Sciencemadness Discussion Board

Bisulfite adduct issues

anewsoul - 28-4-2017 at 16:01

So I made 2.5 g of o-nitrotoluene following the video chemplayer made that used nitric acid in DCM and I used this to make o-nitrobenzaldehyde following this procedure.

25 g of a 60% w/w sulfuric acid solution was prepared and added to a flask with a stir bar and condenser. The 2.5 g of o-nitrotoluene was added and 5 g of MnO2 freshly prepared before the reaction from KMnO4 and MnSO4. The mixture was stirred strongly and refluxed for an hour. After it cooled down, a white solid was visible in the flask along with MnO2.

The mixture was filtered and the flask was washed twice with 10 mL of DCM and filtered. 10 more mL of DCM was used to wash the solid in the filter. The DCM was separated and was added to a saturated solution of sodium metabisulfite and stirred vigorously. The water absorbed some of the yellow color of the DCM layer but no solid adduct seemed to form. The DCM was separated and evaporated and a small amount of o-nitrotoluene was left behind. I added Klean Strip fuel alcohol to the metabisulfite solution and it did get cloudy, so I left it partially uncovered for a week to evaporate some. Now a solid was on the bottom which was filtered off. This was added to a sodium bicarbonate solution but the solid just caused some fizzing and completely dissolved. No o-nitrobenzaldehyde seemed to be formed, if it did it shouldn't dissolve in the water.

What might have happened? I think it might have just over oxidized to nitrobenzoic acid but it did seem that an adduct formed which a carboxylic acid wouldn't do. Could it have anything to do with using metabisulfite and not bisulfite?

CharlieA - 28-4-2017 at 18:05

Do you have a reference for preparing bisulfite adducts with sodium metabisulfite (Na2S2O5)? This is a different animal than sodium bisulfite (NaHSO3). On a quick search I didn't find any reference for preparing bisulfite adducts using sodium metabisulfite.

AJKOER - 29-4-2017 at 05:24

Per Atomistry on NaHSO4 (link: http://sodium.atomistry.com/sodium_hydrogen_sulphate.html ), to quote:

"Various sulphates of sodium and hydrogen have been prepared. With absolute sulphuric acid sodium sulphate reacts, forming a complex crystalline derivative melting at 40° C., and having the formula Na2SO4,8H2SO4. d'Ans has prepared another example with the composition Na2SO4,NaHSO4. Kendall and Landon have described 2Na2SO4,9H2SO4, an unstable substance at its melting-point, 60° C. (by extrapolation); Na2SO4,2H2SO4, unstable at its melting-point; and Na2SO4,H2SO4, melting at 186° C. Other compounds of similar type have been prepared."

Texium - 29-4-2017 at 06:03

Quote: Originally posted by AJKOER  
Per Atomistry on NaHSO4 (link: http://sodium.atomistry.com/sodium_hydrogen_sulphate.html )
That's completely irrelevant. We're talking about sodium bisulfite, not bisulfate.

Sodium metabisulfite should work fine for forming bisulfite adducts because it converts to bisulfite automatically when it is dissolved in water.

Ozone - 29-4-2017 at 07:23

It is quite possible you went too far and got the o-nitrobenzoic acid, instead.

O3

AJKOER - 30-4-2017 at 03:21

A thought, apparently there is an aqueous redox reaction occuring with transition metal salts like Fe(ll), Cu(l),...in the presence of H+ and oxygen (see my comments and references at https://www.sciencemadness.org/whisper/viewthread.php?tid=66...).

And assuming the transition metal Mn was also in one of its lower valence as well, allowing O2 exposure while boiling could alters things (Mn goes up one valent).

In other words, scrubb oxygen from your system and try again.

Or, actually, it could be the reverse situation. The redox with O2 proceeds, in my opinion, via a radical path (see link above) and removing O2 could sidetrack the radical action on your organic compound.

Note, this last possibility, with an excess of acid and transition metal, especially one with many valence states, could foster a case of going too far per Ozone's comment.

[Edited on 30-4-2017 by AJKOER]

unionised - 30-4-2017 at 07:24

Does sulphite/ SO2 reduce nitro compounds?
I have a feeling that I read somewhere that it can, but I can't find a reference.

byko3y - 30-4-2017 at 08:26

First of all, bisulfite adduct is perfectly soluble in water, this mistake is repeated over and over again due to the absence of detailed explanation and despite the fact the reaction itself is very straightforward.
Nitrobenzene is indeed reduced to aminobenzenesulfonate (Piria reaction), but this reaction is much slower than adduct formation.

anewsoul - 1-5-2017 at 04:12

Quote: Originally posted by CharlieA  
Do you have a reference for preparing bisulfite adducts with sodium metabisulfite (Na2S2O5)? This is a different animal than sodium bisulfite (NaHSO3). On a quick search I didn't find any reference for preparing bisulfite adducts using sodium metabisulfite.


I remember reading a thread on here that said that metabisulfite would work the same as bisulfite dissolved in water. I can't find the link right now.

[Edited on 1-5-2017 by anewsoul]

anewsoul - 1-5-2017 at 04:17

I'll try this reaction again once I make more nitrotoluene and test to see if the product was a carboxylic acid. If it is, would the best thing to do be to use less MnO2?

I think the reaction mentioned above about bisulfite reducing nitro groups could have affected it, I had to leave the metabisulfite solution sitting there for a week because I had to go back to college.

[Edited on 1-5-2017 by anewsoul]

Amos - 1-5-2017 at 05:47

Quote: Originally posted by CharlieA  
Do you have a reference for preparing bisulfite adducts with sodium metabisulfite (Na2S2O5)? This is a different animal than sodium bisulfite (NaHSO3). On a quick search I didn't find any reference for preparing bisulfite adducts using sodium metabisulfite.


Sodium metabisulfite is just dehydrated sodium bisulfite; it dissolves in water as so:

Na2S2O5 + H2O = 2Na+ + 2HSO3-

chemplayer... - 3-5-2017 at 08:20

Try to find a reference for the bisulfite adduct being insoluble... lots of them we've found are actually soluble and so adding an aldehyde to a saturated sodium bisulfite solution appears to just simply go into solution. Vanillin is a good example of this.

Either that, or as others have mentioned, you probably over-oxidised the aldehyde (very easy to do).

byko3y - 4-5-2017 at 01:12

o-nitrobenzoic acid is insoluble in water, so you can always see when you got this one instead of aldehyde.
Quote:
The water absorbed some of the yellow color of the DCM layer but no solid adduct seemed to form. The DCM was separated and evaporated and a small amount of o-nitrotoluene was left behind
That doesn't seem to be the case though.

Dan Vizine - 17-5-2017 at 12:12

I think the reaction with the bicarbonate tells you everything you need to know. CO2 was evolved, therefore the solid was appreciably acidic. You over-oxidized and got the acid. Solubilities can't always be trusted. They are true for pure compounds, much less trustworthy with impure materials. It just took a while to come out of solution.