Note: Descriptions are shown in the official language in which they were submitted.
116~5~
- ~5o-2239
LeA 20, 581
--1--
PROCESS FOR THE PRODUCTION OF N- AND O-
SUBSTITUTED MONO- OR BIS-URETHANES AND THE
USE THEREOF AS STARTING MATERIAL FOR THE
_ . _
PRODUCTION OF ALIPHATIC ISOCYANATES
5BACKGROUND OF THE INVENTION
.
This invention relates to a new process for
the production of mono- and bis-urethanes aliphatically
substituted on the nitrogen and oxygen by transesteri-
fying the corresponding 0-(2-hydroxyalkyl)-substituted
10 urethanes using high-boiling, primary monohydric alco-
hols or using dihydric aliphatic alcohols containing
primary hydroxyl groups which are not arranged in the
2-position to one another, and to the use of the pro-
ducts obtained by this process as starting materials
15 for the production of organic isocyanates.
` It is known that primary amines containing
aliphatically- or cycloaliphatically-bound amino
groups react with glycol carbonate to form the corres-
ponding N-substituted carbamic acid-~-hydroxy ethyl
20 esters in a substantially quantitative yield in accord-
ance with the following equation:
CH2- 2
O O + R-NH2 R-NH-CO-O-CH2-CH2-OH
CO
The ethylene glycol carbonate used, which
may even be replaced in the reaction, for example, by
propylene glycol carbonate, may in turn be readily
30 obtained in known manner from inexpensive, industri-
ally used starting materials (carbon dioxide and
Mo-2239
LeA 20,581
65~)
ethylene (or propylene) oxide) in accordance with the
following equation:
C2 + CH ~ / CH2 ~ CH2 - f~2
O O O
\CO/
Accordingly, it is possible to produce a variety of
N-substituted carbamic acid-~-hydroxyalkyl esters from
the simple, industrially used starting materials men-
tioned above, depending on the type of primary amine
used. The idea of using these reaction steps for the
phosgene-free production of organic isocyanates,`par-
ticularly containing aliphaticaIly-bound isocyanàte
groups, is frustrated by the fact that the carbamic
acid-~-hydroxyalkyl esters mentioned cannot be thermal-
ly split into the isocyanate and the glycol on which
they are based.
Accordingly, an object of the present inven-
tion is to provide a process by which the carbamic
acid-~-hydroxyalkyl esters, which cannot be split into
isocyanates and glycol, may be converted into carbamic
acid esters of the type which are susceptible to
thermal splitting with formation of the isocyanate
on which they are based.
DESCRIPTION OF THE INVENTION
According to the present invention, this
object is achieved by transesterifying the above-
mentioned carbamic acid-~-hydroxyalkyl esters using
certain alcohols described in more detail below in
the presence of certain catalysts, the reaction being
Mo-2239
LeA 20,581
65~)
--3--
accompanied by liberation of the glycols on which the
carbamic acid esters are ~ased.
The transesterification of carbamic acid
esters using higher alcohols is known. According to
German Patent 565,319 the reaction is carried out
at temperatures of from 190 to 230C using sodium
metal or alcoholate as catalyst. According to U.S.
Patent 2,934,559, bis-carbamic acid ester may be
produced from carbamic acid esters and alkane diols
using aluminum alcoholates as catalysts. Furthermore,
German Offenlegungsschrift 2,655,741 describes the
production of carbamic acid esters based on relatively
high-boiling alcohols by the transe~terification of
carbamic acid esters based on low-boiling alcohols
using relatively high-boiling alcohols in the presence
o~ titanium alcoholates as catalysts.
In all these known processes, carbamic acid
esters, i.e. urethanes unsubstituted on the nitrogen,
are used. Obviously, the transesterification of
N-substituted carbamic acid-~-hydroxyphenyl esters
cannot be compared with the known processes. This
may be explained, on the one hand, by the substitution
on the nitrogen and, on the other hand, by the greater
sensitivity thereof to thermal degradation, because
carbon dioxide and water are readily eliminated at
temperatures above 60C, amines and oxazolinones
being formed. Thus, it is not surprising that the
hitherto proposed catalysts are either ineffective
(aluminum alcoholates) or do not provide for a smooth
reaction i.e. optimal yields (sodium alcoholate or
titanium tetrabutylate).
