Author Topic: Short Questions Thread (Read 10820 times)

timecube · « **Reply #380 on:** January 30, 2010, 01:09:26 PM »

It seems to work with proper catalysis, at least for mono o-methylation. See klute's nice p-methoxyphenol write up (patent it's based off of is attached a few posts before it):

http://www.sciencemadness.org/talk/viewthread.php?tid=9835#pid116136

Is there no way to extend this to complete o-methylation, such as for methylating 5-hydroxyvanillin to 3,4,5-trimethoxybenzaldehyde?

Edit: Here we go, I think. See attached patent "Process for the production of alkyl aryl ethers"

If it's not applicable, I guess MeBr can always be used, just more work-up involved.

Prepuce · « **Reply #381 on:** January 31, 2010, 06:35:28 AM »

This thread is a great idea.

Does anyone know of a practical way of reclaiming I2 from iodoform? I've found lots of information on iodoforms in textbooks but none of them answer this question.

Thanks,
PP

timecube · « **Reply #382 on:** January 31, 2010, 07:15:18 AM »

Chloroform can be made into phosgene, which can be hydrolyzed into HCl. Both of the processes are slow, but some work on speeding them up is available.

It seems that doing similar with iodoform should give HI, which can be neutralized to NaI then oxidized with H2SO4, but it seems like more trouble than it's worth and involves poisonous intermediates.

Sedit · « **Reply #383 on:** February 01, 2010, 06:02:44 AM »

Iodoform decomposes with heat to release Iodine, there is a nice writeup on woelens page that details the process. Some I₂ is more then likely lost in the process but you should be able to sublime pure dry I2 out of the iodoform.

Prepuce · « **Reply #384 on:** February 02, 2010, 04:52:31 AM »

Sedit, i've looked all over SM and Googled, but can't find Woelen's page. The link I found at SM doesn't work.

Some of what I read during the search makes me wonder if I've asked the right question, though. I'm still pretty sure but I could be wrong.

What I'm calling iodoform is produced by combining acetone or a non-polar solvent like xylene or toluene with I2. Every non-polar solvent I've used forms this substance. It has no odor but fumes it gives off are extremely irritating to the eyes.

I've tried subliming it directly, but the clinging, runny substance evaporates at a temperature either the same or lower than the sublimation temperature of I2, so it condenses in the same form. It will also quickly contaminate any "clean" I2 in the same container.

Timecube, the process you describe is the kind of thing I had imagined, and if that's the only way I would agree it's not worth it. Thanks, though.

PP

Sedit · « **Reply #385 on:** February 02, 2010, 06:25:31 AM »

Iodoform is just like chloroform except its produced with I2 and NaOH on acetone instead of Cl2 and NaOH on acetone thru the haloform reaction. Iodoform is a solid unlike chloroform and precipitates from the reaction. Dry the iodoform in a dessicator and heat to decompose. If the link on SM does not work look thru some of his old threads he has many links to his page there. Its a wounderful page with well written and researched writeups plus many pretty pictures to look at. Truely the work of an artist I feel.

timecube · « **Reply #386 on:** February 11, 2010, 07:13:38 PM »

I tried to make a magnetic stirrer from an old motor and a few neodynium magnets. the magnets were given some spacing between them, and the poles are opposite facing so that each one attracts a different end of the stirbar. But when I tried it, rather than spinning around horizontally as expected, the stirbar just spins around its long axis. I tried taking one of the magnets off of the stirrer so just one end is magnetized, but ended up with similar results.

I haven't tried the stirbar in a proper stirrer but I can't imagine it's designed incorrectly. Do I need to try to slow down the stirrer? Maybe it's just moving the field around to fast for the stirbar to keep up.

Vesp · « **Reply #387 on:** February 12, 2010, 03:03:09 AM »

If it spins to fast, at least in my experience, the bar will fling to the side and just vibrate. Perhaps the magnetic attraction is too strong, or to weak? an odd shape of spin bar?

timecube · « **Reply #388 on:** February 12, 2010, 04:51:44 AM »

This may not be the exact length but it's the same model.

http://www.onlinesciencemall.com/Shop/Control/Product/fp/vpid/1787925/vpcsid/0/SFV/30852

They're definitely not too weak, they're doubled up neodynium magnets on each side. I'll put a pot. on it and see if starting it out slower helps. The magnets may just be spinning too fast before making a solid attraction, and it makes sense that longitudinal rotation is the path of least resistance.

