Introduction
C11H14O2 denotes a chemical compound comprising eleven carbon atoms, fourteen hydrogen atoms, and two oxygen atoms. The molecular formula alone is insufficient to specify a unique structure; several distinct isomers share this empirical composition. Among these, the most widely studied species is the ester known as methyl 3-phenylpropionate, which has the systematic name 3-phenylpropanoic acid methyl ester. This compound is a colorless liquid with a characteristic fruity aroma and finds use in perfumery, flavoring, and as a building block in organic synthesis.
Other structural variants, including isomeric esters of phenylpropionic acids and related phenylpropanoids, possess the same formula but differ in their functional arrangement. The existence of multiple isomers illustrates the importance of stereochemistry and regiochemistry in interpreting chemical data based solely on molecular formulae. In the context of chemical literature, the identifier C11H14O2 is often used to refer to the ester of interest, especially in databases that categorize compounds by empirical composition.
IUPAC Naming and Systematic Identification
Standard Nomenclature
The International Union of Pure and Applied Chemistry (IUPAC) provides a systematic framework for naming organic molecules. For the compound commonly referred to as methyl 3-phenylpropionate, the IUPAC name is 3-phenylpropanoic acid methyl ester. The name conveys the presence of a phenyl substituent at the third carbon of a propanoic acid backbone, which is subsequently esterified with a methyl group.
In a more compact notation, the compound may be represented as CH3O2C–CH2–CH2–Ph, where “Ph” denotes the phenyl ring. This representation highlights the ester linkage (–O–C(=O)–) and the adjacent carbon chain bearing the phenyl substituent.
Synonyms and Trivial Names
Various synonyms are used in commercial and academic contexts:
- Phenylpropyl methyl ester
- 3-Phenylpropionic acid methyl ester
- Methyl 3-phenylpropionate
- Methyl 3-phenylpropionyl ester
These names, while interchangeable in practice, may carry subtle differences in emphasis. For instance, “Phenylpropyl methyl ester” emphasizes the phenylpropyl skeleton, whereas “3-Phenylpropionic acid methyl ester” explicitly indicates the position of the phenyl group relative to the carboxylic acid core.
Structural Isomers
Several isomeric structures satisfy the formula C11H14O2. Key examples include:
- Methyl 2-phenylpropionate – the phenyl substituent positioned at the second carbon of the propanoic acid chain.
- Methyl 4-phenylbutanoate – an ester derived from 4-phenylbutanoic acid, featuring a longer carbon chain.
- Methyl 3-phenyl-1-propenoate (methyl cinnamate) – a conjugated ester with an α,β‑unsaturated double bond.
- Other aromatic esters and aliphatic ketones that maintain the same empirical formula.
While these isomers share the same molecular formula, they exhibit distinct physicochemical properties, such as boiling points, solubility, and odor thresholds. Consequently, accurate identification requires spectroscopic confirmation (e.g., NMR, IR, MS) rather than reliance on formula alone.
Physical and Chemical Properties
General Physical Data
The reference compound, methyl 3-phenylpropionate, is a clear, colorless liquid under standard laboratory conditions. Its melting point is reported as –45 °C, and the boiling point ranges from 151 °C to 152 °C, depending on the purity and atmospheric pressure. The density at 20 °C is 0.896 g cm⁻³, indicating it is less dense than water.
The refractive index (nD) at 20 °C is approximately 1.456, and the specific gravity is 0.896. The compound is slightly soluble in water (approximately 2 g per 100 mL) and highly soluble in organic solvents such as ethanol, acetone, and diethyl ether.
Spectroscopic Signatures
Key spectroscopic features that aid in identification include:
- Infrared (IR) spectrum: strong absorption at 1735 cm⁻¹ characteristic of the ester carbonyl group; aromatic C–H stretching near 3030 cm⁻¹; aliphatic C–H stretching around 2850–2920 cm⁻¹.
- ¹H Nuclear Magnetic Resonance (NMR): aromatic multiplets between 7.1–7.3 ppm; methylene protons adjacent to the carbonyl at 2.6–2.9 ppm; methyl ester protons as a singlet near 3.7 ppm.
- ¹³C NMR: carbonyl carbon at 170–172 ppm; aromatic carbons between 125–140 ppm; aliphatic methylene carbons near 35–45 ppm; ester methyl carbon at 52–54 ppm.
- Mass Spectrometry (MS): molecular ion at m/z 158; characteristic fragment at m/z 91 (tropylium ion) indicative of the phenyl group; other fragments from cleavage of the ester bond.
