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Topic: Preparation of Benzoic Acid (C6H5COOH)  (Read 19357 times)

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Offline joeflsts

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Preparation of Benzoic Acid (C6H5COOH)
« on: September 07, 2006, 08:54:12 PM »
This preparation was found on the web and has pour yeilds but does create a useful chemical.  Let me know if you don't find these useful.  I enjoy sharing some of my results.

5.75ml Toluene (C7H8)
350ml Distilled Water (H2O)
17g Potassium Permanganate (KMnO4)
10ml Hydrochloric Acid (HCl)

Experiment Preparation:
Prepare a mixture of Toluene, Water, and Potassium Permanganate in 500ml boiling flask
Add boiling stones to even out boiling
Place the reflux condenser over the boiling flask
Gently boil solution for 4 hours - Started timer when boiling started.

**  Beads used may have been too big.  I notice that vapor is pushed quite a way up the condenser. **


Hour 1 - 2:
During the 1st hour of boiling I noticed that a film was clearly visible on the reaction flask.  This has a metallic color and is reflective.  At about 2hrs this metallic film was removed and it appears to have remixed with the solution.

Hour 2 - 3:
Continued boiling with no visible change to the reaction mixture.

Hour 3 - 3.5:
Still little if any change to the reaction material color.  Continue violent boiling due to boiling chips being too large.

Hour 3.5 - 4:
Boiling appears to have become very violent.  Solution is still very dark.  I'm starting to suspect the reason for the smaller boiling chips is to keep the boiling calm allowing the MnO2 to seperate from solution.

Post hour 4:
Clear seperation of layers.  Clean layer at the top and dark (MnO2) at the top.

Placed approx. 250ml liquid on burner on high heat setting.  - Object is to boil the solution down to 75ml.

Boiled down to about 75ml and filtered.  I ended up doubling the filters in order to remove all the excess MnO2.

I then added enough HCl to acidify the solution and precipitate the Benzoic Acid.  The reaction was immediate and the newly formed acid was visible.

I collected the acid and placed it out to dry.

MnO2 Test:
I tested the dry MnO2 by reacting it with H2O2 to determine a tradtional oxidation test.  I verified that it is in fact MnO2.

Final Yield: 2.5g - impure (strong HCl odor)

Offline AWK

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Re: Preparation of Benzoic Acid (C6H5COOH)
« Reply #1 on: September 08, 2006, 02:23:57 AM »
This is a typical undergraduate oxidation. Yields are usually about 50 %. To improve yield you shou use additional very intensive agitation.

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