UV−Visible and ¹H or ¹³C NMR Spectroscopic Studies on the Specific Interaction between Lithium Ions and the Anion from Tropolone or 4-Isopropyltropolone (Hinokitiol) and on the Formation of Protonated Tropolones in Acetonitrile or Other Solvents

Abstract

The specific interaction between lithium ions and the tropolonate ion (C(7)H(5)O(2)-: L-) was examined by means of UV-visible and 1H or 13C NMR spectroscopy in acetonitrile and other solvents. On the basis of the electronic spectra, we can propose the formation of not only coordination-type species (Li+(L-)2) and the ion pair (Li+L-) but also a "triple cation" ((Li+)2L-) in acetonitrile and acetone; however, no "triple cation" was found in N,N-dimethylformamide (DMF) and in dimethylsulfoxide (DMSO), solvents of higher donicities and only ion pair formation between Li+ and L- in methanol of much higher donicity and acceptivity. The 1H NMR chemical shifts of the tropolonate ion with increasing Li+ concentration verified the formation of (Li+)2L- species in CD3CN and acetone-d6, but not in DMF-d6 or CD(3)OD. With increasing concentration of LiClO(4) in CD(3)CN, the 1H NMR signals of 4-isopropyltropolone (HL') in coexistence with an equivalent amount of Et(3)N shifted first toward higher and then toward lower magnetic-fields, which were explained by the formation of (Li+)(Et(3)NH+)L'- and by successive replacement of Et(3)NH+ with a second Li+ to give (Li+)2L'-. In CD(3)CN, the 1,2-C signal in the 13C NMR spectrum of tetrabutylammnium tropolonate (n-Bu(4)NC(7)H(5)O) appeared at an unexpectedly lower magnetic-field (184.4 ppm vs TMS) than that of tropolone (172.7 ppm), while other signals of the tropolonate showed normal shifts toward higher magnetic-fields upon deprotonation from tropolone. Nevertheless, with addition of LiClO(4) at higher concentrations, the higher and lower shifts of magnetic-fields for 1,2-C and other signals, respectively, supported the formation of the (Li+)2L- species, which can cause redissolution of LiL precipitates. All of the data with UV-visible and 1H and 13C NMR spectroscopy demonstrated that the protonated tropolone (or the dihydroxytropylium ion), H(2)L+, was produced by addition of trifluoromethanesulfonic or methanesulfonic acid to tropolone in acetonitrile. The order of the 5-C and 3,7-C signals in 13C NMR spectra of the tropolonate ions was altered by addition of less than an equivalent amount of H+ to the tropolonate ion in CD(3)CN. Theoretical calculations satisfied the experimental 13C NMR chemical shift values of L-, HL, and H(2)L+ in acetonitrile and were in accordance with the proposed reaction schemes.

Coordination phenomena of alkali metal, alkaline earth metal, and indium ions with the 1,3,6-naphthalenetrisulfonate ion in protic and aprotic solvents

“…In aprotic solvents such as acetonitrile (MeCN), the specific coordination reactions between alkali metal or alkaline earth metal ions with some simple ions such as halides (Cl -, Br -) [4,5], tropolonate [6], sulfonates, and carboxylates [7] have been demonstrated by means of various analytical methods. With the increasing concentration of M + (an alkali metal ion), the specific reaction may proceed in three steps: at first, a half equivalence or less than that amount of M Fuoss and Kraus [9] have introduced the concept of triple ion between free ions and triple ions in the solvents of low permittivity (ε r < 10 or 23.2).…”

A generic framework for constructing cross‐realm C2C‐PAKA protocols based on the smart card

“…The importance of polar ‘aprotic’, or polar non‐hydrogen bond donor (non‐HBD) solvents for chemistry and chemical technology is difficult to overestimate 1–6…”

“…These solvents can be divided into two main groups, namely, protophobic [e.g., propylene carbonate, sulfolane, acetonitrile (AN), acetone (AC), and especially nitrobenzene and nitromethane] and protophilic ones [hexamethyl phosphortriamide, dimethyl sulfoxide (DMSO), N , N ‐dimethyl formamide (DMF), N , N‐ dimethylacetamide, etc.] 1–6. The latter are characterized by higher basicity, in particular, by high donor numbers (DN) and negative values of the logarithm of proton activity coefficients of transfer from water (w) to the given solvent (s), $\log {}_{{\rm tr}}^{\rm w} \gamma _{{\rm H}^ + }^{\rm s} $ .…”

“…The pH scales of both types of these solvents are around 30 units, and all of them display a strong differentiating influence on the acidic strength 1–10. It means that for different acids, HA, …”

“…AC is widely used in analytical, physical, and organic chemistry, as well as in technology as a useful medium for many processes, including acid–base reactions 1–6. However, the state of protolytic equilibria in this solvent is strongly influenced by traces of moisture, because of the extremely low basicity of AC 1–6, 17–19. This phenomenon hinders both quantitative studies of the properties of a lot of organic acids and understanding of reaction mechanisms in AC.…”