Preparation and properties of carbamates, nitrocarbamates and their derivatives

by Howard Millard Curry

Institution: Boston University
Year: 1950
Record ID: 1554527
Full text PDF: http://hdl.handle.net/2144/4138


Since representative alipahtic N-Nitrocarbamates have been found by Dr. J. Philip Mason and Mr. Robert T. Pollock to be suitable additives for Diesel fuels, it was thought desirable to synthesize several members of the series not recorded in the literature. Accordingly plans were made for the synthesis of a series of nitrocarbamates having various aliphatic, alicyclic, aromatic, and heterocyclic groupings within the molecule. The carbamates were usually prepared by treating a mixture of an amine and aqueous sodium hydroxide with ethyl chloroformate but in some cases where this procedure failed to give a satisfactory yield or a reasonably pure product, the carbamates were prepared either by mixing the amine and ethyl chloroformate in an organic solvent or by the Hoffman rearrangement of an amide in alcohol solution. The carbamates were nitrated with mixtures of fuming nitric acid (sp.gr.1.49) and acetic anhydride. In general, it was observed that one and one-half equivalents of nitric acid were sufficient to effect complete nitration when acetic anhydride were employed as the dehydrating agent. Earlier investigators found that large excesses of nitric acid were required if this latter substance were used by itself as a nitrating agent. In the aliphatic and alicyclic series the carbamates were easily nitrated to yield the corresponding N-nitro carbamates. However, nitration of aromatic carbamates, such as ethyl N-phenyl carbamate, led to the introduction of a nitro group into the ortho and para positions of the benzene nucleus. When the ortho and para positions were blocked with methyl groups, as in the case of ethyl N-(2,4,6-trimethylphenyl) carbamate, nitration then took place in the meta position to yield ethyl N-(3,5-dinitro-2,4,6-trimethylphenyl) carbamate. This latter compound, since all ring positions were blocked, was nitrated to yield ethyl N-nitro-N-(3,5-dinitro-2,4,6-trimethylphenyl) carbamate, the only aromatic N-nitrocarbamate which was obtained during the course of this investigation. In the heterocyclic series attempts at nitrating ethyl N-[4-(1,2,4-triazolyl)] carbamate, ethyl N-(2-thiazolyl) carbamate, ethyl N-(2-pyridyl) carbamate and ethyl N-(s-pyridyl) carbamate with fuming nitric acid and acetic anhydride resulted in each case in recovery of the original material. Attempts at nitrating ethyl N-(2-furfuryl) carbamate and ethyl N-(2-thenyl) carbamate resulted in the formation of dark, viscous tarry substances. However ethyl N-(2-pyridyl) carbamate and ethyl N-(3-pyridyl) carbamate were nitrated in the nucleus by refluxing them with a mixture of fuming nitric acid and concentrated sulfuric acid to yield ethyl N-[2-(5-nitropyridyl)] carbamate and ethyl N-[3-(2-nitropyridyl)] carbamate respectively. In the case of ethyl N-[2-(5-nitropyridyl)] carbamate the position of the nitro group was ascertained by hydrolyzing it to 5-nitro-2-aminopyridine, a known compound. The ethyl N-[3-(2-nitropyridyl)] carbamate was hydrolyzed to 2-nitro-3-aminopyridine, a new compound, and the latter substance was…