Note: Descriptions are shown in the official language in which they were submitted.
20~223
Mo3360
LeA 26,273
A PROCESS FOR THE PREPARATION OF POLYISOCYANATES
BACKGROUND OF THE INVENTION
This invention relates to a novel process for the
preparation of organic polyisocyanates by thermal decomposition
of the corresponding carbamic acid esters upon which the
polyisocyanates are based.
It has long been known that N-substituted urethanes
can be thermally decomposed in the gaseous or the liquid phase
into isocyanates and alcohol. Fsr example, A.W. Hofmann, Ber.
o Dtsch. Chem. Ges., 3, 653 (1870); and H. Schiff, Ber. Dtsch
Chem. Ges., 3, 649 (1870).
U.S. Patent 2,409,712 discloses a process in which
recombination of the products obtained from the solvent-free
decomposition of carbamic acid esters can be prevented by
introducing the products into a cyclohexane-water mixture.
This process, however, provides only moderate isocyanate yields
because of the partial hydrolysis of the resulting isocyanate
at the phase interface.
The processes according to U.S Patents 3,962,302 and
3,919,278, for example, take place in the presence of inert
high boiling solvents. In these processes, the two products of
decomposition, that is, the alcohol and the isocyanate, are
together continuously distilled from the decomposition medium
and separated by fractional condensation. The disadvantages of
these processes lie in the considerable technical expenditure
required for the separation of the alcohol and isocyanate
vapors and the moderate yields obtained. Readily volatile
isocyanates are difficult to remove from the decomposition
medium by distillation because of the high dilution and
consequent low partial vapor pressure. Less volatile
isocyanates, such as polyisocyanates of the diphenylmethane
series, cannot be produced by these processes.
Le A 26 273
2~ 5223
In the process according to U.S. Patent 3,919,279,
German Offenlegungsschrift 2,635,490 or German Offenlegungs-
schrift 2,942,543, homogeneous or heterogeneous catalysts are
used for increasing the volume/~ime yields. According to
5 European Application 61,013, secondary isocyanate reactions are
suppressed by the addition of stabilizing additives, but such
additives cannot reduce the difficulties encountered in the
required distillation of the isocyanates.
The object of the present invention is to provide a
o new process for the preparat;on of organic polyisocyanates by
ther~al decomposition of the carbamic acid esters corresponding
to the desired polyisocyanates, whereby the polyisocyanates
obtained would be prevented from recombining with the alcohol
formed and would be carefully isolated from the decomposition
15 medium. Such a process would be particularly suitable for the
preparation of difficultly volatile polyisocyanates. This
object has been accomplished by the process of the invention
described below.
SUMMARY OF THE INVENTION
The present invention relates to a process for the
preparation of a polyisocyanate comprising
(a) thermally decomposing a solution of an N-substituted
carbamic acid ester corresponding to said polyisocyanate
at temperatures above about 150-C in a solvent or solvent
mixture serving as a decomposition medium and with
provision for continually removing by distillation the
alcohol produced by the thermal decomposition of said
carbamic acid ester, where~n said solvent or solvent
mixture (i) is capable of dissolving the carbamic acid
ester, (ii) is stable at the decomposition temperature and
chemically inert towards the carbamic acid esters and the
polyisocyanate formed during the decomposition reaction,
and (iii) has at least one miscibility gap with an
extracting agent used according to extraction step (b~;
Le A 25 273
2~223
(b) extracting the polyisocyanate from the decomposition
medium (optionally after concentrating said polyisocyanate
by fractional distillation) with an extracting agent,
wherein said extracting agent is at least partly
immiscible with the decomposition medium and is a solvent
for the polyisocyanate, and optionally distilling the
resultant solution of the polyisocyanate in the extracting
agent, thereby yielding the polyisocyanate in
substantially purified form; and
o (c) recycling the portion of the decomposition medium
remaining after the polyisocyanate is extracted in
extraction step (b) (preferably by addition to the
decomposition step (a)).
