Cu(OAc)2-2,4-lutidine-ZnCl2 as an effective catalyst of functionalization of isobutylene oligomers and 1,2-polybutadiene with methyl diazoacetate

Article abstract of DOI:10.1134/S1070427209070271

The possibility of [1+2]-cycloaddition of methoxycarbonylcarbene generated by catalytic decomposition of methyl diazoacetate in the presence of the Cu(OAc)₂-2,4-lutidine-ZnCl₂ system to the carbon-carbon double bound in isobutylene o

Full text of DOI:10.1134/S1070427209070271

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 7, pp. 1305−1309. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © V.F. Gareev, T.A. Yangirov, V.P. Volodina, R.M. Sultanova, R.Z. Biglova, V.A. Dokichev, 2009, published in Zhurnal Prikladnoi
Khimii, 2009, Vol. 82, No. 7, pp. 1209−1212.
MACROMOLECULAR COMPOUNDS
AND POLYMERIC MATERIALS
Cu(OAc)2–2,4-Lutidine–ZnCl2 as an Effective Catalyst
of Functionalization of Isobutylene Oligomers
and 1,2-Polybutadiene with Methyl Diazoacetate
V. F. Gareev, T. A. Yangirov, V. P. Volodina, R. M. Sultanova, R. Z. Biglova, and V. A. Dokichev
Institute of Organic Chemistry, Ufa Scientific Center, Russian Academy of Sciences, Ufa, Bashkortostan, Russia
Bashkir State University, State Educational Institution of Higher Professional Education, Ufa, Bashkortostan, Russia
Received April 20, 2009
Abstract—The possibility of [1+2]-cycloaddition of methoxycarbonylcarbene generated by catalytic
decomposition of methyl diazoacetate in the presence of the Cu(OAc)2–2,4-lutidine–ZnCl2 system to the
carbon–carbon double bound in isobutylene oligomers and syndiotactic 1,2-polybutadiene was examined.
A comparative analysis of physicochemical properties of the starting compounds and their functionalized
products was performed.
DOI: 10.1134/S1070427209070271
however, is very complex, and chemical modification of
a macromolecular compound is preferable.
One of important lines in the development of
macromolecular chemistry is chemical modification of
polymers, allowing the physical and chemical properties
of products to be varied in a wide range.Addition reactions
as a functionalization route occupy a particular place in
the chemistry of diene polymers because of high activity
of the C=C bond in the macromolecule unit [1].
This paper deals with the reaction of syndiotactic
1,2-polybutadiene and of isobutylene oligomers
with methyl diazoacetate in the presence of the
catalytic system Cu(OAc)2–2,4-lutidine–ZnCl2 and with
comparative analysis of the properties of the starting
compounds (isobutylene oligomers and syndiotactic
1,2-polybutadiene) and their functionalized derivatives.
Syndiotactic 1,2-polybutadiene and isobutylene
oligomers are convenient unsaturated substrates for
chemical modification. The presence of reactive double
bonds in pendant substituents in syndiotactic 1,2-
polybutadiene and of terminal or trisubstituted C=C
bonds in oligoisobutylene allows introduction of various
chemical groups and preparation of products with new
properties on the basis of these polymers. Substances of
diverse classes, e.g., epoxides and aromatic amines, can
be used as addition reagents [2].
EXPERIMENTAL
1
The H and 13C NMR spectra were recorded
on a Bruker AM-300 spectrometer (300.13 and 75.47
MHz, respectively) in CDCl3, and the IR spectra, on
a Shimadzu IR-Prestige-21 Fourier spectrometer, with
samples prepared as liquid films. In our study we
used Cu(OAc)2 (Vekton), anhydrous ZnCl2 (Reaktiv),
isobutylene oligomers I (n = 7, Mn ≈ 504, nD20 = 1.4671)
and II (n = 10, Mn ≈ 700, n 20 = 1.4701), and syndiotactic
1,2-polybutadiene (III) (EfDremov Synthetic Rubber Plant,
Joint-Stock Company; Mn = 52600, Mw = 116600, degree
of crystallinity 18%, syndiotacticity 53%). The solvents
used in this study (Et2O, CH2Cl2, C6H14, (CH3)2CO,
petroleum ether, EtOH, CHCl3) and 2,4-lutidine were
purified by standard procedures [5, 6].
