CA1120051A

CA1120051A - Process for preparing polymethylene polyphenyl polycarbamates

Info

Publication number: CA1120051A
Application number: CA000341827A
Authority: CA
Inventors: Katsuharu Miyata; Seiji Hasegawa; Shinobu Aoki; Isao Hara
Original assignee: Mitsui Toatsu Chemicals Inc
Current assignee: Mitsui Toatsu Chemicals Inc
Priority date: 1978-12-14
Filing date: 1979-12-13
Publication date: 1982-03-16
Also published as: FR2444057B1; DE2950386A1; GB2044252A; NL185077B; FR2444057A1; GB2044252B; NL7908982A; IT7927992A0; DE2950386C2; IT1126563B; NL185077C

Abstract

Abstract of the Disclosure:
In the preparation of polymethylene polyphenyl polycarbamates by reacting an N-phenyl carbamic acid ester with formaldehyde or a formaldehyde-producing compound in the presence of water and an acid catalyst, the acid catalyst is used in the form of its aqueous solution having an acid catalyst concentration, at the start of the reaction, of at least 10% by weight and in an amount, at the start of the reaction, of from 0.01 to 100 moles per mole of the N-phenyl carbamic acid ester, and the reaction is carried out at a temperature of from 20 to 150°C. After completion of the reaction, the aqueous acid catalyst solution containing small amounts of organic impurities may be recovered, subjected to adjustment of its acid catalyst concentration, and then reused directly for a subsequent reaction.

Description

S~

SPECIFICATION

~¦ Title o-f the Invention:
I . . .. _ j i Process for Preparing Polymethylene Polyphenyl Polycarbamates Background of the Invention:
! j~
1) Filed of the Invention This invention relates to an improved process for preparing polymethylene polyphenyl polycarbamates from N-phenyl carbamic acid esters and ~ormaldehyde. 1,

2) Descrip~ion of the Prior Art Polymethylene polyphenyl polycarbamates are substances that are useful in the manufacture of agricultural chemicals, drugs, I
polyamides polyurethanes, and the like. In addition, polymethyle~e polyphenyl polycarbamates can be thermally decomposed to produce ¦ the corresponding polymethylene polyphenyl polyisocyanates.
Il Accordingly~ it is desirabIe to develop new processes for pre-- jl paring polymethylene polyphenyl polycarbamates with industrial !l advantages.
One well known prior art process for preparing polymethylene polyphenyl polycarbamates comprises reacting a corresponding polymethylene polyphenyl polyisocyanatewith alcohol. However, ~ the preparation of the polymethylene polyphenyl polyisocyanate : . .
~, used as a starting material involves the use of highly toxic ! aniline and phosgene and, moreover, requires a complicated procedure.
Another well-known prior art process for preparing polymethy ; I lene polyphenyl polycarbama~es comprises reacting a corresponding polymethylene polyphenyl polyamine with a chloroformic acid alkyl ester. However, ~he polymethylene polyphenyl polyamine and . .
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.
chloroformic acid alkyl ester used as starting materials both have, such severe intoxicating and irritating properties that they are very difficult to handle, and the procedures for preparing them are complicated. For these reasons~ this process cannot be regarded as useful in industrial applications.
There is still another well-known prior art process for preparing polymethylene polyphenyl polycarbamates by reacting an N-phenyl carbamic acid ester with formaldehyde. For example, as is described in German Patent No. 1,042,891, an N-phenyl carbamic ,~ -acid ester and formaldehyde may be heated in an aqueous solution of hydrochloric acid to obtain a condensation product which consists mainly of polymethylene polyphenyl polycarbamates.
While much is known about the reaction of an aromatic amine ~e.g., aniline) with formaldehyde, the aforesaid German Patent is ¦the only publication that deals with the reaction of an N-phenyl carbamic acid ester with formaldehyde. Accordingly, nothing is known about the reactivity of N-phenyl carbamic acid esters as wel !
as the action of an aqueous acid solution used as catalyst and its activity after completion of the reaction. The commonly prac~iced reaction of aniline with formaldehyde involves a great difficulty in that the aqueous acid solution used as catalyst, which reacts with the resulting polyamine to form a salt, is neutralized and discharged as waste water instead of being recovered for recycling Moreover, the process described in the aforesaid German Paten~
No. 1,042,891 exhibits such a low reaction rate that large amounts of unreacted starting materials remain even after the reaction has been carried out for a long period of time. Furthermore, the selectivity to the desired useful diphenylmethane-4,4-dicarbamic acid diester is so low that polymethylene polyphenyl polycarbamates, called polynuclear compounds, having three or more phenyl radicals as well as various by--products and intermediate products are formed in large amounts.

