US5116996A
Expired / Lapsed
US
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Purification of indigo
Assignee: Dystar Colours Distribution GmbH
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Filing: 1991-07-17
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Granted: 1992-05-26
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Expires: 2011-07-17
Abstract
Abstract A process for purifying indigo comprises stripping the as-synthesized aqueous alkaline indoxylate solution before its oxidation to indigo of impurities in the absence of oxygen by distillation or by passing in steam or an inert gas and then treating the indigo precipitated on oxidation of the stripped indoxylate solution with dilute hydrogen peroxide solution.
Inventors
- 👤 Reinhold Kohlhaupt
- 👤 Walter Bieg
- 👤 Ernst Lang
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 05:05
CPC Classifications
C; C09; C09B; C09B7/00; C09B7/02
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
56 words
A process for preparing purified indigo, which comprises stripping the as-synthesized aqueous alkaline indoxylate solution before its oxidation to indigo of impurities in the absence of oxygen by distillation or by passing in steam or an inert gas and then treating the indigo precipitated on oxidation of the stripped indoxylate solution with dilute hydrogen peroxide solution.
Claim 2
Dependent Claim
56 words
A process for preparing purified indigo, which comprises stripping the as-synthesized aqueous alkaline indoxylate solution before its oxidation to indigo of impurities in the absence of oxygen by distillation or by passing in steam or an inert gas and then treating the indigo precipitated on oxidation of the stripped indoxylate solution with dilute hydrogen peroxide solution.
Claim 3
Dependent Claim
40 words
A process as claimed in claim 1, wherein the stripping of the indoxylate solution is effected by distillation or by passing in steam or an inert gas at from 55° to 80° C., preferably at from 65° to 75° C.
Claim 4
Dependent Claim
38 words
A process as claimed in claim 1, wherein the stripping of the indoxylate solution is effected by distillation or by passing in steam at a pressure of from 150 to 450 mbar, preferably from 250 to 350 mbar.
Claim 5
Dependent Claim
35 words
A process as claimed in claim 1, wherein from 5 to 30% by weight, preferably 10% by weight, of the water present in the indoxylate solution is distilled off in the course of the stripping.
Claim 6
Dependent Claim
50 words
A process as claimed in claim 1, wherein, if the stripping of the indoxylate solution is to be effected by passing in an inert gas, from 40 to 120, preferably from 60 to 80, parts by volume of inert gas are passed in per part by volume of indoxylate solution.
Claim 7
Dependent Claim
35 words
A process as claimed in claim 1, wherein the stripping of the indoxylate solution is effected in the course of from 0.5 to 5 hours, preferably in the course of from 1 to 2 hours.
Claim 8
Dependent Claim
59 words
A process as claimed in claim 1, wherein the dye obtained on stripping and oxidizing the indoxylate solution is treated in the weight ratio of from 1:10 to 1:40, preferably from 1:15 to 1:35, with a from 0.1 to 10% strength by weight, preferably 3% strength by weight, hydrogen peroxide solution which has been acidified with aqueous sulfuric acid.
Claim 9
Dependent Claim
30 words
A process as claimed in claim 7, wherein the hydrogen peroxide treatment of indigo is carried out at from 10° to 90° C., preferably at from 20° to 50° 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 |