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Electron Spin Resonance Studies of the Sulfur Catalysis of the Industrial Dichlorination of Benzene.

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Table 2. Calculated enthalpies of formation (MNDO, kcal/mol), total energies (in Hartrees), and relative energies (kcal/mol) for CH,Fo' 2 and
H F - C H ? ~ 3.
2
3
- 138.429312
- 138.440611
223.2
183.5
7.1
0
[a] 4-3IG/STO-3G indicates complete optimization of geometry at an STO3G-level and single point energy calculation using 4-31G.
[3] In the CA spectrum of the [M-C02]00
ion generated from CH2FC02D,
the signal for m / r 20 (HFoo) is displaced to m / z 21 (DF'"), whereas the
signal for m/r 14 (CHPG) experiences no mass shift. This result also is
3.
consistent only with one structure DF-CH?'
[4] a) M. J. S. Dewar, W. Thiel, J. Am. Chem. SOC.99 (1977) 4889,4907; b) R.
Ditchfield, W. J. Hehre. J. A. Pople, J. Chem. Phys. 54 (1971) 724.-The
program No. 368 from QCPE, Indiana University, Bloomington, Indiana
was used for the ab inirio calculations.
[5] a) Y. Apeloig, B. Ciommer, G. Frenking, M. Karni, A. Mandelbaum, H.
Schwarz, A. Weisz, J . Am. Chem. Soc.. in press; b) W. J. Bouma, J. K.
MacLeod, L. Radom, ibid. I01 (1979) 5540; c) J. L. Holmes, F. P. Losing,
J. K. Terlouw, P. C . Burgers, ibid.. in press.
A).
C-F bond lengths (according to STO-3G, 1.47
Comand H F
parison of the data for 3 with that for 2, CH2FB@,
leads to the following interpretation: 3 is a slightly bent
complex of CH?* with HF, in which the C-F bond is
formed by interaction of an empty sp2-hybridized orbital
of CHYe with one of the npnbonding electron pairs of
HF; it is approximately 0.08 A longer than the C-F bond
in 2. Th? C-H and F-H bond lengths in 3 are hardly
(<O.OI A) different from those in CH?@ and HF.
Complex formation does, however, have a considerable
effect on the charge distribution; whereas in CH?@ 60% of
the charge is located on the carbon atom and 20% on each
of the hydrogen atoms, only 14% of the charge is located
on the carbon atom in 3. The greatest amount of charge is
distributed on the hydrogen periphery: the H atom of the
HF component accepts 49%, whereas each of the H atoms
carry 16%;the F atom only accepts 4%. The unpaired electron of radical cation 3 is, on the whole, localized in a carbon atom 2p, orbital. Complexation of CHF@ with H F
provides a stabilization of at least 43 kcal/mol (estimated
from the known experimental A@ values of 2, CH'@, and
HF assuming that 3 is at least 7 kcal/mol more stable than
2 1.
That 2 and 3 exist as discrete, non freely-interconverting species, follows directly from the MNDO barrier for
[1,2]-H migration: the transition state 4 (one and only one
negative eigenvalue of the force-constant matrix) lies approximately 70.2 and 30.5 kcal/mol higher than 3 and 2,
respectively. Therefore, if 2 and 3 are generated, they
should be considered as stable isomers, which according to
their spectral data (e. g. the CA spectra) must be distinguishable. This is exactly what is observed (Table 1). The existence of 3 and other more stable ion-dipole complexes
X - + C H ? @(X=CH3C1[5a1,CH2=015b1,
H20, HzS, HCI, and
HBr'"]), which are in part, however, only obtainable via
Electron Spin Resonance Studies of the
Sulfur Catalysis of the Industrial
Dichlorination of Benzene**
By Hans Bock*, Udo Stein, and Peter Rittmeyer
Dedicated to Professor Klaus Weissermel on the occasion
of his 60th birthday
In the dichlorination of benzene in suspensions with
1.5% FeCI, it is known"] that the addition of sulfur (or sulfur compounds such as dichlorodisulfane or thianthrene[*I)
considerably improves the selectivity: the yield of 1,4-dichlorobenzene increases from 47% to approximately 75%
and that of the ortho-isomer decreases from 37% to ca.
22%[I.2'.
The conditions of the industrial chlorination suggest a
radical cation intermediate. ESR spectroscopy with its
M, temperatures
high sensitivity, (concentration ca.
up to 180 K) therefore offers a possibility of obtaining information on the course of the sulfur-catalyzed, selective
dichlorination of benzene. Preliminary results are summarized in Scheme I :
0
ClSSC
R
(R = H,
F,
\
3
4
Scheme 1
more complicated and less efficient routes, indicates that a
general structural type is involved: the high stability and
formally straightforward mode of formation (complexation of the ubiquitous CH?@ with polar neutral molecules)
indicate that this could be significant also in interstellar
processes.
