Oxidative carbonylation of methanol to dimethyl carbonate by chlorine-free homogeneous and immobilized 2,2′-bipyrimidine modified copper catalyst

Article abstract of DOI:10.1135/cccc20071094

A chlorine-free catalyst, prepared in situ from Cu(II) acetate and 2,2′-bipyrimidine, can be used for the oxidative carbonylation of methanol to dimethyl carbonate. In situ high pressure IR and NMR spectroscopic studies suggest the formation of [Cu(2,2′-bipyrimidine)(CO)(OMe)] as one of the key intermediates. The catalytic performance of the 2,2′-bipyrimidine- modified Cu-catalyst is similar to the CuCl-based system. The chlorine free catalyst can be immobilized by using the copolymer of 5-vinyl-2,2′- bipyrimidine and styrene.

Full text of DOI:10.1135/cccc20071094

1
094
Csihony, Mika, Vlád, Barta, Mehnert, Horváth:
OXIDATIVE CARBONYLATION OF METHANOL TO DIMETHYL
CARBONATE BY CHLORINE-FREE HOMOGENEOUS AND
IMMOBILIZED 2,2′-BIPYRIMIDINE MODIFIED COPPER CATALYST
a1
a2
a3
a4
Szilárd CSIHONY , László T. MIKA , Gábor VLÁD , Katalin BARTA ,
b
a5,
Christian P. MEHNERT and István T. HORVÁTH
*
a
Institute of Chemistry, Eötvös University, Pázmány Péter sétány 1/A H-1117, Budapest, Hungary;
e-mail: szcsihony@yahoo.com, laszlo.t.mika@hotmail.com, vladgabor@yahoo.com,
barta@itmc.rwth-aachen.de, istvan.t.horvath@att.net
Corporate Strategic Research, ExxonMobil Research and Engineering Company,
1
2
3
4
5
b
Route 22 East, Annandale, 08801 New Jersey, U.S.A.; e-mail: mehnert.christian@adlittle.com
Received May 19, 2007
Accepted Jun e 15, 2007
This paper is dedicated to Professor Štefan Toma on the occasion of his 70th birthday.
A ch lorin e-free catalyst, prepared in situ from Cu(II) acetate an d 2,2′-bipyrim idin e, can be
used for th e oxidative carbon ylation of m eth an ol to dim eth yl carbon ate. In situ h igh pres-
sure IR an d NMR spectroscopic studies suggest th e form ation of [Cu(2,2′-bipyrim idin e)(CO)-
(
OMe)] as on e of th e key in term ediates. Th e catalytic perform an ce of th e 2,2′-bipyrim idin e-
m odified Cu-catalyst is sim ilar to th e CuCl-based system . Th e ch lorin e free catalyst can be
im m obilized by usin g th e copolym er of 5-vin yl-2,2′-bipyrim idin e an d styren e.
Keyw ord s: Hom ogen eous catalysis; Oxidative carbon ylation ; Meth an ol; Dim eth yl carbon ate;
Copper; 2,2′-Bipyrim idin e; Im m obilized catalysts.
Dim eth yl carbon ate (DMC) is a safe, n on -corrosive, an d en viron m en tally
frien dly altern ative to th e carbon ylatin g, carboxym eth ylatin g an d m eth yl-
atin g agen ts ph osgen e, m etoxycarbon yl ch loride, dim eth yl sulfate, an d
m eth yl h alides, respectively1 . DMC can also be used as solven t, octan e
,2
booster in gasolin e, an d oxygen ate to reduce CO an d NO em ission s from
x
autom obiles. Th e con ven tion al DMC process is based on th e reaction of
3
m eth an ol with th e h igh ly toxic ph osgen e usin g ch lorin ated solven t .
Th e first altern ative process was based on th e oxidative carbon ylation of
4
m eth an ol in th e presen ce of CuCl at 2–3 MPa an d 100–130 °C . Alth ough
th e exact m ech an ism of th e process h as n ot been establish ed, it h as been
proposed, th at th e reaction of CuCl, m eth an ol an d oxygen leads to th e for-
m ation of th e key in term ediate Cu(OMe)Cl, wh ich reacts with CO to yield
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 8, pp. 1094–1106
©
2007 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc20071094