Enkidu · « **Reply #389 on:** February 12, 2010, 08:05:02 PM »

Quote from: Vesp on February 12, 2010, 03:03:09 AM

If it spins to fast, at least in my experience, the bar will fling to the side and just vibrate.

This happens as well if the bottom of the flask isn't perfectly flat. For instance, my FBFs have slightly concave bottoms, so the stir bar ends up against the wall a lot.

Evilblaze · « **Reply #390 on:** February 12, 2010, 09:12:42 PM »

Has anyone got an idea how effective catalyst could be the ethylenediamine for the henry reaction between benzaldehyde and nitroethane? The goal is to form the corresponding nitroalcohol and not the nitroalkene.

The reaction would go on -10 or -15 Celsius with 1:1 molar ratio.

I know that triethylamine or diethylamine would be the best, but I don't have too much diethylamine, and I don't have any triethylamine. The other reagent what is available is guanidine or hexadecyl trimethyl ammonium bromide (what didn't gave so good yields as I thought: http://www.organic-chemistry.org/abstracts/literature/527.shtm ).

The goal would be +80% yield

timecube · « **Reply #391 on:** February 16, 2010, 09:01:08 AM »

My stirrer was just spinning too fast. It works when slowed down a bit, or at least started slow and then brought up to speed.

I've seen a number of biodiesel websites promote making sodium methoxide by combining MeOH and NaOH, but no steps are taken to remove the water that would be formed. Wouldn't any methoxide that actually forms just hydrolyze right back into NaOH and MeOH?

eg.
http://alternativefuels.about.com/od/biodiesel/ss/makebiodiesel1_5.htm

Evilblaze · « **Reply #392 on:** February 16, 2010, 12:35:04 PM »

Quote from: timecube on February 16, 2010, 09:01:08 AM

I've seen a number of biodiesel websites promote making sodium methoxide by combining MeOH and NaOH, but no steps are taken to remove the water that would be formed. Wouldn't any methoxide that actually forms just hydrolyze right back into NaOH and MeOH?

It works, just distill out the water from the reaction mix. On this patent: http://www.google.com/patents?id=7UoBAAAAEBAJ&zoom=4&pg=PA4#v=onepage&q=&f=false they describe almost 20% conversatin with actually 0 special conditions. Just boil them together and woala

There are also other ways, such as: removing the water with azeotropic distillation with abs. benzene. The benzene can be dehydrated again with CaCl2 and the reaction goes on (:

So we don't need to use the valuable sodium to produce NaOEt/NaOMe.

Another thing:
Some cases magnesium methoxide and ethoxide can be also used instead of the sodium alkoxides. Mg-methoxide is also an easy compound, just add activated magnesium to hot alcohol and it will react.

//A sodium-ethoxide thread would be useful for the forum, what do you think?

Prepuce · « **Reply #393 on:** February 16, 2010, 05:43:43 PM »

Quote from: timecube on February 11, 2010, 07:13:38 PM

I tried to make a magnetic stirrer from an old motor and a few neodynium magnets. the magnets were given some spacing between them, and the poles are opposite facing so that each one attracts a different end of the stirbar. But when I tried it, rather than spinning around horizontally as expected, the stirbar just spins around its long axis. I tried taking one of the magnets off of the stirrer so just one end is magnetized, but ended up with similar results."

The problem is that the neodymium magnets have the poles on the front and back surfaces, but your stirbar magnets have them at either end. You should replace the neodymium magnets anyway, as they will permantently lose their magnetism when exposed to heat.

PP

Prepuce · « **Reply #394 on:** February 16, 2010, 05:52:05 PM »

Quote from: Sedit on February 02, 2010, 06:25:31 AM

Iodoform is just like chloroform except its produced with I2 and NaOH on acetone instead of Cl2 and NaOH on acetone thru the haloform reaction. Iodoform is a solid unlike chloroform and precipitates from the reaction. Dry the iodoform in a dessicator and heat to decompose. If the link on SM does not work look thru some of his old threads he has many links to his page there. Its a wounderful page with well written and researched writeups plus many pretty pictures to look at. Truely the work of an artist I feel.

