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Article

Vapor Pressure of Ionic Liquids with a Common Tetrabutylammonium Cation and Three Different Anions

by
Ivan Fabrizi
1,2,*,
Simone Di Muzio
3,4,
Fabio Ramondo
1,
Francesco Trequattrini
3,5,
Oriele Palumbo
3 and
Annalisa Paolone
3
1
Dipartimento di Chimica, Sapienza Università di Roma, Piazzale A. Moro 5, 00185 Roma, Italy
2
Istituto Nazionale per la Scienza e Tecnologia dei Materiali, Via G. Giusti 9, 50121 Firenze, Italy
3
Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, Piazzale A. Moro 5, 00185 Roma, Italy
4
Istituto di Fotonica e Nanotecnologie, Consiglio Nazionale delle Ricerche, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
5
Dipartimento di Fisica, Sapienza Università di Roma, Piazzale A. Moro 5, 00185 Roma, Italy
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(11), 6040; https://doi.org/10.3390/app15116040
Submission received: 8 April 2025 / Revised: 23 May 2025 / Accepted: 26 May 2025 / Published: 27 May 2025
Browse Figures
Versions Notes

Abstract

The vapor pressures, pv, of three ionic compounds used as starting materials of deep eutectic systems, namely, tetrabutylammonium bromide (TBA-Br), tetrabutylammonium trifluoromethanesulfonate (TBA-TFO), and tetrabutylammonium bis(trifluoromethanesulfonyl)imide (TBA-NTF2), were measured using isothermal thermogravimetry. TBA-Br displays large values of pv, reaching ≈700 Pa at 170 °C. TBA-NTF2 is the less volatile liquid, with a vapor pressure of ≈1 Pa at 240 °C, while TBA-TFO has a slightly higher value of pv, of about 3 Pa at the same temperature. The values of pv for the NTF2-containing ionic compound are comparable to those of ionic liquids containing the same anion. The obtained mean vaporization enthalpy, ΔHvap, for TBA-Br and TBA-TFO (≈170 kJ mol−1) is higher than for TBA-NTF2 (≈145 kJ mol−1). The obtained vaporization enthalpy values fall within the typical range observed for ionic liquids.

