CA1119609A

CA1119609A - Process for preparing polymethylene polyphenyl polycarbamates

Info

Publication number: CA1119609A
Application number: CA000341545A
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: 1978-12-13
Filing date: 1979-12-10
Publication date: 1982-03-09
Also published as: GB2039898A; FR2444054A1; JPS5757028B2; IT7927991A0; JPS5579358A; FR2444054B1; NL7908935A; GB2039898B; DE2950260A1; IT1126562B

Abstract

Abstract of the Disclosure:

In a process for preparing polymethylene polyphenyl polycarbamates by reacting an N-phenyl carbamic acid ester with formaldehyde or a formaldehyde-producing compound in the presence of an acid catalyst, the use of an acid having an acid dissocia-tion constant (Ka) of not less than 1.25 x 10 7 in acetic acid at 25°C brings about an enhanced reaction rate as compared with those which have been attainable by prior art processes. For example, when an N-phenyl carbamic acid ester is reacted with a 35% aqueous solution of formaldehyde in the presence of trifluoromethane-sulfonic acid, the reaction rate is greatly enhanced as compared with the cases in which prior art acid catalysts such as sulfuric acid, hydrochloric acid, etc. are used.

Description

9~a~ 1 i .'1 , E(',IFICATION

Title of the Invention:
Process for Preparing Polymethylene Polyphenyl Polycarbamates ¦ Background of the Invention:
~ 1. Piled of the Inven~ion ¦ This invention relates to an improved process for preparing polymethylene polyphenyl polycarbamates. More particularly, l it relates to as improved process for preparing polymethylene ¦I polyphenyl polycarbamates by reacting an N-phenyl carbamic acid ¦¦ ester with formaldehyde or a formaldehyde-producing compound in ¦ the presence of an acid catalyst.
1, 2. Description of the Prior Art ,I Polymethylene polyphenyl polycarbamates are substances ¦1~ that are useful in the manufacture o-f agricultural chemicals, drugs, polyamides, polyurethanes, and the like. In addition, polymethylene polyphenyl polycarbamates can be thermally l decomposed to produce the corresponding polymethylene polyphenyl ¦ polyisocyanates. Accordingly, i~ is desirable to develope new 1 processes for preparing polymethylene polyphenyl polycarbamates ¦ with industrial advantages.
¦ One well-known prior art process for preparing polymethylene ¦ polypheny polycarbamates comprlses reacting a corresponding ¦ poly;nethylene polyphenyl polyisocyanate with alcohol. However, ¦I the preparation of the polymethylene polyphenyl polyisocyanate ¦ used as a starting material involves the use of highly toxic I aniline and phosgene and, moreover, requires a complicated f ¦ procedure.
I Another well-known prior art process for preparing . , ' . . . ' ~

.. : ~ , , .': , polymethylene polyphellyl polycarba~a~es comprises reacting a corresponding polymethylene polyphenyl polyamine with a chloro~ormic acid ester. I~owever, the polymethylene polyphenyl polyamine and chloro~ormic acicL es-ter used as starting materials both have such severe intoxicating and irritating properties that they are very difficult to handle, and the procedures ~or preparing them are complicated. For these reasons, this process cannot be regarded as useful in industrial applications.
There is still another well-~nown prior art process for preparing polymethylene polyphenyl polycarbamates by reacting an N-phenyl carbamic acid ester with formaldehyde. ~or 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.
However, the process described in the a~oresaid German Patent exhibits such a low reaction rate that large amounts of unreacted starting materials remain even after the reaction has been carried ou. for a long period of time.
,', Summary of the invention: -It is an object of the present invention to provide aprocess for preparing polymethylene polyphenyl polycarbamates byl ~
reacting an N-phenyl carbamic acid ester with formaldehyde ~ i hich process can achieve a higher reaction rate than has been attainable by well-known prior art processes.
In accordance with one feature of the present invention, I
an N-phenyl carbamic acid ester is reacted with formaldehyde in the presence o~ an acid having an acid dissociation constant tKa) oE not less than 1.25 x 10 7 in acetic acid at 25C, .' I

, ' I .

, ~119~0g 1 1 .1 whereby a higher reaction rate than has been attainable by prior art processes can be achieved.
' ~ I
Il Description of the Preferred_ mbodiments The present invention provides a process for preparing a polymethylene polyphenyl polycarbamate of the general formula . N-C-O-R
Rl-O-C-N ~ ~ CH2 ~ ~ CH2 ~ N-C-O-Rl ~I) (R2)n ~R2)n m (R2)n . where Rl is a lower alkyl radical of from 1 to 6 carbon atoms or a cycloalkyl radical, R2 is a hydrogen atom, a halogen atom~, a 1 lower alkyl radical of from 1 to 6 carbon atoms, or a lower alkox~ .
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 ~o 5, which comprises reacting an N-phenyl carbamic acid ester of the general formula .

