Received: May 2024

DOI 10.17677/fn20714807.2024.03.01

Fluorine Notes, 2024, 154, 1-2

IONIC SERIES OF HEXAKIS (TRIFLUOROMETHYLTHIO)- AND HEXAKIS (TRIFLUOROMETHYLSELENO) BENZENES AND FLUOROBENZENES WITH PERFLUOROALKYL SUBSTITUENTS

N. D. Kagramanov, E.I. Mysov

A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119991, GSP-1, Moscow, B-334, Vavilov St. 28
e-mail: ndkagram@gmail.com

Abstract: The present report is a continuation of the earlier studies by studying the ionic series of benzene, 1,3,5,7-cyclooctatetraene, [18]-annulene, perfluorobenzene, hexamethylbenzene and hexakis (trifluoromethyl) benzene. The aim of the invention is to explain how the sulfur and selenium atoms change the fragmentation of benzenes with trifluoromethyl substituents.

Keywords: mass spectra and ionic series C₁₂F₁₈S₆, C₁₂F₁₈Se₆, C₁₂F₁₈, C₁₀F₁₄, C₁₆F₂₆.

Introduction

According to the L.M. Yagupolskii, N.V. Kondratenko, V.P. Sambur [1] invention, F₃CSCu has been shown to be a convenient reagent for replacing halide atoms in aryl- and heterohalides with a trifluoromethylthio- group. Hexasubstituted benzenes with perfluorinated groups separated from benzene ring by sulfur and selenium atoms were synthesized for the first time. The structures of compounds C12F18S6 and C12F18Se6 have been confirmed by NMR spectra 19F, IR spectra, UV spectra and mass spectra [2]. Mass spectra were obtained by Senior researcher of INEOS RAS USSR organofluoric compounds laboratory E.I. Mysov (head of a laboratory – acad. I.L.Knuniants), on a device MX-1310, with an ionizing voltage of 18 eV. The spectra contained only molecular ions, since the format of the short message excludes the possibility of complete mass spectra publication of two polyisotopic compounds with masses of 678 and 966 amu. Since the samples were preserved, their mass spectra were repeated at a standard voltage of 70 eV on a Finnigan Polaris Q mass spectrometer. Thus, the present message is a continuation of studies previously performed on the study of the ionic series of benzene, 1,3,5,7-cyclooctatetraene, [18]-annulene, perfluorobenzene [3], hexamethylbenzene and hexakis(trifluoromethyl)benzene [4]. The aim of the invention is to identify the sulfur and selenium atoms effect on changing the fragmentation of benzenes with trifluoromethyl substituents. Heavy atoms of sulfur and selenium themselves are able to form six-member cycles S₆ and Se₆. For this reason, at the fragmentation of C₁₂F₁₈S₆ and C₁₂F₁₈Se₆ is likely to occur in successive emissions of six F and CF₂ atoms with the formation of stable cation-radicals ⁺C₆S₆ and ⁺C₆Se₆ with novel sulfur-sulfur and selenium-selenium bonds, and then the separation of sulfur and selenium atoms begins. In contrast to fragmentation of hexakis(trifluoromethylthio)- and hexakis(trifluoromethylseleno)benzenes, in ionic series of two isomers of C₁₂F₁₈, unprotected by heavy atoms S and Se along with primary separation one fluorine atom primary separation there is a primary synchronous release of two, as well as three fluorine atoms with formation of new bonds and three main ionic series. Apparently, sulfur and selenium atoms, more specifically, six bonds with CF₃ groups and six bonds with a C₆ cycle take part of the excitation energy ⁺M, which is necessary for primary synchronous detachments of two or three fluorine atoms. The perfluoroalkyl ionic series C₁₂F₁₈S₆ and C₁₂F₁₈Se₆ differ. In spectrum C₁₂F₁₈Se₆ intensive (46%) peak ⁺CF₃ is formed, while in spectrum C₁₂F₁₈S₆ there is a series of ions: ⁺C₃F₇ (4%), ⁺C₂F₅ (0.4%), ⁺CF₃ (4%). One of the ionic series C₁₂F₁₈S₆ after successive separation of three radicals .CF₃ branches, since there is a break of the C₆ cycle with a C₃S₃ emission and the formation of an ion ⁺C₃S₃(CF₃)₃ m/z 339 (0.4%).

As a result of the following detachments: C₃, two fluorine atoms and three sulfur atoms, there is a rearrangement ion ⁺C₃F₇ with m/z 169 (4%).

