Example Notebook: Oxidation of Toluene to Benzoic Acid

Example Notebook: Oxidation of Toluene to Benzoic Acid

Hazards and Toxicity:

Reagent	Hazard	Flamibility	Personal Safety
Potassium permanganate	Harmful if swallowed. Irritant. Readily absorbed through skin. R8 Contact with combustible material may cause fire. R22 Harmful if swallowed.	S17 Keep away from combustible material.	Safety glasses. Adequate ventilation. S26 In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. S36 Wear suitable protective clothing. S37 Wear suitable gloves. S39 Wear eye / face protection. S45 In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.)
Sodium Hydroxide	Very corrosive. Causes severe burns. May cause serious permanent eye damage. Very harmful by ingestion. Harmful by skin contact or by inhalation of dust. Causes severe burns. Safety glasses, adequate ventilation, Neoprene or PVC gloves.		S26 In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. S37 Wear suitable gloves. S39 Wear eye / face protection. S45 In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.)
Toluene	Toxic by inhalation, ingestion or by absorption through skin. Serious irritant. Experimental teratogen. Harmful by inhalation.	Highly flammable. S16 Keep away from sources of ignition.	Safety glasses. Good ventilation. S25 Avoid contact with eyes. S29 Do not empty into drains. S33 Take precautionary measures against static discharges
Manganese dioxide	Harmful by inhalation or ingestion. Long term exposure to manganese compounds may reduce fertility in men. Harmful by inhalation. Harmful if swallowed.		Safety glasses, adequate ventilation. Avoid contact with eyes
Sulfuric acid	Extremely corrosive, causes serious burns. Highly toxic. Harmful by inhalation, ingestion and through skin contact. Ingestion may be fatal. Skin contact can lead to extensive and severe burns. Chronic exposure may result in lung damage and possibly cancer. R35 Causes severe burns. R36 Irritating to eyes. R37 Irritating to respiratory system. R38 Irritating to skin. R49 May cause cancer by inhalation.	S30 Never add water to this product. Can heat up very quickly when added to water	Safety glasses or face mask; acid-resistant gloves. Suitable ventilation. S23 Do not breathe vapour. S36 Wear suitable protective clothing. S37 Wear suitable gloves. S39 Wear eye / face protection. S45 In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.)
Sodium Bisulfite	Harmful if swallowed or inhaled. May cause allergic reaction in sensitive individuals, especially asthmatics. Irritant. R20 Harmful by inhalation. R22 Harmful if swallowed. R36 Irritating to eyes. R37 Irritating to respiratory system. R38 Irritating to skin.		Safety glasses, adequate ventilation. In case of contact with eyes, rinse immediately Wear suitable protective clothing.
Benzoic Acid	May be harmful if swallowed. May act as an eye or respiratory irritant. May cause allergic respiratory or skin reaction. R36 Irritating to eyes. R37 Irritating to respiratory system. R38 Irritating to skin. Use safety glasses.		S26 In case of contact with eyes, rinse immediately with plenty of water and seek medical advice.

Reference: http://ptcl.chem.ox.ac.uk

Physical Properties:

Reagent	Properties
Potassium permanganate	KMnO₄ Appearance: dark purple to bronze crystals Melting point: ca. 150 C (decomposes) Specific gravity: 2.70 Stable, but contact with combustible material may cause fire. Substances to be avoided include reducing agents, strong acids, organic material, combustible materials, peroxides, alcohols and chemically active metals. Strong oxidant.
Sodium Hydroxide	NaOH Appearance: odourless white solid (often sold as pellets) Melting point: 318 C Boiling point: 1390 C Vapour pressure: 1 mm Hg at 739 C Specific gravity: 2.12 Water solubility: High (Note: dissolution in water is highly exothermic) Stable. Incompatible with a wide variety of materials including many metals, ammonium compounds, cyanides, acids, nitro compounds, phenols, combustible organics. Hygroscopic. Heat of solution is very high and may lead to a dangerously hot solution if small amounts of water are used. Absorbs carbon dioxide from the air.
Toluene	C₇H₈ Appearance: Colourless liquid with a benzene-like odour (odour threshold 0.17 ppm) Melting point: -93 C Boiling point: 110.6 C Specific gravity: 0.865 Vapour pressure: 22 mm Hg at 20 C (vapour density 3.2) Flash point: 4 C Explosion limits: 1% - 7% Autoignition temperature: 536 C Stable. Substances to be avoided: oxidizing agents, oxygen, moisture. Highly flammable. Hygroscopic.
Manganese dioxide	MnO₂ Appearance: black powder Melting point: 535 C Specific gravity: 5.02 Stable. Incompatible with strong acids, strong reducing agents, organic materials.
Sulfuric acid	H₂SO₄ Appearance: Colourless oily liquid Melting point: -2 C Boiling point: 327 C Specific gravity: 1.84 Vapour pressure: <0.3 mm Hg at 20 C (vapour density 3.4) Water solubility: miscible in all proportions Stable, but reacts with moisture very exothermically, which may enhance its ability to act as an oxidizing agent. Substances to be avoided include water, most common metals, organic materials, strong reducing agents, combustible materials, bases, oxidising agents. Reacts violently with water - when diluting concentrated acid, carefully and slowly add acid to water, not the reverse. Reaction with many metals is rapid or violent, and generates hydrogen (flammable, explosion hazard).
Sodium Bisulfite	NaHSO3 Appearance: white powder Melting point: ca. 150 C (decomposes) Density (g cm-3): 1.48 Water solubility: appreciable Stable. Incompatible with strong oxidizing agents, strong acids.
Benzoic Acid	C6H5COOH Appearance: white crystals or powder Melting point: 122 C Boiling point: 249 C Vapour density: 4.2 (air = 1) Density (g cm-3): 1.32 Flash point: 121 C (closed cup) Water solubility: slight Stable. Combustible. Incompatible with strong bases, strong oxidizing agents, alkalies.

