Ethyl 2-(triphenylphosphoranylidene)propionate
[CAS 5717-37-3]

Identification

• Classification: Organic raw materials >> Organic phosphine compound
• Name: Ethyl 2-(triphenylphosphoranylidene)propionate
• Synonyms: (Carbethoxyethylidene)triphenylphosphorane; CEETPP
• Molecular Formula: C₂₃H₂₃O₂P
• Molecular Weight: 362.40
• CAS Registry Number: 5717-37-3
• EC Number: 227-215-4
• SMILES: CCOC(=O)C(=P(C1=CC=CC=C1)(C2=CC=CC=C2)C3=CC=CC=C3)C

Properties

• Melting point: 157-159 °C

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H302-H312-H315-H319-H332-H335-H413
• Safety Statements: P261-P264-P264+P265-P270-P271-P273-P280-P301+P317-P302+P352-P304+P340-P305+P351+P338-P317-P319-P321-P330-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Specific target organ toxicity - single exposure	STOT SE	3	H335
Eye irritation	Eye Irrit.	2	H319
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	4	H332
Acute toxicity	Acute Tox.	4	H302
Acute toxicity	Acute Tox.	4	H312
Chronic hazardous to the aquatic environment	Aquatic Chronic	4	H413
Eye irritation	Eye Irrit.	2A	H319

Discovery and Applications

Ethyl 2-(triphenylphosphoranylidene)propionate is an organophosphorus ylide commonly used in synthetic organic chemistry as a stabilized Wittig reagent precursor. It consists of a triphenylphosphoranylidene group attached to an α,β-unsaturated ester framework derived from ethyl propionate. The molecule belongs to the class of phosphonium ylides, which are key intermediates in carbon–carbon bond-forming reactions.

Structurally, the compound contains a central phosphorus atom bonded to three phenyl groups, forming a triphenylphosphine-derived moiety. The phosphorus atom carries a formal positive charge in the ylide representation, while the adjacent carbon bears a formal negative charge, resulting in a resonance-stabilized phosphonium ylide system. This charge-separated structure is a defining feature of Wittig-type reagents.

The propionate portion of the molecule consists of a three-carbon chain bearing an ester functional group at one end (–COOEt) and a ylide carbon at the α-position. The ester group contains a carbonyl (C=O) bonded to an ethoxy substituent, making it an electron-withdrawing group that stabilizes the adjacent ylide through resonance and inductive effects. This stabilization classifies the ylide as a “stabilized ylide,” which influences its reactivity and selectivity in olefination reactions.

The triphenylphosphine-derived segment consists of a phosphorus atom bonded to three phenyl rings. These aromatic rings are planar systems with delocalized π-electrons, contributing hydrophobic character and steric bulk. The phenyl groups also influence the electronic properties of the phosphorus center, stabilizing the ylide through conjugation and dispersing charge density.

The phosphorus–carbon double bond representation (P=CH–) is best described as a resonance hybrid between a phosphonium ylide form and a betaine-like structure. In one resonance contributor, phosphorus bears a positive charge and carbon bears a negative charge; in another, partial double-bond character exists between phosphorus and carbon. This delocalization contributes to the compound’s stability.

The ester functional group plays an important role in modulating the electronic properties of the ylide carbon. The electron-withdrawing nature of the carbonyl group reduces the nucleophilicity of the carbanion center, making reactions with aldehydes and ketones more controlled compared with unstabilized ylides. This often leads to preferential formation of thermodynamically more stable alkene products in Wittig reactions.

From a structural standpoint, the molecule contains regions of both rigidity and flexibility. The triphenylphosphine unit is relatively rigid due to the aromatic rings, while the ester side chain has conformational freedom around single bonds. The overall geometry is influenced by steric repulsion among phenyl rings and electronic interactions at the ylide center.

Physicochemically, ethyl 2-(triphenylphosphoranylidene)propionate is predominantly nonpolar in its aromatic region but contains polar functional groups at the ylide and ester sites. The compound typically exhibits limited water solubility and is more soluble in organic solvents. The large aromatic system contributes significantly to hydrophobicity and crystalline stability.

Chemically, the most important feature is the ylide carbon–phosphorus interaction, which enables nucleophilic attack on electrophilic carbonyl compounds. In the Wittig reaction, the ylide reacts with aldehydes or ketones to form betaine intermediates and subsequently undergoes cyclization to produce alkenes and triphenylphosphine oxide as a byproduct.

The ester substituent distinguishes this reagent from non-stabilized ylides by reducing reactivity and increasing selectivity. This allows for more controlled olefination, often favoring E-selective alkene formation depending on reaction conditions.

Overall, ethyl 2-(triphenylphosphoranylidene)propionate is a stabilized phosphonium ylide featuring a triphenylphosphine-derived phosphorus center linked to an ester-substituted carbanion. Its resonance-stabilized electronic structure and nucleophilic reactivity make it an important reagent for carbon–carbon double bond formation in organic synthesis.

References

2025. Beyond coumarin: the rise of benzocoumarins in chemical and biomedical sciences. Chemical Papers.
DOI: 10.1007/s11696-025-04422-9

2020. Female-Produced Sex Pheromone of Tetrastichus planipennisi, a Parasitoid Introduced for Biological Control of the Invasive Emerald Ash Borer, Agrilus planipennis. Journal of Chemical Ecology.
DOI: 10.1007/s10886-020-01188-0

2019. Development of a multistep reaction cascade for the synthesis of a sacubitril precursor in continuous flow. Journal of Flow Chemistry.
DOI: 10.1007/s41981-019-00058-5