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Author Topic: Fun with silica gel  (Read 196 times)

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Fun with silica gel
« on: November 27, 2009, 01:52:07 AM »
If one was to use silica gel to dry a reaction mix to help imine formation, one might want to think twice about adding acid haphazardly to the post reaction mix and cooking the volume down before work-up.

The little bit of silica gel that gets solvated & left behind, and it is a little bit, so small one would swear that all the original silica gel was accounted for, when acidified and cooked turns into a big mess down the road. Sodium silicate is an additive for all sorts of stuff one doesn't want in something one is wishing to separate. Water glass, adhesive additive, transfer agent... Sol gels get really big with very little.

Also, manufacturers of this stuff state the indicator and the structure and ability to hold water are damaged by high heat. I don't care what designer drugs desiccant table or old hive posts say, 250-300C is out of the manufacturers recommended reconditioning temps. Way out.

120-130C for 4 to 6 hours if you want to be able to reuse the stuff over and over, and who doesn't?

Prepuce1

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Re: Fun with silica gel
« Reply #1 on: November 27, 2009, 01:49:44 PM »
Mmmm. Drug pudding.

PP

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Re: Fun with silica gel
« Reply #2 on: November 30, 2009, 06:40:04 PM »
...even stranger than straight drug pudding.

The initial product from gassing looked good, but recrystallization showed the demons within. The initial product was too light for its size. ReXtal gave a plastic puck. Doubling the alcohol volume and heating, researchers could watch the sparkles of goodness go into solution leaving plasticy bits that would then dissolve. Cooking down the reXtal alcohol is when it turned to gel.

Distillation fixes almost all evils, this one included. Even with a sketchy vac, hardly any freebase was lost. Do not fear vac fractional distillation! It is our friend! Once you compare end products you will never think of proceeding with out doing it first.

Prepuce1

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Re: Fun with silica gel
« Reply #3 on: December 15, 2009, 03:57:41 AM »
One of the grand masters of this board suggested that molecular sieves are the end-all drying material. With that recommendation I purchased a pound, and have found it to be extremely effective, and much better than anything I've tried before. It can also be reused by heating it. I'm not sure it's true of all of them, but the one I have is not compatible with acids, but I believe it's find with almost everything else.

You may already know all about the matter and although I had heard of molecular sieves I've never tried one out. Knowing nothing else about your reaction, I"m wondering it this might be a better answer than silica gel. There's no way it's going to swell or go into solution. It's made of ceramics (Some sort of zeolite, IIRC.)

PP

hypnos

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Re: Fun with silica gel
« Reply #4 on: December 16, 2009, 02:40:00 AM »
hey PP what type  of things are you 'separating'? and what was it you bought a pound of? just curious amigo, ??? ,not wanting you to 'justify/prove' your comments :o
"the two things you can give away and never lose, are what you know, and how you feel...."

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Re: Fun with silica gel
« Reply #5 on: December 18, 2009, 09:07:30 PM »
That is awesome. I was bumbling down that road when you posted. Yeah, MolSieves. Just FYI, find industrial users and source there. Less questions and the stuff costs the same for a 50lb bag as it does from the local sketchy meth lab supply shops for little containers with 500g.

I was hoping for larger pieces. The big bags are "granular" in 3A. I remember old hive stuff about cones, but I'll be damned if I could find it. I know my already shit yields go even further down the drain with higher surface areas and more washings of the agent.

Another thing I am working on is the stainless container with dispensing port and tube fitting. With the tube hooked to the hydrogenator lines, the ss container/oven can be heated and vac'ed, then pressurized with dry n2 when done,once again when cool. The aspirator keeps you from having to smell the "whatever" coming off when you cook it, too. Then the same oven is a handy storage container. I guess one could even flow the n2 while pouring to keep the agent dry until gone.

Modified stove top espresso rigs or pieces of pipe tossed in the dot5 bath?

Anyone have experience with drying ovens? The ones on ebay mostly say only good to 260C and have flat glass fronts, not the most ideal shape for resisting atmospheric pressure.

Prepuce1

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Re: Fun with silica gel
« Reply #6 on: January 07, 2010, 05:38:38 AM »
My molecular sieve is 3A and comes in a paint can in 1/16 inch pellets. It has worked very well for me. I bought a single pound for $10 just to try it out since I had never used it, but larger sizes are available a much lower price per pound. I bought it from manufacturer, BTW.

As far as I know it used just like any other drying agent, but it works much better. I put some in a jar with very damp I2, left it overnight and the next day it was dry as a bone.

It can be regenerated by heating it. I've often used a microwave oven for drying dessicants, but you have to watch it. They can get hot enough to melt the glass tray in your oven.

PP
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