Method for Producing an Aliphatic Triisocyanate

This invention relates to a method for producing a novel aliphatic triisocyanate.

It has long been known that aliphatic isocyanates impart premium properties to urethanes derived therefrom in terms of light stability. However, a conventional aliphatic isocyanate such as hexamethylene diisocyanate is characterized by toxicity which renders its handling and use extremely hazardous.

Accordingly, they are often converted to polyisocyantes having a higher molecular weight before subjecting to a practical use in order to lower the toxicity. Such a conversion may be carried out by reacting a relatively low molecular weight polyisocyanate with various polyfunctional compounds such as polyhydroxyl compounds and biuret derivatives. Examples of those converted polyisocyanates, as derived from hexamethylene diisocyanate, are as follows; ##STR2##

In such a conversion, however, a considerable amount of the starting isocyanates, hexamethylene diisocyanate in the above examples, tends to remain unreacted. As a result the mixtures thus obtained are often still toxic. Such conversion processes also involve a higher production cost. The converted polyisocyanates as mentioned above are usually so viscous that they inevitably require diluents for convenient handling and use, and may be unsuitable for usage as high solid type coatings.

Therefore, it has long been desired to produce polyisocyanates that have a low toxicity and viscosity, and that can give a polyurethane resin or coatings having excellent properties with respect to light stability, water-proof, stabilities against organic and inorganic substances and so on.

It is therefore an object of the present invention to provide a novel aliphatic polyisocyanate especially suitable for preparation of a non-yellowing polyurethane. It is a further object to provide a process to produce the novel polyisocyanate from readily available raw materials in high yield by a simple process.

We have now discovered that a novel aliphatic triisocyanate, 1,6,11-undecanetriisocyanate represented by following Formula (I) ##STR3## is produced by a method which comprises: a. Forming 1,6,11-undecanetriamine into a crystalline salt in the presence of an alcohol having at least three carbon atoms,

b. Forming the resulting salt into a fine powder,

c. Reacting the resulting fine powder with phosgene to produce the 1,6,11-undecanetriisocyanate product, or a method which comprises:

a. Adding 1,6,11-undecanetriamine at 0.degree.-20.degree. C. into an inert solvent which contains phosgene in a concentration of 20-50 wt.%,

b. Heating the resulting mixture at 65.degree.-75.degree. C. in the presence of phosgene,

c. Then raising the temperature of the resulting mixture to above 120.degree. C. in one hour in the presence of phosgene,

d. Reacting the resulting mixture with phosgene at above 120.degree. C. more than 6 hours,

e. Purifying the resulting triisocyanate by vacuum distillation under a lower pressure than 0.8 Torr.

The novel triisocyanate of the present invention is produced by reacting 1,6,11-undecanetriamine or its salts with carbonyl dihalide. The starting triamine can be produced by processes already known. For example, 7-(5'-aminopentyl)-3,4,5,6-tetrahydro-2H-azepine (hereinafter referred to as the "Schiff's base"), represented by the following Formula, ##STR4## can be converted to the triamine by catalytic hydrogenation in the medium of an aqueous solution of ammonia.

The "Schiff's base" can be readily produced by thermolysis of .epsilon.-caprolactam, .epsilon.-aminocaproic acid or an oligomer or polymer thereof in the presence of a hydroxide or oxide of an alkali metal or alkali earth metal such as lithium and calcium.

The triamine thus produced is converted to the novel triisocyanate of the present invention by reacting with a carbonyl dihalide, preferably phosgene, in liquid or gaseous form. The phosgenation is carried out in one step or a multi-step, for example, two step method.

In one step method, the amine may be supplied to the reaction zone in the form of amine salts formed with hydrogen chloride, sulfuric acid, phosphoric acid, carbonic acid or carboxylic acids such as acetic acid. The amine hydrochloride in a form of a fine powder may be preferably employed as the amine salt. The fine powder is produced by forming 1,6,11-undecanetriamine into a crystalline salt in the presence of an alcohol having at least three carbon atoms, preferably isopropyl alcohol and pulverizing the resulting crystalline salt to an average size of below 1 mm, more preferably below 0.3 mm, since the amine salts scarcely dissolve in the reaction mixture. In the absence of said alcohols, the crystalline salt of 1,6,11-undecanetriamine is difficult to be obtained.

The amine salt is dispersed in an inert liquid reaction medium, and phosgene is added thereto preferably in a stoichiometrical excess to the amino group existing in the reaction system. The temperature of the reaction medium is maintained within the range of from about 100.degree. C. to about 230.degree. C., preferably about 180.degree. C.

