Note: Descriptions are shown in the official language in which they were submitted.
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A PROCESS FOR THE PREPA~ATION OF
BIS-(ETHOXYCARBONYLAMINO)TOLUENES
AND FOR THE PREPARATION OF
DIISOCYANATOTOLUENES THEREFROM
BACKGROUND OF THE INVENTION
This invention relates to a process for the preparation of
bis-(ethoxycarbonylamino)-toluenes (also known as
tolylene-bis-(O-ethylurethanes)) and to a process for the
preparation of diisocyanatotoluenes therefrom.
The preparation of urethanes by the reaction of amines
with organic carbonates is known. Various procedures have been
described in the literature for working up the reaction
mixtures and isolating the pure products.
Monourethanes, for example, may be purified and isolated
by distillation (DE-OS 3,035,354, EP-A-0,323,514 and
EP-A-0,391,473). This method, however, cannot be used for
tolylene-bis-(O-alkylurethanes) because these urethanes cannot
be distilled without decomposition.
Another method of purifying the urethanes formed from the
reaction of amines with carbonates is recrystallization.
According to DE-OS 2,160,111,~for example, diphenylurea formed
as by-product from the reaction of aniline with
dimethylcarbonate is filtered off, the filtrate is concentrated
by evaporation and the residue is recrystallized from hexane to
obtain N-phenyl-O-methyl urethane. The product of the process,
however, still contains about 20% of N-alkylated anilines as
impurity af$er recrystallization, these anilines having been
formed as by-products of the reaction.
According to Example 8 of DE-OS 3,035,354, 2,4-bis-
(ethoxycarbonylamino)toluene can be isolated after the titanium
tetrabutylate catalyzed reaction of 2,4-diamino-toluene with
excess diethylcarbonate by filtering off the polyurea form~d as
the main product, concentrating the filtrate by evaporation and
recrystallizing the residue from toluene. Disadvantages of this
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process are the low yield of diurethane (26% of theoretical)
and the formation of large quantities of polyurea which ~ust be
converted into the diurethane in an additional process step.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a
process for the preparation of tolylene-bls-(O-alkylurethanes)
by which the products can be prepared and isolated in a very
pure form by a simple and efficient method of working up
without the above-described disadvantages of known processes.
It was surprisingly found that this problem could be
solved in the specific example of bis ~thoxycarbonylamino)-
toluenes (tolylene-bis-(O-ethylurethanes)) by reacting a
diaminotoluene with a large excess of the diethylcarbonate in
the presence of a suitable catalyst. The use of such excess
1~ amounts of the diethylcarbonate prevents the formation of large
amounts of by-products, in particular of prematurely
crystallizing polyureas. Consequently, the desired product can
easily be isolated in a very pure form in high y;elds.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENTS OF THE INVENTION
This invention relates to a process for the preparation of
a bis-(ethoxycarbonylamino)toluene by the reaction of a
diaminotoluene with diethylcarbonate in the presence of a --
catalyst at 100 to 300DC with simultaneous or subsequent
removal of the alcohol formed by distillation. The
diethylcarbonate is used in an at least 5-times molar excess,
based on the amino groups of the diaminotoluene. The
bis-(ethoxycarbonylamino)-toluenes formed are isolated in the
form of very pure crystals after cooling and optionally partial
concentration by evaporation of the reaction mixture without
previous removal of by-products. The present invention also
relates to a process for the production of a diisocyanato-
toluene by thermal decomposition of the bis-(ethoxycarbonyl-
amino)toluene thus produced.
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Any diaminotoluenes may be used in the process of the
invention but 2,4-diaminotoluene and its commercial mixtures in
which up to 40% by weight, preferably up to 35% by weight of
2,6-diaminotoluene, based on the quant~ty of diamine mixture,
is present are preferred.
Metal compounds of the 1st to 5th Main Group and the 1st
to 8th sub-Croup of the Periodic System of Elements may be used
as the catalyst. The catalysts used are preferably metal
compounds of the 4th Main Group and the 2nd sub-Group of the
Periodic System. Compounds of tin, zinc and lead are
particularly preferred.
Examples of suitable catalysts include: Lewis acids such
as salts or compounds of zinc, lead, titanium or zirconium,
e.g., zinc ( I I ) chloride, zinc ( I I ) acetate and other
zinc(II)carboxylates, lead ~II) acetate and other lead (II)
carboxylates, titanium tetrabutylate and zirconium
tetrapropylate; organic tin compounds, e.g. dibutyl tin oxide
or dibutyl tin dilaurate; and basic compounds such as alkali
metal or alkaline earth metal hydroxides or alkoxides.
It is preferred to use catalysts which, if they remain in
the product, do not deleteriously affect subsequent
decomposition of the urethanes formed by the process of the
present invention into the corresponding isocyanates and
alcohols. Oatalysts which have this characteristic include
those identified above as being particularly preferred
catalysts.
The catalyst is used in a quantity of from about O.Cl to
about 20 mol%, preferably from about 0.05 to about 15 molX,
most preferably from about 0.1 to about 10 mol%, based on the
amount of diamine used ;n the prucess.
The reaction temperature is generally in the range of from
about 100 to about 300~C, preferably from about 120 to about
250C.
The process may be carried out at normal pressure or
elevated pressure. Elevated pressure is necessary if the
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reaction temperature is above the boiling point of the reaction
mixture at normal pressure.