Oxidative Carbonylation of Methanol
1095
DMC an d CuCl (Sch em e 1). Due to th e form ation of wet HCl by th e h ydro-
lysis of ch loride con tain in g copper species, th e process is extrem ely corro-
sive an d all com m ercial equipm en t, exposed to th e CuCl–MeOH–H O–HCl
2
m ixture, m ust be glass lin ed. In addition , th e form ation of ch lorin ated
organ ic side-products could be an en viron m en tal issue for subsequen t, pre-
sum ably green application s of DMC.
SCHEME 1
Oxidative carbon ylation of m eth an ol
An altern ative n on -corrosive process was publish ed by En iCh em usin g
cobalt catalysts with oxygen an d n itrogen don or ligan ds such as carboxyl-
5
ates, acetylaceton ates, picolin ates, an d Sch iff bases . Th e perform an ce of
th e Sch iff base-m odified cobalt(II) com plexes was th e best; th e con version
of m eth an ol was in th e ran ge of 10–30% with 96–99% selectivity to DMC.
6
a–6c
6d
Palladium
an d selen ium
based system s h ave been also reported for
liquid ph ase oxidative carbon ylation of m eth an ol to DMC. An altern ative
approach is th e con version of carbon dioxide an d m eth an ol to DMC, al-
th ough th e by-product water could lower th e catalytic activity by th e de-
com position of th e organ otin catalysts7
a,7b
. It sh ould be n oted th at
7
c
supercritical carbon dioxide can be also used as th e reaction m edium for
DMC syn th esis from acetals . Fin ally, h eterogen eous copper-based cata-
7
d
7
e,7f
7g
lysts
an d zeolites h ave been used succesfully for th e oxidative carb-
on ylation of m eth an ol.
We report h ere th e developm en t of a ch lorin e-free h om ogen eous cata-
lytic system based on Cu(II) acetate an d 2,2′-bipyrim idin e an d its h etero-
gen ized version usin g th e co-polym er of 5-vin yl-2,2′-bipyrim idin e an d
styren e.
EXPERIMENTAL
CuCl, Cu(II) acetate, coum alic acid, piperidin e, 2-ch loropyrim idin e, an d AIBN were pur-
ch ased from Aldrich Ch em ical an d used as received. 2,2′-Bipyrim idin e was syn th esized
8
accordin g to literature m eth od . Carbon m on oxide (purity > 99.9%, Lin de AG.) an d air
(
purity > 99.9%, Lin de AG.) were used with out furth er purification . Oth er ch em icals an d
solven ts were obtain ed from Rean al Ch em ical Co., Hun gary. All h igh -pressure NMR experi-
m en ts were perform ed in 10-m m sin gle crystal sapph ire tube equipped with a titan ium
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 8, pp. 1094–1106

