Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Patent
1994-06-13
1996-10-22
Richter, Johann
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
548178, C07D27768, C07D27782
Patent
active
055678220
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/FR92/ON65 filed Dec. 9, 1992.
FIELD OF THE INVENTION
The present invention relates to a process for the preparation of 2-amino-7-nitrobenzothiazoles of formula: ##STR4## in which R represents an alkyl, alkoxy, alkylthio, polyfluoroalkyl, polyfluoroalkoxy, phenyl, alkenyl, alkylsulphonyl, alkoxycarbonyl, cyano, sulphonamide or dialkylcarbamoyl radical.
BACKGROUND OF THE INVENTION
Direct nitration of 2-aminobenzothiazoles substituted in the 6-position leads to a mixture of 2-amino-4-nitro- and 2-amino-5-nitrothiazoles (EP 374,041).
It is also known to prepare 4-, 5-, 6- or 7-nitro-2-aminobenzothiazoles by reacting dinitrochlorobenzenes or dinitrophenyl thiocyanates with thiourea or ammonium thiocyanate (U.S. Pat. No. 4,808,723, R. Hamprech, Chem. Abstr., 101, 211131 and J. Schulze et al., Z. Chem., 20, 436 (1980)); by reacting nitrophenylthioureas with S.sub.2 Cl.sub.2 or a lead(IV)-phosphate complex (S. Claude et al., Helv. Chim. Acta, 64, 1545 (1981); S. A. Von Mahmoud et al., Prakt. Chemie, 316, 154 (1974)). However, these cyclisations are not always regioselective.
DESCRIPTION OF THE INVENTION
There has now been found, and this forms the subject of the present Application, a process making it possible to obtain industrially the compounds of formula (I) in good yields.
This process consists in
a) nitrating a derivative of formula: ##STR5## in which R has the same meanings as in formula (I), and
b) reacting the compound of formula: ##STR6## in which R has the same meanings as in formula (I), thus obtained with ammonium hydroxide.
It is particularly advantageous to carry out the nitration of step a) using a nitric acid/sulphuric acid mixture.
Generally, a nitric acid/sulphuric acid mixture containing 1 part by volume of concentrated nitric acid and 1 to 5 parts by weight of concentrated sulphuric acid is used. It is preferred to use a mixture containing 1 part of concentrated nitric acid and 3.7 parts of concentrated sulphuric acid.
The amount of the nitric acid/sulphuric acid mixture is between 1 and 10 parts by volume per part by weight of the derivative of formula (I) used.
The reaction temperature is preferably between 0.degree. C. and 20.degree. C.
Step b) is generally carried out in an inert organic solvent such as an alcohol (methanol or ethanol for example) in a closed reactor.
It is particularly advantageous to perform the process at a temperature between 10.degree. C. and 150.degree. C.
5 to 20 parts by weight of ammonium hydroxide are generally used per part by weight of the derivative of formula (III) used.
The derivatives of formula (III) may be obtained by application or adaptation of the method described in Patent EP 43013.
The compounds of formula (I) may be separated from the reaction mixture according to the usual separation techniques (extraction, chromatography, crystallisation etc.).
The compounds of formula (I) are useful as medicaments or intermediates for preparing medicaments (EP 282,971 and 374,041) or as intermediates for dyes (Patents U.S. Pat. Nos. 2,149,051, 4,363,913, GB 2,163,174).
EXAMPLES
The example which follows shows how the invention may be used.
EXAMPLE 1
a) Preparation of 2-chloro-7-nitro-6-trifluoromethoxybenzothiazole
10 g of 2-chloro-6-trifluoromethoxybenzothiazole are added dropwise over one hour to a mixture, cooled to 10.degree. C., of concentrated sulphuric acid (50 cm.sup.3) and concentrated nitric acid (25 cm.sup.3). The mixture is then heated for one hour at 60.degree. C. After cooling, the mixture is poured into an ice/water mixture (1/1 by weight) and extracted with 3 times 100 cm.sup.3 of chloroform. The organic phases are dried over magnesium sulphate and concentrated under vacuum (2.7 kPa). The residue is purified by flash chromatography with a chloroform/cyclohexane mixture (4/6 by volume) as eluent. 6.4 g of 2-chloro-7-nitro-6-trifluoromethoxybenzothiazole are thus obtained, melting at 64.degree. C.
b) Preparation of 2-amino-7-nitro-6-trifluoromethoxybenzothiazole
A mixture of 0.4 g of 2-chloro-7-nitro-6
REFERENCES:
patent: 2149051 (1939-02-01), Helberger et al.
patent: 3978124 (1976-08-01), Fried et al.
patent: 4154934 (1979-05-01), Bernstein et al.
patent: 4363913 (1982-12-01), Clark et al.
Chem. Abstracts vol. 41, 1947, Abstract No. 754c.
Suzuki et al., Chem. Pharm. Bull. 27(1), 1979, pp. 1-11.
Elguero et al., Bull. Soc. Chem. Belg., 86, n1-2, 1977, 95-96.
Martvon et al., Coll. Czech. Chem. Commun., 39, 1974, 1356-65.
L. E. Fisher et al., Can. J. Chem. 72, 142-145 (1994).
R. T. Morrison et al., Organic Chemistry 2nd ed., Allyn and Bacon, Inc., Boston (1969).
Audiau Fran.cedilla.ois
Jimonet Patrick
Mignani Serge
Cross Laura R.
Rhone-Poulenc Rorer S.A.
Richter Johann
LandOfFree
Process for the preparation of 2-amino-7-nitrobenzo-thiazoles does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the preparation of 2-amino-7-nitrobenzo-thiazoles, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the preparation of 2-amino-7-nitrobenzo-thiazoles will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2359536