MXPA99010608A - Method for the preparation of organic isocyanates - Google Patents

Abstract

Method for the preparation of aromatic monomeric or polymeric isocyanates by decomposing aromatic monomeric or polymeric carbamates of the formula R1(NHCOOR2)x wherein x is at least 1, R1 is an aromatic radical of valency x and R2 is a monovalent organic radical, into aromatic monomeric or polymeric isocyanates of the formula R1(NCO)x and alcohols of the formula R2OH, characterised in that the radical R2 is substituted by a group containing at least one halogen group.

Description

METHOD FOR THE PREPARATION OF I SOC IANATO S ORG NICOS BRIEF DESCRIPTION The present invention relates to a method for the preparation of monomeric or polymeric aromatic isocyanates by thermal decomposition of monomeric or polymeric aromatic carbamates. EP-A 611,243 describes the preparation of organic isocyanates by thermal decomposition of the corresponding carbamate dissolved in an isocyanate solvent and an alcohol in multiple and independent steps. In intermediate steps the solvent is treated with an agent of s po j ami on to remove the alcohol formed during the heat treatment and finally a solution rich in isocyanate is recovered. US Pat. No. 5,453,536 describes the pyrolysis of polycarbamates substantially in the absence of a solvent under reduced pressure and at a temperature of about 150 to about 270 ° C to form the corresponding pyridine and a secondary alcohol. Alcohols containing a halogen atom are not mentioned.

US Pat. No. 4,547,322 discloses a method for making MDI from an N-1-carbamazepine comprising the mecha nization of an N-pheny1-carbamoy to produce a diphenylmethane di-cabama and to submit the latter to a process of thermal decomposition consisting of dissolving the dinuclear diphenylmethane dicarbamate in a solvent having a boiling point between 120 and 350 ° C, allowing the solution to flow into a reactor and into contact with the reactor. countercurrent with a vehicle introduced into the reactor upstream to produce an organic hydroxyl compound and recover said hydroxyl compound as steam and the vehicle at the upper end and the isocyanate solution at the lower end of the reactor. It is mentioned that the method can be used with, among others, N-f eni 1 carb ats substituted with 2, 2, 2-tric 1 oroeti 1 and 2, 2, 2-trif 1 or roeti 1 but no examples are presented thereof. US Pat. No. 3,746,689 describes the use of halogenated alcohols having between 1 and 6 carbon atoms as blocking agents for isocyanates. An improved method for the preparation of monomeric or polymeric isocyanates by thermolysis of the corresponding monomeric or polymeric carbamates has now been found. The invention therefore relates to a method for the preparation of monomeric or polymeric aromatic isocyanates by the decomposition of monomeric or polymeric aromatic carbamates of the formula Rx (NHCOOR2) x where x is at least 1, R 1 is a aromatic radical of valence x and R2 is a monovalent organic radical, in monomeric or polymeric isocyanates of the formula Ri (NCO) x and alcohols of the formula R20H, characterized in that the radical R2 is replaced by a group containing at least one carbon atom. halogen It is possible to obtain organic isocyanates at reduced temperatures with high yield in the absence of a solvent or concentrated solutions. Ri is a substituted or substituted, saturated or unsaturated aromatic hydrocarbon radical containing optionally l e t th e r th e r t o n s. R2 is preferably substituted by at least one chlorine or fluorine atom. The carbamate composition which is subjected to decomposition may be a mixture of polymeric carbamate compounds of different functionalities which, after decomposition, result in a mixture of polymeric isocyanates. It should be understood that in such cases the value of x is an average of the functionalities of all the species present in the carbamate mixture. The term 'functionality' as used in this documentation means numerical average functionality. The average value of x is generally between 1 and 15, preferably between 2 and 10 and more preferably between 2 and 3. The term "polymeric" as used in this documentation refers to any functionality above 1. Preferred radicals like Rj are toluene, diphenylene or polymethylene polyphenylene pre-mixtures or mixtures thereof. The alcohols that can be formed include, for example, 2, 2, 2-trif 1, or roet ano 1, 2,2,2-tric 1, no 1, tric 1 or orne t a 1, 1,1,1 , 3,3,3-hexafluorine oi s or ropanol, nonafluoro tert.butanol, fluorophenols, chlorophenols and polysubstituted halogenated phenols. Representative monomeric isocyanates which can be formed include f-ilisocyanate, 4-chlorophenylisocyanate, 2-f-1 or rof-en-11-isocyanate, 3, 4-di-1-orophene, and 1-isocyanate, to 1 and 1 is oci ana toy di is op r op i 1 f eni 1 is oc i ana to. Some examples of isocyanates differing from one to the other are that they can be manufactured according to the present method include di-phenylamino-isocyanates such as 4,4'-diphenylmethane diisocyanate, 2, 4'-di f This invention relates to 2,2'-diphenylmethane diisocyanate and mixtures thereof, toluene diisocyanates such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate and mixtures thereof. , m-phenylene diisocyanate and 1,5-naphthylene diisocyanate. The method of the present invention can be used advantageously for the preparation of diphenylmethane diisocyanates, toluene diols, polymethylene polyisocyanates, or mixtures of any of the foregoing. The isocyanates T r i f un a 1 e s and superior functionality that can be manufactured include 2,4, 6-toluene t r i i ss oci ana and polymethylene polyphenylene polyisocyanates. As already mentioned, any monomers of mono-, di- and polyfunctional isocyanates can be obtained according to the composition of the initial carbamate mixture. The reaction can be carried out in an inert solvent, ie of any solvent that does not interact with the isocyanates or alcohols under the reaction conditions applied. However, the isocyanates formed in the decomposition reaction can also serve as a solvent for the reaction. Suitable inert solvents that may be employed include, for example, aromatic hydrocarbons such as benzene, halogenated aromatic hydrocarbons such as no or no, ortho-dichlorobenzene, trichloro-benzene or 1-chloronaphthalene. "alkyl aromatic hydrocarbons such as toluene, xi 1 ene, ~ ethylbenzene, eumeno otetr ah i onate phta 1 ene, other aromatic hydrocarbons, such as anisole, diphenylether, et oxibe nc eno, b in z oni tri 1 or, 2-fluoroanisol, 2,3-dimethylanisole or trifluorotoluene or mixtures thereof. Among the preferred solvents are the monoblock r.ob in the ceo or ortho-di el or r obe nce no. Any of the aforementioned solvents can also be used to generate "the gaseous vehicle." The gaseous vehicle serves to physically remove any alcohol without forming a chemical bond therewith.

