ozonolysis reaction

[Awuah29]

When alkene react with O3 you have either aldehyde or ketone forming. When do you determine which product will form? Or do both form at the same time?

---

Members don't see this ad.

 

[Lonely Sol]

When alkene react with O3 you have either aldehyde or ketone forming. When do you determine which product will form? Or do both form at the same time?

Well, Carboxylic acid can form too. Here is the difference:

For aldehyde to form: Must be a terminal alkene and must have Zn/cl as the reagent in order to stop the further oxidation to carboxylic acid.

For Keytone to form: Must be a secondary alkene.

For carboxylic acid to form: Must be a terminal alkene, that is missing the zn/cl reagant. Do the aldehyde formed gets further oxidized by air to carboxylic acid.

 

[poc91nc]

Actually...ozone/Zn/water reacted with an alkene will always give the product of the form HCOH, RCOH, RCOR'...no carboxy acid with ozone

However, ozone/hydrogen peroxide will give carboxy acid if a hydrogen is present on the carbon. ethylene gives 2 HCOOH...RC=CH2 gives RCOOH and HCOOH...see the pattern?

Then comes Alkene reacted hot potassium permanganate. If two H's are present on the carbon we get full blown oxidation
Ethylene reacted with hot KMnO4 gives two Carbon dioxide

If R-CH=CH-R then we just get two R-COOH

Most of the practice questions I've seen (and I have seen A LOT of Ochem practice questions) don't really expose understanding of the last two reactions.....but ozone/Zn/water is a must

 

[Lonely Sol]

Actually...ozone/Zn/water reacted with an alkene will always give the product of the form HCOH, RCOH, RCOR'...no carboxy acid with ozone

However, ozone/hydrogen peroxide will give carboxy acid if a hydrogen is present on the carbon. ethylene gives 2 HCOOH...RC=CH2 gives RCOOH and HCOOH...see the pattern?


Most of the practice questions I've seen (and I have seen A LOT of Ochem practice questions) don't really expose understanding of the last two reactions.....but ozone/Zn/water is a must

Yea, but since our atmosphere is the best oxidizing agent, would it just oxid the RCHO to RCOOH, if not Zn/H30 present?! (I always thought it would, but i might be wrong)

 

[poc91nc]

True...BUT for DAT purposes go with the immediate product...check any practice question...destroyer achiever etc

Yes...aldehydes oxidize very easily in the presence of oxygen...the same goes for ethanol...wine + air = acetic acid

 

[poc91nc]

Immediate....further oxidations take time to develop....but a lot of the choices will have a carboxy acid...stay away

 

[Lonely Sol]

Immediate....further oxidations take time to develop....but a lot of the choices will have a carboxy acid...stay away

Thanks, I guess thats what happens when you get too technical! Would they have ambigous ques. like that on real DAT?!

 

[Greensalad]

However, ozone/hydrogen peroxide will give carboxy acid if a hydrogen is present on the carbon. ethylene gives 2 HCOOH...RC=CH2 gives RCOOH and HCOOH...see the pattern?

Where did you find this? I can't find it anywhere.

 

[poc91nc]

Did you try looking in your ochem textbook? If I recall correctly...I think the McMurry book has that reaction....most textbooks should have that reaction.

Here is an immediate source I was able to find online

http://www.cem.msu.edu/~reusch/VirtualText/addene2.htm

Keep scrolling and you'll find it

 

[skyisblue]

For ozonolysis of an alkene, it depends on how many substituents there are on the double bond.

We know that ozonolysis/reduction cleaves the double bond and carbonyl functional group forms...

If it's tetra substituted, then you get 2 ketones when the molecule splits.

If it's tri substituted, then you get a ketone and an aldehyde.

If it's di substituted, then you get 2 aldehydes.....etc. etc....

Draw it out, then everything will make sense to you.

 

[poc91nc]

The variations with hot KMnO4 and hydrogen peroxide are worth noting....just to have something up your sleave with respect to the DAT's bag of tricks

 

[skyisblue]

The variations with hot KMnO4 and hydrogen peroxide are worth noting....just to have something up your sleave with respect to the DAT's bag of tricks

That would be so tricky if the DAT had something like that.

 

[Awuah29]

For ozonolysis of an alkene, it depends on how many substituents there are on the double bond.

We know that ozonolysis/reduction cleaves the double bond and carbonyl functional group forms...

If it's tetra substituted, then you get 2 ketones when the molecule splits.

If it's tri substituted, then you get a ketone and an aldehyde.

If it's di substituted, then you get 2 aldehydes.....etc. etc....

Draw it out, then everything will make sense to you.

do you have a links that I can visualize it
thanks

 

[skyisblue]

do you have a links that I can visualize it
thanks

I don't have links to this, but just draw it out. You'll see a pattern, and this will no longer be a mystery for you.

 

[Greensalad]

The variations with hot KMnO4 and hydrogen peroxide are worth noting....just to have something up your sleave with respect to the DAT's bag of tricks

I can't find that in my book. Mind explaining it please?

 

[Greensalad]

Did you try looking in your ochem textbook? If I recall correctly...I think the McMurry book has that reaction....most textbooks should have that reaction.

Here is an immediate source I was able to find online

http://www.cem.msu.edu/~reusch/VirtualText/addene2.htm

Keep scrolling and you'll find it

I have that book, but I can't find the hydrogen peroxide reaction under ozone.

 

[poc91nc]

You're right...I just checked the book...instead they have a variation with KMnO4 w/ H+ (not acetic acid)....

I would just take the time to memorize hot KMnO4....usually when you see an oxidizing agent in harsh conditions...it should send a red flag for full blown oxidation...thus if alkene is terminal think +4 oxidation = carbon dioxide

But....don't confuse hot KMnO4 w/ cold KMnO4

Check out that link....all variations are there!!!

This link is good too, if you need to put yourself through an ochem boot camp!!!

http://www.chemistry.ohio-state.edu/organic/flashcards/

 

[poc91nc]

Whoops...I originally posted that link for the variation w/ ozone and hydrogen peroxide. Sorry!!!

I remember now...I saw that variation of hot KMnO4 in a book called How to Succeed in Organic Chemistry. All alkene oxidations were layed out very nicely in that book. Unfortunately that book is out of print.

If you're are that bent on finding an explanation for that reaction...go to your undergraduate library...I am sure you can find a textbook with that reaction