US5116997A
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: 1992-05-26
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Expires: 2011-04-15
Abstract
Abstract A process for the purification of indigo comprises treating the indigo with sulfuric acid to give indigo sulfate, separating off and subsequently hydrolyzing the latter to re-form indigo, and then treating the dye with dilute hydrogen peroxide solution.
Inventors
- 👤 Reinhold Kohlhaupt
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 05:38
CPC Classifications
C; C09; C09B; C09B7/00; C09B7/02; C09B67/00; C09B67/0001; C09B67/0017; C09B67/0096
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
39 words
A process for the purification of indigo, which comprises reacting the indigo with sulfuric acid to give indigo sulfate, separating off and subsequently hydrolyzing the latter to re-form indigo, and then treating the dye with dilute hydrogen peroxide solution.
Claim 2
Dependent Claim
39 words
A process for the purification of indigo, which comprises reacting the indigo with sulfuric acid to give indigo sulfate, separating off and subsequently hydrolyzing the latter to re-form indigo, and then treating the dye with dilute hydrogen peroxide solution.
Claim 3
Dependent Claim
34 words
A process as claimed in claim 1, wherein indigo is reacted with from 65 to 85% strength, preferably with 75% strength, sulfuric acid in a weight ratio of from 1:10 to 1:20, preferably 1:15.
Claim 4
Dependent Claim
38 words
A process as claimed in claim 1, wherein the reaction of indigo with sulfuric acid is carried out at from 0° to 60° C., preferably at 25° C., for from 0.5 to 3 hours, preferably for 1 hour.
Claim 5
Dependent Claim
43 words
A process as claimed in claim 1, wherein the dye is treated with an aqueous, from 0.1 to 10.0% strength, preferably 3% strength, sulfuric acid solution of hydrogen peroxide in a weight ratio of from 1:10 to 1:40, preferably from 1:6 to 1:25.
Claim 6
Dependent Claim
30 words
A process as claimed in claim 4, wherein the hydrogen peroxide treatment of indigo is carried out at from 0° to 100° C., preferably at from 20° to 90° C.
References Cited (Backward Citations)
JPS54124027A
Cited
EP0335524A2
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1995-05-26 | 1995-11-25 | 1996-05-26 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1999-05-26 | 1999-11-25 | 2000-05-26 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2003-05-26 | 2003-11-25 | 2004-05-26 | $7700.00 | Window Closed / Lapsed |