1. Introduction

Ionic liquids (ILs) are a class of materials composed exclusively of ions and exhibiting melting points lower than 100 °C [1]. Many of them are liquid around room temperature and below. ILs can be obtained by combining a large variety of ions with different physico-chemical properties, and, therefore, the properties of the ILs can be finely tailored and adapted to desired requirements for various applications [2]. Despite difficulties in generalization, the experimental studies of the last 20 years have pointed out that, usually, ILs have some common properties, such as high thermal stability, low flammability, and low volatility, certainly lower than that of largely used organic solvents [1]. For this reason, ILs have found applications as solvents for the synthesis of new compounds [3,4], as extractant media [5,6], or as lubricants [7,8]. Moreover, most ionic liquids and their decomposition products are not flammable and, therefore, are considered as safe components of electrolytes for batteries, especially lithium batteries, that possess high energy densities and could, in principle, be prone to reach high temperatures in case of malfunctioning [9].
Volatility is strictly linked to the vapor pressure, pv, of liquids, which is certainly an important physical quantity to be considered for applications. In the case of ILs, in 2005, Paulechka et al. first measured the vapor pressure of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI-NTF2) in the temperature range 185–250 °C [10]. This work was an important milestone, as no quantification of the vapor pressure of ionic liquids was available before, and ILs were generically considered to be non-volatile. The paper by Paulechka et al. opened the way to a large investigation of the vapor pressure of ILs in the subsequent years. A series of 1-alkyl-3-methylimidazolium NTF2 ILs were investigated, and it was pointed out that pv increases as the length of the alkyl chain decreases [11,12,13]. It was also shown that the vapor pressure of the series of 1-alkyl-3-methylimidazolium hexafluorophosphate ILs with various lengths of the alkyl chain is lower than in the corresponding ILs containing NTF2 as the anion [11]. ILs with other anions were investigated, and it was shown that pv decreases in the order Br (bromide) > dicyanamide > tetrafluoroborate > NTF2 > hexafluorophosphate > trifluoromethanesulfonate (TFO) [14]. More recently, dication ionic liquids (DILs) were also studied concerning their vapor pressure [15,16]. DILs are ILs in which a single cation has a double positive charge and is coordinated to two anions. Usually, DILs have higher melting points of monocation ILs, but they are more thermally stable [15]. Meanwhile, studies on the vapor pressure of ILs were also extended to liquids containing less usual anions, such as tetrafluoroborate [17], methanesulfonate [18], alanine or threonine [19], taurine [20], or nonafluorobutane-1-sulfonate [21]. An important thermodynamic quantity is vaporization enthalpy, which can be obtained from the temperature dependence of the vaporization pressure. The typical values of the vaporization enthalpy of ionic liquids range between 100 and 200 kJ mol−1 [11,12,13,15,22].
In the last few years, to extend the liquid range of solvents to even lower temperatures and in search of more eco-friendly materials, eutectic systems were explored. These systems are particularly intriguing since one can obtain a liquid phase from solid components by mixing them. In some cases, a depression of the melting point of the mixtures with respect to the ideal thermodynamic behavior was observed and, in these cases, the obtained mixtures are indicated as Deep Eutectic Systems (DESs) [23]. DESs are classified according to the chemical structure of their precursor components and fall into different categories. The first three include mixtures of quaternary ammonium salts or ionic liquids with a metal chloride, a metal chloride hydrate, or a hydrogen bond donor, respectively. The vapor pressure of DESs is much less investigated than that of ILs. Many reports, instead, deal with the vaporization of binary mixtures of ILs with solvents: not surprisingly, the vaporization of mixtures mainly depends on the most volatile component [24,25].
In this context, we recently investigated some eutectic systems involving quaternary ammonium salts, composed of the tetrabutylammonium cation and different anions, such as bromide (Br) or trifluoromethanesulfonate (TFO), combined with maleic, fumaric or octanoic acid, or octanoic alcohol [26,27,28]. We could evidence by DFT calculations and infrared spectroscopy measurements the changes in the interactions between the constituents of the ionic couple or among the acid molecules after mixing them. Mainly, the strong hydrogen bond network present in the acids is largely suppressed, and new weaker hydrogen bonds form between acid molecules and the ionic couple, in agreement with similar investigations in other DESs. At the same time, the ionic couple becomes less bound, and the ions interact with the acid molecules [26,27].
In the past few years, several methods have been used to investigate the vapor pressure and the vaporization enthalpy of ionic compounds and, in particular, of ILs. The most used are: (1) isothermal thermogravimetry, similarly to those here reported, which derives pv from the mass loss measured at fixed temperature by a thermogravimetric apparatus [14]; (2) the Knudsen effusion apparatus, which measures the mass loss of samples through an orifice by a quartz crystal microbalance [29]. The latter method can measure pv in the range between 0.01 and 1 Pa, while thermogravimetric measures are more accurate for higher pressures (and therefore for higher temperatures). In some sporadic cases, AC-chip calorimetry was also exploited to derive the vapor pressures of ILs, such as 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [30].
Given their large use in eutectic systems, we measured the vapor pressure of tetrabutylammonium bromide and tetrabutylammonium trifluoromethanesulfonate; moreover, we compared these values with those of tetrabutylammonium bis(trifluoromethanesulfonyl)imide, which was previously investigated [31], and that we measured again in the present work for confirmation. The vaporization enthalpy of the three ionic samples was derived. All investigations were based on isothermal treatments in a thermogravimetric system, as largely used for the derivation of the vapor pressure [14,15,22].

2. Materials and Methods

2.1. Materials

Tetrabutylammonium trifluoromethanesulfonate (TBA-TFO, CAS No.: 35895-70-6) and tetrabutylammonium bis(trifluoromethanesulfonyl)imide (TBA-NTF2, CAS No.: 210230-40-3) were purchased from Sigma Aldrich (Darmstadt, Germany), while tetrabutylammonium bromide (TBA-Br, CAS No.: 1643-19-2) was obtained from TCI (Zwijndrecht, Belgium). All samples had a purity ≥ 99% (see Table 1). The geometry and chemical composition of the ions making up the materials used in this study or those ones used for comparison are reported in Figure 1. It must be noted that in a large portion of the literature, the TFSI or TFSA acronyms for the bis(trifluoromethanesulfonyl)imide are adopted, especially in the field of electrochemistry [32,33,34]. These specific ionic compounds have some interesting properties concerning their safety. Indeed, TBABr has been reported to be environmentally friendly, operationally simple, non-corrosive, and easily recyclable [35].