Mixtures of at least one of the mentioned solvents can also be used with an inert low-boiling solvent used as a gaseous carrier. Examples of such additional lower boiling point solvents are alkanes such as n-pentane, n-hexane, n-heptane or higher or branched alkanes, cyclic alkanes such as cyclopropyl, cyclohexane or its derivatives, alkanes halogenated as chloroform, diisocyanate, carbon tetrachloride, and alkanes with other functional groups such as diethyl ether, acetonitrile, dioxane and the like. The method can be carried out at atmospheric pressure, preferably under nitrogen. However, in the absence of a solvent, the reaction preferably takes place under reduced pressure, in which case the pressure is preferably reduced to between 10-4 and 50 mbar, and more preferably between 0.1 and 10 mbar. Sometimes, upward pressure may be necessary, depending on the type of solvent used.The reaction time depends on the temperature and type and amount of the carbamate compound, but normally it will not exceed 5 hours.

Reaction times of less than 3 hours are common, and reaction times of less than 1 hour have been achieved without any problem. The reaction temperature depends to a large extent on whether or not a solvent is present. In general, it will be between 50 and 350 ° C. In a solvent-free method the temperatures will normally be between the melting point of the carbamate and 350 ° C, whereas in the presence of a solvent the temperature will preferably be between 100 and 200 ° C and more preferably between "120 and 190 ° C. With the method of the present invention, isocyanate yields of more than 90% can be easily obtained. The yields of at least 95% are possible.The method can be practiced in any suitable apparatus which can be equipped, if necessary, with stirring and heating means and / or cooling means for maintaining the temperature within the desired range In general a distillation column is also attached to said apparatus The method of the present invention can be conducted in batch processes or as semi-continuous processes or continuous.

The order of incorporation of the reagents can be modified to adapt them to the specific devices and / or reagents used. In general, the presence of any other compounds, such as catalysts or coolants, in addition to the carbamate and opium compound is not required in the solvent. The isocyanates and alcohols obtained by this method are generally of high purity and no additional treatment is required to continue purifying said products.It is only necessary to remove the solvent, if present, if a degree of purity is particularly required. Highly elevated, the reaction products formed can be subjected to known purification methods, such as filtration, extraction, recrystallization or distillation.The invention is illustrated in a non-limiting manner by the following examples.

