Patent GB-748400-A (GB)
Title: Unsaturated nitro-esters and the production of amino acids and their derivatives therefrom
Inventor: ALLEN SIDNEY JAMES
IPC: C07C205/50
Filed: 1952-10-06
Abstract: A mixture of an amino acid ester and lactam obtained by catalytic hydrogenation of a nitro ester of the general formula <FORM:0748400/IV(a)/1> where R is a hydrocarbon radical, and where each of the bonds which are shown as being free carries hydrogen or a hydrocarbon radical (see Group IV (b)), may be used as starting material for polymerization in the production of polyamides.ALSO:The invention comprises as new compounds nitro-esters of the general formula <FORM:0748400/IV(a)/1> where R is a hydrocarbon radical, preferably an alkyl radical, and each of the bonds which are shown as being free carries hydrogen or a hydrocarbon radical.  They may be obtained by reacting a nitroalkane having at least one hydrogen atom attached to the same carbon atom as the nitro group with an equimolecular proportion of a 1 : 3-diene-1-carboxylic ester in which any substituents contain only hydrogen and carbon.  The nitro-esters may be converted to esters and/or lactams of 6-amino aliphatic carboxylic acids by catalytic hydrogenation so as to reduce the nitro group and the ethylenic double bond without substantially affecting the ester group.  In preparing the nitro-esters the nitroalkane may be used in molecular excess, e.g. up to 5 to 10 moles of nitromethane may be used for each mol. of a 1 : 3-butadiene-1-carboxylic ester. The reaction is preferably carried out in the presence of a base, especially a strong base such as caustic soda, caustic potash, or a quaternary ammonium base, e.g. trimethyl benzyl ammonium hydroxide. The nitro-esters may be selectively hydrogenated with the aid of active nickel or active cobalt which may be supported on kieselguhr or pumice, or may be Raney nickel or Raney cobalt. The temperature used is generally between room temperature and about 150 DEG  C., and the hydrogen pressure from about 30 to 3000 pounds per square inch. Alternatively, a platinum or palladium catalyst, e.g. Adam's platinum catalyst, may be used. Temperature, hydrogen pressure and duration of treatment are regulated so as to avoid reduction of the ester group. In order to avoid or reduce the formation of secondary amines, the hydrogenation may be carried out in the presence of ammonia, or a source of formyl or acetyl radicals, e.g. methyl or ethyl formate, or methyl or ethyl acetate; or Adam's platinum catalyst may be used in the presence of acetic anhydride.  In preparing the nitroester it is advisable to have present a small amount of hydroquinone or other polymerization inhibitor.  When the hydrogenation of the nitro-ester is carried out in the absence of formyl or acetyl radicals some of the product is usually obtained in the form of the ester and some in the form of lactam, while when formyl or acetyl radicals are present the N-formyl or N-acetyl derivative of the amino acid ester is formed.  The lactams or the amino acid esters or their formyl or acetyl derivatives may be hydrolysed to form the free amino acids and any of these derivatives may be used as starting materials for the production of polyamides.  A mixture of the ester and lactam obtained by direct hydrogenation of the nitro-ester may itself be the starting material for the polymerization.  In examples: (1) nitromethane is added to a solution containing caustic potash and a small amount of hydroquinone in ethanol and ethyl 1,3-butadiene-1-carboxylate added slowly to the solution.  The mixture is then heated to 40-45 DEG  C., neutralized with hydrochloric acid and the ethanol and residual nitromethane evaporated off under reduced pressure to yield crude 5-nitro-2-pentene-1-carboxylic acid ethyl ester; (2) the product of (1) is hydrogenated at 100-126 DEG  C. under a hydrogen pressure of 250-400 pounds per square inch, using Raney nickel wet with ethanol as catalyst.  The catalyst is filtered off and the product fractionated under reduced pressure to yield e -caprolactam. Reference is also made to the use of a sorbic ester and/or a homologue of nitromethane, e.g. nitroethane as starting materials. The 1,3-diene carboxylic esters may be made by hydrolysing the corresponding nitriles and then esterifying, e.g. with methyl or ethyl alcohol, but are preferably prepared by the direct alcoholysis of the nitrile, e.g. 1,3-butadiene-1-nitrile may be treated with methanol or ethanol in the presence of hydrochloric acid to yield methyl or ethyl 1,3-butadiene-1-carboxylate.