DETAILED DESCRIPTION OF THE LNYENTION
The carbamic acid esters used in the process
according to the invention are compounds or mixtures of
compounds corresponding to the formula
Rl(NHCOOR2)n
wherein
Rl is an aliphatic hydrocarbon containing about 4 to about 18
carbon atoms and optionally containing inert substituents,
a cycloaliphatic hydrocarbon group containing about 6 to
about 25 carbon atoms and optionally containing inert
substituents, an araliphatic hydrocarbon group containing
7 to about 25 carbon atoms and optionally containing inert
substituents, or an aromatic hydrocarbon group containing
6 to about 30 carbon atoms and optionally containing inert
substituents,
30 R is an alkyl group containing 1 to about 18 carbon atoms, a
cycloalkyl group containing 5 to about 15 carbon atoms, an
aralkyl group containing 7 to about 10 carbon atoms, or an
aryl group containing 6 to about 10 carbon atoms; and
n is an integer of from 2 to about 5,
Le A 26 273
201~223
-4-
with the proviso that the corresponding alcohols R2-OH, wherein
R2 has the meaning indicated above, have boil;ng points at
atmospheric pressure at least lO-C lower than the boiling point
of the solYent used as the decomposition medium and the boiling
point of the corresponding polyisocyanate Rl(NCO)n, wherein
has the meaning indicated above.
The preferred carbamic acid esters of the above
formula used for the process according to the invention are
those wherein
o Rl is preferably an aliphatic hydrocarbon group containing 4
to 12 (more preferably 6 to 10) carbon atoms, a
cycloaliphatic hydrocarbon group containing 6 to 15 carbon
atoms, a xylylene group, or an aromatic hydrocarbon group
containing a total of 7 to 30 carbon atoms and optionally
carrying methyl substituents and/or methylene bridges;
R is preferably an alkyl group having 1 to 6 (preferably 1
to 4) carbon atoms, a cyclohexyl group, or a phenyl group;
and
n is from 2 to 5.
