Author Topic: Optimum drying temperature for LSA?  (Read 10947 times)

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luminescent

  • Guest
Optimum drying temperature for LSA?
« on: September 01, 2004, 02:50:00 PM »
Can anyone here give any specifics on the optimum drying temperature for LSA under 30'hg reduced atmos?


Lilienthal

  • Guest
RT
« Reply #1 on: September 01, 2004, 04:53:00 PM »
RT

armageddon

  • Guest
as low as possible
« Reply #2 on: September 01, 2004, 06:32:00 PM »
As low as possible (depends on how much time you can spare for the drying step; lower temp. = more time = more gentle drying).

Greetz, A


luminescent

  • Guest
Gradual increase
« Reply #3 on: September 01, 2004, 07:12:00 PM »
Vacuum was first turned on to 30"hg then vacuum oven was turned on and heated up to 90C over a 5 hour period then turned off.Waiting till oven temp cools to 25-30C then slowly equalizing threw bleed valve.Then weighed.


armageddon

  • Guest
not good
« Reply #4 on: September 01, 2004, 07:14:00 PM »
Too much heat. Try 30-40°C next time to avoid partial decomposition. The "heat" function is mainly for hard-to-dry compounds, not sensitive ones!


luminescent

  • Guest
Psychedelic chemistry
« Reply #5 on: September 01, 2004, 07:46:00 PM »
Michael valentine smiths book

Psychedelic Chemistry says:

on page 125.

filter cake is broken up and dried to constant weight under high vacuum at 90C in a dessicator.Or An oven I presume.


armageddon

  • Guest
?
« Reply #6 on: September 01, 2004, 09:05:00 PM »
Why do you ask then?  ;D

My opinion is that 90° are too much, especially when 30mmHg are applied - as water boils at far below this temperature with this pressure..

(Don't you trust "Psychedelic Chemistry" on that one?  :)  Or is it because you were unsure about oven/desiccator? In the latter case: I can reassure you that it makes no difference...)


hest

  • Guest
Vacuum
« Reply #7 on: September 02, 2004, 12:30:00 AM »
use torr *grrrr* nothing else.
30"Hg isent tat like 0 torr ????

../rhodium/chemistry
/equipment/conversion.html


Look at

../rhodium/chemistry
/equipment/nomograph.html

and wather boils at 0°C @ 10 torr so mopre than that is overkill

Lilienthal

  • Guest
The boiling point of pure water is completely...
« Reply #8 on: September 02, 2004, 01:57:00 AM »
The boiling point of pure water is completely irrelevant in this context, simply because we don't have pure water but traces of water sticking to something. 30 mmHg is a shitty vacuum, you can reach it with water suction pumps. Melting or decomposition points have nothing to do with a compound's stability under real world conditions, e.g. in the presence of water or oxygen over longer times. Ergolines are known to be sensitive, so why heat them above RT? Beside that, I can't imagine why somebody needs ultra-dry ergolines for synthesis. Just use a slight excess of reagents in the next step. A desiccator is a good alternative to dry compounds in a closed vacuum over drying agent (e.g. CaCl). And better use a better vacuum source, i.e. an oil pump, 30 mmHg is not much, and if you draw it from a water pump it makes even less sense to use that vacuum to dry compounds (at least without a liquid nitrogen trap or a column of drying agent).

hypo

  • Guest
inches!
« Reply #9 on: September 02, 2004, 03:06:00 AM »
> 30 mmHg is a shitty vacuum

of course the original poster was talking in inches and not absolute, but inches
relative to outside pressure which (of course) he didn't give us. (my pet peeve -
what's the fascination with nonsensical units? ARGH!)


armageddon

  • Guest
vac strength and ambient pressure
« Reply #10 on: September 02, 2004, 04:31:00 PM »
Hypo:
When talking about evacuated vessels on this planet  :) : diminished pressure is the difference between outer pressure and remaining pressure.

