Patented Apr. 13, 1954 2,675,378

UNITED STATES PATENT OFFICE 2,675,378 CYCLIC PROCESS FOR PREPARING OAZOALKANES Frank S. Fawcett, Wilmington, Dei, assignor to E.I. du Pont de Nemours and Company, Wil mington, Del, a corporation of Delaware No Drawing. Application July 22, 1952, Serial No. 300,333 2 Claims. (CI. 260-239) 1. 2 This invention relates to the preparation of In practice, an N,N'-dialkyloxamide in Solution aliphatic diazo compounds and more particularly or as a slurry in a suitable solvent is nitroSated to a cyclic process for obtaining such products. by treating it with oxides of nitrogen, convenient The aliphatic diazo compounds are an excep ly generated by reacting 56% nitric acid with tional class of chemical intermediate character 5 arsenious oxide, or by other suitable means for ized by versatility in their reactions. Thus, diazo generating nitrogen oxides known to the art. methane is particularly useful in organic Syn The resulting N,N'-dialkyl-N,N'-dinitrosooX theses, for example, in the methylation of acidic amide is then treated with an alkylnonoamine, organic compounds, the lengthening of carbon preferably one whose alkyl group is the same as chains of carboxylic acids by the well-known 10 that attached to the nitrogen of the OXamide. Arndt-Eistert synthesis (“Organic Reactions,' The aliphatic diazo compound, if it boils lower vol. I, p. 38, John Wiley & Sons, Inc. (1942)), and than the solvent, continuously distills as it forms, in a variety of useful reactions with carbonyl and is collected in Suitably refrigerated traps. If compouilds and unsaturated Organic derivatives. the aliphatic diazo compound boils above the Sol Diazomethane is also unique among the diazo 5 vent, tinen it can be isolated by extraction, by alkanes because of the ease with which it is coin precipitation by drowning in a nonsolvent, by verted to high molecular weight polymethylenes. distillation, or by other means known to those In the laboratory diazomethane is readily ob skilled in the art. The N,N'-dialkyl-OXamide, tained by the alkaline cleavage of N-nitroso-N- which is formed along with the aliphatic diazo methylurethane or N-nitroso-N-methylurea. 20 compound, can be recycled in the process by ni These procedures are not adaptable, however, to trosating it and repeating the treatment with large scale operation because in each case a large alkylimonoamine. The present method thus ac fragilent of the starting molecule is lost by deg complishes the conversion of an amine to the Cor radation to products which are not suitable for responding diazo compound by utilizing only low re-use in the process. 25 cost oxides of nitrogen and an amine. Thus, no It is an object of this invention to provide a valuable materials are lost as by-products, costs novel process for the preparation of aliphatic are reduced and overall economics of the process diazo compounds. A further object is to provide are outstanding in comparison with the processes a cyclic process for the preparation of aliphatic of the art. diazo compounds in which the starting materials 30 The examples that follow illustrate certain are converted to the aliphatic diazo compound preferred embodiments of this invention but are and to a product capable of re-use in the process. not to be construed as limitations thereof. A still further object is to provide a process for Eacample I the preparation of aliphatic diazo compounds which utilizes as the essential starting materials 35 A 100 cc. round bottomed reactor was equipped a dialkyl oxamide, primary aliphatic monoamine with two dropping funnels and a condenser ar and a nitrosating agent, such as an oxide of ni ranged for distillation with delivery of the dis trogen. Another object is to provide a cyclic tillate below the surface of a cooled diethyl ether process for obtaining diazomethane as Substan solution containing 6.08 grams (0.0498 equiv.) tially the only ultimate product. Other objects 40 of benzoic acid. Ether was placed in One drop will appear hereinafter. ping funnel and 5.5 cc. (approximately 0.045 These objects are accomplished by the follow equiv.) of a 25% aqueous solution of methyl ing invention of a process for preparing aliphatic amine in the other. A solution of 3.48 garns diazo compounds which comprises reacting an (0.02 mole, 0.04 equiv.) of N,N-dimethyl-N,N'- N,N'-dialkyl-N,N'-dinitrosooxamide, of the type 45 dinitrosooxamide in 50 cc. of diethyl ether was more fully described hereinafter, with an alkyl placed in the reaction flask and slow distillation primary monoamine