Experimental part

The electrons ionization mass spectra are recorded on a chromatography-mass spectrometer «Finnigan Polaris Q» ion trap, a range of 14-1000 Da, energy of 70 eV, and direct input of DIP (heating at a rate of 10°/min).

Mass spectra and ionic series of hexakis (trifluoromethylthio)-and (trifluoromethylseleno) benzenes

Figures 1 and 2 shows the mass spectrum and the ionic series of hexakis(trifluoromethylthio)benzene.

Figure 1. The mass spectrum of hexakis (trifluoromethylthio) benzene C₁₂F₁₈S₆ MW:678.

Figure 2. The ionic series of hexakis (trifluoromethylthio) benzene C₁₂F₁₈S₆ MW:678 mass spectrum.

The mass spectrum of hexakis(trifluoromethylthio)benzene (Figures 1 and 2) consists of one ion series with intense fragmentation peaks (marked with blue color) and a subset with less intense peaks (marked with a dotted line blue). In the main series, successive separation: F, CF₂, (F, F, CF)₂, (F, CF₂)₃ lead to ion ⁺C₆S₆ with m/z 264 (19%), fragmented first with separation S₄, and then with the separation of three carbon atoms. The main series branches at least twice. The first branching of the main series (marked with a dotted line of blue color) starts with the detachment of S=CF₂ from the ion with m/z 659, and then four consecutive emissions of CF₃, with the formation of an ion ⁺C₆S₅CF₃ with m/z 301 (9%). This ion ejects the latter group CF₃ (301-69 = m/z 232) and three sulfur atoms, turning into ion ⁺C₆S₂ with m/z 136.

Another branching of the main ionic series (marked with red color) is the alternative fragmentation result of the ion with m/z 471, terminating in the rearrangement ion ⁺C₃F₇ formation. After detachment of the three radicals, the resulting asymmetric ion with m/z 471 fragments with the interruption of the benzene cycle in half and the separation of the C₃S₃ molecule to form an ion ⁺C₃(SCF₃)₃ with m/z 339 (0.4%). The ion with m/z 339 loses two fluorine atoms, turning into an ion ⁺C₆S₃F₇ with m/z 301 (8.6%). It should be noted that ions with a nominal mass m/z 301 arising in two different branches of the main series have different structures: ⁺C₆S₅CF₃ and ⁺C₆S₃F₇. Next, the ion ⁺C₆S₃F₇ loses C₃ (-36) and, as a result of successive detachments of three sulfur atoms, turns into a rearrangement ion ⁺C₃F₇ with m/z 169 (4%).

Figures 3 and 4 shows the mass spectrum and the ionic series of hexakis (trifluoromethylseleno) benzene C₁₂F₁₈Se₆.

Figure 3. The mass spectrum of hexakis (trifluoromethylseleno) benzene C₁₂F₁₈Se₆ MW:966.

Figure 4. The ionic series of hexakis (trifluoromethylseleno) benzene C₁₂F₁₈Se₆ MW:966 mass spectrum.

The mass spectrum of C₁₂F₁₈Se₆ hexakis (trifluoromethylseleno) benzene (Figures 3 and 4) consists of one ion series (marked with blue color). It branches at least three times, since in the spectrum along with ion m/z 621 C₆Se₆CF₃ ions arise: with m/z 483 (m/2), as well as ion c m/z 487 (6%) ⁺M-C₂Se₂(CF₃)₂, -F. In addition to the molecular ion, with a nominal mass of m/z 966 (1.4%), the series comprises six stacks of isotopic peaks. The peaks correspond to six consecutive separation of the atom of F and CF₂ (Σ CF₃) to form ⁺C₆Se₆ with nominal mass with m/z 552 (5%). In contrast to the mass spectrum of C₁₂F₁₈S₆, in the basic ionic series of which more energy-intensive successive emissions occur twice (‑F, ‑F, -CF), in the ionic series C₁₂F₁₈Se₆ this does not occur. Their spectra differs by the fact that the base peak in the spectrum of C₁₂F₁₈Se₆ is the peak ⁺C₆Se₂ with m/z 232 (also in the spectrum Se₆), while in the spectrum C₁₂F₁₈S₆ the intensity of the peak ⁺C₆S₂ with m/z 136 is only 5%. The base peak in the C₁₂F₁₈S₆ spectrum is the peak ⁺C₈S₆F₆ with m/z 402 (⁺M -4CF₃), whereas in the C₁₂F₁₈Se₆ spectrum the intensity of this peak with a nominal mass m/z 690 is 21%. Another difference in their fragmentation is that, unlike the C₁₂F₁₈S₆ spectrum, where after separation of the three CF₃ radicals, the C₉F₁₅S₆ cycle decay on C₃S₃ and ⁺C₃S₃(CF₃)₃ occurs, this does not occur in the C₁₂F₁₈Se₆ spectrum. In the spectrum C₁₂F₁₈Se₆, a single intense ion peak ⁺CF₃ (46%) occurs, whereas in the ⁺C₃S₃(CF₃)₃ spectrum, a series of low-intensity peaks of perfluoroalkyl ions are observed: ⁺C₃F₇, ⁺C₂F₅ and ⁺CF₃.