Of particular interest are polymers containing along
with unsaturated bonds cyclopropane rings. To such
polymers belong polycyclopropane derivatives of fatty
acids isolated form Streptoverticillium fervens and
Streptomyces [3].
A cyclopropane fragment can be introduced into
a macromolecule by cyclocopolyisomerization
of 1,3-butadiene and ethylene [4]. This procedure,
1305

1306
GAREEV et al.
Isobutylene oligomers I and II were purified by
H 13.07, 12.98; O 4.15, 4.21. C51H100O2. Calculated,
%: C 82.26; H 13.44; O 4.30. H NMR spectrum, δ,
1
reprecipitation in the hexane–acetone system. The solvent
was removed under reduced pressure. Oligomers I and II
were analyzed by 13C NMR and IR spectroscopy.
ppm: 0.94, 0.96 both s (6H, 2Me) 1.06 m (1H, CH in
cyclopropane ring); 1.25, 1.32 both s (6H, 2Me); 1.41 s
(2H, CH2); 1.50, 1.52 both s (6H, 2Me); 1.87 m (1H,
CHCO2Me, in cyclopropane ring); 3.67 s (3H, OMe).
13C NMR spectrum, δC, ppm: 12.2, 17.4 (2CH); 27.3
(Me); 29.4 (Me); 29.7 (CH2); 31.4 (CH); 32.9 (C); 51.3
(OMe); 167.3 (C=O). IR spectrum, ν, cm–1: 550, 1101 and
1177 (C–O); 1242, 1291 (OMe), 1364, 1377, 1452 (CH
in cyclopropane ring); 1734 (C=O); 2868, 2930.
Syndiotactic 1,2-polybutadiene was purified to remove
the stabilizer by reprecipitation from chloroform–ethanol.
Then the polymer was washed twice with alcohol and
vacuum-dried at 60°C to constant weight.
Syndiotactic 1,2-polybutadiene III, n = 974. Found,
%: 88.52, 88.47; H 11.42, 11.45.Calculated, %: C 88.87,
1
H 11.13. H NMR spectrum, δ, ppm: 1.17 m (2H);
The reaction of syndiotactic 1,2-polybutadiene with
methyl diazoacetate in the presence of the catalytic
system Cu(OAc)2–2,4-lutidine–ZnCl2 was performed
by slow addition of 37 mmol (1 : 1, counting on
monomeric unit of the polymer chain) of methyl
diazoacetate in 10 ml of CH2Cl2 to a stirred solution
containing 0.06 mmol of anhydrous ZnCl2, 0.32 mmol
of 2,4-lutidine, 0.037 mmol of Cu(OAc)2, and 37 mmol
of syndiotactic 1,2-polybutadiene III in 50 ml of
CH2Cl2 until the gas evolution ceased. Then the solvent
was removed under reduced pressure, petroleum ether
was added to the residue, and the catalytic system was
separated in the form of a dark brown oil. The petroleum
ether was evaporated under reduced pressure, and the
product was purified by double reprecipitation in the
chloroform–ethanol system, followed by vacuum drying
at 60°C to constant weight.
2.09 m (1H); 4.85, 4.95 m (2H, CH2=); 5.34 m (1H,
CH=). 13C NMR spectrum, δC, ppm: 39.0 (CH), 41.4
(CH2), 114.7 (CH2=), 143.2 (CH=). IR spectrum, ν,
cm–1: 376, 669, 908, 993 (=CH); 1074, 1151, 1377, 1417
(=CH2); 1456, 1639 (C=C); 2853, 2922, 2951.
