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Russ. Chem. Bull., Int. Ed., Vol. 70, No. 5, May, 2021
(25, 29), 153 [M – Br – HBr]+ (100), 133 [M – Br – HBr – HF]+
(90). Found (%): C, 22.91; H, 1.80. C6H6Br2F4. Calculated (%):
C, 22.96; H, 1.93.
5,5,6,6-Tetrafluorocyclohexa-1,3-diene (9).46 B.p. 54—56 °С
(150 Torr). 1H NMR (CDCl3, 300.1 MHz) δ: 5.98—6.12 (m, 2 Н,
СH=СН); 6.22—6.35 (m, 2 Н, CH=СН). 13C NMR (CDCl3,
125.8 MHz), δ: 112.24 (tt, C(5) and С(6), J = 249 Hz,
J = 26.3 Hz); 124.47 (t, C(1) and С(4), J = 27.7 Hz); 128.96
(tt, C(2) and С(3), J = 12.9 Hz, J = 4.7 Hz). 19F NMR (CDCl3,
282.4 MHz), δ: –122.8 (br.s, 4 F, 2 CF2). MS, m/z (Irel (%)):
152 [M]+ (100), 132 [M – HF]+ (44), 112 [M – 2HF]+ (15),
101(30), 83 (31).
Synthesis of 1-bromo-2,3-difluorobenzene 7a by dehydro-
halogenation of dibromotetrafluorocyclohexane 6а. A 50% aque-
ous solution of KOH (140.0 g, 1.25 mol) was added for 1.5 h to
a mixture of 3,4-dibromo-1,1,2,2-tetrafluorocyclohexane (6а)
(100.0 g, 318 mmol) and TEBAC (0.94 g, 4 mmol) maintaining
temperature in a range of 20—30 °С. Then the reaction mixture
was stirred at 80—85 °С for 2 h, after which the organic product
was distilled off with water vapor, dried over CaCl2, and distilled.
2,3-Difluorobromobenzene (7a) (b.p. 157—158 °С) was obtained
in a yield of 54.1 g (88%).
Chlorination of tetrafluorocyclohexene 2. Gaseous Cl2 (79.5 g,
1.12 mol) was bubbled at 25—35 °С for 6 h with vigorous
stirring through a solution of tetrafluorocyclohexene 2 (150.9 g,
980 mmol) in CHCl3 (300 mL) containing FeCl3 (4.0 g,
24 mmol). The reaction mixture was heated to 30—35 °С, kept
for 2 h with stirring, and washed with a 10% aqueous solution of
Na2SO3 and water. The organic product was washed over CaCl2,
then CHCl3 was removed, and the residue was distilled on a rotary
evaporator under reduced pressure. 3,4-Dichloro-1,1,2,2-tetra-
fluorocyclohexane (6b) (b.p. 60—62 °С, 13 Torr) was obtained
in a yield of 173.1 g (78%).
3,4-Dichloro-1,1,2,2-tetrafluorocyclohexane (6b). B.p.
60—62 °С (13 Torr). 1H NMR (CDCl3, 300.1 MHz), δ:
1.95—2.27 (m, 2 Н, СН2); 2.27—2.52 (m, 2 Н, СН2); 3.90—4.07
(m, 1 Н, СНСl); 4.08—4.24 (m, 1 Н, СНСl). 13C NMR (CDCl3,
75.5 MHz), δ: 29.03 (t, C(6), J = 22.2 Hz); 29.72 (d, C(5),
J = 9.6 Hz); 57.71 (t, C(4), J = 2.4 Hz); 62.38 (td, C(3),
J = 21.2 Hz, J = 2.2 Hz); 112.95 (tdd, C(1), J = 258.0 Hz,
J = 32.5 Hz, J = 22.7 Hz); 116.23 (tt, C(2), J = 253.9 Hz,
J = 26.6 Hz). 19F NMR (CDCl3, 282.4 MHz), δ: –117.7 and
–120.3 (AB system, 2 F, CF2, 2J = 257.0 Hz, 3J = 29.5 Hz),
–125.5 (m, 2 F, CF2). MS, m/z (Irel (%)): 228, 226, 224 [M]+
(5, 28, 46), 191, 189 [M – Cl]+ (43, 48), 190, 188 [M – HCl]+
(12, 27), 171, 169 [M – HCl – F]+ (2, 7), 153 [M – HCl – Cl]+
(32), 133 (37), 125 (42), 111 (31), 90 (31), 77 (92), 75 (100),
64 (28), 51 (30), 39 (35). Found (%): C, 32.15; H, 2.46. C6H6Cl2F4.
