DE3202687A1 - Process for the preparation of methylenebisphenylcarbamic esters and polymethylenepolyphenylcarbamic esters - Google Patents

Abstract

Process for the preparation of methylenebisphenylcarbamic esters and polymethylenepolyphenylcarbamic esters by reaction of N-phenylcarbamic esters with formaldehyde in a methanolic solution and removal of the methanol from the reaction mixture during the course of the reaction by distillation.

Description

process for the production of methylene-bis-phenylcarbamine

acid esters and polymethylene polyphenylcarbamic acid esters This invention relates to a new process for the preparation of methylene-bis-phenylcarbamic acid esters and polymethylene polyphenylcarbamic acid esters by reacting N-phenylcarbamic acid esters with a methanolic formaldehyde solution in the presence of strong acids.

Methylene-bis-phenylcarbamic acid esters and higher ones derived therefrom Homologues are valuable starting materials for the production of methylene-bis-phenyl isocyanates and the corresponding polymethylene polyphenyl isocyanates known for the Find the production of polyurethanes use (DE-OS 26 35 490). The ones in the trade available isocyanates of the type mentioned are generally obtained by phosgenation of the in the condensation of aniline with formaldehyde in the presence of aqueous acids available amines produced, This production method has the disadvantage that the use of the highly toxic phosgene is an expensive one for safety reasons Technology requires. In addition, the environment is created by the separation of the individual On the one hand, conversions are required and, on the other hand, they are incurred as by-products Acids heavily loaded.

The acid alysierte condensation of N-Phenylcarbaminsäureeste e with Formaldehyde to the corresponding? Olymë'hylen ffi phenylcarbaminsSureestern is in itself for a long time b a Fnt.

This condensation is, for example, according to the information in US Pat. No. 2 X -768 in the presence of aqueous acids rfrt. Thereby are condensation products obtained, which still contain N-benzyl compounds, which by an expensive Acid-catalyzed rearrangement converted into the desired polycarbamic acid ester (U.S. Patent 4,146,727). U.S. Patent 4,162,362 teaches a one-step condensation process described using very strong acids.

What these known processes have in common is that they contain polycarbamic acid esters of the diphenylmethane series, which contain methyl n-bis-diphenylcarbamic acid esters from 20 to 85% by weight, the ratio between the 4,4'- and 2,4'-isomers is generally 4: 1 (EP-PS 16 441, page 2, lines 22 to 26).

Recently, however, it has been shown that polyisocyanates of the diphenylmethane series with a high ortho-isomeric content has a number of advantages over the conventional polyisocyanates with a high content of methylene bis (4-phenyl isocyanate) own. For example, they are liquid and therefore easier to handle and more storage-stable and can be used in many new areas (DE-OS 29 30 411, EP-PS 3 303, DE-OS 19 37 685).

Since these sought-after polyisocyanates so far only after the conventional Environmentally harmful phosgene processes are produced (DE-OS 29 30 411), was after to look for a more advantageous process that also allows polycarbamic acid esters the diphenylmethane series with a high content of ortho isomers.

It has now been found that in the preparation of methylene-bis-phenylcarbamic acid esters and polymethylene polyphenylcarbamic acid esters by reacting -? henyi carbamic acid esters with formaldehyde in the presence of a strong acid the carbamic acid esters mentioned with a high proportion of methylene-bis-phenylcarbamic acid esters and the corresponding 2,4'-isomers are obtained when the formaldehyde is used in a methanolic solution and the methanol is distilled off from the reaction mixture in the course of the reaction.

In the event that methylene-bis-phenylcarbamic acid methyl ester is formed, the reaction scheme can be represented by the following formulas: Examples of N-phenylcarbamic acid esters are compounds of the formula into consideration, in the R z.3. denotes an alkyl radical having 1 to 4 carbon atoms and the phenyl radical can be substituted in the o and / or m positions by methyl or methoxy groups or by halogen atoms such as chlorine or bromine atoms.

suitable N-phenylcarbamic acid esters are, for example -phenylcarbamic acid methyl-, ethyl or propyl ester, N-o-tolylcarbamic acid methyl or ethyl ester, N-2,6-dimethylphenylcarbamic acid ethyl ester or ethyl N-o-chlorophenylcarbamate.

