Abstract:
A process for synthesizing an aminosulfur trifluoride is provided. The process includes reacting a secondary amine with SF 4  to produce the aminosulfur trifluoride product and a liquid amine-HF adduct. Substantially no solid amine-HF adduct is produced in the one-step reaction of the process. The reaction is conducted in a reaction solvent containing a tertiary amine. The process produces aminosulfur trifluorides, such as dialkyl, diaryl and arylalkyl aminosulfur trifluorides, in high yields.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The invention generally relates to methods for synthesizing aminosulfur trifluorides and more particularly to methods for synthesizing dialkyl, diaryl, and arylalkyl aminosulfur trifluorides. 
     In view of the importance of organo-fluorine compounds in the pharmaceutical and agrochemical industries, efforts aimed at the development of simple, safe, and efficient methods for their synthesis have escalated in recent years. The conversion of carbon-oxygen to carbon-fluorine bonds by nucleophilic fluorinating sources (deoxofluorination) represents one such technique which has been widely used for the selective introduction of fluorine into organic molecules. This transformation has been accomplished routinely with dialkylaminosulfur trifluorides, such as DAST (NEt 2  SF 3 ) and more recently with bis(2-methoxyethyl) aminosulfur trifluoride. 
     Middleton, 40(5) J. Org. Chem. 574 (1975), describes a process for obtaining dialkylaminosulfur trifluorides, such as DAST, in a two-step process starting from a secondary amine. The amine is silylated with trimethyl silyl chloride or hexamethyl disilazane. After isolation, the silylated amine is reacted with sulfur tetrafluoride to obtain the trifluoride. 
     As a two-step process, the Middleton process is typically carried out in two reaction vessels. In addition, the process requires the isolation of a pure intermediate, adding to the complexity and cost of the process. 
     SU Patent No. 1864289 (Markovskii et. al.) describes a more concise process for preparing dialkylaminosulfur trifluorides, as well as an arylalkyl aminosulfur trifluoride. Markovskii et al. prepared aminosulfur trifluorides in a one-step reaction by reacting the corresponding secondary amine with sulfur tetrafluoride in the presence of an amine base that produces a solid amine-HF adduct. This adduct is filtered to obtain the trifluoride in solution of the reaction solvent. Unfortunately, it is difficult to cleanly remove the solid amine-HF adduct from the product because small particles of adduct can escape the filter. In addition, a small amount of adduct is soluble in the reaction solvent and is retained in the product after filtration and evaporation of the solvent. 
     Accordingly, it is desired to provide a method for producing aminosulfur trifluorides which does not suffer from the aforementioned deficiencies of prior art methods. 
     All references cited herein are incorporated herein by reference in their entireties. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention addresses at least the foregoing deficiencies of the prior art by providing a process for synthesizing an aminosulfur trifluoride, said process comprising reacting a secondary amine with SF 4  under conditions such that said aminosulfur trifluoride and a liquid amine-HF adduct are produced. Substantially no solid amine-HF adduct is produced in the one-step reaction of the process. The reaction is conducted in a reaction solvent containing a tertiary amine. The process produces aminosulfur trifluorides, such as dialkyl, diaryl and arylalkyl aminosulfur trifluorides, in high yields. 
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     Not applicable. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a process for the synthesis of aminosulfur trifluorides, such as, e.g., dialkyl, diaryl and arylalkyl aminosulfur trifluorides. The process involves reacting a secondary amine with SF 4  in the presence of a tertiary amine to produce the aminosulfur trifluoride and a liquid amine-HF adduct, which is immiscible in the reaction solution containing the aminosulfur trifluoride. The adduct separates out as a heavy layer, thus providing for the facile separation from the reaction product mixture. 
     Unlike certain prior art processes, embodiments of the inventive process can be carried out in one reaction vessel which makes it more convenient and less expensive for industrial utility. Another economic advantage is that the process does not require the isolation of a pure intermediate. Furthermore, because a liquid amine-HF adduct rather than a solid HF-adduct is produced, a greater product yield is obtained. This is because in the prior art process it is difficult to cleanly remove the solid HF-adduct from the product owing to retention of small particles of adduct which can escape the filter. In addition, a small amount of adduct is soluble in the reaction solvent and is retained in the product after filtration and evaporation of the solvent. 