Calculated (%): C, 32.03; H, 2.69.
1-Bromo-2,3-difluorobenzene (7а).8 B.p. 157—158 °С. 1H NMR
(CDCl3, 300.1 MHz), δ: 7.00—7.16 (m, 1 Н, Ar); 7.17—7.29
(m, 1 Н, Ar); 7.34—7.47 (m, 1 Н, Ar). 13C NMR (CDCl3, 75.5
MHz), δ: 110.40 (d, C(1), J = 17.5 Hz); 116.40 (d, C(4),
J = 17.7 Hz); 124.70 (dd, C(5), J = 7.1 Hz, J = 5.0 Hz); 128.23
(d, C(6), J = 3.6 Hz); 148.10 (dd, C(2), J = 248.8 Hz,
J = 14.3 Hz); 150.92 (dd, C(3), J = 251.9 Hz, J = 13.3 Hz).
19F NMR (CDCl3, 282.4 MHz), δ: –130.9 (m, 1 F, Ar), –134.8
(m, 1 F, Ar). MS, m/z (Irel (%)): 194, 192 [M]+ (100, 99), 113
[M – Br]+ (88), 63 (60). Found (%): C, 37.54; H, 1.50.
C6H3BrF2. Calculated (%): C, 37.34; H, 1.52.
Bromination of tetrafluorocyclohexene 3. A solution of Br2
(24.0 g, 150 mmol) in CHCl3 (40 mL) was added by portions at
20—25 °С for 2 h to a solution of tetrafluorocyclohexene 3 (21.1 g,
137 mmol) in CHCl3 (30 mL) containing FeCl3 (0.15 g, 1 mmol),
and the mixture was stirred at 25—30 °С for 2 h. The reaction
mixture was washed with a 10% aqueous solution of Na2SO3 and
water, and the obtained organic product was dried over CaCl2
and distilled under reduced pressure. 4,5-Dibromo-1,1,2,2-
tetrafluorocyclohexane (8) (b.p. 70—72 °С, 12 Torr) was obtai-
ned in a yield of 39.1 g (91%).
4,5-Dibromo-1,1,2,2-tetrafluorocyclohexane (8). B.p. 74—75 °С
(12 Torr). 1H NMR (CDCl3, 300.1 MHz), δ: 2.45—2.75 (m, 2 Н,
2CHH); 2.88—3.08 (m, 2 Н, 2CHH); 4.05—4.23 (m, 2 Н,
2CHBr). 13C NMR (CDCl3, 125.8 MHz), δ: 40.36 (t, C(3) and
C(6), J = 22.1 Hz); 46.48 (d, C(4) and C(5), J = 7.5 Hz); 114.32
(tdd, C(1) and C(2), J = 255 Hz, J = 31.4 Hz, J = 21.7 Hz).
19F NMR (CDCl3, 282.4 MHz), δ: –116.6 and –123.2 (AB
system, 4 F, 2CF2, 2J = 256.0 Hz). MS, m/z (Irel (%)): 316, 314,
312 [M]+ (6, 12, 6), 235, 233 [M – Br]+ (88, 88), 154 [M – 2Br]+
(6), 153 [M – Br – HBr]+ (72), 133 [M – Br – HBr – HF]+
(100), 89 (26). Found (%): C, 32.05; H, 2.66. C6H6Br2F4.
