What is linoleic acid, and what is its chemical formula and common notation?

Linoleic acid (LA) is an organic compound with the chemical formula CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH. It is classified as a polyunsaturated omega-6 fatty acid. It is commonly denoted as 18:2 (n-6) or 18:2 cis-9,12, indicating it has 18 carbon atoms, two double bonds, and the second double bond is located at the sixth carbon from the methyl end of the fatty acid chain. Linoleic acid is a fundamental building block in human nutrition.

What are the key structural characteristics of linoleic acid regarding its double bonds?

Linoleic acid features two alkene groups, which are carbon-carbon double bonds (C=C). Crucially, both of these double bonds are in the cis configuration, meaning that the hydrogen atoms attached to the double-bonded carbons are on the same side of the bond. This specific spatial arrangement is vital for its chemical properties and biological functions.

How does linoleic acid typically occur in nature, and what are its basic physical properties?

In nature, linoleic acid is most commonly found as a triglyceride, which is an ester formed from glycerol and three fatty acid molecules, rather than as a free fatty acid. Physically, it is a colorless liquid that is virtually insoluble in water but readily dissolves in many organic solvents, typical behavior for a fatty acid with a long hydrocarbon chain.

Why is linoleic acid considered an essential fatty acid for humans?

Linoleic acid is considered an essential fatty acid because humans cannot synthesize it themselves and must obtain it through their diet. It serves as the primary building block from which the body can synthesize other necessary fatty acids, making its dietary intake crucial for overall health.

What is the origin of the name 'linoleic acid'?

The name 'linoleic acid' originates from Latin. It is derived from 'linum,' meaning 'flax,' and 'oleum,' meaning 'oil.' This naming reflects the historical fact that linoleic acid was first isolated from linseed oil, a common oil derived from flax seeds.

Who first isolated linoleic acid, and from what source?

Linoleic acid was first isolated in 1844 by F. Sacc, working in the laboratory of the renowned chemist Justus von Liebig. The source material for this isolation was linseed oil, which is derived from the seeds of the flax plant.

When was the existence of two double bonds in linoleic acid determined, and by whom?

The presence of two double bonds within the linoleic acid molecule was determined by K. Peters in 1886. This structural detail was important for understanding its chemical reactivity and properties.

When was the essential role of linoleic acid in human nutrition discovered, and by whom?

The critical role of linoleic acid in human nutrition was discovered in 1930 by G. O. Burr and his colleagues. This finding established linoleic acid as one of the essential fatty acids that must be obtained from the diet for proper bodily function.

Who determined the chemical structure of linoleic acid, and who first synthesized it?

The chemical structure of linoleic acid was determined by T. P. Hilditch and his team. Later, in 1950, the synthesis of linoleic acid was successfully achieved by R. A. Raphael and F. Sondheimer, confirming its structure through chemical synthesis.

Describe the metabolic pathway from linoleic acid to arachidonic acid.

The conversion of linoleic acid (LA) to arachidonic acid (AA) involves several enzymatic steps. First, LA is converted to gamma-linolenic acid (GLA) by the enzyme Δ6 desaturase. GLA is then further processed into dihomo-γ-linolenic acid (DGLA), which is the immediate precursor that undergoes further elongation and desaturation to form arachidonic acid (AA).

What types of molecules are derived from arachidonic acid, and what are their functions?

Arachidonic acid (AA) is a precursor to several vital signaling molecules. These include prostaglandins, which are involved in inflammation and pain; leukotrienes (like LTA, LTB, LTC), which play roles in immune responses and inflammation; thromboxane (TXA), which is important for blood clotting; and N-acylethanolamines such as arachidonoylethanolamine (anandamide), which function as endocannabinoids.

What is the significance of linoleoyl ethanolamide (LOE) in relation to linoleic acid metabolism?

Linoleoyl ethanolamide (LOE) is an N-acylethanolamine derived from linoleic acid. It is notable because it, along with hydroperoxides derived from anandamide, acts as a natural inhibitor of FAAH (Fatty Acid Amide Hydrolase), the enzyme responsible for breaking down endocannabinoids like anandamide. LOE was the first naturally occurring inhibitor of FAAH to be identified.

How is linoleic acid utilized in the production of paints and varnishes?

Linoleic acid is a key component in quick-drying oils, which are essential for oil paints and varnishes. Its utility stems from the presence of doubly allylic C-H groups adjacent to its double bonds. These groups are highly reactive towards oxygen in the air, undergoing autoxidation, which leads to crosslinking and the formation of a durable, stable film upon drying.

What is the role of linoleic acid in the cosmetics and beauty industry?

