Sciencemadness Discussion Board

A few questions about Nitric Acid and Nitrations

Teal - 17-10-2010 at 08:42

What is the influence of dissolved nitric oxides on poly-alcohol nitration?

If NO2 + H2O --> HNO3, why does conc. nitric acid turn yellow when heated or exposed to light?

What occurs when a substance is left for too long a time in HNO3? I've seen it briefly mentioned that it destroys the product. What if I left a poly-alcohol in cold fuming nitric acid overnight?

Can HNO3 be concentrated with anhy. MgSO4? (looking for an alternative to H2SO4)

hissingnoise - 17-10-2010 at 10:17

NO2 reacts with water to form nitric and nitrous acid . . .
2NO2 + H2O--->HNO3 + HNO2.
NO2 dissolved in nitrating acid can oxidise a substrate which often leads to a runaway reaction.
It is a deeply reddish gas and small quantities in HNO3 colours the acid yellow to orange.
Anhydrous MgSO4, if you can get it, can be used to concentrate HNO3 but its hydrate decomposes when heated so that the anhydrous salt cannot be regenerated by heating.

spirocycle - 17-10-2010 at 11:34

you can heat hydrated magnesium sulfate to get anhydrous.
what are you saying exactly?

hissingnoise - 17-10-2010 at 11:48

Quote:
. . .what are you saying exactly?

Good question spirocycle?
I got my sulphates and nitrates mixed up . . .
The nitrate salt, not the sulphate, is used industrially to reconcentrate used, diluted HNO3!
The hydrated nitrate of Mg gives off NO2 + O2 + H2O when heated!


Teal - 17-10-2010 at 14:30

I tried to extract some 70% HNO3 (produced by boiling down dilute HNO3) into DCM today. The HNO3 was intially quite yellow. It was mixed with DCM and large quantities of anhy. MgSO4 were added. Initially it formed a fluid yellow mass at the bottom of the beaker and the aqueous phase dissapeared. As more was added, it formed a hard clear mass and the DCM took on the yellow color.

The nitric acid however stayed glued to the MgSO4. Adding more dessicant did not alleviate this.

CZip - 17-10-2010 at 21:17

Quote: Originally posted by hissingnoise  
Quote:
. . .what are you saying exactly?

Good question spirocycle?
I got my sulphates and nitrates mixed up . . .
The nitrate salt, not the sulphate, is used industrially to reconcentrate used, diluted HNO3!
The hydrated nitrate of Mg gives off NO2 + O2 + H2O when heated!





He talked abaut magnesium sulfate.

hissingnoise - 18-10-2010 at 05:01

Teal, for HNO3 distillation, there is no *good* alternative to H2SO4 . . .
Mg(NO3)2 does work but it is essentially a one-use desiccator because the hydrate decomposes (Mg(NO3)2 --->MgO + 2NO2 + O) on heating.
It's unlikely that MgSO4 would be a suitable desiccant for HNO3!