Methanol - Structure, Uses and Properties

Methanol is the first and simplest member of the alcohol family in organic chemistry. It is a one-carbon alcohol. It is often addressed by its common name, methyl alcohol. Another common name of methanol is wood spirit or wood alcohol. Methanol got these names due to its historical relevance when it is first discovered to be a product that forms when cellulose (the main sugar component present in wood) gets fermented by any form of bacteria. Also, when the ancient people used to do pyrolysis (thermal decomposition at high temperature) of wood, methanol was obtained as one of the products.

Structure of Methanol

The chemical formula of Methanol is CH3OH. Since its chemical structure is a linkage between a methyl (–CH3) group and a hydroxyl group (–OH), it is sometimes also written as MeOH, where Me stands for Methyl. The molecular weight (or molar mass) of Methanol is 32.04 g/mol. The various forms in which the molecular structure of Methanol can be represented are given below:

The carbon present in the Methanol is sp3 hybridised. Due to the presence of hydroxyl group, the structure of Methanol can easily form intermolecular hydrogen bonds with hydrogen bond acceptors. The mixture of water-methanol mixtures is one of the classical examples studied for hydrogen bonding.

Physical Properties of Methanol

  • • Methanol exists as a clear and colourless volatile liquid at room temperature

  • • The density of Methanol is 792 kg/m3

  • • The melting point of Methanol is -97.6 °C

  • • Its odour is very similar to Ethanol (which is used as drinking alcohol) and is often mistaken for Ethanol and results in alcohol poisoning. (Note: Methanol is highly toxic if inhaled or ingested and may even lead to death. It causes retinal damage leading to terminal blindness. Inhaled fumes of Methanol may lead to coughing and/or headache. It is very harmful topically too and may cause skin damage if someone comes in direct contact with it. Its toxicity is basically due to the metabolic products it forms when acted upon by biological enzymes such as alcohol dehydrogenase and aldehyde dehydrogenase)

  • • Methanol is a highly flammable liquid and hence should not be used near flame or in high-temperature surroundings as it may easily catch fire (Its boiling point is very low – 64.7 °C

  • • Methanol is highly polar in nature due to the presence of the hydroxyl group, thus making it a good solvent

  • • Methanol is completely miscible with water (solubility > 100 mg/Ml at 25 °C) and ethanol, benzene, ether and many other organic solvents. It is also soluble in acetone and chloroform

  • • Methanol vapours are relatively higher than air

  • • The flash point of Methanol is 9.7 °C

  • • Its vapor pressure is 127 mm Hg at 25 °C

  • • Its LogP is -0.77

  • • It is generally stable at normal laboratory storage conditions

  • • Its viscosity is 0.544 mPa at 25°C

  • • Its heat of combustion and heat of vaporization are 726.1 Kj/mole and 37.34 Kj/mole (at 25 deg C), respectively, at 25 °C

  • • Its surface tension is 22.07 Mn/m at 25 °C

  • • Its pKa (dissociation constant) is 15.3

  • Chemical Properties of Methanol (Reactions of Methanol)

  • Oxidation Reaction: The oxidation reaction of Methanol is used for the formation of industrially and commercially used chemical named formaldehyde. The reaction occurs as follows – when Methanol is allowed to react with nascent oxygen in the presence of potassium dichromate as a catalyst in an acidic medium, it leads to the formation of formaldehyde and water. The elucidation of the reaction is given below:

  • CH3OH + [O] → HCHO + H2O
    (Methanol) (Nascent oxygen) (Formaldehyde) (Water)

  • Ester formation: When alcohol is reacted with a carboxylic acid, it results in the formation of another class of compounds found in organic chemistry called the esters. An example of the formation of ester (methyl ethanoate) when Methanol reacts with acetic acid is given below:

    (Methanol) (Acetic acid) (Methyl Ethanoate)

    This reaction occurs in an acidic medium (preferably a dilute solution of sulfuric acid is generally used).
    Since Methanol is a simple alcohol, it easily reacts with any member of the carboxylic acid family and leads to the formation of fruity smelled fragrant esters. Esters have a lot of industrial and commercial applicability in various industries such as the food industry and perfume industry.

