Ind. Eng. Chem. Res. 2000, 39, 4011-4013
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APPLIED CHEMISTRY Pentaerythrityltetramine† William S. Anderson,* Harry J. Hyer,‡ John E. Sundberg,§ and Thomas P. Rudy| Chemical Systems Division, United Technologies Corporation, P.O. Box 49028, San Jose, California 95161-9028
Treating pentaerythrityl tetrachloride with excess hot, highly compressed ammonia yields the tetramine C(CH2NH2)4 in 57% yield at 52% conversion; unconverted starting material is easily recovered for recycling. The ammonolysis may be conducted either in supercritical ammonia alone or in methanol as the solvent. The product amine is isolated by precipitating it as the water-insoluble disulfate; simply washing the precipitate with water yields disulfate of high purity. Introduction Pentaerythrityltetramine1,2 has been suggested as a precipitant for nitric acid3 and as a starting material for several products. Although at least three laboratory procedures1,4,5 for preparing it are available, the tetramine has never been available as a high-volume, staple item. There is a need for a preparative procedure suitable for large-scale manufacture. Tetramine Preparation Ammonolysis. It has now been found that treating the readily available tetrachloride C(CH2Cl)4 with excess supercritical ammonia at 175 °C generates the tetramine in fair yield in one stepsa process that seems suitable for scale-up. The starting material can be made from pentaerythritol and hydrogen chloride6 or perhaps by chlorination of neopentane present in natural gas. An organic solvent is not required for the tetrachloride ammonolysis; excess supercritical ammonia will serve as the reagent, solvent, and heat-transfer agent. Nevertheless, it is convenient to transfer materials in and out of the reactor by using methanol as the solvent. At the pressure and temperature used, methanol is not supercritical; if a methanol-rich liquid phase exists in the reactor, the ammonolysis products will collect in that phase and may be removed by draining only the liquid phase. Progress of the ammonolysis may be monitored by pressure measurements with or without the use of methanol as the reaction solvent. As expected for a nucleophilic displacement (especially a “sterically hindered” one),7,8 the rate of ammonolysis † Presented in part at the Pacific Conference of the American Chemical Society, Foster City, CA, October 21, 1992. * To whom correspondence should be addressed. Permanent address: 5987 Peacock Ridge Road #115, Rancho Palos Verdes, CA 90275. Phone: (310) 377-3357. ‡ Deceased. § Permanent address: Chevron Products Co., 100 Chevron Way, P.O. Box 1627, Richmond, CA 94802-0627. | Permanent address: 21142 Sarahills Drive, Saratoga, CA 95070.
is highly pressure-dependent (especially near the critical point).9-11 Thus, ammonolysis in a large excess of methanolic ammonia at 175 °C and 0.7 MPa proceeds to less than 10% conversion in 24 h; the process becomes practical only when the pressure is raised to at least 20-30 MPa. At 175 °C the ammonolysis product is not stable, and the reaction is therefore best terminated before complete conversion is reached. Fortunately, unconverted tetrachloride is easily recovered for recycling. As the ammonolysis proceeds, the rate of ammonia consumption increases. The autoacceleration is probably caused by the formation of salts as byproducts (ammonium chloride and transition-metal chlorides arising from reactor corrosion). If tetramethylammonium bromide or chloride is included in the charge, the ammonolysis is more rapid from the start. The salt effect is known in hydrolyses in supercritical water;12 apparently it exists in analogous reactions in compressed ammonia. The product disulfate is precipitated from the crude ammonolysis product by adding excess cold aqueous sulfuric acid. Hydrogen chloride is released in this step; this might be recovered and used for converting pentaerythritol to pentaerythrityl tetrachloride. Ammonolysis byproducts are washed out of the collected precipitate with cold water, and unconverted pentaerythrityl tetrachloride is washed out with a hydrocarbon solvent. Many kilograms of disulfate have been prepared by the method described. Several byproducts may be formed during the ammonolysis: cracking products, secondary and tertiary amines, chlorine-containing amines, neopentyl rearrangement products, corrosion products, and methanol products. These products, if present, are removed during the washing step. Needed Process Improvements. The next logical step in process development is to build a 150 MPa, tubular, chloride-resistant, semicontinuous-flow reactor with a cyclone as the product collector. This apparatus should resemble the plant described in 1966 for the rapid ammonolysis of ethylene dichloride.13 If raising the pressure to 150 MPa allows a decrease in the
