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All 24 posts Subject: Simplification of Bariums SnCl2 ketone procedure Please login to post Down

Bandil
(The Archetypical "Good Guy")
04-26-04 16:26
No 503137
 Simplification of Bariums SnCl2 ketone procedure

Hi!

After some work with bariums methods on the SnCl₂ reduction of nitropropenes to the corresponding ketone, I have arrived at a method, which I find extremely easy and high yielding. It was actually an accident with a really ugly emulsion that led to this method. It has only been tested on 4-fluoro-P2NP, but here goes:

220 mmole (50 g) SnCl₂ was added to 200 mL water.
50 mL's of 30% HCl was added to this in one portion, and heavy stirring was commensed.

100 mmole (18.1 g) of (4-fluro-phenyl)-2-nitropropene was dissolved in 50 mL's toluene. This was added to the aqueous solution in one portion and stirred violently. A reflux condensor was attached and the whole mess heated to reflux for 2½ hour. At this point the colour was strangely pink, but i decided to proceed anyway.

400 mL's of water was added and internal steam distillation was commenced. Once the receiving flask had more than 200 mL's of distillate in it, 200 mL's was charged in the reaction vessel. This was continued untill 1 L distillate was collected and no more oily droplets came over. At this point the reaction flask had a nice colourless appearance. The distillate was composed of an upper toluene phase with the ketone in it, and a lower water phase.

The toluene phase was collected, and the water phase extracted with 2*150 mL toluene. The toluene was dried over a little MgSO₄ and then distilled off at aspirator vacuum.

14.4 mL's yellow oil remained, which reminded an awfull lot of every ketone i've come across wink . This corresponds to a 94% yield with a very minimum effort. It will be subjected to GC-MS tomorrow.

The shortcut taken here is the intermediate separation as performed in barium procedure. Theres really no reason to waste the toluene present in the reaction. React - steam distill - get your goodies wink

Regards
Bandil

Nuke the whales!

armageddon
(Hive Bee)
05-06-04 10:43
No 505264
 simpler?

Hi!
Nice writeup,Bandil - but what's new, simplified? I read that you toss in water, SnCl₂, HCl, nitrostyrene and toluene, reflux for 2,5 hours and then steam distill - which is exactly what Barium already did, just read his SnCl₂-thread (the first xperiments are using EtoAc, but later Ba successfully uses toluene as solvent, he too skips the separation step and steam distills the rxn mixture directly)..

Post 322410 (Barium: "Now it´s even easier", Novel Discourse)

Post 323065 (Barium: "Update", Novel Discourse)

So I wonder what your simplification might bee?

If you want to save time (and/or have not enough SnCl₂) you can put in some tin(2)chloride, together with a correct amount of elemental Sn and HCl (let's say, ~25g SnCl₂, ~13.2 grams tin and additional ~30 ml HCl 31% - instead of 50g tinchloride). The tin will form SnCl₂ WAY faster than if you just reflux it in dil. HCl, you can save a lot of time this way - if you normally prepare your tin(2)chloride by yourself (it can be very annoying to watch a metal not fully dissolve in acid for hours..).

I think the two posssible explanations for this fast dissolution are:

1. the equation is shifted to the right as SnCl₂ gets oxidized - SnCl₄ is soluble in both polar and nonpolar solvents, so it is being removed from the water phase (maybe not)

2. (my favourite exp.) the elemental tin reduces the tin(4) to tin(2) - et voilà, two Sn(2+) ions - which reduce something, get oxidized to Sn(4), react with Sn(0) each, et voilà: four tin(2) ions...

I don't know if these are correct explanations - but I know for sure that 8 grams of tin in a SnCl₂ reduction dissolved in a matter of minutes (half an hour maybe), and it saves a lot of time/effort/SnCl₂!

This reminds me of iron/HCl reductions - just a little bit of the appropriate chloride salt to start the rxn..

(BTW I got the same good yields with SnCl₂ without reading your writeup, but with using some elemental tin/tin(2)chloride together wink )

Greetz A

"..ein Trank von unterschiedlicher Farbe, in ihm ist Heilung für die Menschen."

