US5075458A
Expired / Lapsed
US
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Purification of indigo
Assignee: Dystar Colours Distribution GmbH
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Filing: 1991-04-15
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Granted: 1991-12-24
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Expires: 2011-04-15
Abstract
Abstract A process for the preparation of purified indigo comprises extracting the aqueous alkaline indoxylate solution arising from the synthesis with an inert water-insoluble solvent in the absence of oxygen before oxidizing the indoxylate solution to give indigo.
Inventors
- 👤 Reinhold Kohlhaupt
- 👤 Manfred Gaeng
- 👤 Lothar Haas
- 👤 Guenter Engelhardt
- 👤 Walter Bieg
- 👤 Matthias Fankhaenel
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 16:03
CPC Classifications
C; C07; C07D; C07D209/00; C07D209/02; C07D209/04; C07D209/30; C07D209/32; C07D209/36; C09; C09B; C09B7/00; C09B7/02
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
38 words
A process for the preparation of purified indigo, which comprises extracting the aqueous alkaline indoxylate solution arising from the synthesis with an inert water-insoluble solvent in the absence of oxygen before oxidizing the indoxylate solution to give indigo.
Claim 2
Dependent Claim
38 words
A process for the preparation of purified indigo, which comprises extracting the aqueous alkaline indoxylate solution arising from the synthesis with an inert water-insoluble solvent in the absence of oxygen before oxidizing the indoxylate solution to give indigo.
Claim 3
Dependent Claim
28 words
A process as claimed in claim 1, wherein the extraction of the indoxylate solution is carried out at from 55° C. to 75° C., preferably at 65° C.
Claim 4
Dependent Claim
40 words
A process as claimed in claim 1, wherein the extraction is carried out using an indoxylate solution : solvent ratio by weight of from 1 : 0.1 to 1 : 1, preferably from 1 : 0.2 to 1 : 0.6.
Claim 5
Dependent Claim
13 words
A process as claimed in claim 1, wherein the solvent used is toluene.
References Cited (Backward Citations)
US4966979A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1994-12-23 | 1995-06-24 | 1995-12-24 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-12-23 | 1999-06-24 | 1999-12-24 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-12-23 | 2003-06-24 | 2003-12-24 | $7700.00 | Window Closed / Lapsed |