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Author: Subject: The Short Questions Thread (4)
Panache
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[*] posted on 21-4-2017 at 13:19


Quote: Originally posted by clearly_not_atara  
https://erowid.org/archive/rhodium/chemistry/redamin.dithion...

Quote:
General Procedures

Method A.

The oxime (20 mmol) was mixed with water (15 ml) containing sodium dithionite (28 mmol). The suspension was stirred overnight at room temperature. (Warming to 40°C reduced reaction times to several hours.) In some cases, a precipitate formed.This product was very high melting and, on treatment with 2 M hydrochloric acid, liberated the carbonyl compound and sulfur dioxide. It was therefore assumed to be the bisulfite addition compound of the carbonyl compound and was not isolated. A slight excess of 2 M hydrochloric acid was added to the reaction mixture and nitrogen was bubbled through the mixture to expel the sulfur dioxide. Solid sodium carbonate was added carefully to alkalinity; the aqueous mixture was allowed to stand for 30 min and was extracted with ether (2x10 ml) which was dried (MgSO4) and evaporated. The residue was essentially pure carbonyl compound (by t.l.c.)

Method B.

The reaction described under Method A was performed in the presence of sodium hydrogen carbonate (28 mmol). Cleavage by means of this modification appeared to proceed considerably faster. The usual workup gave the carbonyl compound in comparable yield.


Notably there are some claims that sodium dithionite reduces oximes, however, upon inspection, dithionite is only reported to reduce alpha-keto oximes, produced by nitrosation of the ketones. It's worth noting that alpha-keto oximes tend to be present as the nitroso compound rather than the oxime, unlike all other oximes, and the nitroso compound is more susceptible to reduction.


So unless my oxime is alpha keto dithionite likely will not work. Any other reactants you know of.
I've tried % sulphuric, 35% yield lots of oximetry back could be worked into a continuous method.
Problem is both the oxime and the ketone steam distill, so you end up with it dissolved in your ketone and that separation is tedious.
Any input is welcomed




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S.C. Wack
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[*] posted on 21-4-2017 at 14:12


The oxime, dissolved in 10 to 12 vol. of 50% aqueous ethanol,
was refluxed with 3.5 molar equiv of sodium bisulfite until
thin layer chromatography indicated complete reaction. After
removal of the ethanol by distillation, the residue was admixed
with chloroform and an excess of dilute hydrochloric acid, and
the ketone or aldehyde was extracted into the organic layer.
In the case of the aldehydes, hydrolysis of the bisulfite adduct
required stirring with acid for up to 30 min to obtain two clear
layers.

The extracts gave near-quantitative yields of “crude” product,
usually single spot by tlc.

JOC 31, 3446 (1966)




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clearly_not_atara
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[*] posted on 21-4-2017 at 16:28


Quote: Originally posted by Panache  

So unless my oxime is alpha keto dithionite likely will not work. Any other reactants you know of.
I've tried % sulphuric, 35% yield lots of oximetry back could be worked into a continuous method.
Problem is both the oxime and the ketone steam distill, so you end up with it dissolved in your ketone and that separation is tedious.
Any input is welcomed


I think you were confused by my wording. "Reducing" an oxime in almost all contexts refers to conversion to the primary amine, and I wanted to say that this would not happen. Conversion to a ketone or aldehyde is called "oxime cleavage" or "hydrolysis" because usually no redox occurs, although some reaction sequences cleave the N-O bond and hydrolyse the resulting imine.

Dithionite converts normal oximes to carbonyl compounds, and alpha-ketooximes to alpha-ketoamines, according to the literature.

However as noted, bisulfite alone is sufficient for cleavage of oximes into the respective carbonyl compounds. It's possible that in the dithionite methods, dithionite reacts with air and bisulfite is the actual cleaving reagent. Since NaHCO3 should accelerate the decomposition of dithionite (it's an alkali) this seems particularly likely.

[Edited on 22-4-2017 by clearly_not_atara]

[Edited on 22-4-2017 by clearly_not_atara]
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[*] posted on 24-4-2017 at 17:12


Is it possible to safely heat glass media bottles made by Corning, Schott Duran, Pyrex or VWR? I have some of each and they all seem identical in size, shape and weight and looking at some data on them (from Corning), they seem to be made of borosilicate 7040 or 7070. They say they can be autoclaved and heated but I'm curious if anyone has ever tried heating them with a hot plate or flame.

I would think if it is the same glass as flasks and beakers, I don't see a reason it wouldn't be able to be heated - except maybe the plastic seal at the top - so cut it off or don't heat past XX degrees.

For the 7040 glass it showed a linear expansion with heat up to softening point of 800C - it was basically a 40-45 degree angle - so it seems like it may have the proper characteristics for heating.

