NO782288L - PROCEDURE FOR PREPARING CARBAMATE DERIVATIVES - Google Patents

Description

Method of manufacture of

carbamate derivatives.

The present invention relates to a method for the production of diphenylmethane mono-and-dicarbamate and polymethylene-polyphenyl-carbamate homologues and derivatives thereof, and the distinctive feature of the method according to the invention is that an (alkoxycarbonyl)-phenylaminomethylphenyl compound with the general formula

and the higher homologues of said compounds, wherein x, y and z, which are different substituents on the ring, are an alkyl group with from 1 to 3 carbon atoms, a -NHCOOR, -CH ArNHCOOR or -N(COOR)CH2Ar group, R is a 1 to 3 carbon alkyl group and Ar is phenyl which can be substituted with an alkyl group with from 1 to 3 carbon atoms, x, y and z can also be at least one hydrogen, under essentially water-free conditions react at a temperature in the range from about 50°C to 170°C in the presence of an effective amount of a proton acid catalyst having a strength of at least equivalent to a 7B% sulfuric acid, or a Lewis acid having a concentration of at least 0.5% by weight based on the total reaction mixture, for conversion of the r(alkoxycarbonyl)-phenylaminomethylphenyl compounds into the mono- and di-carbamates and the polymethylene polyphenyl carbamates and derivatives thereof, after which the desired carbamates are recovered.

These and other features of the method according to the invention appear in the patent claims.

The invention thus relates to a method for production

of esters of aromatic carbamic acids (urethanes) especially diphenylmethane carbamates and related higher homologues and derivatives,

by acid-catalyzed rearrangement of an (alkoxycarbonyl)phenylaminomethylphenylph orbind such as e.g. 2-(ethoxycarboxyl)phenylaminomethyl]phenylcarbamic acid alkyl ester.

Polymeric aromatic carbamic acid esters (polyurethanes) such as e.g. Diphenylmethane dicarbamates and the related higher homologous polymethylene polyphenylcarbamates are increasingly important products especially for use in the preparation of the commercially valuable diphenylmethane diisocyanates and mixtures of diisocyanates and polyisocyanates by cleavage of these polymeric aromatic carbamic acid esters in a suitable solvent, as shown in US patent documents/^ . 919. 279 and 3,962,302.

To date, no viable commercial method has been known

for the direct production of polymeric aromatic esters of carbamic acid. The corresponding commercially available diphenylmethane diisocyanates and polyisocyanates are largely produced by phosgenation of mixtures of diamines and polyamines obtained by condensation of aniline and formaldehyde with catalytic amounts of a mineral acid, such as e.g. referred to in US patent 4,014,914.

A previously proposed method for the production of polymeric aromatic carbamic acid esters (polyurethanes) is discussed in US patent 2,946,768 and includes condensation of aryl carbamic acid esters with carbonyl compounds in dilute aqueous acidic condensation medium. In this process, however, the carbonyl compound such as formaldehyde like to react at the nitrogen in the carbamate together with the desired polyurethanes and produce varying amounts, i.e. usually between 15 and 50% by weight of unwanted these compounds (also referred to herein as "N-benzyl" compounds). Attempts to prepare mono- or diisocyanates or polyisocyanates or otherwise utilize the mixture containing the desired N-benzyl compounds, which cannot be converted into an isocyanate by pyrolysis, and the polyurethanes present many problems as no method is known to separate the polyurethanes from the N-benzyl impurities.

The present invention thus relates to a method

for the production of diphenylmethane mono and dicarbamates and the higher molecular weight homologues, namely the polymethylene polyphenyl carbamates, comprising catalytic rearrangement of an (Alkoxycarbonyl)phenylaminomethylphenyl compound (N-benzyl compound) with a particularly acidic medium. More particularly, the invention relates to a method for producing the carbamates by catalyzed rearrangement of the N-benzyl compounds which, in addition to the urethanes, are produced as by-products in the condensation of lower alkyl esters of phenylcarbamic acid with carbonyl compounds, such as e.g. formaldehyde,