2.2. Thermal Analysis and Vapor Pressure Calculation Procedure

Concomitant TGA and DTA measurements were conducted with a Setaram Setsys Evolution 1200 instrument (Caluire-et-Cuire, France). A protective helium atmosphere with a flux of 60 mL min−1 was maintained during the measures. A first type of experiment was conducted in scanning mode, that is, continuously increasing the sample temperature. We used a scanning rate of 10 °C min−1 on specimens with a typical mass of 15 mg to evaluate the thermal stability of the samples and their melting points. In this way, we were able to define the liquid ranges of samples where no massive decomposition occurred, and then we conducted isothermal experiments in this defined range to measure the vapor pressure of the liquid phase. The isothermal experiments were conducted on specimens with an initial mass of about 50 mg to measure the time evolution of the mass loss due to the vaporization. The temperature of the sample was increased by steps and the mass variation as a function of time was recorded at each step. Indeed, at each temperature, the mass loss increased linearly with time and the slope, kT, of this mass variation vs. time (t) at each temperature, T, was fitted by a linear regression:
kT = dm/dt
According to the previous literature, the vapor pressure, pv, is related to kT by the equation [14]
ln pv (bar) = a ln kT + b
where a and b are coefficients that can be determined by a calibration of the TGA apparatus used for the specific measurements. In our case, we previously calibrated our TGA apparatus by means of glycerol, a liquid material with a well-characterized and documented pv [36]. Indeed, in a previous paper of our group [22], we measured the time dependence of the mass loss of glycerol at various temperatures and fitted these lines by a linear regression that provided kT,glycerol. For glycerol, the vapor pressure values are well known [36], and Equation (2) was used to calculate the parameters a and b of the thermogravimetric apparatus. As we previously reported, the coefficients a and b for our apparatus are 1.05 ± 0.02 and −3.77 ± 0.05, respectively [22]. These figures were used in the present paper to calculate the pv values of the ionic compounds containing TBA, applying Equation (1), where the kT values are obtained from the isothermal measures here reported.

2.3. Infrared Spectroscopy

To avoid possible spurious contribution from water absorbed in the samples, the specimens were heated at 100 °C for 2 h in the TGA apparatus before the measurements. Infrared spectroscopy measurements confirmed the absence of OH stretching vibrational bands (Figure 2) after the thermal treatment. Indeed, in the spectral region between 2500 and 3700 cm−1, one can observe only bands below 3000 cm−1, which are attributable to the CH stretching vibrations, while possible OH stretching bands, which should be centered above 3100 cm−1, are completely absent. Infrared absorbance spectra were collected on a Bruker Alpha instrument (Billerica, MA, United States of America) equipped with an Attenuated Total Reflectance (ATR) accessory. The spectral resolution was fixed at 4 cm−1, and 256 scans were mediated for each spectrum.

3. Results and Discussion

3.1. Decomposition and Melting Points by Thermal Analysis

The thermal decomposition temperatures and the melting points of the three compounds were evaluated by thermogravimetric measures performed in scanning mode.
Figure 3a displays the TGA curves of the three samples. The specimens display a 2% mass loss around 195, 316, and 364 °C, respectively (Table 2) for TBA-Br, TBA-TFO, and TBA-NTF2. In view of these figures, the thermal stability follows the expected order: TBA-Br < TBA-TFO < TBA-NTF2. The previous values will be considered in the following as the decomposition temperatures, Td. Above Td, a massive decomposition occurs, which completes around 300, 396, and 446 °C for TBA-Br, TBA-TFO, and TBA-NTF2. It is interesting to note that the decomposition occurs in a single step for TBA-TFO and TBA-NTF2, while it involves two steps for TBA-Br.
In the concomitant DTA measurements (Figure 3b), one can observe the endothermic peaks centered above 200 °C which are due to the decomposition of the samples. Moreover, all specimens show endothermic peaks due to melting, which are centered around Tm = 120, 115, and 93 °C for TBA-Br, TBA-TFO, and TBA-NTF2, respectively (Table 2). These peaks are preceded by a small endothermic peak around 100 °C in TBA-Br and a well-visible endothermic peak around 58 °C in TBA-TFO. These additional processes were attributed to solid–solid phase transition in TBA-Br [26] and TBA-TFO [27]. The melting points are in good agreement with the values reported by Sigma-Aldrich and TCI. In view of the values of Tm, only TBA-NTF2 is strictly speaking an ionic liquid; TBA-Br and TBA-TFO should be considered as ionic solids, despite their melting points being only a few degrees above 100 °C.

