TRIETHYL CITRATE

Triethyl citrate (TEC) is an ester derived from citric acid by esterification with ethanol. 
Esters of citric acid have been used for many decades as plasticizers and solvents because of their favourable physicochemical properties—namely low volatility, good solvency for many organic and polymeric materials, and relatively low toxicity compared to traditional phthalate plasticizers. 
TEC emerged as an attractive alternative to phthalate plasticizers in applications where regulatory pressure and consumer preference pushed for less toxic, more biodegradable additives.

Historically, citrate esters (mono-, di-, and tri-alkyl citrates) were developed in the 20th century as commercial plasticizers and additives. 
Triethyl citrate specifically found uses in cellulose acetate and other polymeric systems, coatings, and as a solvent and stabilizer in food and cosmetic formulations. 
Over time, its low toxicity and biodegradability have expanded its adoption in specialty applications such as pharmaceutical film-coatings and food-contact materials.

CAS number: 77-93-0
Other names / synonyms: TEC; Triethyl 2-hydroxypropane-1,2,3-tricarboxylate; Citrate triethyl ester; Triethyl 2-hydroxypropane-1,2,3-tricarboxylate; Ethyl citrate (triethyl ester); Tris(ethyl) citrate; 2-hydroxypropane-1,2,3-tricarboxylic acid triethyl ester.

Physical and chemical properties
Key properties (summary)
Appearance: Clear, colorless liquid
Odor: Mild, faint, characteristic ester-like odor
Density: ~1.1 g·cm⁻³ at 20 °C (typical literature range 1.10–1.12 g·cm⁻³)
Boiling point: High; decomposes before distillation under atmospheric pressure; often reported boiling point around 258–260 °C (under atmospheric pressure) — many industrial users use reduced-pressure distillation for purification.
Melting point: Typically below 0 °C (liquid at room temperature)
Vapor pressure: Very low at ambient temperatures (low volatility)
Flash point: Typically >150 °C (closed cup) — classified as non-flammable under many handling standards
Solubility: Miscible with many organic solvents (alcohols, esters, ketones); limited miscibility with water but some water solubility because of hydroxyl group and polarity (solubility in water is finite; moderately soluble — often reported in grams per liter range).
Partition coefficient (log P): Moderately lipophilic; exact values vary with method but tri-ester nature increases lipophilicity relative to shorter esters.
Refractive index: Reported near 1.430–1.435 at 20 °C in many supplier data sheets
Viscosity: Low to moderate, dependent on temperature; typical kinematic viscosity values at 40 °C are in an easily pumped liquid range.
Chemical behavior
Hydrolysis: Ester groups are susceptible to hydrolysis, particularly under acidic or basic catalysis. Hydrolysis yields citric acid and ethanol; hydrolysis rates are slow under neutral conditions but can be accelerated in harsh pH conditions or by esterases in biological environments.
Transesterification: Under catalytic conditions, TEC can undergo transesterification with alcohols or polyols to yield mixed esters.
Thermal stability: Stable under typical formulation and processing temperatures but decomposes on excessive heating; can undergo ester cleavage and decarboxylation under strong pyrolytic conditions.
Oxidation: The molecule lacks easily oxidizable aromatic systems; oxidative degradation is generally minor compared to hydrolysis but autoxidation pathways under radical conditions may occur at elevated temperatures.

Synthesis and production methods
Industrial synthesis
The industrial production of triethyl citrate is typically performed via direct esterification of citric acid with ethanol using acid catalysis (common catalysts: concentrated sulfuric acid, p-toluenesulfonic acid, or ion-exchange acidic resins for heterogeneous catalysis). 
The reaction proceeds through sequential esterification of the three carboxyl groups and removal of water to drive equilibrium toward ester formation.
General reaction:
Citric acid + 3 EtOH ⇌ Triethyl citrate + 3 H2O
Key operational features:
Catalyst choice: Homogeneous strong acids (e.g., H2SO4) yield high conversion but require neutralization and careful downstream treatment. 
Heterogeneous acid catalysts (acidic ion-exchange resins; sulfonated polymers) offer easier product separation, catalyst reuse, and reduced corrosion.
Water removal: Continuous removal of water (e.g., azeotropic distillation with toluene, use of molecular sieves, or reduced-pressure distillation) shifts equilibrium to product side and improves yields.
Temperature control: Elevated temperatures accelerate reaction rate but can promote side reactions; typical industrial temperatures range from 90–150 °C depending on catalyst and process design.
Ethanol excess: An excess of ethanol is often used to push the reaction to completion and maintain a liquid phase for effective mixing.

Alternative routes
Transesterification: One can prepare TEC by transesterification of other citrate esters (e.g., triethyl citrate from triacetin derivatives) with ethanol under catalytic conditions, although direct esterification from citric acid is most common.

Enzymatic catalysis: Lipases and esterases can catalyze esterification under milder conditions (lower temperature, solvent-free, or low-water activity systems) — attractive for specialty or high-purity applications though less common at large scale due to cost and throughput.