bearing hydrogen on the al of ether was established by means of a Warm pha carbon atom of the alkyl group, i. e., the water bath. As the ether distilled, it was re carbon attorn attached to amino nitrogen, and placed by addition from the dropping funnel. separating therefrom an aliphatic diazo con- : The amine was added dropwise during four min pound and an N,N'-dialkyloxamide. The result utes, causing an active reaction with evolution ing N,N'-dialkyloxamide is nitrosated thereby re of diazomethane. The yellow diazomethane dis forming an N,N'-dialkyl-N,N'-dinitroSooxanide tilled with the ether and was collected in the and the thus re-formed N,N'-dialkyl-N,N'-dini benzoic acid solution, where it was immediately trosooxamide is subjected to reaction with an decolorized by conversion to methylbenzoate and alkyl primary monoamine as aforesaid. nitrogen. As the amine was added, a white Solid 2,675,378 3 4. separated from the ether solution in the flask. tube for delivering distillate into a receiver Heating was continued with occasional Swirling cooled with Dry-Ice and containing ether. An for an additional 10 minutes, during which time hydrous methylamine gas was passed into the the yellow color of the distillate and reaction solution with the resulting formation of a white mixture disappeared. After a further 5 minute precipitate and the evolution of heat. As the period (making a total of approximately 26 min addition was continued, boiling of the ether Oc utes), heating was discontinued. Titration curred and the yellow diazomethane codistilled showed that 0.0258 equivalent of benzoic acid With the ether into the receiver. The mixture had been consumed, corresponding to a 65% was warmed on a water bath until the distillate yield of two moles of diazomethane. Evapora 0 was no longer colored. There was isolated from tion of the contents of the reaction fiask to dry the residue 0.25 g. or 38% of a white Solid, melt ness yielded 1.89 g. (82%) of white Solid which ing at 211.5 to 213.5° C. This was identified as melted at 200-202 C. and which was identified N,N'-dimethyloxamide by mixed melting point as N,N'-dimethyloxamide by mixed melting point with an authentic sample prepared from diethyl with an authentic Sample. 5 oxalate and aqueous methylamine. The preS The N,N'-dimethyloxamide obtained as above ence of diazomethane in the distillate was shown can be nitrosated and recycled in the process as by its characteristic yellow color, and by its in described below. - mediate decolorization with benzoic acid. This Eacample II N,N'-dimethyloxamide can be nitrosated and 20 thus recycled into the process for preparation The N,N'-dimethyloxamide produced in the process of Example I was suspended in glacial Of diazomethane. - - - acetic acid and treated with nitrogen oxides Eacample. W generated from arsenic trioxide and 56% nitric acid at essentially room temperature. The N,N'- 25 A clear solution of 2.6 g. of N,N'-di-n-hexyl dimethyl-N,N'-dinitroSooxamide was purified by oxamide in 25 ml. of glacial acetic acid was dissolving in chloroform and precipitating by treated with oxides of nitrogen generated from adding petroleum ether and cooling. The puri arsenic trioxide and 56% nitric acid. The ini fied nitroso derivative melted at 61-64° C. and tially colorless Solution gradually turned yellow was a bright yellow crystalline Solid. 30 and finally dark green. Occasionally tests were To a solution of 1.74 g. of the N,N-dimethyl made for completion of the reaction by diluting N,N'-dinitrosooxamide thus obtained in 50 ml. Small Samples and it was found that after two of ether there was added 2.5 ml. of 25% aqueous hours reaction time dilution with ice Water pro methylamine. Gas evolution began immediate duced a yellow precipitate of the nitroso de ly and the mixture was warmed with a water rivative. The total aqueous mixture after Such bath to aid distillation of diazomethane. The dilution was extracted with ether and the yell yellow distillate of diazomethane and ether WaS low ether Solution washed with cold dilute so collected in Dry-Ice-cooled Solution of 4.0 g. Of diurn bicarbonate and then With cold Water. benzoic acid and 40 ml. of ether. After a pe The addition of n-hexylamine to the ether riod of 25 minutes, during which time ether was 40 Solution resulted in the immediate formation of added to replace that which distilled, the resid a precipitate accompanied by boiling of the ether. ual material was essentially colorleSS. Titra The mixture was filtered and washed on the fil tion of the benzoic acid