Examples of suitable carbamic acid esters include
l-(butoxycarbonylamino)-3,3,5-trimethyl-5-(butoxycarbonylamino-
methyl)cyclohexane, l-methyl-2,4-bis(ethoxycarbonylamino)-
benzene, l-methyl-2,6-bis(ethoxycarbonylamino)benzene, 1,10-
bis(methoxycarbonylamino)decane, 1,12-bis(butoxycarbonylamino)-
dodecane, 1,12-bis(methoxycarbonylamino)dodecane, 1,12-bis-
(phenoxycarbonylamino)dodecane, 1,18-bis(butoxycarbonylamino)-
octadecane, 1,18-bis(benzoyloxycarbonylamino)octadecane,
1,3-bis[(ethoxycarbonylamino)methyl]benzene, 1,3-bis(methoxy-
carbonylamino)benzene, 1,3-bisl(methoxycarbonylamino)methyl]-
benzene, 1,3,6-tr~s(methoxycarbonylamino)hexane, 1,3,6-tris-
(phenoxycarbonylamino)hexane, 1,4-bis(2,4-dimethylphenoxy)-
carbonylamino]butane, 1,4-bis(ethoxycarbonylamino)butane,
1,4-bis(ethoxycarbonylamino)cyclohexane, 1,5-bis~ethoxy-
carbonylamino1naphthalene, 1,6-bis(ethoxycarbonylamino)hexane,
1,6-bis(methoxycarbonylamino~hexane, 1,6-bis~methoxymethyl
Le A 26 ~73
201~223
carbonylamino)hexane, 1,8-bis(ethoxy-carbonylamino)octane,
1,8-bis(phenoxycarbonylamino)-4-(phenoxycarbonylaminomethyl)-
octane, 1,8-bis(propoxycarbonyl-amino)octane, 2,2'-bis(4-
propoxycarbonylaminophenyl)propane, 2,2'-bis(methoxycarbonyl-
5 amino)diethyl ether, 2,4'-bis(ethoxy-carbonylamino)diphenyl-
methane, 2,4-bis(methoxycarbonylamino)-cyclohexane, 4,4'-bis-
(ethoxycarbonylamino)dicyclohexylmethane, 4,4'-bis(ethoxy-
carbonylamino)diphenylmethane, 2,2-bis[(4-methoxycarbonyl-
amino)cyclohexyl]propane, 4,4'-bis(methoxy-carbonylamino)-
biphenyl, 2,2 bis[(4-butoxycarbonylamino)cyclohexyl]propane,
4,4'-bis(phenoxycarbonylamino)dicyclohexyl-methane, and 4,4'-
bis(phenoxycarbonylamino)diphenylmethane. Also suitable are
mixtures of the above exemplified 2,4'- and 4,4'-bis(alkoxy-
carbonylamino)diphenylmethanes with corresponding higher
15 nuclear homologues in which more than two alkoxycarbonylamino-
substituted benzene rings are joined together by methylene
bridges. Such "carbamate mixtures of the diphenylmethane
series" may be obtained, for example, by acid catalyzed
condensation of mono-alkoxycarbonylamino-substituted benzenes
20 Wi th formaldehyde.
Suitable solvents for use as the reaction media for
carrying out the decomposition of the invention are polar
solvents that have a boiling point above 150-C (preferably
above 200C) under the decomposition conditions of the process
or that cannot be distilled at all without decomposing and, in
addition to these properties, must also satisfy the following
requirements. Suitable solvents must dissolve both the
carbamic acid ester starting materials and the isocyanate
reaction prDducts under the conditions of the extraction method
described below, must be substantially stable to heat under the
decomposition conditions, must be chemically inert towards the
carbamic acid esters used ~n the process and the isocyanates
formed in the process, and must have at least one miscibility
gap with the extracting agent used in the extraction step of
35 the process of the invention.
Le A 26 273
2 ~ 2 3
Examples of solvents which conform to these criteria
and are suitable as the reaction medium for the process of the
invention include aliphatic sulfones, such as diethyl sulfone,
dipropyl sulfone, dibutyl sulfone, and ethyl propyl sulfone;
cyclic sulfones, such as sulfolane, 2-methylsulfolane,
3-methylsulfolane, and 2,4-dimethylsulfolane; araliphatic
sulfones, such as methyl phenyl sulfone and ethyl phenyl
sulfone; aromatic sulfones, such as diphenyl sulfone and
4-methylphenyl phenyl sulfone; aromatic nitro compounds, such
as nitrobenzene, 2-nitrotoluene, 3-nitrotoluene, and
4-chloronitrobenzene; and mixtures of such compounds.
Preferred solvents include sulfolane, 3-methyl sulfolane, and
nitrobenzene, particularly sulfolane.
Suitable extracting agents include, in particular,
aliphatic and cycloaliphatic hydrocarbons and aliphatic ethers
having a boiling point or boiling range of from about 30 to
about 200C (preferably from 30 to 150C) at 1013 mbar.
Examples of suitable extracting agents include hexanet
isooctane, petroleum hydrocarbon fractions conforming to the
above definitions, cyclohexane, methylcyclohexane, and
aliphatic ethers containing at least 4 (preferably 4 to 12)
carbon atoms, such as diethyl ether, isomeric butyl ethers,
tert-butyl methyl ether, and heptyl methyl ether. Aromatic
hydrocarbons such as benzene, toluene, and xylene are also
suitable but less preferred. The aliphatic and cycloaliphatic
hydrocarbons exemplified above are particularly preferred
extracting agents. Any mixtures of the extracting agents
exemplified above may, of course, also be used.
The process according to the invention may be carried
out according to several variations. Generally, a solution
containing 1 to 99X by weight (preferably S to 90% by weight
and most preferably 15 to 75% by weight) of the carbamic acid
ester in a solvent or solvent mixture of the type described
above serving as reaction medium is heated to temperatures from
150 to 350-C (preferably from 150 to 280- C), optionally in the
Le A 26 273
_ . .
