Acetone replacement in dry ice bath?
Amer Akhras
I'm looking for an alternative to acetone to use in a dry ice bath,
since
acetone comes out of my GC at the same time as another important
(isopentane)
component in my reaction. Anyone have any experience with using
alternative
fluids?
Thanks...
Mike Simpson
m...@phoenix.princeton.edu
Norman L. Reitzel
Sure, Mike. 99% isopropanol works just fine, also, and it's cheap.
However, you will note that the bath does not cool as quickly as the
acetone bath. The reason for this is that CO2 is significantly soluble in
acetone at or near -78C, so litre for litre the acetone bath has a
somewhat larger cooling capacity. All this means is you need to use a bit
more dry ice in the isopropanol bath.
------------------------------------------------------------------------
Norman L. Reitzel, Jr. | "When you live beside the graveyard,
nrei...@lonestar.utsa.edu | you can't cry for every funeral."
Blue Water Ventures, dba. | Russian Proverb
------------------------------------------------------------------------
Antoni S. Gozdz 21131
>
>I'm looking for an alternative to acetone to use in a dry ice bath,
>since
>acetone comes out of my GC at the same time as another important
>(isopentane)
>component in my reaction. Anyone have any experience with using
>alternative
>fluids?
I have used hexanes, methanol, ethanol... be careful with the
first two, esp. MeOH.
Tony
---------------------
Antoni S. Gozdz
to...@nyquist.bellcore.com
Winston K. Chan 21111
Look in the Chemist's Campanion by A. J. Gordon and R. A. Ford,
published by Wiley 1972. On page 451 is a table with low temperature
baths.
Winston Chan
Antoni S. Gozdz 21131
>In article <1994May6.1...@Princeton.EDU> awak...@phoenix.princeton.edu. (Amer Akhras) writes:
>>
>>I'm looking for an alternative to acetone to use in a dry ice bath,
>>since
>>acetone comes out of my GC at the same time as another important
>>(isopentane)
>>component in my reaction. Anyone have any experience with using
>>alternative
>>fluids?
>
>However, you will note that the bath does not cool as quickly as the
>acetone bath. The reason for this is that CO2 is significantly soluble in
>acetone at or near -78C, so litre for litre the acetone bath has a
>somewhat larger cooling capacity. All this means is you need to use a bit
>more dry ice in the isopropanol bath.
But is it viscous...
Tony Houthaeve
Using Methanol or Ethanol also keep the temperature down.
Perhaps these peaks/chemicals do not disturb ?
Tony
SMITH RANDALL SCOTT
isopropanol/dry ice will get you down to ca. -80 deg. C, about the same
temperature as acetone/dry ice.
Bharat Singh
Ether/Dry Ice can be used as a substitute
Bharat.
Stephen Miller
>|> >> since
>|> >> acetone comes out of my GC at the same time as another important
>|> >> (isopentane)
>|> >> component in my reaction. Anyone have any experience with using
>|> >> alternative
>|> >> fluids?
>|> >>
>|> >> Thanks...
>|> >> Mike Simpson
>|> >> m...@phoenix.princeton.edu
>|> >
>|> temperature as acetone/dry ice.
>|>
>|> Randy
>|> smi...@ucsu.colorado.edu
> Ether/Dry Ice can be used as a substitute
> Bharat.
Isopropanol/dry ice is the way to go. About the same temperature as acetone/CO2
but the isopropanol is less volatile so the solvent lasts longer. Ether/CO2
is much colder; I think -100C vs -80C or so for acetone and isopropanol.
Steve.
Derek S. Tan
>Isopropanol/dry ice is the way to go. About the same temperature as acetone/CO2
>but the isopropanol is less volatile so the solvent lasts longer. Ether/CO2
>is much colder; I think -100C vs -80C or so for acetone and isopropanol.
Correct me if I'm wrong, but I believe the limiting factor in terms
of low temperature is the sublimation point of dry ice which is
-78 C, yes?