Linoleic acid has gained popularity in the beauty products industry due to its beneficial effects on the skin. Research suggests that when applied topically, it possesses anti-inflammatory properties, can help reduce acne, lighten skin tone, and improve the skin's ability to retain moisture, contributing to healthier-looking skin.

In which common vegetable oils is linoleic acid found in high concentrations?

Linoleic acid is particularly abundant in safflower oil and corn oil, often comprising over half of their composition by weight. It is also present in significant quantities in soybean oil, sesame oil, and almonds.

Which specific oils are listed as having the highest percentage of linoleic acid content?

According to the provided data, Salicornia oil has the highest reported linoleic acid content at 75%. Poppyseed oil follows closely at 74%, with Safflower oil ranging from 72% to 78%.

What is the reported linoleic acid content in common oils like corn oil, soybean oil, and olive oil?

Corn oil contains approximately 51.9% linoleic acid. Soybean oil has about 50.9% linoleic acid. Olive oil contains a lower percentage, around 8.4% linoleic acid.

What unusual behavior related to linoleic acid is observed in cockroaches?

When cockroaches die, they release oleic and linoleic acids. This chemical release acts as a deterrent, signaling to other cockroaches to avoid the area, likely preventing them from entering a space associated with death, which is a survival mechanism.

What is the relationship between linoleic acid consumption and cardiovascular health?

Consumption of linoleic acid has been associated with a reduced risk of cardiovascular disease. High-quality evidence indicates that increasing intake of linoleic acid can lower overall blood cholesterol and low-density lipoprotein (LDL) cholesterol levels. Furthermore, higher levels of linoleic acid in the body are linked to a decreased risk of major cardiovascular events.

What health benefits are associated with linoleic acid consumption according to research?

Research suggests that consuming linoleic acid is linked to a lower risk of cardiovascular disease, diabetes, and premature death. Clinical trials have also indicated that increased linoleic acid intake does not negatively impact markers of inflammation or oxidative stress in the body.

What recommendation does the American Heart Association make regarding linoleic acid?

The American Heart Association advises individuals to replace saturated fats with linoleic acid in their diet. This substitution is recommended as a strategy to help reduce the risk of cardiovascular disease.

What is the acidity (pKa) of linoleic acid?

The acidity of linoleic acid, measured by its pKa value, is 4.77 at 25°C. This value is similar to that of other carboxylic acids and indicates its acidic nature.

What is the NFPA 704 rating for linoleic acid, and what do the numbers signify?

Linoleic acid has an NFPA 704 rating of 2 for health, 1 for flammability, and 0 for instability. A health rating of 2 suggests that intense or continued exposure could cause temporary incapacitation or residual injury. A flammability rating of 1 indicates it must be pre-heated before ignition can occur, with a flash point over 93°C. An instability rating of 0 means it is normally stable and not reactive with water.

What is the flash point of linoleic acid?

The flash point of linoleic acid is 112°C (234°F). This is the lowest temperature at which the liquid can vaporize to form an ignitable mixture in air.

What is the solubility of linoleic acid in water?

Linoleic acid has very low solubility in water, reported as 0.139 mg/L. This limited solubility is typical for fatty acids due to their long, nonpolar hydrocarbon chains.

What is the molar mass of linoleic acid?

The molar mass of linoleic acid is approximately 280.452 grams per mole (g/mol). This value is calculated based on its chemical formula, C18H32O2.

What is the chemical formula for linoleic acid?

The chemical formula for linoleic acid is C18H32O2, indicating that each molecule contains 18 carbon atoms, 32 hydrogen atoms, and 2 oxygen atoms.

What are the names used to identify linoleic acid in chemical contexts?

Linoleic acid is identified by its Preferred IUPAC name, which is (9Z,12Z)-Octadeca-9,12-dienoic acid. It is also known by other names such as cis,cis-9,12-Octadecadienoic acid, and is classified using lipid numbers as C18:2.

What are the various identifiers provided for linoleic acid in chemical databases?

Linoleic acid is cataloged with several identifiers across different chemical databases. These include its CAS Number (60-33-3), Beilstein Reference (1727101), ChEBI ID (CHEBI:17351), ChEMBL ID (ChEMBL267476), ChemSpider ID (4444105), DrugBank ID (DB14104), ECHA InfoCard (100.000.428), EC Number (200-470-9), Gmelin Reference (57557), IUPHAR/BPS ID (1052), KEGG ID (C01595), PubChem CID (5280450), UNII (9KJL21T0QJ), and CompTox Dashboard ID (DTXSID2025505).

What is the InChI representation for linoleic acid?

