Diethylaminosulfur trifluoride

English Name: Diethylaminosulfur trifluoride
English Synonyms: DAST; ET2NSF3; DIETHYLAMINOSULPHUR TRIFLUORIDE; (diethylamino)trifluorosulfur; Diethylamine sulfur trifluoride
CAS No.: 38078-09-0
EINECS No.: 253-771-2
Chemical Formula: C₄H₁₀F₃NS
Molecular Weight: 161.19 g/mol
InChI: InChI=1/C4H10F3NS/c1-3-8(4-2)9(5,6)7/h3-4H2,1-2H3
Density: 1.220 g/mL (25°C)
Boiling Point: 30-32°C (3 mmHg); 163.7°C (760 mmHg)
Flash Point: 23°C (73.4°F)
Water Solubility: Decomposes (Decomposes in water to produce HF)
Vapor pressure: 2.0±0.3 mmHg (25°C)
Refractive index: 1.41-1.416
Storage conditions: 2-8°C, low temperature, nitrogen protection, dry environment
Sensitivity: Moisture sensitive
Appearance: Pale yellow to brownish-yellow transparent liquid
Specific gravity: 1.22
Color: Colorless to yellow to orange
BRN: 1849066
MDL: MFCD00000363
Hazard symbols: C, T, F (Corrosive, Toxic, Flammable)
Risk terms: R10 (Flammable), R14 (Reacts violently with water), R20/21/22 (Harmful if inhaled/skin contact/ingested), R34 (Causes burns), R35 (Causes severe burns), R40 (May have irreversible effects)
Safety terms: S16 (Keep away from fire), S26 (Rinse eyes immediately upon contact), S36/37/39 (Wear appropriate protective clothing, gloves, and goggles), S45 (Seek immediate medical attention in case of accident or discomfort)

Customs Code: 29309070

Properties: Diethylaminosulfur trifluoride (DAST) is a nucleophilic fluorinating agent, belonging to the (dialkylamino)sulfur trifluoride family. It is a liquid at room temperature and pressure, relatively stable, but sensitive to moisture, reacting violently with water to form hydrofluoric acid (HF). It has poor thermal stability; heating above 40-50°C may cause an explosion, and it decomposes at 90°C. It is soluble in most nonpolar organic solvents (such as CH₂Cl₂, CHCl₃, CCl₄) and can be used in standard glassware, but will corrode glass. Vapor/air mixtures are explosive when intensely heated.

Applications

DAST is one of the most widely used fluorinating reagents in organic synthesis, mainly used for:
Converting hydroxyl groups of alcohols to fluoroalkanes (primary alcohols react at -78°C, secondary alcohols require heating or reflux)
Converting aldehydes and ketones to geminal difluorides
Converting acyl chlorides to acyl fluorides
Reacting with sulfoxides to give α-fluorothioethers, followed by oxidation to give α-fluorosulfoxides
Fluoride addition in the synthesis of anticancer drugs
Preparation of fluorinated drug intermediates (such as leflunomide, elexylamine, etc.)
Recently used in the baseless amidation reaction of carboxylic acids and amines
Preparation
DAST can be prepared by reacting diethylaminotrimethylsilane with sulfur tetrafluoride:
Dissolve 96 g (0.66 mol) of diethylaminotrimethylsilane in 100 mL of trichlorofluoromethane, and add dropwise to 40 mL (0.72 mol) of sulfur tetrafluoride in 200 mL of water. In a 10 mL solution of trichlorofluoromethane, the temperature is controlled at -65°C to -60°C. The reaction mixture is heated to room temperature and then distilled to give a pale yellow liquid product in approximately 84% yield.
Boiling point: 46-47°C (10 mmHg) or 30-32°C (3 mmHg)
Safety Information
Hazard: Class 8 Corrosive (UN…) 2920), its primary hazard is corrosiveness, and its secondary hazard is flammability; it may explode when heated above 40-50°C; it reacts violently with water, releasing toxic gases.

Handling Requirements: Must be carried out in a fume hood, away from heat sources, avoid contact with moisture, and use protective shields; wear full chemical-resistant work clothes, flame-retardant and anti-static protective clothing, and a full-face respirator.

Storage: Low temperature (2-8°C), nitrogen protection, dry environment, away from oxidizers, strong acids, strong alkalis, and ketones.

Emergency Measures: If it comes into contact with skin or eyes, immediately flush with plenty of water. In case of an accident, seek immediate medical attention.

Alternatives: When higher temperatures are required, it is recommended to use the safer BAST (Deoxofluor), which decomposes slowly upon heating without exploding.