GB2039898A

GB2039898A - Process for preparing polymethylene polyphenyl polycarbamates

Info

Publication number: GB2039898A
Application number: GB7942812A
Authority: GB
Original assignee: Mitsui Toatsu Chemicals Inc
Current assignee: Mitsui Toatsu Chemicals Inc
Priority date: 1978-12-13
Filing date: 1979-12-12
Publication date: 1980-08-20
Also published as: FR2444054A1; JPS5757028B2; IT7927991A0; GB2039898B; JPS5579358A; NL7908935A; FR2444054B1; CA1119609A; IT1126562B; DE2950260A1

Abstract

In a process for preparing polymethylene polyphenyl polycarbamates of general formula <IMAGE> by reacting an N-phenyl carbamic acid ester of general formula <IMAGE> with formaldehyde or a formaldehyde- producing compound in the presence of an acid catalyst, the use of an acid having an acid dissociation constant (Ka) of not less than 1.25 x 10<-7> in acetic acid at 25 DEG 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

SPECIFICATION Process for preparing polymethylene polyphenyl polycarbamates This invention relates to an improved process for preparing polymethylene polyphenyl polycarbamates.

More particularly, it relates to an improved 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.

Polymethylene polyphenyl polycarbamates are substances that are useful in the manufacture of agricultural chemicals, drugs, polyamides, polyurethanes, and the like. In addition, polymethylene polyphenyl polycarbamates can be thermally decomposed to produce the corresponding polymethylene polyphenyl polyisocyanates. Accordingly, it is desirable to develop new processes for preparing polymethylene polyphenyl polycarbamates with industrial advantages.

One well-known prior art process for preparing polymethylene polyphenyl polycarbamates comprises reacting a corresponding polymethylene polyphenyl polyisocyanate with alcohol. However, the preparation of the polymethylene polyphenyl polyisocyanate used as a starting material involves the use of highly toxic anilene and phosgene and, moreoever, requires a complicated procedure.

Another well-known prior art process for preparing polymethylene polyphenyl polycarbamates comprises reacting a corresponding polymethylene polyphenyl polyamine with a chloroformic acid ester. However, the polymethylene polyphenyl polyamine and chloroformic acid 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. However, the process described in the aforementioned German Patent 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.

It is an object of the present invention at least in a preferred example, to provide a process for preparing polymethylene polyphenyl polycarbamates by reacting an N-phenyl carbamic acid ester with formaldehyde which process can achieve a higher reaction rate than has been attainable by well-known prior art processes.

In one form of the present invention, an N-phenyl carbamic acid ester is reacted with formaldehyde in the presence of an acid having an acid dissociation constant (Ka) of not less than 1.25 x 1 10-7 in acetic acid at 25"C, whereby a higher reaction rate than has been attainable by prior art processes can be achieved.

The present invention provides 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 for 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 25"C.

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, R1 is an alkyl radical such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, any of the penyl radicals derived from n-pentane and its isomers, any of the hexyl radicals derived from n-hexane and its isomers, etc.; or a cycloalkyl radical such as cyclopentyl, cyclohexyl, 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-pentene and its isomers, any of the hexyl radicals derived frm 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 R1 is an alkyl radical as defined above and R2 is a hydrogen atom; halophenyl carbamic acid alkyl esters of the genera formula (II) in which R1 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 R1 and R2 are alkyl radicals as defined above; alkoxyphenyl carbamic acid alkyl esters of the general formula (II) in which R1 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 R1 is a cyclopentyl or cyclohexyl radical and R2 is a hydrogen atom; halophenyl carbamic acid cyclopentyl orcyclohexyl esters of the general formula (II) in which P1 is a cyclopentyl or cyclohexyl radical and R2 is a halogen atom as defined above; alkylphenyl carbamic acid cyclopentyl or cyclohexyl esters of the general formula (II) in which R is a cyclopentyl or cyclohexyl radical and R2 is an alkyl radical as defined above; alkoxyphenyl carbamic acid cyclopentyl or cyclohexyl esters of the general formula (II) in which R1 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, phenyl carbamic acid n-propyl ester, phenyl carbamic acid isoprpyl ester, phenyl carbamic acid n-butyl ester, phenyl carbamic acid sec-butyl estser, phenyl carbamic acid isobutyl ester, phenyl carbamic acid tert-butyl ester, phenyl carbamic acid pentyl ester, phenyl carbamic acid hexyl ester, o-chlorophenyl carbamic acid methyl ester, o-chlorophenyl carbamic acid ethyl ester, o-chlorophenyl carbamic acid isopropyl ester, o-chlorophenyl carbamic acid 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, phenyl carbamic acid cyclopentyl ester, and m-methoxyphenyl carbamic acid methyl ester.Among 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.

