Drying MSs

Topic created by Charlie
on Fri, 8 Oct 2021 at 20:29

Charlie said on Fri, 8 Oct 2021 at 20:29...

Professor, some help please ;-)

I have everything together after many weeks, except for high quality 3A sieves. Still waiting to see what comes through. In the meantime, I ordered some Loudwolf 4A that I want to try to use. Recently, Loudwolf commented on Amazon that they are pre-activated. For the price, really, wow?

I want to try to regenerate some of them myself to be sure they are dry and I know we've done this dance before in another thread. I am interested in the microwave method. You said you've had success after initially breaking some Boro glass. I've read some people do a 5mm layer @ 30 second intervals and stir until there is no condensation left on the sides of the dish, and air out the microwave with a fan after a couple minutes.

What did your microwave method look like?

The Professor said on Fri, 8 Oct 2021 at 21:04...

microwave has the best chance , IMO, to dry sieve without lab gear; a standard oven doesn't get hot enough or needs 6-8 hours of run-time.
microwave ovens operate at a a frequency that vibrates water molecules, which heats them up.

you can probably find a microwave re-activation method on youtube.

IIRC, our microwave is 1100W at full power;
1100W at 50% power is 550W, 30% power is 350W.

I got sick of breaking beakers or cracking sieve, so I quit trying for 550W in 30 second bursts, but 350W at 2 minute intervals worked for me, and heated the sieve to about 360C

Charlie said on Fri, 8 Oct 2021 at 21:30...

Thanks Prof.

Those are some good tips to get me started. These are cheapo MSs so I'm not so concerned if I try and fail at first!

Charlie said on Fri, 8 Oct 2021 at 22:07...

Professor, when you're describing your microwave, are you using a standard microwave or one of the inverter microwaves like the newer Panasonics?

I have a standard microwave and I thought when I changed the power level it just cycles on and off at 100% power, so that power level 1 for example is on like 10% of the time at 100% power. Or are you using one of the special Panasonic inverter microwaves that actually reduce the total power based on the setting?

The Professor said on Fri, 8 Oct 2021 at 22:21...

It's an old school microwave

Charlie said on Sat, 9 Oct 2021 at 00:00...

Thank you Prof.

I have noticed that alcohol and reagents arrive with what looks like electrical tape sealing the caps. Is that a good idea to continue to seal them up with new electrical tape? Please remember my only experience in a lab was probably biology 101!

The Professor said on Sat, 9 Oct 2021 at 18:18...

For this preparation, the state of the alcohol isn't that important, just that it IS a primary, secondary or tertiary alcohol with a nitrosatable hydroxyl group.

The alcohol will become a bit more dilute as it is used, but that doesn't matter to this synthesis. The yield only cares that they're are x methyl groups and a hydroxyl group in the alcohol

The Professor said on Sat, 9 Oct 2021 at 18:18...

There

Charlie said on Sat, 9 Oct 2021 at 23:02...

TY Prof.

May I ask you about stir speed?

You may recall I got another stirrer because the first was way too fast. This one has a manual knob and starts at 60 RPMs. It is lab grade.

I've been testing my apparatus out trying to figure out the right stir bar. I am testing with a 300ml Pyrex beaker with the airline tubing taped to the bottom of the beaker and filled with 200ml water (to simulate starting a 1 mol n-butyl synthesis). This is placed in an 8C Pyrex measuring cup on top of the stirrer. I am having some trouble with getting a stir that is slow enough with no vortex, even at 60 rpms.

I have tried the stirbar you recommended:
https://www.amazon.com/gp/aw/d/B002VBW6YE?

The stirbar you recommended with my stirrer produced a very significant vortex.

I also tried this set:
https://www.amazon.com/gp/aw/d/B083VS17JT?

The only stirbar that tracked OK over time and didn't give me any vortex was the "Length 10mm x Diameter 4mm" from that second set. It is really tiny, like the size of a Benadryl tablet. It tracks ok, seems like it may get thrown off maybe once every 5 minutes and then goes back to being ok without any adjustment.

Now I understand that the stirbar and stirrer combination is very special and unique. It could be that my apparatus testing is not accurate because I am using water and not using alcohol and NaNO2. I understand it may change if I am using alcohol, NaNO2 & HCL and it is all cold.

Would you mind elaborating on what kind of stir I should be looking using the actual alcohol, NaNO2 & HCL? Such as very gentle, with absolutely no surface movement? Is a tiny little vortex ok or absolutely no vortex? And is it better to have too slow than too fast? (Does that make sense? In other words, can it ever been too slow of a stir?)

