SI9300427A - Process for preparing isocyanates by decomposition of n,n,n'-three substituted ureas - Google Patents

Abstract

Process for the preparation of isocyanates, which is characterised in that N,N,N'-trisubstituted ureas of the formula <IMAGE> in which R1, R2 and R3 are identical or different and denote a straight-chain, branched or cyclic (C1-C24) alkyl radical which is unsubstituted or substituted by (C1-C6) alkoxy, optionally substituted phenyl, halogen or by other radicals which are inert under the reaction conditions used, or R2 and R3 together denote a heterocyclic non-aromatic ring which can optionally also contain further heteroatoms, are decomposed at elevated temperature in a diluent which is inert under the reaction conditions to a readily volatile isocyanate of the formula R1NCO and a poorly volatile secondary amine of the formula R2R3NH whose boiling point lies above the boiling point of the isocyanate and above the reaction temperature used, after which the isocyanate is stripped off at the top by means of a carrier gas stream.

Description

Chemie Linz Gesellschaft m.b.H.

A process for the preparation of isocyanates with decomposition of Ν, Ν, Ν′-trisubstituted urea

The invention relates to a process for the preparation of isocyanates with decomposition of Ν, Ν, Ν′-trisubstituted urea.

Isocyanates are an economically important group of intermediates that are used, inter alia, in the plastics industry, in the manufacture of varnishes and in the preparation of plant protection products.

For this reason, a number of processes for the preparation of isocyanates, which have several defects, are also known. Thus, for example, older processes mainly from phosgene or from phosgene-derived products, while newer processes that avoid the use of phosgene yield isocyanates only in poor yields.

The processes resulting from the substitution of thermally degraded urea have also been described. In FR-PS 1,473,821 decompose trisubstituted ureas into isocyanic acid esters and amines at a temperature below 200 ° C in a solvent with a dielectric constant below 40. However, isocyanates are only obtained in a yield of about 60%. US-PS 3,936,484 proposes a process for the thermal decomposition of disubstituted ureas, in particular for the preparation of toluene-2,42 diisocyanate. Preferably, the resulting amine is removed from the reaction mixture by a carrier gas stream, to which additional solvent may be added.

The disadvantages of this process, however, are that they can mainly take the emerging amine through the top and the actual product remains at the bottom and must then be isolated and cleaned, and that they achieve good yield only with the addition of additional solvent.

We have now unexpectedly been able to find a process for the preparation of isocyanates derived from certain Ν, Ν, tr′-trisubstituted ureas, which does not require phosgene and yields the desired isocyanates in an easy way with high yield and purity.

The subject of the invention is therefore a process for the preparation of isocyanates, characterized in that Ν, Ν, Ν'isubstituted urea of the formula I ^R 2 ^R 1

R ₃

in which R _p R ₂ and R ₃ are the same or different and represent a level, branched or cyclic, unsubstituted or substituted by (C 1 -C 6 alkoxy, optionally substituted phenyl, halogen or other radicals in use under the reaction conditions used) The C 1 -C 6 alkyl residue or R ₂ and R ₃ together represent a heterocyclic non-aromatic ring which may optionally contain further heteroatoms, decomposed in a diluent inert under the reaction conditions, at elevated temperature, into a lightly volatile isocyanate of the formula R 1 NCO and into a heavy a volatile secondary amine of the formula R ₂ R ₃ NH whose boiling point is above the boiling point of the isocyanate and above the reaction temperature used, and then the isocyanate is discharged via the carrier gas stream over the top.

In principle, all Ν, Ν, Ν'-trisubstituted ureas which, under thermal loading, decompose into a readily volatile isocyanate and into a hardly volatile secondary amine whose boiling point is above the isocyanate boiling point and above the reaction temperature are suitable as starting compounds. These are compounds of formula I in which R _p R ₂ and R ₃ are the same or different and represent straight, branched or cyclic, unsubstituted or (C 1 -C 4 alkoxy, optionally substituted phenyl, halogen or other radicals, inert under the reaction conditions used, a substituted (C 1 -C ₂₄ ) alkyl residue, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, tert-butyl, hexyl, octyl, decyl, dodecyl , tetradecyl, hexadecyl, octadecyl, cyclohexyl or benzyl residues.

(C 1 -C 6 alkoxy residues are, for example, methoxy, ethoxy, propoxy, butoxy and hexoxy. The phenyl residue may, for example, be substituted by (C 1 -C 6 alkyl, (C 1 -C 6 alkoxy, halogen, amino or nitro. R ₂ and R ₃ they may also together form a heterocyclic non-aromatic ring which may contain further heteroatoms such as pyrrolidine, piperidine, piperazine or morpholine.

Preferred starting compounds are compounds of formula I, in which _R} linear, branched or cyclic (C ₂ -C ₁₀₎ alkyl radical or a benzyl radical and R ₂ and R ₃ a linear, branched or cyclic (C ₄ -C ₂₀₎ alkyl residue or benzyl residue.

Particularly preferred Ν, Ν, Ν'-trisubstituted ureas are therefore, among others, N, Ndioctyl-N'-ethylurea, N, N-dioctyl-N'-propylurea, N, N-dicyclohexyl-N'-propylurea, N, N- dioctyl-N'-isopropylurea, N, N-dibenzyl-N'-butylurea, N, N-dioctylN'-butylurea, N, N-dioctyl-N'-benzylurea and N, N-dioctyl-N'-cyclohexylurea.

Urea can be prepared e.g. via N-alkylated urea as described in EP 0 471 983.