     In the inventive process, the secondary amine is reacted with SF 4  in a solvent containing the tertiary amine. The insoluble liquid is separated. After removal of the solvent (preferably by distillation), the product is preferably redissolved into a less polar extraction solvent to remove residual amine-HF adduct. Separation of the latter followed by distillation affords the pure aminosulfur trifluoride. 
     Preferred secondary amines include dialkyl, diaryl and aryl alkyl amines. 
     Suitable tertiary amines produce a liquid amine-HF adduct at a temperature ranging from -78° C. to the boiling point of the reaction solvent. Preferred tertiary amines include trimethylamine, ethyl dimethylamine, N-methylpyrrolidine, tripropylamine, tributylamine, tripentylamine, trihexylamine, N-methyl-N-propyl-N-butylamine, and N-ethyl-N-isopropyl-N-butylamine. 
     The reaction solvent is any solvent which will not react with SF 4  or the aminosulfur trifluoride product of the process and which will not dissolve the amine-HF adduct. Preferred reaction solvents include organics, such as dialkyl ethers, hydrocarbons, and halogenated hydrocarbons. A particularly preferred reaction solvent is methyl-t-butylether (MTBE). 
     The extraction solvent used for extraction is any solvent which will selectively dissolve the trifluoride over the amine-HF adduct, e.g., organics, such as alkanes and alkenes. Preferred extraction solvents include pentane and hexane. 
     The invention will be illustrated in more detail with reference to the following examples, but it should be understood that the present invention is not deemed to be limited thereto. 
     Reaction temperature may be in the range of -78° C. to the boiling point of the solvent. Table 1 summarizes the products obtained using this process. 
     EXAMPLE 1 
     Diethylaminosulfur trifluoride using N-methylpyrrolidine as HF scavenger 
     A solution of N-methylpyrrolidine (12.77 g, 150 mmol) in methyl-t-butyl ether (100 mL) was charged into a 300 mL Parr reactor equipped with a magnetic stirring shaft, and via swage connections one port was attached to a 100 mL pressure equalized dropping funnel. The reactor was connected by a N 2  inlet tube, and a SF 4  gas inlet tube to a metal vacuum line manifold which was in turn attached to a SF 4  cylinder, a 1 L stainless steel ballast equipped with a pressure gauge, a soda-lime trap and a vacuum pump. The reactor was cooled to -30° C. with a dry ice/acetone bath. The 1 L ballast in the manifold was filled with SF 4  from a gas cylinder to produce a pressure of SF 4  of 52.2 psia (150 mmol). The reactor was evacuated in vacuo and the SF 4  was introduced into it slowly. A solution of diethylamine (10.95 g, 150 mmol) in methyl-t-butyl ether (25 mL) from the dropping funnel was slowly added to the solution. After stirring for 30 min, the excess SF 4  was pumped out of the solution through the soda-lime trap and the reactor was filled with N 2  to approximately atmospheric pressure (˜15 psi). The lower layer was separated and the solution was evaporated in vacuo. The residue was dissolved into 20 mL of pentane and the lower layer was again separated. The solvent was evaporated to afford 15.2 g (63% yield) of product. 
     EXAMPLE 2 
     Diphenylaminosulfur trifluoride using N-methylpyrrolidine as HF scavenger 
     Diphenylaminosulfur trifluoride was prepared as described above by reacting diphenylamine (150 mmol, 25.35 g) with SF 4  (150 mmol) in methyl-t-butyl ether in the presence of N-methylpyrrolidine (12.77 g, 150 mmol). Work up as above afforded 29.68 g (77% yield) of product. H NMR (CDCl 3 ) d 7.5-7.3 (m, 10H), F (CDCl 3 ) d 69.5 (d, 2F), 31 (t, IF). 