Charlie said on Sat, 9 Oct 2021 at 23:37...

Professor, one more question: ;-)

Is the viscosity of cold n-butyl and the NANO2 thicker than room temp water and might that change the stir bar needed?

(I plan to temporarily keep all the stirbars that I've ordered (including some that I didn't list) to see what works when I start, but I don't want to start without having at least one adequate stirbar on hand. I am concerned that the stirrer or stirbars I currently have are still not appropriate to begin, depending on your answer.)

The Professor said on Sun, 10 Oct 2021 at 02:25...

A standard stirrer should work fine with HCL; for sulfuric, very strong magnets and a beefy power supply will help to power through the precipitate.

I can set my stirrer to a slow crawl, which works fine with a crossbar flea; there's very gentle vertical agitation, with little to no vortex.

Some cheaper stirrers don't have a very powerful motor; they rely on momentum to keep things spinning, and will stall at slow speeds

The only problem I had with mine (i didn't spend $$$ or $, just $$) was that elevating the beaker just slightly above the bottom of the chilling bath wasn't working very well; I replaced the magnets inside with more powerful ones from hobby lobby.

The Professor said on Sun, 10 Oct 2021 at 02:28...

I had no luck getting this one to spin slowly

https://www.amazon.com/gp/product/B072K24X5P/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

this one worked fine after modifying the magnets

https://www.amazon.com/gp/product/B002OSX2Q0/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Charlie said on Sun, 10 Oct 2021 at 03:05...

Ty Professor,

Rewriting this as I lost the first draft.

I also tried the cheapo and returned it! Before that, I also tried a $50 digital - way too fast at 250 RPMs.

The Hanna you referenced shows it starts at 100 RPMs. My Labline starts at 60 so it should work... I believe that I will have to just see what happens when I'm into the weeds and not testing the apparatus with just water. I've been wanting to make sure I have the right stir bars on hand for when I start, but will just have to go for it once the elusive sieves arrive. (It's always one small thing missing, right?!) The calculus probably changes when the real inputs are cold?...

I got a really neat pear shaped borosilicate dropping funnel from China with an 8" long stem and glass stopcock. Should work well for this. #grinning

As for agitation, would perfection be absolutely no surface turbulence whatsoever?

The Professor said on Sun, 10 Oct 2021 at 16:53...

There's always going to be some amount of circulation; I'm suggesting that by minimizing it (particularly minimizing circulation that vigorously churns the yield back into the reactants), you get a nearly anaerobic condition.

Think of the vortex as an inverted cone; if you have 2mm of vortex, once the yield layer is more than 2mm deep, the yield will stay within its own layer; if you spin up a 1 inch deep vortex, the outer rim is falling towards the center, and will penetrate the yield layer, down into the reactant layer, plus a bit more from the momentum of the liquid.

Charlie said on Sun, 10 Oct 2021 at 17:08...

Ty Prof.

I see, that makes sense and clears things up quite a bit.

Charlie said on Sun, 10 Oct 2021 at 20:51...

Professor, would it be better to learn the technique starting with a full mol synthesis rather than a half-mol? Are the larger amounts more forgiving in any way?

The Professor said on Mon, 11 Oct 2021 at 00:11...

yes, it makes a difference. If you are preparing 100ml (nearly a full molar batch), when compared to preparing a 10ml batch (sounds ridiculous, but at least one 'specialist' here used to do what he called 'micro brews' to save on reactant costs if a batch was lost.

It's virtually impossible to attain reaction control with such small batches.

The problem with doing that (trying to prep 10ml instead of 100ml for example); it magnifies any measuring errors by 10, it requires even MORE precision and regularity with the drop rate, and there is less mass available to sink heat (exacerbating the drop rate even more).

TLDR;
don't try to save on reactants by making micro batches; a half molar batch is the smallest I'd suggest. You will likely ruin a batch or several, but you'll soon get control of the reaction, whereas trying to pin down a small volume micro-brew into something that is repeatable isn't likely to be successful

Charlie said on Mon, 11 Oct 2021 at 02:24...

TY Prof.

Makes complete sense. I will start out following the guide for a full mol...I figured the guide was written that way with intent.

I have measured out the equivalent of half a mol to see what I'd be working with and even that seems to be too tedious, at least to start. The amounts are so small.