1
096
Csihony, Mika, Vlád, Barta, Mehnert, Horváth:
h ead9 usin g a 250 MHz Bruker NMR in strum en t. Ch em ical sh ifts are given in ppm (δ-scale).
In frared spectra were collected on a Mettler-Toledo AutoCh em ReactIR™ 1000 in strum en t
usin g a SiCom p™ h igh -pressure probe. High -pressure experim en ts were con ducted in stain -
less steel reactors (100, 300 an d 1000 m l). Th e reaction products were an alyzed by GC usin g
a capillary HP-1 colum n with H2 as carrier gas on a HP 5890 Seies II gas ch rom atograph
equipped with a flam e ion ization detector usin g cycloh exan e or aceton e as th e in tern al
stan dard.
2
-Oxo-2H-pyran -5-carbon yl Ch loride (2)
1
2.5 g (90 m m ol) of 2-oxo-2H-pyran -5-carboxylic acid (1) an d 25 m l (344.5 m m ol) of SOCl2
were placed in a two-n ecked flask fitted with a reflux con den ser, a N2 in let, an d a m agn etic
stirrer. Th e reaction m ixture was h eated to 100 °C for 8 h , durin g wh ich th e brown solution
turn ed to a reddish -brown solid. Th e precipitate was dissolved in a m ixture of 50 m l CH Cl
2
2
an d 200 m l of n-h exan e an d crystallized to give an off-wh ite solid. Yield 84%. M.p. 68–70 °C.
1
13
H NMR (250 MHz, CDCl ): 6.38 d, 1 H; 7.56 d, 1 H; 8.6 s, 1 H. C NMR (250 MHz,
3
CDCl ): 162.8, 162.7, 158.1, 140.2, 116.5, 115.3.
3
2
-Oxo-2H-pyran -5-carbaldeh yde (3)
6
3
.152 g (38.8 m m ol) of 2-oxo-2H-pyran -5-carbon yl ch loride (2) was added to a m ixture of
0 m l xylen e an d 0.3 g of Pd/BaSO4 (10%) as th e catalyst in a roun d-bottom ed flask
equipped with reflux con den ser an d gas in let. Th e reaction m ixture was stirred at 110 °C
an d h ydrogen was slowly bubbled th rough for 12 h . After th e rem oval of th e catalyst at th e
reaction tem perature by filtration un der N , 6 m l of n-h exan e were added. Th e solution was
2
kept in a refrigerator overn igh t to get wh ite crystals. It sh ould be n oted th at th e product
1
becom es yellow in air at room tem perature. Yield 41.5%. H NMR (250 MHz, CDCl ): 9.7 s,
3
1
3
1
1
H; 8.8 dd, 1 H; 7.8 dd, 1 H; 6.4 d, 1 H. C NMR (250 MHz, CDCl ): 185.0, 162.6, 159.2,
3
38.1, 119.7, 116.5.
Pyrim idin e-2-carbon itrile (7)
Th e preparation of 7 was don e in two steps. 6.94 g (61 m m ol) of 2-ch loropyrim idin e (5) was
dissolved in a m ixture of 120 m l ben zen e an d 0.27 m ol of Me N at 0 °C to form N,N,N-tri-
3
m eth ylpyrim idin -2-am in ium ch loride. Th e solution was allowed to warm slowly to room
tem perature an d stirred overn igh t. Th e precipitate was filtered un der in ert atm osph ere an d
wash ed with dried dieth yl eth er. 6 was dried un der vacuum . Yield 4.55 g (91%). 60 m l of
CH Cl an d 5.6 g (35.88 m m ol) of tetraeth ylam m on ium cyan ide were placed in a roun d-
2
2
bottom ed flask with a m agn etic stirrer. 5.66 g (32.62 m m ol) of 6 was slowly added to th e
m ixture, stirred at room tem perature for 30 m in , an d wash ed with ice-water (3 × 60 m l).
Th e organ ic ph ase was dried with an h ydrous MgSO4 an d th e solven t was evaporated. 7 was
1
distilled at 100 °C at 0.5 m m Hg. Yield 93%. M.p. 39–41 °C. H NMR (250 MHz, CDCl ):
3
8
.8 d, 2 H; 7.5 t, 1 H. 13C NMR (250 MHz, CDCl ): 158.1, 145.3, 123.6, 115.6.
3
Pyrim idin e-2-carboxim idam ide Hydroch loride (9)
2
.6 g (25 m m ol) of 7 was added to 0.67 g (12.4 m m ol) of CH ONa in 45 m l of m eth an ol in
3
a roun d-bottom ed flask an d th e m ixture was stirred at room tem perature overn igh t. After
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 8, pp. 1094–1106

Oxidative Carbonylation of Methanol
1097
th e addition of 2 g (37.4 m m ol) NH Cl, th e reaction m ixture was stirred un til th e in organ ic
4
salt dissolved (3 h ). After filtration , th e m eth an ol was evaporated an d th e product wash ed
1
13
with dieth yl eth er. Yield 90%. H NMR (250 MHz, CDCl ): 9.2 d, 2 H; 7.8 t, 1 H. C NMR
3
(
250 MHz, CDCl ): 125.7, 159.2.7, 153.6, 161.
3
5
-Vin yl-2,2′-bipyrim idin e (10)
5
-Vin yl-2,2′-bipyrim idin e (10) was syn th esized by th e reaction of 3-piperidin o-2-vin yl-
propen al (4) (for syn th esis see Sch em e 2) an d pyrim idin e-2-carboxim idam ide h ydroch loride
9) by m odified literature m eth ods sh own in Sch em es 3 an d 4. 0.637 g (7.5 m m ol) of
(
piperidin e in 0.75 m l of aceton itrile was stirred with a solution of 0.93 g (7.5 m m ol) fresh ly
distilled 3 in 7.5 m l of aceton itrile at 0 °C for 5 m in . Th e form ation of 4 an d th e con com i-
tan t evolution of CO2 was com plete in 3 h , an d th e oran ge-yellow solution becam e red. Th e
solution of 4 was added to a 1.25 M m eth an olic solution of 9 (6 m l) an d stirred at 80 °C for
3
h . Th e solution was filtered at room tem perature an d th e solven t was rem oved in vacuo.
Th e crude product was purified by colum n ch rom atograph y on silica usin g CHCl ·MeOH
3
1
9:1 as eluen t. Th e first yellow fraction was sublim ed at 100 °C at pressure of 10 m m Hg.
1
3
Yield 42%. C NMR (250 MHz, CDCl ): 119.0 (C 1), 121.2 (C 2), 130 (C 3), 130.6 (C 4),
3
1
55.0 (C 5,6), 157.7 (C 7,8), 161.5 (C 9), 162.6 (C 10).
SCHEME 2
1
0,11
Syn th esis of 3-piperidin o-2-vin ylpropen al (4)
SCHEME 3
1
2,13
Syn th esis of pyrim idin e-2-carboxim idam ide h ydroch loride (9)
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 8, pp. 1094–1106