--
Derek S. Tan ta...@leland.stanford.edu
Stanford University Department of Chemistry
Sam Tahmassebi
Derek S. Tan <ta...@leland.Stanford.EDU> wrote:
>
>Correct me if I'm wrong, but I believe the limiting factor in terms
>of low temperature is the sublimation point of dry ice which is
>-78 C, yes?
>--
>Derek S. Tan ta...@leland.stanford.edu
Sorry Derek. You are wrong. I don't know if I understand this but the
limiting factor is not the sublimation point of dry ice. Dry ice baths
vary in temperature depending on what the solven is. For instance,
Et2O/CO2 bath is at -100C but CH3CN/CO2 bath is at -40C and (CH3)2CO/CO2
bath is at -78C. You can look up all the different baths in Chemists
Companion.
Sam
Phil Felton
No, otherwise salt water baths would not be able to go below 0 C!
according to 'Physical Chemistry' W.J Moore
DeltaT = RT^2m/lf 1000
Iguess it's also possible that some compounds form azeotropes with CO2
which
could have a minimum b.p. below that of either constituent.
Phil.
David J Heisterberg
Sam Tahmassebi <s...@u.washington.edu> wrote:
>Sorry Derek. You are wrong. I don't know if I understand this but the
>limiting factor is not the sublimation point of dry ice. Dry ice baths
>vary in temperature depending on what the solven is. For instance,
Hmm, according to Lange's:
The assertion that certain baths with CO2 snow, especially the
acetone bath, give a temperature materially lower than pure dry
CO2 snow is erroneous. Cf. Theil and Caspar, Z. Physik. Chem.
86, 257-93 (1914).
The table lists
EtOH/CO2 -72C
CHCl3/CO2 -77C
(Et)2O/CO2 -78C
A recommended solvent is 1-methoxy-2-propanol, Dow's DOWANOL 33-B.
--
David J. Heisterberg Gee, it's so beautiful, I gotta
Department of Chemistry give somebody a sock in the jaw.
The Ohio State University -- Little Skippy (Percy Crosby)
David J Heisterberg
Phil Felton <fel...@phoenix.princeton.edu> wrote:
>No, otherwise salt water baths would not be able to go below 0 C!
>according to 'Physical Chemistry' W.J Moore
>
>DeltaT = RT^2m/lf 1000
But this is refering to the colligative property of freezing
point depression. It tells us nothing about whether the
solution of a solute will raise or lower the temperature.
That's governed by the heat of solution, which for salt,
ammonium nitrate, and others does lead to cooling; in sharp
contrast to sodium hydroxide. Yet all of these will lower
the freezing point of a dilute solution by roughly the same
amount per mole. Heat of solution is not a consideration in
your typical dry-ice bath.
Stephen Miller
>Stephen Miller <smi...@picasso.ucsf.edu> wrote:
>>Isopropanol/dry ice is the way to go. About the same temperature as acetone/CO2
>>but the isopropanol is less volatile so the solvent lasts longer. Ether/CO2
>>is much colder; I think -100C vs -80C or so for acetone and isopropanol.
>Correct me if I'm wrong, but I believe the limiting factor in terms
>of low temperature is the sublimation point of dry ice which is
>-78 C, yes?
No, I don't think so. Consider ice-salt baths. Is the limiting temperature
the freezing point of pure water? No. In this case the freezing point is
depressed by a nonvolatile solute to as low as -20 or so.
In the case of dry ice, the temperature of the bath depends on the solvent
used; with ethanol it's -72, with acetone it's -77, with ether it's -100.
Why this is so I'm not sure; perhaps some kind of colligative property. It's
intuitively appealing to ascribe it to the heat of vaporization of the
solvent, such that more volatile solvents will yield the coldest bath
temperatures. Whether this has any validity I don't know. Ask a physical
chemist.
The reference for the bath temperatures given is "Purification of Laboratory
Chemicals", 3rd edition, by Perrin and Armarego, pages 42-43.
Steve.
Stephen Miller
>Hmm, according to Lange's:
> The assertion that certain baths with CO2 snow, especially the
> acetone bath, give a temperature materially lower than pure dry
> CO2 snow is erroneous. Cf. Theil and Caspar, Z. Physik. Chem.