The reaction of isobutylene oligomers with methyl
diazoacetate in the presence of the catalytic system
Cu(OAc)2–2,4-lutidine–ZnCl2 was performed by
slow addition of 4 mmol of methyl diazoacetate
in 7 ml of CH2Cl2 at 40°C to a stirred solution
containing 0.005 mol of anhydrous ZnCl2, 0.03 mmol
of 2,4-lutidine, 0.04 mmol of Cu(OAc)2, and 4 mmol of
isobutylene oligomer I or II in 17 ml of CH2Cl2 until
the gas evolution ceased. Then the solvent was removed
under reduced pressure, petroleum ether was added to
the residue, and the catalytic system was separated
as a dark brown oil. The petroleum ether was removed
under reduced pressure, and the residue was analyzed
by 1H and 13C NMR and IR spectroscopy. The yields of
Functionalized syndiotactic 1,2-polybutadiene
VI. Yield 20%. Found, %: C 80.34, 80.32; H 10.36,
1
1
IV and V were determined from the H NMR spectra
10.37; O 7.94, 7.98. H NMR spectrum, δ, ppm: 0.58
using benzene as internal reference.
(E isomer), 0.60 m (Z isomer, 1H, CH2 in cyclopropane
ring); 0.95 m (Z isomer), 1.02 m (E isomer) (1H, CH2
in cyclopropane ring); 1.16 m (1H, CH); 1.57 m (1H,
CH in cyclopropane ring); 3.65 s (3H, OMe). 13C NMR
spectrum, δC, ppm: 14.1 (Z isomer), 14.2 (E isomer)
(CH2); 25.4 (Z isomer), 25.5 (E isomer) (CH); 27.6 (Z
isomer), 27.9 (E isomer) (CH); 39.1 (CH2); 41.7 (CH);
51.3 (OMe); 174.2 (C=O). IR spectrum, ν, cm–1: 669,
758, 908, 994 (=CH); 1084, 1168, 1263 (OMe); 1342,
1417 (=CH2); 1448 (CH in cyclopropane ring); 1639
(C=C); 1752 (S=O); 2843, 2916, 2970, 3072 (CH2 in
cyclopropane ring).
Functionalized isobutylene oligomer IV, n = 7,
nD20 = 1.4583. Yield 32%. Found, %: С 81.32, 81.36,
H 13.44, 13.08; O 5.54, 5.56. C39H76O2. Calculated,
%: C 81.25; H 13.19; O 5.56.1H NMR spectrum, δ,
ppm: 0.94, 0.96 both s (6H, 2Me); 1.11 m (1H, CH in
cyclopropane ring); 1.34, 1.35 both s (6H, 2Me); 1.43 s
(2H, CH2); 1.52, 1.54 both s (6H, 2Me); 1.88 m (1H,
CHCO2Me, in cyclopropane ring); 3.68 s (3H, OMe).
13C NMR spectrum, δC ppm: 12.0, 17.4 (2CH); 27.3 (Me);
,
29.4 (Me); 29.7 (CH2); 31.5 (CH); 33.0 (C); 51.3 (OMe);
167.1 (C=O). IR spectrum, ν, cm–1: 546, 1095 and 1169
(C–O); 1242, 1278 (OMe); 1364, 1375, 1433, 1454 (CH
of cyclopropane ring); 1732 (C=O), 1748, 2868, 2954.
Thermal gravimetric analysis (TGA) of the initial and
modified syndiotactic 1,2-polybutadiene was performed
with a Q-1000 derivatograph (MOM, Hungary) in air
at a heating rate of 5 deg min–1. As the temperature of
Functionalized isobutylene oligomer V, n = 10,
nD20 = 1.4689. Yield 19%. Found, %: С 82.78, 82.84,
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 82 No. 7 2009

Cu(OAc)2–2,4-LUTIDINE–ZnCl2 AS AN EFFECTIVE CATALYST
1307
decomposition onset we took the temperature at which
the sample undergoes 1 wt % weight loss.
It should be noted that the catalytic system Cu(OAc)2–
2,4-lutidine–ZnCl2 shows the activity similar to that in
the reaction of terminal monoolefins (1-hexene) and
1,3-dienes with methyl diazoacetate. With an increase
in the length of the carbon chain, the yield of the target
esters decreases [8].
The solution viscosities were measured at 25°C
in an Ubbelohde-type suspended-level capillary
viscometer. We measured the outflow time for polymer
and oligomer solutions of various concentrations in
chloroform. From the experimentally determined
concentrations of the solvent and polymer solutions,
we calculated the relative (ηrel = τ/τ0) and specific (ηsp
= ηrel – 1) viscosities. The intrinsic viscosity was found
by double extrapolation of the ln ηrel/c and ηsp/c values
to zero concentration.