3.2. Vapor Pressure Determination

To obtain the vapor pressure of the samples, isothermal treatments at different temperatures were performed. Figure 4 reports the time evolution of the relative mass variation for the three samples at various temperatures within the liquidity range, that is, above Tm and below Td. As expected, for all samples, the mass loss increases as the temperature increases. For all samples and temperatures, the time dependence is well described by a straight line. A fit by a linear regression provided the kT values (see lines in Figure 4) is used in Equation (1) to calculate the vapor pressure. To transform the kT values into the absolute values of the vapor pressure, we used the calibration of our thermogravimetric apparatus previously obtained by glycerol, reported in Ref. [22]. The derived pv values are reported in Table 3, Table 4 and Table 5 as data and in Figure 5 in graphical form. The uncertainties on pv values are calculated from the statistical errors on the slopes of the best-fit lines of Figure 4, but the corresponding error bars are smaller than the symbol dimension in Figure 5.
The lowest values of the vapor pressure (Figure 5, Table 3, Table 4 and Table 5) are observed for TBA-NTF2; the values calculated for TBA-TFO are higher by no more than one order of magnitude, depending on the specific temperature. The highest pv values are obtained for TBA-Br, which exceed those obtained for TBA-NTF2 and TBA-TFO by many orders of magnitude. The pv values here obtained for TBA-NTF2 are close to those reported by Liu et al. in a recent publication [31].
One can note in Figure 5 that the vapor pressure of TBA-NTF2 is similar to that previously measured for N-trimethyl-N-propylammonium-NTF2 (N1113-NTF2) [22], an ionic liquid with the same anion and with a cation which is based on a quaternary ammonium with shorter alkyl chains compared to TBA-NTF2 (the structure of the cations is reported in Figure 1). This comparison is interesting because the previous literature pointed out that the vapor pressure of ionic liquids with the NTF2 anion and quaternary ammonium cations decreases as the length of the alkyl chain increases [11,12,13]. However, these results mainly considered cations in which three of the alkyl chains consisted of methyl groups, and only the length of the fourth alkyl chain was varied. In the presently investigated cation, all alkyl chains have a length of four carbon atoms.
The vapor pressure of TBA-TFO is intermediate between the values of N1113-NTF2 and those of N-trimethyl-N-butylammonium -bis(fluorosulfonyl)imide (N1114-FSI) [22], which contains the FSI anion that seems to be particularly volatile. Ionic liquids or solids containing the TFO anion have been much less investigated than those containing halides or NTF2. Absolute vapor pressures and vaporization enthalpies of a series of ILs containing the imidazolium cation were measured by using a quartz crystal microbalance at 100 °C and they were found in the range of 0.01–0.1 Pa [37]. The measures were extended to 200 °C in refs. [38,39].
TBA-Br is the more volatile sample, even though it was measured at much lower temperatures than the other two samples here investigated. Indeed, previous literature also pointed out that ionic liquids containing halide anions are much more volatile than ILs with the same cation and bulkier anions, such as NTF2 or TFO [14,40]. To the best of our knowledge, the vapor pressure of TBABr has not previously been measured; only pv of mixtures of TBABr with water or acetonitrile or water and acetonitrile are available in the temperature range between 25 and 50 °C [41]. The vapor pressure values of TBABr are comparable to, but higher than, those reported for ionic liquids with the same anion and imidazolium-based cations. C2C1Im-Br was reported to display a pv of 0.47 (27) Pa at 130 (175) °C, while C4C1Im-Br showed values of 8 (453) Pa at 149 (194 °C) [42].