Thermal Stability and Decomposition
When subjected to heating beyond its boiling point, the compound undergoes gradual decomposition, primarily via decarboxylation of the ester group and loss of the phenyl moiety. The decomposition temperature is reported to be above 250 °C, indicating good thermal stability under typical laboratory conditions.
Reactivity
The ester functional group is susceptible to hydrolysis in the presence of acids or bases, yielding the corresponding phenylpropionic acid and methanol. The compound can also participate in nucleophilic substitution reactions at the methyl ester carbonyl, especially under catalytic conditions involving organometallic reagents or Lewis acids.
Methods of Preparation
Industrial Synthesis
Commercial production of methyl 3-phenylpropionate typically employs Fischer esterification, a classical acid-catalyzed condensation of the corresponding acid with methanol. The general procedure involves the following steps:
- Mixing of phenylpropionic acid (C11H12O2) with an excess of methanol.
- Adding a catalytic amount of concentrated sulfuric acid or p-toluenesulfonic acid.
- Heating under reflux to drive the equilibrium toward ester formation.
- Removal of water by azeotropic distillation (often using toluene or benzene as the co-solvent).
- Separation of the ester product by distillation or crystallization.
The Fischer route is favored for its simplicity, cost-effectiveness, and scalability. Typical yields in industrial settings range from 70 % to 85 %, depending on reaction conditions and purification efficiency.
Laboratory-Scale Syntheses
In a laboratory environment, the ester can be prepared using the same Fischer esterification protocol with minor adjustments. Alternative methods include:
- Use of acid chlorides: converting phenylpropionic acid to its acid chloride (phenylpropionyl chloride) using thionyl chloride, followed by reaction with methanol in the presence of a base (e.g., pyridine) to form the ester.
- Steglich esterification: employing dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP) to activate the carboxylic acid in the presence of methanol.
- Enzymatic esterification: using lipase catalysts in aqueous or solvent-free media to achieve ester formation under mild conditions.
Each method offers distinct advantages. Acid chloride routes provide high yields but require handling of corrosive reagents. Steglich esterification proceeds under neutral conditions and avoids strong acids but generates dicyclohexylurea byproducts. Enzymatic processes are environmentally benign but typically yield lower conversion rates.
Green Chemistry Approaches
Recent research has focused on developing greener synthesis routes, such as:
- Using ionic liquids as catalysts or solvents to reduce waste and enhance reaction rates.
- Employing microwave-assisted synthesis to accelerate esterification while reducing energy consumption.
- Implementing solvent-free, solid-supported reactions that minimize solvent usage.
These strategies align with the principles of green chemistry by reducing hazardous reagent use, enhancing atom economy, and improving process efficiency.
Natural Occurrence and Applications
Occurrence in Natural Sources
While methyl 3-phenylpropionate is primarily a synthetic compound, derivatives of phenylpropionic acids occur naturally in various plant species. For example, phenylpropionic acids and their esters are found in certain fruits, herbs, and essential oils, contributing to flavor and aroma profiles. The methyl ester of phenylpropionic acid may arise as a minor component in fermented foods or as a degradation product during cooking.
Applications in Perfumery and Flavor
Due to its pleasant, sweet, and slightly fruity odor, methyl 3-phenylpropionate is widely used as a fragrance ingredient. It is employed in the formulation of perfumes, soaps, detergents, and personal care products. In the flavor industry, it contributes to the aroma of apple, pear, and certain berry products. The compound is listed as a flavoring agent under several regulatory frameworks, including the Food and Drug Administration (FDA) and the European Food Safety Authority (EFSA).
Use as an Intermediary in Organic Synthesis
The ester functionality and the phenylpropyl backbone make methyl 3-phenylpropionate a useful building block in the synthesis of more complex molecules. Key applications include:
- Formation of chiral centers via asymmetric catalysis when coupled with stereoselective reductions or oxidations.
- Cross-coupling reactions (e.g., Suzuki, Heck) that introduce additional aryl or alkenyl groups onto the phenyl ring.
- Conversion to the corresponding acid or alcohol, enabling derivatization into amides, ethers, or alcohols.
These transformations are valuable in the pharmaceutical industry, where phenylpropanoid scaffolds are present in various therapeutic agents.
Industrial Uses Beyond Perfumery
Although less prominent, the compound serves in certain industrial processes, such as:
- Solvent or co-solvent in the extraction of natural products.
- Intermediate in the production of specialty polymers where phenylpropyl side chains enhance mechanical properties.
- Additive in the formulation of lubricants or greases to improve aromatic content.
Biological Activity and Toxicology
Biological Activity
Current literature indicates limited direct pharmacological activity of methyl 3-phenylpropionate. Studies suggest it functions primarily as an odorant rather than a bioactive ligand. However, related phenylpropionic acids have been investigated for their antimicrobial, anti-inflammatory, and antioxidant properties. Future research may uncover subtle bioactivities attributable to the ester structure or its metabolites.
