(2Z)-2,3,4,5,5-Pentachloropenta-2,4-dienic acid as a minor product in the synthesis of 5,5-dimetoxytetrachlorocyclopentadiene from hexachlorocyclopentadiene

Article abstract of DOI:10.1007/s11172-019-2650-9

Pentachloropentadienic acid was isolated, apart from the expected 5,5-dimetoxytetrachlorocyclopentadiene, in the reaction of hexachlorocyclopentadiene with potassium hydroxide in methanol. The structure of this minor product was established by X-ray crystallography. The plausible mechanism of its formation is discussed.

Full text of DOI:10.1007/s11172-019-2650-9

1940
Russian Chemical Bulletin, International Edition, Vol. 68, No. 10, pp. 1940—1943, October, 2019
Brief Communications
(
2Z)-2,3,4,5,5-Pentachloropenta-2,4-dienic acid as a minor product
in the synthesis of 5,5-dimetoxytetrachlorocyclopentadiene
from hexachlorocyclopentadiene
a
b
a
a
V. A. Egorov, L. M. Khalilov, F. A. Gimalova, and M. S. Miftakhov
aUfa Institute of Chemistry,
Ufa Federal Research Center, Russian Academy of Sciences,
6
9 prosp. Oktyabrya, 450054 Ufa, Bashkortostan, Russian Federation.
Fax: +7 (347) 235 5560. E-mail: bioreg@anrb.ru
b
Institute of Petrochemistry and Catalysis,
Ufa Federal Research Center, Russian Academy of Sciences,
41 prosp. Oktyabrya, 450075 Ufa, Bashkortostan, Russian Federation
1
Pentachloropentadienic acid was isolated, apart from the expected 5,5-dimetoxytetrachloro-
cyclopentadiene, in the reaction of hexachlorocyclopentadiene with potassium hydroxide in
methanol. The structure of this minor product was established by X-ray crystallography. The
plausible mechanism of its formation is discussed.
Key words: hexachlorocyclopentadiene, potassium methoxide, 5,5-dimetoxytetrachloro-
cyclopentadiene, pentachloropenta-2,4-dienic acid, X-ray diffraction.
5
,5-Dimetoxytetrachlorocyclopentadiene (1) is used
diene is isolated by distillation under reduced pressure. It
should be noted that the aqueous layer was not previously
analyzed. We performed this reaction under the same
conditions, treated the reaction mixture as described
earlier, and analyzed the aqueous layer. For this purpose,
we acidified the aqueous phase to pH 2 and extracted
it several times with chloroform, concentrated the com-
bined extracts, and obtained a white powder. The crystal-
lization of the latter from petroleum ether gave trans-
in organic synthesis as a diene in Diels—Alder reactions,
thereby providing a convenient route to functionalized
norbornene derivatives and original polycyclic structures that
were previously difficult to access.1
—3
The synthesis of
5
,5-dimetoxytetrachlorocyclopentadiene (1) from hexa-
chlorocyclopentadiene (2) by the reaction with a KOH solu-
4
tion in methanol was described back in 1949 (Scheme 1).
According to this procedure, the mixture, which is obtained
after the completion of the reaction, is diluted with water,
the organic layer is separated, washed with water, and
dried, and the target 5,5-dimetoxytetrachlorocyclopenta-
1
3
parent plate-like crystals. Studies by C NMR spectro-
scopy and mass spectrometry showed that this compound
is (2Z)-2,3,4,5,5-pentachloropenta-2,4-dienic acid (3).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1940—1943, October, 2019.
066-5285/19/6810-1940 © 2019 Springer Science+Business Media, Inc.
1

