Abstract
We demonstrated in this work the use of affinity ionic liquids, AIL 1 and AIL 2, for chemoselective detection of amine and alcohol gases on a quartz crystal microbalance (QCM). These detections of gaseous amines and alcohols were achieved by nucleophilic aromatic substitution reactions with the electrophilic 1,3,5-triazine-based AIL 1 thin-coated on quartz chips. Starting with inexpensive reagents, bicyclic imidazolium ionic liquids AIL 1 and AIL 2 were readily synthesized in six and four synthetic steps with high isolated yields: 51% and 63%, respectively. The QCM platform developed in this work is readily applicable and highly sensitive to low molecular weight amine gases: for isobutylamine gas (a bacterial volatile) at 10 Hz decrease in resonance frequency (i.e., ΔF = −10 Hz), the detectability using AIL 1 was 6.3 ppb. Our preliminary investigation on detection of the much less nucleophilic alcohol gas by AIL 1 was also promising. To our knowledge, no example to date of reports based on nucleophilic aromatic substitution reactions demonstrating sensitive gas detection in these triazine ionic liquids on a QCM has been reported.
Highlights
Results and DiscussionScheme 1A illustrates the synthesis of AIL 1 of which the affinity element could be readily assembled from the commercially inexpensive cyanuric chloride (3), with a freshly prepared amine ionic liquid at ambient temperature
We commenced our synthesis of affinity ionic liquid AIL 1 from an inexpensive 2-(2-aminoethoxy)ethanol (1), which underwent a series of reactions (i.e., amine protection, alcohol mesylation, nucleophilic substitution with a bicyclic 6,7-dihydro-5H-pyrrolo[1,2-a]imidazole (2) previously developed in our laboratory [16], amine deprotection, and, lastly, anion methathesis with lithium bis(trifluoromethane)sulfonimide (LiNTf2) in water) to afford first an amine-functionalized ionic liquid
Using a different synthetic approach shown in Scheme 1B, the control ionic liquid AIL 2 was assembled first from the SNAr reaction of the amine 1 with commercial 2-chloro-4,6-dimethoxy-1,3,5-triazine (4) under heated conditions followed by alcohol mesylation, nucleophilic substitution with 2, and lastly an anion metathesis to give AIL 2
Summary
Scheme 1A illustrates the synthesis of AIL 1 of which the affinity element could be readily assembled from the commercially inexpensive cyanuric chloride (3), with a freshly prepared amine ionic liquid at ambient temperature. ItIt iiss clearly demonstrated that, using the same concentration (100 ppb) for all gaseous samples tested, AIL 1 only reacted cchheemmoselectively wwiitthh aammiinnee ggaass:: ∆ΔFF == −−175 Hz for isobutylamine [22]. This reaction-based AIL-on-QCM system worked well and was totally unreactive to common VOCs gases ssuucchh aass wwaatteerr, acetone, mmeetthhaannooll,,eetthhyyllaacceettaattee,,TTHHFF, ,ananddhhexeaxnaene(∆(ΔFF~~0 0HHz)z,)a,nadn,da,saas raesreusltu,lth, ethferefqrueqeunceyncdyrodproinp tihnitshciosnctoinutionuusofluoswflomweamsuearesmureenmt ewnatswnaost antoatlal tdaulel dtouaentyo nanonysnpoencisfipcepcihfiycspishoyrpsitsionrpotfiognasoof ngtaosioonntioc liioqnuiicd.liqItuiisdw. All reactions were carried out under an inert atmosphere using anhydrous solvents
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