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 conditions of the present invention, and specific examples thereof include paraformaldehyde, methylal, and otherformals. Usually, an aqueous solution of formaldehyde is used.

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 1.25 x 10-7 in acetic acid at 25"C. The term "acid dissociation constant (K8)" 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 equilibration reaction by which 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 (K8) is defined by [X-][SH-] K8 [HX] Specific examples of the acid include hydroiodic acid, hydrobromic acid, perchloric acid, chlorosulfonicacid, fluorosulfonic acid, tribluoromethanesulfonic acid, and polysulfuric acids of fhe formulas H2S207, H2S301o, H2S4013, etc. These acids may be used alone or in the form of a mixture of two or more thereof.Moreover, they may be used in the form of a mixture with one or more common acids such as hydrochloric acid, sulfuric acid, acetic acid, etc. All the common acids, such as hydrochloric acid, sulfuric acid, phosphoric acid, boric acid, etc., that are described in the aforesaid German Patent No. 1,042,819 have an acid dissociation constant (K8) of less than 1.25 x 10-7 in acetic acid. Accordingly, when used alone, they fail to provide a satisfactorily high reaction 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 examples of the suitable solvents include aliphatic hydrocarbons such as hexane, heptane, etc.; alicyclic hydrocarbons such as cyclopentane, cyclohexane, etc.; halogenated hydrocarbons such as chloroform, methylene chloride, carbon tetrachloride, dichloroethane, trichloroethane, tetrachloroethane, etc.; fatty acid alkyl esters such as ethyl acetate, etc.; aromatic compounds such as benzene, toluene, nitrobenzene, monochlorobenzene, dichlorobenzene, etc.; and the like. Water is one of the suitable solvents, too.

In carrying out the process of the present invention, no particular limitation is placed on the amounts of N-phenyl carbamic ester, formaldehyde, or formaldehyde-producing compound, and acid used. However, the formaldehyde or formaldehyde-producing compound is usually used in an amount of from 0.1 to 10 moles and preferably from 0.2 to 2.0 moles per mole of the N-phenyl carbamic acid ester. The acid is usually used in an 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. Similarly, 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-phenyl carbamic acid ester.

The reaction temperature may range from 20to 1508C and preferably from 30to 100 C.

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-producting compound and the acid thereto, and then 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 of the N-phenyl carbamic acid ester and the acid.

Furthermore, the process of the present invention may be carried out in a continuous operation system 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 amounts of starting materials and acid used, the type of operation, reaction conditions, and the like. In the case of batch operation, it may generally range from 0.5 to 40 hours.

After completion of the reaction product is usually obtained in the form of an oily layer or solid which spontaneously separates from the aqueous acid solution layer. Thus, the reaction product or the layer containing it may be isolated by any suitable technique such as the use of a separating funnel, filtration, etc., washed with water, stripped of solvent, and then dried to obtain an end product.

According to the process of the present invention, a variety of polymethylene polyphenyl polycarbamates of the general formula (I) can be prepared depening on the N-phenyl carbamic acid ester used as a starting material. Under ordinary reaction conditions, the reaction produced is a mixture comprising a greater amount of binuclear compounds of the general formula (I) in which m is equal to zero and a smaller amount oftrinuclear, tetranuclear, pentanuclear, and higher polynuclear compounds of the general formula (I) in which m is equal to 1,2,3, or more, respecitvely.

The process of the present invention can achieve a reaction rate which is two or more times as high as has been attainable by well-known prior art processes using common acids. This enhancement in reaction rate has a gresat industrial advantage in that the yield per unit per unit time of the end product can be increased and the size of the reaction equipment can be reduced.

The process of the present invention is further illustrated by the following examples. In each of these examples, the initial reaction rate constant (k) was determined by taking small amounts of samples at intervals of 30 minutes or an hour, measuring the N-phenyl carbamic acid ester concentrations of the samples, and then calculating the value fork according to the following equation: Reaction Rate = - d[N-phenyl carbamic acid ester] dt = k[N-phenyl carbamic acid esterj[formaldehyde] where square brackets denote the moles of the enclosed compound that is present in each liter of the organic layer. The molar concentration of formaldehyde was calculated on the assumption that one mole of the N-phenyl-carbamic acid ester reacted with one-half mole of formaldehyde.In all cases, the reaction of the present invention was in close accord with the above equations at its initial stage.

