April 19, 2024, 04:42:22 AM
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To start, I’m sorry that I can’t add any images - I’m on mobile and can’t figure out how to add one. Basically, my professor wants us to propose a mechanism for reacting diethyl malonate with HONO to form an oxime (so the oxime is on the alpha carbon and the rest of the molecule is the same). The first mechanism I did was:

1. HONO forms the nitrosonium ion (gets protonated by H3O+)
2. The carbonyl on diethyl malonate tautomerizes to the enol
3. The electrons from that double bond attach to the N in nitrosonium, the carbonyl reforms, and the electrons from the N-O+ triple bond go to the O
4. The nitroso O gets protonated
5. H2O takes the H from the alpha carbon, those electrons form the C=N bond, and the electrons in the N=O bond go to the O.

The problem is, I was just using a generic H3O+ because every mechanism I have seen for the formation of nitrosonium uses a stronger acid to protonate HONO. Specifically, I’ve mostly seen NaNO2 and HCl used. But my professor said we’re not allowed to use anything other than HONO - so no stronger acid, and no water, either. So my questions are:

1. Is this even the right track for this mechanism?
2. Does the nitrosonium ion form when just HONO is present (do acids protonate themselves?)
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Then make a new Standard.
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UPDATE:  As it turned out, someone in a previous semester mixed the standard Fe solution wrong, so the concentration isn't 10 mg/L we don't know what it is. 
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Organic Chemistry Forum / Re: torasemide
« Last post by Babcock_Hall on April 15, 2024, 09:47:05 AM »
I would also highly recommend PubMed for searching the biochemistry literature.
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Organic Chemistry Forum / Re: Use of SiO2
« Last post by rolnor on April 14, 2024, 01:22:13 PM »
It seems like a ring closure under mild acidic conditions, but you need the full paper to really know this. SiO2 is a little acidic and also contains some water. The b-conditions are divided into 2 parts so its 2 steps really as far as I understand
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Organic Chemistry Forum / Re: torasemide
« Last post by Borek on April 14, 2024, 11:54:16 AM »
Please read the forum rules, you have to show your efforts at answering the question to receive help.

Wikipedia has plenty of links to papers dealing with torasemide, have you read them?
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Organic Chemistry Forum / torasemide
« Last post by olki on April 14, 2024, 10:59:49 AM »
torasemide metabolic reactions, identification and quantification of all possible options
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Sorry for maybe too late reply, I hope you were able to solve the column.
Anyway, here is my advice:

1) your column feels way too small for such amount. I prefer to use shorter but wider columns because its faster (you trade number of theoretical plates for their size and since the size has square relation to column diameter unlike the number of plates vs lenght which is linear). I would use 2 or 3 cm diameter and maybe 10-12 cm of silica in the column

2) for such amount, taking 2 ml fractions is overkill. 10 or 20 is good volume here in my opinion - cuts time, glassware use and number of TLCs to do.

3) you dont have to TLC all your fractions, I like to make a grid on TLC plate, check which fractions has SOMETHING and then elute only those containing something. I also run TLC during the column. This way you can figure out when to stop (you obviously stop when your compound of interest is eluted)

4) as one of my advisers told me commonly: "Color is five percent". It is SOME indication but hardly conclusive. Ofc, after you run the same column multiple times you can get more information from the color of fractions ("my compound is eluting AFTER this yellowish band so I can take all the stuff into a beaker before it starts eluting")

5) you can increase polarity of your mobile phase over time to get better separation

6) Based on by experinece, I feel you might need to run more fractions, run TLC on maybe each fifth fractions to get SOME idea but 90 ml of mobile phase doesnt seem to be enough in your case.

I agree, I use a 30cm column (diameter) for this. But it is usually very nice to have TLC on all fractions, you dont need to speculate and guess what has happened. But its more work.
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Organic Chemistry Forum / Use of SiO2
« Last post by LiZzz on April 13, 2024, 03:57:29 PM »
Hello all,

I am studying the homoallyl radical rearrangement and I just ran into these reaction conditions (see image). I don't get why they used SiO2? Do you have any idea ?

Thanks in advance for your help.

Best,
Liz
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