2~5223
-7-
presence of up to 10 mole% (preferably up to 1 mole%) of a
catalyst, in a suitable reaction vessel at a pressure of from
about 0.001 to about 5 bar. The alcohol vapors that result
from decomposition are distilled off, optionally using a
5 dephlegmator. To ensure that the alcohol decomposition product
will be rapidly and effectively removed from the decomposition
reactor, it may be advisable to pass through the reaction
mixture an inert gas or an inert liquid that is low boiling
under normal conditions and is easily separated from the
o alcohol.
The decomposition reaction may be carried out
continuously, batchwise, or intermittently in known apparatus
known. If the reaction mixture is a solution of up to 30% by
weight of the carbamic acid ester in a solvent of the type
15 described above, the decomposition reaction is preferably
carried out continuously in a cascade of tanks designed to
provide a sufficient dwell time of the solution fed into the
tanks to ensure substantial decomposition of the carba~ic acid
ester. The reaction time may vary from a few minutes to
20 several hours, depending on the reactivity of the carbamic acid
ester to be decomposed and on the reaction temperature
employed.
The conditions are preferably chosen that at least
10% (prefer2bly more than 50%) of the theoretical amount of
25 starting materials undergo conversion within reaction times of
from about 30 minutes to about 5 hours. Because of the luw
concentrations used in the react~on mixture, the formation of
polymeric by-products is to a large extent avoided.
It has been found that if thP solutions have a
carbamic acid concentration above 3CX by weight, it is
advantageous to carry out the decomposition reaction by passing
the solution in a thin layer along the internal wall of a
heated tube. The dwell time of the solution in the reaction
tube is kept very short in order to suppress side reactions.
The alcohol released in the decomposition reaction is removed
LP A 26 273
~O~L~J~23
~verhead as gaseous product, whereas the isocyanate-containing
reaction mixture is discharged as sump product. If the tube
reactors are placed vertically, the reaction mixture introduced
into them may be distributed over the internal walls of the
s tubes without the aid of special apparatus, if the reaction
mixture is applied uniformly over the wall of the tube by means
of a suitable device, for example, a nozzle. Distribution of
the reaction mixture may, however, also be achieved with the
aid of a mechanical stirrer or s;milar devices. If the tube
reactors are not placed vertically, it is generally necessary
to use a mechanical stirrer or some other suitable device.
As previously indicated, suitable decomposition
catalysts, such as those described, for example, in German
Offenlegungsschrift 2,635,490 and U.S. Patent 3,919,279, may be
added to the reaction mixture to accelerate the decomposition
reactions.
The thermal decomposition step of the process of the
invention may be carried out at elevated or reduced pressure in
the range of from about 0.001 to about 5 bar but is preferably
carried out at reduced pressures in the range of from 0.005 to
0.5 bar to ensure rapid removal of the alcohol from the
reaction mixture.
The decomposition reaction ~hould be carried out
at fiuch temperatureC and pre~ ures, within the ranges
indicat~d aboYe, that the alcohol~ g3nerated will be the
only componenL l~aving tho rsaction mixture in a gaseou-
for~. This r~qUiremQnt ~ay ba ensured not only by
suit~ble c~oice of the decomposition ~mperature but
ecpoci~lly al~o by cu;table choice of the dephlegmator
~mparatur0~
When c~rrying out th~ process of ~h~ in~ention, it
is i~port~nt for bo~h ~h~ csrb~mic acid ~cters b3ing
deco~poced ond tha icocyan~tes bsing formed to be in
~olution under the condition~ u~ed for extraction that
follow6 the decomposition rea~tion.
The cruds solution obt~in~d from the thermal
decomposition of carb~mic ~cid e6~rfi, which con~ist
Le A 26 273
2~1 ~i223
predominantly of the polyisocyanate products but also of
residues of carbamic acid esters that have not decomposed or
have only partly decomposed, are cooled to a temperature below
the decomposition temperature and extracted in the second stage
5 of the process. If desired, the crude solution may~ of course,
be concentrated by fractional distillation before carrying out
the extraction.