Bandil
(The Archetypical "Good Guy")
05-06-04 13:28
No 505293
 Correction to myself

Sorry I didn't post this earlier - dumb of me!

Some kind soul analyzed the ketone. It was only 60% pure!! The remaining 40% was the benzaldehyde. It seems that the nitropropene was only partially reduced to the oxime. The remains where cracked up into nitroethane and benzaldehyde because of the acidic environment.

The benzaldehyde was simply distilled of fractinally at reduced pressure to give the pure ketone...

But the method needs some work before it can be labeled "handy-dandy"... I'll try some more tweaks!

Regards
Bandil

Nuke the whales!

armageddon
(Hive Bee)
05-06-04 14:42
No 505306
 interesting

Hm, that would explain the faint almond smell of p2ps made via SnCl₂ reduction... perhaps if an appropriate buffer is found the aldehyde/nitroalkane backformation can be minimized?

But I wonder how GC_MS was able to detect benzylalcohol in traces, along with some 5% benzaldehyde impurities?

here's the post...

Post 493114 (GC_MS: "1-phenyl-2-propanone", Novel Discourse)

Greetz A

"..ein Trank von unterschiedlicher Farbe, in ihm ist Heilung für die Menschen."

Barium
(Heavyweight Chempion(eer))
05-06-04 14:47
No 505308
 I have also got the ketone/aldehyde mix but...

I have also got the ketone/aldehyde mix but also got very pure ketone. The trick lies in when acidification is done. Form the oxime then acidify. The ketoxime can't be hydrolysed back to the benzaldehyde since the C=C bond is gone. Acetone is a useful solvent to make oximes in using this reduction system. *hint hint*

Severe Aztecoholic and President of Sooty's fanclub - Sooty for President!!

armageddon
(Hive Bee)
05-06-04 16:30
No 505327
 acetone

Hi!

Barium, do you mean "catalytic" amounts of acetone as kind of PTC or acetone as a replacement for EtOAc/toluene?

And is the tinchloride oxidized during hydrolysis of the ketoxime or before (while it is formed)?

THX A

"..ein Trank von unterschiedlicher Farbe, in ihm ist Heilung für die Menschen."

Barium
(Heavyweight Chempion(eer))
05-06-04 18:06
No 505349
 Acetone

Dissolve the nitroalkene in acetone then add 2,2-2,5 eq SnCl₂ dihydrate. When the reduction is over (when the temp has returned to ambient) add 5 eq HCl and water. Strip off the acetone (save and reuse), boil the oxime and aqueous HCl for a while and then steam distill.

Severe Aztecoholic and President of Sooty's fanclub - Sooty for President!!

imp
(Hive Bee)
05-06-04 18:25
No 505352
 Acetone - did you try it?

Did you try this Barium? Varma and Karbalka reported using acetone as the solvent in Chem. Ind., pp. 735 (1985). SWIM has the paper, the highest yield of oxime they got was 75%, but typically 65%. Plus the solvent was unsuitable for nitroethenes.

Also, could you please clarify one of your procedures a couple of years ago in Post 321226 (Barium: "This nitroalkene --> ketoxime --> ketone ...", Novel Discourse)... when you used EtOAc/SnCl2 to reduce 3,4-MDPNP to the ketone with the 94% yield, how did you isolate the MDP2P? A very lengthy steam distillation?? Or did you just extract with DCM? SWIM is aware steam distillation is used to shift the equilibrium rxn to the right, but with MDP2P this is a difficult task. Thanks.

Barium
(Heavyweight Chempion(eer))
05-06-04 18:36
No 505356
 The reason for the shitty yields Varma and...

The reason for the shitty yields Varma and Kabalka got was the horrendous workup they used. Their actual yield was higher.
Sorry, I can't clairify anything about those two since I wasn't the one doing those synths. I have never made MDP2P or P2P.