Any ideas or experience with this?
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[*] posted on 24-4-2017 at 17:33


I suspect that the thickness and shapes of bottles would make thermal stresses much greater than in an rbf for example,
I'd have more confidence in a soda-glass rbf than a borosilicate-glass bottle.




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[*] posted on 24-4-2017 at 17:42


I unfortunately don't have any media bottles, but I think that their glass is thicker than normal beakers and flasks. Thicker glass increases the chance of breaking while heating. Heating on a hotplate and autoclaving are two very different things. The heating in an autoclave is much more even and gradual than on a hotplate. A simple beaker and watch glass as a cover is going to be much safer on a hotplate, and cheaper. A water bath would probably be fine but I wouldn't risk direct heating.
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[*] posted on 24-4-2017 at 18:50


I think a water bath would be fine for heating a media bottle too but wouldn't heat one directly on a hotplate and certainly wouldn't expose one to a flame. Several of my media bottles have plastic coatings that would be destroyed. While the others could probably withstand some uneven heating, I don't think they are really designed for it.



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[*] posted on 24-4-2017 at 22:25


Quote: Originally posted by Geocachmaster  
I unfortunately don't have any media bottles, but I think that their glass is thicker than normal beakers and flasks. Thicker glass increases the chance of breaking while heating. Heating on a hotplate and autoclaving are two very different things. The heating in an autoclave is much more even and gradual than on a hotplate. A simple beaker and watch glass as a cover is going to be much safer on a hotplate, and cheaper. A water bath would probably be fine but I wouldn't risk direct heating.


I agree with the thicker part being more prone to cracking. I've seen some thick wall flasks (ideal for filtering) and they seem about the same thickness as the bottles.

There are some small dots on the bottom of the bottle so they don't stick to counters or form suction if set in water - these wouldn't work well with a hot plate I would think, which is why I suggested a flame (and not a torch or bunsen burner) like an alcohol lamp.

Maybe I'll try a water bath, then oil bath followed by an alcohol burner (slow steady heat) and see how it handles it. I'd try a sand bath but I don't have that ATM..
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[*] posted on 26-4-2017 at 13:55


Hi folks! I bought a memory foam mattress but after a week I had to get rid of it, I could not bear the smell. It constantly oozed some sweet odour that first seemed the "new smell" but later it became ubearable.
It is funny for me to be chemofobic considering all the crazy stuff I inhaled in the last decades still I could not bear the thought that I sleep on cancer...
Do you have anything on this? I pinched out small pieces from the foam then analyzed it with HSGC-MS, nothing could be detected which is funny because I could smell it on the matress during the sampling.
Anyway thanks for your help in advance. And please dont buy this cancerous memory crap especially if its from china, so basically never ever buy these kind of things, you have been warned!
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[*] posted on 26-4-2017 at 16:34


Smell is one thing. Cancer-causing is quite another.
Both are reasons to get rid of a mattress but do not conflate the two.

Not sure why you could not detect it though.
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[*] posted on 27-4-2017 at 13:45


I did not add one thing to the story which is important to me, but for you it might be just a subjective observation, which actually is.
So after the 4th day I started to develop -apart from the constant headache- funny illnesses like dry eyes, twitching arm muscles, ear ringing etc. These were all mysteriously disappeared 3 days after I dumped the mattress.
I read some stuff on the internet:) based on the writings these mattress manufacturers are worse than Hitler and Stalin combined, however polybrominated diether type flame retardans may indeed cause something unwanted...
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[*] posted on 27-4-2017 at 15:25



The auld story. Bad memories from a memory mattress encounter.
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Panache
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[*] posted on 30-4-2017 at 16:47


Quote: Originally posted by RogueRose  
Is it possible to safely heat glass media bottles made by Corning, Schott Duran, Pyrex or VWR? I have some of each and they all seem identical in size, shape and weight and looking at some data on them (from Corning), they seem to be made of borosilicate 7040 or 7070. They say they can be autoclaved and heated but I'm curious if anyone has ever tried heating them with a hot plate or flame.

I would think if it is the same glass as flasks and beakers, I don't see a reason it wouldn't be able to be heated - except maybe the plastic seal at the top - so cut it off or don't heat past XX degrees.

For the 7040 glass it showed a linear expansion with heat up to softening point of 800C - it was basically a 40-45 degree angle - so it seems like it may have the proper characteristics for heating.

Any ideas or experience with this?


If they are from schott my experienc is they are absolutely fine on a hot plate or direct flame heating (as in Meker type Bunsen burner used for sterilising or drying glass.
They are fairly useless on a hot plate as far as heating rate goes so I scrunch some al foil wetted with silicon oil between them and the plate.
Thousands of times I have heated these bottles fairly vigourously on the flame and the only time i experienced a failure was with new generically branded bottles I Was testing. Schott never failed




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[*] posted on 5-5-2017 at 14:06


Today I boiled water and iron hydroxide, to form iron oxide, but a penetrating kinda sulfur like smell scared me. Is that normal? Something like welding fumes?
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[*] posted on 6-5-2017 at 20:39


Brauer calls for using diluted conc nitric to wash cro3 crystals, but I just ran out (well I ran out weeks ago but haven't replenished. Anyone know of or can think of an alternative minerL acid or salt solution that's suitable?