EXAMPLES EXAMPLE 1 It was introduced in a suitable container -equipped with a condenser, 3 g of diphenylmethane bis (1, 1, 1, 3, 3, 3 - hexa f luo r oi s op r opi 1 ca rbama t o). The carbamate was heated to a temperature of 52 ° C. After the carbamate melted, the pressure was reduced to 0.1 mbar. As the reaction evolved, the 1, 1, 1, 3, 3, 3 - he xa f 1 uo r o i op op op a or 1 was removed from the system. After 25 minutes at 240 ° C, diphenylmethane diisocyanate containing 33.6% by weight of NCO groups remained in the pyrolysis vessel.

EXAMPLE 2 Example 1 was repeated, but 4.2 g of polyphenylene polymethylene pol 1 (1,1,1,3,3,3-hexafluoroisopropylcarbamate) was used in place of diphenylmethane bis (1,1,1,3,373- hexa f 1 uor ois op r opi 1 carbama to). The carbamate was heated to a temperature of 220 ° C. After the carbamate was melted, the pressure was reduced to 2 mbar. The 1,1,1,3,3,3-He x a f 1 u or r o s op op op 1 was removed from the system as 1 a r e a c c t ion evolved. After _20 minutes at 220 ° C, the polyphenylene polymethylene polymer pyrolysis vessel containing 30% by weight of NCO groups remained in the container.

EXAMPLE "3 (comparative) Example 1 was repeated, but 2 g of diphenylmethane bis (isopropylcarbamate) was used in place of diphenylmethane" bis (1,1,1,3,3,3-hexafluoroisopropylcarbamate). The carbamate was heated to a temperature of 220 ° C. After the carbamate was melted, the pressure was reduced to .1-3 mbar.The isopropanol was removed from the system as the reaction evolved. minutes at 220 ° C remained in "the pyrolysis vessel diphenylmethane diisocyanate containing 5.7% by weight of NCO groups.

EXAMPLE 4- (comparative) - Example 1 was repeated, but were used 2. 1 g of diphenylmethane bis (1-methyl t-oxy-2-pr or 1 carbamate) instead of diflethymethane bis (1, 1, 1, 3, 3, 3-hexafluor or isopropylcarbamate). The carbamate was heated to a temperature of 220 ° C. After the carbamate melted, the pressure was "reduced to 1-5 mbar." "The 1 -me t oxy-2-pr opane 1 was removed from the system as the reaction resolved. After 25"" minutes at 220 ° C, diphenylmethane diisocyanate containing 23.5% by weight of the NCO remained in the pyrolysis vessel.

Comparative examples 3 and 4 show that a significantly lower yield is obtained compared to example 1 when the alcohol formed does not contain a halogen atom.

EXAMPLE 5 It was introduced into a suitable vessel equipped with a condenser and a funnel, and a 5% dispersion of di f amethyl bis (1,1,1,3,3,3-hexaf 1 or rois op op i 1 carbamate) in chlorobenzene (MCB). The dispersion was heated to about 134 ° C and the mixture of s or 1 ven t e / a 1 c oh or 1 was removed by distillation. The volume was kept constant in the pyrolysis vessel by the addition of MCB. After 1 hour at 134 ° C, diphenylmethane diisocyanate containing 30.5% by weight of NCO groups was obtained.

EXAMPLE 6 Example 5 was repeated, but a 10% dispersion of polyphenylene polymethylene poly was used (1, 1, 1, 3, 3, 3 -hexa f luor oi s opr op i 1 carbama t o) in MCB.

The dispersion was heated to about 134 ° C and the mixture of 1 or 1 t / a 1 c o 1 was distilled off. The volume was kept constant in the pyrolysis vessel by the addition of MCB. After 1 hour at 134 ° C, polyphenylene p "or limethylene polyisocyanate containing 31.2% by weight of NCO groups was obtained.

EXAMPLE 7 Example 5 was repeated, but a 5% dispersion of diphenylmethane bis (2,2,2-t r i f 1 uo r o e t i 1 c a r b a t) was used in o r t o - di c 1 o r ob e n c e n (ODCB). The dispersion was heated to about 180 ° C and the mixture of 1 or 2 n / a 1 c or 1 was distilled off. The volume was kept constant in the pyrolysis vessel by means of the ODCB aggregate. After 1 hour at 180 ° C, diphenylmethane diisocyanate containing 27.4% by weight of NCO groups was obtained. - EXAMPLE 8 Example 5 was repeated, but a 5% dispersion of polyphenylene polymethylene poly was used (2, 2, 2 - t r i f 1 u o r o e t i 1 c a r b ama) in a mixture of MCB / ODCB. The dispersion was heated to about 180 ° C. The volume was kept constant in the pyrolysis vessel by means of the ODCB aggregate. After 1 hour at 180 ° C, polyphenylene polymethylene polyisocyanate containing 28.2% by weight of "NCO groups" was obtained.

