Author Topic: vacuum refluxing  (Read 6738 times)

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pickler

  • Guest
vacuum refluxing
« on: March 05, 2002, 07:36:00 AM »
Swim's vacuum pump boils safrole at 70-72c. So swim wants to do a vacuum reflux to convert safrole to iso. Now in the write up on Rhodium's page, the safrole isomeraton says at 125c to vacuum reflux it overnight. Swim knows since the reflux temp is lower that the reaction will go longer, but how much longer? Any ideas on time for a reflux at that low of a temp?

We'll soon FIND OUT if I'm a chemist or not!

hest

  • Guest
Re: vacuum refluxing
« Reply #1 on: March 05, 2002, 11:50:00 AM »
Usual 10°C gives a factor 2
So 125-70=55 55/10 ~ 5
2^5=32
32*overnight = 16 dayes (give or take
)

pickler

  • Guest
Re: vacuum refluxing
« Reply #2 on: March 05, 2002, 01:44:00 PM »
Your kidding right.

We'll soon FIND OUT if I'm a chemist or not!

Chromic

  • Guest
Re: vacuum refluxing
« Reply #3 on: March 06, 2002, 07:01:00 AM »
No, and furthermore, Hest assumes that there is a great enough activation energy at 125C to have this reaction happen at all. You should reflux it at a higher temp. Why not boil safrole and 1.5wt% KOH with no vacuum until the temperature of the vapour hits 254C? It works well and with the monitoring, you're able to stop the rxn as soon as it is finished as to not "overcook" the safrole.

pickler

  • Guest
Re: vacuum refluxing
« Reply #4 on: March 06, 2002, 07:15:00 AM »
Hydro, swim has a ritchie yellowjacket pump used for hvac. 6cfm. Swim couldn't believe it at first. But sure enough it does.

We'll soon FIND OUT if I'm a chemist or not!

goiterjoe

  • Guest
Re: vacuum refluxing
« Reply #5 on: March 06, 2002, 07:16:00 AM »
pickler, SWIM has been in your same situation before, and will attest to it being able to work in 18 hours.  Be sure to grease you joints and seal them really well, and proceed to reflux for a period of 18 hours @ 75C.  After about 8 hours, you can turn your vacuum off and let it hold it's vacuum.  The gradual leak down will allow you to hit temperatures around 100-110C after about 4 hours. 

If Pacman had influenced us, we'd run around dark rooms eating pills and listen to repetitive music

RoundBottom

  • Guest
Re: vacuum refluxing
« Reply #6 on: March 06, 2002, 01:34:00 PM »
SWIM has sucessfully ISOd 2400mL saf using a vacuum for only the first hour, then removing the vacuum and then continuing at ~160°C for another 20h.  recovered a stunning 2370mL between 142°C-146°C.

i learned a thing or two from charlie dontcha know.

pickler

  • Guest
Re: vacuum refluxing
« Reply #7 on: March 06, 2002, 01:53:00 PM »
nice. :o

We'll soon FIND OUT if I'm a chemist or not!

LaBTop

  • Guest
Re: vacuum refluxing
« Reply #8 on: March 06, 2002, 02:39:00 PM »
Roundbottom, how much KOH did you use there, what grade, and did you have an extensive amount of tar left or not, when distilling the blackish raw Isosafrole?
That's the highest yield of Saf to Iso I saw mentioned till now! LT/

WISDOMwillWIN

Rhodium

  • Guest
Re: vacuum refluxing
« Reply #9 on: March 06, 2002, 06:08:00 PM »
Roundbottom: 142-6°C - at what pressure?

goiterjoe

  • Guest
Re: vacuum refluxing
« Reply #10 on: March 06, 2002, 10:33:00 PM »
I think he means just heating without refluxing.

If Pacman had influenced us, we'd run around dark rooms eating pills and listen to repetitive music

RoundBottom

  • Guest
Re: vacuum refluxing
« Reply #11 on: March 07, 2002, 12:14:00 AM »
i'm not 100% certain of the vacuum pressure, as my gauge is analog.  it reads about 29.5" maybe a smidgen less (i know i should report it in milimetres, but the gauge doesn't read as well in milimetres, flog me if you must) when the gauge is connected directly to the hose with nothing else attached.