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[*] posted on 7-5-2017 at 16:02


That's a tough one... it would have to be something extremely acidic and not reducing that will evaporate easily. I think you could probably use phosphoric acid, but it doesn't evaporate as easily. I would like to know the answer to this also.



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[*] posted on 7-5-2017 at 19:34


M/ethanesulfonic acid are my first guesses. Maybe ring-chlorinated benzoic acids.
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[*] posted on 12-5-2017 at 18:36
Question


I have a question regarding making solutions. I know that this is a super basic knowledge but the trouble I am having with this regards making specific percentages (I.e 13%) in a really weird amounts (I.e. 127ml). I get the concept sort of. I know that 30 grams of something dissolved 100 grams of water is a 30% solution of whatever.
The part I really choke up at is when I need to make an odd solution in an odd amount. Especially with like and acid. (I.e 36% HCl to a 12% HCl solution) and pretty much the same with other acids. I always end up guesstimating instead of doing exact calculation.
I guess what I am asking is if there are any formulas that I need to know or if anyone could shed some light on this. It would also be great if someone has like a link to a helpful video or page that explains how to precisely calculate a solution percentage. (Molar and by weight). Hope this isn't too simple of a question. Thanks in advance.
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[*] posted on 12-5-2017 at 18:57


30 grams of something dissolved in 100 grams of water is a 23% solution. 30 grams / (30 grams + 100 mL * s.g. of water).



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[*] posted on 12-5-2017 at 19:00


molarity: weight of solute / mol.wt of solute / (wt of solute + wt of solvent) / s.g. of solution / 1000



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[*] posted on 12-5-2017 at 19:05


Very simple. But you need some algebra.

Concentration is expressed in amount per litre. This could be

(a) a molar amount. 0.25 mol per litre means 0.25 moles of the substance has been dissolved in the solvent and the n the volume increased to 1 litre. (The 1 litre is the total amount of the solution and not the total amount of solvent used. They can be quite different for concentrated solutions. You can for example make a litre of sucrose solution using only 500mL of water.)
(b) percentage solutions. This is based on mass. I generally do this on a scale. For a 13% solution you would weigh out 130 of your solute and then make up to 1kg with the solvent. (Note that your description is not quite correct here. For 30% you do not use 30 grams dissolved in 100g of water. Instead you use 70g of water.)

If you wish to make up a different amount than 1 litre or one kilogram then you simply scale up or down appropriately. Thus for 225 mL of a molar solution (in (a) above) you would simply calculate the amount that you need and then multiply by 225/1000.
It is pretty normal to make up a stock solution of the concentration that you need and then measure out the amount that you need. So, make up 500mL and then measure out your 127mL leaving 373mL for later. Just label everything.



Diluting a solution is pretty easy if you are using molar amounts. There is a tidy little formula to use:
c1v1=c2v2

Concentration times volume is constant. Add some more solvent and the concentration decreases while the volume increases. But the product remains the same. Rearranging this formula allows you to calculate what your new volume needs to be for your new concentration and hence how much you need to dilute your solution.

You can do exactly the same for percentage solutions (b). A little care is required though. I always restate the concentration in grams per kg rather than as a percentage. This reinforces to me that I need to be calculating and measuring mass and not volume.

I don't know of any videos off the top of my head but I suspect that Khan Academy would have something pretty explanatory.


[edit] Pipped by Jjay. Also corrected some formatting.



[Edited on 13-5-2017 by j_sum1]
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[*] posted on 12-5-2017 at 19:15


I should add that weight/volume solutions are a bit more tricky. This is because the density of your solution changes upon dilution.
If your solution is sufficiently dilute then it probably does not matter. For example say you are mixing up a solution of phenolphthalein, a 0.5 gram per litre solution will be pretty much the same as a 0.5 gram per kilogram solution. The same could not be said for a 50% solution of sulfuric acid. If you want to pull out your density tables you could probably work it out.
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[*] posted on 13-5-2017 at 06:53


Thank you all very much! This has been quite helpful. I see that I have a lot of practicing to do lol.
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[*] posted on 25-5-2017 at 08:44


For the extraction and isolation of piperine using IPA, can I substitute KOH with NaOH? KOH is difficult to procure in my area.
Thanks.
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[*] posted on 25-5-2017 at 15:23


If someone has KOH flake and NaOH prill and needs to dissolve one or the other in an alcohol, the KOH is often chosen because it's easier.



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