Perfluorohexyl phases

D. P. Curran, S. Hadida, Tris(2-(Perfluorohexyl)tin Hybride A New Fluorous Reagent for Use in Traditional Organic Synthesis and Liquid Phase Combinatorial Synthesis , J. Am. Chem. Soc 1996,118,2531. 

On the heels of work by Zhu and Horvath and Rabai, perfluorocarbon solvents and fluorous reagents have been used increasingly in organic syntheses. Ruorous compounds often partition preferentially into a fluorous phase in organic/fluorous liquid-liquid extraction, thus providing easy separation of the compounds. Tris[(2-perfluorohexyl)ethyl]tin hydride combines the favorable radical reaction chemistry of trialkyltin hydrides with the favorable separation features of fluorous compounds. 

Tris[(2-perfluorohexyl)ethyl]tin hydride has three perfluorinated segments with ethylene spacers and it partitions primarily (> 98%) into the fluorous phase in a liquid-liquid extraction. This feature not only facilitates the purification of the product from the tin residue but also recovers toxic tin residue for further reuse. Stoichiometric reductive radical reactions with the fluorous tin hydride 3 have been previously reported and a catalytic procedure is also well established. The reduction of adamantyl bromide in BTF (benzotrifluoride) " using 1.2 equiv of the fluorous tin hydride and a catalytic amount of azobisisobutyronitrile (AIBN) was complete in 3 hr (Scheme 1). After the simple liquid-liquid extraction, adamantane was obtained in 90% yield in the organic layer and the fluorous tin bromide was separated from the fluorous phase. The recovered fluorous tin bromide was reduced and reused to give the same results. Phenylselenides, tertiary nitro compounds, and xanthates were also successfully reduced by the fluorous fin hydride. Standard radical additions and cyclizations can also be conducted as shown by the examples in Scheme 1. Hydrostannation reactions are also possible, and these are useful in the techniques of fluorous phase switching. Carbonylations are also possible. Rate constants for the reaction of the fluorous tin hydride with primary radicals and acyl radicals have been measured it is marginally more reactive than tributlytin hydrides. ... 

Curran DP, Hadida S, Tris(2-(perfluorohexyl)ethyl)tin hydride A new fluorous reagent for use in traditional organic synthesis and liquid phase combinatorial synthesis, J. Am. Chem. Soc., 118 2531-2532, 1996. 

A two-phase thermochromic behavior, as in PDDT and poly(3-methyl-4-octyloxythiophene), is related to the formation of delocalized conformational defects upon heating. These defects are possible due to the presence of sterically demanding substituents between each consecutive repeating unit [330]. In the solid state at room temperature, PDDT and poly(3-octyloxy-4-methyl-thiophene) have a coplanar conformation for the main chain. Heating (25 to 150°C) increases the repulsive intrachain steric interactions and introduces some conformational disorder in the side groups, forcing the polymer backbone to adopt a nonplanar conformation [331, 332]. Temperature dependent UV/vis absorption measurements of fluorinated PTs, e.g., poly(3 -perfluorohexyl-2,2 5, 2"-terthiophene), poly[3-(pentadecafluorooctyloxy)-4-methylthiophene] and poly[3-(tridecafluorononyl)thiophene], show a blue shift of the maximum... 

Group A containing the perfluorophenyl phases (e.g.. Discovery F5 HS and Fluophase PFP, column nos. 20 and 26), Group B the perfluorohexyl branched alkyl endcapped (e.g., Fluofix, column no. 24) and perfluoroctyl phases (e.g., Fluophase RP and FluoroSep RP Octyl, column nos. 27 and 28), and Group C the perfluorohexyl non-endcapped (e.g., Fluofix, column no. 25) and perfluoropropyl (e.g., Perfluorpropyl ESI, column no. 72) phases. 

A fluorous hydrazine-carbothioate organocatalyst was recently prepared from 2-perfluorohexyl ethanol by sequentially treating it with 1,1 -thiocarbonyl diimidazole and hydrazine. The fluorous catalyst together with N-chlorosuccinimide (NCS) efficiently catalyzed the acetalization of aldehydes [48]. The fluorous catalyst was recovered by fluorous solid-phase extraction with high purity for direct reuse for four times. According to the author, the formation of Cl" from NCS and catalyst might be catalyzing the acetalization reaction (Scheme 7.32). 

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