- N-C-O-Rl (II) . ~R2) I where Rl, R2, and n have the same meanings as described above :Eor ¦ the general formula (I), with formaldehyde or a formaldehyde- .
producing compound in the presence of an acid having an acid dissociation constant ~Ka) of not less than 1.25 x 10 7 in acetic acid at 25C
iThe N-phenyl carbamic acid ester used in the process of the:
present invention is a compound represented by the general :Eormul ~II). In this formula, Rl is 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 derived ~rom n-hexane and its isomers, etc.; or a cycloalkyl radical such as cyclopentyl, cyclohexyl, etc.; and R2 is a hydrogen a~om; a halogen atom such as chlorine, bromine, fluorine, etc.; an alkyl radical such as methyl, ethyl, n-propyl, isopropyl, _-butyl, sec-butyl, isobutyl, tert-butyl, any of the pentyl radicals derived from n-pentane and its isomers, any of the hexyl radicals derived from n-hexane and its isomers, etc.; or an alkoxy radical composed of any one of the foregoing alkyl radicals and an oxygen atom.
More specifically~ they include phenyl carbamic acid alkyl esters of the general formula ~II) in which Rl is an alkyl radical as defined above and R2 is a hydrogen atom; halophenyl carbamic acid alkyl esters of the general formula ~II) in which Rl is an alkyl radical as defined above and R2 is a halogen atom as defined above; alkylphenyl carbamic acid alkyl esters of the general formula ~II) in which Rl and R2 are alkyl radicals as defined above; alkoxyphenyl carbamic acid alkyl esters of the general formula ~II) in which Rl is an alkyl 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 cyclopentyl or cyclohexyl esters of the general formula (II) in which Rl is a cyclopentyl or cyclohexyl radical and R2 is a halogen atom as defined above; alkylphenyl carbamic acid cyclopentyl or cyclohexy~
esters of the general formula ~II) in which ~1 is a cyclopentyl or cyclohexyl radical and Rz is an alkyl radical as defined above~
alkoxyphenyl carbamic acid cyclopentyl or cyclohexyl esters of th general formula ~II) in which Rl is a cyclopentyl or cyclohexyl radical and R2 is an alkoxy radical as defined above; and the ., I '.

., .
~. l , like.
,i The preferred N-phenyl carbamic acid esters are phenyl i carbamic acid methyl ester, phenyl carbamic acid ethyl ester, ¦~ phenyl carbamic acid n-propyl ester, phenyl carbamic acid isopropyl ester, phenyl carbamic acid _-butyl ester, phenyl carbamic acid sec-butyl ester, phenyl carbamic acid isobutyl ester, phenyl carbamic acid tert-butyl ester, phenyl carbamic acid pentyl ester, phenyl carbamic acid hexyl ester, o-chlorophenyl carbamlc acid methyl ester~ o-chlorophenyl carbamic ¦ acid ethyl ester, o-chlorophenyl carbamic acid isopropyl ester, o-chlorophenyl carbamic acid isobutyl ester~ o-methylphenyl ¦I carbamic acid methyl ester, o-methylphenyl carbamic acid ethyl i ester, phenyl carbamic acid cyclohexyl ester, o-chlorophenyl l carbamic acid cyclohexyl ester, o-methylphenyl carbamic acid ¦, cyclohexyl ester, phenyl carbamic acid cyclopentyl ester, and l m-methoxyphenyl carbamic acid methyl ester. Amon~ these compounds, phenyl carbamic acid methyl ester, phenyl carbamic acid ethyl ester, phenyl carbamic acid isopropyl ester, and phenyl carbamic acid isobutyl ester are particularly preferred.
i In the process o-f 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 conditions of the present invention, and specific examples thereof include paraformaldehyde, methylal, and other 'l formals. Usually, an aqueous solution of formaldehyde is used.
¦I The acid used in the process of the present invention may be any acid that has an acid dissociation constant (Ka) Of not less than l.25 x ~10 in acetic acid at 25~C. The term "acid dissociation constant ~a)" as used herein means the dissociation constant which is generally defined for the dissociation of an acid in its solution. Let us suppose that the equiiibratio reaction by ~rhich an acid HX dissociates in a solvent S is represented by the following equation:
HX (acid) ~ S (solvent) X (conjugate base of acid) ~ SH (conjugate acid of solvent) Then, the acid dissociation constant (Ka) is defined by Ka = [X ] [SH ]
[HX]
` Speicific examples of the acid include hydroiodic acid, hydrobrom c '' acid, perchloric acid, chlorosulfonic acid, fluorosulfonic acid, ! trifluoromethanesulfonic acid, and polysulfuric acids of the ; ~ ulas H2S27~ H2S3lo, H2S4O13, etc- These acids may be used alone or in the form of a mixture of two or more thereof.
~ioreover, they may be used in the form of a mixture with one or more common acids such as hydrochloric acid, sulfuric acid, aceti acid, etc. All the common acids, sùch as hydrochloric acid, sulfuric acid, phosphoric acid, boric acid9 etc., that are ' described in the aforesaid German Patent No. 1,0~2,819 have an acid dissociation constant ~Ka) of less than 1.25 x 10 7 in i' acetic acid. Accordingly, when used alone, they fail to provide ¦j a satisfàctorily high raction rate.
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 starting materials and/or reaction products having high melting points.
In this case, the solvent must be inert to formaldehyde. Specific ii examples of the suitable solvents include aliphatic hydrocarbons !
i~ such as heXane? heptane, etc.; alicyclic hydrocarbons such as ¦
cyclopentane, cyclohexane, etc.; halogenated hydrocarbons such as chloro~orm~ methylene chloride, carbon tetrachloride, li ! !