Received: April 16, 1982 [Z 14 IE]
German version: Angew. Chem. 94 (1982) 547
[I] H. Bock, B. Solouki, Angew. Chem. 93 (1981) 425; Angew. Chem. Int. Ed.
Engf. 20 (1981) 427.
[2] R. D. Bowen, D. H. Williams, H. Schwarz, Angew. Chem. 91 (1979) 484;
Angew. Chem. Int. Ed. Engl. 18 (1979) 45 1.
Angew. Chem. Int. Ed. Engl. 21 (1982) No. 7
DTsd
R
2
(R = OCH,, CHp
H, F, NO,. .
Scheme 1
1. If dichloromethane solutions of benzene, or its alkylor fluoro-derivatives containing two ortho-hydrogens at
['I
[**I
Prof. Dr. H. Bock, Dr. U. Stein, P. Rittmeyer
Institut fur Anorganische Chemie der Universitat
Niederurseler Hang, D-6000 Frankfurt am Main 50 (Germany)
Radical Cations, Part 53. This work was supported by the Land Hessen,
the Deutsche Forschungsgemeinschaft, the Fonds der chemischen Industrie, and the Schlosser-Stiftung (f'. R.).-Part 5 2 : J. Giordan, M.
Eiser, H. Bock, H.-W. Roesky, Phosphoms Surfur 12 (1982), in press.
0 Verlag Chemie GmbH, 6940 Weinheim. 1982
0570-0833/82/0707-0533 $02.50/0
533
529-532 Advertisement
180-200 K are treated with S2C12and AICI3 or with S8 and
SbCIS, the ESR spectra of the radical cations generated,
displaying hyperfine structural details, are observed. Based
on 33S,I3C, and 'H isotopic labeling, the parent compound
( R = H) can be assigned a structure with CZv symmetry:
Presumably a ring-closed benzodithiete radical cation is
present in solution. Upon warming to room temperature,
the known['] ESR signals of stable thianthrene radical cations appear in addition at high field ( R = H :
9 = 2.01 53-2.0084).
2. Oxidation of numerous benzene derivativesI2l- 1,2benzenedithiol, chloro(phenyl)disulfane, and tris(1,3,2benzodithiaboroly1)amine are shown as examples in
Scheme 1 -using the tested anhydrous and oxygen-free
oxidation systems AIC13/H2CC12L3h1
or SbCIS/H2CC1213"1
also results in solutions in which the ESR signals of the
unknown o-phenylenedithio radical cation and of the
known thianthrene radical cation can be measured.
3. The oxidation of thianthrene and diphenyldisulfanes
bearing the same substituents led in each case to identical
thianthrene radical c a t i o n ~ [ ~ .Addition
~I.
of dichlorodisulfane and increasing the temperature result in the appearance of additional ESK signals of the substituted o-phenylenedithio radical cations.
Information on the preferred 1 ,4-dichlorination of benzene can be drawn from the ESR result that no signals are
observed for substituents R in the "nodal planes" indicated in Scheme I by dotted lines, i. e. only a small positive
charge and hence the highest electron density for an electrophilic attack is found here[2.31.
Gas phase pyrolyses, optimized by photoelectron spectroscopy121-e. g. the cleavage of propene from 2-methyl2,3-dihydro-1,4-benzodithiane-suggest that benzodithiete
can be isolated preparati~ely'~]
and hence its chlorination
investigated. Further ESR experiments with the aim of detecting reactive sulfur species, such as CISS'AICI,e, via
their reaction products show that the oxidation in presence
of sulfur can also be applied to other n-systems. For example under the conditions shown in Scheme 1, substituted
phenylacetylenes d o not react to give o-phenylenedithio
and thianthrene radical cations,
to 3-phenyl-1,2-di-
(R = H; g = 2.0148)
(R = H; g = 2.0082)
thiete and further to 2,s-diphenyl-1 ,Cdithiin radical cations.
Received: April 14, 1982 [Z 1 I IE]
German version: Angew. Chem. 94 (1982) 540
The complete manuscript of this communication appears in:
Angew. Chem. Suppl. 1982, 1145-1 154
[I] The chlorination of benzene in presence of FeC1,/Ss is carried out on the
industrial scale in Werk Griesheim by Hoechst AG (R. Sammet, lecture
"Aromatische Zwischenprodukte", Universitat Frankfurt, Winter semester 1978179); cf. Ullmanns Encyklopadie der Technischen Chemie, 4th Ed.,
Vol. 9, p. 499f., Verlag Chemie, Weinheim 1975; K. Weissermel, H. J.