EXAMPLE 9 (comparative) Example 5 was repeated, but a 5% dispersion of diphenylmethane bis (isopropylcarbamate) in a mixture of MCB / ODCB was used. The dispersion was heated to about 180 ° C. The volume was kept constant in the pyrolysis vessel by means of the ODCB aggregate. After 2 hours at 180 ° C, diphenylmethane diisocyanate containing 8.6% by weight of group NCO was obtained. Compared to Example 5, this comparative example demonstrates that a much lower yield is obtained when an alcohol not having a halogen atom is removed.

EXAMPLE 10 (Comparative) Example 5 was repeated, but a 10% dispersion of polyphenylene polymethylene (poly 1 -me t oxy-2 -p r or i 1 ca rbama t) in ODCB was used. The dispersion was heated to about 180 ° C. The volume was kept constant in the pyrolysis vessel per m of the ODCB aggregate After 2 and 1/2 hours at 180 ° C, polyphenylene polymethylene polyisocyanate containing 9% by weight of NCO groups was obtained. Comparative Example 10 again illustrates, by comparison with Example 6, that the yield is significantly lower when an alcohol without the characteristics of the invention is formed in the decomposition.

EXAMPLE 11 A 10% dispersion of toluene 2,4 bis (2,2,2-trifluoroeti 1 carb ama to) in or to the benzene was introduced into a suitable vessel equipped with a condenser and a funnel. (ODCB). The dispersion was heated to about 180 ° C and the mixture of s or 1 ven t e / a 1 c oh or 1 was removed by distillation. The volume was kept constant in the pyrolysis vessel by the addition of ODCB. After 90 minutes at "about 180 ° C, toluene diisocyanate containing more than 43% by weight of NCO groups was obtained, corresponding to more than 89% yield.

EXAMPLE 12 A 10% dispersion of toluene 2,4 bis (1,1,1,3,3,3-hexafluoride) was introduced into a suitable vessel equipped with a condenser and a funnel. ) in ortho - di c 1 or ob ence no (ODCB). The dispersion was heated to about 180 ° C and the mixture of s or 1 in t e / a 1 coho 1 was removed by distillation. The volume was kept constant in the pyrolysis vessel by the addition of ODCB. After 90 minutes at about 180 ° C, toluene diisocyanate containing more than 47% by weight of NCO groups was obtained, corresponding to approximately 99% yield.

Claims (12)

RE IVIND I CAC I ONE S

1. Method for the preparation of monomeric or polymeric aromatic isocyanates by means of the decomposition of monomeric or polymeric aromatic carbamates of the formula R (NHCOOR) x where x is at least. 1, Ri is an aromatic radical of valence x and R2 is a monovalent organic radical, in monomeric or polymeric aromatic isocyanates of the formula Ri (NCO) x and alcohols of the formula R2OH, characterized in that the radical R2 is replaced by a group containing the least-a halogen group.

. 2. The method of clause 1 characterized in that R2 is substituted by at least one chlorine or fluorine atom.

3. The method of any of the preceding clauses-Characterized in that Ri comprises methylene diphenylene or polymethylene polyphenylene radicals or mixtures thereof.

4. The method of any of clauses 1 to 3"characterized in that Ri comprises toluene radicals.

5. The method of any of the preceding clauses characterized in that the decomposition is carried out in the presence of a solvent.

6. The method of clause 5 characterized in that the solvent comprises mon o c 1 or r ob e n c o no or ortho-dichlorobenzene.

7. The method of clause 5 or 6 characterized in that the decomposition temperature is between 100 and 200 ° C.

8. The method of clause 7 characterized in that the decomposition temperature is between 120 and 190 ° C.

9. The method of any of Claims 1 to 8 characterized in that the solvent is mixed with a lower boiling point solvent used to generate a gaseous vehicle.

10. The method of any of clauses 1 to 4 characterized in that the decomposition is carried out in the absence of a solvent.

11. The method of Clause 10 characterized in that the decomposition is carried out at a temperature between the melting point of the monomeric or polymeric carbamate and 350 ° C.

12. The method of "clause 10 or 11 characterized in that the decomposition is effected" under reduced pressure.