Scr0t
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Reduction of Nitrotoluenes via Al/H2SO4 (US2533203 & US2446519)
p-Toluhydroquinone via Al/H2SO4 reduction of p-Nitrotoluene
This procedure is based on US patent 2533203 Example II.
35g p-Nitrotoluene, 75ml 96% H2SO4 in 1000ml H2O was heated to 90-100°C while magnetically stirred, 12g Al powder (400mesh, spherical) was added in
16 roughly equal portions over 1.5hrs. Some H2 evolution was observed.
The mixture became dark brown over the course of the additions. Stirring and heating was maintained for an additional 1hr after the Al had been added.
The smell of Cresol was present with no remaining odor of NT at the end.
The mixture was filtered which removed a trace of Al and some black solids. The filtrate was boiled down (~700ml collected) to give a small amount of
Cresol as a white to light brown solid in the distillate. Towards the end a small amount of a pink/red solid came across.
The remaining black liquid precipitated large crystals of Al2(SO4)3 overnight. It was filtered and the filtrate extracted with 5x50ml EtOAc (NB
solvent displaces more Al2(SO4)3 from solution and can clog a Sep. funnel).
The pooled organic extracts were distilled free of solvent leaving a black liquid that was boiled with ~300ml of solvent mixture (Toluene/Pet. Ether
(bp 90-100°C) in a 2:1 /v ratio) and decanted hot leaving behind black tar. On cooling 10.4g white to pale-green crystals precipitated mp 124-125°C,
Yield 33% 2,5-Dihydroxytoluene.
Notes:
Recrystallization from Pet. Ether (bp 90-100°C) alone is inefficient and gave ~0.15g/100ml but was a pure white sample melting sharply at 125°C.
Basification of the remaining acid water and steam distillation afforded 4.5g of p-Toluidine as large rhomboid crystals; the smell of NH3 was also
evident during this distillation.
In the patent, the procedures described in Examples I & II gave pre-recrystallization yields of 28% and 54% respectively for this compound, the
difference being that Example II uses 20% less Al. The claimed color changes during the reaction were not observed; patent claims a lighter or yellow
colored reaction at the end.
3-Methyl-4-aminophenol via Al/H2SO4 reduction of o-Nitrotoluene
This procedure is based on US patent 2446519 Example 1.
In a 2L flask set for reflux 68.5g o-Nitrotoluene mixed with 1200ml H2O and 19g Al powder was heated to 80-100°C with stirring, a solution of 82ml
96% H2SO4 in 300ml H2O (~33% /w) was dripped in over ~2hrs. Stirring and heating was maintained for an additional 2hrs. When finished the NT smell had
disappeared and the solution was brown-black.
The aqueous portion was treated with 3g Sodium metabisulphite and sufficient 50% NaOH solution so that pH was 7-7.5; it was then heated to boiling and
vacuum-filtered with the aid of diatomaceous earth. The Aluminium hydroxide sludge was rinsed a couple of times with boiling water (2x500ml).
The combined aqueous portion and washings were boiled down until ~750ml clear amber-brown solution remained (1-2ml of o-Toluidine steam-distils
across).
On cooling fluffy yellow crystals precipitate. Filtering, rinsing with water containing a little SO2 and drying in a vacuum desiccator produced 40.2g
light-brown needles of mp 175-177°C (lit. 176-179°C). Yield 74% 3-Methyl-4-aminophenol.
Notes:
Patent claims a yield of 75% for 4-Aminophenol from Nitrobenzene.
During filtration the mixture should be kept hot or filtered quickly as some of the product will precipitate, diatomaceous earth and a large Buchner
funnel are helpful.
After neutralizing with NaOH, separation of black oil smelling of Toluidine floats to the top but appears to be largely retained by the Al sludge
during filtration. During steam distillation the black impurities in the Toluidine which passed through adheres to the wall of the flask as a solid
and does not appear to contaminate the product.
m-Nitrotoluene could also be used in the same fashion to make 2-Methyl-4-aminophenol.
This transformation can also be done in two steps through the Phenylhydroxylamine and Bamberger rearrangement as described in Vogel.
This 4-Aminophenol can be converted to p-Toluhydroquinone by oxidation with Dichromate (like o-Toluidine) followed by Dithionite or Zn/HCl reduction.
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Hexavalent
International Hazard
Posts: 1564
Registered: 29-12-2011
Location: Wales, UK
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Mood: Pericyclic
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Nice, perhaps this would be more appropriate and valued in prepubs?
Nice writeup BTW, I like this synthesis and you have a clear, simplistic writing style.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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