Severe Aztecoholic and President of Sooty's fanclub - Sooty for President!!

armageddon
(Hive Bee)
05-12-04 15:38
No 506667
 acetone as solvent?

Hi Bees!

A friend of mine (we'll call him SWIA for simplicity) recently tried to reduce p2np to its ketone with SnCl₂. He used acetone as solvent, and got not very good yields (74% of theory). Although he told me the rxn boiled over a bit when adding additional water during hydrolysis (releasing some water/HCl/oxime/ketone mix into his oil bath, stinky thing shocked laugh ), he also noted that when starting to steam distill, there was kind of a "forerun" containing mainly acetone, although he used vacuum and ~60°C to remove it prior to starting w/hydrolysis. He also mentioned that temperature slowly, but constantly climbed up to over 60°C when he tried to remove the acetone (using vacuum of course) - at this temperature he thought "well, there shoudn't be any acetone left anymore, 60 torr and 60 degrees should be enough for removal".

Well, obviously 60°C with 60torr pressure were NOT enough, and this could be the reason for the strange behaviour/bad yield of SWIAs reduction. Perhaps the acetone distills azeotropically together with dil.HCl? That could be an explanation for the constant temperature rise to 70° when trying to remove the acetone (before starting to reflux).

Oh, and hydrolysis time was 2 hours, steam distillation was complete after another 4 hours, and he xtracted the ketone 4x with DCM, which was dried over Na₂SO₄ and stripped of solvent using high vac - I doubt he lost much product during this workup...

Perhaps the problem could be overcome by first adding the acetone/tinchloride/oxime mix to water, then removing the acetone and finally adding HCl and starting to reflux..
But looks like more work/time would be needed that way.
My opinion: use ethyl acetate, it seems to work better!

Greetz A

"..ein Trank von unterschiedlicher Farbe, in ihm ist Heilung für die Menschen."

armageddon
(Hive Bee)
05-14-04 05:06
No 507057
 avoiding benzaldehyde impurities

Bandil: I think if you use ethyl acetate as solvent, add the nitrostyrene carefully to avoid temperature climbing to over 40°, and wait a few minutes before adding water/HCl, you're on the better side.
The ketone will be very pure that way, so distillation/purification won't be necessary - contrary to the "toluene,tinchloride,nitrosytrene and HCl AT ONCE" - variation...

(ok perhaps you could do an additional aequ.NaOH wash after xtracting your ketone from the distillate, to remove traces of benzyl alcohol)

But as you can see, the time you save when skipping the removal of solvent (45 minutes?) is spent afterwards having to clean your impure ketone (bisulfite/distillation need at least same time..), so the hoped simplification is gone... frown

In your first post you mentioned a pink color. I also have experienced this - and read somewhere (I think "Vogel's", the chapter about ketones?) that phenylmethylketones give a pink coloration when being hit with NaOH...
(my experience is too that ketones reacting with strong base give pink color, sometimes with sulfuric acid, too - but not with HCl!)

Maybe this could work out to a procedure similar to Fe/HCl - but using nonferromagnetic metal? I know that the reaction as described by you also works good with only a part of the needed SnCl₂ and with addtional tin and HCl, which dissolve within 1-2 hours, forming the needed SnCl₂ in situ. I think the reason for the quick dissolution of the metal is that SnCl₄ is soluble in toluene, too - tin(2)chloride is not. So the water phase is continually freed from its Sn(2+) ions, making room for new sn(2+). Anyway, perhaps this could be tweaked a bit to become a reaction similar to Fe/HCl, where the metal is used directly - in connection with a small amnt. of its (less oxidated) chloride (to get things running) and HCl/water...
But for purer ketone, one should use Ba's original procedure.

Greetz A

"..ein Trank von unterschiedlicher Farbe, in ihm ist Heilung für die Menschen."

