3-Hydroxy-2-methyl-4-pyrone
[CAS# 118-71-8]

Identification

• Classification: Flavors and spices >> Synthetic spice >> Lactone and oxygen-containing heterocyclic compound >> Furan and pyran
• Name: 3-Hydroxy-2-methyl-4-pyrone
• Synonyms: Maltol; 3-Hydroxy-2-methyl-4H-pyran-4-one
• Molecular Formula: C₆H₆O₃
• Molecular Weight: 126.11
• CAS Registry Number: 118-71-8
• EC Number: 204-271-8
• FEMA: 2656
• SMILES: CC1=C(C(=O)C=CO1)O

Properties

• Density: 1.3±0.1 g/cm³ Calc.^*
• Melting point: 160 - 164 °C (Expl.)
• Boiling point: 284.7±40.0 °C 760 mmHg (Calc.)^*, 254.2 °C (Expl.)
• Flash point: 127.3±20.8 °C (Calc.)^*, 95 °C (Expl.)
• Solubility: methanol: 50 mg/mL (Expl.)
• Index of refraction: 1.561 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H302
• Safety Statements: P264-P270-P301+P317-P330-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335
Acute toxicity	Acute Tox.	5	H303
Skin mild irritation	Skin Mild Irrit. 99	3	H316
Eye irritation	Eye Irrit.	2A	H319

Discovery and Applications

3-Hydroxy-2-methyl-4-pyrone, commonly known as maltol, is a naturally occurring organic compound belonging to the class of hydroxypyrones. It is characterized by a six-membered aromatic ring containing oxygen atoms at positions 1 and 4, with a hydroxyl group at position 3 and a methyl group at position 2. It appears as a white crystalline solid with a pleasant, caramel-like odor, which has contributed to its widespread use as a flavor enhancer and fragrance agent.

Maltol was first identified in the early 20th century as a component of malted grain, from which it derives its common name. Its presence was later confirmed in a variety of natural sources, including pine needles, larch trees, roasted malt, and baked goods, where it contributes to the characteristic aroma of cooked or heated foods. The compound was isolated and structurally characterized through classical organic chemistry techniques such as distillation and crystallization, followed by spectroscopic analysis including infrared and nuclear magnetic resonance methods.

The primary commercial application of 3-hydroxy-2-methyl-4-pyrone is in the flavor and fragrance industry. It is used as a flavoring agent in baked products, beverages, confections, and tobacco products due to its ability to impart a sweet, toasty aroma. Maltol enhances the perception of sweetness and blends well with a wide variety of food ingredients. It is recognized as a safe additive and is approved for use in food by numerous regulatory agencies, including those in the United States, Europe, and Asia.

In the fragrance industry, maltol is used in formulations for perfumes, soaps, and personal care products. Its warm, sugary scent complements other aromatic compounds and contributes to gourmand fragrance profiles. The compound's stability and solubility in both aqueous and alcoholic media make it suitable for diverse cosmetic applications.

Beyond flavor and fragrance, 3-hydroxy-2-methyl-4-pyrone has been studied for its chelating properties, particularly its ability to form stable complexes with metal ions such as iron(III) and copper(II). This property has attracted attention in analytical and coordination chemistry, where maltol and its derivatives have been used in the synthesis of metal-organic complexes for potential applications in catalysis, bioinorganic studies, and materials science.

Pharmacologically, maltol has demonstrated various biological activities, including antioxidant and antimicrobial properties. Its antioxidant action is attributed to its ability to scavenge free radicals and to chelate metal ions that catalyze oxidative reactions. These effects have prompted further investigation into its potential therapeutic applications. However, while these biological activities are documented in the literature, its primary use remains industrial and commercial rather than medical.

In the field of pharmaceuticals, maltol is also employed as a solubilizing agent to enhance the bioavailability of certain poorly soluble drugs. Its ability to form soluble complexes with active pharmaceutical ingredients facilitates drug formulation and delivery. Additionally, maltol has been included as an excipient in formulations to improve taste and mask bitterness.

Maltol is typically synthesized via chemical processes involving the cyclization of suitable precursors such as ethyl acetoacetate in the presence of oxidizing agents or via the Maillard reaction during the thermal degradation of carbohydrates. Industrial production methods have been optimized to yield high-purity maltol suitable for food and fragrance applications.

Toxicological studies have confirmed that maltol is of low acute toxicity and is generally recognized as safe when used within prescribed limits. Its safety profile, combined with its sensory and chemical properties, has sustained its demand across multiple sectors.

3-Hydroxy-2-methyl-4-pyrone continues to be a valuable compound in food science, perfumery, and coordination chemistry. Its unique combination of aroma, stability, and chemical reactivity ensures its role in both consumer products and research applications.

References

1979. Antimicrobial activity of aroma chemicals and essential oils. Journal of the American Oil Chemists' Society, 56(5).
DOI: 10.1007/bf02660245

2007. The identification of antioxidants in dark soy sauce. Free Radical Research, 41(4).
DOI: 10.1080/10715760601110871

2018. Resveratrol-maltol hybrids as multi-target-directed agents for Alzheimer’s disease. Bioorganic & Medicinal Chemistry, 26(20).
DOI: 10.1016/j.bmc.2018.08.011