Tributyl phosphate
[CAS 126-73-8]

Identification

• Classification: Organic raw materials >> Inorganic acid ester
• Name: Tributyl phosphate
• Synonyms: TBP
• Molecular Formula: C₁₂H₂₇O₄P
• Molecular Weight: 266.32
• CAS Registry Number: 126-73-8
• EC Number: 204-800-2
• SMILES: CCCCOP(=O)(OCCCC)OCCCC

Properties

• Density: 1.0±0.1 g/cm³ Calc.^*, 0.979 g/mL (Expl.)
• Melting point: -79 °C (Expl.)
• Boiling point: 288.3±8.0 °C 760 mmHg (Calc.)^*, 328.6 - 332.5 °C (Expl.)
• Flash point: 193.3 °C (Calc.)^*, 145 °C (Expl.)
• Solubility: water: 0.6 g/100g (Expl.)
• Index of refraction: 1.43 (Calc.)^*, 1.424 (Expl.)

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: Pictogram(s)
• Risk Statements: H351-H302-H315
• Safety Statements: S36/37;S46

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Skin irritation	Skin Irrit.	2	H315
Carcinogenicity	Carc.	2	H351
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Acute toxicity	Acute Tox.	4	H332
Chronic hazardous to the aquatic environment	Aquatic Chronic	2	H411
Eye irritation	Eye Irrit.	2	H319
Carcinogenicity	Carc.	2	H350
Specific target organ toxicity - repeated exposure	STOT RE	2	H373

chemBlink Chemical Story

Tributyl phosphate, usually abbreviated TBP, illustrates how a liquid can do more than dissolve another substance. Its structure combines a phosphorus-oxygen center with three normal-butyl groups. The phosphoryl oxygen can interact with suitable dissolved species, while the hydrocarbon groups help make the molecule compatible with an organic liquid environment. This combination underlies its importance as a neutral extractant.

The word neutral has a specific chemical meaning here. TBP is the triester of phosphoric acid: all three acid hydroxyl positions have been esterified. It therefore differs from acidic organophosphorus extractants that retain a proton which can be exchanged during metal extraction. Putting these compounds in one broad phosphorus-containing family does not make their extraction mechanisms interchangeable.

In solvent extraction, the practical objective is to move selected components between liquid phases. A useful carrier helps stabilize a species in one phase, but the outcome also depends on the rest of the chemical system. The identity of the dissolved complex, the aqueous composition, and the organic formulation all matter. A high extraction percentage for one feed cannot be treated as an intrinsic constant of TBP or as a prediction for every metal-containing solution.

TBP became especially well known through nuclear-fuel separation chemistry. That history has also made solvent durability an important research question. Ngelale and colleagues examined radiation-induced degradation of uranyl-loaded TBP in a 2019 study, considering different radiation types and chemical environments. The work shows why selecting an extractant requires attention to what happens to the liquid during service as well as to its initial ability to bind and transfer solutes.

Degradation introduces a second layer of chemistry. A used solvent can contain products with behavior different from that of the original triester. Consequently, monitoring the intact compound and understanding changes in composition are separate tasks from measuring how much target material entered the organic phase. These distinctions are relevant whenever a separation medium is expected to circulate through repeated contact and recovery steps.

The chemical story of TBP is therefore one of molecular recognition embedded in a process. The same molecule contributes a donor atom, an organic-compatible exterior, and a set of stability constraints. Successful use depends on matching all three to the actual mixture being separated.

References:
1. NIST Chemistry WebBook. Tributyl phosphate, CAS 126-73-8: identity and structure. https://webbook.nist.gov/cgi/cbook.cgi?ID=126-73-8
2. Ngelale R et al. Radiolytic Degradation of Uranyl-Loaded Tributyl Phosphate by High and Low LET Radiation. Solvent Extraction and Ion Exchange. 2019;37(1). https://impact.ornl.gov/en/publications/radiolytic-degradation-of-uranyl-loaded-tributyl-phosphate-by-hig/

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