Rhodium
(Chief Bee)
05-18-04 00:51
No 507809
User Picture Varma & Kabalka: SnCl2 Nitroalkene -> Oxime
(Rated as: good read)

^{Article referenced in Post 505352 (imp: "Acetone - did you try it?", Methods Discourse)}

Stannous Chloride Reduction of Nitroalkenes to Oximes in Acetone
R. S. Varma, M. Varma & G. W. Kabalka
Chem. Ind. 735-736 (1985) (https://www.rhodium.ws/pdf/varma-kabalka.sncl2-oxime.pdf)

^{The Hive - Clandestine Chemists Without Borders}

armageddon
(Hive Bee)
05-18-04 03:26
No 507842
 acetone vs. EtOAc

Hi!

First: cool thing, that new V&K article!!

But still I think that (although it requires almost 10x the time needed for oxime formation in acetone) EtOAc is the solvent of choice here: the yields when forming the oxime in EtOAc (followed by hydrolysis/steam distillation) are a striking >90% - compared to max. 70% when using acetone.

And I don't like the thought of having to extract a mixture of acetone/ice/water/tin(4)chloride/carbonate/oxime crazy 6x with ether - not when I also can do same thing in a very smooth, clean way (then only extraction here is pulling the ketone from the steam distillate, e.g. only water/ketone)
(Barium all the way!!)

But nice to know about it anyway! Maybe useful if the oxime is the preferred product..

Greetz A

"..ein Trank von unterschiedlicher Farbe, in ihm ist Heilung für die Menschen."

armageddon
(Hive Bee)
05-29-04 14:21
No 510173
 easier steam distillation

Hi!

I'm not sure if it doesn't perhaps decrease the amount of ketone coming over (seen relative to amount of water) - but steam distillation UNDER VACUUM appears to be a lot quicker, and you can use a simple steam bath for heating (easy)...

The question is: although distillation itself proceeds a lot quicker, maybe the distillate has a lower ketone content if concentration is made under vacuum? Or does the distillate contain the same percentage of ketone? In the latter case, steam distilling under vacuum would be a big improvement.

I don't know if this is old news to the hive, but I didn't know steam distillation was even POSSIBLE using low pressure...

...nor that it works so well..

Anybee familiar with this?

Greetz A

"..ein Trank von unterschiedlicher Farbe, in ihm ist Heilung für die Menschen."

Barium
(Heavyweight Chempion(eer))
05-29-04 16:43
No 510176
 Old news

*ahem* UTFSE!

Severe Aztecoholic and President of Sooty's fanclub - Sooty for President!!

armageddon
(Hive Bee)
05-30-04 09:03
No 510278
 UTFSE - sure

Well, I don't see why I should UTFSE (and browse through hundreds of useless posts with "steam distillation" and "vacuum" laugh ) when I have just realized steam dist. under vac. is possible and want to share my knowledge, thinking that other bees are maybe as stupid as I am sometimes and could benefit from this info?

(I performed EVERY FUCKING steam distillation at ambient pressure until now frown )

I would guess that the vapor pressure of both liquids equals the remaining atmosphere pressure (or strength of vacuum) - but the ratio of the partial vapor pressures stays the same if vacuum is applied, therefore reducing pressure only increases speed of evaporation in general and doesn't change the vapor composition. Right?

"..ein Trank von unterschiedlicher Farbe, in ihm ist Heilung für die Menschen."

starlight
(Hive Bee)
05-30-04 09:49
No 510284
 More info

There is a little more info on steam distillation under vacuum in this thread: Post 500295 (homeslice: "future of safrole", Methods Discourse).

Info on this board with regard to steam distillation at reduced pressure is somewhat contradictory. For example: Post 294100 (chem_123: "steam distillation!?", Newbee Forum), Post 294104 (terbium: "Solvent extraction is good here.", Newbee Forum), Post 501475 (Barium: "Well you can steam distill under reduced ...", Methods Discourse).

I couldn't find an answer to the issue of whether a reduced pressure changes the ratio of water to product in the distillate, but I believe it should as a reduced pressure will affect the vapor pressure of a higher boiling compound more than it affects the vapor pressure of water (lower boiling).

It is vapor pressures, not partial vapor pressures that are important here I believe.

