Elsevier

Chemical Physics Letters

Volume 613, 3 October 2014, Pages 34-39
Chemical Physics Letters

Photoinduced rotamerization and dissociation of o-fluorobenzoyl chloride in solid Ar

https://doi.org/10.1016/j.cplett.2014.08.053Get rights and content

Highlights

  • Infrared spectrum of o-fluorobenzoyl chloride (FBC) was measured in solid Ar.

  • Upon UV irradiation, the rotamerization from anti- to gauche-FBC was confirmed.

  • Isomerization to 6-chloro-2-fluoro-2,4-cyclohexadien-1-ylidenemethanone was observed.

  • Prolonged UV irradiation resulted in the formation of o-chlorofluorobenzene and CO.

Abstract

UV light-induced reactions of o-fluorobenzoyl chloride (FBC) were investigated using infrared spectroscopy in a cryogenic Ar matrix. Photoinduced rotational isomerization from anti- to gauche-FBC was confirmed by comparison with calculated spectra. In addition, photolysis products were found to be ketene species (6-chloro-2-fluoro-2,4-cyclohexadien-1-ylidenemethanone), o-fluorobenzoyl radical, o-chlorofluorobenzene, m-chlorofluorobenzene and CO.

Introduction

Benzoyl chloride derivatives have been used as a reagent for the syntheses of anticancer [1], antileukemic [2] and antiadenoviral [3] agents. Despite its practical use, the available properties on the structure and spectroscopy are relatively scarce. Using gas electron diffraction, the conformations of ortho-halobenzoyl chloride were studied by Johansen et al. [4] who determined that as the size of a halogen atom increases, the equilibrium torsion angles of φ(C(X)single bondCsingle bondC(double bondO)single bondCl) for gauche and anti conformers also increase due to the steric effect. They found φ(C(F)single bondCsingle bondC(double bondO)single bondCl) to be +44.4(24)° and −179.9(6)° for gauche- and anti-o-fluorobenzoyl chloride (FBC), respectively, and the ΔG°(gauche–anti) to be +0.48(42) kcal mol−1 at 386 K [4]. They also performed theoretical calculations at different levels. Contrary to observations, non-planar geometries were found for both conformers, and φ(C(F)single bondCsingle bondC(double bondO)single bondCl) was calculated to be 33.4° to 44.2° and −147.4° to −157.5° for the gauche- and anti-FBCs, respectively. Despite previous investigations of the infrared spectrum of FBC [5], no spectral interpretation of conformers has been conducted.

In the photolysis of benzoyl chloride in solid Ar, a ketene species (6-chloro-2,4-cyclohexadien-1-ylidenemethanone) was formed as an intermediate product followed by its dissociation to yield chlorobenzene and CO [6]. In contrast to the photolysis of benzaldehyde [7], the formation of a benzoyl radical was not confirmed.

In the present study, FBC's infrared spectra were measured in a low-temperature Ar matrix. Due to the narrower bandwidth and lesser complexity of the spectrum in the matrix-isolated species than in vapor and liquid, the absorption bands for different conformers can be separated. Coexistence of the anti and gauche conformers was confirmed in FBC through matrix-isolation infrared spectroscopy combined with UV irradiation and DFT calculations. The observed infrared bands of each conformer were separated and assigned.

Section snippets

Experimental

FBC (Wako Pure Chemicals Industries, Ltd.) was purified by a freeze–pump–thaw cycle at 77 K and was diluted with argon gas (Nippon Sanso, Japan, 99.999% purity) to approximately 1/1000 (0.2 Torr FBC and 200 Torr Ar). It was then slowly sprayed onto a CsI plate cooled by a closed-cycle helium refrigerator (Iwatani CryoMini M310/CW303) to approximately 7 K. For product identification, o- and m-chlorofluorobenzenes (CFB, Wako Pure Chemicals Industries, Ltd.) were used as authentic samples. Infrared

Separation and assignments of the infrared bands of the conformers

An FBC/Ar mixture was deposited on a CsI window (FBC/Ar = 1/1000). In the infrared spectrum obtained after deposition, strong bands were observed at 1794 cm−1 and 886 cm−1, which were attributed to the Cdouble bondO and Csingle bondCl stretching vibrations of FBC, respectively [5]. Figure 1 shows (a) the observed infrared difference spectrum obtained by subtracting the spectrum measured before Hg lamp irradiation from that measured after 120 min of irradiation and (b) the calculated infrared difference spectra of FBC,

Conclusions

UV light-induced reactions of FBC were investigated using infrared spectroscopy in a cryogenic Ar matrix. Photoinduced rotational isomerization from anti- to gauche-FBC was confirmed by comparison with calculated spectra. In addition, the photolysis products were found to be 6-chloro-2-fluoro-2,4-cyclohexadien-1-ylidenemethanone, o-fluorobenzoyl radical, o-chlorofluorobenzene, m-chlorofluorobenzene and CO.

References (20)

  • D.S. Prasanna et al.

    Eur. J. Med. Chem.

    (2010)
  • N.D. Patel et al.

    J. Mol. Spectrosc.

    (1973)
  • N.D. Patel et al.

    J. Mol. Spectrosc.

    (1973)
  • J.H.S. Green

    Spectrochim. Acta

    (1970)
  • T. Tamezane et al.

    Chem. Phys. Lett.

    (2006)
  • S. Cortez-Maya et al.

    Synth. Commun.

    (2012)
  • C.T. Öberg

    J. Med. Chem.

    (2012)
  • T.H. Johansen et al.

    Struct. Chem.

    (2013)
  • H.N. Al-Jallo et al.

    Spectrochim. Acta

    (1972)
  • N. Tanaka

    Int. Res. J. Pure Appl. Chem.

    (2014)
There are more references available in the full text version of this article.

Cited by (3)

  • Photoinduced reactions of chloroacetone in solid Ar: Identification of CH<inf>2</inf>=COClCH<inf>3</inf>

    2014, Chemical Physics Letters
    Citation Excerpt :

    This is probably due to the cage effect that makes subsequent addition and abstraction reactions effective. Unlike the photoinduced reactions of chloroacetyl chloride [24] and o-fluorobenzoyl chloride [30] in solid Ar, where the rotational isomerization reached an equilibrium and the less stable conformer was decomposed upon further irradiation, in our case the concentration of syn-chloroacetone continued to grow during the entire irradiation period, as shown in Figure 2. This might indicate that in the photolysis of syn-CH2COClCH3 a considerable amount of chloroacetone is produced by recombination, in parallel to the formation of 2-chloro-2-methyloxirane.

View full text