# US 4,393,206 A · Process for the production of 2,3-Dihydro-4H-1,4-benzothiazines

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- Number: US 4,393,206 A
- Document ID: US4393206A
- Status: Granted
- Kind: A
- Application number: 06/359,221
- Filed: 1982-03-18
- Granted: 1983-07-12
- Earliest claimed: 1981-03-24
- Assignees: Bayer Aktiengesellschaft
- Inventors: Paul Uhrhan; Edmund Krauthausen
- Web page: https://patentgrep.com/patent/US4393206A

## CPC

- C07D 279/20: with hydrogen atoms directly attached to the ring nitrogen atom
- C07D 279/16: condensed with one six-membered ring
- C08K 5/3725: {containing nitrogen}
- C07D: HETEROCYCLIC COMPOUNDS (macromolecular compounds C08)
- C08K: Use of inorganic or non-macromolecular organic substances as compounding ingredients (paints, inks, varnishes, dyes, polishes, adhesives C09)

## Abstract

Process for the preparation of 2,3-Dihydro-4H-1,4-benzothiazines by cyclisation of suitable 2-(2-Hydroxyalkyl)-thioanilines under elimination of water in the presence of phosphorous acid.

## Claims

### Claim 1

A process for the production of 2,3-dihydro-4H-1,4-benzothiazines, characterised in that 2-(2-hydroxyalkyl)-thioanilines are cyclised using phosphorous acid with the release of water.

### Claim 2 (depends on 1)

A process according to claim 1, characterised in that 2-(2-hydroxyalkyl)-thioanilines corresponding to the following general formula (I) are cyclised: ##STR9## wherein R.sup.1 to R.sup.4, which may be the same or different, each represents hydrogen, lower alkyl having from 1 to 4 carbon atoms, cycloalkyl having from 5 to 8 carbon atoms, aralkyl having from 7 to 11 carbon atoms or aryl, or
R.sup.1 and R.sup.2 or R.sup.3 and R.sup.4 together with the carbon atom to which they are attached complete a cycloalkyl radical having from 5 to 8 carbon atoms, or one of
R.sup.3 and R.sup.4 together with R.sup.1 or R.sup.2 may represent an alkylene radical having from 3 to 6 carbon atoms,
R.sup.6 and R.sup.8, which may be the same or different, each represents hydrogen, halogen, nitro, linear or branched alkyl having from 1 to 12 carbon atoms, linear or branched alkenyl having from 2 to 12 carbon atoms, aralkyl having from 7 to 11 carbon atoms, cycloalkyl having from 5 to 8 carbon atoms or alkoxy, and
R.sup.5 and R.sup.7, which may be the same or different, each represents hydrogen, halogen, nitro, linear or branched alkyl having from 1 to 12 carbon atoms, linear or branched alkenyl having from 2 to 12 carbon atoms, cycloalkyl having from 5 to 8 carbon atoms, aralkyl having from 7 to 11 carbon atoms, alkoxy, the radical: ##STR10## wherein p represents an integer of from 0 to 20, preferably from 8 to 16, and
A represents --(CH.sub.2).sub.q --, --O--(CH.sub.2).sub.q --, --NH--(CH.sub.2).sub.q -- or --S--(CH.sub.2).sub.q -- wherein
q represents 0 to 4, preferably 0 or 1, or the radical: ##STR11## wherein R.sup.1 to R.sup.6 and R.sup.8 are as defined above, and
R.sup.9 and R.sup.10 independently represent hydrogen, optionally substituted aryl, linear or branched alkyl having from 1 to 12 carbon atoms, cycloalkyl or cycloalkenyl having from 5 to 8 carbon atoms, or
R.sup.9 and R.sup.10 together with the carbon atom to which they are attached complete a cycloalkyl radical having from 5 to 7 carbon atoms,
using phosphorous acid with the release of water, into 2,3-dihydro-4H-1,4-benzothiazines corresponding to the following general formula (II): ##STR12## wherein R.sup.1 to R.sup.8 are as defined above.

### Claim 3 (depends on 1)

A process according to claim 1, characterised in that water is split off at from 100.degree. to 200.degree. C.

### Claim 4 (depends on 1)

A process according to claim 1, characterised in that the water produced by the reaction is removed from the reaction mixture.

### Claim 5 (depends on 1)

A process according to claim 1, characterised in that the water is split off in the presence of from 0.1 to 100%, by weight, of phosphorous acid.

### Claim 6 (depends on 1)

A process according to claim 1, characterised in that the water is split off in the presence of from 5 to 25%, by weight, of phosphorous acid.