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dichloroethane, trichloroe-thane, tetrachloroethane, etc.; fatty acid alkyl esters such as ethyl acetate, etc.; aroma-tic compounds such as benzene, toluene, nitrobenzene, monochlorobenzene, i dichlorobenzene, etc.; and the like. Water is one o the suitable solvents, too.
, In carrying out the process of the presen~ invention, no particular limitation is placed on the amounts of N-phenyl carbamic acid ester, formaldehyde or formaldehyde-producing compou Id, and acid used. However, the formaldehyde or formaldehyde- ¦
, producing compound is usually used in an amount of from 0.1 to I
10 moles and preferably from 0.2 to 2.o moles per mole of the N- ¦
phenyl carbamic acid ester. The acid is usually used in ~n amount ¦ of from 0.001 to 20 equivalents and preferably from 0.1 to 10 equivalents per mole of the N-phenyl carbamic acid ester.
Simllarly, no particular limitation is placed on the amount of ¦ solvent used. However, the solvent is usually used in an amount of from 0.1 to 20 parts by weight per part by weight of the N-I' phenyl carbamic acid ester.
- 1 The reaction temperature may range from 20 to 150C and preferably from 30 to 100C.
Generally speaking, the process of the present invention may be carried out by providing the N-phenyl carbamic acid ester as it is or in the form of its solution or suspension in a properly selected solvent, adding the formaldehyde or a formaldehyde-producing compound and the acid thereto, and then stirring the resulting reaction mixture at a predetermined temperature.
Alternatively, the process ofthe present invetnion may also be ¦
carried out by adding a formaldehyde solution drop by drop to a solution or suspension of the N-phenyl carbamic acid ester~and the acid.

,l - 7 -' ~ 6~ 9 Furthermore, the process of the present invention may be ; carried out in a continuous operation sys~em in which a solution or suspension containing the starting materials and the acid in an appropriate proportion is continuously fed to a reactor and continuously withdrawn therefrom after a predetermined residence time.
The reaction time depends on the types or amount o~ startin~
materials and acid used, the type of operatio~9 reaction -conditions, and the like. In the case of batch operation, it may generally range from 0.5 to ~0 hours.
,1 After completion of the reaction, the reaction product is - ~ usually obtained in the form of an oily layer or solid which ,, spontaneously separates from the aqueous acid solution layer. I
c ,I Thus, the reaction product or the layer containing it may be , isolted by any suitable technique such as the use of a ! separating -funnel, filteration,`etc., washed with water, stripped I'~ of solvent, and then dried to obtain an end product.
¦l According to the process of the present invention, a variet) .
of polymethylene polyphenyl polycarbamates of the general 1l formula (I) can be prepared depending on the N-phenyl carbamic il acid ester used as a starting material. Under ordinary ,I reaction conditions, the reaction product is a mixture comprisin~ r - i' a greater amount o~ binuclear compounds of the general formula 1~ ~I) in which m is equal to zero and a smaller amount of trinuclear, tetranuclear, pentanuclear, and higher polynuclear compounds o~ the general formula (I~ in which m is equal to 1,

2, 3, or more, respectively.
The process o-f the present invention can achieve a reactlon rate which is two or more times as high as has been attainable I ~
by l~ell-known prior art processes using common acids. This I ,i enhancement ln reaction rate has a great inclustrial a-lvantage ¦

