Methyl Ester

Methyl Esters are mono-alkyl esters of long-chain fatty acids derived from vegetable oils or animal fats. These compounds are commonly used in various fields, including chemistry, biochemistry, and mass spectrometry. Methyl esters are simple in structure and are widely used for fatty acid analysis, particularly for polyunsaturated fatty acids and those with functional groups.

This article covers Methyl Esters, their structure, properties, preparation of methyl ester, and others in detail.

What is Methyl Ester?

Methyl esters are mono-alkyl esters of long-chain fatty acids derived from vegetable oils or animal fats. They are commonly used in biodiesel production as a clean-burning renewable fuel. Methyl esters are typically prepared by acid-catalyzed reactions with methanol, a process known as transesterification. They can be purified by preparative thin-layer chromatography, and various derivatization techniques are available for their use in analytical methods.

Chemical Formula of Methyl Ester

Chemical formula for methyl ester is

RCOOCH₃

where R is any alkyl group

Properties of Methyl Ester

Methyl Ester has various physical and chemical properties that are discussed below as,

Molecular Formula	RCO2CH3
IUPAC Name	Methyl Acetate
Molecular Mass	74.079 g·mol−1
Odor	Fruity Smell
Melting Point	−98 °C
Boiling Point	56.9 °C
Solubility in Water	~25% (20 °C)

• Specific Gravity: It has a specific gravity of 0.87-0.90 g/cm³
• Viscosity: Viscosity of methyl esters is 1.9-6.0 mm²/s
• Flashpoint: Flashpoint of methyl esters is 130-170°C
• Density: Density of methyl esters is 0.92 g/cm³
• Methyl esters have a high content of fatty acid unsaturated esters (>89%)
• Methyl esters are water-soluble, show low toxicity, and can bind to cholesterol within the membrane.

Structure of Methyl Ester

Methyl esters have a simple structure as shown in the image added below,

Structure of Methyl Ester

Production Methods of Methyl Ester

Methyl esters are commonly produced by several methods, each with a specific process and reaction mechanism. The following are the main production methods:

Acid-Catalyzed Reactions with Methanol

Acid-catalyzed reactions with methanol most frequently prepare methyl esters. General reaction for the production of a methyl ester from a carboxylic acid and methanol is as follows:

RCOOH + CH₃OH —–> RCOOCH₃ + H₂O

Transesterification of Fats with Methanol

The transesterification of fats with methanol involves the reaction of a glyceride with methanol in the presence of a catalyst, typically a strong base or a strong acid. General reaction for the production of methyl esters from transesterification of fats with methanol is as follows:

R’COOR + CH₃OH ——-> RCOOCH₃ + R’OH

Combination of Methanol and Carbon Monoxide (Carbonylation)

Industrial methyl formate, a type of methyl ester, is usually produced by combining methanol and carbon monoxide (carbonylation). Process involves the reaction of methanol and carbon monoxide to produce methyl formate, as shown in the following equation:

CH₃OH + CO ——-> HCOOCH₃

Enzyme-Catalyzed Transesterification

Specific reactions and mechanisms involved in enzyme-catalyzed transesterification depend on the type of lipase and the conditions used for the reaction. As an example, the production of biodiesel from waste sardine oil using immobilized lipase enzyme can be represented by the following reaction:

3ROH + R’COOH ———> 3R’COOR + H₂O

Purification of Methyl Ester

Methyl esters can be purified through various methods, including wet purification, thin-layer chromatography, and saponification, followed by methylation.

Preparative Thin-Layer Chromatography

Preparative thin-layer chromatography is a method used to purify methyl esters. The technique involves using a mobile phase, hexane-diethyl ether (9:1, v/v). The mixture of methyl esters is applied to a thin layer of silica gel or alumina on a glass plate. Plate is then placed in a developing chamber containing the mobile phase. The mobile phase moves up the plate by capillary action, and the different components of the mixture are separated based on their polarity. The separated components can then be collected and analyzed.

Wet Purification

Wet purification involves washing the methyl esters with different solutions. One approach is to use two consecutive washing steps, with neutralization achieved by hydrochloric acid during the first washing step. This method is commonly used in industrial biodiesel purification.

Saponification Followed by Methylation

Saponification followed by methylation is a classical method for preparing fatty acid methyl esters (FAMEs) from glycerolipids and sterols. This method is effective for eliminating troublesome impurities after transesterification.

Uses of Methyl Ester

Methyl esters have diverse applications across various industries, making them valuable compounds for different purposes. Some of the critical uses of methyl esters include:

Biodiesel Production

Methyl esters, particularly fatty acid methyl esters (FAME), are used as biodiesel, either as a pure fuel (B100) or blended with petroleum diesel. They are derived from natural plant oils such as soybean, palm, and others, making them a renewable and environmentally friendly alternative to petroleum diesel.

Substitute for Petroleum Diesel

Methyl esters can be used as a direct replacement for petroleum diesel or blended with petroleum diesel fuel in any proportion, serving as a sustainable alternative to traditional diesel fuel.

Industrial Applications

Methyl esters are used in various industrial applications, such as in the textile screen ink and graphics arts industries, where mineral spirits can be replaced. They offer benefits such as low volatility and are widely used in these applications.

Mass Spectrometry

Methyl esters are utilized for the mass spectrometric identification of fatty acids, especially for polyunsaturated fatty acids and those with functional groups. They provide valuable information for identifying fatty acids, such as molecular weight and gas chromatographic retention data, making them essential for fatty acid analysis.

Chemical Derivatives

Methyl esters are used as chemical derivatives in various chemical processes, including producing detergents and other commercially important compounds.

Health Hazards of Methyl Ester

Health hazards of methyl esters can vary depending on the specific compound. For example, the safety data sheet for L-Alanine methyl ester hydrochloride lists the following health hazards: skin irritation, eye irritation, and may cause respiratory irritation. Additionally, the safety data sheet from Sigma-Aldrich mentions the possibility of hazardous reactions, indicating that vapors of methyl esters may form explosive mixtures with air.

Methyl Ester Frequently Asked Questions

What are Methyl Esters?

Methyl esters are compounds formed by replacing the hydrogen in a fatty acid with a methyl group. They are often derived from natural oils through a process called transesterification.

What are Common Uses of Methyl Esters?

Methyl esters are commonly used as biodiesel, a renewable fuel for vehicles. They also serve as ingredients in soaps, detergents, and cosmetics.

Is Methyl Ester Hazardous to Health?

Methyl esters are considered safe when handled properly. However, inhaling high concentrations may cause respiratory irritation. Safety precautions should be followed.

What are Benefits of Methyl Ester?

Methyl Ester is used in production of various types of reagents and is mainly used in production of fatty acids.