The molar ratio of formaldehyde: carbamic acid ester is general at 1: 0> 5 to 1:10, preferably 1: 1.5 to 1: 3 To prepare methylene-bis-phenylcarbamic acid esters, the ratio is set to be zwecX-wise to 1: 4 to 1: Q.

The acids are practically all strong acids, such as sulfuric acid, Methanesulfonic acid, toluenesulfonic acid or trifluoromethanesulfonic acid are suitable. Strongly acidic organic cation exchangers are particularly advantageous because they are light and can be separated without pollution and without additional treatment can be reused directly. As organic cation exchange resins, the z.3. used in an amount of 5 to 50 parts per mole of N-phenylcarbamic acid ester are, for example, those under the registered trademarks Lewasorb AC-10, Lewatit SPC-103, Amberlyst-15 or Nafion - acid commercially available sulfonic acids Curing resins. These are either in the reaction mixture according to known methods suspended or arranged in a fixed bed.

You can condensation both without and in the presence of an inert Solvents such as toluene, methylcyclohexane, methyl acetate, nitrobenzene, chlorobenzene, Dichlorobenzene or a chlorinated aliphatic hydrocarbon carried out will. In most cases, however, that introduced with the formaldehyde is sufficient Methanol as a solvent.

According to the process of the invention, the formaldehyde is in a methanolic solution used. It is also necessary in the course of implementation distilling off the methanol from the reaction mixture. The methanolic formaldehyde solution has a formaldehyde content of 10 to 40% by weight. The implementation is carried out, for example The starting materials are heated to temperatures of up to 6000 and then continue by heating to temperatures of 100 to 1500C to, with methanol together with the water formed is distilled off.

In detail, one proceeds, for example, in such a way that either a mixture of N-phenylcarbamic acid ester, methanolic formaldehyde solution and ion exchanger heated with stirring to 40 to 60 ° C and 0.1 to 10 hours at this temperature stirs or that one is a mixture of N-phenylcarbamic acid ester and ion exchanger heated to 40 to 6000, the methanolic Formaldehydldsunb continuously within from 0.2 to 2 hours and finally the mixture for 1 to 8 hours at 40 stirs up to 600C. The reaction mixture is then increased to 100 bis with stirring 15,000 heated, at the same time methanol and parts of the condensation water distilled off. For example, hold at 100 to 1500C for 5 to 20 hours and then separate the catalyst off. Possibly excess N-Phenylcarj- 'amic acid ester is removed by distillation. The process product obtainable as a residue can can be used directly to produce the corresponding isocyanates.

Surprisingly, the new process produces polymethylene polyphenylcarbamic acid esters with a high proportion of methylene-bis-phenylcarbamic acid esters and the corresponding 2,4'-IsLmeres obtained. The beneficial result is only achieved if you the methanol is removed by distillation in the course of the reaction If the reaction does not distill off, mixtures are obtained which still contain products of con ensation with C-N linkage and therefore unsuitable for the production of isocyanates are. Another advantage of the process is that the methanolic formaldehyde solution can be produced easily and directly by the dehydrogenation of methanol and that the recovered ethanol can be used directly for formaldehyde recovery can be used.

The condensation can take place either without pressure or under pressure in individual batches or carried out as a continuous process.