1
098
Csihony, Mika, Vlád, Barta, Mehnert, Horváth:
SCHEME 4
1
4
Syn th esis of 5-vin yl-2,2′-bipyrim idin e (10)
Preparation of Copper-Modified 5-Vin yl-2,2′-bipyrim idin e–Styren e Copolym er (Cu-VBS)
A m ixture of 0.184 g (1 m m ol) 5-vin yl-2,2′-bipyrim idin e an d 3.120 g (30 m m ol) styren e was
placed in to a Sch len k flask with 25 m g (0.155 m m ol, 0.5 m ole %) AIBN. Th e flask was de-
gassed five tim es an d sealed un der vacuo. Th e flask was placed in a 60 °C bath for 24 h . Th e
polym er form ed was dissolved in 130 m l toluen e an d m ixed with 0.2 g (1 m m ol) of
Cu(OOCCH ) ·H O in 20 m l of m eth an ol. Th e solven ts were evaporated, th e polym er was
3
2
2
dissolved in 20 m l of toluen e an d wash ed with water. Th e Cu-VBS was precipitated with
3
1
00 m l of m eth an ol to give 3.18 g (90%) of pale-blue solid. An alysis: 87.43% C, 7.03% H,
.48% N.
Gen eral Procedure for Oxidative Carbon ylation of Meth an ol in a Batch Reactor
CAUTION: The oxidative carbonylation experiments are extremely hazardous, must be ap-
proached with care, and a thorough safety assessment must be made.
A 1000-m l stain less steel autoclave equipped with a safety relief, m an om eter, tem perature
con troller (Parr 4842 PID), sam plin g lin e, an d direct h ollow sh aft stirrer was used. Th e auto-
clave was filled with m eth an ol an d th e catalyst com pon en ts, an d pressurized with CO. Th e
desired pressure was set with O , followed by h eatin g th e reaction m ixture to reaction tem -
2
perature. Th ese reaction s were carried out un der n on -isobaric con dition s, an d th e reaction
progress was followed by m easurin g th e pressure drop in th e autoclave. In all experim en ts
th e oxygen con cen tration was n ot h igh er th an 4%. Wh en th e pressure decreased to a con -
stan t value, th e reactor was refilled from an O2 cylin der.
Preparation of DMC with Copper Cu-VBS in a High -Pressure NMR Tube
0
.225 g of Cu-VBS was dissolved in 5 m l of toluen e an d placed in to a h igh -pressure NMR
tube. Th e solven t was rem oved in vacuo an d 1 m l of m eth an ol was added to th e pale-blue
solid. Th e tube was first pressurized with 5.5 MPa CO an d th en with O2 to give a total pres-
sure of 6.2 MPa. Th e tube was h eated at 100 °C. Th e color of th e solid ch an ged to brown .
After 1 h th e tube was cooled to room tem perature an d re-pressurized with 5.5 MPa CO an d
th en with O2 to give a total pressure of 6.0 MPa. Th e tube was h eated up to 100 °C. Th is
procedure was repeated th ree tim es (th us th e tube was totally re-pressurized five tim es). Af-
ter coolin g th e tube to room tem perature, th e pressure was released an d th e colorless liquid
was poured in to a vial. 10 wt.% of aceton e was added as in tern al stan dard. Th e reaction
m ixture was an alyzed by GC. Th e con cen tration of DMC was 0.028 m ol/l in th e reaction
m ixture (0.025 m m ol).
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 8, pp. 1094–1106

