Undecanoyl chloride is an organic compound with the chemical formula C₁₁H₂₁ClO. It is a long-chain fatty acid chloride, specifically the acid chloride derivative of undecanoic acid. This compound typically appears as a colorless to pale yellow liquid and is characterized by its high reactivity due to the presence of the acyl chloride functional group. Its primary application is as a versatile acylating agent and building block in organic synthesis. It is used to introduce the undecanoyl group into various molecules, facilitating the synthesis of esters, amides, and ketones. This makes it a valuable intermediate in the production of surfactants, lubricants, plasticizers, and specialty polymers. It also serves as a precursor for the synthesis of other fine chemicals and pharmaceutical intermediates. The compound is moisture-sensitive and reacts vigorously with water, alcohols, and amines, releasing hydrogen chloride. It requires careful handling under anhydrous conditions and appropriate personal protective equipment due to its corrosive and lachrymatory nature.