Process for preparing aromatic amine compounds and reducing agent therefor
AssigneeSandoz Ltd.
InventorsBaldev K. Bandlish, Robert V. Casciani
Life of this patent
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Abstract
An improved process for reducing aromatic nitro compounds to form the corresponding aromatic amine compounds, and intermediates therefore, and a reducing agent therefor, are disclosed. According to the process, a titanium(IV)oxy salt such as titanium(IV) oxysulfate is electrochemically reduced to form a titanium(III)oxy reducing agent, which can be employed to chemically reduce the aromatic nitro compounds, and the resulting re-oxidized titanium salts may be recycled to the electrochemical reduction step of the process. The titanium(III)oxy salt product is highly soluble in strong acid solutions and exhibits improved oxidation stability.
Claims29
A process for reducing aromatic nitro compounds to form the corresponding aromatic amine compounds and intermediates therefor which comprises the steps of:
- a. electrochemically reducing a titanium(IV)oxy salt in an acidic aqueous electrolyte solution to form a dissolved titanium(III) reducing agent,
- said titanium(IV)oxy salt being characterized by being hydrolysis stable in a 7% (wt./vol.) strong acid aqueous solution at room temperature over a period of 24 hours,
- and said titanium(III) reducing agent characterized by being soluble at a concentration of 1 Normal in a 20% (wt./vol.) strong acid aqueous solution at room temperature, and by being reoxidizable to a hydrolysis stable titanium(IV)oxy salt;
- and
- b. reacting said titanium(III) reducing agent with an aromatic nitro compound in an aqueous acidic reaction medium for a time sufficient to reduce at least a portion of the amount of the nitro compound to the corresponding amine compound or intermediate therefor and to oxidize at least a portion of the amount of the titanium(III) reducing agent to a soluble, hydrolysis stable titanium(IV)oxy salt.
A process for reducing 4,4'- dinitrostilbene-2,2'-disulfonic acid to 4,4'-diaminostilbene-2,2'-disulfonic acid which comprises:
- a. electrochemically reducing titanium(IV) oxysulfate in an aqueous strong acid electrolyte solution comprising 1-50 wt./vol. % C.sub.1-4 alkylsulfonic acid to form a dissolved titanium(III) reducing agent,
- said titanium(IV)oxy sulfate being characterized by being hydrolysis stable in a 7% (wt./vol.) sulfuric acid solution at room temperature over a period of 24 hours,
- and said titanium(III) reducing agent characterized by being soluble at a concentration of 1 Normal in a 20% (wt./vol.) sulfuric acid solution at room temperature, and by being reoxidizable to a hydrolysis stable titanium(IV)oxy salt;
- and
- b. reacting said titanium(III) reducing agent with 4,4'-dinitrostilbene-2,2'-disulfonic acid in an aqueous acidic reaction medium at a temperature of about 50.degree.-100.degree. C. for a time sufficient to reduce at least a portion of the nitro compound to 4,4'-dinitrostilbene-2,2'-disulfonic acid, thereby reoxidizing at least a part of the titanium(III) reducing agent to form a soluble, hydrolysis stable titanium(IV)oxy salt;
- c. separating the amine compound from the resulting solution;
- and
- d. recycling the resulting reoxidized titanium(IV)oxy salt to step (a).
Dependencies are inferred from the claim text.