  • Reaction with halo-acids: The reaction of alcohols with halogen acids (also commonly known as the halo-acids) is one of the most preferred ways of producing alkyl chlorides. When Methanol is reacted with a halogen acid (such as hydrochloric acid, the most common acid of this family), it leads to the production of methyl chloride along with the formation of water as a by-product. The reaction is elucidated as follows:

  • CH3OH + HCl → CH3Cl + H2O
    (Methanol) (Hydrochloric (Methyl (Water)
    acid) chloride)

    Methods of Preparation of Methanol

  • Catalytic Hydrogenation: This is one of the oldest and traditional methods of Methanol production in which carbon monoxide is hydrogenation in the presence of zinc oxide-chromium oxide catalysts (ZnO – Cr2O3) at high temperature and high pressure.

  • CO+ 2H2→ CH3OH
    (Methanol) (Hydrogen (Methanol)

    This method traditionally made use of coal, oil or natural gas as a source of carbon monoxide. However, this method was not environment-friendly and was resulting in the depletion of these limited natural resources and hence has now been replaced by a more environment-friendly method and is termed as “green” methanol production which makes use of agricultural, industrial and other urban wastes as a source of carbon monoxide. The use of carbon dioxide produced as a waste product from a number of processes is another “green” way to produce Methanol.

  • Commercial bioreactors: Methanol is nowadays prepared at a commercial level by using large fixed bed reactors which operate at high temperature (approximately 550-575 °C) and high-pressure conditions (around 100 atmospheric pressure) which utilizes alumina coated copper and zinc oxides as a catalyst. This method is found to achieve a 97% conversion rate of the reactants into Methanol. Although the mechanism by which methanol is formed by this process is still not known, many theories have been hypothesized to explain its formation.

  •   Biochemical method of production: Since the first natural occurrence of alcohols was discovered as an end product of fermentation, it is one of the cheapest and oldest used methods even today to do so. Certain enzymes, such as methane monooxygenases, can be used which perform the catalytic conversion of methane to methanol. These enzymes are oxygenases by origin and perform a mixed function, i.e. production of methanol by oxygenation is accompanied with the formation of other by-products such as water and NAD+ but is not a problem as these can be separated by end processing steps. The biochemical reaction of production of Methanol from Methane gas with the help of enzymes occurs as follows:

  • CH4 + O2+ NADPH + H+→ CH3OH + H2O + NAD+
    (Methane) (Oxygen) (Reduced form (acidic (Methanol) (Water)(Nicotinamide  of Nicotinamide media) adenine adenine dinucleotide dinucleotide phosphate) phosphate)

    Uses of Methanol

  • • Since ancient times, Methanol was used as a fuel, particularly biofuel.

  • • It is often used in car racing events or stunts performing tricks since it is comparatively less inflammable than other fuel options available and also due to its readily soluble nature with water.

  • • Methanol is used as a laboratory solvent for carrying out of a lot of reactions due to its polar nature.

  • • Methanol is commercially used for the production of other industrially applicable chemicals such as formaldehyde, acetic acid and certain heavy chemicals such as methyl tertiary butyl ethers and other polymers.

  • • Methanol is used in the production of alkyl halides which are a class of compounds from which other important compounds are readily formed by nucleophilic substitution reactions.

  • • Methanol is used as an anti-freeze agent in many cold regions such as European countries.

  • • Methanol is used as an alcohol denaturant during the commercial production of ethanol for keeping a check on prohibited access to ethanol by the factory workers.

  • • Methanol can be used for the production of hydrocarbons such as gasoline and olefins and other higher complex aromatic compounds by undergoing condensation reactions catalyzed by heterogeneous catalysts such as zeolites.

  • • Methanol is occasionally also used as an automobile fuel since on thermal decomposition it produces carbon dioxide and water. The carbon dioxide produced acts as a thermal energy source for the combustion engine of vehicles.

  • • Many stove based cooking appliances used methanol as their source of energy fuel.

  • • In polyacrylamide gel electrophoresis (PAGE), methanol is used as a destaining agent to remove the dye initially added to detect proteins or nucleic acids in the gel.

  • • Methanol is also used as one of the components in the perfume industry.

  • • Methanol is a common medium for a lot of reactions involved in pharmaceuticals.