The InChI (International Chemical Identifier) for linoleic acid is provided in two forms: the standard InChI is InChI=1S/C18H32O2/c1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18(19)20/h6-7,9-10H,2-5,8,11-17H2,1H3,(H,19,20)/b7-6-,10-9-. The corresponding InChIKey is OYHQOLUKZRVURQ-HZJYTTRNSA-N. An older version of the InChI is also listed.

What is the SMILES string for linoleic acid?

The SMILES (Simplified Molecular Input Line Entry System) string for linoleic acid is CCCCC/C=C\C/C=C\CCCCCCCC(=O)O. This string provides a linear notation for the chemical structure, representing the carbon chain, double bonds, and the carboxylic acid group.

What are the reported melting points for linoleic acid?

Linoleic acid has several reported melting points, varying slightly across different sources. These include -12°C (10°F), -6.9°C (19.6°F), and -5°C (23°F). These values indicate that linoleic acid is a liquid at standard room temperature.

What are the boiling points reported for linoleic acid?

The boiling point of linoleic acid is reported as 229°C (444°F) at 16 mmHg, 230°C (446°F) at 21 mbar, and also 230°C (446°F) at 16 mmHg. These measurements are taken under reduced pressure, as the compound would likely decompose at its atmospheric boiling point.

What is the density of linoleic acid?

The density of linoleic acid is reported as 0.9 g/cm³. This means that one cubic centimeter of linoleic acid has a mass of 0.9 grams, indicating it is slightly less dense than water.

What is the appearance of linoleic acid?

Linoleic acid typically appears as a colorless oil. This liquid form is consistent with its classification as a fatty acid with a relatively low melting point.

What is the vapor pressure of linoleic acid?

The vapor pressure of linoleic acid is noted as 16 Torr at 229°C. However, this specific data point is marked as needing verification with reliable sources.

What are the health effects associated with linoleic acid intake, particularly concerning cholesterol?

There is strong evidence that increasing the dietary intake of linoleic acid is beneficial for cholesterol levels. Specifically, it is associated with lowering both total blood cholesterol and low-density lipoprotein (LDL) cholesterol. These effects contribute to its role in cardiovascular health.

What is the relationship between linoleic acid and inflammation or oxidative stress?

Clinical studies have investigated the impact of linoleic acid intake on inflammation and oxidative stress. The findings suggest that increased consumption of linoleic acid does not lead to higher levels of these markers, indicating a potentially neutral or beneficial effect in these regards.

What are some other fatty acids that are structurally similar or related to linoleic acid?

Related compounds include conjugated linoleic acid (CLA), alpha-linolenic acid (an omega-3 fatty acid), linolein (a triglyceride ester of linoleic acid), and taxoleic acid, which is isomeric to linoleic acid. These share structural similarities but differ in the position or configuration of their double bonds or in their overall structure.

What role does linoleic acid play in the context of plant cuticles?

While polyunsaturated fatty acids are uncommon in plant cuticles, a derivative of linoleic acid, octadeca-c6,c9-diene-1,18-dioate, has been identified as a component of the surface waxes or polyesters in certain plant species, such as Arabidopsis and Brassica napus.

Which plant oils are noted for their high linoleic acid content, and what are their approximate percentages?

Several plant oils are noted for their high linoleic acid content. These include Salicornia oil (75%), Poppyseed oil (74%), Safflower oil (72-78%), Grape seed oil (70%), Evening Primrose oil (65-80%), Cardoon oil (60%), Wheat germ oil (56%), Hemp oil (54.3%), Cottonseed oil (54%), Corn oil (51.9%), and Walnut oil (50-72%).

What is the significance of the omega-6 classification for linoleic acid?

The 'omega-6' classification indicates that the first double bond in the fatty acid chain occurs at the sixth carbon atom counting from the methyl (omega) end. This specific position influences how the fatty acid is metabolized in the body, particularly its role as a precursor to other omega-6 fatty acids like arachidonic acid.

What is the typical role of linoleic acid in the context of essential fatty acids?

Linoleic acid is one of the two essential fatty acids for humans, meaning it cannot be produced by the body and must be obtained from the diet. It is considered the most fundamental essential fatty acid because it serves as the starting point for the synthesis of other important polyunsaturated fatty acids required by the body.

What is the chemical difference between linoleic acid and linolenic acid?

Linoleic acid and linolenic acid are both polyunsaturated fatty acids but differ in the number and position of their double bonds. Linoleic acid (18:2 n-6) has two double bonds, while linolenic acid (18:3 n-3) has three double bonds, with the first double bond in linolenic acid located at the third carbon from the omega end, classifying it as an omega-3 fatty acid.