in the presence of an aqueous acidic solution as described e.g. in the above-mentioned US patent specification 2,946,768. The product mixture produced by such a condensation process containing diurethanes and polyurethanes, N-benzyl compounds, unreacted alkylphenyl carbamates and other by-products such as e.g. amines can at temperatures of from approximately 50°C to 170°C be brought into contact with a protonic acid medium with a strength corresponding to at least 75% sulfuric acid such as e.g. concentrated sulfuric acid or an acidic medium comprising a Lewis acid with a concentration of at least 0.5% by weight based on the total reaction mixture, while maintaining a minimum amount of water in the system, to catalytically convert or rearrange said N-benzyl compounds to the desired mono-, di- and polyurethanes. Alternatively, the unreacted alkyl-phenyl carbamate can be removed from the mixture by e.g. vacuum distillation prior to treatment. Acid rearrangement of N-benzyl compounds which arise from other production methods, as described in the following, constitutes an embodiment of the method according to the invention.

It is therefore an object of the present invention to provide a process for the production of diphenylmethane mono- and dicarbamates and the related polymethylene-polyphenylcarbamates in high yield by conversion or rearrangement of (alkoxycarbonyl) phenylaminomethylphenyl compounds where a suitable proton acid or Lewis acid is used as catalyst .

It is a further object of the invention to provide

a method for the acid-catalyzed conversion or rearrangement of .(alkoxycarbonyl)phenylaminomethylphenyl compounds formed during the preparation of di- and higher polymeric carbamic acid esters by dilute aqueous acid condensation of N-aryl-carbamic acid esters such as e.g. ethyl phenyl carbamate with a carbonyl compound to the useful di- and polyurethane compounds.

These and other purposes and advantages of the invention will be apparent

of the following description.

The method according to the invention is preferably carried out under atmospheric pressure, with or without the addition of an inert solvent.

The production of e.g. a diphenylmethane dicarbamate diethyl ester is carried out according to the following assumed reaction using a 2-/(ethoxycarbonyl)phenylaminomethyljphenylcarbamic acid ethyl ester:

2,4'-Methylenebis(phenylcarbamic acid) diethyl ester; (diphenylmethane-2,4'-dicarbamate diethyl ester)

The acid-catalyzed rearrangement reaction can be carried out in any suitable reactor which is usually equipped with means for stirring. A common method is to fill in the N-benzyl compounds together with the proton acid or Lewis acid catalyst and possibly a solvent in the reaction vessel and then heat the mixture to the desired temperature for the appropriate period of time. The reaction can be carried out in portions or as a continuous process and the order of addition of the materials can be varied to suit the particular apparatus used. The reaction products are isolated and processed by any conventional method such as e.g. extraction of the acidic medium with water or neutralization with a base and separation of the resulting phases and distillation to remove any solvent used, or filtration to remove the catalyst.

The (Alkoxycarbonyl)phenylaminomethylphenyl compounds which can be converted or rearranged by the method according to the present invention and which are characterized by the above general formula include e.g. the compounds which may correspond to the following formulas in which R is an alkyl group containing from 1 to 3 carbon atoms:

2-: and 4- /"(Alkoxycarbonyl)phenylaminomethylphenylcarbamic acid alkyl ester, 4-1(Alkoxycarbonyl)phenylaminomethylf-2,4'-methylenebis-(phenylcarbamic acid)dialkyl ester, 4 and 3£4-/" (Alkoxycarbonyl)phenylaminomethyljphenyl (Alkoxycarbonyl)aminomethyljphenylcarbamic acid alkyl ester, and

4-['4-f(Alkoxycarbonyl)phenylaminomethylphenyl(Alkoxycarbonyl)aminomethylj-2,4'-methylenebis(phenylcarbamic acid)dialkyl ester.

These (Alkoxycarbonyl)phenylaminomethylphenyl compounds which are specifically shown by formulas and names are only representative of other than benzyl compounds, especially the various isomers of such compounds. which fall within the definition of the general formula described above for the compounds which can be converted or rearranged into the desired carbamates, especially the polycarbamates, by means of the method according to the invention. In general, they are ethyl esters, i.e. in which R is a C2HJ- group and which are prepared by condensation of ethyl phenyl carbamate

(phenylurethane) by a carbonyl compound such as e.g. formaldehyde, preferred for the production of the diethyl esters of diphenylmethane dicarbamate and the polymethylene polyphenyl carbamates which can be split into the valuable polymeric isocyanates as described earlier.