(
2Z)-2,3,4,5,5-Pentachloropenta-2,4-dienic acid Russ. Chem. Bull., Int. Ed., Vol. 68, No. 10, October, 2019
Table 1. Bond lengths (d) in structure 3
1941
The formation of compound 3 in this reaction was not
previously reported.
Bond
d/Å
Bond
d/Å
Cl(01)–C(007) 1.710(3) C(007)–C(008) 1.487(4)
Cl(02)–C(010) 1.714(4) C(007)–C(011) 1.327(5)
Cl(03)–C(011) 1.714(4) C(008)–O(012) 1.231(4)
Cl(04)–C(009) 1.720(4) C(009)–C(010) 1.275(5)
Cl(05)–C(010) 1.708(4) C(009)–C(011) 1.499(5)
Scheme 1
O(06)–C(008)
1.267(4)
perpendicular to each other, as evidenced by the dihe-
dral angle of 92.2(5). The dichlorobutene moiety has
a Z configuration.
The O(06)—C(008)—C(007)—C(011) torsion angle is
71.3(4), which indicates that the carboxy group deviates
1
from the plane of the dichlorobutene moiety. The C—Cl
bond lengths (Table 1) are in agreement with the corre-
9
Crystalline acid 3 melts in the range of 119.5—121 C.
sponding values in perchloroacrylic acid. Compound 3
Literature sources give different melting points for com-
crystallizes in the centrosymmetric monoclinic space group
4
5
6,7
pound 3: 124.5—125 C, 123 C, 121—123 C, and
Р2 /c. In the crystal structure, molecules 3 are linked
1
8
…
1
20—121 C. Since the formation of both compounds 3
to form cyclic dimers via O—H O hydrogen bonds
2
2
…
and 4 with  -cis- and  -trans-double bonds cannot
be ruled out, the structure of 3 was additionally con-
firmed by X-ray diffraction. The structure of 3 is displayed
in Fig. 1.
(dH(06)…O(012) = 1.81(7) Å, the O(06)—H(06) O(012)
angle is 179.0(8)) (see Fig. 1, b). In the crystal of 3,
…
there are also short intermolecular Cl Cl contacts
(dCl(02)…Cl(02) = 3.498(2) Å, dCl(02)…Cl(03) = 3.432(2) Å,
and dCl(02)…Cl(05) = 3.498(2) Å).
Let us consider the plausible mechanism of the forma-
tion of acid 3. The attack of the complex of MеOH with
The X-ray diffraction study demonstrated that the
planes of the dichlorobutene and trichloropropene moieties
in pentachloropenta-2,4-dienic acid 3 (see Fig. 1) are
c
a
a
0
b
Cl(01)
H(06)
O(012)
Cl(02)
Cl(02)
b
Cl(03)
O(06)
С(007)
Cl(03)
С(011)
Cl(02)
Cl(02)
Cl(02)
H(06)
Cl(03)
С(008)
Cl(03)
Cl(03)
Cl(02)
С(009)
С(010)
O(012)
Cl(04)
Cl(05)
Fig. 1. (a) Molecular structure of compound 3 with displacement ellipsoids for nonhydrogen atoms at the 50% probability level.
b) The crystal structure projected along the c axis; O–H…O hydrogen bonds and short Cl…Cl contacts are indicated.
Note. Figure 1 is available in full color on the web page of the journal (https://link.springer.com/journal/volumesAndIssues/11172).
(