The 13C NMR spectra confirm the presence of
a cyclopropane fragment in compounds IV and V. The
characteristic signals of carbon atoms of the cyclo-
propane ring are manifested in the range of δC 12–
17 ppm. The signal of the quaternary carbon atom of the
ester group is observed at 169–171 ppm. In the IR spectra
of products IV and V, as compared to those of the initial
oligomers, the following bands appear (cm–1): C=O
stretching (1732–1747), C–O stretching (1170–1177),
and C–H bending of the ring and OMe group. The
authenticity of structures IV and V was confirmed by
determining their molecular weights from the measured
thermal effects of condensation (MTEC method). It was
shown that the Mn values for the compounds modified
with methoxycarbonylcarbene and starting compounds
differ by 72 units.
The quantity Ms[η] for the samples under consideration
was found by the formula
Ms[η] = {S0η0[η]1/3NA/Φ1/3p−1(1 − vρ0)}3/2,
where S0 is the sedimentation constant; η0, solution
viscosity (P); [η], intrinsic viscosity (dl g–1); NA,
Avogadro number (6 × 1023 mol–1); Ф1/3p–1 = 2.5 × 106;
1 – νρ0,Archimedean factor (buoyancy factor); v, specific
partial volume; and ρ0, solvent density.
The initial isobutylene oligomers and functionalized
products IV and V are readily soluble in many organic
solvents (benzene, hexane, chloroform, diethyl ether).
The intrinsic viscosities of oligomers I and II and of
compounds IV and V in chloroform (dl g–1) differ
insignificantly ([η] = 0.0171 for IV, [η] = 0.0165 for
starting isobutylene oligomer I; [η] = 0.021 for product
V, [η] = 0.019 for starting oligomer II). The calculated
Huggins constants for the participants of both processes
exceed 103, suggesting weak thermodynamic affinity of
both the starting oligomers and their reaction products for
chloroform. The Kh values for IV and V are lower than
those for oligomers I and II.
The sedimentation coefficients Sc were determined
with an MOM-3180 ultracentrifuge at a rotor rotation
frequency of 50000 rpm, 25°C, in the interval of polymer
solution concentrations of 0.1–0.5 g dl–1.
Previously we developed a new effective catalytic
system Cu(OAc)2–2,4-lutidine–ZnCl2 allowing products
of reactions of low-molecular-weight unsaturated
compounds with methyl diazoacetate to be prepared
selectively in a high yield [7].
Isobutylene oligomers Iand II containing trisubstituted
C=C bond react with methyl diazoacetate in the presence
of the Cu(OAc)2–2,4-lutidine–ZnCl2 system to form the
corresponding methyl esters of cyclopropanecarboxylic
acid IV and V in 32 and 19% yield, respectively. Along
with esters IV and V, we isolated from the reaction
mixture dimethyl fumarate and dimethyl maleate formed
by recombination of methoxycarbonyl carbene (total
yield 20%):
With the aim of chemical modification of syndiotactic
1,2-polybutadiene (SPB) III, we performed its reaction
with methyl diazoacetate in the presence of the
catalytic system Cu(OAc)2–2,4-lutidine–ZnCl2. The
macromolecular compound VI functionalized with
cyclopropane fragments is formed in 20% yield:
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 82 No. 7 2009

1308
GAREEV et al.
Average molecular weights of III and VI
Δm, %
The presence of characteristic signals of the ester
1
group and cyclopropane ring in the H and 13C NMR
spectra and of the corresponding bands in the IR spectrum
of VI confirms incorporation of cyclopropane fragments
by carbene addition to the C=C bond. The NMR spectrum
also proves that cycloaddition of methoxycarbonylcarbene
to the C=C bond of SPB occurs periodically, to one of ten
vinyl C=C bonds on the average. The carbon atoms of
the cyclopropane ring give signals at 13, 25, and 28 ppm
in the 13C NMR spectrum of polymer VI. The fractions
of cis and trans isomers of functionalized units of VI are
approximately equal.