3.3. Calculation of the Vaporization Enthalpy

Figure 6 displays the natural logarithm of the calculated pv of the three investigated samples as a function of the inverse of the absolute temperature. The slope of the graph is the mean enthalpy of vaporization in the investigated temperature range, ΔHvap. From a linear fit of the data, we obtained the vaporization enthalpy, as reported in Table 6. The uncertainties were calculated from the fit. TBA-Br and TBA-TFO display the highest values that are of the order of ≈170 kJ mol−1, while ΔHvap for TBA-NTF2 is ≈145 kJ mol−1. All these values are similar to those of most ionic liquids reported in the literature until now [11,12,13,15,21,22], which span the range between 120 and 200 kJ mol−1. In particular, ΔHvap here derived for TBA-NTF2 is consistent with the value of 144.2 kJ mol−1 reported by Liu et al. for the same compound [31]. The other two ionic solids were not previously investigated in terms of their vaporization enthalpy. It can be noted that ΔHvap of a series of ionic liquids with the Br anion and imidazolium-based cations increased with the length of the alkyl chain, varying from 136.5 ± 1.5 kJ mol−1 for C2C1Im-Br to 160.8 ± 1.2 kJ mol−1 for C10C1Im-Br and 229 ± 9 kJ mol−1 for C18C1Im-Br [42]. The same phenomenology was reported for the series of ionic liquids with the trifluoromethanesulfonate anion and imidazolium cations with various lengths of the alkyl chain [37,38,39]. In this case, ΔHvap increased from 126.4 ± 1.0 kJ mol−1 for C2C1Im-TFO to 149.5 ± 1.0 kJ mol−1 for C10C1Im-TFO and 161.8 ± 1.0 kJ mol−1 for C14C1Im-TFO [37]. For the presently investigated TFO-containing sample, the vaporization enthalpy is similar to that of the samples with the longest alkyl chain reported in Ref. [37].
The present results can be useful for a comprehensive understanding of the tetrabutylammonium salts also in view of their applications. In fact, in the last few years, many uses of these compounds have been proposed, especially in the field of energy storage. As an example, TBATFO has been used as an additive to extend the anodic stability in magnesium batteries [43], to form a stable solid–electrolyte interphase in lithium–sulfur batteries [44], and in the electrolytes of sodium–oxygen batteries [45]. Moreover, tetrabutylammonium bromide was used for the production of high-quality perovskite films with enhanced crystallinity and a smooth surface for applications in solar cells [46,47].
From a conceptual point of view, the determination of the vapor pressure provides a valuable contribution in several fields. Indeed, a relation between the vaporization enthalpy and the viscosity of ionic liquids based on Eyring’s theory has been proposed for selected ionic liquids [48]. Moreover, vaporization enthalpy is useful to derive the sublimation enthalpy and the cohesive properties, thanks to the complementarity with DFT calculations [49]. Finally, some preliminary vapor pressure values should be included in the PC-SAFT parametrization of ionic liquids [50].

4. Conclusions

The thermal stability of tetrabutylammonium cation-based ionic compounds increases from 195 to 316 and 364 °C when the anion changes from Br to TFO and NTF2. Their melting points follow the opposite trend as they pass from 120, to 115 and 93 °C for TBA-Br, TBA-TFO, and TBA-NTF2, respectively. The highest values of the vapor pressure are found for TBA-Br, which reaches a value of ≈700 Pa at 170 °C. On the contrary, TBA-NTF2 and TBA-TFO have a pv of the order of 1 Pa even at 240 °C. The vaporization enthalpy is higher for TBA-Br and TBA-TFO (≈170 kJ mol−1) and lower for TBA-NTF2 (≈145 kJ mol−1). These values are consistent with those previously found for other ionic salts.

Author Contributions

Conceptualization, A.P. and O.P.; methodology, A.P.; validation, I.F.; formal analysis, I.F., F.T., A.P. and O.P.; investigation, I.F., F.T., A.P. and O.P.; resources, S.D.M., F.R. and F.T.; data curation, I.F.; writing—original draft preparation, A.P.; writing—review and editing, all authors; visualization, I.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

The authors wish to thank Sergio Brutti for the use of the Bruker Alpha infrared spectrometer.

Conflicts of Interest

The authors declare no conflicts of interest.