Alternatively, the phosgenation of the amine can be carried out in a multi-step method. In a preferred embodiment of the invention, the phosgenation of the amine is first carried out by adding 1,6,11-undecanetriamine at 0.degree.-20.degree. C. into an inert solvent, preferably o-dichlorobenzene, which contains phosgene in a concentration of 20-50 wt. %. Then the reaction mixture is heated at 65.degree.-75.degree. C. in the presence of phosgene for a sufficient period to produce a slurry with good fluidity.

The temperature of the resulting slurry is then raised to above 120.degree. C. in one hour in the presence of phosgene. A longer period to raise the temperature causes formation of a mass of sticky substance from the slurry. Then the resulting slurry is reacted with phosgene at above 120.degree. C. more than 6 hours.

This two step procedure may have advantages over the one step method because the one step method tends to produce side products which result from the secondary reaction of the isocyanate with the starting amine.

In any procedure for phosgenation in the invention, the molar ratio of phosgene to the amine group may be from about 1.1:1 to 10:1 and preferably at least 2:1. Suitable inert liquid reaction media for the phosgenation include aromatic hydrocarbons, chlorinated aromatic hydrocarbons, chlorinated aliphatic hydrocarbons, etc. After completion of the phosgenation, the product, 1,6,11-undecanetriisocyanate may be purely isolated by vacuum distillation from the reaction medium under a lower pressure than 0.8 Torr. However, in case trace amounts of impurities which have hydrolyzable chlorine compounds are contained in the product, the distillation can be carried out in the presence of anhydrous bases such as calcium oxide, potassium carbonate, sodium carbonate, etc, to allow recovery of the isocyanate, which is practically free from the chlorine compounds.

The triisocyanate thus produced has been found to have several unusual properties, and confirmed to be a novel compound, which belongs to a new type of aliphatic triisocyanates. The triisocyanate of the present invention possesses advantages over aliphatic isocyanates of the prior art. This isocyanate differs significantly from the other aliphatic isocyanates, such as hexamethylene diisocyanate or 2'-isocyanatoethyl-6-isocyanatocaproate because of its substantially reduced toxicity and strong resistance to the action of alkaline substances. Some of these properties may be attributed to the chemical structure of the novel isocyanate as it has neither any hetero-atoms such as oxygen and nitrogen, nor any unsaturated bonds in the molecule except for the three NCO groups. The novel isocyanate of the present invention boils at 166.degree. C. to 167.degree. C. under a vacuum of 0.2 Torr. This range of boiling point will be appreciated to be well-balanced from the view-point of purification and toxicity: this isocyanate generates scarcely any odor or vapor irritating to the nose, eyes, throat, etc, because of its low vapor pressure, whereas it can be easily purified by a vacuum distillation.

Moreover, the NCO group content in the novel triisocyanate of the present invention reaches as high as about 45 wt. %, based on the total weight of the triisocyanate. Furthermore, the novel triisocyanate has low viscosity so that it does not necessarily require a process to dilute it with solvents for the purpose of lowering viscosity for practical usage. Before this invention, we have not known of any aliphatic polyisocyanates possessing such high purity, low toxicity, high NCO content, and moderately low viscosity.

The novel isocyanate of the present invention may be used in the same fields as aliphatic polyisocyanates of prior art have been used. For example, it can be used in the fields such as polyurethane by reacting various compounds, including polymers, containing active hydrogen groups such as polyols, as well as intermediates for producing other novel compounds or polymers, and so on. Polyurethane are used for paints, films, foams, elastomers, adhesives, treating agents for textiles, and so on. Especially, the employment of the novel triisocyanate for producing polyurethanes brings satisfactory advantages to the products with respect to durability, water resistance, resistance to the acids or bases as well as organic solvents, and light-stability in comparison with that derived from available aliphatic polyisocyanates.

The following examples will serve to further illustrate the present invention.

In a 100 ml autoclave were placed 14 g of 7-(5'-aminopentyl)-3,4,5,6-tetrahydro-2H-azepine, 30 ml of 28% aqueous ammonia and 3 ml of Raney-Nickl. After the inside of the autoclave was flushed with hydrogen, the autoclave was pressurized with hydrogen until a pressure of 80 atm was reached, and heated at 90.degree. C. for 8 hrs. After the catalyst was filtered off, the water and ammonia were distilled off and the resulting residue was analysed by gas-chromatography and found to contain 13 g of 1,6,11-undecanetriamine and 1.8 g of 2-(5'aminopentyl)-perhydroazepine. The residue was distilled at 132.degree. C. at 2 Torr to give the pure triamine.