Calculated (%): C, 32.03; H, 2.69.
Dehydrohalogenation of dibromotetrafluorocyclohexane 8.
A 50% aqueous solution of KOH (45.0 g, 401 mmol) was added
at 20—25 °С for 30 min to a mixture of 4,5-dibromo-1,1,2,2-
tetrafluorocyclohexane 8 (37.14 g, 118 mmol) and TEBAC (0.23 g,
1 mmol), and the reaction mixture was stirred at 60—65 °С
for 4 h. The obtained organic product was diluted with water,
extracted with CH2Cl2, dried over CaCl2, and distilled.
5,5,6,6-Tetrafluorocyclohexa-1,3-diene (9) (b.p. 54—56 °С,
150 Torr) was obtained in a yield of 9.57 g (53%), and the yield
of 4-bromo-1,2-difluorobenzene (5а) was 2.82 g (12%).
Synthesis of 1-chloro-2,3-difluorobenzene 7b by dehydro-
halogenation of dichlorotetrafluorocyclohexane 6b. A 50% aqueous
solution of KOH (285.0 g, 2.54 mol) was added at 20—30 °С for
2 h to a mixture of 3,4-dichloro-1,1,2.2-tetrafluorocyclohexane
(6b) (142.9 g, 635 mmol) and TEBAC (1.85 g, 8 mmol). The
reaction mixture was stirred at 80—85 °С for 3 h. The obtained
organic product was distilled with water vapor, dried over CaCl2,
and distilled. 2,3-Difluorochlorobenzene (7b) (b.p. 136—137 °С)
was obtained in a yield of 82.1 g (87%).
1-Chloro-2,3-difluorobenzene (7b).30 B.p. 136—137 °С.
1H NMR (CDCl3, 300.1 MHz), δ: 7.00—7.25 (m, 3 Н, Ar).
13C NMR (CDCl3, 125.8 MHz), δ: 115.71 (d, C(4), J = 17.5 Hz);
122.70 (d, C(1), J = 14.3 Hz); 124.02 (dd, C(5), J = 7.5 Hz,
J = 5.1 Hz); 125.47 (d, C(6), J = 3.4 Hz); 147.21 (dd, C(2),
J = 250.5 Hz, J = 14.4 Hz); 151.15 (dd, C(3), J = 251.0 Hz,
J = 12.3 Hz). 19F NMR (CDCl3, 282.4 MHz), δ: –134.7 (m, 1 F,
Ar); –138.5 (d, 1 F, Ar, J = 19.5 Hz). MS, m/z (Irel (%)): 150,
148 [M]+ (34, 100), 113 [M – Cl]+ (36), 63 (13). Found (%):
C, 48.36; H, 2.08. C6H3ClF2. Calculated (%): C, 48.52; H, 2.04.
Synthesis of halosubstituted tetrafluorocyclohexenes 10a,b.
A 50% aqueous solution of KOH (11.80 g, 105 mmol) was
added for 30 min with stirring to a mixture of dibromotetrafluoro-
cyclohexane 6a (30.2 g, 96 mmol) and TEBAC (0.23 g, 1 mmol)
maintaining temperature of the reaction mixture at 15—20 °С,
and then the mixture was kept at 25—30 °С with stirring for 2 h
and diluted with water. The organic phase was washed with
water, dried over CaCl2, and distilled. 1-Bromo-5,5,6,6-tetra-
fluorocyclohex-1-ene (10а) (b.p. 80—81 °С, 52 Torr) was ob-
tained in a yield of 20.56 g (92%).
1-Chloro-5,5,6,6-tetrafluorocyclohex-1-ene (10b) (b.p.
93—94 °С, 80 Torr) was synthesized in a yield of 17.1 g (91%)
using a similar procedure by the dehydrochlorination of dichloro-