Palmitoyl Chloride: Properties, Synthesis & Lab Applications

Palmitoyl chloride is a highly reactive C16 fatty acid acyl chloride widely used in organic synthesis, lipid chemistry, and surface functionalization as a versatile acylating agent.

Chemical Name

Hexadecanoyl chloride (Palmitoyl chloride)

Molecular Formula

C₁₆H₃₁ClO

Molecular Weight

274.87 g/mol

CAS Number

112-67-4

Physical State

Colorless to pale yellow liquid at room temperature

Key Reactivity

Reacts vigorously with water, alcohols, and amines; moisture-sensitive

Primary Applications

Acylation reactions, lipid synthesis, surface modification, polymer chemistry

Chemical Identity and Physical Properties

Palmitoyl chloride (systematic name: hexadecanoyl chloride; CAS 112-67-4) is the acyl chloride derivative of palmitic acid, a saturated C16 fatty acid. Its molecular formula is C₁₆H₃₁ClO with a molecular weight of approximately 274.87 g/mol. At room temperature, it presents as a colorless to pale yellow liquid with a pungent, acrid odor characteristic of acyl chlorides.

The compound is highly moisture-sensitive: contact with water or atmospheric humidity rapidly generates hydrochloric acid (HCl) and palmitic acid via hydrolysis. This reactivity necessitates storage under anhydrous, inert-atmosphere conditions, typically in a tightly sealed vessel under nitrogen or argon, at cool temperatures away from light. Its long saturated alkyl chain (C15) confers relative hydrophobicity and contributes to its utility in introducing lipophilic palmitate moieties into target molecules.

Key physicochemical parameters include a boiling point in the range of approximately 195–200 °C at reduced pressure, a density slightly above 0.9 g/mL, and limited miscibility with water but good solubility in common organic solvents such as dichloromethane, chloroform, tetrahydrofuran, and toluene.

Reactivity and Handling Precautions

As a member of the acyl chloride functional class, palmitoyl chloride is among the most electrophilically reactive acylating agents. The carbonyl carbon is highly susceptible to nucleophilic attack, enabling rapid acylation of hydroxyl groups (esterification), primary and secondary amines (amide bond formation), and thiol groups (thioester formation). These reactions typically proceed without the need for coupling reagents or elevated temperatures, and often require only a mild base such as triethylamine or pyridine to neutralize the liberated HCl.

From a safety perspective, palmitoyl chloride is corrosive and a lachrymator. HCl gas released upon hydrolysis or reaction poses an inhalation hazard. All manipulations should be conducted inside a well-ventilated fume hood. Appropriate personal protective equipment — including chemical-resistant gloves, safety goggles, and a lab coat — is mandatory. Spills should be neutralized carefully with sodium bicarbonate before disposal according to local regulations for halogenated organic waste.

Incompatibilities include water, strong oxidizing agents, alcohols, amines, and bases. The compound should be stored separately from these materials. Opened containers should be re-sealed under inert gas immediately to prevent moisture ingress and reagent degradation.

Laboratory Applications in Synthesis and Research

Lipid and Phospholipid Synthesis: Palmitoyl chloride is a cornerstone reagent in the synthesis of structurally defined lipids, glycerophospholipids, and sphingolipids. It enables the selective introduction of the palmitoyl (C16:0) fatty acyl chain at specific positions of glycerol or sphingosine backbones, facilitating the preparation of model membrane components such as DPPC (dipalmitoylphosphatidylcholine) and related analogues for biophysical studies.

Protein and Peptide Palmitoylation Mimetics: In chemical biology, palmitoyl chloride is employed to install N-palmitoyl groups on amino acids, peptides, and small-molecule scaffolds, mimicking the post-translational lipid modification (S- or N-palmitoylation) that regulates protein membrane association and signaling. Such lipidated peptides are valuable tools for studying membrane-protein interactions.

Surface and Polymer Functionalization: The reagent is widely used to acylate hydroxyl-bearing surfaces such as cellulose, silica, chitosan, and carbon nanomaterials, imparting hydrophobicity and improving compatibility with nonpolar matrices. In polymer science, palmitoyl chloride reacts with polyol backbones to create amphiphilic or hydrophobically modified polymers for drug delivery, emulsification, and coating applications.

Analytical Chemistry Derivatization: Palmitoyl chloride can serve as a derivatizing agent for the preparation of fatty acid standards and for converting polar analytes into less polar, GC- or HPLC-amenable derivatives, aiding in the separation and detection of trace components in complex biological or environmental matrices.

Experimental Protocol: Acylation of a Primary Alcohol with Palmitoyl Chloride

The following general protocol outlines a Schotten-Baumann-type esterification using palmitoyl chloride under anhydrous conditions. Researchers should adapt concentrations, stoichiometry, and workup procedures to their specific substrate.