So every kind of vacuum measurement (mmHg, torr, mbar or whatever) depends on the ambient pressure, i.e. weather or vertical position relative to MSL (mean sea leavel). The number is just the difference between the ambient pressure that pushes from the outside against the (glass) walls of the evacuated vessel, and the remaining (diminished) pressure that pushes against it from the inside. When there is no diminished pressure inside the vessel, the inner pressure equals the outer pressure, but as said: every type of vacuum measurement depends on the ambient pressure - but this is commonly known to be ~760torr or ~1000mbar. Only occasion where I personally would try to work with different standard ambient pressures in when living in a gold mine, 100 feet under the surface, or maybe if I would have my lab space on top of the himalaya - or maybe inside the eye of a hurricane or a place with other pressure anormalities... :)  (come on, make yourself a nice, handy table and you don't have to bother with different measurement units anymore)

Anyway - dry your LSA at room temp, as said this will suffice. No matter if the bp of water matters or not, 90°C is quite a bit too high. And although the bp of water plays no role in drying processes, according to lilienthal: I'm quite sure that as long as there aren't any salts or other hygroscopic substances present, heating under vacuum until the water begins to boil helps a lot in drying. As long as the water will be vaporized, the only remainder will be the small amnt. of vapor filling the vessel at your achievable vacuum. Everything else is simply sucked away. And if I'm wrong; please feel free to correct me - as long as the correction is reasonable and not only a statement  ;) .

PS. about "shitty vacuum": on the moon, 30 mmHg (relative) means a lot less remaining vapor than 30 mmHg on earth. And the moon is indeed pretty dry...  ;D

Greetz A


Bubbleplate

  • Guest
Lysergic Acid Is Not That Sensitive
« Reply #11 on: September 02, 2004, 07:30:00 PM »
The melting point/decomposition temperature of Lysergic Acid is approx. 240 C.
In order to obtain Anhydrous Lysergic Acid, it needs to be heated at a fairly high temperature in a very good vacuum.
Lysergic Acid obtained from alkaline hydrolysis of ergot alkaloids crystalizes out with 1 mol. of H2O:

../rhodium/chemistry
/ergotinine2lysergic.html


"Lysergic acid (although rather sparingly soluble) can be recrystallized best from water. It crystallizes as very thin hexagonal leaflets which melt with decomposition at 238°C. The melting point varies somewhat with the rate of heating. Repeated recrystallization failed to raise the MP. It separates with approximately 1mol of water of crystallization. This water is held very tenaciously and can be removed completely only on drying at 140°C/2mmHg."

IMHO, If one is going to use Lysergic Acid in a reaction that utilizes moisture sensitive chemicals (i.e. the CDI LSD synthesis) it is better to use anhydrous Lysergic Acid then to have moisture form and "use up" the other chemicals such as N.N. Carbonyldiimidazole, etc.

hypo

  • Guest
[OT] what?
« Reply #12 on: September 03, 2004, 01:04:00 AM »
sorry, as usual i have to disagree.  ;)

> So every kind of vacuum measurement (mmHg, torr, mbar or whatever) depends on the
> ambient pressure

this is definitely not true (i object the every): high vacuum measurement works with
conductivity or stuff like that and depends on the type of gas inside the vessel. or how
do you think your barometer works - against which outside pressure would it measure?

chemists aren't interested in the pressure difference at all (as long as the reaction
container survives it). it's all about the force per surface _inside_ the vessel. because
that will matter in respect to where your liquid boils.

> but this is commonly known to be ~760torr or ~1000mbar.

erm, the problem is the "~". suppose i have nice weather and 1010mbar ambient pressure.
i evacuate my vessel to 10mbar and proudly proclaim: "i've got a 1000mbar vacuum!". how
is anyone supposed to know that the weather at my place is nice and i got an ok 10mbar
vacuum instead of an fantastic 0.1mbar vacuum? do you see the problem?

of course cheap vacuummeters are useless for measuring good vacuums.

(and i guess we both agree on the madness of inch Hg or pound per square inch,
relative or not  ;) )


armageddon

  • Guest
It's all about the force per surface ..
« Reply #13 on: September 03, 2004, 04:15:00 AM »
It's all about the force per surface _inside_ the vessel. because
that will matter in respect to where your liquid boils.
.

