D
H. Langhals, M. Eberspächer
Paper
Synthesis
Table 3 Solubility of 1 in Perfluorinated Hydrocarbons and Silicone Oil
ure 2, equipped with distilled water (300 mL) and isohexane (300
mL), heated to reflux (bath 125 °C) so that steam distillation and
phase separation proceeded simultaneously and steam distilled and
extracted until colorless condensation of isohexane (1–2 days). The
deep-blue phase of isohexane was washed with 2 M aqueous HCl
(3 × 100 mL), distilled water, then dried with Na2SO4, evaporated, pu-
rified by column separation (basic alumina, activity II, isohexane, first
intensely blue band), filtrated through a D5 glass filter and evaporat-
ed.
Based on UV/Vis Spectroscopic Measurementsa
Solvent
Solubility of 1 (mmol·L–1
)
Perfluorohexane
2.7
(CAS Reg. No. 355-42-0)
Perfluoromethylcyclohexane
(CAS Reg. No. 355-02-2)
3.4
3.6
5.7
2.6
650
3.1
Yield: 4.4 g (36%); bluish black leaflets; mp 99–100 °C (Lit.21 99–
100 °C); Rf = 0.67 (Al2O3 neutral, isohexane).
Perfluorodecalin
(CAS Reg. No. 306-94-5)
Perfluoro-2-methyl-2-pentene
(CAS Reg. No. 1584-03-8)
IR (ATR): 3075.8 (vw), 2958.5 (vw), 2923.8 (w), 2853.8 (vw), 1816.3
(w), 1641.8 (br), 1569.9 (w), 1530.5 (w), 1475.8 (m), 1452.3 (w),
1437.8 (w), 1389.2 (w), 1296.0 (w), 1260.8 (vw), 1204.3 (m), 1151.9
(vw), 1051.7 (w), 1012.2 (w), 984.2 (w), 965.0 (m), 952.1 (m), 897.3
Perfluorotributylamine
(CAS Reg. No. 311-89-7)
(w), 823.6 (w), 792.2 (w), 755.0 (vs), 725.3 (s), 674.3 (m) cm–1
1H NMR (600 MHz, CDCl3, 27 °C, TMS): δ = 7.18 (t, 3JH–H = 9.8 Hz, 2 H,
.
Hexafluorobenzene
(CAS Reg. No. 392-56-3)
3
3
Poly-1,1,2,3,3,3-hexafluoropropylene oxide
(CAS Reg. No. 69991-67-9; HT110, b.p. 110 °C,
CHAr), 7.41 (d, JH–H = 3.7 Hz, 2 H, CHAr), 7.60 (t, JH–H = 9.9 Hz, 1 H,
3
3
CHAr), 7.92 (t, JH–H = 3.7 Hz, 1 H, CHAr), 8.36 (d, JH–H = 9.1 Hz, 2 H,
M
n 580)
CHAr).
Silicone oil (Baysilon Grüssing 250 °C; Wacker
silicone oil AK 100, n = 70, Mn 5000)
110
UV/vis (CHCl3): λmax (εrel) = 327.40 (0.71), 340.60 (1.00), 353.20 (0.21),
579.20 (0.08) nm.
MS (DEI+/70 eV): m/z (%) = 129.1 (7) [M+ + H], 128.1 (100) [M+], 127.0
(16) [M+ – H], 126.0 (7) [M+ – 2H], 102.0 (10), 84.9 (1), 82.9 (2), 81.9
(1), 78.0 (1), 76.0 (2), 75.0 (3), 74.0 (4), 63.0 (3), 51.0 (1), 50.0 (2), 50.0
(2), 50.0 (2), 50.0 (2), 43.0 (1).
a Molar absorptivity of 1: ε (340.6 nm) = 4446 L·mol–1·cm–1, ε (578.4 nm) =
323 L·mol–1·cm–1
.
To conclude, azulene (1) could be efficiently prepared by
Ziegler and Hafner’s route, wherein the use of pyrrolidine
as the required intermediary secondary amine allowed a
simple procedure. The obtained yields were similar and
were unaffected by batch size. Workup by continuous close-
loop steam distillation with an interlinked extraction
makes synthesis of 1 more convenient, even in larger scales,
and is thus well accessible. The UV/Vis spectra of 1 could be
simulated with high precision by using a series of Gaussian
functions. Applications of 1 in cosmetics and for the color-
ation of silicone oil and of perfluorinated organic com-
pounds including those applied in eye surgery are of techni-
cal interest.
HRMS (DEI-C1 + C EI Full ms [39.50–440.50]): m/z calcd for C10H8:
128.0626; found: 128.0626, Δ = 0.0 mmu.
Anal. Calcd for C10H8: C, 93.71; H, 6.29. Found: C, 93.03; H, 6.24.
References
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Azulene (1)
1-Chloro-2,4-dinitrobenzene (20.3 g, 100 mmol) and anhydrous pyri-
dine (120 mL) under nitrogen atmosphere were heated with stirring
at 90 °C for 4 h (formation of a voluminous precipitate, initially color-
less, then turning from yellow to finally brown), cooled to 0 °C, then
slowly treated dropwise with pyrrolidine (18.1 mL, 220 mmol, clear-
ing and turning to red) and stirred at r.t. for 16 h. The red solution was
then treated with freshly (!) distilled cyclopentadiene (8.68 mL, 105
mmol) and then a solution of sodium methoxide in methanol [freshly
prepared from sodium (2.30 g, 100 mmol) and MeOH (40.0 mL)] was
added dropwise. The reaction mixture was then stirred at r.t. for 16 h,
then concentrated by distillation with the application of a Vigreux
column (30 cm, bath 130 °C) until 95 °C of the distillate, and subse-
quently allowed to cool to r.t. The distillate was treated with anhy-
drous pyridine (200 mL), then heated to reflux for 6 d (bath 135 °C),
and allowed to cool to r.t. After addition of distilled water (200 mL),
the reaction flask was attached to a phase separator according to Fig-
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–E