As indicated earlier, the reaction product which includes the N-benzyl compounds which result in non-separable by-products during the condensation of the alkyl esters of phenylcarbamic acid such as e.g. ethyl phenyl carbamate with carbonyl compounds such as formaldehyde, in the presence of the dilute aqueous acid solution is treated by means of the method according to the present invention either as such or after removal of unreacted ethylphenylcarbamate starting material. In addition, N-benzyl compounds which are produced by other known methods can be used in the method according to the invention. E.g. can N-phenylbenzylamine and alkyl chloroformate, e.g. methyl, ethyl or propyl chloroformate is reacted to produce the relevant alkyl-N-benzylphenylcarbamate. N-phenyl-2-aminobenzylamine and N-phenyl-4-aminobenzylamine prepared according to the method indicated in British patent document 1,177,557 can be reacted with an excess of the alkyl chloroformate, e.g. ethyl chloroformate,

to give 2- and 4-(jtethoxycarbonyl)phenylaminomethylphenylcarbamic acid ethyl ester. The 2- and 4- /^(alkoxycarbonyl)phenylaminomethyl-phenylcarbamic acid alkyl esters can also be prepared by reacting a substituted benzyl alcohol such as e.g. a carbamic acid benzyl hydroxyethyl ester (ethylphenylcarbamate-2-methylol) with ethylphenylcarbamate and an acid catalyst.

The proton acid medium which is used as catalysts and which is suitable for use in the present invention can be either inorganic or organic if it only constitutes a strong acid and has a strength of at least equivalent to 75% sulfuric acid. The proton acid catalysts are usually used in concentrations of from 0.1 to 25% by weight based on the total reaction mixture and preferably from 1 to 10% by weight. Higher concentrations can also be used. Representative proton acid catalysts particularly suitable for use in the present invention are concentrated

(75% or more) .sulfuric acid, p-toluene .sulfonic acid, trifluoromethane-sulfonic acid, hydrofluoric acid, fluorosulfonic acid and strong acids

sulfonated polyaromatic ion exchange resins (sold e.g.

such as "Amberlyst 15" by Rohm and Haas Co.) and having a bulk density of about 5 95 g/l, a hydrogen ion concentration of about 4.9 milliequivalents/g dry weight, a surface area of from about 40 to 50 m 2 /g and an average pore diameter of

from about 200 to 600 Angstrom units. Mixtures of acid catalysts can be used, but it is preferred to use an individual acid catalyst to reduce any recycling problems.

The Lewis acid catalysts that can be used as catalysts

in the present invention can e.g. be tin (IV) chloride, iron (III) chloride, aluminum chloride, antimony pentafluoride and boron trifluoride. The Lewis acid catalysts can be supported on e.g. graphite and is used in a concentration of at least 0.5 preferably in the range of from 0.5 to 20% by weight based on the total reaction mixture. The protonic acids are the preferred acidic catalyst medium. Mixtures of proton acid and Lewis acid catalysts can be used, e.g. BF^ and H^SO^, but not preferred.

Although the method according to the present invention can be carried out in the absence of solvents, especially at higher reaction temperatures. of 100°C or more, solvents or mixtures of solvents which are stable and chemically inert towards the components of the reaction system can generally be used due to the viscosity of the mixture of the N-benzyl compounds in the form of dimers, trimers, tetramers, etc. Suitable solvents which are used mainly in an anhydrous state and generally in amounts of from 0 to 50% by weight based on the reaction mixture include e.g. nitrated and halogenated aromatic hydrocarbons with up to 12 carbon atoms, such as nitronebenzenes, nitrotoluenes, dichlorobenzene, dibromobenzene, alkanes and substituted alkanes with up to 16 carbon atoms such as e.g. n-pentanes, iso-pentane, ::n-hexane, 2-methylpentane, n-heptane, 3, 4-dimethylhexane, 2-methylhexane, 3-ethylpentane-cyclopentane, cyclohexane, methyl-cyclohexane, ethylcyclopentane, cyclooctane, chloroform, carbon tetrachloride, dichloroethane, etc, lower aliphatic acids ..with up to lower aliphatic alcohols with up to 8 carbon atoms such as e.g. methanol, ethanol, propanols, butanols, etc. Nitrobenzene, nitrotoluene and dichlorobenzene are the preferred solvents. Larger amounts of solvent can be used but are generally not necessary due to the additional measures of recycling. Although mixtures of solvents can be used, as discussed in 1 above, it is preferred to use individual solvents to ease possible recycling problems.