Oxidative Carbonylation of Methanol
1099
Gen eral Procedure for Oxidative Carbon ylation of Meth an ol in a Con tin uous Reactor
In a typical experim en t, th e con tin uous h igh -pressure autoclave was ch arged with th e cata-
lyst an d m eth an ol (Fig. 1). Th e m ixture was pressurized at room tem perature with CO/air
(
150/400 m l/m in ) to adjust th e desired pressure. Th e reactor was h eated to th e reaction tem -
perature an d th e flow rates were reduced to 15/40 m l/m in CO/air, respectively. Th e tem pera-
ture was con trolled by Parr 4842 PID con troller. Sam ples were collected for off-lin e GC
an alysis by takin g a sm all am oun t of sam ples with a dip-leg in to a sam ple h older, cooled
with dry ice.
RESULTS AND DISCUSSION
Th e oxidative carbon ylation of m eth an ol in th e presen ce of CuCl results in
th e form ation of DMC an d water. Un fortun ately, th e h ydrolysis of ch loride
con tain in g copper species leads to aqueous HCl, wh ich could cause sign ifi-
can t corrosion an d th e form ation of ch lorin ated organ ic by-products.
Th erefore, we h ave tried to overcom e th ese problem s by th e addition of
2
,2′-bipyrim idin e, wh ich h as successfully been used as a ligan d in h ot sulfu-
FIG. 1
Flowch art of th e con tin uous reactor. 1 Mass flow con troller, Brooks 5850 E; 2 safety relief,
Nupro SS-4C-1/3; 3 h igh -pressure con den ser; 4 MityMite, Grove S-91XV; 5 electron ic m odule,
Parr 4842; 6 electron ic h eater; 7 h igh -pressure reactor; 8 coolin g in ; 9 coolin g out; 10 gas
m ixer; T th erm ocouple; P1 an d P2 m an om eters
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 8, pp. 1094–1106

1
100
Csihony, Mika, Vlád, Barta, Mehnert, Horváth:
ric acid even at h igh tem peratures by Perian a15a, to rem ove th e by-product
HCl via proton ation of th e two n on -coordin atin g N atom s. It sh ould be
n oted th at th e ben eficial addition of various pyridin es an d bipyridin es h as
been dem on strated for th e stoich iom etric carbon ylation of Cu(OMe)Cl in
1
5b
MeOH
h ave n ext tested com bin ation s of Cu(OOCCH ) ·H O with pyridin e,
. In order to develop a n ovel ch lorin e-free catalyst system , we
3
2
2
2
,2′-bipyridin e, an d 2,2′-bipyrim idin e (Table I).
Sin ce th e total am oun t of oxygen in th e reactor is lim ited for safety rea-
son s, th e batch reactor h ad to be rech arged several tim es. Wh ile th e reac-
tion took place in th e presen ce of pyridin e, th e stability of th e catalyst was
lim ited as eviden ced by th e form ation of m etallic copper durin g th e reac-
tion . Furth erm ore, th e lower catalytic activity at h igh er Cu con cen tration s
in dicated th e form ation of polyn uclear copper com plexes. Th e catalyst sta-
bility was im proved by usin g biden tate N-h eterocyclic ligan ds, am on g
wh ich 2,2′-bipyrim idin e h as sh own h igh er catalytic activity th an th at of
2
,2′-bipyridin e. Th e best DMC production was ach ieved usin g th e 2,2′-bi-
pyrim idin e-Cu(OOCCH ) catalyst (Table I, run s 6 an d 7), wh ich could be
3
reused with out losin g catalytic activity (Table I, run 8), sim ilarly to th e ac-
5
tivity of Co-based system s . In order to evaluate an d com pare th e ch loride-
free an d CuCl-based catalysts, we h ave also studied th eir perform an ce in a
con tin uous reactor in wh ich volatile gases can be separated from m eth an ol,
DMC, water, an d th e catalysts (Fig. 1). Wh ile th e m axim um an d steady-
state con cen tration of DMC (~1.2 m ol/l at 100 °C, 2.5 MPa total pressure,
an d 15/40 m l/m in CO/air flow rates) was reach ed after 12 h usin g th e
2
,2′-bipyrim idin e m odified copper catalyst, it took about 22 h for th e
CuCl-based system an d it appeared th at th e reaction is equilibrium -lim ited
in both cases (Fig. 2).
In order to con firm th at th e oxidative carbon ylation of m eth an ol is equi-
librium -lim ited, we h ave m on itored th e reaction of 4.9 m m ol (0.415 m l)
CH OCOOCH , 4.9 m m ol (0.090 m l) D O, 24.6 m m ol (1.0 m l) CD OD
3
3
2
3
in th e presen ce of 0.060 m m ol Cu(OOCCH ) ·H O an d 0.060 m m ol bi-
3
2
2
pyrim idin e in a h igh -pressure NMR tube. Th e solution was first pressurized
with 3.0 MPa CO an d th en with O givin g a total pressure of 3.3 MPa. Th e
2
tube was h eated at 100 °C for 16 h , cooled to room tem perature, an d th e
pressure was released. In deed, 13C NMR h as sh own th e form ation of
CH OH from CH OCOOCH an d CD OCOOCD3 from CD OD, sim ulta-
3
3
3
3
3
1
6
n eously . It sh ould be em ph asized, th at th e form ation of DMC-d in th e
6
absen ce of Cu catalyst could n ot be detected.
We h ave also studied th e reaction m ech an ism usin g Cu(OOCCH ) ·H O
3
2
2
an d 2,2′-bipyrim idin e as th e catalyst in m eth an ol by in situ IR. A solution
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 8, pp. 1094–1106