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Thus, no process for preparing polyrnethylene polyphenyl polycarbamates with industrial advantages has been available so far.
Summary of the Invent on:
It is an object of an aspect of the present invention to provide a process for preparing polymethylene polyphenyl poly-carbamates from N-phenyl carbamic acid esters and formaldehyde which process can achieve a higher reaction rate than has been attainable by prior art processes.
It is an object of an aspect of the present invention to provide a process for preparing polymethylene polyphenyl poly-carbamates from N-phenyl carbamic acid esters and formaldehyde which process can exhibit a high selectivity to the correspond-ing diphenyl-methane-4,4'-dicarbamic acid diester.
It is an object of an aspect of the present invention to provide a process for preparing polymethylene polyphenyl poly-carbamates from N-phenyl carbamic acid esters and formaldehyde in which process, after completion of the reaction, the aqueous acid solution used as catalyst can be recycled to a subsequent 20 reaction.
These and other objects of the present invention are accomplished by a process for preparing a polymethylene poly-; phenyl polycarbamate of the general formula , .

. N-C-O-Rl R1-0-C-rl ~ ~ CH2 -CH ~ ~ r~-C-O-R (I) (R2)n (R2)n m (R2)n .

.

1~,2~ ~-5 where Rl is an alkyl radical of from 1 to 6 carbon atoms or a cycloalkyl radical of from 5 to 10 carbon atoms, R2 is a hydrogen I
atom~ a halogen atom, an alkyl radical of from 1 to 6 carbon atoms, or an alko~y radical o:E from 1 to 6 carbon atoms, n is a positive i integer of from 1 to 4, and m is zero or a positive integer of from 1 to 5, by reacting an N-phenyl carbamic acid ester of the general, -formula ~l O
N~ O-Rl (II) )n where Rl, R2, and n have the same meanings as described-above for 1 formula (I), with formaldehyde or a formaldehyde-producing compound in the presence of water and an acid catalyst, wherein the improvement comprises (a) using the acid catalyst in the form of ¦its aqueous solution having an acid catalyst concentration, at the start of the reaction, of at least~10% by weight and in an amount, at the start of the reaction, of from 0.01 to 100 moles ¦¦per mole of the N-phenyl carbamic acid ester and (b) carrying out the reaction at a temperature of from 20 to 150C.
After completion of the above-described reaction, the solid reaction product or the organic layer containing it is separated from the aqueous acid catalys~ solution containing small amounts ~,of organic impurities, and the desired polymethylene polyphenyl polycarbamate is isolated from the organic layer. On the other hand the aqueous acid catalyst solution may be reused for a suhsequent reaction of the N-phenyl carbamic acid ester with formaldehyde or a formaldehyde-producing compound without removing the organic impurities contained therein but after adjusting its acid catalyst concentration to such a level as to provide an aqueous acid catalys~ solution having an acid catalyst concentration, ' '' `' l - 4 -, .... . .. .
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at the start of the subsequent reaction, of at least 10~ by weight.
I
Detailed Description of the Invention:
Close examination of the reaction of an N-phenyl carbamic acid ester with -formaldehyde has revealed that, if this reaction 1~ is carried out in the presence of water and an acid catalyst, a ¦I solid reaction product or an oily layer containing it spontaneously separates rom the aqueous acid solution used as catalyst.
Accordingly, the aqueous acid solution can be recovered with ease. The recovered aqueous acid solution contains, in addition to unreacted formaldehyde, a total of from 0.1 to 3~ by weight ! o organic impurities which are considered to be unreacted carbamic acid ester, reaction product, by-products, and intermediate products. Most of the aqueous acid solution used as catalyst is recovered without mixing in the reaction product layer. ~lowever, i the recovered aqueous acid solution is reused directly or a subsequent reaction, the reaction rate becomes so low that it is dificul~ to repeat its reuse many times. Upon examination of the ,I reason for this, it has been ound tha~ the reduction in the activity o the recovered aqueous acid solution is not attributabl e to the presence of organic impurlties therein, but to the decrease n its acid concentration resulting from the formation of water during the reaction, the loss caused by af~er-treatment, and the ¦ ;
like. It has also been ound that, when an aqueous acid solution is used as catalyst in this reaction, it should have an acid concentration o at least 10% by weight at the start of the reaction and higher acid concentrations give higher reaction rates. This is quite unexpected and surprising in view of the fact that, in the well-known reaction of an aromatic amino compound (particularly, aniline) with formaldehyde, the reaction !l i rate becomes higher as the acid concentrat;on is decreased (see, , , '.

