Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2002-08-20
2004-04-13
O Sullivan, Peter G (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C560S347000, C564S330000, C564S307000
Reexamination Certificate
active
06720455
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for the production of polyamines of the diphenylmethane series and to a process for the production of polyisocyanates of the diphenylmethane series with a reduced color value. These polyisocyanates are obtained by reacting the corresponding polyamines of the diphenylmethane series with phosgene.
Polyisocyanates of the diphenylmethane series are understood to mean isocyanates and mixtures of isocyanates of the following type:
Similarly, polyamines of the diphenylmethane series are understood to mean compounds and mixtures of compounds of the following type:
The industrial production of isocyanates by the reaction of amines with phosgene in solvents is known and is described in detail in the literature (See, e.g., Ullmanns Enzyklopädie der technischen Chemie, 4
th
edition, volume 13, pages 347-357, Verlag Chemie GmbH, Weinheim, 1977.). Based on this process, a mixture of polyisocyanates is produced. Such polyisocyanates are used as the polyisocyanate component in the production of polyurethane foams and other polyurethane plastics produced by the polyaddition process.
It is generally known that undesirable coloring components are also formed in this process. These coloring components are retained upon processing to produce polyurethane foams or other polyurethane plastics. Although the inherent color of the polyisocyanate polyaddition products does not have a negative effect on their mechanical properties, substantially colorless products are desired by the consumer. The absorbance at different wavelengths serves as a measure of the discoloration of the polyisocyanate.
For some time, therefore, the reduction of the color values of polyisocyanates of the diphenylmethane series has been the goal of numerous experiments and works that are described in the literature. For example, DE-A1-4208359 describes the treatment of isocyanates with hydrogen in the presence of supported catalysts. DE-A1-4232769 describes the addition of amines, ureas and antioxidants to the isocyanate. DE-A1-19815055 teaches that the color of polyisocyanates of the diphenylmethane series may be improved by irradiation with light over a prolonged period. DE-A1-19804915 describes the brightening of polyisocyanates of the diphenylmethane series by a complicated time- and temperature-stepped addition of formaldehyde to the polyamine step to produce an amine which is then converted to the desired isocyanate by phosgenation.
A disadvantage of all of these procedures is that they are technically complex and/or require the use of non-isocyanate auxiliary substances or are of low efficiency.
SUMMARY OF THE INVENTION
The object of the present invention was therefore to provide a technically simple and safe process for the production of polyisocyanates of the diphenylmethane series with low color values.
The object of the present invention was also to provide a simple process for the production of polyamines of the diphenylmethane series from which polyisocyanates of the diphenylmethane series with low color values can be produced by phosgenation.
These objects are achieved by
a) reacting aniline and formaldehyde in the presence of an acidic catalyst to produce a polyamine, and
b) neutralizing the reaction mixture from step a) with a base either at a temperature of more than 110° C. or by neutralizing the reaction mixture from step a) and heating the neutralized reaction mixture to a temperature of more than 110° C. after neutralization.
These objects are also achieved by a process for the production of polyisocyanates of the diphenylmethane series in which
a) aniline and formaldehyde are reacted in the presence of an acidic catalyst to produce a polyamine,
b) the reaction mixture from step a) is neutralized with a base either at a temperature of more than 110° C. or the reaction mixture from step a) is neutralized and then heated to a temperature of more than 110° C. after neutralization, and
c) phosgenating the polyamine produced in b) is phosenated to produce the corresponding polyisocyanate.
DETAILED DESCRIPTION OF THE INVENTION
The processes for the production of polyamines and polyisocyanates in accordance with the present invention can be carried out both continuously and non-continuously.
Polyisocyanates with low color values can be produced by the process according to the invention. Color value here is understood to mean the measured absorbance of a solution of polyisocyanate in monochlorobenzene, containing 2 wt. % polyisocyanate, in a layer thickness of 10 mm and at room temperature, against monochlorobenzene at defined wavelengths.
The polyamine or mixture of polyamines of the diphenylmethane series used in the process of the present invention is obtained by condensation of aniline and formaldehyde in the presence of an acidic catalyst. (See, e.g., H. J. Twitcheft, Chem. Soc. Rev. 3(2), 209 (1974), W. M. Moore in: Kirk-Othmer Encycl. Chem. Technol., 3
rd
ed., New York, 2, 338-348 (1978).) It is of no importance to the process of the present invention whether aniline and formaldehyde are first mixed in the absence of the acidic catalyst and the acidic catalyst is then added or whether a mixture of aniline and acidic catalyst is reacted with formaldehyde.
Suitable polyamines and mixtures of polyamines of the diphenylmethane series are conventionally obtained by condensation of aniline and formaldehyde in a molar ratio of aniline to formaldehyde of from 20 to 1.6, preferably from 10 to 1.8, and a molar ratio of aniline to acidic catalyst of from 20 to 1, preferably from 10 to 2.
Formaldehyde is conventionally used in industry as an aqueous solution. However, other compounds providing methylene groups can also be used, such as e.g. polyoxymethylene glycol, para-formaldehyde or trioxane.
Strong organic and preferably inorganic acids have proven suitable as acidic catalysts. Examples of suitable acids are hydrochloric acid, sulfuric acid, phosphoric acid and methanesulfonic acid. Hydrochloric acid is preferably used.
In a preferred embodiment of the process, aniline and acidic catalyst are first combined. In another step, this mixture is mixed with formaldehyde in a suitable manner at temperatures between 20° C. and 100° C., preferably at 30° C. to 70° C., optionally after dissipation of heat, and then subjected to a preliminary reaction in a suitable residence-time apparatus. The preliminary reaction takes place at temperatures between 20° C. and 100° C., preferably in the temperature range of from 30° C. to 80° C. Following the mixing and preliminary reaction, the temperature of the reaction mixture is brought, stepwise or continuously and optionally under excess pressure, to a temperature of from 100° C. to 250° C., preferably from 100° C. to 180° C., most preferably to a temperature of from 100° C. to 160° C.
In another embodiment of the process, however, it is also possible to mix aniline and formaldehyde first in the absence of the acidic catalyst at a temperature in the range of from 5° C. to 130° C., preferably from 40° C. to 100° C., most preferably from 60° C. to 85° C., and to react them. This leads to the formation of condensation products of aniline and formaldehyde (a so-called “aminal”). Following the aminal formation, water present in the reaction mixture can be removed by phase separation or other appropriate process steps, e.g. by distillation. The condensation product is then mixed with the acidic catalyst in a suitable manner in another process step and subjected to a preliminary reaction in a residence-time apparatus at a temperature of from 20° C. to 100° C., preferably from 30° C. to 80° C. The temperature of the reaction mixture is then brought, stepwise or continuously and optionally under excess pressure, to a temperature of from 100° C. to 250° C., preferably from 100° C. to 180° C., most preferably to a temperature of from 100° C. to 160° C.
The reaction of aniline and formaldehyde in the presence of an acidic catalyst to produce a polyamine of the diphenylmethane series can take place in the presence of other substances
Hagen Torsten
Kämper Friedhelm
Koch Daniel
Müller Heinz-Herbert
Bayer Aktiengesellschaft
Gil Joseph C.
O Sullivan Peter G
Whalen Lyndanne M.
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