Another difference in the mass spectra of C₁₂F₁₈S₆ and C₁₂F₁₈Se₆ is the fact that only in the spectrum C₁₂F₁₈Se₆ an ion peak M/2 with m/z 483 (2%) is formed, whereas in the spectrum C₁₂F₁₈S₆ the peak intensity M/2 c m/z 339 (0.4%) is formed.

Mass spectra and ionic series of fluorobenzenes with perfluoroalkyl substituents

Figures 5 and 6 shows the mass spectrum and the ionic series of hexakis(trifluoromethyl)benzene C₁₂F₁₈.

Figure 5. The mass spectrum of hexakis (trifluoromethyl) benzene C₁₂F₁₈ MW:486

NIST #: 151287ID #: 302846 DB: mainlib.

Figure 6. The ionic series of hexakis (trifluoromethyl) benzene C₁₂F₁₈ MW:486 mass spectrum.

NIST#: 151287 ID#: 302846 DB: mainlib.

Mass spectrum of hexakis (trifluoromethyl) benzene (Figure 5) includes three ionic series M1-M3 (Figure 6) and two branches of series M1 [4].

Three series M1-M3 of spectrum С₁₂F₁₈ is a result of molecular cation-radicals ⁺M_1-3 fragmentation, three times differing in energy of fluorine atoms primary separation.

This is the separation of one fluorine atom ^+.M₁-F m/z 467, synchronous separation of two atoms ^+.M₂-2F m/z 448 and synchronous separation of three fluorine atoms ^+.M₃-3F m/z 429. As a result of the subsequent CF₂ (-50) regular emissions, three ionic series are formed, with the last significant masses digits: 7, 8 and 9. It should be noted that similar synchronous primary detachments of one, two and three radicals occur and in the n-alkanes and n-perfluoroalkanes [5] fragmentation, as well as polyoxaperfluoroalkanes and polyoxaalkyl halides [6].

Separation of fluorine atom from one of terminal CF₃ groups of perfluorotertbutylamine (series M-F) is also accompanied by two more fluorine atoms synchronous detachment from two other groups CF₃, so that first peak of this series of spectrum is peak of ion M-3F m/z 614 (4%) [7]. The synchronous primary detachments of three fluorine atoms also take place in the perfluorocyclohexane fragmentation [5].

Figures 5 and 6 shows the mass spectrum and the ionic series of 1,2,3,4-tetrafluoro-5,6-bis(heptafluoropropyl) benzene C₁₂F₁₈ MW:486.

Figure 7. The mass spectrum of 1,2,3,4-tetrafluoro-5,6-bis(heptafluoropropyl) benzene

C₁₂F₁₈ MW:486. NIST #: 110830 ID#: 298066 DB: mainlib.

.

Figure 8. Four ionic series of 1,2,3,4-tetrafluoro-5,6-bis(heptafluoropropyl)benzene

C₁₂F₁₈ MW:486 mass spectrum. NIST#: 110830 ID#: 298066 DB: mainlib.

In the ionic series of two isomers of C₁₂F₁₈, symmetrical (Figure 6) and asymmetric (Figure 8), unprotected by sulfur and selenium heavy atoms, primary synchronous breaks of three (⁺M₃ -3F), two (⁺M₂ -2F), and one fluorine atom (⁺M₁ -1F) occur.

In the ionic series of hexasubstituted benzenes C₁₂F₁₈S₆ and C₁₂F₁₈Se₆ with trifluoromethyl groups separated from the benzene ring by sulfur and selenium atoms, the primary synchronous detachments of three and two fluorine atoms do not occur. They are fragmenting by six consecutive emissions of F и CF₂ atoms to form stable cation-radicals ⁺C₆S₆ and ⁺C₆Se₆. Subsequent separations of sulfur and selenium atoms is then initiated. The sulfur and selenium atoms, more specifically six of their bonds with the CF₃ groups and six bonds with the C₆ cycle appear to take part of the excitation energy ⁺M, which is necessary for synchronous primary detachments of two, as well as three fluorine atoms.