> 86, 257-93 (1914).
>The table lists
> EtOH/CO2 -72C
> CHCl3/CO2 -77C
> (Et)2O/CO2 -78C
>A recommended solvent is 1-methoxy-2-propanol, Dow's DOWANOL 33-B.
>--
>David J. Heisterberg Gee, it's so beautiful, I gotta
>Department of Chemistry give somebody a sock in the jaw.
>The Ohio State University -- Little Skippy (Percy Crosby)
Out of curiosity I checked Chem Abstracts this afternoon and found
the above article plus one from 1906 (Phys Rev 23 p308) that refuted the
idea that any CO2 baths go below -78C. The 1906 paper began "Owing to the
contradictory data given in the literature...", so presumably there were
reports of dry ice baths with < -78C temperatures in the literature. What
is especially curious is why Perrin & Armarego's "Purification of Laboratory
Chemicals", 3rd edition (1988) still lists the temperature of an ether/CO2
bath as -100C, some 80+ years later. Are they misinformed, or has an article
appeared after 1914 refuting the findings of Zelany & Zelany (1906) and
Thiel & Caspar (1914)?
Steve.
hamil...@ix.wcc.govt.nz
>Hmm, according to Lange's:
>
> The assertion that certain baths with CO2 snow, especially the
> acetone bath, give a temperature materially lower than pure dry
> CO2 snow is erroneous. Cf. Theil and Caspar, Z. Physik. Chem.
> 86, 257-93 (1914)
> CHCl3/CO2 -77C
> (Et)2O/CO2 -78C
Interesting, because according to the Merck Index ( 9th Ed )
Misc-71 the table lists
Alcohol at 4C with solid CO2 -72C
chloroform with solid CO2 -77C
acetone with solid CO2 -86C
ether with solid CO2 -100C
solid CO2 ( dry ice ) sublimes at -78.5C
Now I've never had a thermometer calibrated to go that low, and
have always assumed acetone/CO2 was close to the sublimation
point. Maybe somebody with a later Merck Index can confirm the
above are still reported. These are also reported in Vogel's
Practical Organic Chemistry, which cites the 1972 "The Chemist's
Companion" as their reference.
Bruce Hamilton
David J Heisterberg
>Interesting, because according to the Merck Index ( 9th Ed )
>Misc-71 the table lists
>
This is really getting interesting. My 11th Merck lists this as well,
but with no reference. My ancient little 17th CRC however, gives it
as -77C, the data being from the Smithsonian tables.
I'm inclined to think that the -100C figure is a mistake that's gotten
handed down through generations of tables. CO2 is not very soluble in
ether, so can anyone think of a mechanism that could account for this
effect?
David J Heisterberg
David J Heisterberg <dhei...@magnus.acs.ohio-state.edu> wrote:
>This is really getting interesting. My 11th Merck lists this as well,
>but with no reference. My ancient little 17th CRC however, gives it
>as -77C, the data being from the Smithsonian tables.
One more datum. The 70th CRC doesn't list anything but acetone/CO2,
at -78C. If (Et)2O/CO2 could really get you -100C it would probably
get a mention.
Toby J. Sommer
>In article <2rmasm$b...@golem.wcc.govt.nz>, <hamil...@ix.wcc.govt.nz> wrote:
>>Interesting, because according to the Merck Index ( 9th Ed )
>>Misc-71 the table lists
>>
>> ether with solid CO2 -100C
[...]
I know this may not do much to settle the question here, but I plopped
some dry ice into ether in a beaker; when the bubbling subsided, I
measured the temp with a cheap low temp thermometer. With only the bulb
immersed, it hit -98 C pretty quickly and stayed there.