10.1021/ie990805j CCC: $19.00 © 2000 American Chemical Society Published on Web 10/03/2000
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reaction temperature, then the needed lower corrosion rate and lower product decomposition rates will follow. Neopentylamine is said to arise from the Raneynickel-catalyzed reaction of neopentyl alcohol with hot ammonia and hydrogen;14 this and some analogous catalytic amination reactions15 are reported to proceed at high rates at moderate pressures. A similar catalytic conversion of pentaerythritol could offer many advantages over pentaerythrityl tetrachloride ammonolysis; the “greenness” of catalytic amination could be particularly attractive. Adequate product stability at the amination temperature needs to be demonstrated, however. Cognate Preparations. Treating dipentaerythritol with thionyl chloride in pyridine yields the hexachloride (ClCH2)3CCH2OCH2C(CH2Cl)3.1 This material is ammonolyzed by treatment with excess methanolic ammonia at 175 °C and 21 MPa. Adding 25% sulfuric acid to the reaction product yields no precipitate, however. When the hexatosylate of dipentaerythritol is treated with sodium azide in diethylene glycol at 135 °C, the hexaazide (N3CH2)3CCH2OCH2C(CH2N3)3 is obtained in 65% yield.16 This azide is not as impact-sensitive as pentaerythrityl tetraazide and does not detonate with the extraordinary violence17 of the tetraazide explosion. The hexaazide may be distilled at reduced pressure, albeit with some explosion risk. Preparing the pure octaazide from the octatosylate of tripentaerythritol is less successful. An insoluble tar is the major product; a 35% yield of a crude liquid nondistillable azide mixture is obtained.16 The azide nitrogen content of this octaazide mixture is slightly lower than the theoretical content, perhaps because the starting tripentaerythritol contains some pentaerythritol formals. The mixture can be pyrolyzed without a detonation; hydrogenation of the hexa- and octaazides to the corresponding amines has not been attempted. Experimental Section 2,2-Bis(chloromethyl)-1,3-dichloropropane [322899-7]. This material (pentaerythrityl tetrachloride) is commercially available from several sources. It may be prepared in 92% yield from pentaerythritol and thionyl chloride in pyridine1 and purified by steam distillation, recrystallization from methanol, distillation, or sublimation. 2,2-Bis(aminomethyl)-1,3-propanediamine Disulfate [69898-47-1]. A 1-gal 316 stainless steel autoclave rated at 5000 psi (34.5 MPa) working pressure is fitted with a magnetically driven dasher, thermowell, external heaters, pressure gauge, dip tube, rupture disk, temperature controller, two 10-gal polyethylene product collectors, and an air-driven reciprocating pump fed from an elevated tank of liquid anhydrous refrigerationgrade ammonia. The reactor is charged with 300 g of pentaerythrityl tetrachloride, 2 L of methanol, and 5 g of tetramethylammonium bromide. The reactor is closed, and air is purged from it by adding nitrogen until the pressure reaches 7 MPa and then releasing the gas; this operation is performed three times. The dasher, heaters, and pump are started, and liquid ammonia is pumped in until the pressure in the reactor reaches 23.5 MPa at 175 °C. Ammonia consumption starts immediately; when the pressure falls to 20.7 MPa, additional liquid ammonia is pumped in to restore the pressure to 23.5 MPa. During the next 2 h, the temperature is maintained at 174-175 °C and the pressure is maintained at 20.7-23.5 MPa by repeated additions of liquid
ammonia. The reactor is then drained through the dip tube into the series-connected polyethylene product collectors. The expanding ammonia instantly cools the reaction product to ambient or subambient temperature. Ammonia escaping from the product collectors is delivered to a scrubbing tower or a stack. All high-pressure operations are conducted in a ventilated, remote-controlequipped, concrete cell. The product is transferred from the polyethylene collection bottles to a 10-gal stainless steel bucket and is slowly brought to a boil to expel dissolved ammonia (hood). The liquid is then cooled to room temperature, and 400 mL of cold 25% sulfuric acid is stirred in to precipitate the tetramine disulfate and release HCl. The precipitate is collected on a Bu¨chner funnel, where it is washed with two 400 mL portions of ice water, with two 300 mL portions of warm petroleum ether, and then again with 400 mL of ice water. The off-white solid is dried in a vacuum oven at 50 °C to give 137 g of tetramine disulfate. From the hydrocarbon wash, 145 g of unchanged tetrachloride is recovered for recycling. The yield of tetramine disulfate based on the amount of tetrachloride consumed is 57% of the theoretical amount; conversion of tetrachloride is 52%. Identity of the tetramine disulfate is established by its equivalent weight in acid-base titration18 (theoretical, 82 g/equiv; found, 84 g/equiv) and by its elemental composition. Confirmation is obtained by converting the disulfate to the tetrachloride and the tetrabromide by triturating with the corresponding acids; identity of these salts is also established from their elemental composition. 