Oxidative Carbonylation of Methanol
1101
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 8, pp. 1094–1106

1
102
Csihony, Mika, Vlád, Barta, Mehnert, Horváth:
FIG. 2
Form ation of DMC with Cu(OOCCH ) ·H O-2,2′-bipyrim idin e (᭹, 6.1 m m ol) an d CuCl (ꢀ, 6.1
3
2
2
m m ol) catalysts in 80 m l of MeOH (2.47 m ol) at 2.5 MPa total pressure an d 15/40 m l/m in
CO/air flow rates
0
0
.3500
.3000
A
0
0
.2500
.2000
4.5
3
.5
0
0
.1500
.1000
2
.5
1
.5
0
0
.0500
.0000
0
.5
Hours
2
000
1000
–
1
Wavenumbers, cm
FIG. 3
In situ IR spectra of the oxidative carbonylation of MeOH in the presence of 2,2′-bipyrim idine-
m odified Cu(II) acetate catalyst
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 8, pp. 1094–1106

Oxidative Carbonylation of Methanol
1103
of 1 m m ol Cu(OOCCH ) ·H O an d 1 m m ol 2,2′-bipyrim idin e in 10 m l of
3
2
2
m eth an ol was placed in a h igh -pressure reactor, ch arged with 6.0 MPa CO,
an d h eated to 100 °C resultin g in a total pressure of 7.3 MPa. Th e ch aracter-
istic IR ban ds of Cu(OOCCH ) an d free 2,2′-bipyrim idin e at 1626 an d
3
2
–
1
1
2
559 cm , respectively, h ave disappeared an d a n ew ban d appeared at
100 cm wh ich is probably due to th e form ation of [Cu(2,2′-bipyrim idin e)-
–
1
(
CO)(OMe)] (Fig. 3). Th e form ation of a sim ilar [CuCl(CO)L ] (L = H O) spe-
2 2
1
7
cies h as been reported , wh ich is stable on ly un der CO. Furth erm ore, th e
appearan ce of th e sam e ban d at 2100 cm –1 could be observed wh en
Cu(OMe) was used as th e catalyst precursors . Th e n ew species reach ed
1
8
2
a m axim um con cen tration after two h ours. Wh en th e reactor was ch arged
–
1
with O2 to give a total pressure of 7.3 MPa, th e peak at 2100 cm disap-
–
1
peared an d th e IR ban ds for DMC at 1749, 1455, an d 1285 cm started to
in crease reach in g a m axim um value after two h ours wh en all th e O2 was
con sum ed. Th e form ation of th e n ew species was also in vestigated by
h igh -pressure NMR. Wh en a solution of a regen erated Cu-2,2′-bipyrim idin e
catalyst (isolated from run 8 in Table I) in CD OD was ch arged with 4.0 MPa
3
1
3
CO, a broad peak was observed at 184.3 ppm , n ext to th e dissolved CO at
84.7 ppm , in dicatin g th e presen ce of a carbon yl group. Th e broaden in g of
1
th e n ew peak is probably due to th e exch an ge process with free CD OD.
3
Th us, we propose th e form ation of [Cu(2,2′-bipyrim idin e)(CO)(OMe)] as
th e key in term ediate.
Th e proposed reaction m ech an ism based on th e literature19,20 an d our
data is sh own on Sch em e 5. Sin ce a term in al carbon yl group con tain in g
in term ediate was observed startin g from both Cu(OOCCH ) ·H O an d
3
2
2
Cu(OCH ) , th e form ation of [Cu(2,2′-bipyrim idin e)(CO)(OMe)] was pro-
3
2
posed. Th e facile in sertion of CO in to th e copper–oxygen bon d followed by
th e coordin ation of m eth oxide or th e n ucleoph ilic attack of OCH on th e
3
coordin ated carbon yl group will result in a m eth oxy–m eth oxycarbon yl–