Does anyone have access to materials (I'm not near my usual resources)
to find out what Trapp solvent mixture is? I've used it, but I can't
remember if it's ether/pentane/LN2 or ether/pentane/CO2 (ether:pentane =
4:1 ?). It hits -110 reliably. LN2/ethyl acetate slush is hard to
maintain, but also hits a stable low temp that I can't remember.
mlb...@skcla.monsanto.com
>
> Out of curiosity I checked Chem Abstracts this afternoon and found
> the above article plus one from 1906 (Phys Rev 23 p308) that refuted the
> idea that any CO2 baths go below -78C. The 1906 paper began "Owing to the
> contradictory data given in the literature...", so presumably there were
> reports of dry ice baths with < -78C temperatures in the literature. What
> is especially curious is why Perrin & Armarego's "Purification of Laboratory
> Chemicals", 3rd edition (1988) still lists the temperature of an ether/CO2
> bath as -100C, some 80+ years later. Are they misinformed, or has an article
> appeared after 1914 refuting the findings of Zelany & Zelany (1906) and
> Thiel & Caspar (1914)?
>
> Steve.
>
I just tried making a dry ice/ether bath out of curiosity. I could get a
temperature of -88C out of it, but it didn't want to go lower. This is
lower than -78C though, even if not -100C. This was with a lot of dry
ice relative to ether.
Mark
David J Heisterberg
<mlb...@skcla.monsanto.com> wrote:
>I just tried making a dry ice/ether bath out of curiosity. I could get a
>temperature of -88C out of it, but it didn't want to go lower. This is
I just tried a few experiments myself. Using a not too accurate
thermometer:
CO2 snow only -75C (not particularly well packed)
IPA/CO2 snow -83C
(Et)2O/CO2 snow -87.5C
The same thermometer reads about 1.8C in ice water.
This was the first time I've ever made a slush, and the first time I've
done anything in a lab in at least 10 years, but I had the kind help of
Yvonne, Ellen, and Marsi.
Nicolas LeBlond
>
>Interesting, because according to the Merck Index ( 9th Ed )
>Misc-71 the table lists
>
> chloroform with solid CO2 -77C
> acetone with solid CO2 -86C
>
>Now I've never had a thermometer calibrated to go that low, and
>have always assumed acetone/CO2 was close to the sublimation
>point. Maybe somebody with a later Merck Index can confirm the
>above are still reported. These are also reported in Vogel's
>Practical Organic Chemistry, which cites the 1972 "The Chemist's
>Companion" as their reference.
>
> Bruce Hamilton
The Merck Index 11th edition (1989) also lists ether/dry-ice bath at
-100C... I did a little experimentation myself yesterday and I couldn't
get my ether/dry-ice mixture to go below -81C. An acetone/dry-ice slush
gave me -78C; pure dry-ice also gave -78C. The measurements were made
using a pentane thermometer (-200 to 30C) and were double-checked with a
thermocouple.
Does anybody else want to try?
--
------------------------------------------------------------------------------
"I have a dream... I believe that one day everyone, everywhere will know
the wonders of my nipples." - Stimpy 'Rubber Nipple Salesman'
Nic LeBlond, Chemistry Department, McMaster University, CANADA
David J Heisterberg
Nicolas LeBlond <g922...@mcmail.cis.mcmaster.ca> wrote:
>-100C... I did a little experimentation myself yesterday and I couldn't
>get my ether/dry-ice mixture to go below -81C. An acetone/dry-ice slush
>gave me -78C; pure dry-ice also gave -78C. The measurements were made
These sound reasonable. I could buy getting a few more degrees from
ether than IPA given the former's volatility. When I was making the
slush, in a hood, there was still a quite noticeable smell of ether,
so evaporation might cool things down a bit. But I'm not happy with
the -100C number. If you could achieve that you would figure that a
beaker of ether at room termperature would be quickly covered in ice
or at least lots of condensate. The aligned right margin was almost
completely by accident!
Louis William Gascoigne
I measured the temperature with an inexpensive alcohol thermometer as
being approximately -74C. (this was after the "slurry" was created).
My O-Chem lab TA told me that that temperatures as low as -100C are possible
using dry ice and various solvents, but I tend to believe what I see...
Another step in the experiment required a -25C temperature to which
normal ice (frozen water) and sodium bromide should have produced
(-28C according to the literature value). I measure this one as being
approximately -14C.
