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Ebao-lu
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Vanillin indeed seems to be quite an unusual aldehyde. Thus, it does not undergo Cannizzarro at all, because of OH group in p-position. I dont know
why it happens, probably because OH is deprotonated by base first, and the phenoxide anion is stabilized via delocalization and conjugation with CHO
group, giving a structure like O=C6H3(OCH3)=C(O-)H, that can't further be attacked by OH- like aldehyde at carbonyl. I donk know wether it can undergo
1,6 michael OH- addition into same position, but either because of electrostatic repulsion it can't, or because the resulting product is present at
very low concentrations in equilibrium, or because it further can't be deprotonated because of there are already 2 negative charges in the molecule.
And anisic aldehyde unlike vanillin can undergo cannizzarro, because there is no OH
As for acetal formation, on the one hand this problem should be deminished in acidic conditions, but on the other - OH group is still much better
electron donor to be conjugated with CHO(then for example OCH3), because H is more flexible. This difference can also be critical to form an acetal
with acid/EtOH. The case is not all carbonyl compounds can give acetals (at appropriate rate of reaction, or equilibrium constant) with using ethanol
and acid, thus ethyl ortho-formate is used for making acetals of arylalkylketones. Maybe vanilin is also a problematic carbonyl conpound in this
regard
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kclo4
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Does anyone know how to determine if a chemical will pass the blood brain barrier?
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sparkgap
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Usually, you can reasonably suspect that a drug possessing predominantly lipophilic (a.k.a. nonpolar) groups, or can be metabolized to something like
that will pass the blood-brain barrier.
sparky (~_~)
"What's UTFSE? I keep hearing about it, but I can't be arsed to search for the answer..."
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Sedit
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Im starting to create some lead electrodes for an electro chemical cell.
Now I have to admit that I am scared of this.
Im a plumber by trade and have used the material Im making the electrods out of many many times,(old plumbing pipes), yet working with them the right
way scares the hell out of me(go figure).
How can I minimize any risk I might have and what may they be?
Please dont say lead poisoning because yes I understand that but what is the biggest concern with this? Salts seem pretty scary due to there
solubility.
What other concerns does one have and has most worrys been "over rated"?
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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querjek
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| Quote: | Originally posted by kclo4
Does anyone know how to determine if a chemical will pass the blood brain barrier? |
I believe I heard once that its MW had to be below 600 or 550ish or something, but don't quote me on any of that...
it's all about chemistry.
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chemrox
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I tried registering at thevespiary and was blocked by yet another silly riddle. This time one had to know something about a movie I would probably
never see. It's too bad becaue it seemed like an interesting site but the honchos seem to be making sure all their members share common esthetic
values. Thanks all the same.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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Sedit
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? Iv never seen any riddle chemrox, are you clicking the link provided here?
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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Paddywhacker
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| Quote: | Originally posted by Ebao-lu
Does anyone know about vanillin diethylacetal (or other, maybe cyclic acetal) synthesis? Can it be made from vanillin/alcohol + acidic catalyst(like
with benzaldehyde, piperonal, anisic aldehyde)? Or it is less reactive and requires ethyl ortho-formate?
... |
Acetal formation can be catalyzed by H2SO4 or by toluene sulphonic acid, but perhaps the nicest catalyst is acid ionic resin, especially if you wash
the junk out of it with methanol first.
But acetal formation is very sensitive to water. Sometimes, even a Dean & Stark will not help because the amount of water that can dissolve in
the hot toluene is enough to scupper the equilibrium.
One of the best procedures is to use a zeolite molecular seive in a soxhlet apparatus to trap the water from refluxing toluene. Unfortunately you
don't get a visual confirmation of the reaction the way that you do by watching water accumulate in a Dean & Stark.
But another way to make difficult acetals is to trans-acetal from excess of a lower molecular weight acetal. For example, an acid catalyst plus
excess of the ethylene glycol acetal of acetone would probably work. The acetone would come off at it's boiling point, driving the reaction forward.
But you'd still need to exclude water with a drying tube, etc.
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Nicodem
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| Quote: | Originally posted by kclo4
Does anyone know how to determine if a chemical will pass the blood brain barrier? |
You might want to read about the Lipinski's Rule of Five (and the links therein). The part most pertaining the absorption trough various lipid bilayer membranes, like the blood-brain barrier and similar, is the rule about the logP upper and lower limits. If the logP is too high (the compound being too lypophilic)
the drug gets absorbed in the lipids. If it is too low (the compound being too hydrophilic) then it can not pass trough the hydrophobic blood-brain
barrier and is rapidly excreted by the kidneys. Molecular size is less important, but must be whiting the limits of the rule just like all the other
parameters. Of course, the prerequisite is metabolic stability, or else the compound never makes it to the target organ.