As indicated above, the reaction according to the present invention can conveniently be carried out by charging the N-benzyl compounds contained in a condensate or otherwise, together with the proton acid catalyst or the Lewis acid catalyst and the solvent into a suitable reactor while keeping the reaction conditions essentially anhydrous, and then the mixture is heated to the desired temperature. The reaction will take place at temperatures of from about 50°C to about 170°C. It is usually preferred to carry out the process at temperatures of from 80°C

to 130°C to achieve a suitable reaction rate. Heating and/or cooling devices can be used either inside and/or outside the reactor to keep the temperature within the desired range.

The method according to the present invention is generally carried out at atmospheric pressure, although higher pressures can also be used at the higher reaction temperatures. Subatmospheric pressures can be used but offer no particular advantages.

The reaction time is generally dependent on the mixture of N-benzyl compounds being reacted, or the condensate being treated, the temperature and the amount and type of acid catalyst used and will vary depending on whether the process is continuous or proportional but will usually be between about 2 minutes and up to several hours.

The following examples are given to illustrate the invention.

Although the method according to the present invention is primarily directed to the production of diphenylmethane dicarbamate ethyl esters and polymethylene polyphenylcarbamate ethyl esters by means of the acid-catalyzed conversion or rearrangement of (ethoxycarbonyl) phenylaminomethylphenylcarbamic acid ethyl ester, including the higher homologous trimers, tetramers, etc., which are prepared e.g. as byproducts in the condensation of ethylphenylcarbamate and a carbonyl compound as described above, the method is not limited to the production of these (ethoxycarbonylXphenylaminomethylphenylcarbamic acid compounds and the person skilled in the art will recognize that the invention in a broader sense is applicable to the treatment of other (alkoxycarbonyl)phenylaminomethylphenyl compounds such as eg the methyl and propyl esters and higher homologues.

In the following examples, the reactions were carried out in 300 ml three-neck glass flasks equipped with a mechanical stirrer, reflux condenser and thermometer. The reaction components were filled into the flask and the flask immersed in an oil bath at a constant temperature. At the end of the reaction time, water was added to the flask to terminate the reaction and extract the acidic medium or the catalyst was removed and recovered by filtration. Conversion of the filled N-benzyl compounds as well as product yield and distribution spectrum were determined by means of rapid liquid chromatography.

EXAMPLE 1 (comparison example)

2-0ethoxycarbonyl)phenylaminomethylfphenylcarbamic acid ethyl esters (N-benzyl compound), was prepared by reacting 10 g of N-phenyl-2-aminobenzylamine (prepared by the method described in Beilstein Organische Chemie, Volume XIII, System No. 1740-1871,

page 166) with 1.2 g of ethylene chloroformate in the presence of 1 ml of pyridine and 50 ml of tetrahydrofuran as solvent for 1 hour at 50°C

and subsequent filtration to remove pyridine hydrochloride and evaporation of the solvent.

0.3 g of the N-benzyl compound prepared above together with 1.0 g of 37% by weight hydrochloric acid was heated at 100°C for 60 minutes on a

bath with a constant temperature. After completion of the reaction, 10 ml of water was added to terminate the reaction and extract hydrochloric acid medium. Analysis of the resulting reaction product by flash liquid chromatography showed that 89% of unreacted added N-benzyl compounds were recovered along with some ethyl phenylcarbamate resulting from simple cleavage of the N-benzyl compound and other unidentified reaction by-products. No rearrangement to diuretan products was detected.