In mass spectra of fluorobenzenes with perfluoroethyl substitutes isolated from each other by two fluorine atoms, primary synchronous separations of two and three fluorine atoms does not occur. Figures 9 and 10 shows the mass spectrum and ionic series of 1,2,3,4-tetrafluoro-3,6-bis (pentafluoroethyl) benzene.

Figure 9. The mass spectrum of 1,2,4,5-tetrafluoro-3,6-bis(pentafluoroethyl) benzene

C₁₀F₁₄ MW: 386, P&M Invest.

Figure 10. The ionic series of 1,2,3,4-tetrafluoro-3,6-bis(pentafluoroethyl) benzene

C₁₀F₁₄ MW: 386, P&M Invest.

In the mass spectrum of 1,2,3,4-tetrafluoro-3,6-bis(pentafluoroethyl)benzene (Figures 9 and 10) with pentafluoroethyl substitutes, located in para-position relative to each other and separated by two fluorine atoms, occurs only successive separation of the atoms of F and CF₂, as well as CF₂ and F. But there are no primary synchronous detachments of three and two fluorine atoms, since both perfluoroethyl groups are isolated from each other by two fluorine atoms.

An interesting examples are that two perfluoroisopropyl benzene substituents in the fourth and sixth positions and one trifluoromethyl substituent in the fifth position are fragmented by primary synchronous separation of one, two and three fluorine atoms are mass spectrum (Figure 11) and ionic series (Figure 12) of 1,3-difluoro-2,4,6-tris(perfluoroisopropyl)-5-trifluoromethyl benzene.

Figure 11. The mass spectrum of 1,3-difluoro-2,4,6-tris(perfluoroisopropyl)-5-trifluoromethyl benzene C₁₆F₂₆ MW: 686, INEOS RAS.

Figure 12. Three ionic series of 1,3-difluoro-2,4,6-tris(perfluoroisopropyl)-5-trifluoromethylbenzene C₁₆F₂₆ MW: 686.

As a result of primary synchronous detachments of one fluorine atom, two fluorine atoms and CF₂ group, as well as three fluorine atoms and CF₂ group, there are three ionic series branching and changing into each other.

The regular fragment group CF₂ (-107 and -88) addition to three (-57) and two fluorine atoms (-38) detachments does not violate the separation rules of three and two radicals, since this is the result of peaks ⁺M-3F and ⁺M-2F low intensity and higher intensities of peaks with additional separation of the regular fragment group CF₂. Similar primary separations ⁺M-3F, -CF₂ (-107) also occur in the of perfluoro-2,4-dimethyl-3-ethylpentane-C₉F₂₀ and perfluoroeicosane-C₂₀F₄₂ [5] fragmentation.

In the case of synchronous separation of three as well as two fluorine atoms from two or one of perfluoroisopropyl substituents (Figure 12), a trifluoromethyl substituent is also involved in fragmentation. Fragmentation of C₁₆F₂₆ is completed by two ionic series (Figure 12) marked with blue and red. In the series marked with red color arising as a result of the primary synchronous separation of three fluorine atoms and CF₂ group, two perfluoroisopropyl substituents are involved, as well as a trifluoromethyl substituent. The perfluoroisopropyl substituent in the second position, separated from other substituents by fluorine atoms in the first and third positions, is involved in fragmentation only at the final stage, forming a series of perfluoroalkyl ions: ⁺C₃F₇ m/z 169 (6%), ⁺C₂F₅ m/z 119 (31%) and ⁺CF₃ m/z 69 (100%).

Conclusions

During the ionization of molecules, depending on the number and energies of their electronic bonds, absence or presence of sulfur or selenium atoms chains, molecular ions either acquire three-fold differing excitation energies, or energy, leveled with electronic links, insufficient for three-fold energy difference of primary separations. In the mass spectra of perfluorobenzenes with perfluoroalkyl substituents, synchronous separation of one, two and three fluorine atoms does not occur if the perfluoroalkyl substituents are separated from each other by two fluorine substituents. In contrast to primary synchronous detachments of three fluorine atoms in ionic series of perfluorotributyl amine [7], in 2,4,6-tris(perfluoroalkyl)-1,3,5-triazines mass spectra, primary synchronous separation of three fluorine atoms does not occur [8], since their perfluoroalkyl substituents are separated from each other by three nitrogen atoms. An interesting example of that two perfluoroisopropyl benzene substituents at positions 4 and 6 and one trifluoromethyl substituent at position 5 are fragmented by primary synchronous separation of one, two and three fluorine atoms is a mass spectrum and an ionic series of 1,3-difluoro-2,4,6-tris(perfluoroisopropyl)-5-trifluoromethyl benzene.