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.
for example, Y. Ogata, et al.: J. Am. Chem. Soc. 37, 1715 (1951)).
The N-phenyl carbamic acid ester used in the process of the present invention is a compound represented by the general formula (II). In this formula, Rl is an alkyl radical such as methyl, l ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-I butyl, any of the pentyl radicals derived from _-pentane and its isomers, any of the hexyl radicals derived from n-hexane and its isomer5, etc.; or a cycloalkyl radical such as cyclopentyl, jcyclohexyl, etc.; and R2 is a hydrogen atom; a halogen atom such as chlorine, bromine, fluorine, etc.; an alkyl radical such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, any of the pentyl radicals derived from n-pentane and its isomers, any of the hexyl radicals d~rived from n-hexane and its isomers, etc.; or an alkoxy radical composed of any one of the¦
llforegoing alkyl radicals and an oxygen atom.
More specifically, the useful N-phenyl carbamic acid esters ! include phenyl carbamic acid alkyl esters of the general formula (II) in which Rl lS an alkyl radical as defined above and R2 ~5 a I
hydrogen atom; halophenyl carbamic acid alkyl esters of the general formula ~II) in which Rl is an alkyl radlcal as defined above and ~2 is a halogen atom as defined above; alkylphenyl carbamic acid alkyl esters of the general formula ~II) in which R
and R2 are alkyl radicals as defined above; alkoxyphenyl carbamic acid alkyl esters of the general formula (II) in which Rl is an llalkyl radical as defined above and R2 is an alkoxy radical as -~defined above; phenyl carbamic acid cyclopentyl or cyclohexyl ester of the general formula (II) in which Rl is a cyclopentyl ' or cyclohexyl radical and R2 is a hydrogen atom; halophenyl ;carbamic acid cyclopen~yl or cyclohexyl esters oE the general formula (II) in which Rl is a cyclopentyl or cyclohexyl radical ~Z~5~

and R2 is a halogen atom as defined above; alkylphenyl carbamic acid cyclopentyl or cyclohexyl esters of the general formula (II) in which Rl is a cyclopentyl or cyclohexyl radical and R2 is an alkyl radical as defined above; alkoxyphenyl car~amic acid cyclopentyl or cyclohexylesters of the general formula ~II) in l ¦
which Rl is a cyclopentyl or cyclohexyl radical and R2 is an alkoxy radical as defined above; and the like. ¦
The preferred N-phenyl carbamic acid esters are phenyl carbamic acid methyl ester, phenyl carbamic acid ethyl ester, l i phenyl carbamic acid n-propyl ester, phenyl carbamic acid isopropyl ester, phenyl carbamic acid n-butyl ester, phenyl ¦
carbamic acid sec-butyl ester, phenyl carbamic acid isobutyl esterl phenyl carbamic acid tert-butyl ester, phenyl carbamic acid pentyll i ester, phenyl carbamic acid hexyl ester, o-chlorophenyl carbamic acid methyl ester, o-chlorophenyl carbamic acid ethyl ester, o-chlorophenyl carbamic acld isopropyl ester, o-chlorophenyl carbamicacid isobutyl ester, o-methylphenyl carbamic acid methyl ¦
ester, o-methylphenyl carbamic acid ethyl ester, phenyl carbamic acid cyclohexyl ester, o-chlorophenyl carbamic acid cyclohexyl !
ester, o-methylphenyl carbamic acid cyclohexyl ester, m-methoxy-phenyl carbamic acid methyl ester, phenyl carbamic acid cyclopentyl ester, and the like.
In the process of the present invention, the aforesaid N- ¦
phenyl carbamic acid ester is reacted with formaldehyde or a formaldehyde-producing compound. The formaldehyde-producing compound may be any compound that can produce formaldehyde under the reaction conditionsof the present invention, and specific examplesthereof include paraformaldehyde, methylal~ and other formals. Usually, an aqueous solution of formaldehyde is used.
The acid used in the process of the present invention may be a mineral acid such as hydrochloric acid, sulfuric acid, ', phosphoric acid, boric acid, etc. or an organic acid such as ' i formic acid, acetic acid, oxalic acid, toluenesul-fonic acid, etc.
The so-called super acids such as hydrobromic acid, perchloric acid, chlorosulfonic acid, trifluoromethanesulfonic acid, etc. may also be used ef:Eectively. Usually, hydrochloric acid or sulfuric ~ i acid is preferred. In order to recover and reuse it, the acid need be used in the form of its aqueous solution. However, the acid and water may be added to the reactor in any suitable way that results in the formation of an aqueous acid solution in the l i reactor. For example, the acid and water may be added separately ii to the reactor, or the acid and an aqueous formaldehyde solution may be added to the reactor.
Although the process of the present invention can be carried out in the absence of solvent, a suitable solvent may be used, for example, in order to facilitate the handling of staring materials and/or reaction products having high melting points.
In this case, the solvent must be inert to formaldehyde. Specific examples of the suitable solvent include aliphatic hydrocarbons ¦
such as hexane, heptane, etc.; alicyclic hydrocarbons such as ' cyclopentane, cyclohexane, etc.; halogenated hydrocarbons such as chloroform, methylene chloride, carbon tetrachloride, dichloro-ethane, trichloroethane, ~etrachloroethane, etc.; fatty acid alkyl esters such as ehtyl acetate, etc.; and the like. Aromatic compounds such as benzene, toluene, etc. are generally unsuitable ~
for use in the process of the present invention, because they tend ;
to react with formaldehyde. However, they can be used under those conditions which do not allow them to react materially with formaldehyde.
In carrying out the process of the present invention, the formaldehyde (or formaldehyde-producing compound) is generally ' -used in an a~ount oE :Erom 0.1 to 10 moles and preferably :Erom ,., ;
. - 8 - .