It could be that the temperature of the bath also depends on the vessel
the coolant is contained in. In my case, uninsulated pyrex glass.
Phil Felton
dhei...@magnus.acs.ohio-state.edu (David J Heisterberg) wrote:
>
> In article <1994May24.1...@muss.cis.mcmaster.ca>,
> Nicolas LeBlond <g922...@mcmail.cis.mcmaster.ca> wrote:
> >-100C... I did a little experimentation myself yesterday and I couldn't
> >get my ether/dry-ice mixture to go below -81C. An acetone/dry-ice slush
> >gave me -78C; pure dry-ice also gave -78C. The measurements were made
>
> These sound reasonable. I could buy getting a few more degrees from
> ether than IPA given the former's volatility. When I was making the
> slush, in a hood, there was still a quite noticeable smell of ether,
> so evaporation might cool things down a bit. But I'm not happy with
> the -100C number. If you could achieve that you would figure that a
> beaker of ether at room termperature would be quickly covered in ice
> or at least lots of condensate. The aligned right margin was almost
> completely by accident!
Hmm.... I recall placing a beaker of ether in a pool of water as a High
school experiment, ice formed quite readily, of course its not so warm
in Wales at the best of times!!
Phil.
Timothy Melton
>>Hmm, according to Lange's:
>>
>> The assertion that certain baths with CO2 snow, especially the
>> acetone bath, give a temperature materially lower than pure dry
>> CO2 snow is erroneous. Cf. Theil and Caspar, Z. Physik. Chem.
>> 86, 257-93 (1914)
I think that the authors may have been mistaken.
>> EtOH/CO2 -72C
>> CHCl3/CO2 -77C
>> (Et)2O/CO2 -78C
>
>Interesting, because according to the Merck Index ( 9th Ed )
>Misc-71 the table lists
>
> Alcohol at 4C with solid CO2 -72C
> chloroform with solid CO2 -77C
> acetone with solid CO2 -86C
> ether with solid CO2 -100C
> solid CO2 ( dry ice ) sublimes at -78.5C
>
A simple explanation for DI/solvent baths temperatures being below -78.5C?
Subcooling of the solvent due to vaporization. The DI cools the ether to
-78.5C. The ether's vapor pressure at this temperature is sufficient to
case enough vaporization to lower the temperature of the bath. Any heat
added to the bath is absorbed by the DI and used as the heat of sublimation
for CO2. (To make a long story short). I suspect that the temperature of
an ether bath would be fairly low itself. The CO2 would supply cooling
initially and a heat sink for outside heat transfer.
Of course this is merely speculation assuming that the ether/DI bath info
given above is correct.
My $0.02
Tim
>
> Bruce Hamilton
--
Dr. Tim Melton quest1!t...@constellation.ecn.uoknor.edu
Quest Consultants Inc. (if email replies don't work, use this address)
P.O. Box 721387 (405) 329-7475
Norman, Ok 73070-8069 Fax: (405) 329-7734
wrig...@vax.sbu.ac.uk
I'd guess that if you start with DryIce which itself is at -78oC, it would be
tricky to cool a liquid below this temperature. After all, if you did, then
when you added more Dry Ice at -78oC, this would warm it up!!
I can believe that the temperature recorded could be a little lower than -78oC
due to the foaming of the liquid and the resultant evaporation cooling it
slightly. But I find -100oC from Dry Ice at -78oC hard to believe. -80ish, yes,
maybe even -85oC.
--BUT-- Who said the Dry Ice is at -78oC??? That's the _maximum_ temperature it
can be at, there's nothing to stop you having a sample of Dry Ice at -80, -85,
-90, -100oC or whatever if it comes from a refridgerated store. If you have made
a slush bath and measured the temp of it, now check the pure Dry Ice's temp as
well. If it's lower than -78oC, then _of course_ you can cool the solvent more.
When I worked with slush baths for ten years, I found the limiting factor was
the freezing point of the solvent used. So if you use ether, you'll be able to
cool it with liq N2 to about -120oC before it solidifies. And if your Dry Ice
is very cold, yes, you can get it down to about -100oC.