solution showed a 62% ter with ether giving 0.2 g. Of White Solid, melt yield of 2 moles of diazomethane. The White ing point 131-133° C., which was identified as solid remaining with the ether in the reaction 4.5 N,N'-di-n-hexyloxamide, by mixed melting point flask when dried amounted to 1.12 g., eSSential With an authentic Sample. The diaZO-n-hexane ly the theoretical quantity, of N,N'-dimethyl in the filtrate was identified by its conversion oxamide, melting point 185-200° C.; after re to the n-hexyl ester of 3,5-dinitrobenzoic acid by crystallization from ethanol, melting point reaction. With 3,5-dinitrobenzoic acid (see Adam 210-213° C. The IN,N'-dioxamide obtained as 50 Son and Kenner, J. Chem. Soc. 1935, p. 287). above can again be recycled in the process and There was thus obtained 0.1 g, of the n-hexyl thus re-utilized. - ester of 3,5-dinitrobenzoic acid, melting point Eacample III 54-55° C. which was identified by mixed melting The procedure of Example II was repeated point With an authentic Sample prepared from using 3.48 g. of the N,N'-dimethyl-N,N'-dini 5 5 In-hexyl alcohol and 3,5-dinitrobenzoyl chloride. troSooxamide and 3.8 m. of 25% aqueous methyl The N,N'-di-n-hexyloxamide was prepared by amine. Titration showed that a 56% yield of the addition of diethyl oxalate to a solution of 2 moles of diazomethane was formed and 2.27 g. in-hexylamine in absolute ethanol. The White of slightly yellow N,N'-dimethyloxamide, melt Crystalline Solid was isolated in approximately 60 75% yield and after recrystallization showed a ing point 190-198° C. were recovered from the melting point of 130 to 130.8° C. reaction mixture. After recrystallization from Anal-Calc'd for C14H23N2O2: N, 10.9. Found: ethanol the melting point of the N,N'-dimethyl N, 11.66. . oxamide was raised to 206-209° C. This N,N'- The nitrosation reaction which leads to the dimethyloxamide can be nitrosated to N,N'-di formation of N,N' - dialkyl-N,N' - dinitroSOOX methyl-N,N'-dinitrosooxamide and thus used amide is conducted at temperatures of from 0° for preparation of the desired diazomethane. to 30° C., depending upon the method used. Eacample IW Temperatures of 5 to 25° C. are generally em ployed because good yields of the desired dini A reaction flask containing a clear yellow so 70 troSOOXanilide at good reaction rates are realized lution of 1.0 g. of N,N'-dimethyl-N,N'-dinitroSo in this range. Because the nitrosation reaction OXamide in 50 ml. of ether was fitted with a drop is exothermic, Once it is initiated, regulation is ping funnel for the addition of ether, a gas in necessary either by cooling or by adding the ni let tube for the addition of anhydrous gaseous troSating agent at Such rate that the amount of methylamine from a cylinder, and a delivery 75 heat of reaction evolved is just enough to main 2,675,378 S 6 tain the temperature within the range selected Saturated aliphatic radicals of up to i8 carbon for Operation. atoms. Examples are N,N'-diethyl-N,N'-dinitro The amount of nitrosating agent used is at sooxamide, N,N'-dibutyl-N,N'-dinitroSooxanide, least one mole per annido hydrogen in the N,N'- N,N'-dihexyl-N,N'-dinitrosooxamide, N,N'-dido dialkyloxamide. 5 decyl-N,N'-dinitroSooxamide, N,N'-dioctadecyl Although in the examples the nitrosation has N,N'-dinitrosooxanide, and the like. The pre been effected with oxides of nitrogen formed by ferred nitroSOOxamides are those having short, reaction of arsenious oxide with 56% nitric acid, chain alkyl substituents, i. e., those in which the this is only because of convenience. Oxides of alkyl groups have from 1 to it carbon atoms. nitrogen may be generated in other ways, for ex 0. As previously indicated, the alkyl monoamines ample, by the reaction of nitric acid on Sodium used in the ammonolysis of the N,N'-dialkyl nitrite. Alternatively, the bis-nitrosooxamide can N,N'-dinitroSooxamides are those which have the be made by reacting the N,N'-dialkyloxamide amino nitrogen linked to a carbon carrying at with nitrous acid, nitrosyl chloride, or nitrosyl least one hydrogen atom. Examples are methyl Sulfuric acid. The nitrous acid can be made con amine, ethylamine, butylamine, 2-aminoplopane, veniently by reacting dilute hydrochloric acid octylamine, dodecylamine, hexadecylamine, 4 with isoamyl nitrite or other ester of nitrous acid, aminoheptane, and the like. The preferred al Sodium nitrite, and the like. kylimonoamines are those having short chain The nitrosation reaction is preferably carried alkyl substituents of 1 to 7 carbon atoms. out in the presence of inert