EXAMPLE 2 (comparison example)

The procedure in Example 1 was repeated using 0.3 g of 2-t-(ethoxycarbonyl)phenylaminomethyl-phenylcarbamic acid ethyl ester, prepared as shown in Example 1, and 2.0 g of 49% by weight sulfuric acid. The mixture was filled into the reaction flask and heated to

100°C for 60 minutes, after which the reaction mixture was quenched with 10 ml of water and the acidic medium extracted. Chromatographic analysis showed that 99% of the 2£(ethoxycarbonyl)phenylaminomethylphenylcarbamic acid ethyl ester originally introduced was recovered unchanged along with an undetermined amount of ethylphenylcarbamate and traces of the diethyl ester of 2,4'-methylenedicarbanilic acid.

EXAMPLE 3' (comparison example)

0.3 g of a mixture of 2 /T(ethoxycarbonyl)phenylaminomethylphenylcarbamic acid ethyl ester and 4-£(ethoxycarbonyl)phenylaminomethylphenylcarbamic acid ethyl ester (46 and 54% of the 2-isomer and the 4-isomer respectively) and which was prepared by reacting a mixture of N-phenyl-2- and 4-aminobenzylamine, prepared by the method described in British patent document 1,177,557, with ethyl chloroformate as described in example 1 above, together - with 1.0 g of 60% by weight sulfuric acid was introduced into the reaction flask and heated at 110°C for 60 minutes. Analysis showed that essentially all of the 4-isomer had been converted to 4,4'-methylene(phenylcarbamic acid)-diethyl ether, but that 84% of the 2-isomer remained unreacted. The 2-isomer could not be separated from the reaction mixture to allow further processing of the desired diethyl ester urethane.

EXAMPLE 4

0.3 g of an ethyl ester of 2-(ethoxycarbonyl)phenylaminomethylj-phenylcarbamic acid (N-benzyl compound), prepared as in Example 1, together with 1.0 g of 96.4% by weight concentrated sulfuric acid was introduced into a 300 ml reaction flask. The mixture was heated to 100°C in a constant temperature bath for 60 minutes. Rapid liquid chromatographic analysis showed conversion

of the ethyl ester of 2-£(ethoxycarbonyl)phenylaminomethyljphenylcarbamic acid to the diethyl ester of 2,4'-methylenebis(phenylcarbamic acid)

and higher homologues to more than 99% with small amounts of ethyl phenylcarbamate..' After acid extraction with water, the resulting 2,4'-methylenebis(phenylcarbamic acid) diethyl ester (diurethane) was subjected to thermal cleavage by the method described in US Patent No. 3,962,302 to give diphenylmethane-2,4'-diisocyanate i^od±^jrt^yt±e.

EXAMPLE 5

Example 4 was repeated using a mixture of 1.0 g of the N-benzyl compound of Example 4 together with 3.7 g of 96.4% by weight concentrated sulfuric acid and 4.0 g of absolute ethyl alcohol as solvent. The mixture was heated to a temperature of 90°C for 70 minutes. Analysis showed that conversion of the N-benzyl compound to diurethane was 95% with the byproduct ethylphenylcarbamate and other unidentified byproducts present.

EXAMPLE 6

A condensation product of the reaction between ethyl phenyl carbamate

and a 30% aqueous formaldehyde solution and 37% by weight hydrochloric acid in water was prepared according to Example 2 of US Pat. ), 4% triurethanes,

15% N-benzyl compound dimer (2 and 4-^(ethoxycarbonyl)phenylaminomethylfphenylcarbamic acid ethyl ester), 8% N-benzyl compound trimer as 4£(ethoxycarbonyl)phenylaminomethylf-2,4'-methylenebis-(phenylcarbamic acid)diethyl ester and a small amount of other unidentified by-products. 6.0 g of the condensation product together with 6.0 g of nitrobenzene solvent and 2.0 g of 96.4% by weight sulfuric acid were introduced into a reaction flask and heated to 80°C for 30 minutes. After completion of the reaction and acid extraction, analysis of the product showed 100% conversion of N-benzyl compound dimers and trimers to the aromatic di- and triurethane compounds with the desired methylene group bridge.