It has now surprisingly been found that
Mo-223g
LeA 20,581
650
--4--
N-substituted carbamic acid-~-hydroxyalkyl esters may
be successfully transesterified using relatively
high-boiling alcohols, accompanied by liberation of
the glycols on which the starting materials are based,
providing the reaction is carried out in the presence
of the catalysts according to the present in~ention
which are described in more detail below.
Accordingly, the present invention reIates
to a process for the production of N- and O-substituted
mono- or bis-urethanes, characterized in ~hat urethanes
corresponding to the following general formula:
Rl(-NH-CO-O-R )n
wherein
Rl represents either an n-functional, aliphatic Cl-C6
hydrocarbon radical optionally containing ether
bridges or an n-functional cycloaliphatic C6-C13
hydrocarbon radical; R2 represents a hydroxy alkyl
group containing 2 or 3 carbon atoms, 2 carbon atoms
being arranged between the oxygen atom of the hydroxyl
group and the oxygen atom of the urethane group; and
n represents 1 or 2; are subjected to a transesterifi-
cation reaction using alcohols containing only primary
hydroxyl groups and corresponding to the following
general ormula:
R -(OH)m
wherein
R3 represents (a) a monofunctional (m = 1), linear or
branched, saturated, aliphatic C8-C18 hydrocarbon
radical optionally containing ether bridges, (b) a
monofunctional (m = 1), araliphatic C8-C15 hydrocarbon
radical or (c) a difunctional (m = 2), linear or
Mo-2239
LeA 20,581
5U
--5--
branched, saturated, aliphatic C3-C18 hydrocarbon
radical optionally containin~ ether bridges, in
which at least three carbon atoms are arranged between
two hydroxyl groups; and m represents 1 or 2, with'the
5 proviso that not both m and n represent 2; '
in the presence of ca'talysts selected from:
(i) thallium oxides,,thallium hydroxides, thallium
salts of organic acids,,thallium salts of weak inorganic
acids and organic complex compounds of monovalent thal-
lium and (ii) salts of organic acids of divalent and
tetravalent tin and organic compounds of tetravalent tin
~ith organic radicals which are not bound like salts, the
reaction being accompanied by the eIimination of alcohols
corresponding to the following general formula:
R -OH.
The present invention also reIates to the
use of the products obtained by the proces's according
to the present invention as starting materials in the
production of organic isocyanates.
Starting material for the process according
to the present invention are carbamic acid esters
corresponding to the following general formula:
Rl(-NH-CO-O-R2)n
and alcohols containing only primary hydroxyl groups
corresponding to the' following general formula:
R3(-OH)m.
In thése general formulae,,Rl, R2, R3, m and n are
as defined above. Preferably,,
R represent9 a saturated, unsubstituted aliphatic
hydrocarbon radical containing from 1 to 6 carbon atoms;
Mo-2239
Le'A 20,'581
~, I
--6--
R2 represents a 2-hydroxy propyl or a hydroxy ethyl
radical, particularly a hydroxy ethyl radical;
R3 represents a saturated, unsubstituted, aliphatic
hydrocarbon radical containing from 8 to 18, more
particularly from 10 to 14, carbon atoms; and
m and n each represent 1.
As mentioned above, the N-substituted carbamic
acid-~-hydroxyalkyl esters used in the process accora-
~ng to the present invention are obtained in known
manner by reacting the corresponding glycol carbonates
with the corresponding amines.
Glycol carbonates suitable for this purpose
are, in particular, propylene glycol carbonate and
ethylene glycol carbonate. Ethylene glycol carbonate
is the preferred starting material. The glycol car-
bonates are in turn formed by reacting the alkylene
oxides on which they are based with carbon dioxide.
Suitable amines are compounds corresponding
to the following general formula:
Rl(-NH2)n .