Example I Into a 100-ml flask fitted with a thermometer, a stirrer, and a dropping funnel were charged 20 g of phenyl carbamic acid ethyl ester, 18 g of tribluoromethanesulfonic acid (having an acid dissociation constant (K8) of 1.26 x 10-5 in acetic acid at 250C), and 50 g of water. After the flask was heated to 100 C 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 100 C for 5 hours, cooled to room temperature, and then shaken with 100 ml of chloroform. The chloroform layer was separated from the aqueous layer, washed three times with 100 ml each of water, and then concentrated to obtain 20 g of a product.When the product was dissolved in tetrahydrofuran 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 oftrinuclear and higher polynuclear compounds, and 18% by weight of unreacted phenyl carbamic acid ethyl ester. These results means 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 e/min.mole.

Examples 2 to 4 In these examples, the procedure of Example 1 was repeated except that each of three acids other than trifluoromethanesulfonic acid was used. The results thus obtained, together with the acid dissociation constants (K8) of those acids in acetic acid. are shown in Table 1.

Comparative Examples 1 and2 In these comparative examples, the procedure of Example 1 was repeated except that hydrochloric acid or sulfuric acid was used in place of the trufluoromethanesulfonic acid. The results thus obtained are shown in Table 1. For a fixed reaction time, all the examples shown in Table 1 exhibited a 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.

TABLE 1 Charged Materials: Phenyl carbamic acid ethyl ester (0.12 mole), acid (0.12 mole), formaldehyde (0.06 mole), and water (50 g).

Reaction Temperature: 98-100"C.

Number of Super Acid Results Example or Initial Reaction Reaction Comparative Type K8 Rate Constant k Time Example (x 105t/min.mole) (hours) Example 2 Perchloric 1.26 x 10-5 22 5 acid Example3 Hydrobromic 2.5x 10-6 7 5 acid Example 4 Hydroiodic 1.59 x 10-6 7 5 acid Comparative Hydrochloric 2.5 x 10-9 3 5 Example 1 acid Comparative Sulfuric 6.3 x 10-8 3.5 5 Example 2 acid Number of Conversion of Yield Based on acid Carbamic Acid Example or Carbamic Acid Ester Consumption (%) Comparative Ester (%) Binuclear Trinuclear and Higher Example Compounds Polynuclear Compounds Example 2 77 48 12 Example 3 66 42 9 Example 4 60 40 10 Comparative Example 1 48 42 6 Comparative 50 50 4 Example 2 Examples 5 and 6 In these examples, the procedure of Example 1 was repeated except that each of two N-phenyl carbamic acid esters was used. The results thus obtained are shown in Table 2. For purpose of comparison, the initial reaction rate constants, determined by using hydrochloric acid in place of the trifluoromethanesulfonic acid are also shown in Table 2.

Charged materials: N-phenyl acid ester (0.12 mole),trifluoro - methanesulfonic acid (0.12 mole), formaldehyde (0.06), and water (50 g).

Reaction Temperature : 98-100"C.

Reaction Time: 4 Hours.

Results Number of N-Phenyl Carbamic Initial Reaction Conversion of Example Acid Ester Rate Constant K Carbamic Acid (x 106 {/min-mole Ester (%) Example 5 Phenyl carbamic acid 50 87 methyl ester Example 6 Phenyl carbamic acid 5 52 isobutyl ester Initial Reaction Rate Constant as Yield Based on Carbamic Acid Determined with Ester consumption (%) Hydrochloric Acid Numberof Binuclear TrinuclearandHigher (x 106) Example Compounds Polynuclear Compounds Example 5 45 22 7 Example 6 20 30 0.8

Claims

1. A process for preparing a polymethylene polyphenyi polycarbamate ofthe 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, andm is zero our 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 means as described above, with formaldehyde or a formaldehydeproducing compounds in the presence of an acid having an acid dissociation constant (K8) 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 H2S207, H2S301o, H2S4O3, etc.

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-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.

9. A process according to claim 1, substantially as exemplified herein.

10. A polymethylene polyphenyl polycarbamate produced by a process according to any one of the preceding claims.