

Yea, if we could get back to the question that would be great!

[damocov]

Erm long time ago and Organic wasn't my forte but I think on the second one, you use the base to promote production of a Carbanion as a starting point.

But it has been *cough* years since I saw an organic lab.