Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE I~J~NTION
Present processes for the direct oxidation of
dioiefins to furan compounds are ~rimarily vapor phase
processes which are ~enerally characterized by low ccnversions
and poor selectivities. These disadvantages are brought
about by the lnstability of furan compounds at high tempe-atures
in the presence of oxygen which leads to the formation of
resinous compounds, charring and uncontrolled polymerization.
The iiquid phase process of the present invention eliminates
these disadvantages by operating at moderate tempera~u~es.
Althou~h several liquid phase processes are known
for the production of furan compounds, they involve ~he use
of oxy~enated compounds as starting materials. For exam~le,
.S. 3,932,468, issued January 13, 1976, and U.S. 3,996,2~C,
issued December 7, 1976, pertain to the rearrangemen~ o
butadiQne monoxide, and U.S. 3,933,861, issued Janua~y 2~,
1976, involves the reaction of an alkene and an aikene oxide
to yield substituted furans. Both of these processes recuire
oxygenated starting materials, whereas in the preser.~ ~r.ven~ion,
furan compounds are obtained by the direct oxidation cf t~e
2~ con~ugated diolefin.
Whiie Japanese ~atent No. 77 77,049 discloses a
process fo. the oxidation of butadiene 'o furan _n an acueous
acidic medium, the process of the presen~ invention is
1- ...
~3
(5063~
dlstlnguished from this process in that the present process
is conducted in an organ~c solvent medium in which the
catalyst and furan products are more stable.
SUMMARY OF THE INVENTION
In accordance wlth the process of the present
inventlon, acyclic conJugated dloleflns containlng from 4 to
10 carbon atoms are converted to furan and alkyl-substltuted
furan compounds by the direct oxldatlon of the diolefln wlth
molecular oxygen ln a liquld phase reactlon. The reactlon
is carried out ln a non-aqueous reactlon medlum ln the
presence of a transltlon metal organo-metalllc catalyst
complex.
The liquld phase oxidatlon reactlon of this invention
ls a free radlcal reaction, and these reactions appear to be
lnltlated by means of the formatlon of an lnitial free
radical. Thls inltlal free radlcal may generate the desired
product (furan) dlrectly, or proceed to form other radlcal
intermediates whlch can yleld elther furan, other oxygenated
products, such as a dlolefin monoxide, 2,5-dihydrofuran,
crotonaldehyde, or ollgomers and/or polymers.
The role of the catalyst of this invention is to
react with the lnltial key radical intermediates, convertlng
them directly to furan products before deleterious by-
products can be produced. It ls thls selective catalytic
behavior, coupled wlth speciflc reaction conditions herein
defined that result in the enhanced selectivity of the
oxidation of the diolefins to the desired furan compounds.
Suitable feeds in this inventlon for converslon to
furan compounds comprise acyclic alkadienes having from 4 to
3 10 carbon atoms. ~xamples include butadiene-1,3, pentadiene-
133, isoprene, hexadiene-1~3, decadiene-1,3, and the like,
~3~' (5063)
and mixtures thereof. The acycllc alkadienes having from 4
to 5 carbon atoms are preferred in this process. The furan
compounds produced by the process of the present in~ention
have the ~ormula:
R-C-C-R
R-C C-R
o
wherein each R ls indl~dually selected from the group
consisting of hydrogen and an alkyl radlcal havlng from
1 to 6 carbon atoms, the total carbon atoms in the R
radicals being in the range of 0 to 6. Representative
products include furan, 2-methylfuran, 3-methylfuran,
2,5-dlethyl~uran, 2-n-hexylfuran, 2-isopropyl-3-methylfuran,
3,4-n-dipropylfuran, 3-methyl-4-n-butylfuran, and the like.
The catalysts of this invention are organo-metallic
complexes or salts of the metals of Groups IVB, VB, VIB,
VIIB or VIII of the Periodic classlflcation of elements.