- measured 2400mL of safrole double crystalized from sassy oil (brazillian)
- measured 60g, (guessing 85%) KOH flakes, ground to small chunks (not to a powder)
- put in 5L 2N RBF with a 24/40 - 45/50 adapter and a 6 bulb ahllin condenser in one neck, and a therm and adapter in second neck, seated in a 5L aluminum heating mantle

- mag stirring was very difficult to get started w/ 1" egg stirrer so switched to 2" octagonal stirrer which worked a bit better
- outlet adapter was put in top of condenser, vacuum hose was attached to nipple
- heating was turned on to 26 (out of 100)
- left vacuum on for 30m (sorry, didn't consult notes in above post)

Time   Temp   Heat
+   0m    24°C   0/26
+  30m    36°C   26   vac off
+ 210m   112°C   26/30
+ 300m   144°C   30/28
+ 540m   156°C   28/27
+ 600m   164°C   27   sleep
+ 960m   152°C   27
+1290m   151°C   27/0


- liquid was very dark brown and almost opaque
- set up for vac distillation in the same 5L RBF flask


Time   Temp   Heat
+   0m    27°C   0/30
+ 100m    28°C   30/32
+ 120m    28°C   32/34
+ 160m    32°C   34/36
+ 180m    36°C   36/38
+ 210m    42°C   38   (added loose tin foil shroud to distillation flask)
+ 212m   138°C   38/36   coming over > 1 drop/sec
+ 395m   141°C   36/0   replaced receiving flask*, and restarted distillation
+ 570m   144°C   38   replaced receiving flask*, and restarted distillation
+ 705m   146°C   38   stopped distillation**


* don't ask, SWIM only has a 1L receiving flask, it SWIMs largest 19/22 flask.  owing to breaking SWIMs only 24/40 vac adapter, SWIM must use a 24/40 - 19/22 adapter and a 19/22 vac adapter and, therefore, a 19/22 flask.  SWIM is still awaiting a replacement 24/40 adapter.

** you know you are done when the stir bar no longer spins due to being trapped in the solids

total clear, water white fluid recovered: == 2370mL, 98.7% v/v

the distilling flask had a chunk of brown solids on the bottom, and brown solids splashed on the sides.  when the flask had cooled down a bit, maybe 20m but hadn't cooled off completely, it was easily cleaned with water.  no acetone or other solvent was needed.  SWIM was very impressed by the ease of removal, as ketone distillation tar removal is about as fun as chewing glass.


i learned a thing or two from charlie dontcha know.

RoundBottom

  • Guest
Re: vacuum refluxing
« Reply #12 on: March 07, 2002, 12:21:00 AM »
now that i think about it, maybe i put the outlet adapter directly on the 24/40 - 45/50 adapter and left the condenser off while vac refluxing.  in fact, i'm certain of this.  the condenser was added after the vac was turned off.

also, a performic has not been performed on this ISO yet.  safrole, with this setup, usually came over somewhere around 110°C.

i learned a thing or two from charlie dontcha know.

LaBTop

  • Guest
Re: vacuum refluxing
« Reply #13 on: March 07, 2002, 03:10:00 AM »
To be sure that you did not do all that work and are stuck with the same safrole back:

-I-
Please take a dry, clean 1 liter erlenmeyer, put that on a digital scale, add 20°C warm distillated water, until your scale shows exactly 1.000 gram, look at the meniscus of the water, and write a thin line with a pen who's ink sticks to glass, around the flask, so that the concave underside of the meniscus is EXACTLY on that line, when the flask is exactly horizontally placed on the scale on a table, and your eyes are at the same height as the meniscus.

Now you have a 1 liter erlenmeyer calibrated as good as can be, to hold nearly exactly 1.000 liter.
You pour out the water, and dry the flask thoroughly, inside and outside, without removing that line.

Then you warm or cool 1.2 liter of your to be expected Isosafrole to 20°C.
And fill most of that in the erlenmeyer, untill its meniscus concave underside is exactly on the written thin line. Do NOT leave spilled drops above the meniscus, hanging on the glasswalls, but in case of shaky hands because of drug use or alcohol consumption, remove them with a tissue.

Now you have exactly 1 liter of ?Isosafrole? in there, at a temp of 20°C, take care that the glass of the erlenmeyer was ALSO at 20°C when you filled it. Do not check the temp NOW with a thermometer, or you remove weight as Isosafrole oil hanging at your thermometer.

Place this now back on your scale.