You are confusing minimum _possible_ temp at which the bath will still be
_liquid_ with the temperature you will normally get down to. As most of us use
Dry Ice which IS at about -78, that's the normal limit, give or take a few
degrees for evaporative cooling.
If you use a solvent which solidifies at, say, -40oC, then that is the
_practical_ limit at which your slush bath becomes a solid and very dificult
to handle. Hence some of the high temperatures quoted by other posters.
John G Wright
wrig...@vax.sbu.ac.uk
several writers have mentioned using ether, noone seems to have pointed out the
safety hazard when such baths are made.
There is _lots and lots_ of foaming of the ether, lots of it evaporates, and
the bath has to be topped up with fresh ether several times before it's cooled
enough to have solid Dry Ice present. (With liq N2, I found I often used about
three times the volume of ether as ended up in the bath. With Dry Ice it could
be twice the volume used as that of the resultant bath.)
All this ether vapour is in the room. It can make you quite light headed and
dizzy. And if there is a flame anywhere nearby, or even quite far away.......
well, you can guess the rest.
Ether slush baths should always be made in an efficient fume hood, with no
source of a flame or a spark anywhere near by.
Footnote.
I've survived two ether explosions so far. One where some idiot lit a bunsen
next to me as I poured out 20 cm3 into a flask. Very exciting!!
The other occurred when a friend's flask broke. It contained 2 litres of ether
and it landed on a hot plate!!!
We're alive because calculations showed that there wasn't enough oxygen in the
fume cupboard to burn all the ether. Ever stood inside a flame five feet in
diameter??
It's interesting, but not recommended. Even if the temperature is not
particularly high.
John G Wright
Ian Russell Ollmann
Sorry for the multiple messages. I have been working my way through a backlog
of sci.chem and have only now come accross conflicting experiences to my own
with the temperature of a dry-ice ether bath. I am really intrigued by this
wide disparity in bath temperature measurements. I guess it speaks volumes for
including an experimental with your results. In my case, (I am one of the not
much colder than -78 degrees crowd) I used solid dry ice obtained from blocks
of the stuff that is stored in an unrefridgerated insulated box for hours/days
before I get to it, so it's internal temp is probably pretty close to the
sublimation temp of carbon dioxide. Do those of you who claim colder
temperatures use powdered dry ice or dry ice which is kept in storage below
this temperature? Any other hypotheses? I am going to try to repeat it in a
dewar flask with lots of dry ice (finely crushed) to see what I get. Result:
No thermometer that I can find reads less than -81 degrees Celsius. CO2
appears almost transparent in ether. Its presence is revealed by sand-like
resistance to stirring with the thermometer. Larger chunks appear whitish.
Very little bubbling observed once temperature reached minimum, which was
measured to be -79 +- 2 degrees Celcius.
Ian Ollmann
Derek S. Tan
<wrig...@vax.sbu.ac.uk> wrote:
[snip]
[lines edited to fit 79 columns]
>--BUT-- Who said the Dry Ice is at -78oC??? That's the _maximum_
>temperature it
>can be at, there's nothing to stop you having a sample of Dry Ice at -80, -85,
>-90, -100oC or whatever if it comes from a refridgerated store. If you
>have made
>a slush bath and measured the temp of it, now check the pure Dry Ice's temp as
>well. If it's lower than -78oC, then _of course_ you can cool the solvent
> more.
It appears that I have started quite a thread here! Rest assured that
I've been keeping up with it! To me, John's explanation seems the most
plausible, in which case we would have all been overlooking the obvious!
(Surely not the first time this has happened to any of us!) However,
it's obviously key for those experimentalists out there to determine what
the original temperature of their pure dry ice is BEFORE adding solvents.
I recall seeing a recent post stating -75C for pure dry ice (not well
packed) and temperatures lower than -78C in ether. But I wonder how
significant that packing job is. Further, we'd obviously be measuring
the temperature at the air-dry ice interface where sublimation is occuring
and we would expect the temperature to be >= -78C, yes?