1942 Russ. Chem. Bull., Int. Ed., Vol. 68, No. 10, October, 2019
Egorov et al.
Scheme 2
KOH on the C(1)=C(2) double bond of diene 2 affords
intermediate A (Scheme 2). The nucleophilic substitution
of the Cl atom at C(1) with the OH group in the presence
of KOH gives hemiketal B. The labile hydroxyl group in
B is easily deprotonated under the reaction condition to
generate tetrahedral intermediate C. The latter eliminates
KH, which is then hydrolyzed, resulting in hydrogen re-
lease. The saponification of the ester affords potassium
salt of acid 3. The acidification of the latter gives acid 3.
To conclude, we showed that the reaction of diene 2
with a KOH solution in methanol affords, apart from
compound 1, acid 3 with the Z-double bond as the minor
product. The structure of acid 3 was confirmed by X-ray
diffraction. The scatter in the melting point values reported
in the literature is apparently attributed to the fact that,
in some cases, the reaction produces 2Е-acid 4 because
the conditions of the synthesis of 3 by the chlorination
KOH (29.8 g, 0.2 mol) in anhydrous methanol (300 mL), the
temperature being maintained below 50 C. The reaction mixture
was stirred at room temperature for 12 h. The KCl precipitate
Table 2. Crystallographic parameters and the X-ray data
collection and refinement statistics for compound 3
Parameter
Value
C HCl O
2
Molecular formula
Molecular weight
Crystal system
Space group
Unit cell parameters
а/Å
5
5
270.31
Monoclinic
P2 /c
1
12.0274(5)
6.6445(2)
12.2796(6);
90
101.828(4)
90
b/Å
c/Å
α/deg
β/deg
(
Cl , h) of the corresponding perchloropenta-3,4-dienic
2
γ/deg
6
,7
and perchloropenta-4-en-2-ynoic acids are responsible
for the formation of 4.
3
V/Å
960.50(7)
4
Z
dcalc/g cm–3
1.869
–
1
Experimental
Absorption coefficient, μ/mm
F(000)
1.463
528.0
2
θ–Scanning range/deg
3.46—57.98
–15  h  16,
The IR spectrum was recorded on a Shimadzu IR Prestige-21
h, k, l ranges
spectrophotometer using a film from a solution in CHCl . The
3
–
8  k  8,
1
13
H and C NMR spectra were measured on a Bruker
–
16  l  16
AVANCE-500 spectrometer operating at 500.13 and 125.77 MHz,
respectively, with SiMe4 as the internal standard. The mass
spectrum was obtained on a LCMS-2010EV mass spectrometer
Number of reflections
measured
11193
(0.0248)
2357
(
Rint)
(
Shimadzu). The melting point was determined on a Boetius
unique
hot-stage microscope (Germany). The course of the reaction was
monitored by TLC on Sorbfil plates (Russia); the compounds
were visualized by spraying with an alkaline solution of potas-
sium permanganate. The reaction products were isolated by
column chromatography on Macherey-Nagel silica gel (Germany,
Number of reflections
used in the refinement
2357
113
Number of refined parameters
GOOF
Final values of
R1
wR2
1.045
7
0—230 mesh.; 30—60 g of the adsorbent per gram of the
0.0528
0.1123
compound).
(
2Z,4E)-2,3,4,5,5-Pentachloropenta-2,4-dienic acid (3).
Residual electron density
A solution of hexachlorocyclopentadiene (54.6 g, 0.2 mol) in
methanol (200 mL) was added dropwise to a stirred solution of
–
3
(
max/min)/e Å
–0.50/0.94

(
2Z)-2,3,4,5,5-Pentachloropenta-2,4-dienic acid Russ. Chem. Bull., Int. Ed., Vol. 68, No. 10, October, 2019
1943
was filtered off, the filtrate was diluted with water (150 mL),
methanol was evaporated, and the residue was extracted
with chloroform (470 mL). Then the residue was concent-
rated followed by vacuum distillation. The known 5,5-dimet-
oxytetrachlorocyclopentadiene4 was isolated in a yield of
Structures for Optoelectronics"). All physicochemical
studies were carried out using facilities of the Center for
Collective Use "Chemistry" of the Ufa Institute of Chemistry,
Ufa Federal Research Center, Russian Academy of Sciences,
and the Regional Center for Collective Use of Unique
Equipment "Agidel" of the Institute of Petrochemistry and
Catalysis, Ufa Federal Research Center, Russian Academy
of Sciences.
3
4.0 g (64%).
After the extraction, the aqueous layer was acidified with
concentrated hydrochloric acid to pH 2 and extracted with
chloroform (4½50 mL). The combined extracts were washed
with a saturated NaCl solution and dried with MgSO . The
4
solvent was evaporated under reduced pressure. The resulting
white powder was recrystallized from petroleum ether (40—70 C),
and acid 3 was isolated as colorless plates in a yield of 12.0 g
References
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1
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1
This study was performed within the framework of the
state assignment of the Ministry of Education and Science
of the Russian Federation (theme No. AAAA-A17-
Received May 22, 2019;
in revised form July 17, 2019;
accepted July 22, 2019
1
17011910032-4 "Targeted Synthesis of Natural and Non-
Natural Biologically Active Compounds, Design of New