Name: Diethylaminosulfur trifluoride
Other Names: DAST; (Diethylamino)sulfur trifluoride; (Diethylamino)sulphur trifluoride; ET2NSF3; Sulfur trifluoride diethylamine complex
CAS No.: 38078-09-0
EINECS No.: 253-771-2
Chemical Formula: C₄H₁₀F₃NS
Molecular Weight: 161.19
InChI 1S/C₄H₁₀F₃NS/c1-3-8(4-2)9(5,6)7/h3-4H2,1-2H3
Density: 1.22 g/mL (25 °C)
Boiling Point: 30–32 °C (3 mmHg); Approximately 163.7 °C (decomposes) at normal pressure
Flash point 23 °C (73.4 °F)
Water solubility: Decomposes in water
Vapor pressure 2.0 ± 0.3 mmHg (25 °C)
Refractive index 1.41–1.416
Storage conditions: 2–8 °C, sealed, protected from nitrogen, keep away from fire and moisture
Sensitivity: Moisture sensitive
Appearance: Colorless to pale yellow transparent liquid
Specific gravity 1.220 (20/20)
Color: Colorless to yellow to orange
BRN 1849066
MDL No. MFCD00000363
Hazard symbols: GHS02 (flammable), GHS05 (corrosive), GHS07 (health hazards); Signal word: Danger
Risk terms H226 (Flammable liquids and vapors), H302+H312+H332 (Hazardous if swallowed, contacted with skin, or inhaled), H314 (Causes severe skin burns and eye damage), H335 (May cause respiratory irritation), H351 (Possibly carcinogenic). Safety Terms: P210 (Keep away from heat/sparks/open flames), P260 (Do not inhale dust/fumes), P280 (Wear protective gloves/eye protection/face shield), P303+P361+P353 (If skin contact occurs, immediately remove contaminated clothing and rinse), P305+P351+P338 (If eye contact occurs, rinse with water), P310 (Immediately call a poison control center/doctor), P403+P235 (Store in a well-ventilated place, keep cool). Customs Code 29309070 (Common Chinese Classification); 2921.19.6195 (TCI Classification); 2930909090 (Partial Source)
I. Properties
Diethylaminosulfur trifluoride (DAST, CAS 38078-09-0) is a colorless to pale yellow transparent liquid at room temperature and pressure, with a pungent odor. Its density is approximately 1.22 g/mL, and its boiling point is 30–32 °C (3 mmHg) under reduced pressure. It decomposes at approximately 163 °C under normal pressure. Its refractive index is 1.41–1.416, and its flash point is approximately 23 °C. It is a flammable liquid.
DAST is extremely sensitive to moisture and reacts violently with water, decomposing to produce corrosive substances such as hydrofluoric acid (HF). Therefore, strict waterproofing is essential during handling. It is soluble in most nonpolar organic solvents, such as dichloromethane (CH₂Cl₂), chloroform (CHCl₃), and carbon tetrachloride (CCl₄), but decomposes in water. Furthermore, pure DAST may explode upon heating above 40–50 °C, exhibiting poor thermal stability; therefore, for high-temperature reactions, it is recommended to use more stable alternatives (such as Deoxofluor/BAST).
II. Applications
DAST is one of the most widely used nucleophilic fluorinating reagents in organic synthesis, considered a core tool in the field of fluorination. Its main applications include:
* Alcohol fluorination: Converting primary and secondary alcohols to the corresponding fluoroalkanes under mild conditions (typically fed at –78 °C and heated to room temperature).
* Carbonyl compound fluorination: Converting aldehydes and ketones to gem-difluorides; aldehydes require milder reaction conditions, while ketones require appropriate heating or prolonged reflux.
* Acyl chloride conversion: Reacting with acyl chlorides to form acyl fluorides.
Drug Synthesis: Widely used in the preparation of intermediates for anticancer drugs, antiviral drugs, and fluorinated pesticides, DAST is introduced into molecules to improve metabolic stability and bioactivity.
Novel Applications: Recent studies have shown that DAST can also be used as a medium for the Beckmann rearrangement/cyclization reaction of oxime compounds, synthesizing polysubstituted 2-oxazoline, benzimidazole, and benzopyrazole heterocyclic compounds.
III. Preparation Method: The laboratory preparation of DAST typically involves the reaction of diethylaminotrimethylsilane with sulfur tetrafluoride (SF₄): At –65 °C to –60 °C, 96 g (0.66 mol) of diethylaminotrimethylsilane is dissolved in 100 mL of trichlorofluoromethane and slowly added dropwise to 40 mL (0.72 mol, –78 °C) of sulfur tetrafluoride in 200 mL of trichlorofluoromethane solution. After the reaction mixture was heated to room temperature, it was distilled under reduced pressure to obtain a pale yellow liquid, DAST, with a boiling point of 46–47 °C (10 mmHg) and a yield of approximately 84%.
This preparation process requires strictly anhydrous and oxygen-free operation, as both the raw materials and the product are sensitive to moisture. Industrially, DAST is typically produced on a large scale by specialized chemical manufacturers under nitrogen protection, achieving a purity of ≥95%–99%.
IV. Safety Information
DAST is flammable, corrosive, and thermally unstable, requiring extremely strict safe handling:
Health Hazards: Harmful if swallowed, comes into contact with skin, or is inhaled; causes severe skin burns and eye damage; decomposition products contain HF, which can corrode the respiratory tract.
Fire and Explosion Hazards: Flammable liquid and vapor, flash point 23 °C; may explode upon heating above 50 °C.
Reactivity: Reacts violently with water to produce HF; incompatible with glass, alcohols, strong oxidizers, strong acids, and strong bases.
Handling Protection: Must be handled in a fume hood; wear chemically resistant gloves (nitrile or neoprene), goggles/face shield, and lab coat.
Storage Requirements: Refrigerate at 2–8 °C, under nitrogen protection, sealed in a cool, dry place away from sources of ignition and incompatible substances.
Emergency Treatment: Skin contact: Immediately remove contaminated clothing and flush with plenty of water for at least 15 minutes. Eye contact: Immediately flush with running water and seek medical attention. Inhalation: Move to fresh air.
Transport Information: UN Number: UN 2920 (8 Class 3 corrosive/flammable liquid); Packaging category: I
Post time: May-14-2026