Typical examples of suitable amines are methylamine,
ethylamine, n-propylamine, isopropylamine, n-butyla-
mine, isobutylamine, n-pentylamine, n-hexylamine,
cyclohexylamine, ethylene diamine, tetramethylene
diamine, hexamethylene diamine, 4,4'-diaminodicyclo-
hexyl methane or isophorone diamine.
Alcohols suitable for use in the process
according to the present invention are, in principle,
any monohydric and dihydric alcohols which contain
only primary hydroxyl groups, in which there are no
hydroxyl groups in the ~-position to one another and
which have a boiling point at normal pressure at most
Mo-2239
LeA 20,581
~ ~it;65(~
lO C below the boiling point of the glycol formed
during the reaction according to the present invention.
It is preferred to use alcohols having a boiling point
at normal pressure at least as high as the boiling
point of the glycol to be eliminated. Alcohols having
boiling points at normal pressure at least lO C above
the boiling point of the ~lycols to be eliminated are
particularly preferred. Typical examples of suitable
alcohols inclùde octanol, nonanol, decanol, undecanol,
n dodecanol, or stearyl alcohol ~ach o~ 'chese alcohols having
either a linear or a branched carbon chain, 2-phenyl ~thanol,
. .
also dihydric alcohols, such as l,4-butane diol or
l,6-hexane diol. In principle, it is, of course, also
possible to use alcohols containing ether groups, such
as oxylation products of monohydric alcohols, such as
methanol, ethanol or ethylene glycol, providing the
conditions mentioned above regarding the boiling
point are observed. It is also possible in principle
to use higher than dihydric alcohols, such as trimethy-
lol propane
Catalysts suitable for use in the processaccording to the present invention include for example,
dibutyl tin oxide, dibutyl tin dilaurate, dimethoxy
dibutyl tin, ethyl tin tri-iso-octylate, tin dilaurate
and tin acetate; thallium hydroxide, thallium oxide,
thallium carbonate, thallium acetate, thallium octoate,
thallium naphthenate, thallium benzoate or organic
complex compounds of monovalent thallium, particularly
those based on cyclopentadiene and soluble thallium
salts.
The catalysts are used in quantities of from
O.OOl to 1%, preferably from O.Ol to 0.5%, based on
the reaction mixture.
Mo-2239
LeA 20,581
116f;65()
The reaction temperatures are from 100 to
180C, preferably from 120 to 150C.
In the interests of substantially quantitative
transesterification, it is preferred to use the alcohols
in at least equivalent quantities, based on the urethane
groups in the carbamic acid ester to be transesteri-
fied. The alcohol is pre~erably used in from 1.2 to
lO times, more particularly from 1.5 to 5 times, the
equivalent quantity. Where polyhydric alcohols are
10 used, however, it is pre~erred to use only equivalent
quantities of the reactants so that products free from
hydroxyl groups are formed. Separation of the glycol
formed during the reaction according to the present
invention may be facilitated by the simultaneous use
15 of entraining agents, such as xylene, ethyl bezene
or cumene.
To carry out the process according to the
present invention, the reactants are heated together
with the catalyst to the reaction temperature,
20 preferably in vacuo, and the glycol formed (R2-OX) is
continuously distilled off, for example through a
distillation column. Where alcohols having a boiling
point corresponding to, or up to 10 C below, the
boiling point of the glycol are used, the glycol may
25 be separated off in admixture with co-distilling
alcohol present in excess.
If the products of the transesterification
reaction are to be distilled, it is frequently pre-
ferred to remove the transesterification catalyst by
30 treatment with an ion exchanger, such as an acid-
activated Fuller's earth or a sulphonated cross-linked
polystyrene, in order to avoid decomposition.
Mo-2239
LeA 20,581
11f~ti6S()
g
The urethanes corresponding to the following
general formulae:
R (-NH-CO-O-R )n and (R1-NH-CO-O~R
which accumulate as residue in the reaction according
to the present invention may be thermally split in
known manner into the isocyanate on which they are
~ased and which corresponds to the following general
formula:
R tNCO)n
and into the alcohols on which they are based and which
correspond to the following general formula~
R ~OH)m
after the removal of any excess alcohol still present
or after they have been purified by distillation.