Well, the force can't work "from the inside" - the air of our beeloved atmosphere (20 km of air with varying density I think) pushes against the glass walls of the chemist's flask, but the remaining little amount of gas (of whatever type - do you know the "perfect gas" thing BTW?) pushes against the flask wall from the inside with far less power.

So the vacuum measurement will be always the difference between inner and outer pressure, and in a completely gas-free environment (the space for example), a vacuum of exactly 0 torr means no pressure difference between inside and outside of any vessel - your pump won't work..

But when deep inside a coal mine (like a few hundred meters below the surface), a non-evacuated vessel will always have like 790 torr pressure, but a vacuum pump wouldn't be able to pull as much as on the surface (again because the pump works against the atmospherical pressure, which is of course higher when below MSL), resulting in more remaining pressure inside the vessel, too - and thus, the proportions of outer to inner pressure stay the same, no matter if you evacuate your vessel on a mountain or in a cave.

(water will boil at 91°C on the mount everest, and with your pump, you will be able to bring it to a boil at (standard)*0.91 degrees; with (standard) being the temp. at which water boils with your achievable vacuum when you're on the ground)

erm, the problem is the "~". suppose i have nice weather and 1010mbar ambient pressure.
i evacuate my vessel to 10mbar and proudly proclaim: "i've got a 1000mbar vacuum!".


That is indeed a problem - but only if you insist on calculating with ambient pressures other than 1000 mBar...  ;D

(and -1000mbar vac strength is OK, as long as ambient pressure is 1010mbar cuz the difference is still 10mBar; and that's how you measure vacuum strength... The only difference would be if you're using a multiple-stage vacuum system with several pumps, as their achievable individual vacuum then depends on the vacuum strength of all other pumps - then "absolute" and nor "relative" measurement is what is called for, together with the use of a big compensation vessel between last pump and trap)

Greetz


hypo

  • Guest
armageddon!
« Reply #14 on: September 03, 2004, 04:41:00 AM »
think before posting, please!

> Well, the force can't work "from the inside"

but of course it does! the "force" is the kinetic energy of the molecules hitting
against the walls of the vessel.

> the air of our beeloved atmosphere (20 km of air with varying density I think) pushes
> against the glass walls of the chemist's flask

so? what is your point. the glass has to bear the pressure difference (action, reaction
until it breaks), but how does that relate to anything?

> So the vacuum measurement will be always the difference between inner and outer pressure

it's NOT. please check google for how high-vacuum measurement works, it does NOT
measure the pressure difference!

>  the difference [...] the proportions of outer to inner pressure

hello? first you're talking about difference, then about proportions! you know the
difference of multiplication and addition, don't you?

are you seriously telling me that a pump that does 10-4 mbar on a bad weather day
does only 30mbar on a good weather day??? do you REALLY mean that???


MargaretThatcher

  • Guest
Vacuum Measurement
« Reply #15 on: September 03, 2004, 07:04:00 AM »
A true vacuum measurement is an absolute one. Gauges however do not always measure absolute pressure. When you give a pressure measurement, you should always state what type of measurement it is, otherwise it is assumed to be an absolute measurement. There are 3 types of gauge measurement:

Absolute - the real pressure

Differential - pressure difference relative to another pressure

Gauge - pressure wrt to the gauge environment (i.e. atmospheric)


The pressure that luminscent originally stated was 30"Hg negative gauge pressure. Hypo is entirely correct.

Measurements should be given in SI units with multipliers of thousands thereof (there is an exception for the hectopascal, used to replace the millibar for meterological measurements - 1 mbar = 1 hPa).

The SI unit is the Pascal, Pa.
1 bar = 100 KPa.
1 mmHg = 133.332 Pa.


armageddon

  • Guest
hypo!
« Reply #16 on: September 03, 2004, 10:08:00 AM »
are you seriously telling me that a pump that does 10-4 mbar on a bad weather day
does only 30mbar on a good weather day??? do you REALLY mean that???


I am just telling that it doesn't matter if luminescent had used 30mmHg absolute or relative vacuum - and that you shouldn't start to cry each time you encounter a wierd type of measurement.

