[JimmyV]

Why is it necessary to have such cold temperatures (-78 degrees C) for ozonolysis?

Especially as a reductive workup using Zn/AcOH would have to be done at room temperature. In essence, O3 happily oxidises double bonds in natural rubber at room temp. So my best guess is to speed up the process by keeping O3 in solution for longer than it would at room temperature? Am I correct???

I would love to hear your thought on this.

Thanks,
Jimmy

[discodermolide]

Why is it necessary to have such cold temperatures (-78 degrees C) for ozonolysis?

Especially as a reductive workup using Zn/AcOH would have to be done at room temperature. In essence, O3 happily oxidises double bonds in natural rubber at room temp. So my best guess is to speed up the process by keeping O3 in solution for longer than it would at room temperature? Am I correct???

I would love to hear your thought on this.

Thanks,
Jimmy

Ozone is not very stable at ambient temperatures.
It is a gas, not sure of BPt. You can look it up.
The reaction with double bonds is very rapid even at -78°C
The intermediate ozonides are not stable at higher temperatures.
Zn/HOAc may not be the best work-up!
Look for other reductive work-ups

[OC pro]

Usually Me2S is the best for reductive work-up.

[Honclbrif]

Never done an ozonolysis myself, but looks like you have a range of options for your workup to get different products.

http://www.organic-chemistry.org/namedreactions/ozonolysis-criegee-mechanism.shtm

I'm assuming the cold is to control the reaction rate so you don't set things on fire or blow them up.

[orgopete]

Hey, I did some. I really liked the -78°C method. This is what happens. Ozone until it turns blue. Then work it up. If you are trying to get an aldehyde or ketone, avoid the decomposition of the ozonide during ozonization or you can get peroxides. The peroxides can oxidize the aldehyde to acid or ketone to ester. Low temp and no excess of ozone helps.

[g-bones]

The secondary ozonide is typically not stable and can be explosive (Although I think mostly shock sensitive). Best to keep it at low temp to keep it from ripping you and your molecule a new one.