copper(II) in term ediate, wh ich , in turn , could reductively elim in ate th e
product, DMC, an d a copper(0) species. In th e absen ce of stabilizin g
ligan d(s) th is could explain th e form ation of m etallic copper. Th e oxidation
of Cu(0) species probably goes th rough a m on on uclear copper–oxygen
com plex to form a dim eric in term ediate, wh ich could gen erate a copper(II)
oxo com plex wh ich could react with m eth an ol to form th e dim eth oxy-
copper(II) an d restart th e catalytic cycle. Th e n ature of th e ligan ds h as of
course a very im portan t role in con trollin g th e overall catalytic activity an d
catalyst stability.
Fin ally, th e im m obilization of th e ch lorin e-free 2,2′-bipyrim idin e-m odified
Cu catalyst was ach ieved by addin g 0.06 wt.% copper(II) acetate to a co-
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 8, pp. 1094–1106

1
104
Csihony, Mika, Vlád, Barta, Mehnert, Horváth:
SCHEME 5
Proposed catalytic cycle of oxidative carbon ylation of m eth an ol
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 8, pp. 1094–1106

Oxidative Carbonylation of Methanol
1105
polym er prepared from 1 equivalen t of 5-vin yl-2,2′-bipyrim idin e (10) an d
3
2 equivalen ts of styren e (Sch em e 6).
SCHEME 6
Supported catalyst
Th e form ation of 10% of DMC was observed wh en 0.12 m ol m eth an ol
was treated with 6.2 MPa CO an d 1.0 MPa O2 at 104 °C in th e presen ce
of 300 m g copper(II)-m odified copolym er of 5-vin yl-2,2′-bipyrim idin e an d
styren e.
CONCLUSIONS
We h ave developed a ch lorin e-free catalyst for th e oxidative carbon ylation
of m eth an ol to produce dim eth yl carbon ate. Isotope labelin g study h as es-
tablish ed th at th e reaction is reversible an d th erefore equilibrium -lim ited.
Th e ch lorin e-free catalyst can be prepared in situ from copper(II) acetate
an d 2,2′-bipyrim idin e. High -pressure IR an d NMR spectroscopic studies sug-
gest th e form ation of [Cu(2,2′-bipyrim idin e)(CO)(OMe)] as on e of th e key
in term ediates. Th e catalytic perform an ce of th e 2,2′-bipyrim idin e-m odified
Cu catalyst is sim ilar to the CuCl-based system . The chlorine-free catalyst can
be im m obilized by co-polym erizin g 5-vin yl-2,2′-bipyrim idin e with styren e.
This work was partially supported by the ExxonMobil Research and Engineering Company and the
Hungarian National Scientific Research Fund (OTKA-T032850). The donation of the ReactIR 1000
instrument by Applied Systems Inc, a Mettler-Toledo Company is greatly appreciated.
REFERENCES AND NOTES
1
2
3
. Tundo P., Selva M.: Acc. Chem. Res. 2002, 35, 706.
. Shaikh A.-A. G., Sivaram S.: Chem. Rev. 1996, 96, 951.
. a) Abrams E. in: Encyclopedia of Chemical Technology (Kirk–Othmer), 3rd ed., Vol. IV,
p. 758. Wiley, New York 1979, and references therein; b) Cotarca L., Eckert H. in:
Phosgenations – A Handbook. Wiley, Hoboken 2004.
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 8, pp. 1094–1106