Nicodem
(Hive Bee)
05-30-04 10:08
No 510288
User Picture It new to me too

It was only recently that I heard that edible oil “refination” is done by steam distilling oil under vacuum. I always wandered what “refined oil” meant. I could not believe oil could bee distilled but seems like it can bee done under such conditions.

I couldn't find an answer to the issue of whether a reduced pressure changes the ratio of water to product in the distillate, but I believe it should as a reduced pressure will affect the vapor pressure of a higher boiling compound more than it affects the vapor pressure of water (lower boiling).

The inclination of the vapor pressure curve depends on the evaporation entalpy (delta-H) of the liquid and not on the boiling point. It should bee possible too predict the composition of the disstilate by comparring the proportions of the two vapor pressures from these curves at the given reduced pressure (but who knows the evaporation delta-H of P2P anyway, though it should bee lower than for H2O).

“The real drug-problem is that we need more and better drugs.” – J. Ott

lugh
(Moderator)
05-30-04 12:16
No 510292
 Industrial v Laboratory Scale

As mentioned in Post 447871 (lugh: "Steaming", Stimulants), an aspirator/station is best for laboratory scale vacuum steam distillation; in industry, a steam jet ejector tower is used wink

Chemistry is our Covalent Bond

armageddon
(Hive Bee)
05-30-04 18:01
No 510335
 reduced pressure steam distillation

Starlight: THX, that's just the support I needed! *lol*

Barium: well this Post 501475 (Barium: "Well you can steam distill under reduced ...", Methods Discourse) is a quite unsatisfying answer, dare I say! Especially when seen in conjunction with Post 294102 (Rhodium: "Steam distillation", Newbee Forum) laugh (just jokin)

I know I can perform it - but am unsure if reducing pressure results in less goodies per liter H2O...

When taking a look at a nomograph, I realize that with 60 torr vacuum, water boils at ~30°C whereas P2P (just an example wink ) will boil at ~120°C. The boiling point difference is ~90°C. At normal pressure, this difference would be ~115°C if I remember the bp of P2P correctly...

And (without thinking of the difference between bp and vapor pressure) I would guess that the closer together the boiling points are, the more high boiling liquid comes over with the steam (benzaldehyde volatilizes more easily than MDP2P, its bp is closer to water - and it's alot easier to steam distill)...

(BTW nicodem yes, evaporation enthalpy is not vapor pressure isn't boiling point, but the boiling point depends on vapor pressure depends on vacuum strength and vice versa - if you distill a more volatile substance or use stronger vac the bp will always be diminished (as you know). I think you can also roughly calculate the goodie content of the steam distillate with comparing the boiling points - higher goodie bp means lower goodie content per liter distillate..)

But as the distillation itself proceeds ~50% (??) faster with vac, I think using vac for steam distillation should bee recommended only if goodie content in distillate isn't lowered more than 33.3% when using vac (66.6 percent of the amount that would be collected in same time if using ambient pressure) - (x * 1.5) * 0.666 <-> x (where x = amount of distilled oil collected in a certain time).
Hence if the amount of water-immiscible substance in distillate decreases to less than 67% of original, vac steam dist. is slower than normal steam dist. ... smile

IMHO I believe vac steam distillation is quicker.

Perhaps I will do some experiments (steam distill benzaldehyde at STP, stop after a certain time, meaasure amount of distillate collected, determine benzaldehyde content - and then secondly steam distill same amount of benz/water using vacuum, let run exactly same time, and check if there's a difference in amount of aldehyde collected (and calculate how much faster vac distillation really is) to get to a final answer - but as I am incredibly lazy...

Who knows exactly how the composition of distillate changes at certain pressures?

Greetz A

"..ein Trank von unterschiedlicher Farbe, in ihm ist Heilung für die Menschen."

armageddon
(Hive Bee)
05-30-04 20:21
No 510369
 partial vapor pressure

Starlight: Isn't the vapor pressure the sum of the partial vapor pressures of all boiling liquids involved (and total vapor pressure = atmosphere pressure)? And is the vapor pressure of water not lowered much less than the vapor pressure of the higher boiling liquid if atmosphere pressure is reduced? (my nomograph wants to tell me same vac causes different bp lowering, depending on substance/original bp - and bp depends on vapor pressure I think. So same vac will cause different changes of the partial vapor pressures, but maybe proportions of the partial pressures stay the same?)

