Preparation and properties of carbamates, nitrocarbamates and their derivatives
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Abstract
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 reduced to 2,3-diaminopyridine, a compound which has previously been reported.
Earlier investigators has employed N-nitro-carbamates as intermediates in the synthesis of N-nitroamines. The nitrocarbamates in ethereal solution were treated with gaseous ammonia which caused them to undergo ammonolysis to the ammonium salt of the nitroamine, which substance precipitated from the ethereal solution.
It was thought that a similar reaction could be effected by means of primary and secondary amines. Investigation of the reaction showed that this was indeed the cases and the resulting amine salts of N-nitroamines serve as excellent derivatives of either amines or N-nitroamines since they all have melting points within the range 50 degrees Celsius to 150 degrees Celsius. These salts can also be precipitated simply by mixing ethereal solutions of the amine and the nitroamine.
The insolubility of theses substances in organic solvents and the fact that the majority of them were easily soluble in water was a good indication that they were true salts. This fact was born out by conductance measurements on several of these compounds which indicated that they were good electrolytes, comparable in strength with such salts as sodium acetate and sodium propionate.
The ultra-violet absorption spectra of several N-nitrocarbamates and amine salts of N-nitroamines were investigated and it was observed that the maxima of the N-nitrocarbamates fell in the range 235-240 millimicrons with the extinction coefficients in the range 233-235 millimicrons with extinction coefficients ranging from 8080 to 8210. The carbamates themselves did not absorb at all in the entire region that was investigated (220-400 millimicrons).
The overall picture of the results indicates that there is a slight shift toward the visible in the spectra of the N-nitrocarbamates, although the shift is not of such magnitude to serve as a means of distinguishing N-nitrocarbamates from N-nitroamines.
The behavior of one member of the series of aliphatic nitrocarbamates, ethyl N-nitro-N-isopropyl carbamate was studied in the presence of various oxidizing agents. It was predicted that in the presence of alkaline potassium permanganate, this substance would be oxidized to acetone, acetic acid, oxides of nitrogen, carbon dioxide, and water. However it was found that the oxidation products were isopropyl N-nitroamine, acetic acid, and carbon dioxide. In the presence of acidic potassium permanganate the nitrocarbamate appears to be oxidized completely to carbon dioxide, oxides of nitrogen and water.
Ethyl N-nitro-N-isopropyl carbamate is also oxidized to water soluble gaseous products if it is mixed with fuming nitric acid at room temperature, although such mixtures of nitric acid and the nitrocarbamate were observed to stand for extended periods without reacting perceptibly at temperature of 0 degrees Celsius or below.
The new carbamates which have been prepared during the course of this investigation and their physical constants are listed below. The carbamate and its physical constants are arranged in the following order: name of carbamate, boiling point, density at 20 degrees Celsius compared to water at 20 degrees Celsius, the refractive index at 20 degrees Celsius, or if it is a solid the name of the carbamate and its melting point.
Ethyl N-isopropyl carbamate. 64 degrees Celsius @ 7mm, 0.9548, 1.4229: ethyl N-dodecyl carbamate, M.P. 34-35 degrees Celsius; ethyl N-octadecyl carbamate, M.P. 63 degrees Celsius; ethyl N-(beta-diethylaminoethyl) carbamate, 90 degrees @ 3mm, 0.9666, 1.4481; isopropnyl N-(beta-chloroethyl) carbamate, 90 degrees Celsius @ 3 mm, 1.115, 1.4486; n-butyl N-n-butyl carbamate, 88 degrees Celsius @ 3 mm, 0.9238, 1,4359; n-butyl-N-ethyl carbamate, 66 degrees Celsius @ 3 mm, 0.9413, 1.4301; ethyl N-cyclohexyl carbamate, M.P. 58-59 degrees Celsius; ethyl N-(o-cyclohexylcyclohexyl) carbamate, 140-141 degrees Celsius @ 1 mm, 1.002, 1.4805; ethyl N-(3,5,dinitro-2,4,6-trimethylphenyl) carbamate M.P. 180-181 degrees Celsius; ethyl N-(alpha-phenylethyl) carbamate, B.P. 113-115 degrees Celsius @ 3 mm, M.P. 23-25 degrees Celsisus; ethyl N-[4-(1,2,4-triazolyl)] carbamate, M.P. 184-186 degrees Celsius (dec.); ethyl N-(2-thiazolyl) carbamate, M.P. 153-154 degrees Celsius; ethyl N-(2-thenyl) carbamate, 149-150 degrees Celsius @ 9 mm, 1.172, 1.5246; ethyl N-[2-(5-nitropyridyl)] carbamate, M.P. 209-210 degrees Celsius (dec.); ethyl N-[3-(2-nitropyridyl)] carbamate, M.P. 83-84 degrees Celsius.
The new N-nitrocarbamates which have been prepared and their physical constants are as follows:
Methyl N-nitro-N-ethyl carbamate, 72 degrees Celsius @ 11 mm, 1.233, 1.4483; ethyl N-nitro-N-ethyl carbamate, 107 degrees Celsius @ 31 mm, 1.163, 1.4432; ethyl N-nitro-N-n-propyl carbamate, 66 degrees Celsius @ 3 mm, 1.123, 1.4431; ethyl N-nitro-N-isopropyl carbamate, 72 degrees @ 7 mm, 1.112, 1.4381; ethyl N-nitro-N-dodecyl carbamate, and oil which decomposes when heated at 150 degrees Celsius under a pressure of 1 mm, 0.9780, 1.4545; ethyl N-nitro-N-octadecyl carbamate, M.P. 38-39 degrees Celsius; ethyl N-nitro-N(beta-chloroethyl) carbamate, 95 degrees Celsius @ 3 mm, 1.320, 1.4710; isopropyl N-nitro-N-(beta-chloroethyl) carbamate, 96 degrees Celsius @ 3 mm, 1.251, 1.4633; n-butyl N-nitro-N-n-butyl carbamate, 98 degrees @ 3 mm, 1.048, 1.4480; n-butyl N-nitro-N-ethyl carbamate, 120-122 degrees Celsius @ 7 mm, 1.078, 1.4639; ethyl N-nitro-N-(o-cyclohexylcycloheyxl) carbamate, a viscous yellow oil which decomposes without distilling when heated under a pressure of 1 mm, 1.072, 1.4901;
N,N-Dinitro-N,N-dicarbethoxy-1,4-diaminobutane, M.P. 55 degrees Celsius; N,N-dinitro-N,N-dicarbethoxy-1,6-diaminohexane, a liquid which decomposes without distilling when heated under a pressure of 1 mm, 1.221, 1.4762; ethyl N-nitro-N-(3,5-dinitro-2,4,6-trimethylphenyl) carbamate, M.P. 142-143 degrees Celsius; ethyl N-nitro-N-benzyl carbamate, a liquid which decomposes at 150 degrees in a vacuum of 1 mm, 1.213, 1.5203; ethyl N-nitro-N-(alpha-phenylethyl) carbamate, a yellow liquid which decomposes at 190 degrees in a vacuum of 1 mm, 1.197, 1.5233.
In addition to the new compounds listed above the following new compounds were prepared: N,N-dinitro-1,6-diaminohexane, M.P. 106-107 degrees Celsius and 2-nitro-3-aminopyridine, M.P. 195-196 degrees Celsius.
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Thesis (Ph.D.)--Boston University, 1950
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