DE2108462A1 - Process for the preparation of bis (4-aminophenyl) methane - Google Patents

Description

Magyar Tudomanyos Akademia, Budapest / Hungary

METHOD FOR PRODUCING BIS- (4-AMINO-PHENYi.) - MBTHiH

Numerous processes are known from the literature for the preparation of bis (4-aminophenyl) ethane (J. Ohem. Soc. 117, 988 (1920)), French patent specifications 1 · 355 · 124 and 1,398,419, German patent specification .1.205 975. For industrial purposes, processes based on reactions catalyzed with mineral acid, preferably with hydrochloric acid, are used almost exclusively, in that aniline and formaldehyde are used as starting materials.

The increased diphenylmethane diisocyanate requirement due to the widespread distribution of hard polyurethane trees

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gave another occasion "to work out new processes aimed at producing the starting material of the last-mentioned compound, ie bis- (4-aminophenyl) methane (British patents 1.Ö64.559, 1.092.019 and 1.107.480, USA patents 2,683,730 and 3,253,031, Belgian patent 639,351, OSR patent 118,745, J, Org. Chem., 19, 1862 (1954) J Zh. Obsch. Him. 21 * 775 (1957), Neftekhimia II.4 624 (1962)).

Although there are differences between the known methods, they have the following identical features:

1) the mixture of hydrochloric acid and aniline-formaldehyde gradually, slowly added generally at a temperature below 5O ⁰ C, preferably between 0 and 20 ⁰ C;

2) the reaction mixture is then ^{heated to the reaction temperature of 80-100 0} C;

3) the reaction time is generally 4-6 hours, but at least 3 hours;

4) the molar ratio of aniline mineral acid is im

general 3si »exceeds this at least Value

5) According to some procedures, this becomes unreacted aniline removed by steam distillation, since it requires expensive equipment in large-scale operations and dae Creates a considerable amount of wastewater that is difficult to clean;

6) if the procedure is carried out in a large company iet the space and equipment requirements are large.

The product produced according to the known process (J. Chem. Soc. 117. 988 (1920); French patent specification 1.335.125 and 1.398.419, German patent specification 1.2o5.975, Neftekhiraia II.4.624 (1962)) contains im general

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mean 4Ο ~ 6Ο $ polymer, vr- is limited by the further application of the product σ or an expensive cleaning by vacuum distillation at a temperature of 165-168 ⁰ C, and 0.1 Hgmm pressure is required.

The mechanism of bis (4-aminophenyl) methane formation has been investigated by several (J. Org. Chem. 19 , 1862 (1954); Meftekhimia II.4 624 (1962); Zh. Obsch. Him. 27, 775 (1957)), but the contradicting results of the investigations did not allow any significant further development of the manufacturing process.

When investigating the reaction mechanism of bis- (4-araino-phenyl) -methane formation, we found that a methylol compound of the formula (I) is obtained in step 1 according to the reaction scheme below

NH ₂ + CH ₂ O

-H2O

N = CH

which is stabilized by loss of water and immediately transformed into a karbenium-imraonium-ion of the formula on the action of acid (II)

H ^-1

N = CH,

NH-CH,

NH = CH,

is converted.

The carbenium ion reacts with aniline in the electrophylene substitution reaction mainly in the p-position _t, whereby the compound of the formula (III) is obtained, but it reacts relatively easily with the bis (4-aminophenyl) methane formed as the end product with the formation of the compound of the formula (IV)

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IT

The N-C bond of the compound of the formula (III) cleaves after heating in an acidic medium, and the resulting bifunctional ion of the formula (?) Occurs repeatedly reacts in para position with aniline, while bis- - Forms (4-araino-bhenyl) methane.

The undesired side reaction which results in the product of the formula (IV) can be avoided by possibly mixing the in the reaction during the course of the synthesis prevents the formation of karbenium ions and the end product, will. Since the formation of the karbenium ion and its reaction with aniline in the para position is relatively quick, and so does the cleavage of the N-C bond of the compound of the formula (III) - whereby the final product is obtained - only takes place after prolonged heating, was by application

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a tubular reactor found the possibility of preventing the undesired side reaction.