For carrying out the extraction of the invention, the
isocyanate-containing crude solution is vigorously mixed with
o an extracting agent, as exemplified above, that is liquid at
room temperature. This extracting agent is used in about 0.1
to about 25 (preferably 0.5 to 5) times the quantity by weight
of the crude solution to be extracted. The crude solution is
generally mixed with the extracting agent within a temperature
range of from about -20C to about 150~C ~preferably from 10C
to 100-C). This procedure generally results in the spontaneous
formation of a diphasic mixture of two liquid phases which,
after phase deposition, can be separated into a upper phase and
a lower phase. The formation of a diphasic system may in
special cases be promoted by cooling the mixture of the crude
solution and the extracting agent. Thus, for example, mixing
can be carried out at about 70C to 100-C and the resultant
mixture may then be cooled to a lower temperature, for example,
in the range of from 10-C to 40C.
The upper phase of the diphasic system generally
constitutes the main phase and the lower phase the secondary
phase, although the ratio by volume depends to a large extent
on the quantity of extracting agent used. In the process of
the invention, phase separation may be carried out by known
30 methods, for example, by discharging the lower phase, by
decanting, by siphoning, or by other suitable methods of phase
separation. Part of the polyisocyanate that is to be recovered
in pure form is then present in the upper main phase. Other
components of the upper phase include part of the solvent used
35 as decomposition medium and the major proportion of the
Le A 26 273
203. ~23
-lo-
extracting agent used. ~he lower phase consists mainly of the
solvent used as decomposition medium, the unreacted or only
partially reacted carbamic acid esters, the by-products of the
decomposition reaction, and that part of the polyisocyanate
product that has not been transferred into the upper phase. To
obtain this part of the polyisocyanate in pure form, the lower
phase may be subjected to one or more additional extractions
carried out in the manner described.
In a preferred embodiment of the process of the
o invention, mixing the crude solution with the extracting agent
and subsequent phase separation ~that is, extraction of the
crude solution) are carried out continuously using conventional
continuously operating counterflow extraction apparatus.
~he extraction gives rise to one or more upper
S extraction phases containing the polyisocyanate and a generally
homogeneous second phase mainly containing unreacted or only
incompletely reacted carbamic acid ester. Multiple upper
extracts can optionally be combined. The lower phase may be
reused as solvent for the decomposition reaction. It has been
found that when the lower phase is reused, it is advantageous
to discharge a proportion of the phase and replace it with
fresh solvent to avoid accumulation of the by-products present
in the lower phase.
~o obtain the polyisocyanates in the pure form, the
upper extraction phases are wsrked up by distillation, the
extracting agent generally constituting the first fraction to
be removed by distillation. Separation of the polyisocyanates
from residual solvent used as the decomposition medium may also
be carried out by distillation, during which the polyisocyanate
or the solvent used as the decomposition medium forms the
distillation residue. It is generally preferred to use
decomposition solvents having a clearly different boiling point
from that of the polyisocyanate product so that the two can
easily be separated. ~hen the upper extraction phases are
worked up by distillation, the polyisocyanate generally
Le A 26 273
_
2 3
constitutes the distillation residue. Workup by distillation
can also be carried out continuously using known distillation
apparatus. If desired, polyiso~yanates obtained as
distillation residue can be subjected to a further, fine
distillation, but even without such fine distillation the
lo polyisocyanates obtained as distillation residues can sometimes
have a purity of greater than 90% by weight.
It is a particular advantage of the process of the
invention that the polyisocyanates obtained from the
decomposition reaction are isolated not by a distillation
associated with unnecessary exposure to heat but by extraction
under mild conditions of any reaction by-products. As a
result, the known secondary reactions of isocyanates, which can
in some cases be catalyzed by the by-products of the
decomposition reaction and by the carbamic acid esters used in
the process, are to a large extent suppressed. Thus, a
subst~ntially higher proportion of the polyisocyanate formed in
the decomposition reaction remains undecomposed and may be
isolated in pure form.
The following examples further illustrate details for
the proceçs of this invention. The invention, which is set
forth in the foregoing disclosure, is not to be limited either
in spirit or scope by these examples. Those skilled in the art
will readily understand that known variations of the conditions
of the following procedures can be used. Unless otherwise
noted, all temperatures are degrees Celsius and all percentages
are molar percentages.
