Sciencemadness Discussion Board

Isopropyl Alcohol Boilingpoint

oneselections - 20-9-2022 at 03:35

Hi,

I'm new to chemistry and this forum, and wanted to start out with a question.

I am experimenting a little at home, and I want to do a distillation by evaporating IPA from my boiling flask to my receiver flask as a test.

My question is, I have read that you can lower boiling point by using vacuum.

Ay what temperature under vacuum does IPA start to evaporate without boiling?

I have read that under 67mBar around 30-35c should be sufficient.

Best Regards

B(a)P - 20-9-2022 at 03:48

https://en.m.wikipedia.org/wiki/Isopropyl_alcohol_(data_page)

The vapour pressure tab on this site should answer your question.

teodor - 20-9-2022 at 10:02

oneselections, I would put several questions that you can ask yourself before doing the experiment. Maybe they will allow you to understand the process better.

1. What is the purpose of the distillation?
2. Why do you need a vacuum?
3. How do you plan to cool the receiver to prevent product loss?
4. How do you plan to prevent possible peroxide concentration in the source flask?
5. Which portions of distillate do you plan to keep and which portions do you plan to discard?

DraconicAcid - 20-9-2022 at 11:10

IPA boils at such a low temperature, why do you want to muck around with vacuum distillation? That technique is far more applicable to things with very high boiling points.

Dr.Bob - 20-9-2022 at 11:25

"At what temperature under vacuum does IPA start to evaporate without boiling?"

Most solvents can evaporate well below their BP at atmospheric pressure, but slowly, look at water evaporate from a puddle, or acetone from a drip on a fume hood. The question might be at what temperature does it evaporate quickly enough to be useful for a distillation, and for IPA (and many organic solvents), that would be about 100- 200 mbar for a temperature that is fairly low. That is why aspirators used to be used for rotovaps for many years, as they can pull a vacuum at or below that range.

But vacuum distillations provide very little purification of the liquid, unless it is quite high boiling, as most solvents have a high vapor pressure at 100-200 mbar, so they all distill to some degree then, thus a mixture distills. For purification of the solvent, high BPs at sTP are better, for quick evaporation of solvent to get the solute back, a rotovap is great. Same for just removing mostly pure solvent to recover it.

Lionel Spanner - 21-9-2022 at 13:11

Quote: Originally posted by DraconicAcid  
IPA boils at such a low temperature, why do you want to muck around with vacuum distillation? That technique is far more applicable to things with very high boiling points.

Or things that decompose below their boiling points.

Rainwater - 21-9-2022 at 14:17

ipa can be used in a soxhlet extractor to collect anthocyanin from purple cabbage. Lowering the pressure allows the apparatus to run at very low temperatures, preserving the target compound, which is air sensitive.

The distillation took place at room temperature, but special measures were needed to cool the condencer(ice)

oneselections - 21-9-2022 at 20:47

Quote: Originally posted by B(a)P  
https://en.m.wikipedia.org/wiki/Isopropyl_alcohol_(data_page)

The vapour pressure tab on this site should answer your question.


Thank you,

oneselections - 21-9-2022 at 20:55

Quote: Originally posted by teodor  
oneselections, I would put several questions that you can ask yourself before doing the experiment. Maybe they will allow you to understand the process better.

1. What is the purpose of the distillation?
A: Just to test how it workspractically

2. Why do you need a vacuum?
A: To try out my vacuumpump and try something new

3. How do you plan to cool the receiver to prevent product loss?
With an ice bath

4. How do you plan to prevent possible peroxide concentration in the source flask?
Don't know what this is :(

5. Which portions of distillate do you plan to keep and which portions do you plan to discard?

Neither, this is just for fun.

teodor - 22-9-2022 at 03:51

oneselection,

Please read this thread: http://www.sciencemadness.org/talk/viewthread.php?tid=21495 .

The vacuum distillation is very useful but not easy technique which requires much patience before you will get satisfactory results. The good practical way to start is to distill liquids which otherwise require too high temperature. I mean that you can synthesise some interesting things and then purify them by vacuum distillation.

Another interesting experiment is to poor ethanol or acetone in a flask, put the thermometer and look how applying vacuum will decrease the temperature. With some liquids you can go well below 0C. With addition of some solids you probably can get very low temperatures and this could be a topic for investigation.

Another application of your vacuumpump could be drying different solids in a vacuum dessicator.

oneselections - 25-9-2022 at 21:15

Quote: Originally posted by teodor  
oneselection,

Please read this thread: http://www.sciencemadness.org/talk/viewthread.php?tid=21495 .

The vacuum distillation is very useful but not easy technique which requires much patience before you will get satisfactory results. The good practical way to start is to distill liquids which otherwise require too high temperature. I mean that you can synthesise some interesting things and then purify them by vacuum distillation.

Another interesting experiment is to poor ethanol or acetone in a flask, put the thermometer and look how applying vacuum will decrease the temperature. With some liquids you can go well below 0C. With addition of some solids you probably can get very low temperatures and this could be a topic for investigation.

Another application of your vacuumpump could be drying different solids in a vacuum dessicator.


Thank you for this reply and your input, I will look into this option

Texium - 26-9-2022 at 12:09

See my blog post about vacuum distillation: https://texiumchem.com/2020/06/03/vacuum-distillation-of-ani...

Look up the ∆Hvap (heat of vaporization) value for isopropanol, and you can calculate its boiling point at any pressure, or the pressure needed to reach a desired boiling point, using the Clausius-Clapeyron Equation. Make sure to put temperatures in Kelvin.