Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Patent
1998-11-17
2000-07-25
Killos, Paul J.
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C07C20900
Patent
active
060938528
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for preparing 4,6-diamino-resorcinol dihydrochloride from 1,3-dichlorobenzene by dinitration to 1,3-dichloro-4,6-dinitrobenzene, subsequent reaction with sodium benzylate to 1,3-dibenzyloxy-4,6-dinitrobenzene and catalytic hydrogenation.
BACKGROUND OF THE INVENTION
4,6-Diamino-resorcinol dihydrochloride is an important building block for plastics, in particular for polybenzoxazoles (Macromolecules 1981, 915).
EP 0,402,688 describes the synthesis of 4,6-diamino-resorcinol from 1,3-dichloro-4,6-dinitrobenzene by reaction with sodium benzylate to give 1,3-dibenzyloxy-4,6-dinitrobenzene and subsequent catalytic hydrogenation. A disadvantage of the process described is the indicated way of carrying out the heterogeneous catalytic hydrogenation of 1,3-dibenzyloxy-4,6-dinitrobenzene on a Pd/activated carbon catalyst as a batch hydrogenation which, in the form described, does not permit economical recycling of the expensive noble metal catalyst. A further disadvantage is the unsatisfactory product quality, caused by the way, as described, of carrying out the heterogeneous batch hydrogenation, and the low stability of 4,6-diamino-resorcinol in the free form, in particular in water-containing solvents. A further disadvantage is the low solubility of free 4,6-diamino-resorcinol in organic solvents, which leads to an uneconomically large dilution during the operation of the catalytic hydrogenation and the isolation of the product.
It has now been found that 4,6-diamino-resorcinol dihydrochloride can be prepared from 1,3-dibenzyloxy-1,4-dinitrobenzene by reacting 1,3-dibenzyloxy-4,6-dinitrobenzene on a noble metal catalyst in a two-phase mixture of dilute aqueous hydrochloric acid and an organic solvent, which is immiscible or miscible only to a limited extent with dilute aqueous hydrochloric acid, at optionally elevated pressure and normal or elevated temperature by a catalytic hydrogenation, preferably a catalytic pump hydrogenation, to give 4,6-diamino-resorcinol dihydrochloride.
SUMMARY OF THE INVENTION
The invention therefore relates to a process for preparing 4,6-diamino-resorcinol dihyrochloride from 1,3-dibenzyloxy-4,6-dinitrobenzene, which comprises catalytically hydrogenating 1,3-dibenzyloxy-4,6-dinitrobenzene on a noble metal catalyst with hydrogen in a two-phase mixture of dilute aqueous hydrochloric acid and an organic solvent, which is immiscible or miscible only to a limited extent with dilute aqueous hydrochloric acid, at normal or elevated pressure and normal or elevated temperature.
DETAILED DESCRIPTION OF THE INVENTION
In the process according to the invention, for example 1,3-dibenzyloxy-4,6-dinitrobenzene can be employed which is prepared according to EP 0,402,688 from 1,3-dichloro-4,6-dinitrobenzene by reaction with sodium benzylate.
In a highly economical embodiment, pure 1,3-dibenzyloxy-4,6-dinitrobenzene can be obtained from 1,3-dichlorobenzene by containing 0 to 10% by weight of free SO.sub.3, with a mixed acid, containing nitric acid, sulfuric acid and 0.7 to 1.5 mol, preferably 0.8 to 1.2 mol, particularly preferably 0.9 to 1.1 mol, of SO.sub.3 per mol of nitric acid, in a temperature range from 0 to 40.degree. C., the HNO.sub.3 /1,3-dichlorobenzene ratio being 2 to 3, and 1,3-dichloro-4,6/2,4-dinitrobenzene isomer mixtures, which contain 0.1 to 60% of 1,3-dichloro-2,4-dinitrobenzene relative to the total weight of the isomer mixture, with 2 to 5 mol of benzyl alcohol and 2 to 5 equivalents of a strong base in the presence of an inert solvent, this being operated stepwise, initially in the temperature range from -15 to +15.degree. C. and then in the temperature range from 20 to 40.degree. C.
1,3-Dichlorobenzene is first added dropwise to initially introduced anhydrous sulfuric acid containing 0 to 10% by weight of free SO.sub.3, and the mixed acid containing nitric acid, sulfuric acid and at least 0.7 mol of SO.sub.3 per mol of nitric acid is then metered in. The metering times for 1,3-dichlorobenzene are 5 minutes t
REFERENCES:
patent: 5072053 (1991-12-01), Blank et al.
patent: 5414130 (1995-05-01), Lysenko et al.
patent: 5574188 (1996-11-01), Behre et al.
Macromolecules (Nov. 17, 1981) p. 9l5.
Behre Horst
Blank Heinz Ulrich
Eymann Wolfgang
Fiege Helmut
Bayer Aktiengesellschaft
Eyl Diderico van
Gil Joseph C.
Killos Paul J.
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