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Methanol is the simplest alcohol and consists of a methyl group chemically bonded to a hydroxyl group. It is also known as Wood alcohol or Wood Spirit. It was first isolated in 1661 by Robert Boyle. Methanol was produced by the destructive distillation of wood. Methanol is a highly useful industrial product with multiple uses as a raw material for the preparation of other important chemicals like Acetic Acid and Formaldehyde. Although it is a useful chemical, it is also highly poisonous. Ingestion of even small quantities can cause permanent blindness and can also be fatal.
| Table of Content |
Key Terms: Methanol, Alcohol, Hydrogenation, Fermentation, Bioreactors, Hydroxyl groups, Esters, Distillation, Wood, Acetic acid, Formaldehyde, Combustion engine
What is methanol?
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Methanol is an organic chemical and the simplest form of alcohol, with the chemical formula CH3OH. It is a volatile, colorless, flammable liquid with an odor similar to ethanol. It consists of a methyl group linked to the polar hydroxyl group. Methanol is occasionally used as a fuel in internal combustion engines. It burns, forming carbon dioxide and water.
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| Relevant Compounds | ||
|---|---|---|
| Copper(I) oxide | Oxalic Acid | Sodium peroxide |
| Benzoic Acid | Perchloric Acid | Lithium Hydroxide |
Physical Properties of Methanol
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The physical properties of Methanol are as follows:
| Physical Properties | |
|---|---|
| Structure |
|
| State | A colorless liquid at room temperature |
| Boiling Point | 64.7 degree celsius |
| Melting Point | -97.6 degree celsius |
| Molecular weight | 32.04 g/mol |
| Odor | Sweet-smelling, similar to Ethanol |
Preparation of Methanol
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- Catalytic Hydrogenation:
A traditional method of Methanol production involves hydrogenating Carbon Monoxide in the presence of a zinc-oxide chromium-oxide catalyst ( ZnO-Cr2O3) in high-temperature and high-pressure conditions. The reaction is as follows:
CO + 2H2 \( \rightarrow\) CH3OH
(Carbon Monoxide) (Hydrogen) (Methanol)
The source of Carbon Monoxide for this reaction was taken by conventional coal-burning processes. But since this causes enormous levels of air pollution and depletion of coal reserves, a more environmentally-friendly way of Methanol production had to be found and used. Since then, urban, agricultural, and industrial wastes are being recycled for CO production, which is then used for making Methanol.
- Biochemical Methods (Fermentation)
Methane monooxygenases are a certain class of enzymes that can be used to perform the catalytic conversion of methane to methanol. These enzymes produce methanol by oxygenation while also producing by-products like water and NAD+ which can be isolated later. The reaction is as follows:
CH4 + O2 + NADPH + H+ \( \rightarrow\) CH3OH + H2O + NAD+
(Methane) (Oxygen) (Methanol)
- Commercial Bioreactors
A rather new method of Methanol production is using large bed reactors operating at high pressure and in high temperature using alumina coated copper and zinc oxide catalysts. The method has a high conversion rate of 97% and is being widely used these days for the commercial production of Methanol.
Some Important Chemical Reactions of Methanol
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- Oxidation
Methanol is allowed to react with nascent oxygen in the presence of potassium dichromate as a catalyst in an acidic medium, producing Formaldehyde and water. This reaction is widely used for the industrial production of Formaldehyde, hence making it one of the most important commercial reactions.
CH3OH + [O] \( \rightarrow\) CH2O + H2O
(Methanol) (Nascent Oxygen) (Formaldehyde)
- Reaction with Halo-acids:
Methanol reacts with Halogen acids to produce Alkyl Chlorides. An example to show the class of reactions when Methanol reacts with Hydrochloric acid, it produces Methyl Chloride and water.
CH3OH + HCl \( \rightarrow\) CH3Cl + H2O
(Methanol) (hydrochloric acid) (Methyl-Chloride)
- Ester Formation:
When alcohols react with Carboxylic acids they form sweet-smelling compounds called Esters. Since Methanol is alcohol, its reaction with Carboxylic acids produces Esters as well. These reactions are often performed in an acidic medium, usually in the presence of dilute sulphuric acid). An example of Ester formation reaction:
CH3OH + CH3COOH \( \rightarrow\) CH3COOCH3
(Methanol) (Acetic Acid) (Methyl ethanoate)
Uses of Methanol
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Methanol is one of the industrially profound chemicals. Some of the uses include:
- Methanol is used for the production of Formaldehyde, Acetic Acid, and other heavy substances such as Methyl tertiary butyl ethers and other polymers.