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Linoleic Acid: The Fundamentals

Chemical Identity

Linoleic acid (LA) is an organic compound classified as a polyunsaturated omega-6 fatty acid. Its chemical formula is C₁₈H₃₂O₂. The molecule features an 18-carbon chain with two cis double bonds located at the 9th and 12th positions (denoted as 18:2 n-6). It is typically found in nature as a triglyceride, an ester formed with glycerol, rather than as a free fatty acid.^[5]

Physical Properties

In its pure form, linoleic acid presents as a colorless liquid. It exhibits very low solubility in water but readily dissolves in various organic solvents. Its physical state and properties are crucial for its role in biological membranes and its behavior in various chemical processes.^[2]^[3]

Essential Nutrient Status

Linoleic acid is recognized as one of the two essential fatty acids for human health, meaning it cannot be synthesized endogenously and must be obtained through dietary intake.^[7] The body utilizes LA as a foundational precursor for synthesizing other vital fatty acids, underscoring its fundamental importance in metabolic pathways.

Historical Context

Isolation and Characterization

The isolation of linoleic acid from linseed oil was first reported in 1844 by F. Sacc. Subsequent research by K. Peters in 1886 elucidated the presence of two double bonds within its structure. The critical discovery of its essential role in human nutrition was made by G. O. Burr and colleagues in 1930. The precise chemical structure was determined by T. P. Hilditch, and its synthesis was achieved by R. A. Raphael and F. Sondheimer in 1950.^[8]^[9]^[10]^[11]^[12]

Naming Origin

The term "linoleic" originates from the Latin words linum ("flax") and oleum ("oil"), referencing its initial isolation from flaxseed oil, a rich source of this fatty acid.

Physiological Significance

Metabolism and Eicosanoids

Linoleic acid (18:2 n-6) serves as the metabolic precursor to arachidonic acid (AA; 20:4 n-6) through a process involving elongation and desaturation.^[13] Arachidonic acid is a critical intermediate in the synthesis of various signaling molecules known as eicosanoids, including prostaglandins, leukotrienes, and thromboxanes, which play significant roles in inflammation, blood clotting, and other physiological processes.^[14]^[15] LA is also involved in the synthesis of endocannabinoids like anandamide.^[16]

The conversion pathway typically involves:

Linoleic acid (LA) is first converted to gamma-linolenic acid (GLA) by the enzyme Δ6-desaturase.
GLA is then elongated to dihomo-gamma-linolenic acid (DGLA).
DGLA is further desaturated and elongated to arachidonic acid (AA).

Additionally, linoleic acid can be metabolized by lipoxygenases, cyclooxygenases, and cytochrome P450 enzymes into various hydroxy and keto derivatives, such as 13-hydroxyoctadecadienoic acid and 9-hydroxyoctadecadienoic acid, as well as epoxide products like vernolic acid and coronaric acid. These metabolites have implications in both physiological functions and pathological conditions.^[19]

Industrial and Biological Applications

Drying Oils and Coatings

The presence of methylene-interrupted double bonds in linoleic acid makes it a key component of drying oils. These oils, when exposed to air, undergo autoxidation, leading to cross-linking and the formation of durable films. This property is exploited in the formulation of oil paints and varnishes.^[23]

Cosmetic Applications

Linoleic acid has gained prominence in the cosmetic industry due to its beneficial effects on skin health. Topical application has been associated with anti-inflammatory properties, reduction in acne lesions, skin lightening effects, and enhanced moisture retention.^[25]^[26]^[27]^[28]

Other Uses

Linoleic acid also functions as a surfactant, exhibiting a critical micelle concentration of 1.5 x 10^-4 M at pH 7.5. It is incorporated into certain bar soap formulations.^[3] Reduction of its carboxylic acid group yields linoleyl alcohol.^[24]

Dietary Sources

Plant-Based Oils

Linoleic acid is particularly abundant in various vegetable oils, often comprising a significant percentage of their fatty acid composition. High concentrations are found in safflower, poppy seed, and sunflower oils. It is also present in notable amounts in soybean, sesame, and almond oils.