These complexes have the general formùla:
~RXM (L)y]æ
wherein R is an organic li~and selected
from the group conslsting of a kyl,
aryl, alkene, diene, triene or alkyne
radicals containing from 1 to 8 carbon
atoms;
L is a l~gand selected from the grou~
consisting o~ carbon monoxide and a
halogen;
M is a transition metal or their mixtures
selected from the grou~s IVB, VB, VIB,
VIIB and ~III of the Pe-iodic classificatior
of elements,
and wherein x is O to 2,
y is 0 to 6
and x + y is 1 to 6,
and wherein z is 1 to ~.
~13~
Specl~ic examples o~ sultable catalysts lnclude OsC13,
o~3tCo)l2, ~CpMo(C0)3]2 (Cp ~ cyclopentadienyl radlcal),
CpV(C0~4, CpTiC12, CpMn(C0)3, (Cp)2Pe, M ( 6
(CO)2]2, (C4H6)Fe(CO)3, Co2(CO)8~ ~U3(C)12' Rh6(C0)16 and
W(C0)6.
Whlle these complexes and salts are effectlve
catalystæ ln thelr own rlght, it may also be advantageous to
utlllze certaln promoters rOr these catalysts as defined by
the general rormula:
A R m Xn
whereln A can be mercury, thalllum, indlum,
or a Group IV A element such as slllcon,
germanlum, tln or lead;
R can be a hydrlde, alkyl, aryl or an
amlne group;
X can be an anlon of a mineral acid or a
carboxyllc acld,
and whereln m ~s 0-4,
n ls 0-4
and m ~ n ls 1 to 4.
Specirlc examples of these types o~ promoters
lnclude such compounds as Hg(C2~302)2, SnC12, (C2H~)2SnC12~
4 3 3 ~C~3)2, GeI2~ (n-C4Hg)3GeI, (~ -C5H5)Ge(CH )
(C2H5)3 PbCl, (CH3)3 SlH, or SiH3I.
2~ When promoters are employed for the catalysts of
this invention, they may be added to the reaction mixture as
separate species or they may be reacted with the catalyst to
give a separa~e chemical compound which can be isolated and
purified prior to its use as a catalytic agent. Representa-
tive examples of compounds ~ormed by reactions occurring
between the catalyst and the promoter include: ClHgFe(Cp)2,
~Ig[Co(C0)4]2, C12Sn~Fe(CO)2Cp]2, I2Ge[Co(CO)~ 2, [(C2~;5)3Pb~2.-e(CO)4,
H3SiCo(C0)4, Cl(CH3)2Sn[Mn(C0)5], and [Cp(C0)3Mo-Sn(C~3)2-
M~(C0)5].
~ (5063)
The promoter compounds o~ the catalyst system are
ad~antageously employed in molar ratios of from 0.25 to 2.0
moles of promoter per ~ole of the transition metal catalyst~
However preferred molar ratios Or promoter compound to the
transltion metal catalyst are about 0.~:1 to 2:1. The
catalysts o~ thls lnventlon (with or wlthout promoters) may
be dissolved in the reaction medium as homogeneous catalysts,
slurried ln the reactlon medlum as lnsoluble, unsupported
heterogeneous catalysts, or ln some cases where advantageous,
they may be supported on carrlers such as sllica, alumlna,
or polymeric materials and slurrled ln the reactlon medlum.
It ls preferred, however that the catalyst system be a
homogeneous system where the catalyst ls soluble in the
! reaction sol~ent.The ~oncentratlon of the catalyst ln the
15 sol~ent medlum may range rrom 10 6 to 10.0 moles/liter.
Preferably a catalyst concentration of from about 10 5 to
1.0 moles/liter is employed.
The reactlon medium suitable for the process of
this invention is an essentially inert, non-coordinating or
weakly coordinating organic solvent having a boiling point
signiflcantly higher than the boiling points of the feed or
the products obtained. Solvents with boiling points of from
130~ to 22~C are especially preferred. Also desirable are
those solvents having an absence of abstractable hydro~ens
which could lead to oxidation of the solvent or the binding
of the active sites of the metal or metals in the catalyst,
thereby deactivating the catalyst. Examples o~ suitabie
solvents include paraffinic hydrocarbons, aromatic hydrocarbons,
chlorinated hydrocarbons, and nitrile aromatics such as
heptanes, decanes, and the l~ke; toluene and the xylenes;
chlorobenzene, chlorofor~, carbon tetrachioride, etc; and
ber.zonitrile; with chlorobenzene being the most Dre~erred.
