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18th June 2010 @ 07:56
Starting material for the synthesis of N-triflyl phosphoramides - strong chiral Brønsted acid catalysts for asymmetric Pictet-Spengler reactions [1]

Reaction Scheme correction



Table1 correction



Start time: 3:05 PM 18/06/2010
End time: 4:50 PM 18/06/2010

Procedure: [2]
Ammonia gas (30 mL liquid, 25.4 g, 212 mmol, 15 eq.) was condensed in 3-neck-flask fitted with a dry ice condenser at -78°. Trifluoromethanesulfonic acid (2.4 mL, 4.00 g, 14.2 mmol) was added dropwise over a period of 45 min. . The excess of ammonia was evaporated by allowing the reaction to warm to room temperature.

The colorless and solid remain was purified by sublimation under vacuum:
- first sublimation with a cold finger wasn’t successful – bumping mixture
- Second trial: two flasks connected with a distillation bridge, oil bath temperature: 130 °C, pressure ~ 1mbar

Result:
Product MW38-1: 1.41 g (9.47 mmol, 67%) colorless crystalline solid; yield reference: 89% [1]

Analytical data:
m.p. 118.5-120°C. ref
IR (neat): nu = 3388 cm-1, 3279, 1519, 1352, 1147, 943, 611.


References:
[1] “Design of Chiral N-Triflyl Phosphoramide as a Strong Chiral Brønsted Acid and Its Application to Asymmetric Diels-Alder Reaction", D. Nakashima and H. Yamamoto, J. Am. Chem. Soc. 2006, 128, 30, 9626–9627.

[2] "Synthesis of 3,6-dioxa-Δ7-4-trifluoromethyl perfluorooctyl trifluoromethyl sulfonimide: bis[(perfluoroalkyl)sulfonyl] superacid monomer and polymer", B. H. Thomas, G. Shafer, J. Ji Ma, M.-H. Tu and D. D. DesMarteau, J. Fluorine Chem. 2004, 125, 8, 1231-1240.

[3] "500. Fluorinated sulphonic acids. Part I. Perfluoro-methane-, -octane-, and -decane-sulphonic acids and their simple derivatives", J. Burdon, I. Farazmand, M. Stacey and J. C. Tatlow, J. Chem. Soc. 1957, 2574 - 2578, DOI: 10.1039/JR9570002574.

Procedure from reference: [2]

4.7. Preparation of CF3SO2NH2 (11)

Into a specially fabricated addition funnel which could be
evacuated was placed 61.74 g (218.8 mmol) of (CF3SO2)2O.
To a 250 mL two-necked round bottom flask was condensed
115 g (6.7 mol) of anhydrous ammonia. The flask was
removed from the vacuum line and fitted with the addition
funnel containing (CF3SO2)2O, a magnetic stirrer, and a
drying tube to exclude moisture. The reaction mixture was
placed in a -78 °C bath and the anhydride was added
dropwise over a 2 h period. The excess ammonia was
removed by allowing the reaction to warm to room temperature,
leaving a white solid. The product was purified by
sublimation at 80 8C under vacuum to give 28.96 g
(194.3 mmol) of white crystalline product (89% yield).
19F NMR (CD3CN) d(CF3) -79.4 (3F,s); 1H NMR (CD3CN)
d (NH2) 6.6 (2H,s); IR (solid, KBr pellet) 3379 (s); 3372 (s);
1511 (m); 1348 (s); 1232 (m); 1185 (s); 1155 (m).
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Reaction Scheme
Table1
Reaction Scheme correction
Table1 correction