T, °C
TGA data for the starting (III) and functionalized (VI)
1,2-polybutadiene in air. (Δm) Weight loss and (T) tempera-
ture.
the case of the modified 1,2-polybutadiene is two times
lower as compared to the initial samples, and in the range
400–500°C (second step of degradation) the burn-out
of both polymers occurs at an approximately equal rate
(see figure).
A study of the solubility of the initial 1,2-SPB III
and modified polymer VI showed that the product of
cyclopropanation with methyl diazoacetate dissolves
better in chloroform, hexane, and toluene. Comparison of
the intrinsic viscosities of the starting and functionalized
polymers ([η] = 1.72 and 2.38 dl g–1, respectively)
allowed determination of the Huggins constant Kh for
both macromolecular compounds. The Kh value for
functionalized 1,2-SPB VI (Kh = 0.43) is lower than that
for the starting polybutadiene (Kh = 0.59). The value lower
than 0.5 indicates that chloroform is a good solvent for
cyclopropanated product VI [9].
CONCLUSIONS
(1) The Cu(OAc)2–2,4-lutidine–ZnCl2 system
efficiently catalyzes modification with methyl diazoacetate
of the C=C bonds both in isobutylene oligomers and in
syndiotactic 1,2-polybutadiene.
(2) Chloroform is a good solvent for syndio-
tactic 1,2-polybutadiene functionalized with
methoxycarbonylcarbene. An increase in the intrinsic
viscosity of the modified syndiotactic 1,2-polybutadiene
is accompanied by a decrease in the viscometric Huggins
constant.
The average molecular weights Ms[η] of the initial
and functionalized syndiotactic 1,2-polybutadiene
were determined using viscometric and sedimentation
methods.ThesedimentationconstantsS0 weredetermined
by extrapolation of 1/Sc to zero concentration. The
results of determining the average molecular weights
Ms[η] of the initial and functionalized SPB are given in
the table.
(3) Functionalization of syndiotactic 1,2-polybutadiene
with cyclopropane fragments enhances its heat
resistance.
REFERENCES
From the results of calculating Ms[η], we determined
the numbers of elementary units n and k, which for
product VI were equal to 685 and 103, respectively.
1. Kayumova, M.A., Kukovinets, O.S., Sigaeva, N.N., et al.,
Vysokomol. Soedin., Ser. B, 2008, vol. 50, no. 8, pp. 1546–
1552.
According to TGA data, the temperature at which
modified 1,2-polybutadiene VI starts to degrade is 50°C
higher as compared to III. Degradation of both samples
occurs in two steps. The weight loss corresponding to the
first step of the degradation (in the range 250–400°C) in
2. Gainullina, T.V., Kayumova, M.A., Kukovinets, O.S., et al.,
Vysokomol. Soedin., Ser. A, 2005, vol. 47, no. 9, pp. 1739–
1741.
3. Barrett, A., Kasdorf, K., and Williams, D., J. Chem. Soc.,
Chem. Commun., 1994, pp. 1781–1782.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 82 No. 7 2009

Cu(OAc)2–2,4-LUTIDINE–ZnCl2 AS AN EFFECTIVE CATALYST
1309
4. Pragliola, S., Milano, G., Guerra, G., and Longo, P., J. Am. Bashkirsk. Gos. Univ., 2008, vol. 13, no. 4, pp. 886–890.
Chem. Soc., 2002, vol. 124, no. 14, pp. 3502–3503.
8. Gareev, V.F., Sultanova, R.M., Biglova, R.Z., et al., Izv. Ross.
Akad. Nauk, Ser. Khim., 2008, no. 8, pp. 1750–1752.
5. Organikum. Organisch-chemische Grundpraktikum, Becker,
G. et al., Eds., Berlin: Wissenschaften, 1976.
9. Rafikov, S.R., Budtov, V.P., and Monakov, Yu.B., Vvedenie
v fiziko-khimiyu rastvorov polimerov (Introduction to
Physical Chemistry of Polymer Solutions), Moscow:
Nauka, 1978.
6. Reagents for Organic Synthesis, Fieser, L.F. and Fieser, M.,
Eds., New York: Wiley–Interscience, 1967–1979, vol. 5.
7. Gareev, V.F., Yangirov, T.A., Bakeeva, A.D., et al., Vestn.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 82 No. 7 2009