[Bearhat54]

Hey guys, I need some help figuring out what happens in these questions:

Butan-1-ol reacts in the presence of concentrated sulfuric acid.

A 5-carbon alkene is formed when a secondary alcohol undergoes an elimination
reaction

In the presence of a strong base, 2-chlorobutane releases water and another
small entity as it is transformed to an unsaturated compound.

(I should also note that we are required to draw the structural diagrams for them)

I understand the process of these equations, I just need help with understanding how they happen and what the products are. For the first one I think I have Butene-1-ol and excess Hydrogen as the products, but the rest of them are extremely confusing.

[james_a]

OK, in the first reaction, you have an alcohol. What's the first thing that happens when you add acid?

[Arkcon]

You can also try to draw some of these out.  For example, the third one, what is the structure of 2-chlorobutane, and the product?  How can you reconcile the change with the loss of water and ... something small.

[Bearhat54]

OK, in the first reaction, you have an alcohol. What's the first thing that happens when you add acid?

I'm not sure... how would I go about figuring it out?

[discodermolide]

OK, in the first reaction, you have an alcohol. What's the first thing that happens when you add acid?

I'm not sure... how would I go about figuring it out?

As Arkcon said try drawing out the reactions so you can see what you are doing. For example

[Arkcon]

Bearhat54: have you yet heard the term "good leaving group"?  That's a common term in beginning organic chemistry.  Can you name one good leaving group ... maybe by reviewing the properties of sulfuric acid?

[camptzak]

if sulfuric acid and propanol are the ONLY things present.

oxygen is protonated.
propanol attacks by SN₂
you form an ether
elimination is also poosible, but i dont think it would be predominant... then again... what do i know

water is a byproduct. this is an equilibrum rxn so you may have to physically manipulate your vessel to remove product as its formed

[camptzak]

in the presence of a strong base elimination will predominate and you will form an alkene and  a salt

Na OH + C6H13Cl  NaCl C6H12 h20

[discodermolide]

if sulfuric acid and propanol are the ONLY things present.

oxygen is protonated.
propanol attacks by SN₂
you form an ether
elimination is also poosible, but i dont think it would be predominant... then again... what do i know

water is a byproduct. this is an equilibrum rxn so you may have to physically manipulate your vessel to remove product as its formed

Sorry butan-1-ol and sulphuric acid gives the terminal alkene by elimination of water, you do not form an ether.

[camptzak]

really? Im a bit of a novice but I thought that primary alcohol is easily attacked by Sn₂. And since butanol is not a strong nucleophile substitiution would predominate? where am I going awry?
like i said though.. what do iknow

http://pubs.acs.org/doi/abs/10.1021/ed009p1268

[discodermolide]

really? Im a bit of a novice but I thought that primary alcohol is easily attacked by Sn₂. And since butanol is not a strong nucleophile substitiution would predominate? where am I going awry?
like i said though.. what do iknow

I once did an esterification reaction of a benzoic acid dissolved in methanol and conc H₂SO₄ on a 250kg scale. We measured the formation of dimethyl ether over the time course. The maximum value was found to be 120ppm. So not much ether.
I know it's not butanol, but alcohols are not very nucleophillic under these conditions.
Something like butanol will eliminate to give the alkene.
Ethers are usually formed by the Williamson ether synthesis, see
http://en.wikipedia.org/wiki/Williamson_ether_synthesis

[fledarmus]

Alkoxides are much stronger nucleophiles than alcohols. Alkoxides are formed when alcohols are treated with strong bases.

Protonated alcohols have much better leaving groups (water) than non-protonated alcohols (hydroxide). Protonated alcohols are formed when alcohols are treated with strong acids.

So as a general first impression, if an alcohol is participated in a reaction involving a strong acid, the OH functionality is probably acting as a leaving group. Look either for a good nucleophile in the system and a substitution reaction, or an α-hydrogen and an elimination reaction. On the other hand, if the reaction involves a strong base, the OH functionality is probably being deprotonated and acting as a nucleophile - look for something with a good leaving group for it to attack.

[camptzak]

really? Im a bit of a novice but I thought that primary alcohol is easily attacked by Sn₂. And since butanol is not a strong nucleophile substitiution would predominate? where am I going awry?
like i said though.. what do iknow

I once did an esterification reaction of a benzoic acid dissolved in methanol and conc H₂SO₄ on a 250kg scale. We measured the formation of dimethyl ether over the time course. The maximum value was found to be 120ppm. So not much ether.
I know it's not butanol, but alcohols are not very nucleophillic under these conditions.
Something like butanol will eliminate to give the alkene.
Ethers are usually formed by the Williamson ether synthesis, see
http://en.wikipedia.org/wiki/Williamson_ether_synthesis

thankyou.

[orgopete]

if sulfuric acid and propanol are the ONLY things present.

oxygen is protonated.
propanol attacks by SN₂
you form an ether
elimination is also poosible, but i dont think it would be predominant... then again... what do i know

water is a byproduct. this is an equilibrum rxn so you may have to physically manipulate your vessel to remove product as its formed

Sorry butan-1-ol and sulphuric acid gives the terminal alkene by elimination of water, you do not form an ether.

Certainly and ether can form. This is how diethyl ether was discovered and produced, Wikipedia. However, that is probably not the product they are looking for. I wasn't in the class, but based upon the other questions, I presume the topic of discussion was alkenes, hence I am guessing they want the alkene products. In the case of 1-butanol and sulfuric acid, the major products are 1-butene and cis and trans 2-butene.