Dry Ice / Acetone "slush"

[deadman]

I was reading Science Magic by an author that I can't recall at the moment. It claimed that if you place dry ice chips into acetone it will violently boil at the beginning and the more time and chips that are applied it boils less and less until it becomes a calm slushy-like liquid.

The book claimed it reached a temperature of -166 degrees farenheit. A little more online research showed that it is most probable to be around -108.4.

The book implied that a flower could be submerged for a few seconds, pulled out and smashed like many of us have seen done with liquid nitrogen. It also claims that you can make a mercury hammer, by making a paper molding in the slush and pooring mercury into the molding inserting a pencil and waiting for it to solidify to the hammer shape.

Anyways, is there a reason this isn't used with synthesis where cold temperatures are required? Such as acetone peroxide. Or am I overlooking glassware abilities, the required temp needs to be so high for a reaction to occur? Maybe if more acid was used it would still be a suitable cooling media to keep the amount of trimeric to a maximum?

Any replies are appreciated.

[c.Tech]

It is used in some ice baths when needed but it is rare.

The temperature is way too low for most reactions and would freeze most liquids.

AP is to be kept between 5 and 10 Celsius, if it got that low everything would freeze and no reaction would happen.

http://www.frogfot.com/misc/icebath.html take a look at more dry ice baths.

[Alexires]

For AP reactions I try to keep it at -5*C but then again, -78*C is waaaaay to low.

At that temperature, you might be able to liquify Ammonia, which would be absolutely wonderful. Anyone know if thats possible?

Ammonia's boiling point is -33.34*C, so technically, it would be possible to make liquid ammonia with an Acetone/Dry Ice slurry.

Edit: Got the wrong figures, I thought -77*C for boiling sounded a little strange.

[megalomania]

Rare he says :rolleyes: I use acetone dry ice baths almost every day in the lab. I don’t even bother with gloves anymore when scooping up the dry ice. You take a hammer to break up the dry ice and drop the little bits into a Dewar flask, and then you carefully add the acetone until it fills up. The dry ice will boil vigorously at first, froth, foam, and spill if you are not careful. The super cooled acetone actually appears as a viscous oil when it is this cool; strange to think of it that way. The temperature of this bath is supposed to be -78C.

I use these as cold traps for vacuum distillations of thermally unstable materials to improve pump efficiency.

You don’t want your reaction temperature so low that it is thermodynamically frozen! For every 10C, roughly, increase in temperature the rate of a reaction doubles. The reverse is also true, cool the reaction 10C and you will slow the reaction by half. Consider also that the reaction to make AP has some water in it; I can’t specify the freezing point of a mixture of variable consistency since that depends on the formula you choose, but I imagine it may well freeze under such conditions.

Just because some reaction is performed while cold does not mean you should make it as cold as humanly possible. If that were the case then the synthesis literature would be teaming with liquid helium setups. Many reactions perform only within certain temperature ranges.

The concept you need to learn here is called “activation energy.” This is the MINIMUM energy in order for a reaction to start… An example if I may:

Fahrenheit 451, from the book, is the temperature at which paper burns. The activation energy for the combustion of paper is 451F. 450F, nothing, 450.5F still nothing, 450.999F, nada, but at 451F, whoosh! You get the picture right?

[deadman]

OK I thought that might be the case.

Also, 451 is the penal code for arson.