Reference: http://ptcl.chem.ox.ac.uk

Purpose:

The purpose of this experiment is to oxidize toluene through the use of alkaline potassium permanganate.

Theory:

Oxidation is the process of a substance losing electrons to allow the addition of oxygen. This procedure can be carried out aliphatic alkyl groups on stable benzene rings if a benzylic hydrogen is present. The oxidation reaction occurs in tandem with reduction, a reaction that will result in the gain of electrons. Together the reactions are known as reduction-oxidation, or redox reactions. Some common oxidizing agents that are used are alkaline potassium permanganate, chromic acid and dilute nitric acid. Acidic solutions of potassium permanganate will indiscriminately attack organic compounds.

The permanganate ion, MnO₄^-, has an oxidation state of +7 and in a basic solution manganese dioxide (MnO₂) precipitate can form after an oxidation reaction occurs. This product can form colloidal suspensions, so sodium bisulfite is used to convert the unwanted precipitate into soluble manganese sulfate (MnSO₄).

Equations:

MW: 92.15g/mol 158.04g/mol 122.13g/mol

BP: 110.6°C 249°C

m: 0.9g 3.0g 0

n: 0.00977mol 0.01898mol 0

n = m/M

= 0.9g/92.15g/mol

= 0.00977mol

Yield assuming 100% completion.

Since there is a 1:1 molar correspondence between toluene and benzoic acid, 0.00977mol will be present.

Therefore,

n = m/M

0.00977mol = m/122.13g/mol

m = 1.1929g

Therefore, the theoretical yield is 1.1929g of benzoic acid.

Outline:

Set up fractional distillation column

250mL RB flask

3.0g KMnO₄

30mL water

1mL 1%NaOH

Warm

Add boiling chips

Add 1.0mL toluene

Reassemble

Reflux for 60min

Swirl occasionally

Add ~10mL of 10% H₂SO₄ until congo red

Add NaHSO₃, sodium bisulfite to destroy excess permanganate and MnO₂ to produce colourless solution

If necessary, re-acidify to pH 1

Reheat and crystallize, add water only if needed

Filter

Weigh

%Yield

Other Useful Information:

congo red

Approximate pH range for color change: 3.0-5.0
Color of acid form: blue
Color of base form: red

BLUE LITMUS PAPERS: Blue litmus paper turns red in an acid solution below pH 4.5. Blue litmus paper stays blue in a base.
RED LITMUS PAPERS: Red litmus paper turns blue in an alkaline (base, alkai) solution above pH 8.3. Red litmus paper stays red in an acid

Procedure:

(Completed during class)

Conclusion:

Hence, the oxidation of toluene resulted in the formation of benzoic acid. The amount of product obtained was 1.17g which resulted in a percent yield of 98% showing this reaction was nearly quantitative. Loss of product could have occurred during filtration or other instances of compound transfer. The melting point range also indicated purity since its range of 120°C-121°C is close to the literature value of 122°C. Furthermore, the white, needle-like crystal structure also conformed to literature sources (CRC 1996). To improve the procedure, more of the final compound should be synthesized. This would minimize the appearance of losses that occur during the production or retrieval stages. If loss did occur, the deviation would not appear as a dramatic error when the final percentages are calculated.

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