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~Z~05~ , 0.2 to 2 moles per mole of the N-phenyl carbamic acid ester. If , the amount of formaldehyde used is too small, the remaining unreacted N-phenyl carbamic acid ester increases, while if it is , too large, the formation of polymethylene polyphenyl polycarbamates (or polynuclear compounds) having three or more phenyl radicals results.
¦ The acid should be uséd in the form of its aqueous solution l i I having an acid concentration, at the start of the reaction, of i at least 10% by weight. If the acid concentration is lower than 10% by weight, the reaction becomes slow and the selectivity to the corresponding diphenylmethane-~,4'-dicarbamic acid diester is reduced. High concentrations in the vicinity of 100% by Il weight may be used effectively, but are practically unsuitable I for use in industrial applications. Generally, i the acid concentration is too high, side reactions such as hydrolysis are apt to take place and, therefore, the quality and yield of the desired product tencl to be reduced. The preferred range is from ¦, 20 to 95% by weight.
The acid should also be used in an amount, at the start of the reaction, of from 0.01 to 100 moles per mole of the N-phenyl ¦
!i , carbamic acid ester. If the amount of acid used is less than 0 01 mole, the reaction becomes slow and the selectivity to the desired product is reduced. Although it is possible to use more ¦
than lO0 moles of the acid, such large amounts are not needed in ¦
ordinary cases. The pre-ferred range is from 0.1 to 50 moles per mole of the N-phenyl carbamic acid ester and the mos~ preferred ii range is from 0.2 to 10 moles per mole of the N-phenyl carbamic l acid ester.
, The amount of solvent used depends on the properties of the starting materials and the reaction product. ~lo~ever, the solvent is generally used in an amount of from 0.1 to 100 parts ,, '.
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l~Z~(~5~
, . f by weight and preferably from 0.2 to 50 parts by weight per part i by weight of the N-phenyl carbamic acid ester.
I¦ The reaction is carried Ollt at a temperature of from 20 to 150C and preferably from 30 to 100C. If the reaction temperature is lower than 20C, the reaction becomes very slow, while if it is higher than 150C, side reactions such as hydrolysis takes place ¦
so that the amount of by-products is increased and, therefore, the yield and purity of the desired product are reduced.
Generally speaking, the process of the present invention may be carried out by providing the N-phenyl carbamic acld ester I
as it is or in the ~orm of its solution or suspension in a properly selected solvent, adding the formaldehyde or formaldehydle-¦ producing compound and the aqueous acid solution thereto, andthen stirring the resulting reaction mixture at a predetermined temperature. Alternatively, the process of the present invention may also be carried out by adding a formaldehyde solution drop by drop to a solution or suspension containing the N-phenyl carbamic¦
acid ester and the aqueous acid solution. -~ urthermore, the process of the present invention may becarried out in a continuous operation system in which a solution ~
¦ or suspension containing t~.e starting materials, the solvent, and¦
¦ the aqueous acid solution in an appropriate proportion is continuously fed to a reactor and con~inuously withdrawn therefrlom !I after a predetermined resldence time.
¦I The reaction time depends on the types or amounts of starting materials and acid used, the type of operation, reaction conditiols, and the like. In the case of batch operation~ it may generally Il range from 1 to 40 hours.
Il After completion o~ the reaction, the solid reaction product 'll or the oily layer containing it is isolated from the aqueous acid solution by any suitable technique sucl as the use oL a ,1 - 1 0 , 1, .