Lab-scale procedure (representative)
A typical laboratory synthesis involves citric acid monohydrate, excess absolute ethanol, p-toluenesulfonic acid (catalyst), and azeotropic removal of water using a Dean–Stark apparatus. 
After reflux and completion by TLC or GC monitoring, the reaction mixture is neutralized (e.g., sodium bicarbonate), filtered to remove salts, and solvent removed by rotary evaporation. 
Final purification can be performed by vacuum distillation or column chromatography for analytical grade product.

Purification and quality control
Purification techniques
Vacuum distillation: Due to the high boiling point and thermal sensitivity, vacuum distillation is commonly used for purification and solvent removal.
Liquid–liquid extraction: Following neutralization of acid catalysts and removal of inorganic salts, organic phase can be separated and washed to remove polar impurities.
Adsorption and filtration: Activated carbon or silica treatment may remove color bodies and trace impurities.
Quality control parameters
Assay by GC-FID or GC-MS (after appropriate derivatization or direct analysis): purity expressed as % w/w.
Water content (Karl Fischer titration): critical for applications sensitive to water (e.g., polymer processing, pharmaceuticals).
Acid value and ester content: titrimetric determination to ensure complete esterification and absence of free acid.
Heavy metals: ICP-MS or AAS screening for regulatory compliance in food and pharmaceutical grades.
Residual solvents: GC analysis to confirm low residual ethanol or other process solvents.

Analytical methods
Gas chromatography (GC)
GC coupled with flame ionization detection (FID) or mass spectrometry (MS) is commonly used for quantification and impurity profiling of TEC and related esters. 
Typical sample preparation involves dilution in a suitable organic solvent; derivatization is rarely necessary for TEC due to its volatility under GC conditions when appropriately heated and injected.

SAFETY INFORMATION ABOUT TRIETHYL CITRATE

First aid measures:
Description of first aid measures:
General advice:
Consult a physician. 
Show this safety data sheet to the doctor in attendance.
Move out of dangerous area:
 
If inhaled:
If breathed in, move person into fresh air. 
If not breathing, give artificial respiration.
Consult a physician.
In case of skin contact:
Take off contaminated clothing and shoes immediately. 
Wash off with soap and plenty of water.
Consult a physician.
 
In case of eye contact:
Rinse thoroughly with plenty of water for at least 15 minutes and consult a physician.
Continue rinsing eyes during transport to hospital.
 
If swallowed:
Do NOT induce vomiting. 
Never give anything by mouth to an unconscious person. 
Rinse mouth with water. 
Consult a physician.
 
Firefighting measures:
Extinguishing media:
Suitable extinguishing media:
Use water spray, alcohol-resistant foam, dry chemical or carbon dioxide.
Special hazards arising from the substance or mixture
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas
 
Advice for firefighters:
Wear self-contained breathing apparatus for firefighting if necessary.
Accidental release measures:
Personal precautions, protective equipment and emergency procedures
Use personal protective equipment. 
 
Avoid breathing vapours, mist or gas. 
Evacuate personnel to safe areas.
 
Environmental precautions:
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
 
Methods and materials for containment and cleaning up:
Soak up with inert absorbent material and dispose of as hazardous waste. 
Keep in suitable, closed containers for disposal.
 
Handling and storage:
Precautions for safe handling:
Avoid inhalation of vapour or mist.
 
Conditions for safe storage, including any incompatibilities:
Keep container tightly closed in a dry and well-ventilated place. 
Containers which are opened must be carefully resealed and kept upright to prevent leakage.
Storage class (TRGS 510): 8A: Combustible, corrosive hazardous materials
 
Exposure controls/personal protection:
Control parameters:
Components with workplace control parameters
Contains no substances with occupational exposure limit values.
Exposure controls:
Appropriate engineering controls:
Handle in accordance with good industrial hygiene and safety practice.
Wash hands before breaks and at the end of workday.
 
Personal protective equipment:
Eye/face protection:
Tightly fitting safety goggles. 
Faceshield (8-inch minimum). 
Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).
 
Skin protection:
Handle with gloves. 
Gloves must be inspected prior to use. 
Use proper glove
removal technique (without touching glove's outer surface) to avoid skin contact with this product. 
Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices. 
Wash and dry hands.
 
Full contact:
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
Splash contact
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
It should not be construed as offering an approval for any specific use scenario.
 
Body Protection:
Complete suit protecting against chemicals, The type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace.
Respiratory protection:
Where risk assessment shows air-purifying respirators are appropriate use a fullface respirator with multi-purpose combination (US) or type ABEK (EN 14387) respirator cartridges as a backup to engineering controls. 
 
If the respirator is the sole means of protection, use a full-face supplied air respirator. 
Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU).
Control of environmental exposure
Prevent further leakage or spillage if safe to do so. 
Do not let product enter drains.
Discharge into the environment must be avoided.
 
Stability and reactivity:
Chemical stability:
Stable under recommended storage conditions.
Incompatible materials:
Strong oxidizing agents:
Hazardous decomposition products:
Hazardous decomposition products formed under fire conditions. 
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas.
 
Disposal considerations:
Waste treatment methods:
Product:
Offer surplus and non-recyclable solutions to a licensed disposal company. 
Contact a licensed professional waste disposal service to dispose of this material.
Contaminated packaging:
Dispose of as unused product