materials which are 20 Since, in the process of this invention, the solvents for the N,N'-dialkyloxamide. Suitable N,N'-dialkyloxamide is formed along with the Solvents are hydroxylated compounds as glacial aliphatic diazo compound, it can be recirculated acetic acid, water and alcohols, or ethers, hy in the process and this provides substantial op drocarbons, halogenated hydrocarbons, and the erating economies. The process can be per like. formed on a practical basis as a cyclic operation. In the conversion of the N,N'-dialkyl-N,N'-di As many apparently widely different embodi nitrosooxanide to the diazoalkane, there may be ments of this invention may be made without used any primary aliphatic monoamine in which departing from the Spirit and Scope thereof, it the amino nitrogen is attached to a hydrogen is to be understood that this invention is not bearing aliphatic carbon atom. In the preferred 30 limited to the specific embodiments thereof ex practice an alkyl monoamine is used whose alkyl cept as defined in the appended claims. group is identical to those in the N,N'-dialkyl I claim: N,N'-dinitroSooxamide. 1. In a process for preparing diazoalkanes, the The amount of amine used is such as to pro improvement which comprises reacting an N,N'- wide an equivalent per nitroSo group in the N,N'- dialkyl-N,N'-dinitroSooxamide in which the alkyl dialkyl-N,N'-dinitroSOOxamide. Larger amounts, groups are identical and each COntains 1 to 7 up to 2 or more equivalents per nitroso group carbon atoms with hydrogen on alpha carbon in the oxamide, may be used but this generally with a primary alkyl monoamine in which the has no practical advantage and tends to increase alkyl group is identical with the alkyl groups COstS. in said N,N'-dialkyl-N,N'-dinitroSOOXamide, Sep In practice, if the amine is gaseous, it can be arating from the reaction mixture the resulting bubbled into the Solution of the nitroSOOxamide diazoalkane and an N,N'-dialkyloxamide in at such a rate as to maintain the reaction tem which the alkyl groups are identical With the perature within the range Selected for operation. alkyl groups in said N,N'-dialkyl-N,N'-dinitroso On the other hand, if the amine is normally a oxamide, nitrosating said N,N'-dialkyloxamide liquid or solid, it is preferable to add it to the thereby forming the aforesaid N,N'-dialkyl-N,N'- nitroSooxanide in the form of a Solution in a dinitroSooxamide, and recycling the thus formed solvent, which is desirably the same as the sol N,N'-dialkyl-N,N'-dinitroSOoxamide for reaction Went in Which the nitroSooxanide is dissolved. With said primary alkyl monoamine as aforesaid. Water is a convenient Solvent for use with lower 50 2. In a process for preparing diazomethane, molecular weight amines. The rate of addition the improvement which comprises reacting N,N'- is controlled so as to maintain the temperature dimethyl-N,N'-dinitrosooxanide with methyl of the reaction mixture within the range of 20° amine, separating from the reaction mixture the to 40° C. The particular temperature is gen resulting diazomethane and N,N'-dimethylox erally controlled by the nature of the solvent in :5 5 amide, nitroSating said N,N'-dimethyloxamide which the amination of the N,N'-dialkyl-N,N'- thereby forming the aforesaid N,N-dimethyl dinitroSooxamide is conducted. With diethyl N,N'-dinitroSOOXamide, and recycling the thus ether, 30° to 40° C. is a convenient temperature, formed N,N'-dimethyl-N,N'-dinitrosooxamide for and whenever diazomethane is the aliphatic diazo reaction with said methylamine as aforesaid. compound synthesized, it distills over with the (30 ether. In practice, it is desirable to replace the References Cited in the file of this patent ether as it distills in order to avoid the hazards Backer, J. Chem. Soc. (London), vol. 101, pp. of such reaction inixtures involving limited 592-595 (1912). amounts of solvent diluents. Werner, J. Chem. Soc. (London), vol. 115, pp. The N,N'-dialkyi-N,N'-dinitrosooxamides used 1093-1102 (1919). in the practice of this invention are those which Arndt et al., Chem. Abstracts, vol. 24, p. 3985 have at least One hydrogen atom. On each of the (1930). non-acyl carbons which are directly attached to Arndt et al., AngeW, Chem., vol. 46, pp. 47-48 both amido nitrogen atoms, i. e., the carbons (1933). alpha, to the amido nitrogens, the remaining 70 Eistert, Angew, Chem., vol. 54, pp. 99, 100, 129, valencies of each of the said hydrogen-bearing 130 (1941). alpha carbons being satisfied by hydrogen or by Owen, Chem. Abstracts, vol. 38, p. 2006 (1944).