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separating funnel, filtration, etc. The recovered aqueous acid solution can be reused for a subsequent reaction a:Eter its acid Il concentration is adjusted to such a level as to provide an aqueous j acid solution having an acid concentration, at the start of the subsequent reaction, of at least 10% by weight. ~lore ¦~ specifically, the recovered aqueous acid solution is diluted with I an appropriate amount of water if its acid concentration is too ¦I high, or strengthened by concentration or other suitable techniquls -if its acid concentration is too low. I~ is of course that the recovered aqueous acid solution may be directly reused if its aci concentration falls within the above-defined range. However, owing to the formation of water during the reaction, the losses caused by migration to the reaction product layer and evaporationl during the reaction, the loss caused by after-treatment, and the 1-I like, the acid concentration of the recovered aqueous acid I! solution usually difEers: from the original one and tends to I depart from the above-defined range. ThUs, adjustment of the " acid concentration of the recovered aqueous acid solu~ion is more or less required if it is desired to repeat is reuse many times.
Especially when the recovered aqueous acid solution is used in a recycling mannèr, a constant reaction rate and hence consistent ,, results can be obtained by adjusting the acid concentration of the aqueous acid solution recovered Erom each reaction to the same level as the original one.
ll In calculating the acid concentration at the start of the ~i ,I reaction, the water contained in the aqueous :Eormaldehyde solution and the aqueous acid solution should be included.
Although the recovered aqueous acid solution contains organic impurities such as unreacted formaldehyde, intermediate products, by-products, etc., part o:E the unreacted formaldehyde and - intermediate products will e'cEectively be consumed during its . I - 1 1 -"

0~)5~ 1 reuse. Accordingly, the recoverecl aqueous acid solu-tion containing such organic impurities may be reused ~ithout purification, i, whereby little adverse influence is exerted on the reaction oE ¦
the present invention.
A~ter being isolated from the aqueous acid solution, the solid reaction product or the oily layer containing it may be either used directly for intended purposes or subjected to further ~reatment (Eor example, ~ashed with water and dried) to obtain an end product. Where the end product still contains unreacted starting materials and other impurities, it may further be purifie, 1, if desired, by any suitable technique such as distillation, recrystallization, extraction, etc. to obtain a product o-f higher quality. Thus, the process of the present invention can achieve a higher reaction rate than has been attainable by prior art process ~s.
It can also exhibit a higher selectivety to the desired diphenyl-methane-4,4'-dicarbamic acid diester than has been attainable by prior art processes.
Moreover, according to the process of the present invention, a variety of methylene-bridged polyphenyl polycarbamates of a variety of methylene-bridged polyphenyl polycarbamates of the general formula (I) can be prepared depending on the N-phenyl carbamic acid ester used as a starting material. Under ordinary reac~ion conditions, the reaction product is a mixture comprising l a larger amount of binuclear compounds of the general formula (I)¦
in which m is equal to zero and a smaller amount of polynuclear compounds of the general formula (I) in ~hich m is equal to 1 or more. According to the process oE the present invention, the yiel ~
of the binuclear compounds becomes higher as the acid concentration is increased.
Furtherrnore, since the aqueous acid solution recovered from the reaction of the present invention is strongly acidic and 1, ~z~5~ , !

