(S)-(−)-Citronellic Acid: Properties, Uses & Research Guide

(S)-(−)-Citronellic acid is a chiral, naturally occurring monoterpenoid carboxylic acid valued in research for its well-defined stereocenter and utility as an enantiopure building block in asymmetric synthesis and natural product chemistry.

IUPAC Name

(S)-3,7-dimethyloct-6-enoic acid

Molecular Formula

C₁₀H₁₈O₂

Molecular Weight

170.25 g/mol

Stereochemistry

(S)-configuration; single enantiomer

Optical Rotation

(−) levorotatory; specific rotation negative

CAS Number

13558-33-3

Aladdin SKU

S472338

Chemical Identity and Structure

(S)-(−)-Citronellic acid, also known as (S)-3,7-dimethyloct-6-enoic acid, is the levorotatory enantiomer of citronellic acid. Its molecular formula is C₁₀H₁₈O₂ with a molecular weight of approximately 170.25 g/mol. The molecule features a chiral carbon at the 3-position bearing an isogeranyl-type side chain terminating in a trisubstituted double bond, along with a carboxylic acid functional group.

The (S)-enantiomer is closely related structurally to citronellol and citronellal — well-known components of essential oils — sharing the same terpenoid carbon skeleton. The defined (S)-stereocenter makes this compound a valuable enantiopure starting material in stereoselective organic synthesis.

Physical and Chemical Properties

(S)-(−)-Citronellic acid is a colorless to pale yellow oily liquid at room temperature, consistent with many medium-chain terpenoid acids. It is sparingly soluble in water but miscible with common organic solvents such as ethanol, diethyl ether, chloroform, and ethyl acetate. The presence of the carboxylic acid group imparts typical acidic reactivity, enabling esterification, amide coupling, reduction, and decarboxylative transformations.

The compound is levorotatory as indicated by the (−) designation, and its optical purity is a critical specification for use in enantioselective reactions. Researchers should confirm the enantiomeric excess (ee) of the batch in use; the Aladdin SKU S472338 should be consulted for certificate-of-analysis data on ee and purity.

Research and Synthetic Applications

(S)-(−)-Citronellic acid serves as a versatile chiral pool building block in the total synthesis of terpenoid natural products and bioactive molecules. Its pre-existing (S)-stereocenter eliminates the need for de novo asymmetric induction at C-3, streamlining synthetic routes to complex targets containing the 3-methylalkyl motif.

Representative applications include its use as a precursor to chiral lactones, as a fragment in the synthesis of insect pheromones, and as a starting material for preparation of optically active esters and amides used in biological activity studies. The compound is also employed in studies of fragrance chemistry and the biosynthesis of terpenoid metabolites. Its functional group compatibility with standard peptide-coupling reagents (e.g., DCC, EDC) facilitates conjugation to amine-bearing substrates for structure–activity relationship (SAR) investigations.

Handling, Storage, and Safety Considerations

As with most carboxylic acid reagents, (S)-(−)-Citronellic acid should be handled with appropriate personal protective equipment including nitrile gloves, lab coat, and safety glasses. Work in a well-ventilated area or fume hood to avoid inhalation of vapors. The compound should be stored in a tightly sealed container, away from strong bases and oxidizing agents, at cool room temperature or refrigerated (2–8 °C) conditions to preserve optical integrity and prevent decomposition.

Researchers should consult the Safety Data Sheet (SDS) supplied with the product (Aladdin SKU S472338) for complete hazard classification, first-aid measures, and disposal guidelines in compliance with local regulations. Optical rotation and purity should be verified upon receipt if the application requires high enantiopurity.

Frequently asked questions

What is the difference between (S)-(−)-Citronellic acid and (R)-(+)-Citronellic acid?

The two compounds are enantiomers — non-superimposable mirror images sharing the same molecular formula and connectivity but opposite spatial arrangement at the chiral C-3 center. The (S)-(−) form is levorotatory, while the (R)-(+) form is dextrorotatory. In asymmetric synthesis or biological assays, the two enantiomers can exhibit distinctly different reactivity or potency, making selection of the correct enantiomer critical.

How should I confirm the enantiopurity of (S)-(−)-Citronellic acid before use?

Enantiopurity is most reliably assessed by chiral HPLC using an appropriate chiral stationary phase column, or by polarimetry to measure the specific optical rotation and compare it with the literature value for the pure enantiomer. The certificate of analysis (CoA) accompanying Aladdin SKU S472338 should be consulted for the reported ee value and optical rotation data.

What are typical reaction types for which (S)-(−)-Citronellic acid is used as a starting material?

(S)-(−)-Citronellic acid participates in a broad range of transformations typical of carboxylic acids, including Fischer esterification, coupling reactions with amines to form chiral amides, reduction to the corresponding chiral alcohol, and Arndt–Eistert homologation. It is particularly useful in chiral pool synthesis where the intact stereocentre is carried through to a more complex natural product or pharmaceutical intermediate.

Is (S)-(−)-Citronellic acid found naturally?

Yes, citronellic acid and its enantiomers are terpenoid compounds related to the monoterpene metabolic pathway. The citronellic acid skeleton is biosynthetically related to citronellol and geraniol found in essential oils of rose, citronella, and related plants, though the isolated acid itself may be obtained by oxidation or chemical transformation of these natural terpene sources.

References

1. March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure. Wiley-Interscience. General reference for carboxylic acid reactivity.
2. Clayden, J.; Greeves, N.; Warren, S. Organic Chemistry. Oxford University Press. Reference for chiral pool synthesis strategies.
3. Sigma-Aldrich (Merck) Product Listing No. 364428, (S)-(−)-Citronellic acid. [Referenced in source material as sigma NO.364428]

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