In the ionic series of n-alkanes, n-perfluoroalkanes, perfluorocyclohexane and polyoxaperfluoralkanes spectra, the energies of the primary synchronous detachments of the radicals also differ by three times [6].

The specific type of fragmentation is the molecular ions isomerization, typical for cyclic molecules with CH bonds. An examples of molecular ion isomerisation are: six ion series of benzene mass spectrum, arising as a result of its carbon skeleton restructuring, in accordance with five versions of π-conjugates, eight non-aromatic 1,3,5,7-cyclooctatetraene (CH)₈ ionic series and fifteen 18-annulene (CH)₁₈ ionic series [3].

Similar values of carbon atoms number and arising ionic series number are the result of the fact that in fragmentation of excited molecular cation-radicals all possible versions of restructuring of their π-conjugates are realized, as well as version of fragmentation with existing conjugations preservation, when only separation of hydrogen atoms takes place. The benzene ionic series, 1,3,5,7-cyclooctatetraene С₈H₈ and [18]-annulene C₁₈H₁₈ are fragmenting, without branching or intersecting.

Compared to the mass spectrum of benzene, consisting of six ionic series with five options for restructuring π-conjugations, in the spectrum of hexakis (methyl) benzene, the number of ionic series increases to eleven, but only two variants of adjustment are realized: π_1-4 and π_1-3 [4]. That is, methyl substituents make it difficult to re-tune the π-conjugations, which can result from a four-fold increase in the number of electron bonds and a fifteen-fold increase in the CH₃ mass, as compared to the mass of the hydrogen atom.

Replacement in a benzene molecule of one hydrogen atom by a fluorine atom leads to seven new fluorine-containing ionic series, which confirms the presence of π-conjugations not only between CH-groups, but also between CH and CF-groups [3].

The number of hydrocarbon ionic series in the mass spectrum of 1,2-difluorobenzene is reduced to four series. Further hydrogen atoms substitution with fluorine atoms leads not only to a decrease in the number of hydrocarbon ionic series, but also to a decrease in the number of fluorine-containing series [3].

Unlike the six ionic series of benzene, the hexafluorobenzene fragmented to form two ionic series differing by the sequence of separation [3].

The analysis of substituted benzenes ionic series makes it possible to establish fragmentation paths, as well as the presence or absence of the six-membered cycle π-conjugations reconfiguration.

Acknowledgements

This work was supported by the Ministry of Science and Higher Education of the Russian Federation and was performed employing the equipment of Center for Molecular Composition Studies of INEOS RAS.

References

1. L.M. Yagupolskii, N.V. Kondratenko, V.P. Sambur, Synthesis, 1975, 721.
2. A.A. Kolomeitsev, N.V. Kondratenko, V.I. Popov, L.M. Yagupolskii, Hexakis-(trifluoromethylthio)- and (trifluoromethylseleno) benzenes. Zh. Org. Khimii, 1983, XIX (12), 2631-2632. (in Russian)
3. N. D. Kagramanov, Decay sequences - ion series of mass spectra of benzene, 1,3,5,7-cyclooctatetraene, [18]-annulene, hexafluorobenzene and its isomers, Fluorine Notes, 2022, 3(142), 5-6.
4. N. D. Kagramanov, Decay sequences - ion series of mass spectra hexamethylbenzene and hexakis(trifluoromethyl)benzene, Fluorine Notes, 2022, 5(144), 1-2.
5. N. D. Kagramanov, Ratios of primary separations in ionic series of mass-spectra of perfluoroalkanes, perfluorocyclohexane, eicosane, cyclotriacontane, containing regular fragment groups (C₂H₄ or CF₂), Fluorine Notes, 2023, 6(151), 1-2.
6. N. D. Kagramanov, Synchronous separation of three radicals in ionic series of polyoxaperfluoroalkanes and polyoxaperfluoroalkyl halides mass spectra, Fluorine Notes, 2024, 2(153), 1-2.
7. N. D. Kagramanov, Three series ions of perfluorotributylamine mass-spectrum (PFTBA), Fluorine Notes, 2020, 3(130), 1-2.
8. N. D. Kagramanov, Decay sequences - ionic series of mass spectra for 2,4,6-tris(perfluoroalkyl)-1,3,5-triazines, Fluorine Notes, 2023, 4(149), 3-4.

ARTICLE INFO
Received 14 May 2024
Accepted 29 May 2024
Available online June 2024

Recommended for publication by PhD M.A. Manaenkova

eLIBRARY Document Number (EDN) TJUUTI

Fluorine Notes, 2024, 154, 1-2