- Methanol is an extremely popular antifreeze agent, in colder regions like Scandinavian countries.
- It finds immense use as a solvent in labs because of high miscibility and high polarity.
- Methanol is used as an alcohol denaturing agent during the industrial production of ethanol. This is often done to keep a check on the amount of alcohol produced and ensure prohibited access to factory workers.
- Methanol being a great energy carrier is used as a fuel for internal combustion engines.
- Pharmaceuticals, resins, and fragrances are all made using pure methanol.
Polyacrylamide gel electrophoresis(PAGE) process
- Methanol is used in polyacrylamide gel electrophoresis (PAGE) as a destaining agent to remove the dye that was initially added to the gel to detect proteins or nucleic acids.
- Methanol also finds use for the production of hydrocarbons like gasoline and olefins and some other higher complex aromatic compounds by undergoing condensation reactions catalyzed by heterogeneous catalysts such as zeolites.
Things to Remember
- Simplest alcohol; CH3OH
- Oxidizes to form Formaldehyde
- Methanol is used as an alcohol denaturing agent.
- The source of Carbon Monoxide for this reaction was taken by conventional coal-burning processes.
- Methane monooxygenases are a certain class of enzymes that can be used to perform the catalytic conversion of methane to methanol.
- A rather new method of Methanol production is using large bed reactors operating at high pressure and in high temperature using alumina coated copper and zinc oxide catalysts.
- Methanol is an extremely popular antifreeze agent, in colder regions like Scandinavian countries.
- Methanol finds immense use as a solvent in labs because of high miscibility and high polarity.
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Sample Questions
Ques. How do you distinguish between Methanol and Phenol? (2 marks)
Ans. By FeCl3 test: Phenol gives a violet-colored solution, while Methanol doesn’t.
Ques. Why is Phenol more acidic than Methanol? (1 mark)
Ans. Phenol is more acidic than methanol because in phenol, phenoxide ions are more stabilized by resonance than phenol. There is no resonance in methanol.
Ques. What happens when CH3—O—CH3 is heated with HI? (2 marks)
Ans. Methyl Iodide (CH3I) and Methanol (CH3OH) are formed when CH3—O—CH3 is heated with HI.
Ques. Why is the bond length of the C—O bond in phenol shorter than that in methanol? (1 mark)
Ans. It is due to sp2 hybridization (double bond due to resonance) in phenol than single bond (sp3 hybridization) in methanol.
Ques. Why has Methanol been deemed a dangerous chemical? (3 marks)
Ans. Methanol is poisonous and highly inflammable. Direct ingestion of more than 10mL of Methanol can lead to permanent blindness because of optic nerve damage, central nervous system poisoning, coma, and possibly fatal. Such risks also occur even with so much as inhaling methanol vapors.
Ques. Is Methanol acidic or basic? (2 marks)
Ans. Methanol can be called both acidic and basic. By the Bronsted-Lowry concept, acids are Proton donors, and bases are proton acceptors. Methanol is both, as it shows acidic behavior in the presence of stronger bases like NaH. And it accepts a proton and exhibits basic behavior like all alcohols.
Ques. What are some important physical properties of Methanol? (2 marks)
Ans. Methanol is flammable, and so are its vapors. It is a flammable, colorless, warm, volatile, liquid with a very distinguishable sweet smell similar to that of ethanol (drinking alcohol).
Ques. List some daily use products that make use of Methanol? (3 marks)
Ans. Everyday consumer products such as antifreeze, glass cleaner, and paint thinners have Methanol as an essential raw material. Not a lot of drinking products contain Methanol, particularly because of its poisonous nature. Methanol is present in fruit juice and spirits which are distilled naturally.
Ques. What scent does methanol have? (1 mark)
Ans. Methanol and its vapors are combustible. It is a heated, volatile, flammable liquid that is colorless and has a strong aroma resembling that of ethanol (drinking alcohol).
Ques. What connection exists between methanol and biodiesel? (1 mark)
Ans. The manufacture of biodiesel depends heavily on methanol. In order to make an ester, or biodiesel, fats and oils are normally chemically reacted with methanol and a catalyst, usually sodium or potassium hydroxide (lye).
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