I begin to see why someone invented the "evap enthalpy" thingy...

Hm. (maybe I shoud've opened a new thread, too late now)

Greetz A

"..ein Trank von unterschiedlicher Farbe, in ihm ist Heilung für die Menschen."

Nicodem
(Hive Bee)
05-31-04 10:19
No 510514
User Picture Vacuum steam distillation of P2P
(Rated as: excellent)

Vacuum steam distillation of P2P - A theoretical enquiry

In order to fully understand the influence of pressure on the steam distillation phenomena I decided to play a little with the Claussius-Clapeyron's equation:

ln(P₂/P₁)=(1/T₁ - 1/T₂)*deltaH/R

I used approximate data and some idealizations to calculate the evaporation enthalpy (deltaH) and the phase diagram of P2P. Data used: b.p. at 1atm: 215°C ; b.p. at 14torr: 100.5°C. The deltaH for water was taken from literature (40660 J/mol). The enthalpy was idealized to bee non-temperature dependent (off course, this is not true).

Results:

deltaH(P2P) = 52.86 kJ/mol = 393,87 kJ/kg

Table of calculations:

[table]
[tr][td]temperature[/td] [td]vapor pressures[/td] [td]P[kPa] [/td] [td]mixture boils at^a:[/td] [td]steam distillate [/td] [td]composition[/td][/tr]
[tr][td]T[°C][/td] [td]H2O[/td] [td]P2P[/td] [td][kPa][/td] [td]X^b [mol(P2P)/mol][/td] [td]W^c [g(P2P)/g][/td][/tr]
[tr][td]0[/td] [td]0.832[/td] [td]0.004[/td] [td]0.835[/td] [td]0.4%[/td] [td]3.1%[/td][/tr]
[tr][td]10[/td] [td]1.566[/td] [td]0.008[/td] [td]1.574[/td] [td]0.5%[/td] [td]3.7%[/td][/tr]
[tr][td]20[/td] [td]2.825[/td] [td]0.017[/td] [td]2.842[/td] [td]0.6%[/td] [td]4.4%[/td][/tr]
[tr][td]30[/td] [td]4.900[/td] [td]0.036[/td] [td]4.936[/td] [td]0.7%[/td] [td]5.1%[/td][/tr]
[tr][td]40[/td] [td]8.207[/td] [td]0.070[/td] [td]8.276[/td] [td]0.8%[/td] [td]5.9%[/td][/tr]
[tr][td]50[/td] [td]13.313[/td] [td]0.130[/td] [td]13.443[/td] [td]1.0%[/td] [td]6.8%[/td][/tr]
[tr][td]60[/td] [td]20.976[/td] [td]0.236[/td] [td]21.212[/td] [td]1.1%[/td] [td]7.7%[/td][/tr]
[tr][td]70[/td] [td]32.187[/td] [td]0.411[/td] [td]32.598[/td] [td]1.3%[/td] [td]8.7%[/td][/tr]
[tr][td]80[/td] [td]48.206[/td] [td]0.695[/td] [td]48.901[/td] [td]1.4%[/td] [td]9.7%[/td][/tr]
[tr][td]90[/td] [td]70.608[/td] [td]1.141[/td] [td]71.749[/td] [td]1.6%[/td] [td]10.7%[/td][/tr]
[tr][td]100[/td] [td]101.325[/td] [td]1.825[/td] [td]103.150[/td] [td]1.8%[/td] [td]11.8%[/td][/tr]
[tr][td]110[/td] [td]142.689[/td] [td]2.848[/td] [td]145.537[/td] [td]2.0%[/td] [td]12.9%[/td][/tr]
[/table]
Error: Table contains the text "" between [tr] and the next [td] markup tag in the table row "[tr][td]temperature[/td][td]vapor pressures[/td][td]P[kPa] [/td][td]mixture boils ata:[/td][td]steam distillate [/td][td]composition[/td][/tr]".
Error: Table contains the text "" between [/td] and the next [/tr] markup tag in the table row "[tr][td]T[°C][/td][td]H2O[/td][td]P2P[/td][td][kPa][/td][td]Xb [mol(P2P)/mol][/td][td]Wc [g(P2P)/g][/td][/tr]".