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Ebao-lu
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| Quote: | | But another way to make difficult acetals is to trans-acetal from excess of a lower molecular weight acetal. For example, an acid catalyst plus excess
of the ethylene glycol acetal of acetone would probably work. The acetone would come off at it's boiling point, driving the reaction forward. But
you'd still need to exclude water with a drying tube, etc. |
Rather a nice idea. Distilling off acetone will drive the equilibrium to yield more high MW acetal.
By excluding of water, you mean there would be another haemorrhoidsm making the aceton ethylene acetal itself?(because water-toluene azeotrope is
bouling at higher t then acetone). Is it possible to use petroleum ether instead (as its aseotrope should be boiling at lower point then acetone)? As
for the traces of water while reaction of acetone ethyleneacetal + vanillin should not play a big role afaik, because of acetone is distilled off and
water is generally consumed (either by direct hydrolysis of acetone ethyleneketal, or while hydrolysinig of the resulting vanillin ethyleneacetal).
As for acid catalysts, i dont yet know what will be used. I've planned boric acid but found that it is not used to make acetals (though it is a nice
catalyst for esters). Sometimes NH4Cl is used as a catalyst, but in those procedures the RM should stay for several days, so this catalyst is not
quite good. I dont have toluenesulfonic acid also, and have only a dilute solution of H2SO4. Maybe NaHSO4 is usable?
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Ebao-lu
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2 Sedit: Pb is toxic as a vapour (if molten), and as Pb2+ (if ingested), you need only to enquire if Pb2+ can pass through the skin. I dont see any
other potential hazard with Pb. Just protect yourself from physical contact with the solution(even if it does not pass through skin), and from
ingesting it. If the solution from electrochemical cell would be further used, you can analyse the Pb2+ content there and reduce it using some
reagents like Na2S. The same you can do with a waste solution. If there are oxides like PbO, Pb3O4 etc - dont utilize the waste solution in a back
yard, find some special place(and convert Pb to the most inert salt like PbS)
Sorry but do want to compose _anode_ from Pb? You will get plenty of Pb2+ in solution. Resistant anodes are made from PbO2. Myabe there is some way
to "passivate" Pb surface making it PbO2, but i don't remember if it is possible(probably yes).
[Edited on 6-3-2009 by Ebao-lu]
[Edited on 6-3-2009 by Ebao-lu]
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kclo4
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All right, so I am wanting to make some Fatty acid amides.
I was planning on making them by mixing the fatty acid, with urea and heating. This idea was inspired by ScienceSquirrel in his post:
"ScienceSquirrel - 7-9-2008 at 10:36
One of the nicest preparations of acetamide is heating acetic acid with urea. The byproducts are ammonia and carbon dioxide and the acetamide is
distilled using an air condenser."
I don't have the free fatty acids, they are in trigylcerides. I don't really want to bother with making the fatty acid since I don't have much free
time for this and I am running low on sodium hydroxide. Would it be possible for me to react Urea with the triglyceride to form the amides and have
glycerol or something related left behind?
It would be nice if it worked, but I'm not to sure I can see how that reaction would happen.
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Paddywhacker
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Re: Urea plus triglycerides
Something happens, that's for sure.
When heating about 1g urea and 5 ml olive oil in a boiling tube the urea initially dissolves.
On further heating there is a boiling action with the evolution of volatiles. No noticable smell. Non-inflammable.
On strong heating there are whitish fumes given off and a white solid lump develops in the liquid.
There is scope here for somebody to investigate further and report your observations.
Good luck.
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kclo4
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you did this? Thank you very much I find this useful and very interesting!
Think this reaction produces fatty acid amides?
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Paddywhacker
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| Quote: | Originally posted by kclo4
you did this? Thank you very much I find this useful and very interesting!
Think this reaction produces fatty acid amides? |
No problem. Everything was to hand, so I had to give it a go.
I have no idea if the amide was formed.
After posting, the mixture had cooled. I added about 10 ml isopropyl alcohol and heated to boiling. The oil and alcohol misced together, but the
white lump remained apparently unaffected.
I poured off the alcohol/oil mixture and washed the white lump again with alcohol. The combined alcohol/oil extracts were cooled and the oil settled
out as a separate layer. No crystals or other solide were seen.
The white lump was broken up and boiled with isopropyl alcohol. It seemed not to be very soluble. The condensed white material from the fumes of
heating behaved the same as the white lump.
But I'm losing interest. This is your experiment. Pick up thy test tube and run.
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kclo4
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yeah I will when I can haha I don't get to do chemistry much. Interesting though that urea dissolves in oil. Possibly the weirdest thing I've heard in
a while.
