Synthesis of Sulfanilic Acid and Aniline from Nitrobenzene by the Pria Reaction [Lab Report]
Synthesis of Sulfamic acid and Aniline from Nitrobenzene by the Piria
Reaction.
The Paper Procedure:
In the paper[1] the authors use a mixture of NaHSO3/Na2SO3 with a molar relation of
3,93 to 1,31 respectively, with the initial mass of sodium bisulfite being 3 moles to 1 mol of nitrocompound, and a 75% excess. The solution is
prepared by mixing NaOH with NaHSO3 [The necessary NaOH to neutralize ¼ of the bisulfite present] and a reflux time necessary to obtain a
homogeneous solution.
The solution is then boiled to reduce it to half of its volume, acidified with 12M HCl, reflux for another 1 ½ hs and allowed to cool
Then the products are extracted and purified.
Reference:
[1] doi.org/10.1021/ja01355a037
Modified Procedure:
I used 2 molar equivalents od sodium metabisulfite per mol of nitrocompund, and a reflux of 3hs.
On a 250mL Erlenmeyer flask, 95,2g of sodium metabisulfite were added along with 30mL of nitrobenzene and sufficient water to obtain a final mixture
volume of 250mL, the mixture was left to reflux for 3hs. After the 3hs the mixture was not translucent [Excess of Nitrobenzene].
After the mixture was cooled, it was transferred to a 500mL Erlenmeyer flask and added 250 mL of 6M HCl [pH<1], around the flask a distillation
apparatus was made, and the mixture boiled to decompose the sulfaminic acid and recover nitrobenzene by steam distillation. The distillation was
continued until precipitated salts were observed. 6mL of Nitrobenzene were recovered, along with 200mL of reaction mixture after filtration.
As the mixture cooled, a needle like compound precipitated, these was filtered, washed with ethanol and dried, obtaining 8g of sulfamic acid.
The leftover reaction mixture was basified with sodium hydroxide to pH of 12, and the aniline steam distilled. Recovering 4,35g.
Yields:
Aniline 4,35g [19,9%]
Sulfamic Acid 8g [19,7%]
Products Obtained:
ANILINE
![Aniline Sample [I].JPG - 223kB](http://www.sciencemadness.org/talk/files.php?pid=681972&aid=97399) ![Aniline Sample [II].JPG - 223kB](http://www.sciencemadness.org/talk/files.php?pid=681972&aid=97401)
SULFANILIC ACID
![Sulfanilic Acid [II].JPG - 277kB](http://www.sciencemadness.org/talk/files.php?pid=681972&aid=97405) ![Sulfanilic Acid [I].JPG - 253kB](http://www.sciencemadness.org/talk/files.php?pid=681972&aid=97403)
Observations:
_80% of the initial nitrobenzene reacted (20% were recovered by steam distillation), from the reacted nitrobenzene only 30% converted to products, and
60% were lost in side-reactions.
_After the 3hs of refux, when HCl was added, there was no observable SO2 liberation. However during the reflux SO2 could be
smelled.
_After the aniline steam distillation, the leftover salts rapidly turned dark color on contact with air.
Another experiment was performed using only Sodium Sulfite [Na2SO3].
74g of sodium sulfite along with 30mL of nitrobenzene and sufficient water to make a 250mL volume mixture were set to reflux for 1 ½ hs. Then 250 mL
of HCl were added [pH<1]and the mixture distilled. 24mL of Nitrobenzene were recovered, so I didn’t attempt to isolate products.
Notes of these experiment:
_ At ambient temperature the mixture turns yellow color.
_Under reflux the mixture turns red color
_Acidification of the mixture doesn’t liberate SO2
[Edited on 1-3-2023 by Chem Science]
[Edited on 1-3-2023 by Chem Science]
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