And you can tell what you want: vacuum here on earth always depends on the strength of the outer pressure AND the strength of the counterpressure that the gases inside the evacuated vessel put on. Simple physics, no chemistry.

------> | <-- (remember that? Where's the vacuum?)




Margaret_Thatcher:

Differential - pressure difference relative to another pressure

Gauge - pressure wrt to the gauge environment (i.e. atmospheric)


Where's the difference??

;D

A


Rhodium

  • Guest
Vacuum does not vary with the ambient pressure
« Reply #17 on: September 03, 2004, 12:03:00 PM »
And you can tell what you want: vacuum here on earth always depends on the strength of the outer pressure AND the strength of the counterpressure that the gases inside the evacuated vessel put on.

The pressure (= vacuum) inside an evacuated vessel does not vary with ambient pressure - that is only true for the maximum attainable vacuum with a certain vacuum pump, assuming everything else is held constant. It can also be true to a certain extent if the vessel isn't completely rigid (such as a football).

A rigid flask evacuated to 50 torr (absolute vacuum) and then sealed will have a constant pressure (= vacuum) inside, regardless if I place it on my desk (ambient pressure ~1000 torr), on the top of Mount Everest (~250 torr) or if sinking it at the deep end of the swimming pool (~1500 torr).






Pressure Levels and Terminology
http://www.kinequip.com/pressure_terminology.asp

Atmospheric Pressure — The atmosphere that surrounds the earth can be considered a reservoir of low-pressure air. Its weight exerts a pressure that varies with temperature, humidity, and altitude.

For thousands of years, air was considered weightless. This is understandable, since the net atmospheric pressure exerted on us is zero. The air in our lungs and the blood in our cardiovascular system has an outward pressure equal to (or perhaps slightly greater than) the inward pressure of the outside air. Since we feel no pressure, we are unaware of the air's weight.

The weight of the earth's atmosphere pressing on each unit of surface constitutes atmospheric pressure, which is 14.7 psi (101,300 Pa or 0.1013 MPa) at sea level. This pressure is called one atmosphere. In other commonly used units, one atmosphere equals 29.92 inches of mercury (in. Hg), 760 mm Hg (or 760 torr), and 1.013 bar(1 bar=0.1 MPa).

Since atmospheric pressure results from the weight of the overlying air, it is less at higher altitudes. As Fig. 3 shows, atmospheric pressure in Denver, Colorado (altitude 5,280 feet), is only 12.2psi. And in Mexico City, Mexico (altitude 7,800 feet), it is 11.1 psi. On top of Mount Everest, the pressure has fallen to one-third of an atmosphere.

Atmospheric pressure also varies from time to time at a single location, due to the movement of weather patterns. While these changes in barometric pressure are usually less than one-half inch of mercury, they need to be taken into account when precise measurements are required.

Gauge Pressure — Atmospheric pressure serves as a reference level for other types of pressure measurements. One of these is "gauge pressure."

Gauge pressure is either positive or negative, depending on its level above or below the atmospheric pressure reference. For example, an ordinary tire gauge showing 30 pounds (actually, 30 psi) is showing the excess pressure above
atmospheric. In other words, what the gauge shows is the difference between atmospheric pressure and the pressure of the air pumped into the tire. Gauge pressures can be either positive (above atmospheric) or negative (below atmospheric). Atmospheric pressure represents zero gauge pressure.

Absolute Pressure — A different reference level is used to obtain a value for "absolute pressure." This is pressure measured above a perfect vacuum. It is composed of the sum of the gauge pressure (positive or negative) and the atmospheric pressure. Where there might be confusion, gauge and absolute pressures are distinguished by adding the letter "g" or "a," respectively, to the abbreviation for the units ("psig" or "psia").To obtain the'absolute pressure, simply add the value of atmospheric pressure (which averages 14.7 psi at sea level) to the gauge pressure reading. To find the current value of atmospheric pressure in psia at a given location, multiply the barometer reading in in. Hg by 0.491. This conversion factor arises from the fact that a cube of mercury with one inch sides weighs 0.491 pound and thus exerts a pressure of 0.491 psi.

