Synthesis and solid state structure of fluorous probe molecules for fluorous separation applications

Abstract

A series of colored hydrocarbon and fluorocarbon tagged 1-fluoro-4-alkylamino-anthraquinones and 1,4-bis-alkylamino-anthraquinone probe molecules were synthesized from a (fluorinated) alkyl amine and 1,4-difluoroanthraquinone to aid in the development of fluorous separation applications. The anthraquinones displayed stacking of the anthraquinone tricycle and interdigitation of the (fluorinated) alkyl chains in the solid state. Furthermore, intramolecular N-H···O hydrogen bonds forced the hydrocarbon and fluorocarbon tags into a conformation pointing away from the anthraquinone tricycle, with the angle of the tricycle plane normal and the main (fluorinated) alkyl vector ranging from 1 to 39°. Separation of the probe molecules on fluorous silica gel showed that the degree of fluorination of the probe molecules plays only a minor role with most eluents (e.g., hexane-ethyl acetate and methyl nonafluorobutyl ethers-ethyl acetate). However, toluene as eluent caused a pronounced separation by degree of fluorination for fluorocarbon, but not hydrocarbon tagged probe molecules on both silica gel and fluorous silica gel. These studies suggest that hydrocarbon and fluorocarbon tagged anthraquinones are useful probe molecules for the development of laboratory scale fluorous separation applications.

A Research Module for the Organic Chemistry Laboratory: Multistep Synthesis of a Fluorous Dye Molecule

“…13 After encountering difficulty early in the development phase for such a project, a fluorous aminoanthraquinone target was selected (Scheme 1). The rationale for this selection drew upon the precedent that compounds of type 1a (R = CH 2 R F , X = F, where R F is perfluoroalkyl) are known to be useful molecules for visualizing fluorous separations, 14 whereas aminoanthraquinones of type 1b (R = alkyl or aryl, X = OTs) are known to be easily accessed from a readily available, inexpensive starting material (quinizarin, 2). 15 Once the target was selected, a route was devised that would require students to engage in multistep synthesis.…”

“…(21) The 1,4-difluoroanthraquinone precursor (Scheme 1; prices quoted from Sigma Aldrich, October 2013) and the fluorous amines used in ref 14 were purchased for that study.…”

Visual Monitoring of Solid-Phase Extraction Using Chromogenic Fluorous Synthesis Supports

“…For example, if the SPE cartridge remains colored after the elution step additional solvent­(s) can be added to elute all the color. While fluorous dyes have been reported previously, − there do not appear to be any reports of derivatives that also incorporate a reactive functional group for use as a synthesis support or linker (to use solid-phase terminology). Although there are many permutations for a trifunctional molecule comprising a fluorous tag, chromophore, and linker, it is important to retain the fluorous character and high solubility in organic solvents that characterize conventional tags.…”