Example 1 A tubular reactor was made from 60 liters 84 parts by weight of copper (II) oxide, 11.8 parts by weight of zinc oxide and 4.2 parts by weight of tellurium oxide existing catalyst filled. The reactor was then heated to 5500C and continuously charged hourly with 132 parts by weight of methanol vapor. The reaction mixture was then condensed. 20.2 parts by weight of formaldehyde were obtained per hour.

a stirred reactor was a mixture of 151 parts by weight of N-phenylcarbamic acid methyl ester, 75 parts of a 20% strength by weight methanolic formaldehyde solution, as described above was obtained, and 30 parts by weight of ewatit SPC-108 heated to 500C and 3 hours stirred at 600C. The reaction temperature was then increased to 1200C and at the same time methanol and parts of the condensation water are distilled off. The reaction mixture was stirred for 10 hours at 12,000, then the catalyst was filtered off and excess N-phenylcarbamic acid methyl ester is distilled off in vacuo. One received 123 parts of distillation residue which, according to HPLC analysis, is 80% methylene-bis-phenylcarbamic acid methyl ester with a content of 45% 2,4'-diphenylmethane - dicarbamic acid methyl ester.

qewatit SPC-108 is a commercially available macroporous sulfonic acid Cation exchanger made from styrene-divinylbenzene (8) copolymer with a grain size from 0.3 to 1.5 mm, a total capacity of about 4.2 meq / g dry substance, one Pore surface area of approx. 20 m² / g (according to BET) and an average pore diameter of about 500 i (according to BET).

Example 2 In a RüArreaktor a mixture of 302 parts by weight N-phenylcarbamic acid methyl ester and 50 parts by weight Qewatit SPC-103 heated to 40 ° C. 100 parts by weight of a 15% methanolic formaldehyde solution were then added added dropwise from 0.5 hours. After 5 hours at 40 ° C, the reaction mixture was up 1100C heated and at the same time methanol and parts of the condensation water distilled off. The reaction mixture was stirred at 11,000 for 10 hours, and the catalyst was filtered off and over- 'Schüssiger N-phenylcarbamic acid methyl ester in vacuo distilled off. 145 parts of distillation residue were obtained, which corresponds to the HPCL analysis 89 d methylene-bis-phenylcarbamate with a content of 40% 2,4'-diphenylmethanedicarbamic acid methyl ester.

Example 3 A mixture of 248 parts by weight N-phenylcarbamic acid ethyl ester, 50 parts by weight of a 30% strength methanolic formaldehyde solution and 60 parts by weight of #Lewasorb AC-10 heated to 50PC 0 and 3 hours at this temperature touched. The reaction mixture was then heated to 120 ° C. and simultaneously Methanol and parts of the water of condensation are distilled off. After 10 hours at 1200 the catalyst was separated off and excess N-phenylcarbamic acid ethyl ester separated by distillation in vacuo. 152 parts of distillation residue were obtained, according to the HPCL analysis, 84% methylene-bis-phenylcarbamic acid ethyl ester with a content of 43 "2,4'-diphenylmethanedicarbamic acid ethyl ester.

t ewasorb AC-10 is a commercially available gel-like sulfonic acid Cation exchanger made of styrene-divinylbenzene (8%) - copolymer with a grain size from 0.01 to 0.2 mm and a total capacity of about 4.2 meq / g dry matter.

Example 4 (comparative example) As in Example 3, the Mixture of Ausganbsstoffe heated to 50 ° C and 3 hours at this temperature touched. Then the reaction mixture was under Reflux heated to 8500. After 10 hours the catalyst was separated off and in vacuo distilled. 118 parts of distillation residue were obtained, which corresponds to the HPLC analysis contained 16 C-N linked 2- and 3-core products.

Example 5 (comparative example) The Mixture of the starting materials according to Example 3 heated to 50 ° C and 3 hours stirred at this temperature. The mixture was then increased under its own pressure 120 0C heated. After 10 hours at 1200C, the catalyst was separated off and im Vacuum distilled. 145 parts of distillation residue were obtained, the corresponding the HPLC analysis contained 14 P C-N linked 2- and 3-core products.

Claims (1)

A process for the preparation of methylene-bis-phenylcarbamic acid esters and polymethylene polyphenylcarbamic acid esters by reacting N-phenylcarbamic acid esters with formaldehyde in the presence of a strong acid, characterized in that one the formaldehyde used in a methanolic solution and the methanol in the course the reaction is distilled off from the reaction mixture.