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 (https://www.thevespiary.org/talk/index.php?topic=11723.msg32241000#msg32241000)
(Barium: "Now it´s even easier", Novel Discourse)
Post 323065 (https://www.thevespiary.org/talk/index.php?topic=11723.msg32306500#msg32306500)
(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 ;) )
Greetz A
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 (https://www.thevespiary.org/talk/index.php?topic=11723.msg49311400#msg49311400)
(GC_MS: "1-phenyl-2-propanone", Novel Discourse)
Greetz A
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 (https://www.thevespiary.org/talk/index.php?topic=11723.msg32122600#msg32122600)
(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.
Article referenced in Post 505352 (https://www.thevespiary.org/talk/index.php?topic=9579.msg50535200#msg50535200)
(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.thevespiary.org/rhodium/Rhodium/pdf/varma-kabalka.sncl2-oxime.pdf)
(https://www.thevespiary.org/rhodium/Rhodium/pdf/varma-kabalka.sncl2-oxime.pdf)
There is a little more info on steam distillation under vacuum in this thread: Post 500295 (https://www.thevespiary.org/talk/index.php?topic=9790.msg50029500#msg50029500)
(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 (missing)
(chem_123: "steam distillation!?", Newbee Forum), Post 294104 (missing)
(terbium: "Solvent extraction is good here.", Newbee Forum), Post 501475 (https://www.thevespiary.org/talk/index.php?topic=9790.msg50147500#msg50147500)
(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.
Starlight: THX, that's just the support I needed! *lol*
Barium: well this Post 501475 (https://www.thevespiary.org/talk/index.php?topic=9790.msg50147500#msg50147500)
(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 (missing)
(Rhodium: "Steam distillation", Newbee Forum) ;D (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 ;) ) 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. ... :)
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
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:
temperature | vapor pressures | P[kPa] | mixture boils ata: | steam distillate | composition |
T[°C] | H2O | P2P | [kPa] | Xb [mol(P2P)/mol] | Wc [g(P2P)/g] |
0 | 0.832 | 0.004 | 0.835 | 0.4% | 3.1% |
10 | 1.566 | 0.008 | 1.574 | 0.5% | 3.7% |
20 | 2.825 | 0.017 | 2.842 | 0.6% | 4.4% |
30 | 4.900 | 0.036 | 4.936 | 0.7% | 5.1% |
40 | 8.207 | 0.070 | 8.276 | 0.8% | 5.9% |
50 | 13.313 | 0.130 | 13.443 | 1.0% | 6.8% |
60 | 20.976 | 0.236 | 21.212 | 1.1% | 7.7% |
70 | 32.187 | 0.411 | 32.598 | 1.3% | 8.7% |
80 | 48.206 | 0.695 | 48.901 | 1.4% | 9.7% |
90 | 70.608 | 1.141 | 71.749 | 1.6% | 10.7% |
100 | 101.325 | 1.825 | 103.150 | 1.8% | 11.8% |
110 | 142.689 | 2.848 | 145.537 | 2.0% | 12.9% |
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 at<sup>a</sup>:[/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]X<sup>b</sup> [mol(P2P)/mol][/td][td]W<sup>c</sup> [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:
(https://www.thevespiary.org/rhodium/Rhodium/hive/hiveboard/picproxie_docs/000503137-P2P-phase-diagram.gif)
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.