# US 5,708,182 A · Method for preparation of 2-imino 4-oxo-5-phenyloxazolidine > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,708,182 A - Document ID: US5708182A - Status: Granted - Kind: A - Application number: 08/627,951 - Filed: 1996-04-03 - Granted: 1998-01-13 - Earliest claimed: 1995-05-30 - Assignees: SKW Trostberg Aktiengesellschaft - Inventors: Stefan Weiss; Martina Lobensommer - Web page: https://patentgrep.com/patent/US5708182A ## CPC - C07D 263/48: Nitrogen atoms not forming part of a nitro radical - C07D: HETEROCYCLIC COMPOUNDS (macromolecular compounds C08) ## Abstract A process for the preparation of 2-imino-4-oxo-5-phenyloxazolidine, which is used in medical applications under the name of pemolin, is described. The preparation proceeds by reacting at 10.degree. to 150.degree. C., optionally in the presence of a base catalyst, an aliphatic or an aromatic mandelic acid ester with an alkali or alkaline earth metal hydrogencyanamide, which can be prepared in situ; followed by treating the obtained reaction mixture or the metal salt isolated therefrom with a protonic acid, at temperatures from -30.degree. to 150.degree. C. until a pH value from 2 to 10 is reached. ## Claims ### Claim 1 Process for the preparation of 2-imino-4-oxo-5-phenyloxazolidine of the formula: ##STR3## and/or its tautomeric forms, characterized in that a mandelic acid ester is treated with an alkali or alkaline earth metal hydrogencyanamide in a molar ratio of 1:2 to 1:0.5, at temperatures in the range of 10.degree. to 150.degree. C.; and in that thereafter the obtained reaction mixture metal salt is acidified to a PH value of 2 to 10, at temperatures from -30.degree. to 150.degree. C. ### Claim 2 (depends on 1) The process of claim 1 characterized in that molar ration is 1:1.25 to 1:1. ### Claim 3 (depends on 1) The process of claim 1 characterized in that reaction mixture metal salt is acidified to a PH value of 3 to 6. ### Claim 4 (depends on 1) The process of claim 1 characterized in that metal salt is acidified at temperatures from 10.degree. to 80.degree. C. ### Claim 5 (depends on 1) The process of claim 1, characterized in that the mandelic acid esters are aliphatic C.sub.1 to C.sub.10 esters, or phenyl or benzyl esters of DL-, D(-)- or L(+)-mandelic acid. ### Claim 6 (depends on 5) The process of claim 5 characterized in that esters are selected from the group consisting of methyl esters and ethyl esters. ### Claim 7 (depends on 5) The process of claim 5, characterized in that the hydrogencyanamid salt is sodium hydrogencyanamide. ### Claim 8 (depends on 5) The process of claim 5 characterized in that the reaction is preformed in water and/or an organic solvent. ### Claim 9 (depends on 5) The process of claim 5 characterized in that reaction is performed in an alcohol having 1 to 4 carbon atoms. ### Claim 10 (depends on 8) The process of claim 8 characterized in that the intermediate hydrogencyanamide salt is produced via the reaction of cyanamid with an alkoxide or hydroxide of an alkali or alkaline earth metal. ### Claim 11 (depends on 10) The process of claim 10 characterized in that the hydrogencyanamid salt is produced using a 30% methanolic solution of sodium methoxide with a molar ratio of cyanamide to sodium methoxide of 1:1 to 1:1.25. ### Claim 12 (depends on 11) The process of claim 11 characterized in that a base catalyst is added in a mole ratio of 1:0.1 to 1:1 based on the mandelic acid ester. ### Claim 13 (depends on 12) The process of claim 12 characterized in that a base catalyst is added in a mole ratio of 1:0.25 to 1:0.5. ### Claim 14 (depends on 12) The process of claim 12 characterized in that the base catalyst is an alkoxide, hydroxide or phenoxide of an alkali or alkaline earth metal. ### Claim 15 (depends on 14) The process of claim 14 characterized in that hydrochloric or acetic acids are used for the acidification. ### Claim 16 (depends on 15) The process of claim 15 characterized in that the obtained reaction mixture is filtered, the metal salt of pemolin is isolated and thereafter transformed into free pemolin via acidification. ### Claim 17 (depends on 15) The process of claim 15 characterized in that the acidified reaction mixture is stirred up to 15 hours in the temperature range of 10.degree. to 150.degree. C. preferably 20.degree. to 80.degree. C. ### Claim 18 (depends on 17) The process of claim 17 characterized in that the reaction product is washed with water until salt-free. ### Claim 19 (depends on 18) The process of claim 18 characterized in that the reaction product is purified via reflux using water or an alcohol having 1 to 4 carbon atoms.