1. Preparation: Flame-dry all glassware and cool under nitrogen. Dissolve the substrate alcohol (1.0 equiv.) in anhydrous dichloromethane (DCM) at 0 °C under nitrogen atmosphere.
2. Base Addition: Add triethylamine (Et₃N, 1.5–2.0 equiv.) or pyridine dropwise to neutralize HCl generated during the reaction.
3. Reagent Addition: Add palmitoyl chloride (1.1–1.2 equiv.) slowly via syringe. Allow the reaction to warm gradually to room temperature and stir for 1–4 hours, monitoring by TLC (e.g., hexane/ethyl acetate eluent).
4. Workup: Quench the reaction with cold water. Transfer to a separatory funnel and wash sequentially with 5% aqueous HCl (to remove amine base), saturated aqueous NaHCO₃ (to remove residual acid), and brine. Dry the organic layer over anhydrous Na₂SO₄, filter, and concentrate under reduced pressure.
5. Purification: Purify the crude product by silica gel column chromatography or recrystallization as appropriate.

Note: All steps involving palmitoyl chloride must be performed under strictly anhydrous conditions in a fume hood. Dispose of all HCl-containing aqueous waste according to institutional guidelines.

Quality, Purity, and Storage Specifications

For synthetic and analytical applications, the purity of palmitoyl chloride is a critical parameter. High-purity grades (≥97% or ≥98% by GC) are recommended for sensitive reactions such as peptide lipidation or the synthesis of pharmaceutical intermediates, where trace impurities — including residual palmitic acid, palmitic anhydride, or other fatty acid chlorides — can compromise yield and product homogeneity.

Key quality indicators typically assessed by suppliers include: purity by gas chromatography (GC), acid value (reflecting hydrolysis), water content by Karl Fischer titration, and color (APHA scale). Researchers should request a Certificate of Analysis (CoA) to confirm these parameters prior to use.

Storage recommendations: Keep palmitoyl chloride tightly sealed under an inert gas (nitrogen or argon) in a cool (2–8 °C or as specified), dry, well-ventilated location away from incompatible materials. Under appropriate conditions, the reagent is stable for the manufacturer's stated shelf life. Repeated freeze-thaw cycles and exposure to moisture should be strictly avoided to prevent hydrolysis and quality degradation.

Aladdin Scientific offers palmitoyl chloride (SKU: P106415) with documented purity for research use. Consult the product CoA for lot-specific analytical data before initiating critical experiments.

Frequently asked questions

How should palmitoyl chloride be handled and stored safely in the laboratory?

Palmitoyl chloride must be handled exclusively in a well-ventilated fume hood with appropriate PPE (chemical-resistant gloves, safety goggles, lab coat), as it is corrosive and releases HCl gas upon contact with moisture. Store tightly sealed under nitrogen or argon at cool temperatures (typically 2–8 °C), away from water, alcohols, amines, and oxidizing agents. Opened vials should be immediately re-sealed under inert gas to prevent hydrolysis.

What nucleophiles react readily with palmitoyl chloride and under what conditions?

Palmitoyl chloride reacts readily with primary and secondary alcohols (forming esters), primary and secondary amines (forming amides), and thiols (forming thioesters). Reactions are typically carried out in anhydrous aprotic solvents such as dichloromethane or THF at 0 °C to room temperature, in the presence of a base (e.g., triethylamine or pyridine) to scavenge the HCl byproduct. Strict anhydrous conditions are essential to prevent competitive hydrolysis of the reagent.

What purity grade of palmitoyl chloride should I select for my research application?

For most synthetic applications, a GC purity of ≥97% is adequate; however, for sensitive applications such as pharmaceutical intermediate synthesis, lipid membrane studies, or peptide lipidation, ≥98% purity is recommended to minimize the impact of impurities such as residual palmitic acid or mixed anhydrides on reaction outcomes and product characterization. Always verify lot-specific purity data on the Certificate of Analysis (CoA) before use.

Can palmitoyl chloride be used to modify nanoparticle or material surfaces?

Yes, palmitoyl chloride is extensively used to hydrophobically modify hydroxyl-rich surfaces including cellulose nanocrystals, silica nanoparticles, chitosan, and carbon-based nanomaterials. The acyl chloride reacts with surface hydroxyl or amine groups to introduce long-chain palmitoyl groups, increasing surface hydrophobicity and improving dispersibility in nonpolar or polymer matrices. Reaction conditions vary by substrate; anhydrous organic solvents and an amine base are typically employed.

What are the main differences between palmitoyl chloride and palmitic anhydride as acylating agents?

Palmitoyl chloride is significantly more reactive than palmitic anhydride due to the superior leaving-group ability of chloride compared to a carboxylate. This higher reactivity enables faster reactions at lower temperatures and with less-nucleophilic substrates, but also demands stricter anhydrous conditions and careful temperature control. Palmitic anhydride is somewhat milder and may be preferred when selectivity over reactivity is prioritized or when the substrate is base-sensitive, as less HCl is generated. The choice depends on substrate nucleophilicity, required reaction speed, and tolerance for acidic byproducts.

References

1. March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure. 4th ed. Wiley-Interscience, 1992.
2. Clayden, J.; Greeves, N.; Warren, S. Organic Chemistry. 2nd ed. Oxford University Press, 2012.
3. Sigma-Aldrich / Merck Product Safety Data Sheet: Palmitoyl chloride, CAS 112-67-4.
4. Vance, D.E.; Vance, J.E. (Eds.) Biochemistry of Lipids, Lipoproteins and Membranes. 5th ed. Elsevier, 2008.

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