To a solution of 100 g of 1,6,11-undecanetriamine obtained in Example 1 in 100 ml of methanol, 136 ml of concentrated (35 wt. %) hydrochloric acid was added drop wise while cooling to maintain the reaction temperature below 30.degree. C. The reaction mixture was concentrated by means of a rotary evaporator in vacuo on a hot-water bath to yield a thick oil. The oil, which on digestion with 500 ml of isopropyl alcohol was similarly concentrated, was evacuated at about 80.degree. C. under a vacuum below 5 Torr for 10 hrs to give white solids of 1,6,11-undecanetriamine trihydrochloride. The solids thus obtained were crushed and pulverized in a mortar with a pestle under a dry atmosphere to give fine powders of below 175 .mu.m size by passing through a screen of 80 mesh.

A four-necked, round-bottomed flask fitted with a mechanical stirrer, a thermometer, a gas inlet almost reaching the bottom of the flask and a condenser was charged with 66.5 g of the powders of the triamine hydrochloride and 665 ml of o-dichlorobenzene. The mixture was phosgenated by using a phosgene flow of approximately 30 g/hr. The reaction was started at 130.degree. C. and gradually heated to 140.degree. C. after 4 hrs, then maintained for 7 hrs at 140.degree. C. and further for 4 hrs at 150.degree. C. As the reaction proceeds, starting powders suspended in the mixture are disolved. After cooling to room temperature and filtration, the solvent was distilled off at about 40.degree. C. under reduced pressure of about 4 Torr and the product was distilled at 166.degree. C. to 167.degree. C. at 0.2 Torr to give 47.2 g of 1,6,11-undecanetriisocyanate:

Analysis--Calc'd for C.sub.14 H.sub.21 N.sub.3 O.sub.3 (percent):

C 60.19; H 7,58; N 15.05, Found C 59.89; H 7.55; N 14.82.

High-resolution MS--Calc'd for C.sub.14 H.sub.21 N.sub.3 O.sub.3,

M.sup.+ /e=279,1584, Found M.sup.+ /e=279,1585

IR Spectra (cm.sup.-1)--2940, 2860, 2260(NCO), 1460, 1360

NMR Spectra (ppm)--1.45 (singlet 16 H), 3.4 (distorted triplet, 5H).

In a four-necked, round-bottomed 3-liter flask on an ice-water bath, charged with 1.5 l of o-dichlorobenzene and phosgene generated by decomposing 740 g of trichloromethyl chloroformate over activated carbon, was added a solution of 300 g of 1,6,11-undecanetriamine in 200 ml of o-dichlorobenzene for 2 hrs with mechanical stirring. Then the mixture was heated to 70.degree. C. on an oil bath and stirred while being treated with a phosgene flow at 70.degree. C. for 30 min. The resulting mixture continued to be stirred at 130.degree. C. for 2 hrs, at 140.degree. C. for 2 hrs, and finally at 150.degree. C. for 2.5 hrs, while phosgene being blown through the mixture. After cooling the mixture and filtering it, the solvent was distilled off and the product was distilled at 189.degree. C. at 0.6 torr to give 236 g of the crude desired isocyanate. 77 g of the crude product was distilled in the presence of 0.8 g of potassium carbonate at 168.degree. C. at 0.2 torr to give the pure isocyanate. Alternatively, 25 g of the crude product was distilled in the presence of 0.25 g of calcium carbonate at 178.degree.-180.degree. C. at 0.5 torr to give 22 g of the pure isocyanate.

As mentioned in Example 2, into a solution of 300 g of the triamine in 300 ml methanol was added 430 ml of 36 wt. % of concentrated hydrochloric acid drop by drop for 3 hrs, while cooling below 30.degree. C. with mechanical stirring. The mixture, being mixed with 300 ml of isopropyl alcohol, was subjected to distillation at 50.degree.-60.degree. C. under reduced pressure by means of a rotary evaporator. The product, being mixed with 200 ml methanol and 300 ml isopropyl alcohol, was subjected to distillation in the same manner and on repeating distillation once more the product was evacuated at 80.degree. C. at 2 torr for 8 hrs to give white solids. The solids were pulverized and sieved by being passed through a screen of 60 mesh.

A four-necked, round-bottomed 4-liter flask was charged with 2.2 l of o-dichlorobenzene and 350 g of the triamine trihydrochloride produced above. The mixture was phosgenated for 13.5 hrs by using a flow of phosgene generated by decomposing 1.5 l of trichloromethyl chloformate over activated carbon, while the reaction temperature being maintained at 130.degree. C. for 3 hrs, then at 140.degree. C. for 3.5 hrs and further at 150.degree. C. for 7 hrs. After distillation of the solvent in the same manner as described in Example 2, 255.6 g the triisocyanate was distilled at 183.degree.-189.degree. C. at 0.6 torr.

Each component shown in Table 1 was mixed with the isocyanate compound. Thus resulting liquids were coated onto tin panels, and then the coated panels were cured at 120.degree. C. for 2 hrs. The resulting films had various properties and exhibited an excellent gloss.