Le A 26 273
2~ 5223
- 12 -
The first cycle yields are ba6ed on ~he actual
yields obtained in the Examplee. The rontinuou6 pro-
cess yields refer to the to~al amount of diisocyana~e
obtalned by (1) recovering addi~ional diisocyanate from
the first cycle and t2) converting unreacted and par-
tially reacte~ carbamic acid ester ~o produ~ in subse-
quent decompo ition steps. Thi~ y;eld i5 calculated ~s
the limiting value o~ a ~eometric row and is given by:
l-(s1-Y1)/lOO
where y = con~inuous process yield (%)
Y1 = first cycle yield (%)
~1 = sum of total amount of dii~ocy~nate and
unreacted and par~ially reac~ed carbamic
e 6 ters (%)
EXAMPLES
Procedure ~A).
The selected solvent is heated to a temperature
about Z~ C below ~he de~ired decomposition tempersture
in a fla6k equipped with a glass-cover6d blade ~tirrer,
a thermomster, a nitrogen inlet opening below the liquid
~urf~cel and a dephlegmator ti.e., a ro~s flow cooling
device). The carb~mic acid e~t~r to be decomposed (and,
if us~d, cataly6t~ and/or ctabilizerc) are ~dded and the
entire content6 of the ~lac~ are heat~d with vigorous
~tirring under a con~tant stream of nitrog0n to the
required decompositlon temperature. A redused
Le A 26 273
201522~
pressure is regulated to proviae vlgorous reflux in the
dephlegmator. The temperature of the dephlegmator should be
maintained between the boiling points of the solvent used and
the alcohol to be removed. The decomposition gases are
condensed or partially condensed at the upper end of the
dephlegmator with a water-cooled Liebig condenser and collected
in a receiver that is optionally cooled with cooling mixture
(e.g., dry ice-acetone).
The extent of conversion obtain~d by the
decomposition reaction is determined by removing small samples
of the reaction solution with a syringe inserted through a
septum and the isocyanate content of the samples is determined
by titration (i.e., by reaction with dibutyl amine and back
titration of the excess amine with hydrochloric acidj.
When the desired extent of decomposition has been
reached, the decomposition reaction is stopped by cooling the
reaction solution to a temperature suitable for extraction and
by then extracting the solution as described below.
Procedure (B):
~he decomposition reactor for this procedure is a
cylindrical thin-layer evaporator (effective length 3~0 mm and
diameter 35 mm3 equipped with a metal propeller stirrer whose
movable blades extend to the wall of the thin-layer evaporator.
A heatable addition funne1 at the head of the thin-layer
evaporator is used for introducing the carbamic acid ester to
be decomposed. Reaction products which cannot be evaporated
are discharged through a closable tap dt the bottom of the
thin-layer evaporator, whereas components of the reaction
mixture which can be evaporated are removed through a heated
transverse flow condensor placed at the head of the thin-layer
evaporator and having a condensation coil with discharge outlet
at the upper end. Evacuation of the decomposition apparatus is
~e A 26 2?3
2 ~ 3
- 14 -
carried out using a rotary disk pump with a cooling trap behind
the condensation coil.
The isocyanate-containing mixture obtained during the
decomposition reaction is warmed to a temperature suitable for
extraction, optionally after the addition of further solvent,
and extracted by the method described below.
Extraction:
The mixture i5 extracted in a heatable flask which
has a discharge device at the bottom and is equipped with a
glass-covered blade stirrer, a thermometer, and a reflux
condensor. This extraction is carried out by adding the
extracting agent and mixing the two components vigorously for
30 minutes. After the mixture has been allowed to stand for 10
minutes, the resulting two phases are separated. In some
examples, the lower phase is subjected to one or more further
extractions with fresh extracting agent. The upper phases are
combined and then tested for their composition by means of high
performance liquid chromatography ("HPLC"), as are the lower
phases left over after extraction.
