Preparation, Characterization, and Physical Properties of Bis(imidazole)sulfur Difluoride and Bis(4-phenylimidazole)sulfur Difluoride. New Compositions with Unexpected Thermal Stability

Abstract

Two new bis(imidazole)sulfur difluoride compositions, (imid)(2)SF(2) (2) and (4-Ph-imid)(2)SF(2) (4), have been prepared in high yields from the reactions involving the corresponding TMS precursors and excess SF(4) in anhydrous solvent. Mechanisms are proposed to account for the formation of 2 and 4 preferentially over the corresponding SF(3) derivatives or other isomers containing the SF(2) moiety. These new compositions are stable solids which melt at high temperatures and have been characterized in solution by (1)H, (13)C, and (19)F NMR spectroscopy and in the solid state by MS (EI), elemental analysis, and single-crystal X-ray diffraction. The crystal structures of 2 and 4 are each based on a pseudo-trigonal-bipyramidal arrangement of two fluorines and two imidazole groups around the central sulfur, with the fluorines occupying axial positions and the imidazole groups in equatorial positions as predicted for these AX(4)E compounds by the VSEPR model. Thermal decomposition properties of 2 and 4 have been studied using the Radex-Solo thermal hazards screening system. Compounds 2 and 4 have decomposition onset temperatures similar to those of several common R(2)NSF(3) compounds; however, the thermal decomposition of 2 and 4 occurs at much slower rates than that of the R(2)NSF(3) compounds and without the rapid release of gaseous byproducts, which is generally characteristic of explosive decomposition events. Therefore, by comparison, compounds 2 and 4 are inherently safer to handle and use.

(S)-Nitroxycarnitine nitrate production from (S)-carnitine by using acetic anhydride/nitric acid/acetic acid mixtures: safety assessment

“…For scannig runs, a PC-Combilab (by Systag) equipped with a Radex oven [7] was used. In all the runs stainless steel reactors (100 bar) were used and the following operating parameters adopted: initial temperature 293 K, heat rate: 1.5 K min −1 .…”

Kinetic and safety assessment for salicylic acid nitration by nitric acid/acetic acid system

“…For isothermal experiments, a RADEX oven [11] equipped with a closed high pressure stainless steel reactor (V = 0.004 l) and driven by a PC Combilab (SystAG, CH) has been used. Since the reactors do not allow any external addition during the course of the reaction, chemical mixtures were prepared at ambient temperature outside the oven by dissolving a suitable amount of reagents (nitro-derivatives of the salycilic acid) in the proper solution HNO 3 /acetic acid.…”

“…The values of k 10 and E 10 previously estimated have been then inserted in these equations and by a similar procedure, kinetic parameters for the reactions (4), (5) and (11) evaluated from the data gathered for 5-NS nitration (see Table 1). Table 1 Kinetic parameters identified for reactions (4), (5) and (11) k 0 4 (l mol −1 min −1 ) 1.03 × 10 20 E 4 (kJ mol −1 ) 145.38 k 0 5 (l mol −1 min −1 ) 9.73 × 10 17 E 5 (kJ mol −1 ) 136.21 k 0 11 (l mol −1 min −1 ) 4.62 × 10 19 E 11 (kJ mol −1 ) 142.45 Table 2 Kinetic parameters identified for reactions (8), (9) and (12) k 0 8 (l mol −1 min −1 ) 3.95 × 10 21 E 8 (kJ mol −1 ) 147.72 k 0 9 (l mol −1 min −1 ) 1.79 × 10 23 E 9 (kJ mol −1 ) 155.30 k 0 12 (l mol −1 min −1 ) 1.68 × 10 19 E 12 (kJ mol −1 ) 129.93 Table 3 Kinetic parameters identified for reactions (6) and (7) k 0 6 (l mol −1 min −1 ) 1.15 × 10 20 E 6 (kJ mol −1 ) 127.29 k 0 7 (l mol −1 min −1 ) 5.89 × 10 20 E 7 (kJ mol −1 ) 132. 15 Similarly kinetic parameters for the reactions (8), (9) and (12) have been derived from the data collected during 3-NS nitration (see Table 2).…”

Tris(dimethylamino)oxosulfonium Difluorotrimethylsilicate, (Me2N)3SO+Me3SiF2- (TAOS Fluoride)

“…In the reaction of SF 4 with R 2 NSiMe 3 the sulfur-bonded fluorine substituents are exchanged in a stepwise manner for Me 2 N groups [1][2][3][4][5][6][7][8][9][10][11] forming R 2 NSF 3 (DAST) (dialkylaminosulfur trifluoride), (R 2 N) 2 SF 2 , and (R 2 N) 3 S + Me 3 SiF 2 -(TASF) (tris(dialkylamino)sulfonium "fluoride") 7,8,12 Besides SF 4 13 DAST 14 is of great importance in preparative chemistry for the introduction of fluorine into inorganic and organic molecules; the use of (R 2 N) 2 SF 2 is limited because it tends to decompose explosively at higher temperatures. 10,15 TASF is widely used as a reagent containing an almost "naked" fluoride. [16][17][18][19] In its reactivity OSF 4 is similar to SF 4 ; an analogous substitution pattern is expected for the reaction with silylamines.…”

“…In the reaction of SF 4 with R 2 NSiMe 3 the sulfur-bonded fluorine substituents are exchanged in a stepwise manner for Me 2 N groups − forming R 2 NSF 3 (DAST) ( d i a lkylamino s ulfur t rifluoride), (R 2 N) 2 SF 2 , and (R 2 N) 3 S + Me 3 SiF 2 - (TASF) ( t ris(di a lkylamino) s ulfonium “ f luoride”) 7,8,12 Besides SF 4 13 DAST 14 is of great importance in preparative chemistry for the introduction of fluorine into inorganic and organic molecules; the use of (R 2 N) 2 SF 2 is limited because it tends to decompose explosively at higher temperatures. , TASF is widely used as a reagent containing an almost “naked” fluoride. − In its reactivity OSF 4 is similar to SF 4 ; an analogous substitution pattern is expected for the reaction with silylamines. Due to its much more limited availability only a few reactions of this type have been described for OSF 4 .…”