Hey visitors......!!!
The most basic thing that many engineers were aware of that is Boiling point varies with Vapour pressure, and i'll bet you that many of those Engineers donno the exact reason for this, and today i'll reveal that under hidden reason for that behavior of solvents.
For that you should be aware of some damn basic things like what does exactly Vapour pressure, Boiling point means.
What is Vapour Pressure ?
Vapour Pressure means the pressure exerted by the vapour on the surface of liquid at equilibrium, Usually vapour wont have any Vapour pressures, the vapour pressure is the property of solvents, every solvent will have their respective vapour pressures.
What is Boiling Point ?
Boiling point is nothing but a point of saturation where the vapour pressure of a solvent equals the atmospheric pressure, simply toluene is a solvent, whose boiling point is 110.6°C, and at that boiling point the vapour pressure of toluene will be 760 torr, [Dont get confused Torr means mmHg only]. And same is the case with every solvents boiling point.
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Right now, you got a clear idea of the Vapour Pressure & Boiling point, So now i'll start my show about describing the relation ship between Vapour Pressure and Boiling point, the only relation that describes the relation between these two parameters is Antonie Equation.
By using Antonie equation we can calculate the boiling point of solvent at different pressures, it also means that the boiling point of solvents will decrease with Vacuum, and we can calculate it theoretically. In fact, this is the first calculation that i've learned after joining the Pharma Industry.
The basic Antonie Equation is,
Log P = A - B / ( T + C ),
A, B, C are Antonie Constants,
P is Vapour Pressure, T is Boiling point.
Just remember one thing, while selecting the Antonie constants, there are many set of constants available, and they will vary with the units of Pressure that you choose.
So, by now, if you are new to this calculation, this known equation will look something special to you,
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Many of the Pharma Operations will include "Distill off solvent under vacuum below temperature X°C" , here while they include word vacuum just because we can distill off the solvent below its regular boiling point.
I'll show you a small demo and Anyway i'll tell you how to use this practically,
"Distill off toluene under vacuum below 60°C with vacuum NLT 650 mmHg at the end of distillation",
This means the product that is present in our reaction mass is stable upto 60°C, and after that the product may degrade,
And here vacuum should be NLT 650 mmHg at the end of distillation, so now just try to calculate the boiling point at 650 mmHg,
For that you need to know the Antonie constants of Toluene,
Antonie constants data here
A = 6.95, B = 1344.8, C = 219.482,
the Vacuum should be NLT 650 mmHg, so the pressure should be P = 760 - 650 = 110 mmHg.
Log (110 ) = 6.95 - 1344.8 / ( T + 219.482 )
Solving for T, T = 54.4°C.
So, this means at 650 mmHg the boiling point of Toluene will be 54.4°C, which means it came down from 110.6°C to 54.4°C.
So, if you understand what i delivered above, just say cheers,
Still any doubts feel free to contact me,
Comments were most appreciated...............!!!
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About The Author
Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.
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