The abbreviation suffixes used below ha~e the
following meanings: "Dl" denotes polyisocyanates free from
urethane, in particular diisocyanatei ~IU" denotes partially
decomposed product containing urethane and isocyanate groups,
in particular isocyanatourethane; and ~U" denotes unchanged
starting material, in particular diurethane.
Example 1
Using Procedure (A), a solution of 151 9 of
1,5-bis(ethoxycarbonylamino)naphthalene (nNDUn) and 2.60 9 of
dibutyltin dilaurate in 1346 9 of sulfolane is thermolized at
200-C for 300 minutes. The reaction mixture, which has an
isocyanate value of 2.26% by weight (80.7X of theoretical), is
cooled to 70-C and extracted four times each with 4700 9
portions of cyclohexane. According to HPLC analysis, the
collected extracts contain 58.9 9 of 1,5-diisocyanato-
naphthalene (~NDIa~ and 23.9 g of 1-ethoxycarbonylamino-
Le A 26 273
20~.5~23
5-isocyanatanaphthalene ("NIU"). me ~'DU content is belaw the
limit of detection. After extraction, the sulfolane phase
contains 15.6 9 of NIU and 2.4 9 of NDU. The NDI content is
below the limit of detection. The isolable yields of 1,5-di-
5 isocyanatonaphthalene calculated from these figures are 56.0%after a first cycle and 80.6% for a continuous process.
Example ?
Using Procedure tB), a solution of 225 9 of 2,4-bis-
(ethoxycarbonylamino)toluene (nTDU"), 0.55 9 of dibutyltin
dilaurate, and 2.2 9 of stearic acid chloride in 75 9 of
sulfolane and 30 9 of chlorobenzene is introduced over a period
of 6.5 hours (dripping rate of 50 g/h) from the addition funnel
which is thermostatically controlled at 100-C into the thin-
layer evaporator which is heated to 290-C. The pressure in the
15 apparatus is 200 mbar during the decomposition reaction. A
yield of 261 9 of sump product is obtained. According to HPLC,
this sump product contains 70.7 9 of TDU, 99.2 9 of the
corresponding ethoxycarbonylaminoisocyanatotoluene (~TIU")
isomeric mixture, and 24.7 9 of 2,4-diisocyanatotoluene
20 ("TDI"). The sump is extracted at 50-C four times each with
260 9 portions of isooctane. After the last extraction, the
sulfolane phase contains 65.7 9 of TDU, 85.7 g of TIU, and 4.7
g of TDI. The combined extracts contain a total of 2.0 g of
TDU, 15.8 9 of TIU, and 19.4 9 of TDI. The isolable yields of
2,4-diisocyanatotoluene salculated from these figures are 13.3%
after a first cycle and more than 98% for a continuous process.
ExamDle 3
Using Procedure IA), a solution of 85.6 g of a
mixture of 4,4'-bis(ethoxycarbonylamino)diphenylmethane
homologs (npolymeric MDU") having a total MDU content of 73.5%
by weight and 0.26 g of dibutyl tin dilaurate in 1414 9 of
sulfolane is thermolyzed at 250'C for 70 minutes. The reaction
mixture9 which has an isocyanate value of 0.97% by weight
~94.4% of theoretical), is cooled to 20-C and extracted four
times each with 1740 g portions of a mixture of tert-butyl
Le A 26 2?3
201~23
- 16 -
methyl ether and isooctane (1:1). According to HPLC analysis,
the combined extracts contain 28.7 9 of a mixture of 4,4'-di-
isocyanatodlphenylmethane homologs ("polymeric MDI"), 1.0 g of
a mixture of the corresponding ethoxycarbonylaminoisocyanato-
5 diphenylmethane homologs ("polymeric MIU"), and 0.9 g ofpolymeric MDU. The sulfolane phase conta;ns 12.5 g of
polymeric MDI, 3.0 9 of polymeric MIU, and 0.7 9 of polymeric
MDU after extraction. The isolable yields of the mixture of
4,4'-diisocyanatodiphenylmethane homologs calculated from these
o figures are 61.9% after a first cycle and 98.3% for a
continuous process.
