# US 5,710,330 A · Process for preparing alkanephosphonic anhydrides

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- Number: US 5,710,330 A
- Document ID: US5710330A
- Status: Granted
- Kind: A
- Application number: 08/556,859
- Filed: 1995-11-02
- Granted: 1998-01-20
- Earliest claimed: 1994-11-04
- Assignees: Hoechst Aktiengesellschaft
- Inventors: Carl Christoph Mollenkopf; Ernst Ingo Leupold; Gunter Roscher
- Web page: https://patentgrep.com/patent/US5710330A

## CPC

- C07F 9/3895: {Pyrophosphonic acids; phosphonic acid anhydrides}
- C07F: ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM (metal-containing porphyrins C07D487/22)

## Abstract

Process for preparing alkanephosphonic anhydrides of the formula (I) ##STR1## where R is straight-chain or branched unsubstituted C.sub.1 -C.sub.6 -alkyl and n.gtoreq.3, which comprises pyrolytically eliminating water from an alkanephosphonic acid of the formula (II) or a pyroalkanephosphonic acid of the formula (III) ##STR2## where R is straight-chain or branched C.sub.1 -C.sub.6 -alkyl, without addition of solvent and removing the water from the reaction mixture by means of an inert gas stream.

## Claims

### Claim 1

A process for preparing alkanephosphonic anhydrides of the formula (I) ##STR5## where R is straight-chain or branched unsubstituted C.sub.1 -C.sub.6 -alkyl and n.gtoreq.3, which comprises pyrolytically eliminating water from an alkanephosphonic acid of the formula (II) or a pyroalkanephosphonic acid of the formula (III) ##STR6## where R is straight-chain or branched C.sub.1 -C.sub.6 -alkyl, without addition of solvent and removing the water from the reaction mixture by means of an inert gas stream.

### Claim 2 (depends on 1)

The process as claimed in claim 1, wherein R is methyl, ethyl or propyl, and n is from 3 to 150.

### Claim 3 (depends on 1)

The process as claimed in claim 1, wherein the pyrolysis is carried out at a temperature between 220.degree. and 350.degree. C.

### Claim 4 (depends on 1)

The process as claimed in claim 1, wherein the inert gas stream is passed through the melt during the reaction in such a way that with simultaneous evacuation there is obtained a vacuum of from 2 to 10 mbar.

### Claim 5 (depends on 4)

The process as claimed in claim 4, wherein R is methyl and n is from 5 to 100.

### Claim 6 (depends on 5)

The process as claimed in claim 5, wherein the pyrolysis is carried out at a temperature between 250.degree. and 350.degree. C.

### Claim 7 (depends on 6)

The process as claimed in claim 6, wherein the inert gas stream is passed through the melt during the reaction in such a way that with simultaneous evacuation there is obtained a vacuum of from 3 to 4 mbar.

### Claim 8 (depends on 1)

The process as claimed in claim 1, wherein the pyroalkanephosphonic acid of formula (III) is present.

### Claim 9 (depends on 1)

The process as claimed in claim 1, wherein said inert gas is nitrogen or argon.

### Claim 10 (depends on 8)

The process as claimed in claim 8, wherein the inert gas is nitrogen or argon.

### Claim 11 (depends on 4)

The process as claimed in claim 4, wherein the temperature is selected so that in said vacuum the temperature is from 30.degree. to 70.degree. C. below the corresponding boiling or sublimation point of the alkanephosphonic acid or pyroalkanephosphonic acid.

### Claim 12 (depends on 10)

The process as claimed in claim 10, wherein the temperature is selected so that in the vacuum the temperature is from 40.degree. to 60.degree. below the corresponding boiling or sublimation point of the alkanephosphonic acid or pyroalkanephosphonic acid.

### Claim 13 (depends on 6)

The process as claimed in claim 6, wherein the pyrolysis is carried out from 10 to 20 hours.

### Claim 14 (depends on 12)

The process as claimed in claim 12, wherein the pyrolysis is carried out from 10 to 20 hours.

### Claim 15 (depends on 1)

The process as claimed in claim 1, wherein the anhydride content is between 80 and 92% of the product produced.

### Claim 16 (depends on 14)

The process as claimed in claim 14, wherein the anhydride content is between 80 and 92% of the product produced.

### Claim 17 (depends on 16)

The process as claimed in claim 16, wherein R is methyl and n is from 5 to 100.

### Claim 18 (depends on 17)

The process as claimed in claim 17, wherein the pyrolysis is carried out at a temperature between 250.degree. and 350.degree. C.

### Claim 19 (depends on 18)

The process as claimed in claim 18, wherein the inert gas stream is passed through the melt during the reaction in such a way that with simultaneous evacuation there is obtained a vacuum of from 3 to 4 mbar.

### Claim 20 (depends on 1)

The process as claimed in claim 1, wherein said inert gas is nitrogen.