The thermal splitting process may even be carried out
in the presence of suitable catalysts. Suitable
catalysts are solids, such as aluminum oxide, silicon
dioxide, kieselguhr, kaolin, talcum, aluminum powder,
iron powder and pumice stone impregnated with small
quantities of substances, such as antimony trioxide,
iron oxide or vanadium oxide.
The urethanes are preferably passed through
a hot reaction zone, a certain splitting rate being
obtained depending on the temperature and the residence
time. The isocyanates and the higher alcohols are
separated by distillation from the unreacted starting
material which is returned to the splitting process.
The splitting temperatures are generally from
280 to 350C.
The percentages ~uoted in the following
Examples represent percent, by weight.
Mo-2239
LeA 20,581
i6S~)
--10--
ExAMæLEs
Production of the N-alkyl carbamic acid-~-hydroxyethyl
esters
EXAMPLE 1
780 g of a 40% aqueous methylamine solution
(10 moles) are added dropwise with cooling at from
35 to 70C to 800 g (10 moles) of glycol carbonate.
The water is removed at 90C/20 Torr and the residue
is distilled. 1153 g (97~ of the theoretical yield)
of N-methyl carbamic acid-~-hydroxyethyl ester
distilled over at 104-106C/0.6 Torr.
EXAMPLE 2
116 g (1 mole) of hexamethylene diamine are
added dropwise with cooling at from 70 to 80C to
176 g (2 moles) of glycol carbonate. The N, N'-
hexamethylene-bis-carbamic acid-~-hydroxyethyl ester
immediately crystallizes out. Melting point: 89-90C.
Yield: quantitative.
EXAMPLE 3
99 g (1 mole) of cyclohexylamine are added
dropwise at rom 70 to 100C to 88 g (1 mole) of
glycol carbonate. The N-cyclohexyl carbamic acid-~-
hydroxyethyl ester solidifies in crystalline form
on cooling. Melting point: 65-66C. Yield: quanti-
tative.
Production of the N-alkyl carbamic acid alkyl esters
EXAMPLE 4
119 g (1 mole) of N-methyl-~-hydroxyethyl
urethane, 270 g (1.5 moles) of l-dodecanol and 1 g of
dimethoxy dibutyl tin are heated to 140C under 12
Torr in a 40 cm packed column, whilst a two phase
mixture of glycol and a little dodecanol distills of
overhead at from 100 to 103C. After 6 hours, 66 g of
Mo-2239
LeA 20,581
i6SO
--11--
- distillate containing substantially the calcuIated
amount of glycol has been separated off. The residual
excess dodecanol is distilled off at 60-74C/0.1
Torr (87 g), leaving 242 g of residue. 235 g of
crystals melting at 54C precipitate from a solution
of the residue in ligroin. Yield of N-methyl dodecyl
urethane: 97~ of the ~leoretical yield.
EXAMPLE 5
The procedure is as described in Example 4,
except that 0.5 g of ethyl tin-tri-iso-octylate is
used instead of dimethoxy dibutyl tin. After 4.5
nours, 65 g of distillate have been separated off at
a reaction temperature of 130C. After the excess
dodecanol has been distilled off, 238 g of crude
product are obtained. 231 g (= 95~ of the theoretical
yield) of pure product are recovered therefrom by
distillation.
EXAM2LE 6
The procedure is as described in Example 4.
0.1 g of thallium carbonate is used as catalyst. The
reaction temperature is 140C and the reaction time 7
hours. The distillate weighs 71 g and the crude
product 204 g. To remove the catalyst, it is treated
with 10 g of acid-activated Fuller's earth at 100C,
filtered and distilled. 175 g (72~ of the theoretical
yield) of pure product distill over at 112C/0.06 Torr.