In the course of our experiments we have found a very advantageous, continuously feasible process worked out · According to our process, aniline or a mixture of the with Mineral acid formed salt of aniline with the aqueous solution of formaldehyde (or with paraformaldehyde, or · with a formaldehyde-forming compound, e.g. formaldehyde acetal) in a mixing chamber or in one with a pre-picker equipped tubular reactor implemented with such a flow rate that the reverse mixing - and thus the formation of polymers is prevented.

The characteristics of the process according to the invention and thus the differences of the same from the known methods are as followsί

a) In the tubular reactor, the back mismatches - and thus the Reaction of the intermediate substance with the end product - prevented;

b) the response time is different from the previously usual several Hours reduced to 30-40 minutes;

c) the introduction of reaction components takes place simultaneously, at a temperature between 60-90 ⁰ O;

d) by adjusting the proportion of the component and by preventing secondary reactions, the pure blamine content of the product can be increased to 90-95 S * will;

β) the product is reacted with an aniline to the calculated almost theoretical yield of 97-98 <j> recovered and the product may be for the preparation of diphenylmethane diisocyanate directly, without purification, is used;

f) Exceeds the molar ratio of aniline to mineral acid not 1.5: 1;

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g) the unreacted aniline is at a pressure of 15-20 Torr removed from the reaction mixture by vacuum dilution , and the aniline so recovered can be used repeatedly without further purification; h) the space and machine requirements of the present process are minimal.

The implementation of the method according to the present The invention is illustrated using the following exemplary embodiments,

example 1

The device consists of a premixer and an associated double-walled tubular reactor which can be heated with steam. The total volume is 350 ml. Hydrochloric acid prepared solution of 372 g (4 mol) of aniline and at the same time 92 ml of a 37% formaldehyde solution (1.24 mol) introduced. The temperature is maintained in the pre-mixer at 60-65 C »in the reactor at 90 ⁰ C. The mixture is kept in the premiecher for 1-2 minutes and in the reactor for 28 minutes. The mixture emerging from the reactor is mixed with 250 ml of 35% sodium hydroxide solution per hour, and the aqueous and oily phases are separated from one another. 153 g of aniline are recovered from the oily phase by distillation. The hourly capacity of the device is 225-230 g of crude bis (4-aminophenyl) methane, which contains 90-92 1 » diamine and 8-10 % polyamine, yield calculated on aniline 96» 5 - 98 ° C Conversion to aniline calculated 59 J *

The raw product can be used to make diphenylmethane diisocyanate can be used without cleaning.

Example 2

When carrying out the reaction according to Example 1

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with a paraformaldehyde suspension, with an aniline-formaldehyde molar ratio of 1: 0.2, and with an aniline conversion of 70 years, a mixture with a yield of 97.5 # recovered which contains 76 # diamine and 24 # poliamine.

Example 3

The device consists of a mixing chamber of small dimensions, in which the component with a pressure τοη 2.5 atm. are introduced, and from a connected heatable tubular reactor, the total volume is 1000 ml.

A preheated solution of 1860 g of aniline, which is dissolved in 1100 ml of hydrochloric acid with a spec. Weight of 1.18 was prepared and at the same time 460 ml / hour of a 37 # strength formaldehyde solution was introduced. The molar ratio of aniline: formaldehyde is 1: 0.29. The temperature of the premixer and of the tubular reactor is equally wet at 80 ^° C. The reaction mixture stays in the tubular reactor for 40 minutes. 1000 ml / hour of a 40% sodium hydroxide solution are added to the reaction mixture in a stirred vessel, and the organic phase is continuously separated off. The aniline is distilled off therefrom in vacuo.

1200 g of crude bis (4-aminophenyl) methane are obtained per hour, which has a diamine content of 87-88 μl and a polyamine content of 12-13 μl. Yield to the aniline calculated 96-97 Ί * conversion to the aniline 60 calculates i "■

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Claims (2)

PATENT CLAIMS 1. A process for the preparation of bis- (4-amino-phenyl) -methane, characterized in that aniline and the mixture of the salt of aniline formed with mineral acid with the aqueous solution of formaldehyde or with paraformaldehyde, or with a Formaldehyde-forming compound reacted in a tubular reactor, in continuous operation, at a temperature between 60-9O ⁰ C, under atmospheric or a pressure exceeding this, the reaction mixture obtained is treated with the aqueous solution of an alkali hydroxide, and the unreacted aniline is removed by vacuum distillation . 2. The method according to claim 1, characterized in, that hydrochloric acid is advantageously used as the mineral acid. 109838 / 1G89