Process for preparing isocyanates in dialkyl carbonates as solvent

Abstract

The invention relates to a process for preparing isocyanates by reacting primary amines with phosgene in a solvent, where the solvent comprises a dialkyl carbonate.

Claims

1. A process for preparing isocyanates, the process comprising reacting at least one primary amine with phosgene in at least one solvent, to obtain at least one isocyanate, wherein: the solvent comprises a dialkyl carbonate; the reacting occurs in at least two stages, with a first stage being carried out in a mixing device and a second stage being carried out in at least one residence apparatus; and the first stage occurs at a temperature of from 80 to 190 C.

2. The process according to claim 1, wherein the dialkyl carbonate is selected from the group consisting of dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate and diisopropyl carbonate.

3. The process according to claim 1, wherein the dialkyl carbonate is present in admixture with a further solvent.

4. The process according to claim 3, wherein the further solvent comprises an aromatic chlorinated hydrocarbon.

5. The process according to claim 4, wherein the aromatic chlorinated hydrocarbon is selected from the group consisting of monochlorobenzene and o-dichlorobenzene.

6. The process according to claim 4, wherein the solvent comprises from 50 to less than 100% by weight of diethyl carbonate and from greater than 0% to 50% by weight of the aromatic chlorinated hydrocarbon as the further solvent, based on a weight sum of the dialkyl carbonate and the further solvent.

7. The process according to claim 1, wherein the at least one primary amine is selected from the group consisting of toluenediamine (TDA), diphenylmethanediamine (MDA), a polymethylenepolyphenylenepolyamine (pMDA), isophoronediamine, hexamethylenediamine and 1,5-naphthalenediamine.

8. The process according to claim 1, wherein the reaction is carried out in at least three stages, with a third stage being carried out in at least one materials separation apparatus and the pressure in each successive stage being lower than in the preceding stage.

9. The process according to claim 3, wherein the further solvent consists of at least one aromatic chlorinated hydrocarbon.

Description

EXAMPLES

Example 1 (Comparative Example)

(1) 1300 g of monochlorobenzene and 130 g of phosgene were placed in a thermostated stirred vessel at 50 C. A mixture of 100 g of PMDA and 1300 g of monochlorobenzene was metered into the initial charge via an immersed tube over a period of 1 hour, with the temperature being maintained at 50 C. The gas phase was conveyed via a dry ice condenser with reflux into a scrubbing column. After the metered addition was complete, the reaction mixture was heated to about 120 C. and parts of the solvent and residual phosgene were subsequently evaporated. Solvent residues were subsequently separated off from the remaining reaction mixture in a rotary evaporator under reduced pressure (50 mbar), firstly at 100 C. and subsequently at 180 C., in each case for one hour. The NCO number of the sample (proportion by weight of NCO groups in the sample) was subsequently determined by means of titration as a measure of the yield and found to be 31.8% by weight.

Example 2 (According to the Invention)

(2) The above-described experiment was repeated with a mixture of 520 g of diethyl carbonate and 780 g of monochlorobenzene being used instead of 1300 g of monochlorobenzene in the initial charge. The NCO number determined was 32.2% by weight.