Perhaps a good experiment be to freeze a low temperature thermometer in
some CO2 and see if this cooling of CO2 below the sublimation point is
the real cause of bath temperatures lower than -78C. (Aside from a few
degrees possibly due to solvent evaporation.) I, unfortunately,
don't have the capability of doing this experiment myself.
Anyone care to try?
>When I worked with slush baths for ten years, I found the limiting factor was
>the freezing point of the solvent used. So if you use ether, you'll be able to
>cool it with liq N2 to about -120oC before it solidifies. And if your Dry Ice
>is very cold, yes, you can get it down to about -100oC.
>You are confusing minimum _possible_ temp at which the bath will still be
>_liquid_ with the temperature you will normally get down to. As most of us use
>Dry Ice which IS at about -78, that's the normal limit, give or take a few
>degrees for evaporative cooling.
>
>If you use a solvent which solidifies at, say, -40oC, then that is the
>_practical_ limit at which your slush bath becomes a solid and very dificult
>to handle. Hence some of the high temperatures quoted by other posters.
FYI, acetonitrile, for example, is a bath solvent I've commonly used with
a freezing point of -44C. Similarly, salt-ice water baths can get down
to around -15C or so if you add dry ice.
>John G Wright
Regards,
Derek
David J Heisterberg
>several writers have mentioned using ether, noone seems to have pointed out the
>safety hazard when such baths are made.
Yeah, you're right, although that was probably one of the main points
the guy who started this whole thread had in mind. I seem to recall
one of the reasons for prefering the IPA bath over acetone is that
the former's ignition temp. is above the bath temperature, while the
latter's is below, so the acetone bath could be ignited.
I think we've managed to prove to ourselves that ether does not give
a stable CO2 bath temperature significantly lower than any other
solvent, so there's little need to ever use it. If it really did
give a stable -100C bath, well, it might be worth the added risk.
But nowadays LN2 is pretty cheap so there are other baths that can
be used for -100C and lower needs. It's the nitty-gritty details
like this that make me glad I'm really a computer programmer and
can do all my chemistry at precisely 0K.
>Ether slush baths should always be made in an efficient fume hood, with no
You'd think everyone would do that as a matter or course, wouldn't you?
But as they don't, it bears repeating now and again.
Ian Russell Ollmann
--- Isopropanol/dry ice is the way to go. About the same temperature as acetone/CO2
--- but the isopropanol is less volatile so the solvent lasts longer. Ether/CO2
--- is much colder; I think -100C vs -80C or so for acetone and isopropanol.
- ta...@leland.Stanford.EDU (Derek S. Tan) replied:
-- Correct me if I'm wrong, but I believe the limiting factor in terms
-- of low temperature is the sublimation point of dry ice which is
-- -78 C, yes?
Steve Miller <smiller....@picasso.ucsf.edu> rebutted:
- No, I don't think so...
- [rationalization]
- The reference for the bath temperatures given is "Purification of Laboratory
- Chemicals", 3rd edition, by Perrin and Armarego, pages 42-43.
and I now write:
The value of a reference is only so much as the information contained
within matches reality. Conjecture and citation are fine, but ultimately the
experiment must be done. If you will trust this grad student's experimental
technique, the temperature of a diethyl ether/CO2 bath is -78 degrees Celsius.
This is the temperature which my bath has held these last forty minutes. I
tried crushing the dry ice to no real effect. The bath is contained in an
insulated container with a cotton blanket over the top - the sort of bath that
one would use in a standard lab setting. The thermometer is apparently good to
-100C. If my bath requires more insulating conditions than these to reach the
theorized -100 C, then I put to you that it can't be relied on for efficient
cooling of reaction mixtures or what-have-you to that temperature. So, I must
conclude, as I hope you will, that in the absence of special conditions such
as hyper-chilled dry-ice, reduced pressure or addition of liquid nitrogen, it
is incorrect to say that the temperature of a ether/dry ice bath is -100C --
especially from the practical standpoint of a synthetic organic chemist.