I contains considerable amounts of organic substances, its direct discharge will cause severe environmental pollution. In order to treat the recovered aqueous acid solution appropriately prior to its discharge as waste water, very great expenses are required.
¦ ~lowever, the recovered aqueous acld solution may be recycled ¦ according to the process o:E the present invention. Thus, the ¦ process of the present invention has great industrial advantages l in that the amounts of materials used can be saved as compared wit h ¦ prior art processes and in ~hat a closed system can be established¦to eliminate the discharge of waste water and prevent the occurrence o~ environmental pollutlon.
The process of the present invention is ~urther illustrated by the following examples. In each of these examples, the ¦ product was analy~ed by liquid chromatography using naphthalene a- an inte al s anda d ,1 Il !
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Example 1 Into a 100-ml flask fitted with a thermometer, a stirrer, Il and a dropping funnel were charged 20 g of phenyl carbamic acid ¦~ ethyl ester, 37.5 g of 36% hydrochloric acid, and 20 g of water. I i Il AEter the flaslc was heated to 50C in an oil bath while its contents were being stirred, 5.2 g of a 35% aqueous solution of formaldehyde was added thereto through the dropping funnel. The i resulting reaction mixture was stirred at 98 - 100C for 5 hours.
' The oily layer was isolated, washed with water, and then dried to ~ obtain 19.1 g of a product.
!l The product was dissolved in tetrahydrofuran and analyzed by liquid chromatography. Consequently, the product was found Il to contain 47% by weight of diphenylmethane-~,4'-dicarbamic acid ¦I diethyl ester,21% by weight of trinuclear and higher polymethylene! l ! polyphenyl poly(ethyl carbamate)s, and 14% by weight of unreac~edl i !~ phenyl carbamic acid ethyl ester. This result means that the ¦¦ degree of conversion of phenyl carbamic acid ethyl ester used as ¦ -ll a starting material was 86% and the yield of diphenylmethane-4,4'-~
¦l dicarbamic acid diethyl ester based on the amount of phenyl , carbamic acid ethyl ester ~i.e., the selectivity to diphenyl:-methane-4,4'-dicarbamic acid diethyl ester) was 51%.
Comparative Example 1 Il .
According to the process described in German Patent No.
Il 1,042,891, a reaction mixture consisting of 20 g of phenyl carbamic ¦l acid ethyl ester, 10 g of 36% hydrochloric acid, 50 g of water, a~d ,l 7.3 g of a 35% aqueous solution of formaldehyde was ~orked up in the same manner as in Example 1. That is, the reaction mixture was stirred at 98 - 100C -for 5 hours. As a result, the degree o~
conversion of phenyl carbamic acid ethyl ester was 29% and the selectivity ~o diphenylmethane-4,4'-dicarbamic acid diethyl ester " - 1 ~ - .
~, was 40%.
il Examples 2 to 4 and Comparative Example 2 Il i I
The procedure o-f Exmaple 1 was repeated except that varying amounts o~ sul:Euric aci.d were used in place of the hydrochloric acid and the reaction was carried out at 80C for 5 hours. The res~llts thus obtained are shown in Table 1.

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I Example S
i Thr procedure of Example 1 l~as repeated except that 18.1 g I ¦
l of phenyl carbami.c acid me-thyl. ester was used in place of the !~ phenyl carbamic acid ethyl ester and the reaction was carried out ~, at 80C :Eor 4 hours. As a result, the degree of conversion of phenyl carbamic acid methyl ester was 88% and the selectivity to diphenylmethane-4,4'-dicarbamic acid dimet.h~l ester was 68%. ~ ' :
. Examples 6 to 8 and Comparative Example 3 ; The procedure of Example S was repeated except that varying Il amounts of sulfuric acid were used in place of the hydrochloric ¦1 acid. The results thus obtained are shown in Table 2. t ', 1 . ! I
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Example 9 Into a 100-ml flask fit-ted with a thermometer, a stirreT, and a dropping funnel ~ere charged 20 g of phenyl carbamic acid ethyl ester, 37 g of 98% sulfuric acid, and 50 g of water. After ~ the Elask was heated to 80C in an oil bath while its contents l ¦
I were being stirred, 5.2 g of a 35% aqueous solution of formaldehyd,e was added thereto through the dropping funnel. The resulting reaction mixture was stirred at 80C for 4 hours and then separatelld at 50C or above to obtain 21;7 g of an oily layer containing reaction products and 88 g of a recovered aqueous acid solution.
¦ The oily layer was dissolved in tetrahydrofuran and analyzed by liquid chromatography using naphthanlene as an internal 1~ standard. Consequently, the oily layer was found to contain 47%
¦! by weight of binuclear compounds, 2% by weight of trinuclear 1~ compounds, 4% by weight of tetranuclear and higher polynuclear ¦~ compounds, and 27% by welght of unreacted phenyl carbamic acid ethyl ester. This result means that the degree of conversio~
of the carbamic acid ester used as a star~ing material was 71%, the yield of binuclear compounds based on the amount of carbamic acid ester consumed was 60%, and the yield of trinuclearl ;
and higher polynuclear compounds~based on the amount of carbamic i acid ester consumed was approximately 8%. I ;
The recovered aqueous acid solution had an acid concentratio of 38% by weight and contained formaldehyde and very small amounts ~ll of unknown impurities in addition to the sul-furic acid.
I 1~ Using the precedently recovered aqueous acid solution (without adjusting its acid concentration). 20 g of phenyl carbamic acid ethyl ester, and 5.2 g of a 35% aqueous solution of formaldehyde, - ll the above-described procedure was repeated four time. The results thus obtained are shown in Table 3.
¦ Then, another series of repetitive runs was carried out in Il l9 5~ ; ~