The approximate percentage of linoleic acid (LA) in common oils and foods is detailed below:

Source	% LA^†
Salicornia oil	75%
Poppyseed oil	74%
Safflower oil	72–78%
Grape seed oil	70%
Evening Primrose oil	65–80%
Cardoon oil	60%
Wheat germ oil	56%
Hemp oil	54.3%
Cottonseed oil	54%
Corn oil	51.9%
Prickly Pear seed oil	50–78%
Walnut oil	50–72%
Melon seed oil	50–70%
Soybean oil	50.9%
Sesame oil	45%
Pumpkin seed oil	42–59%
Rice bran oil	39%
Argan oil	37%
Pistachio oil	32.7%
Peach oil	29%
Almonds	24%
Sunflower oil	20.5%
Peanut oil	19.6%
Chicken fat	18–23%
Canola oil	17.8%
Egg yolk	16%
Linseed oil (flax), cold pressed	14.2%
Lard	10%
Palm oil	10%
Olive oil	8.4%
Tallow	3%
Cocoa butter	3%
Macadamia oil	2%
Butter	2%
Coconut oil	2%

^† Average value, except where a range is specified.

Non-Dietary Occurrence

Interestingly, linoleic acid, along with oleic acid, is released by deceased cockroaches. This chemical signal serves to deter other cockroaches from entering the vicinity, a mechanism observed in other social insects as well.^[59]

Related Compounds

Isomers and Derivatives

While linoleic acid itself is defined by its specific structure (18:2 n-6, with cis configuration at both double bonds), related compounds exist. Conjugated linoleic acid (CLA) refers to positional and geometric isomers of linoleic acid. Taxoleic acid is structurally isomeric to linoleic acid. Derivatives like linoleyl alcohol are formed via reduction of the carboxylic acid group.^[24]

Plant Cuticle Components

Certain plant species incorporate unique derivatives of linoleic acid into their surface waxes. For example, octadeca-cis-6,cis-9-diene-1,18-dioate, a derivative, has been identified in the cuticles of Arabidopsis and Brassica napus.^[60]

Health Implications

Cardiovascular Benefits

Epidemiological studies and meta-analyses suggest that adequate consumption of linoleic acid is associated with a reduced risk of cardiovascular disease and premature mortality.^[61]^[62] High-quality evidence indicates that increasing linoleic acid intake effectively lowers total blood cholesterol and low-density lipoprotein (LDL) cholesterol levels.^[64] Furthermore, elevated circulating and tissue levels of linoleic acid correlate with a decreased incidence of major cardiovascular events.^[65] Importantly, clinical trials have not shown adverse effects on inflammatory markers or oxidative stress with increased linoleic acid intake.^[66]^[67] The American Heart Association recommends replacing saturated fats with linoleic acid as a strategy for cardiovascular risk reduction.^[68]

Diabetes Risk

Research, including systematic reviews and dose-response meta-analyses, suggests an inverse relationship between dietary linoleic acid intake and the risk of developing type 2 diabetes.^[63]

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References

The Merck Index, 11th Edition, 5382

A full list of references for this article are available at the Linoleic acid Wikipedia page

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This content has been generated by an AI model for educational purposes, drawing exclusively from the provided source material. While efforts have been made to ensure accuracy and clarity, this information should be considered a secondary source and may not be exhaustive or fully up-to-date.

This is not nutritional or medical advice. The information presented here is intended for academic understanding and does not substitute professional consultation regarding diet, health, or biochemistry. Always consult with qualified healthcare professionals or registered dietitians for personalized advice.

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Linoleic Acid: Essential Insights

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Linoleic Acid: The Fundamentals 🔬

🧬 Chemical Identity

💧 Physical Properties

⭐ Essential Nutrient Status

Historical Context 📜

🔬 Isolation and Characterization

💡 Naming Origin

Physiological Significance 🌿

⚙️ Metabolism and Eicosanoids

Industrial and Biological Applications 🛠️

🎨 Drying Oils and Coatings

🧴 Cosmetic Applications

🧼 Other Uses

Dietary Sources 🍽️

🌱 Plant-Based Oils

🪳 Non-Dietary Occurrence

Related Compounds 🔗

⚖️ Isomers and Derivatives

🌿 Plant Cuticle Components

Health Implications ❤️

🛡️ Cardiovascular Benefits

📊 Diabetes Risk

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Dive in with Flashcard Learning!

Linoleic Acid: The Fundamentals

Chemical Identity

Physical Properties

Essential Nutrient Status

Historical Context

Isolation and Characterization

Naming Origin

Physiological Significance

Metabolism and Eicosanoids

Industrial and Biological Applications

Drying Oils and Coatings

Cosmetic Applications

Other Uses

Dietary Sources

Plant-Based Oils

Non-Dietary Occurrence

Related Compounds

Isomers and Derivatives

Plant Cuticle Components

Health Implications

Cardiovascular Benefits

Diabetes Risk

Teacher's Corner

True or False?

Test Your Knowledge!

Gamer's Corner

Discover other topics to study!

References

Feedback & Support

Academic Disclaimer

Important Notice