Metabolism and Biotransformation
Upon ingestion or dermal exposure, the ester is expected to undergo hydrolysis by esterases, yielding phenylpropionic acid and methanol. Phenylpropionic acid can further be oxidized to produce cinnamic acid derivatives or conjugated with glucuronic acid for excretion. The metabolic fate aligns with common ester metabolism pathways observed for aromatic esters.
Acute Toxicity
Acute toxicity data for the compound are sparse. Preliminary tests using zebrafish embryo assays and rat oral LD50 studies suggest low acute toxicity. In zebrafish, LC50 values exceed 200 mg L⁻¹, and in rats, oral LD50 values are above 5000 mg kg⁻¹. These findings imply a high safety margin for typical exposure scenarios.
Chronic Exposure and Environmental Concerns
Long-term exposure to methyl 3-phenylpropionate, especially at high concentrations, could pose environmental risks due to its persistence and potential bioaccumulation. The compound has been detected in wastewater streams originating from perfumery manufacturing plants. Environmental monitoring indicates that it degrades via microbial activity, although rates may vary across ecosystems.
Regulatory Status and Safety Assessments
Under the European Union Regulation (EC) No 1331/2008, methyl 3-phenylpropionate is classified as a fragrance ingredient with a category of "unclassified." The United States Federal Food, Drug, and Cosmetic Act recognizes it as a safe ingredient under the Generally Recognized As Safe (GRAS) status when used within specified limits. EFSA’s Committee on Food Additives (JECFA) also lists it as a flavoring substance with a maximum allowable concentration in foods.
Labeling requirements for cosmetic and fragrance products necessitate that manufacturers disclose the presence of the compound to comply with consumer safety standards. The International Organization for Standardization (ISO) recommends precautionary labeling for potential skin sensitization risks.
Safety, Handling, and Storage
Safety Precautions
While the compound is generally considered safe for use in fragrance and flavor applications, standard laboratory safety protocols apply. Personal protective equipment (PPE) such as gloves, goggles, and lab coats should be worn during handling. The compound should be stored in a tightly sealed, well-ventilated area to prevent volatilization and accidental inhalation.
Fire and Explosion Hazards
Given its relatively low flash point (~45 °C), methyl 3-phenylpropionate is classified as a flammable liquid. Proper fire safety measures, including the use of fire extinguishers rated for organic solvents, should be in place. The compound does not exhibit explosive characteristics under normal laboratory conditions.
Chemical Compatibility
Compatibility with various materials is crucial for handling and storage. The compound reacts with strong acids and bases; therefore, containers made of stainless steel or borosilicate glass are recommended. Contact with alkali metals or reactive metals can lead to exothermic reactions.
Future Directions and Research Opportunities
Exploration of Stereoselective Synthesis
Developing chiral derivatives of methyl 3-phenylpropionate may expand its applicability in medicinal chemistry. Asymmetric synthesis employing chiral catalysts, such as chiral Lewis acids or organocatalysts, offers potential routes to enantiomerically enriched products.
Investigating Bioactivity
Future studies could assess the antimicrobial or anti-inflammatory effects of the ester or its metabolites. High-throughput screening using cell-based assays may uncover novel bioactivities, informing potential therapeutic applications.
Environmental Impact Studies
Evaluating the biodegradability and ecological effects of the compound in aquatic systems will help refine environmental regulations and improve sustainable manufacturing practices. Studies measuring persistence, bioaccumulation, and effects on non-target organisms are essential.
Process Optimization
Improving process yields and reducing byproduct formation in both industrial and laboratory syntheses remain active areas of research. Optimizing reaction parameters, exploring catalytic systems, and leveraging computational modeling to predict reaction outcomes could lead to more efficient production.
Conclusion
Methyl 3-phenylpropionate, a simple aromatic ester with the molecular formula C₁₁H₁₆O₂, serves as a key fragrance and flavoring ingredient, as well as a versatile intermediate in organic synthesis. Accurate identification hinges on spectroscopic methods due to the existence of numerous isomers sharing its empirical formula. Its physical properties, such as a moderate boiling point, moderate solubility, and characteristic odor, make it suitable for various industrial applications. Fischer esterification remains the predominant synthesis route, though greener alternatives are emerging. While biological activity is currently minimal, related phenylpropanoids are of interest in pharmacology, warranting further investigation. The compound’s safe use in fragrance, flavor, and specialized chemical applications is supported by regulatory approvals and toxicity data, ensuring its continued relevance across multiple industries.
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