ExamPle 4
Using Procedure (B), a solution of 140 g of 4,4'-bis-
(ethoxycarbonylamino)diphenylmethane ("MDU") and 0.35 g of
dibutyltin dilaurate in 140 9 of sulfolane and 28 g of
chlorobenzene is introduced over a period of 6.25 hours
(dripping rate of 50 g/h) from the addition funnel which is
thermostatically controlled at 125-C into the thin-layer
evaporator which is heated to 260-C. The pressure in the
20 apparatus during the decomposition reaction is 150 mbar. A
yield of 261 g of sump product is obtained. According to HPLC,
this sump product contains 51.7 9 of MDU, 38.6 9 of the
corresponding ethoxycarbonylaminoisocyanatodiphenylmethane
("MIU"), and 28.4 9 of 4,4'-diisocyanatodiphenylmethane
25 ("MDI"). The sump product is extractcd four times each with
260 9 portions of cyclooctane at 80-C. After the last
extraction~ the sulfolane phase contains 49.3 9 of MDU, 26.8 g
of MIU, and 5.5 9 of MDI. The combined extracts contain a
total of 2.8 9 of MDU, 10.8 9 of MIU, and 25.4 9 of MDI. The
30 isolable yields of 4,4'-diisocyanatodiphenylmethane calculated
from these figures are 24.8% after a first cycle and ~4.7% for
a continuous process~
Le A 26 273
__~ _ _
2~ 23
- 17 -
ExamPle 5
Using Procedure (A~, a solution of 75 g of 1-(ethoxy-
carbonylamino)-3,3,5-trimethyl-5-(ethoxycarbonylaminomethyl~-
cyclohexane ("IPDU") and 0.26 9 of dibutyltin dilaurate in 1425
9 of sulfolane is thermolyzed at 250-C for 60 minutes. The
reaction mixture, which has an isocyanate value of 1.13% by
weight (84.9% of theoretical), is cooled to 20DC and extracted
four times each with 860 g portions of cyclohexane. Accord;ng
to HPLC analysis, the combined extrac~s contain 34.8 9 of
1-isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl)cyclohexane
~"IPDI"), and 2.0 9 of the corresponding (ethoxycarbonylamino)-
(isocyanatomethyl)-3,3~5-trimethylcyclohexane ("IPIU") ;someric
mixture. (The carbamic acid ester IPDU9 which has remained
unchanged in the decomposition reaction, is not detected in the
HPLC analysis.) After the extraction, the sulfolane phase
contains 7.0 g of IPDI and 5.5 g of IPIU. The isolable yields
of 1-isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl~cyclohexane
calculated from these figures are 66.0% after a first cycle and
more than 88% for a continuous process.
Example 6
Using Procedure (B), a solution of 112 9 of TDU, 0.27
g of dibutyltin dilaurate, and 1.1 9 of stearic acid chloride
in 37 9 of sulfolane and 15 9 of chlorobenzene is introduced
over a period of 9 hours (dripping rate of 18 g/h) from the
addition funnel which is thermostatically controlled at 100C
into the thin-layer evaporator which is heated to 290-C. The
pressure in the apparatus during the decomposition reaction is
200 mbar. A yield of 123 9 of sump product is obtained.
According to HPLC, this sump product contains 16.0 9 of TDU,
34.5 9 of the corresponding TIU isomeric mixture, and 30.7 9 of
TDI. The sump is extracted four times each time with 125 S
psrtions of cyclooctane at 20-C. After the last extraction,
the sulfolane phase contains 15.1 9 of TDU, 28.4 9 of TIU, and
5.9 g of TDI. The comhined extracts contain a total of 0.6 9
of TDU, 5.5 9 of TIU, and 25.0 9 of TDI. The isolable yields
Le A 26 2?3
2~1~223
18 -
of 2,4-diisocyanatotoluene calculated from these figures are
34.2% after a first cycle and 82.8% for a continuous process.
Le A 26 273
~ . .