This was the reason I started questioning whether I was really dealing with iodoform, then I remembered that any time I have I2 and acetone or a NP, it always makes it's way into a basified solution before attempts at recycling begin. I'll try drying and heating, thanks.

I did look around at many of his posts are SM, and tend to agree with your impression. I did find his website as well, just couldn't find the particular topic. No big deal, though, as I think you've straightened it out for me.

Cheers,
PP

timecube · « **Reply #395 on:** February 16, 2010, 06:33:11 PM »

Quote from: Prepuce on February 16, 2010, 05:43:43 PM

The problem is that the neodymium magnets have the poles on the front and back surfaces, but your stirbar magnets have them at either end. You should replace the neodymium magnets anyway, as they will permantently lose their magnetism when exposed to heat.

PP

I have them separated a bit with a different pole facing up on each side. This lets it line up properly and attracts the stirbar just fine. I just had it spinning around too fast to begin with, and the inside surface of the jar I was using was a bit curved.

The cheapest neodymium/neodymium alloy magnets (which these probably are) still have a Curie point around 150C, so as long as I can keep them somewhat insulated it should be alright I believe. I have a thin insulating plate from an old clothing iron that originally separated the heating element from the cheap plastic case. I have access to oven insulation too, which I should be able to use to make the whole thing a lot more efficient.

timecube · « **Reply #396 on:** February 16, 2010, 07:38:34 PM »

Thanks too for the alkoxide patent. The ethoxide is what I was interested in, and the water removal should apparently be pretty easy given the lower boiling azeotrope which I wasn't thinking about.

I still don't see how the methoxide version is working for the biodiesel makers unless the vegetable oil is reactive enough with the methoxide to use it up before it can be hydrolyzed. Then it seems you would have a lot of water in your fuel.

Enkidu · « **Reply #397 on:** February 16, 2010, 07:59:52 PM »

I was under the impression that the NaOH/MeOH/Toluene method doesn't really work doesn't work for MeONa.

Prepuce · « **Reply #398 on:** February 18, 2010, 07:20:29 AM »

Quote from: timecube on February 16, 2010, 06:33:11 PM

I have them separated a bit with a different pole facing up on each side. This lets it line up properly and attracts the stirbar just fine. I just had it spinning around too fast to begin with, and the inside surface of the jar I was using was a bit curved.

You're right, of course. I wasn't thinking clearly. It would only be a problem if your stir bar was the magnet with the poles on the flat sides. That might be interesting to watch, though.

When I first made my stirrer I used neodymium magnets recovered from a hard drive, and after the first use they were too weak to do the job. I had a heat shield around them, too, but 150 degrees isn't that hot. When I changed to alnico I lost a bit of "magnetic power", but these are good up to about 500 degrees C, and I haven't had any trouble since.

Hopefully your heat shield is better than mine. It would be nice to have such strong magnets. I've been thinking of using electromagnets (eliminates the need for a motor but requires a controller) but haven't yet tried it. With enough current it should be possible to make a pretty strong stirrer.

PP

timecube · « **Reply #399 on:** February 19, 2010, 08:08:05 AM »

I may just be using this as a lone stirrer now for when a second stirrer is needed (some methylation setups come to mind.)

The hot plate side of this foray had a few design flaws that have put it on hold for a while. I did learn a few interesting things, though.. like that an unregulated heating element from a standard clothing iron can get hot enough to melt 1/8 inch aluminum into a drooping blob.

On an unrelated note, I was reading through a nice paper lately on the synthesis of allylbenzenes and noticed this:

Quote

We studied the effect of the temperature, molar ratios of the components and the reaction time on the yield
of the alkenylaromatic hydrocarbons. It was observed that the alkenylation with allyl alcohol in the presence of
zinc chloride does not go at a temperature below 110 ~ for which reason the alkenytation of benzene was run in
undecane solution.

How does this allow the entire mixture to rise to 110 rather than the benzene and alcohol just distilling out?
Would another high boiling solvent sub in or would this normally need to be done in a pressure bomb?

Author Topic: Short Questions Thread (Read 10820 times)

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