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Applsci 15 06040 g001
Figure 1. Schematic representation of the cations and anions composing the ILs cited in the main text. Dark grey, light grey, purple, light red, yellow, green, and dark red spheres represent carbon, hydrogen, nitrogen, oxygen, sulfur, fluorine, and bromine atoms, respectively.
Figure 1. Schematic representation of the cations and anions composing the ILs cited in the main text. Dark grey, light grey, purple, light red, yellow, green, and dark red spheres represent carbon, hydrogen, nitrogen, oxygen, sulfur, fluorine, and bromine atoms, respectively.
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Figure 2. Infrared absorbance of the three investigated ILs in the region of the CH (below 3000 cm−1) and OH stretching bands (above 3100 cm−1). The spectra are vertically displaced for clarity.
Figure 2. Infrared absorbance of the three investigated ILs in the region of the CH (below 3000 cm−1) and OH stretching bands (above 3100 cm−1). The spectra are vertically displaced for clarity.
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Figure 3. TGA (a) and DTA (b) traces of the three investigated samples.
Figure 3. TGA (a) and DTA (b) traces of the three investigated samples.
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Figure 4. Time dependence of the mass variation curves measured by isothermal treatments at different temperatures for the three samples (colored curves) and best-fit lines (black solid lines).
Figure 4. Time dependence of the mass variation curves measured by isothermal treatments at different temperatures for the three samples (colored curves) and best-fit lines (black solid lines).
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Figure 5. Calculated vapor pressure of the three investigated samples compared to the values of N1113-NTF2 and N1114-FSI reported in [22].
Figure 5. Calculated vapor pressure of the three investigated samples compared to the values of N1113-NTF2 and N1114-FSI reported in [22].
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Figure 6. Logarithm of the vapor pressure calculated (symbols) for the three specimens as a function of the inverse of the absolute temperature and best-fit lines to obtain the evaporation enthalpy.
Figure 6. Logarithm of the vapor pressure calculated (symbols) for the three specimens as a function of the inverse of the absolute temperature and best-fit lines to obtain the evaporation enthalpy.
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Table 1. Name, source, acronyms, purity, and CAS number of the materials used in the study.
Table 1. Name, source, acronyms, purity, and CAS number of the materials used in the study.
NameSourceAcronymPurity (Mass %)CAS No.
tetrabutylammonium trifluoromethanesulfonateSigma AldrichTBA-TFO99.035895-70-6
tetrabutylammonium
bis(trifluoromethanesulfonyl)imide		Sigma AldrichTBA-NTF299.0210230-40-3
tetrabutylammonium bromideTCITBA-Br99.01643-19-2
Table 2. Measured melting points, Tm, and decomposition temperatures, Td, of the three samples.
Table 2. Measured melting points, Tm, and decomposition temperatures, Td, of the three samples.
SampleTm (°C)Td (°C)
TBA-Br120195
TBA-TFO115316
TBA-NTF293364
Table 3. Calculated vapor pressure values of TBA-Br.
Table 3. Calculated vapor pressure values of TBA-Br.
Temperature/°CVapor Pressure/Pa
130(6.6 ± 0.1)
140(3.5 ± 0.1) × 10
150(1.15 ± 0.05) × 102
160(3.1 ± 0.1) × 102
170(7.1 ± 0.1) × 102
Table 4. Calculated vapor pressure values of TBA-TFO.
Table 4. Calculated vapor pressure values of TBA-TFO.
Temperature/°CVapor Pressure/Pa
200(3.02 ± 0.06) × 10−1
220(6.9 ± 0.1) × 10−1
240(3.1 ± 0.1)
260(1.65 ± 0.06) × 10
280(9.3 ± 0.4) × 10
300(4.6 ± 0.2) × 102
Table 5. Calculated vapor pressure values of TBA-NTF2.
Table 5. Calculated vapor pressure values of TBA-NTF2.
Temperature/°CVapor Pressure/Pa
240(1.20 ± 0.05)
260(2.82 ± 0.06)
280(9.4 ± 0.2)
300(2.79 ± 0.08) × 10
320(1.28 ± 0.05) × 102
Table 6. Calculated vaporization enthalpy of the investigated ionic compounds.
Table 6. Calculated vaporization enthalpy of the investigated ionic compounds.
SampleVaporization Enthalpy/kJ mol−1
TBA-Br172 ± 11
TBA-TFO170 ± 12
TBA-NTF2146 ± 11
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MDPI and ACS Style

Fabrizi, I.; Di Muzio, S.; Ramondo, F.; Trequattrini, F.; Palumbo, O.; Paolone, A. Vapor Pressure of Ionic Liquids with a Common Tetrabutylammonium Cation and Three Different Anions. Appl. Sci. 2025, 15, 6040. https://doi.org/10.3390/app15116040

AMA Style

Fabrizi I, Di Muzio S, Ramondo F, Trequattrini F, Palumbo O, Paolone A. Vapor Pressure of Ionic Liquids with a Common Tetrabutylammonium Cation and Three Different Anions. Applied Sciences. 2025; 15(11):6040. https://doi.org/10.3390/app15116040

Chicago/Turabian Style

Fabrizi, Ivan, Simone Di Muzio, Fabio Ramondo, Francesco Trequattrini, Oriele Palumbo, and Annalisa Paolone. 2025. "Vapor Pressure of Ionic Liquids with a Common Tetrabutylammonium Cation and Three Different Anions" Applied Sciences 15, no. 11: 6040. https://doi.org/10.3390/app15116040

APA Style

Fabrizi, I., Di Muzio, S., Ramondo, F., Trequattrini, F., Palumbo, O., & Paolone, A. (2025). Vapor Pressure of Ionic Liquids with a Common Tetrabutylammonium Cation and Three Different Anions. Applied Sciences, 15(11), 6040. https://doi.org/10.3390/app15116040

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