Update for those who care.. I guess: heating urea with olive oil. urea melted and let off ammonia gas, and eventually formed solid white clumps that
did not dissolve easily in water - I suspect it was some form of melamine or something else that is a byproduct of urea decomposition. The oil seem
unaffected.
[Edited on 8-3-2009 by kclo4]
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dann2
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Hello,
Can I make K (or Na) Chromate from K (or Na) Dichromate by adding base (KOH or NaOH) to a solution of the Dichromate?
I am trying to do a Chloride titration using Silver Nitrate. It calls for Chromate as indicator. Have none. Perhaps I could add some K Dichromate
and then add base (to the solution that I am going to titrate) and that would do for the Chromate indicator?
TIA,
Dann2
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Paddywhacker
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| Quote: | Originally posted by dann2
Hello,
Can I make K (or Na) Chromate from K (or Na) Dichromate by adding base (KOH or NaOH) to a solution of the Dichromate?
I am trying to do a Chloride titration using Silver Nitrate. It calls for Chromate as indicator. Have none. Perhaps I could add some K Dichromate
and then add base (to the solution that I am going to titrate) and that would do for the Chromate indicator?
TIA,
Dann2 |
Yes that will work. You know how to work out the stoichiometry?
But it is probably unnecessary. Dilute dichromate will have plenty of chromate in equilibrium.
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dann2
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Thanks Paddywhaker,
I don't know the Stoichiometry. I was simply going to take a (not concentrated as you suggested) solution of Na Dichromate , add some NaOH solution
and use a few drops of that for the indicator. Would that be OK?
This is where I got the suggestion in the first place. http://jchemed.chem.wisc.edu/JCESOFT/CCA/CCA8/MAIN/8/08/32/m...
I have lots of Dichromate.
Will this work as an indicator for a Chloride titration in a solution of Chlorate and/or Perchlorate using silver Nitrate?.
I guess I could try.
Thanks,
Dann2
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querjek
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I need some potassium hydroxide for a reaction, but can't find any. I can, however, find potassium bicarbonate and calcium oxide.
Would the following work:
KHCO3 + CaO + H2O -> KOH(aq) + CaCO3(solid) + H2O
Then filtering the resultant CaCO3 and boiling away excess water?
Thanks!
EDIT: Well, I found some potash, which is a mixture of mostly KCl + K2CO3. Any way to precipitate out those chloride ions?
[Edited on 9-3-2009 by querjek]
it's all about chemistry.
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Picric-A
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Potassium hydroxide used to be manufactured industrially by boiling an aquous soloution of wood ash (K2CO3) with slaked lime (Ca(OH)2.
Boiling KHCO3 with CaO will first produce CaHCO3 which decomposes to CaCO3. Filtering is going to be a bummer though, that CaCO3 formed is very fine,
takes ages. May help if you Pre-decompose the KHCO3…
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kclo4
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In order to aid in filtering the calcium carbonate formed you can reflux it to encourage the particles to become larger. I hear that works with
calcium sulfate, so it should work with calcium carbonate assuming it is at least slightly soluble.
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Sedit
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Iv heard many ways of making (aq) solutions of NaOH and KOH from differnt materials but if one needed dry(as possible) caustic flakes how would one go
about evaportating these solutions with out it reacting with the CO2 in the air forming carbonates?
IE if I had (aq)solution of NaOH how can one produce pure NaOH crystals from said solution?
[Edit]
Picric-A Iv come to the conclusion that if a substance is so fine that it quickly forms that unfilterable mud then leaving it to set for how ever
long and decanting into a filter is the best method of operation. When they are that fine they seem to easyly form a solid clump on setting to make
decantment easy and high yeilding.
[Edited on 9-3-2009 by Sedit]
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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kclo4
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just boil it away. I don't think it would be able to react with hardly any CO2 when the water vapor is coming out of the solution fairly rapidly and
displacing the air around it.
If you were to boil away the water with a condenser above it, I bet it would make it even harder for CO2 to react with it. .. and obviously you
wouldn't have the condenser being cooled or anything.
What is the percentage of CO2 in the air anyways? I bet it doesn't effect it noticeably unless it is left in a container for hours, and even then I
doubt it would effect it that much.
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barbs09
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Hi, This will probably be an easy one for some one.. For the purposes of extracting a crop of NaClO3 from a cell containing NaCl and NaClO3, two
methods are generally proposed 1, concentrating he solution untill the chlorate will crystallise out and 2, salting the chlorate out by the addition
of a salutation solution of NaCl.
My question is: since NaClO3 is over twice the solubility of NaCl for the same volume of water, why does the more soluble of the two salts precipitate
out?? I would have thought the least soluble salt (NaCl) would have crystallised out first. I cannot find a satisfactory answer anywhere.
Thanks in advance
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