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: j in that the yield per unit time o~ the end product can be increased and the size of the reaction equipment can be reduced.
The process of the present invention is urther illustrated by the following examples. In leach of these examples, the I, initial reaction rate constant ~k) was determined by taking small ¦jl amounts of samples at intervals of 30 minutes or an hour, measur-i~' ing the N-phenyl carbamic acid ~ester concentrations o-f the samples, and then calculating the value for k according to the following equation:

! d [N-phenyl carbamic acid esterJ
Reaction Rate = -dt = k[N-phenyl carbamic acid ester][formaldehyde where square brackets denote the moles of the enclosed compound Il that is present in each liter of the organic layer. The molar li concentration of formaldehyde was calculated on the assumption jl that one mole of the N-phenyl carbamic acid ester reacted with ¦l one-half mole of formaldehyde. In all cases, the reaction of the present invention was in close accord with the above equation at its initial stage.
Example l j, ' .
,~ Into a lO0-ml flask fitted with a thermometer, a stirrer, ~ I and a dropping funnel were charged 20 g of phenyl carbamic acid I 1, ethyl ester, 18 g of trifluoromethan0sulfonic acid ~having an acid dissociation constant ~Ka) of l.26 x lO 5 in ace~ic acid ! at 25C), and 50 g of water. After the flask was heated to 100C
il 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 resulting reaction mixture was stirred at 100C for 5 hours, cooled to room temperature, and then shaken with lO0 ml of chloroform. The chlorofor~ layer was I i g ' ' .
.

separated from the aqueous layer, ~ashed three times with 100 ml ¦
each of water, and then concentrated to obtain 20 g of a product.
When the product was dissolved in tetrahydro-furan and analyzed by liquid chromatography using naphthalene as an internal standard, it was found to contain 27% by weight of binuclear compounds, 14% by weight of trlnuclear and higher polynuclear compounds, and 18% by weight of unreacted phenyl carbamic acid ethyl ester. These results mean that the degree of conversion of the carbamic acid ester used as a starting material was 82~, ¦
the yield of the binuclear compound based on the amount of ¦
carbamic acid ester consumed was 36%, and the yield of the trinuclear and higher polynuclear compounds based on the amount of carbamic acid ester consumed was 19%. The initial reaction rate constant (k) was 25 x 10 6~/min mole.
I Examples 2 to 4 l~ In these examples, the procedure of Example 1 was repeated except that each of three acids oter than trifluoromethanesulfoni acid was used. The results thus obtained~ together with the acid dissociation constants (Ka) o-f those acids in acetic acid, are shown in Table 1.
n Comparative Examples 1 and 2 In these comparative examples, the procedure of Example 1 was repeated except that hydrochloric acid or sulfuric acid was used in place of the trifluoromethanesulfonic acid. The results thus obtained are shown in Table 1. For a fixed reaction time, all the examples shown in Table 1 exhibited a ~i higher degree of conversion than the comparative examples shown therein, thus indicating that the process of the present invention can achieve a higher reaction rate.

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Claims

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

1. A process for preparing a polymethylene polyphenyl polycarbamate of the general formula where R1 is a lower alkyl radical of from 1 to 6 carbon atoms or a cycloalkyl radical, R2 is a hydrogen atom, a halogen atom, a lower alkyl radical of from 1 to 6 carbon atoms, or a lower 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, which comprises 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 an acid having an acid dissociation constant (Ka) of not less than 1.25 x 10-7 in acetic acid at 25°C.

2. The process according to Claim 1 wherein the acid is selected from the group consisting of hydroiodic acid, hydrobromic acid, perchloric acid, chlorosulfonic acid, and polysulfuric acids of the formulas H2S2O7, H2S3O10, H2S4O13.

3. The process according to Claim 1 wherein the N-phenyl carbamic acid ester is selected from the group consisting of phenyl carbamic acid methyl ester, phenyl carbamic acid ethyl ester, phenyl carbamic acid n-propyl ester, phenyl carbamic acid isopropyl ester, and phenyl carbamic acid isobutyl ester.

4. The process according to Claim 1 wherein the formaldehyde or formaldehyde-producing compound is used in an amount of from 0.1 to 10 moles per mole of the N-phenyl carbamic acid ester.

5. The process according to Claim 1 wherein the acid is used in an amount of from 0.001 to 20 equivalents per mole of the N-phenyl carbamic acid ester.

6. The process according to Claim 1 wherein the reaction is carried out in an organic solvent which is inert to formaldehyde.

7. The process according to Claim 6 wherein the organic solvent is used in an amount of from 0.1 to 20 parts by weight per part by weight of the N-phenyl carbamic acid ester.

8. The process according to Claim 1 wherein the reaction is carried out at a temperature of from 20° to 150°C.