Decomposition may occur in a diluent inert under reaction conditions. As inert diluents, aliphatic or aromatic hydrocarbons such as e.g. tetradecane, dodecane, hexadecane, octadecane, paraffin or mixtures thereof with high boiling point. An amine formed from urea degradation may also be used as a diluent. The reaction temperature is about 90 to 400 ° C, preferably between 150 and 300 ° C, and particularly preferably 210 to 280 ° C, depending on the urea used. Isocyanates are isolated from the reaction mixture by an inert gas stream, e.g. by means of a stream of nitrogen or argon. The isocyanates are then either condensed in a cooling trap or absorbed in a solvent. Suitable isocyanate solvents are aliphatic or aromatic hydrocarbons, which may optionally be halogenated, such as e.g. chloroform, methylene chloride, trichlorethylene, toluene, and ethers such as e.g. tetrahydrofuran. The solvent or portions thereof may already be introduced as an inert gas stream or into the reaction mixture prior to the onset of decomposition.

The reaction can optionally be carried out under reduced or increased pressure. The pressure level is adjusted according to the selected output products and emerging end products to the desired value.

The reaction time varies between 15 and 120 minutes depending on the reaction temperature, the reaction pressure and the starting compounds. The secondary amine remaining in the decomposition at the bottom may e.g. is isolated by distillation under reduced pressure from the bottom and used as a starting compound for various reactions. The desired isocyanates are obtained in high purity and in yields up to 99.9%.

Example 1

Ethyl isocyanate g N, N-dioctyl-N'-ethylurea in a suitable apparatus, which, in addition to the thermostated reaction vessel, contains a device for introducing and favorable distribution of inert gas flow in the reaction mixture and a column to facilitate the separation of products (eg, use a 30 cm Vigreux mirror column), in 50 g of hexadecane and 2.5 g of CHC1 _{3 are} heated at about 250 ° C for 30 minutes.

The resulting ethylisocyanate is then removed from the reaction mixture by a stream of nitrogen (about 2 l / h) and condensed in a liquid nitrogen-cooled cooling trap as a CHC1 ₃ solution.

Yield: 97%.

Example 2

Propylisocyanate g N, N-dicyclohexyl-N'-propylurea was heated in the apparatus described in Example 1 in 50 g hexadecane for 40 minutes at about 250 ° C, and the resulting propylisocyanate was removed by a stream of nitrogen from the reaction mixture and condensed in a cooling trap, cooled with liquid nitrogen.

Yield: 99.9%.

The following compounds are prepared analogously:

Product Edukt Solvent 1 i-propylisocyanate N, N-dioctyl-N'-isopropyl urea hexadecane 2 butyl isocyanate 3 N, N-dioctyl-N'-butyl- urea hexadecane paraffin octadecane 4 N, N-dibenzyl-N'-butyl- urea hexadecane 5 tert.butylisocyanate N, N-dioctyl-N'-tert.- butylurea hexadecane 6 cyclohexylisocyanate N, N-dioctyl-N'-cyclohexyl- urea hexadecane 7 benzylisocyanate N, N-dioctyl-N'-benzyl- urea hexadecane

For

Chemie Linz Gesellschaft m.b.H.

Claims (4)

PATENT APPLICATIONS A process for the preparation of isoyanates, characterized in that the Ν, Ν, Ν'-trisubstituted ureas of formula I in which R _p R ₂ and R ₃ are the same or different and represent a level, branched or cyclic, unsubstituted or (C C ₁ -Calkoxy, optionally substituted phenyl, halogen or other residues inert under the reaction conditions used, a substituted (C ₁ -C ₂₄ ) alkyl residue or R ₂ and R ₃ together represent a heterocyclic non-aromatic ring which may optionally contain further heteroatoms are decomposed in a diluent inert under reaction conditions, at elevated temperature, into a readily volatile isocyanate of the formula R ^ CO and into a hardly volatile secondary amine of the formula R ₂ R ₃ NH whose boiling point is above the boiling point of the isocyanate and above the reaction temperature used. , then the isocyanate is removed via the carrier gas stream via the top. A process according to claim 1, characterized in that Ν, Ν, Ν'-trisubstituted ureas of formula I are used, in which R _{t represents a} straight, branched or cyclic (C ₂ -C ₁₀ ) alkyl residue or a benzyl residue and R ₂ and R _{3 is a} straight, branched or cyclic (C ₄ -C ₂₀ ) alkyl radical or a benzyl radical. 23005-VII-93-KA Process according to claim 1, characterized in that the reaction temperature is about 150 to 300 ° C, preferably 220 to 280 ° C. Process according to claim 1, characterized in that the urea is decomposed at reduced pressure from about 0.01 to 100 mbar. For Chemie Linz Gesellschaft m.b.H .: PATENT / PUJARNA LOVE SUMMARY A process for the preparation of isocyanates with decomposition of Ν, Ν, Ν′-trisubstituted urea A process for the preparation of isocyanates wherein Ν, Ν, Ν′-trisubstituted urea of formula I Oh H in which R _p R ₂ and R ₃ are the same or different and represent a level, branched or cyclic, unsubstituted or with (C 1 -C 4 alkoxy, optionally substituted phenyl, halogen or other residues inert under the reaction conditions used substituted (C 1 -C 6 alkyl residue or R ₂ and R ₃ together represent a heterocyclic non-aromatic ring which may optionally contain further heteroatoms, decomposed in a diluent inert under the reaction conditions, at elevated temperature, into a readily volatile isocyanate of formula R ₁ NCO and into the hardly volatile secondary amine of formula R ₂ R ₃ NH whose boiling point is above the boiling point of the isocyanate and above the reaction temperature used, and then the isocyanate is discharged via the carrier gas stream over the top.