EXAMPLE 7 (comparison example)'

Example 6 was repeated using 6.0 g of the same condensation reaction product together with 6.0 g of nitrobenzene solvent and 6.0 g of 37% by weight hydrochloric acid. The reaction was carried out at 120°C during 4 hours. Analysis of the product showed that only 2% of the contained N-benzyl compounds had been converted into di- or triurethane compounds.

EXAMPLE 8 (seed comparison example) '.-

Example 6 was repeated using 6.0 g of the same condensation reaction product together with 6.0 g of nitrobenzene solvent and 6.0 g of 47% by weight sulfuric acid. The reaction was carried out at 90°C for two hours. Analysis of the reaction product showed that only 3% of the N-benzyl compounds had been converted to di- or triurethane products.

EXAMPLE 9

Example 6 was repeated using 1.0 g of the condensation reaction product from which substantially all unreacted ethyl phenyl carbamate was removed by vacuum distillation, together with 4.0 g of n-butanol and 3.7 g of 96.4% by weight sulfuric acid. The mixture was heated at 110°C for 1 hour.'; Analysis of the rearrangement reaction product showed 100% conversion of the contained N-benzyl compound dimers and trimers to the desired urethanes.

EXAMPLE 10

A number of trials were carried out in accordance with the method in the example

6 but using 6 g of a condensation reaction product of ethyl phenyl carbamate with a 30% by weight aqueous formaldehyde solution, 85% commercial phosphoric acid and water prepared by the process according to US patent 2,946,768. The condensate contained approximately 28 .8% unreacted ethylphenylcarbamate, 42.4% diphenylmethane dicarbamates (2,4' and 4,4' isomers) 5% tri and higher polymeric urethanes, 16% N-benzyl compound dimers, 6% N-benzyl compound trimers and higher homologues. Different reaction conditions, solvents and acid catalysts were used. The reaction product was analyzed by flash liquid chromatography with respect to N-benzyl compound conversion. The results are given in the following Table 1 showing the percentage conversion.

EXAMPLE 11

An experiment was carried out using 6 g of a condensation reaction product of ethyl phenyl carbamate with trioxane (98%)

and 60% aqueous sulfuric acid. The condensate contained approximately 20% unreacted ethylphenylcarbamate; 44% diphenylmethane carbamates (2,4'

and 4,4' isomers), 10% tri- and higher polymers", urethanes, 12% N-benzyl compound dimers and 13% N-benzyl trimers and higher homologues and a small amount of unidentified by-products. The condensation product was dissolved in 6.0 g of nitrobenzene and brought

in contact with 0.70 g of anhydrous ferric chloride for 30 minutes at 100°C. The reaction was quenched with water and the iron catalyst extracted from the organic product by washing with water. Conversion of the N-benzyl compounds was 100% determined by rapid liquid chromatography of the product.

EXAMPLE 12

A number of trials were carried out according to the method of Example 11 using 6.0 g of nitrobenzene solvent in each trial. Different reaction conditions and Lewis acid catalysts were used. The catalyst was removed from the product mixture by filtration or extracted by washing with water and the reaction product analyzed by rapid liquid chromatography with regard to N-benzyl compound conversion. The results are shown in the following table 2.

Claims (19)