     EXAMPLE 3 
     N-methyl-N-phenylaminosulfur trifluoride using N-methylpyrrolidine as HF scavenger 
     N-methyl-N-phenylaminosulfur trifluoride was obtained as above by reacting N-methylaniline (16.05 g, 150 mmol) with SF 4  (150 mmol) in methyl-t-butyl ether in the presence of N-methylpyrrolidine (12.77 g, 150 mmol). Work up as above afforded 15.60 g (80% yield ) of product. H NMR (CDCl 3 ) d 7.5-7.3 (m, 3H), 7.3-7.0 (m, 2H) 3.4 (s, 3H). F (CDCl 3 ) d 64 (d, 2F), 26 (t,1 F). 
     EXAMPLE 4 
     Bis(2-methoxyethyl)aminosulfur trifluoride using N-methylpyrrolidine as HF scavenger 
     Bis(2-methoxyethyl)aminosulfur trifluoride was obtained as above by reacting bis(2-methoxyethyl)amine (19.95 g, 150 mmol) with SF 4  (150 mmol) in methyl-t-butyl ether in the presence of N-methylpyrrolidine (12.77 g, 150 mmol). Work up as above afforded 24.86 g (75% yield ) of product. H NMR (CDCl 3 ) d 3.5 (t, 4H), 3.15 (t, 4H) 3.05 (s, 6H). F (CDCl 3 ) d 55 (s, br, 2F), 28 (s, br, 1F). 
     EXAMPLE 5 
     Bis(2-methoxyethyl)aminosulfur trifluoride using trimethylamine as HF scavenger 
     Bis(2-methoxyethyl)aminosulfur trifluoride was obtained as above by reacting bis(2-methoxyethyl)amine (19.95 g, 150 mmol) with SF 4  (150 mmol) in methyl-t-butyl ether in the presence of trimethylamine (8.87 g, 150 mmol). Work up as above afforded 26.52 g (80% yield ) of product. H NMR (CDCl 3 ) d 3.5 (t, 4H), 3.15 (t, 4H) 3.05 (s, 6H). F (CDCl 3 ) d 55 (s, br, 2F), 28 (s, br,1 F). 
     EXAMPLE 6 
     Bis(2-methoxyethyl)aminosulfur trifluoride using N,N-dimethylethylamine as HF scavenger 
     Bis(2-methoxyethyl)aminosulfur trifluoride was obtained as above by reacting bis(2-methoxyethyl)amine (19.95 g, 150 mmol) with SF 4  (150 mmol) in methyl-t-butyl ether in the presence of N,N-dimethylethylamine (10.97 g, 150 mmol). Work up as above afforded 26.52 g (80% yield ) of product. H NMR (CDCl 3 ) d 3.5 (t, 4H), 3.15 (t, 4H) 3.05 (s, 6H). F (CDCl 3 ) d 55 (s, br, 2F), 28 (s, br, 1 F). 
     The examples are summarized in Table 1, below. 
     
                       TABLE 1______________________________________Preparation of aminosulfur trifluorides  #STR1##      3°            Physical state of   amine (HF  amine.HF adduct at  Starting 2° amine scavenger) Product (% yield) 25°______________________________________                           C.(C.sub.2 H.sub.5).sub.2 NH      Et.sub.3 N               58          solid  (MeOCH.sub.2 CH.sub.2).sub.2 NH Et.sub.3 N 65 solid   - (C.sub.2 H.sub.5).sub.2 NH                             63 liquid   - Ph.sub.2 NH                             77 liquid   - PhNHMe                             80 liquid   - (MeOCH.sub.2 CH.sub.2).sub.2 NH                             75 liquid   - (MeOCH.sub.2 CH.sub.2).sub.2 NH Me.sub.3 N 80 liquid  (MeOCH.sub.2 CH.sub.2).sub.2 NH Me.sub.2 NEt 80 liquid______________________________________ 
    
     While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. 
     SEQUENCE LISTING 
     Not applicable.