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Method for preparing n-aminopiperidine and its saltsRelated Patent Categories: Organic Compounds -- Part Of The Class 532-570 Series, Azo Compounds Containing Formaldehyde Reaction Product As The Coupling Component, Carbohydrates Or Derivatives, Hetero Ring Is Six-membered Consisting Of One Nitrogen And Five Carbons, Piperidines, Nitrogen Attached Directly To The Piperidine Ring By Nonionic BondingMethod for preparing n-aminopiperidine and its salts description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070173648, Method for preparing n-aminopiperidine and its salts. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of International application No. PCT/FR2005/002,016, filed Aug. 2, 2005, which is incorporated herein by reference in its entirety; which claims the benefit of priority of French Patent Application No. 04/08,700, filed Aug. 5, 2004. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] A subject-matter of the present invention is a novel process for the preparation of N-aminopiperidine of formula [0004] 2. Description of the Art [0005] Several processes for the preparation of N-aminopiperidine are known in the literature: [0006] Raschig process using piperidine and chloramine; [0007] process via hydrazine and N-acetylamino-piperidine; [0008] process via N-nitrosopiperidine (Lunn, Keefer, J. Org. Chem., 1984, 49 (19), 3470); [0009] process via glutaraldehyde and benzotriazole (Katritzky A. R., Wei-Ouiang Fan, J. Org. Chem., 1990, 55, 3205-3209). [0010] All of the references described herein are incorporated herein by reference in their entirety. SUMMARY OF THE INVENTION [0011] The process for the preparation of N-aminopiperidine (I) and its salts according to the present invention is characterized in that: [0012] a) a carbazate of formula: NH.sub.2--NH--COOR (II) in which R represents a (C.sub.1-C.sub.6)alkyl group, a phenyl or a benzyl, is treated with a 1,5-dihalopentane of formula: Hal--(CH.sub.2).sub.5--Hal (III) in which Hal represents a halogen atom; [0013] b) the piperidin-1-ylcarbamate thus obtained of formula: in which R represents a (C.sub.1-C.sub.6)alkyl group, a phenyl or a benzyl, is treated in acidic medium or in basic medium to produce the expected N-aminopiperidine. [0014] If appropriate, a salt of N-aminopiperidine (I) can be prepared by the action of an inorganic or organic acid. DETAILED DESCRIPTION OF THE INVENTION [0015] The term "halogen atom" is understood to mean a bromine, chlorine or iodine atom. [0016] Stage a) is carried out in a solvent, such as acetonitrile or toluene, at a temperature between ambient temperature and the reflux temperature of the solvent. [0017] Stage b) is carried out either in acidic medium, for example in the presence of hydrochloric or hydrobromic acid, or in basic medium, for example in the presence of potassium hydroxide or sodium hydroxide, in a solvent such as water or ethanol and at a temperature between ambient temperature and the reflux temperature of the solvent. [0018] According to a preferred embodiment of the present invention, in stage a), a compound of formula (II) in which R represents an ethyl radical is treated with a compound of formula (III) in which Hal represents a bromine atom, in acetonitrile, by heating at reflux of the solvent. [0019] According to a preferred embodiment of the present invention, in stage b), the compound of formula (IV) in which R represents an ethyl radical is treated with sodium hydroxide in water by heating at reflux of the solvent. [0020] Preferably, an N-aminopiperidine salt, such as the hydrobromide, the hydrochloride or the oxalate, is prepared. For example, N-aminopiperidine hydrobromide can be prepared in a solvent such as methyl tert-butyl ether (MTBE). EXAMPLE [0021] A--Ethyl piperidin-1-ylcarbamate [0022] A mixture of 565.3 g of ethyl carbazate in 373 ml of acetonitrile is prepared. 415.4 g of 1,5-dibromopentane are run onto the preceding mixture brought to reflux. Reflux is maintained for 3 hours. The acetonitrile is removed by concentrating under vacuum. The residue thus obtained is dissolved in a toluene/water mixture. The two-phase mixture is brought to pH=5 by addition of 30% NaOH. The aqueous phase is separated by settling and re-extracted with toluene. Water and 36% HCl are added to the combined toluene phases. The "rich" aqueous phase is washed 3 to 4 times with methyl tert-butyl ether (MTBE) to remove the neutral materials (impurities, diethyl carbazate, residual dibromopentane). The acidic aqueous phase is basified with NaOH and then NaHCO.sub.3 in the presence of toluene. The aqueous phase is re-extracted with toluene. The toluene phases are washed separately with water in order to remove any residual ethyl carbazate. The toluene phases are concentrated to dryness. 252 g of the expected product are obtained in the form of a white powder which is purified by recrystallization from methylcyclohexane. [0023] .sup.1H NMR spectrum at 300 MHz: .delta. (ppm): 1.23: t: 3H; 4.14: qd: 2H; 2.70: t: 4H; 1.66: qt: 4H; 1.36: qt: 2H; 5.54: bs: 1H. [0024] B--N-Aminopiperidine Continue reading about Method for preparing n-aminopiperidine and its salts... 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