Perhaps someone ought to let "Purification of Laboratory Chemicals", 3rd
edition, by Perrin and Armarego know.
Ian Ollmann
P.S. Regarding the theory that volatile solvents make for cooler baths due to
evaporative cooling, I suggest that you consider what the vapor
pressure of ether is at -78 degrees Celsius. I tried removing the
cotton blanket and the bath warmed a little. I blew on it (lots of
frosty vapor) and the temperature rose another degree. I can't quote
you a number, but I don't think that the vapor pressure (an indicator
of rate of evaporative cooling) of ether at -78 degrees Celsius is
much like that at room temp.
hamil...@ix.wcc.govt.nz
>In article <2rmasm$b...@golem.wcc.govt.nz> hamil...@ix.wcc.govt.nz writes:
>>In article <2rgldp$n...@charm.magnus.acs.ohio-state.edu>
>>>Hmm, according to Lange's:
>>>
>>> The assertion that certain baths with CO2 snow, especially the
>>> acetone bath, give a temperature materially lower than pure dry
>>> CO2 snow is erroneous. Cf. Theil and Caspar, Z. Physik. Chem.
>>> 86, 257-93 (1914)
>
>I think that the authors may have been mistaken.
No. Seeing the results coming in has been interesting. I believe
the confusion is caused by the temperature of the CO2 used.
The CO2 here is usually stored in an insulated box, but if it
was stored in a low temperature freezer it would drop lower.
Thus the bath made with it will be lower temperature.
>>Interesting, because according to the Merck Index ( 9th Ed )
>>Misc-71 the table lists
>>
>> Alcohol at 4C with solid CO2 -72C
>> chloroform with solid CO2 -77C
>> acetone with solid CO2 -86C
>> ether with solid CO2 -100C
>> solid CO2 ( dry ice ) sublimes at -78.5C
I suspect that these temperatures are the lowest useable bath
temperatures for the specific solvents. They probably start
to freeze a little below these temperatures. It seems these
are the minimum useable temperatures, _provided_ the Dry Ice
is available at those temperatures.
It seems that we should be careful when comparing cooling bath
data, as many of the ice/salt baths assume the starting temperature
is the melting point of water, but the Dry Ice cooling bath data
assumes that the Dry Ice is available at temperatures below the
sublimation temperature of -78.5C.
Thanks to all who contributed, and I think I'll still continue
to assume the bath was near -78C when using Dry Ice from our
box, but I'm now aware of a potential problem if it has been
stored in a low temperature freezer.
Bruce Hamilton
Norman L. Reitzel
>
>>
>Well in my previous post I had communicated my own experiment. Using a
>vacuum insulated dewar bath I got an ether/dry ice temp. down to -88 C
>This was measured with a thermocouple thermometer, and a regular -80 C
>thermometer showed that the temp was lower than -78 C. Someone else had
>reported reaching a lower temp. It appears to be possible to go below
>-78 C, but I don't know all the factors which determine how low you can
>get. Interesting.
>
Had you considered the effect of ambient pressure? Around -78C, the vapor
pressure of carbon dioxide is changing pretty rapidly with temperature.
From a look in the CRC tables, you could get -85C pretty easily, like
perhaps in Denver. -100C, no way. When I try it, I get -82C, in a 500ml
Dewar with chunks of dry ice in annhydrous diethyl ether. This is using a
+50C to -100C liquid thermometer of unknown origins.
------------------------------------------------------------------------
Norman L. Reitzel, Jr. | "When you live beside the graveyard,
nrei...@lonestar.utsa.edu | you can't cry for every funeral."
Blue Water Ventures, dba. | Russian Proverb
------------------------------------------------------------------------
mlb...@skcla.monsanto.com
vacuum insulated dewar bath I got an ether/dry ice temp. down to -88 C
This was measured with a thermocouple thermometer, and a regular -80 C
thermometer showed that the temp was lower than -78 C. Someone else had
reported reaching a lower temp. It appears to be possible to go below
-78 C, but I don't know all the factors which determine how low you can
get. Interesting.
Mark