~ t5063)
Subst~tuted rurans such as alkyl-furans or 2,3-benzofuran
may also serve as suit~ble solvents in some cases.
The oxidation reaction of the present in~ention is
very sensitive to reaction condltlons and lt ls an essential
~eature of the invention that the reaction be carried out
under conditlons whlch maxlmlze selectivlty. The reactlon
may be carried out at temperatures in the range of from
about 20 to 200C, and pre~erably at temperatures in the
range of ~rom about 50 to 130C. Temperatures above thls
1~ range bring about the formatlon o~ additional oxidation
products such as crotonaldehyde and increase the formatlon
of undeslrable polymer.
The reaction pressure may range from 1 to 20
atmospheres, and pre~erably ~rom 1 to 10 atmospheres. The
partial pressure o~ oxygen ls of particular importance to
the selectivity of the reaction, and oxygen pressures of
from 0.~ to ~ atmospheres and expecially oxygen pressures of
from l to 3 atmospheres are advantageously employed.
Another critical reactlon variable affectin~
selectivlty of the reaction is the ratio of diolefin to
oxygen. While the molar ratio of diolefin to oxygen may vary
from 0.001 to 100.0, a ratio of from 0.33 to 5.0 is preferred.
In those instances where the reaction is carried
out in a sealed reaction vessel, the reaction times may
range from 0.5 to 10 hours and a reaction time of from 1,0
to 4 hours is preferable. Continuous operation in which the
reaction mixture is maintained at constant temperature and
pressure is also contemplated to be within the scope of the
present invention. Under such conditions, the diolefin and
3 air or oxygen are continuously fed to the reactor while
volatile products and the unreacted feed are continuousl~
removed. ~he vo atile products can be collected and the
unreacted feed recycled to the reactor.
~S1;3~L1 ~ ~
(~063)
The reactor vessel may be constructed ~rom stain-
less steel, or in certain instances the reaction vessel may
be lined wlth glass, quartz or a stable resinous material in
order to minimize side reactions between reaction intermediates
and the walls of the reaction vessel.
Specific Examples
Examples 1-12
The oxidation of butadiene to furan in the presence
of a variety Or promoted and unpromoted transition metal
catalyst complexes was conducted in a series of experiments
according to the following procedure:
An amount Or catalyst requlred to give a concentra-
tion of 1 x 10 4 moles of catalyst in the reaction solvent
was weighed into a stainless steel reaction tube (180 mm
long x 9.~ mm diameter) equipped with a stainless steel ball
valve and septum cap. The tube was evacuated and charged
with a mixture of butadiene and oxygen in a 1:1 molar ratio
at an initial oxygen pressure of 2.2 a~tmospheres. Four
milliliters of chlorobenzene solvent was introduced into the
tube wlth a metering pump. The tube and its contents were
heated to a temperature of 110~ in a heating block for a
period of two hours. At ~he end of this time period, the
tube was qu~ckly cooled to room temperature and the reactlon
mixture analyzed by gas chromatography.
4`~
The pexcent conVersion of the hutadiene and the
percent selectivity to uran based on t~e percent of
butadiene converted that were obtained in Examples 1 to
12 are summarized in Table I below.
TABLE I
% Total ~ Selectivity
Exam~le Catalyst Converstion to Furan
1 (Cp)2Fe 2.9 99.0
2 (Cp)2Ee/SnC12 10.2 81.1
3 Mo(CO)6 1.4 97.7
4 Mo(CO)6/Hg(c2H3O2)216.7 65.4
CpV(CO)4 9.4 82.2
6 CpTi2C12 13.3 77.5
7 [CpMo(CO)3]2 17.6 68.2
8 Os3(CO)12* 18.2 92.0
9 S3(C)12/Sncl2 14.2 71.6
OsC13 20.5 57.4
11 Ru3(CO)12 0.1 100.0
12 3(CO)l2/(n-c4H9)3GeI 13-2 99 0
~Cp = cyclopentadiene)
*Reaction conducted in a resin coated stainless
steel reactor.
- 8