^a It is assumed that the vapor pressure of a two phase system like H2O/P2P equals the sum of each phase partial pressures at the given T. Effects of impurities is ignored.
^b X is the molar fraction of P2P in the distillate and if ideal gas assumption is used it equals P(P2P)/P.
^c Since P2P density is 1.003 g/ml (Fluka catalog) the w/w% showed in the table can also be taken to equal vol% of the P2P phase in the distillate. Therefore if W=22% a 1dl of distillate will be composed of 22ml P2P and 78ml of water. Off course, this is only in theory.

Phase diagram:

Conclusion

Doing the steam distillation of P2P in a reduced pressure does have some influence on the composition of the distillate. Doing a steam distillation at 40°C (~8.3kPa) causes the distillate to contain two times less P2P (from 12.9% to 5.9%). However, due to the faster process and working at a lower temperature, it might bee practical if a compromise is done. Steam distillation between 60 to 80°C might be faster while still reducing the P2P/H2O ratio of the distillate in an acceptable range.
This conclusion is not to bee generalized to all steam distillable compounds since the results are (very!) strongly dependent on evaporation deltaH which is a specific property of each compound. Small differences in deltaH cause huge variations in the steam distillation. More specifically:
- if the molar deltaH is higher than that of the water, vacuum steam distillation causes a lowering of the non-polar fraction content in the distillate;
- if the molar deltaH is lower than that of the water, vacuum steam distillation causes a lowering of the water fraction content in the distillate;
- if deltaH are equal or very similar, no considerable effect should bee noted.

PS: If someone needs a theoretical phase diagram for any other liquid I can easily do some (now that I have the Excel template). All I need is two b.p. of the compound at two different pressures (normal b.p. and a reduced pressure b.p.).

The post has been heavily edited to incorporate the changes brought by the exact b.p./P data supplied by Armageddon in the next post in this thread. New phase diagram and huge differences in the colclusions! Sorry for the inconvenience.

“The real drug-problem is that we need more and better drugs.” – J. Ott

armageddon
(Hive Bee)
05-31-04 15:03
No 510537
 THX

WOW!

Now THAT'S a complete answer! Thanks a lot nicodem!

(BTW I just estimated the low pressure bp with a nomograph - literature bp of P2P is 215°C at 760 torr and 100-101°C at 14 torr, it's density is 1.0157 g/cm³ at 20°C (merck index) - but I think it doesn't make any significant difference. Vac distillation is just much quicker than normal dist.)

THX!

A

"..ein Trank von unterschiedlicher Farbe, in ihm ist Heilung für die Menschen."

Nicodem
(Hive Bee)
05-31-04 18:48
No 510568
User Picture Ops! Post revisited.

Armageddon, that little change made a huge difference. You probably used a linear approximation to get the b.p. at 60torr? The problem is that the b.p. to vapor pressure is an logarithmic curve. Before the molar deltaH of P2P and water were much more close together. Unfortunately this small change in deltaH caused exponential changes in partial vapor pressures of P2P. frown
Well, at least I learned something new and interesting. Beside this does not mean the vacuum steam distillation of P2P isn’t a good idea. Like you saw, really small changes cause unpredictable conclusions and in practice you always have small changes that the physical chemistry doesn't predict.
I also think that an addition of some salt (CaCl2, NaCl or Na2SO4) in the distillation flask would lower the partial vapor pressure of the water and give a distillate with a much higher proportion of P2P. This in addition with vacuum might bee faster than doing it at a normal pressure. That is, if speed is really so important to you (<-please note the play of words smile ).

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