1
106
Csihony, Mika, Vlád, Barta, Mehnert, Horváth:
4
. a) Romano U., Tesei R., Mauri M. M., Rebora P.: Ind. Eng. Chem. Prod. Res. Dev. 1980,
1
1
9, 396; b) Paret G., Donati G. Ghirardini M.: U.S, 5,536,864 (1996), Chem. Abstr. 1992,
16, 62046; c) Rivetti F., Romano U.: Eur. 534,545, Chem. Abstr. 1993, 119, 138752.
5
6
. Romano U., Rivetti F., Delledonne D.: J. Organomet. Chem. 1995, 488, C15.
. a) Fenton D. M., Steinwald J.: J. Org. Chem. 1974, 39, 701; b) Rivetti F., Romano U.:
J. Organomet. Chem. 1978, 154, 323; c) Rivetti F., Romano U.: J. Organomet. Chem. 1979,
1
74, 221; d) Kondo K., Sonoda N., Tsutsumi S.: Tetrahedron Lett. 1971, 411.
7
. a) Kizlink J., Pastucha I.: Collect. Czech. Chem. Commun. 1995, 60, 687; b) Kizlink J.,
Pastucha I.: Collect. Czech. Chem. Commun. 1994, 59, 2116; c) Aresta M., Dibenedetto A.,
Pastore C., Pápai I., Schubert G.: Top. Catal. 2006, 40, 71; d) Sakakura T., Saito Y.,
Okano M., Choi J.-C., Sako T.: J. Org. Chem. 1998, 63, 7095; e) Drake I. J., Fujdala K. L.,
Bell A. T., Tilley D. T.: J. Catal. 2005, 230, 14; f) Zhang Y., Drake I. J., Briggs D. N., Bell
A. T.: J. Catal. 2006, 244, 219; g) Richter M., Fait M. J. G., Eckelt R., Schneider M.,
Radnik J., Heidemann D., Fricke R.: J. Catal. 2007, 245, 11.
8
9
. Vlád G., Horváth I. T.: J. Org. Chem. 2002, 67, 6550.
. Horváth I. T., Ponce E. C.: Rev. Sci. Instrum. 1991, 62, 1104.
1
1
1
1
1
1
0. Fried J., Elderfield R. C.: J. Org. Chem. 1941, 6, 577.
1. Kurek J. T., Vogel G. J.: J. Heterocycl. Chem. 1968, 5, 275.
2. Hermann K., Simchen G.: Liebigs Ann. Chem. 1981, 333.
3. Schaefer F., Peters A. G.: J. Org. Chem. 1961, 26, 412.
4. Kvita V.: Synthesis 1986, 786.
5. a) Periana R. A., Taube D. J., Gamble S., Taube H., SatohT., Fujii H.: Science 1998, 280,
5
60; b) Bhattacharya A. K.: U.S. 4,761,467 (1988), Chem. Abstr. 1987, 107, 22960.
1
1
6. CH OCOOCH : 156.99 s and 54.46 s; CD OCOOCD : 53.74 sept; CH OH: 48.91 s;
3
3
3
3
3
CD OD: 48.07 sept.
3
7. a) Bruce M. I.: J. Organomet. Chem. 1972, 44, 209; b) Pasquali M., Floriani C.,
Gaetani-Manfredotti A.: Inorg. Chem. 1981, 20, 3382.
1
1
8. Brubaker C. H., Wicholas M.: J. Inorg. Nucl. Chem. 1965, 27, 59.
9. a) Saegusa T., Tsuda T., Isayama K.: J. Org. Chem. 1970, 35, 2976; b) Pasquali M.,
Floriani C., Gaetani-Manfredotti A.: Inorg. Chem. 1981, 20, 3382.
20. a) Raab V., Merz M., Sundermeyer J.: J. Mol. Catal. A: Chem. 2001, 175, 51; b) Hu J.-C.,
Cao Y., Yang P., Deng J.-F., Fan K.-N.: J. Mol. Catal. A: Chem. 2002, 185, 1.
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 8, pp. 1094–1106