demorol (Hive Bee)
03-22-02 20:19
No 286494
      Possible p-benzoquinone from aniline synth  Bookmark   

I did some research at the library and I read somewhere that p-benzoquinone can be synthesized from aniline using MnO2 as an oxidizing agent. Does anybody have any idea how such a synthesis could be performed and what would be the yields.

Life without chemistry would be a mistake.
04-04-02 18:02
No 292350
      Possible p-benzoquinone from aniline synth  Bookmark   

Found this in an ancient O-Chem. text :

Aniline (20g) is dissolved in water (500cc) and sulfuric acid (87cc), and finely powdered potassium dichromate (70g) is gradually added, the whole being cooled (0-5C) and constantly stirred. When in the course of 2 hours one-third of the dichromate has been used, the mixture is left overnight, cooled again as before, and the rest of the dichromate gradually added. After the lapse of about eight hours, the crude benzoquinone is separated by filtration, and purified by distillation in steam.

No yield is given, but as it is described as the 'usual preparation' so it should be safe to assume the reaction is worthwhile.

The text states that the reaction mechanism isn't understood, but does progress via a very complex intermediate that they refer to as aniline-black (though this was published in 1932)

I wonder if this can be adapted to use a more easily obtained oxidizing agent, such as KMnO4? (Maybe this is what demorol meant by MnO2?)

Any feedback as to success/failure of this rxn using permanganate would be much appreciated!

(Distinctive Doe)
04-04-02 19:15
No 292371
      anilines to benzoquinones
(Rated as: excellent)

Rocks, Is there anythign more OTC?

Enhancement of the selectivity of aniline oxidation to p-benzoquinone.    
Khim. Prom-st. (Moscow)  (1989),   (10),  734-5.
Hydroquinone prodn. by oxidizing PhNH2 with pyrolusite 5 h in 30% aq. H2SO4 and then reducing the resulting p-benzoquinone (I) with powd. Fe was improved by shortening the oxidn. time to 3-4 h, thereby reducing I polymn. and increasing the overall selectivity.

Registry Number: 14854-26-3
CA Index Name: Pyrolusite (MnO2)
Class Identifier: Mineral

Catalytic oxidation of organic compounds.
Patent GB2103615
A reaction product of starch with KMnO4, supported on silica gel and promoted with Ce nitrate was used as a catalyst for the partial oxidn. of org. compds.  Thus, air was bubbled through a mixt. of hydroquinone aq. soln., H2SO4, H2O2, and the catalyst described above to give 80% p-benzoquinone after 1 h.

Benzoquinones by oxidation of anilines.
Patent US3880893
Benzoquinones, useful as intermediates for the prepn. of naphthoquinones, anthraquinones, 1,4-cyclohexanediols, or hydroquinones, were prepd. by oxidn. of anilines with Na2Cr2O7.2H2O and H2SO4 in higher yields at shorter reaction times and higher reaction temps. than those of the known methods.  Thus, Na2Cr2O7.2H2O in 4N H2SO4 was added to PhNH2 in 4N H2SO4 within 18 min at 251 and stirred 1 min at 251 to give 85.3% benzoquinone.  Similarly prepd. were toluquinone and chlorobenzoquinone.

Quinones from aromatic amines.
Patent GB1212417
Quinones were prepd. by oxidn. of aromatic amines with a pentavalent V salt in acid soln.  The spent V reagent may be readily regenerated by electrolysis.  Thus, Na metavanadate was dissolved in 5% H2SO4 and the acidic soln. was added to PhNH2 in Et2O to give p-benzoquinone.  Similarly prepd. were 1,4-naphthoquinone and 2-methyl-p-benzoquinone.

You can even recycle

Process for producing manganese dioxide from crude manganese sulfate.
Patent US872010
MnO2 may be recovered from a Mn sulfate byproduct material obtained from a process involving the oxidn. of aniline sulfate in H2SO4 to p-benzoquinone employing MnO2.  The recovery process generally involves feeding a crude Mn sulfate by-product material and Ca(NO3)2 to a reactor and converting the Mn sulfate to Mn nitrate.  Thereafter, the Mn nitrate is thermally decompd. to MnO2 and various oxides of N.  The oxides of N are used to produce Ca nitrate for feeding to the reactor.  An alterative method is to recycle the oxides of N to the reactor and feed Ca carbonate or hydroxide with the crude Mn sulfate to the reactor to form the Ca(NO3)2 in situ in the reactor.

Quinone production from aniline and its reduction to hydroquinone. 
Patent GB1151673
In the prepn. of quinone (I) by the oxidn. of Ph-NH2 (II), unreacted MnO2 is reduced to water-sol. manganous salts as an alternative to steam distn. to remove the I formed.  Thus, 400 l. water, 115 kg. concd. H2SO4 and 15 kg. MnO2 (85% pure) is stirred, cooled to 5 and 30 kg. II added over 3 hrs. at 5-8.  Simultaneously, an addnl. 60 kg. MnO2 is added in 15 kg.-portions at 30-min. intervals, then the mixt. stirred 7 hrs. at 5-10; 3.13 kg. H2O2 (calcd. as 100% H2O2) is added over 30 min. and the mixt. neutralized to pH 5-6, then reduced with Fe filings at 65-75 until one half the I present was reduced to hydroquinone (III).  Cooling to 10 and filtration yields a ppt. contg. 30 kg. quinhydrone which is then further reduced to III.  NaHSO3 may be used in place of H2O2.

Patent US2624747

Patent US2281327

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