- the same manner as descr~bed above. In this series, hol~ever, a small amount of concentrated sulfuric acid l~as added to the Il aqueous acid solukion recovered from each run so that an acid concentration of 40% by weight might be achieved at the start I o~ the succeeding reac-tion. When the same procedure was repeated 1, Eive times, substantially consi.stent results were obtained. That 1, is, in all runs, the degree of conversion of the carbamic acid ester was kept a~ 70 - 72%, the yield of binuclear compounds at 58 - 60%, and the yield of trinuclear and higher polynuclear , j compounds at 8 - 10%.

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EA~ample 10 An original run was carried out by :Eollowing the procedure o:E Example 9 except that 18 g of phenyl carbamic acid methyl ester was used in place of the phenyl carbamic acid ethyl ester.
~fter completion of the reaction, the reaction mixture was cooled to room temperature. The resulting precipitate was separated by filtration, washed with water, and then dried to obtain 21 g of a so]id product. On the other hand, 76 g of an aqueous acid solution was recovered as the filtrate.
The solid product was dissolved in tetrahydrofuran and analyzed by liquid chromatograph. Consequently, the product was found to contain 54% by weight of binuclear compounds, 5% by weight of trinuclear compounds, not more than 1~ by weight of tetranuclear and higher polynuclear compounds, and 10% by weight of unreacted phenyl carbamic acid methyl ester. This result means that the degree of conversion of the carbamic acid ester used as a starting material was 88%, the yield of binuclear compounds based on the amount of carbamic acid ester consumed was 68%9 and the yield of trinuclear and higher polynuclear compounds based on the amount of carbamic acid ester consumed was 6%.
The recovered aqueous acid solution had an acid concentration of 39% by weight and contained formaldehyde and very small amount of unknown impurities in addition to the sulfuric acid.
Using the precedently recovered aqueous acid solution (without adjusting its acid concentration), phenyl carbamic acid methyl ester, and a 35% aqueous solution of formaldehyde, the above-described procedure was repeated three times. The results thus obtained are shown in Table ~.
Then, another series of repetitive runs was carried out in the same manner as described above. In this series, however, a small amount of concentraterl sulfllric aci.l t~ras added to the ~' Q~

aqueous acid solution recovered from each run so that an acid concentration of 40% by ~eight might be achieved at the start of the succeeding reaction. ~hen the same procedure was repeated five times, substantially consistent results l~ere obtained. That is, in all runs, the degree of conversion o the carbamic acid ester was kept at 88 - 90%, the yield of binuclear compounds at 68 - 70%, and the yield of trinuclear and higher polynuclear compounds at 3 - 5%.
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Claims

The embodiments of the invention in which an exclusive propexty or privilege is claimed are defined as follows:

1. In a process for preparing a polymethylene poly-phenyl polycarbamate of the general formula where R1 is an alkyl radical of from 1 to 6 carbon atoms or a cycloalkyl radical of from 5 to 10 carbon atoms, R2 is a hydrogen atom, a halogen atom, an alkyl radical of from 1 to 6 carbon atoms, ox an alkoxy radical of from 1 to 6 carbon atoms, n is a positive integer of from 1 to 4, and m is zero or a positive integer of from 1 to 5, by reacting an N-phenyl carbamic acid ester of the general formula where R1, R2, and n have the same meanings as described above, with formaldehyde or a formaldehyde-producing compound in the presence of water and an acid catalyst, the improve-ment which comprises (a) using the acid catalyst in the form of its aqueous solution having an acid catalyst con-centration, at the start of the reaction, of at least 10% by weight and in an amount, at the start of the reaction, of from 0.01 to 100 moles per mole of the N-phenyl carbamic acid ester and (b) carrying out the reaction at a temperature of from 20 to 150°C.