EXAMPLE 7
119 g (1 mole) of N-methyl-~-hydroxyethyl
urethane, 316 g (2 moles) of l-decanol and 0.1 g of
thallium carbonate are reacted in the same way as in
Example 4. After 4 hours 125 g of distillate have
been separated off. According to fractional distilla-
tion, the distillate contains 62 g of glycol and 63 g
Mo-2239
LeA 20,581
5~
-12
of decanol. The residue after removal of the remaining
decanol by distillation weighs 216 g. The catalyst
is removed in the same way as in Example 6 and the
reaction product is distilled giving 192 g (88~ of the
theoretical yield) of N-methyl decyl urethane at
95-97C~0.05 Torr. Melting Point: 46C.
EXAMPLE 8
146 g (0.05 mole) of N,N'-hexamethylene-bis-
~-hydroxy ethyl urethane, 465 g (3.5 moles) of dodeca-
nol and 100 mg of thallium oxide are reacted in thesame way as in Example 4. After 5 hours, 76 g of dis-
tillate have been separated off at 90-95C/8 Torr.
The residue is treated with 20 g of acid-activated
Fuller's earth and the unreacted dodecanol (259 g)
is distilled off from the catalyst-free reaction pro-
duct. The crystallized N,N-hexamethylene-bis-dodecyl
urethane i5 left behind as residue. Melting point:
111-112C. Yield: 266 g (98% of the theoretical
yield).
EXAMPLE 9
72 g (0.2 mole) of dicyclohexyl methane-
bis-~-hexylethyl urethane, produced from the 4,4'-
diaminodicyclohexyl methane isomer mixture, 167 g
(0.9 mole) of dodecanol and 0.5 g of dibutyl tin
dilaurate are reacted in the same way as in Example
4. After 5 hours, 28 g of distillate, mainly glycol,
have been separated off. Removal of the excess
dodecanol bY distillation at 77-80C/0.04 Torr leaves
120 g of residue. Yield of N,N'-methylene dicyclo-
hexyl-bis-dodecyl urethane: 98% o~ the theoretical
yield. Melting point (from methanol): 116-127~C.
EXAMPLE 10
59.5 g (0.5 mole) of N-methyl-~-hydroxy-
ethyl urethane, 118 g (1 mole) of 1,6-hexane diol and
Mo-2239
LeA 20,581
-13-
2 g of dibutyl tin oxide are maintained at 125-140C/
0.1 Torr in a 40 cm packed column. After 4 hours, 32
g of glycol have distilled off overhead. The excess
hexane diol is removed from the reaction product at
88-92C/0.04 Torr. 56 g of residue are obtained.
The N,N'-dimethyl hexamethylene bis-urethane is
recrystallized from toluene. Melting point: 124-126C.
Production of isocyanates by splitting urethanes
EXAMPLE ll
30 g of N-methyl carbamic acid dodecyl ester
are added dropwise over a period of 1.5 hours through
a dropping funnel to a flask containing 5 g of
kieselguhr and preheated to 300C by means of a metal
bath, whilst the products formed by splitting, which
15 distill over at from 210 to 220C, are collected in
an ice-cooled receiver filled with chlorobenzene~ The
content of methyl isocyanate is determined by titration
using dibutylamine: 6.4 g = 90~ of the theoretical
yield~
20 EXAMPLE 12
-
54 g (0.1 mole) of N,N'-hexamethylene-bis-
carbamic acid dodecyl ester are introduced dropwise
over a period of 2 hours under 150 Torr into a flask
preheated to 320C, whilst the products formed by
splitting distill over at from 220 to 240C and are
collected in an ice-cooled receiver. According to
titration using dibutyl amine, the distillate contain
13.5 g (80% of the theoretical yield) of hexamethylene
diisocyanate.
Although the invention has been described
in detail in the foregoing for the purpose of illus-
tration, it is to be understood that such detail is
Mo-2239
LeA 20,581
S()
-14-
solely for that purpose and that variations can be
made therein by those skilled in the art without
departing from the spirit and scope of the invention
except as it may be limited by the claims.
Mo-2239
LeA 20,581