Using the simple tire pressure example, the absolute pressure including the atmospheric pressure—exerted by the air within the tire is 44.7 psia (30 psig plus 14.7 psi). Thus, the absolute pressure is 14.7 psi more than would be read on a tire-pressure gauge. Absolute pressure must be used in virtually all calculations involving pressure ratios.

Vacuum — Vacuum is a pressure lower than atmospheric. Except in outer space, vacuums occur only in closed systems.

In the simplest terms, any reduction in atmospheric pressure in a closed system may be called a partial vacuum. In effect, vacuum is the pressure differential produced by evacuating air from the system.

In a vacuum system more sophisticated than a suction cup, the enclosed space would be a valve actuator or some appropriate work device. A vacuum pump would be used to reduce atmospheric pressure in the closed space. The same principle would apply, however.

By removing air from one side of an air-tight barrier of some sort, atmospheric pressure can act against the other side. Just as with the suction cup, this action creates a pressure differential between the closed system and the open atmosphere. The pressure differential can be used to do work.

For example, in liquid packaging (bottling), reducing the pressure in a bottle (the enclosed space) makes the filling operation go much faster because the liquid or other material is literally pulled into the bottle, rather than simply falling by gravity.

Vacuum is usually divided into four levels:

Low vacuum represents pressures above one torr absolute. Flow in this range is viscous, as represented by most common fluids. Mechanical vacuum pumps are used for low vacuum, and represent the large majority of pumps in industrial practice.

Medium vacuum represents pressures between 1 and 10-3 torr absolute. This is a transition range between viscous and molecular flow. Most pumps serving this range are also mechanical.

High vacuum represents pressures between 10"3 and 10"6 ton absolute. Flow in this region is molecular or Newtonian, with very little interaction between individual molecules. A number of specialized industrial applications, such as ion implantation in the semiconductor industry, fall in this range. Nonmechanical ejector or cryogenic pumps (which are not discussed in this book) are usually used.

Very high vacuum represents absolute pressures below 10-6 torr. This isprimarily for laboratory applications and space simulation, Keep in mind that a "perfect" vacuum—that is, a space with no molecules or atoms—is a purely theoretical condition. Only in interstellar space is this condition approached at all closely, and even there a few atoms per cubic meter will be found. In practice, all vacuums are partial.



MargaretThatcher

  • Guest
Gauge vs Differential
« Reply #18 on: September 03, 2004, 12:29:00 PM »
Yes, gauge pressure is a type of differential pressure. You could argue that direct pressure measurement gauges (mercury, etc.) are all forms of differential gauges.

The confusion arises because most gauges are differential rather than absolute and the reference pressure (atmospheric) is not fixed.

As lil. says, you'll need a good pump to outgas water vapour from the crystals. On glass certainly, you need heating at 300 C under vacuum to remove the adsorbed water. Hopefully the water trapped in the crystals isn't as strongly bound as that.


armageddon

  • Guest
I just wonder how the following can be explained:
« Reply #19 on: September 03, 2004, 03:51:00 PM »
I see...

So I can bring a big thick-walled suction flask labelled "Max. 3 bar" on the mount everest, connect it to my hyper two-stage rotary-vane pump I brought with me  :)  and evacuate it to let's say, 10-5 torr. Then I go back to MSL and bang! - somewhere on my way, the flask will explode. Or won't it? I wonder why they print "max. 3 bar" on it (brand manufacturer BTW)... - since according to what you (Rhodium) said, the outer pressure doesn't influence the vacuum inside the suction flask! And although haven't tried it yet, I'm quite sure that glassware being able to withstand high vacuum on the K2 will crack when same thing is done in the Netherlands...

Beecause the imprint "max. 3 bar" maybee has some meaning, and perhaps it is like I said and every vacuum on earth (inside a pressurized atmosphere) depends on the outer pressure??

And nevertheless: if the goal wasn't getting anhydrous lysergic acid but monohydrate, 90°C is pretty much too high. Despite using mmHg (without specifying whether it is absolute, relative or "gauge")....  ::)

Greetz!