If it reads 1120 gram then you have at least 97% Isosafrole.
d20=1.120 for Isosafrole.
Density at 20°C and at purity 97%.(a mix of cis and trans isosafrole btw, both will rearrange to epoxide and/or diol=glycol with oxone or performic/peracetic methods)

If it reads 1095 gram then you have at least 97% Safrole.(back, nothing happened!)
d20=1.095 for Safrole. Density at 20°C and at purity 97%.

If it reads anything inbetween, do the simple math to calculate what % is Safrole and what % is Isosafrole.

Density is gram per cubic centimeter, at 20°C.

-II-
You can also use a refractometer, MUCH faster:
n20/D Safrole=1.5370 (at 20°C and purity 97%)
n20/D Isosafrole=1.5760 (at 20°C and purity 97%)

-III-
And you can fast check the boiling points of both at atmospheric pressure in a test tube, a few ml, heated with a gas flame, and a thermometer inside, untill the fluid boils, hang the thermometer 0.5 cm above the boiling fluid, so you measure the temp of the saturated vapour of the boiling oil!
bp Safrole=232-234°C at 1 atm.
bp Isosafrole=254-255°C at 1 atm.

-IV-
And you can just aminate and see/hope if it works, the wacko way.

-V-
And you can use TLC to compare to a known sample.

-VI-
And you can use NMR.

-VII-
And you can use a gaschromatograph.

Thank you for your patience reading this,  ;) . LT/

WISDOMwillWIN

RoundBottom

  • Guest
Re: vacuum refluxing
« Reply #14 on: March 07, 2002, 11:25:00 AM »
wow, that is some detailed writeup to confirm my writeup!  thank you very much, SWIM will try the weight method today.  should SWIM use a graduated cylinder instead of an erlenmyer?  SWIM has a 250mL.  this would increase the margin of error 4 fold, though.

> And you can just aminate and see/hope if it works, the wacko way

this is the fourth ISO SWIMs done this way.  both performics done on the first three ISOs worked, but with less yield than SWIM was used to with the benzo wack (as is to be expected).  the yields on the previous three were:

94mL saf, 1.6g KOH -> 79mL ISO (bad distil technique lowered yield)
500g saf, 8g KOH -> 478g ISO
1000mL saf, 19.8g KOH -> 954mL ISO

SWIM keeps detailed but non-professional notes (doesn't know what a proper lab report looks like). 

and thx again for detailed response.

i learned a thing or two from charlie dontcha know.

RoundBottom

  • Guest
Re: vacuum refluxing
« Reply #15 on: March 07, 2002, 01:57:00 PM »
well, SWIM did the first procedure as best SWIM could.  final result, 1000mL of above ISO == 1120.50g.  there was about 0.11g of fluid that wouldn't evaporate from the flask; probably water, not acetone (acetone was user to remove as much excess water as possible).  SWIM was disappointed, as SWIM thought the scale was to read 1200g.  when SWIM checked LTs post again, SWIM was elated. 

SWIM knows of someone who had access to a NMR and is trying to find if it is still available.  if so, a test will be performed.

also of note: man those graduated erlenmyers are inaccurate.  1000mL was slightly above 950mL on the graduations.  granted, it does state +- 5%, but that is about the most accurate data on the flask  ;)

i learned a thing or two from charlie dontcha know.

Vibrating_Lights

  • Guest
Re: vacuum refluxing
« Reply #16 on: March 08, 2002, 08:53:00 AM »
Swim does his Iso the same as round bottom.  the initial vaccume cuts down on the tar produced by the reaction by first removing the H2O. Cleaning is a breeze and yeilds are high.
VL_

RoundBottom

  • Guest
Re: vacuum refluxing
« Reply #17 on: March 08, 2002, 11:43:00 AM »
no luck accessing an NMR.  the window has passed.

VL, did you do the measuring method as per LT?  it really points out the inaccuracies of your glassware's graduations.

i learned a thing or two from charlie dontcha know.

Vibrating_Lights

  • Guest
Re: vacuum refluxing
« Reply #18 on: March 09, 2002, 01:33:00 AM »
no safrole forrun ever. havn't bothered to check the density.
VL_

wyndowlicker

  • Guest
Re: vacuum refluxing
« Reply #19 on: March 18, 2002, 12:56:00 PM »
swiw has the 1.5 cfm yellowjacket and If swiw is pulling safrole over at 72c then hes just stupid That cant bee possible.It cant bee!Are you trying to say you get better than perfect vacuum.How those pumps are rated at 15-20 microns.I believe this is bullshit.

I will choke untill I swallow!Who are you to judge or strike me down!