It is essential that the diethylcarbonate should be used
in large excess, based on the diamine. It is generally used in
an at least 5-times molar excess, preferably an at least
10-times and most preferably 10- to 30-times molar excess,
based on the amino groups of the diamine.
The diethylcarbonate present in excess has the important
function of a solvent which appears to maximize the yield and
enable the product bis-(ethoxycarbonylam~no)-toluene to be
obtained in a pure form by simple crystallization. The alcohol
formed du~ing the reaction in accordance with the following
reaction equation
R-(NH2)n + n (R'0~2CO~ R-(NHCOOR')n + n R'OH
in which the groups R and R' represent the inert groups of
the reactants in this equation (shown here only to
illustrate the principle of the reaction)
2Q ;s removed by distillation either continuously during the
reaction or at a suitable stage after the reaction has been
completed.
Surprisingly, the product of the process of the present
invention (in contrast to the process of DE-OS 3,035,354), has
no significant quanti~ies of by-products, which crystal-
lize on cooling of the reaction mixture tin particular
polyureas). The bis-10-ethylurethanes) formed an ~here-
fore be obtained in a very pure crystalline form (d~gree
of purity at least 95% by weight, preferably at least
97% by weigh~) wi~hout further puri f i ca~ion after cool-
ing of the reac~ion mixture to below 80C (preferablY
below 50C), and op~ionally conc@ntration of th~ re-
action mixture. The high purity produc~ can be isolated
by simple filtration, optionally af~er b~ing washed with
diethylcarbonate. ~he distribution of isomers in ~he
products of the process ~hus obtained
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corresponds substantially to that of the diaminotoluenes used
as the start;ng material. The products of the process are
therefore substantially 2,4-bis-(ethoxycarbonylamino)-toluene
or mixtures thereof with up to 40% by weight, preferably up to
35% by weight, based on the mixture, of 2,6-bis-(ethoxy-
carbonylamino)toluene and have a degree of purity of at least
95% by weight, preferably not less than 97% by we~ght.
The filtrate remaining after separation of the
bis-(ethoxycarbonylamino)-toluene produced by the process of
~he presen~ invention contains mainly diurethanes.
Aminourethanes and other by-products and intermediate
produ~s which can be con~er~ed into diurethane~ by re-
newed reaction wi~h dialkylcarbonates are also present.
The filtrate may also contain small suan~ities of N-
alkylated compounds. The filtrate may be returned to the
process according to ~he in~ention~ optionally after
separation of the alroh~l formed in ~he reaction and
optionally af~er separa~ion of part of the N-alkylated
by-product. Any distillation obtained during ~he
optional concen~ration of ~he reaction mix~ure by
evaporating may also be returned to the process afte~
separation of the alcohol formed in the reaction.
The process of the present invention may be carried out
continuously or discontinuously.
The urethanes prepared by the process of the present
invention may be used to produce the corresponding isocyanates
without further working up. The urethanes may be converted into
the corresponding isocyanates and alcohols by thermal
decomposition and the resulting products of decomposition
subsequently separated.
The process of the present invention is illustrated in
more detail with the aid of the following Examples. All
percentages are based on weight.
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EXAMPLES
Example 1
A mixture of 48.8 9 (0.4 mol) of 2,4-diaminotoluene, 1890
9 (16 mol) of diethylcarbonate (corresponding to a molar ratio
of amino groups to carbonate of 1:20) and 3.6 9 of a catalyst
solution made up of a mixture of lead salts of 2-ethylhexanoic
and isononanoic acid dissolved in m;neral spirits (lead content
of the solution 24%) was heated to 200C in a 3 liter
autoclave. The reaction was stopped after 2 hours by cooling
the reaction mixture to 254C. The reaction mixture was
concentrated by evaporation in a water jet vacuum. The solid
which precipitated was filtered off, washed with 50 ml of
diethylcarbonate and dried. 75.7 9 of 2,4-bis-(ethoxycarbonyl-
amino)-toluene (purity 98%, melting point 133C) were obtained.
This corresponds to a yield of 71% of the theoretical yield.
The yield of isolated 2,4-bis-(ethoxycarbonylamino)-toluene may
be increased to about 95% of the theoretical by returning the
filtrates to the reaction vessel for further reaction.
Example 2
A mixture of 48.8 g (0.4 mol) of diaminotoluene
(commercial mixture of 2,4- and 2,6-isomers in a ratio by
weight of 65:35), 1890 9 (16 mol) of diethylcarbonate and 3.6 9
of the catalyst solution described in Example 1 was heated to
200C in a 3-liter autoclave. The reaction was stopped after 4
hours by cooling the reaction mixture to 25~C. The reaction
mixture was concentrated by evaporation in a water jet vacuum.
The precipitated solid was filtered off, washed with gO ml of
diethylcarbonate and dried. 63.2 9 of 2,4-/2,6-bis-(ethoxy-
carbonylamino)-toluene were obtained (2,6-isomer content 32X).
This corresponds to a yield of 59% of the theoretical yield.
The yield of isolated 2,4-12,6-bis-(ethoxycarbonylamino~-
toluene may be increased to more than 90% of the theoretical
yield by returning the filtrates to the reaction vessel for
further react;on.
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Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be
understood that such deta;l is solely for that purpose and tha$
variations can be made therein by those skilled in the art
without departing from $he spirit and scope of the invention
except as it may be limited by the claims.
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