Arpe: Induslrielle Orgonische Chemie. 2th Ed., p. 329, Verlag Chemie,
Weinheim 1978.
121 U. Stein, Dissertation, Universitat Frankfurt 1980; P. Rittmeyer, Diplomarbeit, Universitat Frankfurt 1981, and literature cited therein; cf. also J.
Giordan, H. Bock, Chem. Eer. 115 (1982) in press, and literature cited
therein.
534
0 Verlag Chemie GmbH. 6940 Weinheim, 1982
[3] For generation of sulfur and silicon radical cations cf. e . g . a) H. Bock, G.
Brahler, D. Dauplaise, U. Henkel, J. Meinwald, W. Schulz, R. Schlecker,
D. Seebach, A. Semkow, U. Stein, Chem. Eer. 113 (1980) 289, 3280; 114
(1981) 2622, 2632; b) H. Bock, W. Kaim, Ace. Chem. Res. I S (1982) 9.
141 3,4-Bis(trifluoromethyl)- 1.2-dithiete can be synthesized from hexafluoro2-butyne and sulfur vapor [structural determination: J. L. Hencher, Q.
Sheng, D. G . Tuck, J. Am. Chem. SOC.98 (1976) 8991 and oxidized by
conc. H2SO4to the radical cation [G. A. Russel, R. Tanikoga, E. R. Talaty, ibrd. 94 (1971) 6125, and literature cited therein].
The Molecular Structure of Gaseous Titanium
Tris(tetrahydridob0rate) as Determined by
Electron Diffraction**
By C. John Dain. Anthony J. Downs*, and
David W . H . Rankin
The tetrahydridoborate group is remarkable for the versatility of its ligation to metal centers which may entail triple""], double""], or even single[''] hydrogen bridges. To
date direct methods of structural analysis have been applied to only one gaseous molecule in which the tetrahydridoborate groups function as tridentate ligands, namely
zirconium tetrakis(tetrahydridoborate), Zr(BH,),["]. Here
we wish to report the structure of the gaseous titanium
tris(tetrahydridob0rate) molecule which we have deduced
by analyzing its electron diffraction pattern. The results
have added significance in view of the dearth of structural
information about molecular titanium(ir1) derivatives with
a trigonal disposition of ligands around the metal atom.
Ti(BH4)3 was prepared by the passage of a slow stream
of TiBr4 vapor through a bed of powdered, freshly recrystallized LiBH4 held at room temperature, the volatile products being removed under continuous pumping and trapped at 77 K. Fractionation in vacuo gave samples of
Ti(BH4)3which were judged to be pure on the evidence of
analysis (via methanolysis) and of the IR['"I and UV photoelectron12h1spectra of the vapor; the preparative procedures previously reported"] appear, by contrast, to have
yielded only impure products. The purified product is a
green solid highly susceptible to attack by traces of oxygen
or moisture and with a vapor pressure at room temperature
in the order of 1 torr; changes in the color and IR spectrum of the solid at lower temperatures imply the existence
of more than one solid phase.
The electron diffraction pattern of gaseous Ti(BH4)3 at
room temperature was measured photographically using
the Edinburgh/Cornell gas-diffraction
over a
range of 22- 140 n m - ' (scattering variables). Since the IR
and UV photoelectron spectra of the vapor were found to
exhibit the patterns characteristic of tri-hydrogen bridged
tetrahydridoborate ligands12"-c1, we based the analysis
of the electron scattering pattern on a model of the type
Ti[(p-HXBHJ3 involving five independent geometrical parameters and five amplitudes of vibration; data reducti0nI~~1
and least-squares refinement[5d1followed established procedures. Convergence of the structural refinement proceeded satisfactorily, the optimum refinement
achieved to date corresponding to RG = 0.05 1
( R D = 0.037).
['I
[**I
Dr. A. J. Downs, C. J. Dain
Department of Inorganic Chemistry, University of Oxford
South Parks Road, Oxford OX1 3QR (England)
Dr. D. W. H. Rankin
Department of Chemistry, University of Edinburgh
West Mains Road, Edinburgh EH9 3JJ (Scotland)
We thank the Science Research Council for the award of research grants
and of a research studentship (to C. J. D.).
0570-0833/82/0707-0S34 $02.50/0
Angew. Chem. Inr. Ed. Engl. 21 (1982) No. 7
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