2. The process according to claim 1 wherein the acid catalyst is used in the form of its aqueous solution having an acid catalyst concentration, at the start of the reaction, of from 20 to 95% by weight.

3. The process according to claim 1 wherein the acid catalyst is used in an amount, at the start of the reaction, of from 0.1 to 50 moles per mole of the N-phenyl carbamic acid ester.

4. The process according to claim 1 wherein the reaction is carried out at a temperature of from 30 to 100°C.

5. The process according to claim 1 wherein the N-phenyl carbamic acid ester is phenyl carbamic acid methyl ester, phenyl carbamic acid ethyl ester, phenyl carbamic acid isopropyl ester, or phenyl carbamic acid isobutyl ester.

6. The process according to claim 1 wherein the acid catalyst is sulfuric acid, hydrochloric acid, phosphoric acid, boric acid, formic acid, acetic acid, oxalic acid, toluenesulfonic acid, hydrobromic acid, perchloric acid, chlorosulfonic acid, or trifluoromethanesulfonic acid.

7. The process according to claim 6 wherein the acid catalyst is hydrochloric acid or sulfuric acid.

8. In a process for preparing a polymethylene polyphenyl polycarbamate of the general formula where R1 is an alkyl radical of from 1 to 6 carbon atoms or a cycloalkyl radical of from 5 to 10 carbon atoms, R2 is a hydrogen atom, a halogen atom, an alkyl radical of from 1 to 6 carbon atoms or an alkoxy radical of from 1 to 6 carbon atoms, n is a positive integer of from 1 to 4, and m is zero or a positive integer of from 1 to 5, by reacting an N-phenyl carbamic acid ester of the general formula where R1, R2, and n have the same meanings as described above, with formaldehyde or a formaldehyde-prodcuing compound in the presence of water and an acid catalyst, the improvement which comprises (a) using the acid catalyst in the form of its aqueous solution having an acid catalyst concentration, at the start of the reaction, of at least 10% by weight and in an amount, at the start of the reaction, of from 0.01 to 100 moles per mole of the N-phenyl carbamic acid ester; (b) carrying out the reaction at a temperature of from 20 to 150°C; (c) after completion of the reaction, separating the solid reaction product or the organic layer containing it from the aqueous acid catalyst solution containing small amounts of organic impurities; (d) isolating the desired polymethylene polyphenyl polycarbamate from the organic layer; and (e) reusing the aqueous acid catalyst solution for a subsequent reaction of the N-phenyl carbamic acid ester with formaldehyde or a formaldehyde-producing compound without removinc the organic impurities contained therein but after adjusting its acid catalyst concentration to such a level as to provide an aqueous solution having an acid catalyst concentration, at the start of the subsequent reaction, of at least 10% by weight.

9. The process according to claim 8 wherein the acid catalyst is used in the form of its aqueous solution having an acid catalyst concentration, at the start of the reaction, of from 20 to 95% by weight.

10. The process according to claim 8 wherein the acid catalyst is used in an amount, at the start of the reaction, of from 0.1 to 50 moles per mole of the N-phenyl carbamic acid ester.

11. The process according to claim 8 wherein the reaction is carried out at a temperature of from 30 to 100°C.

12. The process according to claim 8 wherein the N-phenyl carbamic acid ester is phenyl carbamic acid methyl ester, phenyl carbamic acid ethyl ester, phenyl carbamic acid isopropyl ester, or phenyl carbamic acid isobutyl ester.

13. The process according to claim 8 wherein the acid catalyst is sulfuric acid, hydrochloric acid, phosphoric acid, boric acid, formic acid, acetic acid, oxalic acid, toluenesulfonic acid, hydrobromic acid, perchloric acid, chlorosulfonic acid, or trifluoromethanesulfonic acid.

14. The process according to claim 13 wherein the acid catalyst is hydrochloric acid or sulfuric acid.