1. Process for the production of diphenylmetamono- and dicarbamates and polymethylene polyphenylcarbamate homologues and derivatives thereof, characterized by reacting under substantially anhydrous conditions a (alkoxycarbonyl)phenylaminomethyl-phenyl compound with the general formula including the higher homologues of said compounds, wherein x, y and z are different substituents on the ring, an alkyl group having from 1 to 3 carbon atoms, a group -NHCOOR, -CH^ ArNHCOOR or -N(COOR)CH2 Ar in which R is an alkyl group with 1 to 3 carbon atoms and Ar is phenyl which can be substituted with an alkyl group with from 1 to 3 carbon atoms, x, y and z can also be in at least one hydrogen atom, at a temperature in the range of from about 50°C to about 170°C in the presence of an effective amount of a proton acid catalyst having a strength of at least equivalent to 75% sulfuric acid, or a Lewis acid having a concentration of at least 0.5% by weight based on the total reaction mixture, to catalytically convert or rearrange the (alkoxycarbonyl)phenylaminomethylphenyl compounds to the mono- and dicarbamates and poly-methylene polyphenyl carbamates and derivatives thereof followed by recovery of the desired carbamates. 2. Method as stated in claim 1, characterized in that (Alkoxycarbonyl). The phenylaminomethylphenyl compound is obtained by the condensation reaction of an N-arylcarbamic acid ester with a carbonyl compound in the presence of a dilute aqueous acid solution. 3. Method as stated in claim 2, characterized in that the N-arylcarbamic acid ester is ethylphenylcarbamate. 4. Method as stated in claim 2, characterized in that the carbonyl compound is formaldehyde. 5. Process as set forth in claim 1, characterized in that the (alkoxycarbonyl)phenylaminomethylphenyl compound is the ethyl ester of 2-{(ethoxycarbonyl)phenylaminomethylphenylcarbamic acid or 4-{ethoxycarbonyl)phenylaminomethylphenylcarbamic acid. 6. Method as stated in claim 1, characterized in that the protonic acid catalyst is an inorganic or organic acid and is used in concentrations of from 0.1 to 25% by weight based on the reaction mixture. 7. Method as stated in claim 6, characterized in that the concentration is from 1 to 10 weight*;. _ 8. Method as stated in claim 6, characterized in that the protonic acid catalyst is selected from the group consisting of sulfuric acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, hydrofluoric acid, fluorosulfonic acid and strongly acidic sulfonated polyaromatic ion exchange resins. 9. Method as stated in claim 8, characterized in that the acidic catalyst is sulfuric acid. 10. Method as stated in claim 1, characterized in that the reaction is carried out in the presence of a solvent selected from the group consisting of nitrated and halogenated hydrocarbons with up to 12 carbon atoms, alkanes and substituted alkanes with up to 16 carbon atoms, lower aliphatic acids and lower aliphatic alcohols with up to 8 carbon atoms. 11. Method as stated in claim 10, characterized in that the solvent is nitrobenzene, nitrotoluene or dichlorobenzene. 12. Method as stated in claim 11, characterized in that the solvent is nitrobenzene. 13. Method as stated in claim 1, characterized in that the reaction is carried out at a temperature of from 80 to 130°C. 14. Method as stated in claim 1, for the production of a diphenylmethane dicarbamate diethyl ester, characterized by and put the ethyl ester of 2-E(ethoxycarboryl)phenylaminomethylphenylcarbamic acid or 4-C(ethoxycarbonyl)phenylaminomethylphenylcarbamic acid is kept from the condensation reaction between ethylphenylcarbamate and a carbonyl compound in the presence of a dilute aqueous solution, at atmospheric pressure and a temperature in the range from about 80°C to about 130°C in the presence of sulfuric acid with a strength of between 75 and 100% and recovery of the desired diphenylmethane dicarbamates. 15. Method as stated in claim 1, characterized in that the Lewis acid catalyst is selected from the group consisting of tin (IV) chloride, iron (III) chloride, aluminum chloride, antimony pentafluoride and boron trifluoride. 16. Method as stated in claim 1, characterized in that the Lewis acid is used in concentrations of from 0.5 to 20% by weight based on the total reaction mixture. 17. Method as stated in claim 1, characterized in that the Lewis acid catalyst. is supported on a carrier. 18. Method as stated in claim 17, characterized in that the carrier is graphite. 19. Process as stated in claim 1, for the production of a diphenylmethane dicarbamate diethyl ester, characterized by reacting the ethyl ester of 2-{(ethoxycarbonyl)phenylaminomethylj-phenylcarbamic acid or 4-lf (ethoxycarbonyl)phenylaminomethyl-phenylcarbamic acid is held from the condensation reaction of ethyl phenylcarbamate with a carbonyl compound in the presence of a dilute aqueous acid solution, at atmospheric pressure and a temperature in the range of about 80°C to 130°C in the presence of antimony pentafluoride at a concentration of from 0.5 to 20% by weight based on the total reaction mixture and recovery of the desired diphenylmethane dicarbamates.