2,2-Bis(aminomethyl)-1,3-propanediamine [474200-1]. The free tetramine C(CH2NH2)4 is obtained by treating the disulfate with an equivalent of sodium methoxide in methanol and distilling the amine at reduced pressure. It is identified by its mass spectrum (base peak at m/q 30, M + 1 peak at m/q 133, and no parent ion), its proton magnetic resonance spectrum5 in CDCl3, and its infrared spectrum taken between salts [3250 (broad, intense), 1600, 1435, and 900 cm-1]. The tetramine is extremely hygroscopic. 2,2-Bis(aminomethyl)propane-1,3-diamine Tetranitrate [14259-94-0]. Finely ground tetramine disulfate (5.7 g, 0.017 mol) is placed in a 30 mL fritted glass filter funnel closed at the bottom with a rubber dropper bulb. A total of 25 g of 9 M nitric acid is added with stirring and allowed to remain in contact with the amine sulfate for 1 h. The bulb is then removed, and the acid is drawn through the funnel, discarded, and replaced with a fresh 25 g charge of 9 M nitric acid. After an additional 1 h, this acid is drained and the solid is washed with two 5 g portions of ice water. The solid is then dried overnight at room temperature at reduced pressure. The yield of tetranitrate is 6.7 g (99% of the theoretical amount). Its identity is established by its elemental composition, its equivalent weight in acid-base titration18 (theoretical, 96 g/equiv; found, 95 g/equiv), its proton magnetic resonance spectrum in D2O [δ 3.5 (8H) and 4.7 (12H)], its infrared absorption spectrum (which resembles that of ammonium nitrate), and its X-ray diffraction pattern19 (see the Acknowledgments section). Finely ground tetranitrate, 0.01 g, does not dissolve or change in appearance when stored in 10 g of 9 M nitric acid for 30 days at 25 °C. Solubility in this
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medium is thus less than 0.1% and oxidation by HNO3 does not consume the solid tetranitrate under these conditions. Caution: the tetranitrate is an explosive.2 Acknowledgment The late C. J. Pedersen (Nobelist in chemistry) suggested to us that pentaerythrityltetramine might be made in large quantities by ammonolysis of pentaerythrityl tetrachloride. We are indebted to Duane Elder, Michael Jeffries, John Quinonez, Hector Delarosa, and Daniel Adelman for help with the ammonolyses, to Ron Main for help with salt preparations and solubility determinations, and to Y. Oyumi, T. B. Brill, A. L. Rheingold, and C. Lowe-Ma for repeating our disulfate-to-tetranitrate conversion and determining the crystal structure of the tetranitrate by X-ray diffraction. The experimental work on ammonolysis was a part of the Independent Research and Development program of Chemical Systems Division, United Technologies Corp. Literature Cited (1) Berlow, E.; Barth, R. M.; Snow, J. E. The Pentaerythritols; Reinhold: New York, 1958. (2) McDonnell, C. H. Pentaerythritylamines. In Encyclopedia of Explosives and Related Items; Kaye, S. M., Ed.; National Technical Information Service, U.S. Department of Commerce: Springfield, VA, 1978; Vol. 8, p 125. (3) Anderson, W. S.; Hyer, H. J.; Sundberg, J. E.; Rudy, T. P. Pentaerythrityl Tetramine: A Precipitant for Nitrate Ion. Presented at the 219th National Meeting of the American Chemical Society, San Francisco, CA, March 2000; Paper I&EC 239. (4) Willer, R. L. Insensitive Polynitramine Compound. U.S. Patent 4,485,237, Nov 27, 1984. (5) McAuley, A.; Subramanian, S.; Whitcombe, T. W. Synthesis and Crystal Structure of an Octahedral Nickel(II) Complex Derived from Pentaerythrityl Tetramine. Can. J. Chem. 1989, 67, 1650. (6) Mann, H. J. Verfahren zur Herstellung von Pentaerythrittetrachlorid. German Patent 935,362, Nov 17, 1955.
(7) Hamann, S. D. High-Pressure Chemistry. Annu. Rev. Phys. Chem. 1964, 15, 349. (8) Sera, A. Nucleophilic Substitution at Saturated Carbon Atoms. In Organic Synthesis at High Pressure; Matsumoto, K., Acheson, R. M., Eds.; Wiley: New York, 1991. (9) Drljaca, A.; et al. Activation and Reaction Volumes in Solution. 3. Chem. Rev. 1998, 98, 2167. (10) Jurczak, J.; Gryko, D. T. Organic Synthesis at High Pressure. In Chemistry under Extreme or Non-Classical Conditions; van Eldik, R., Hubbard, C. D., Eds.; Wiley: New York, 1997. (11) Subramian, B.; McHugh, M. A. Reactions in Supercritical FluidssA Review. Ind. Eng. Chem. Process Des. Dev. 1986, 25, 1. (12) Savage, P. E.; Gopalan, S.; Mizan, T. I.; Martino, C. J.; Brock, E. E. Reactions at Supercritical Conditions: Applications and Fundamentals. Am. Inst. Chem. Eng. J. 1995, 41, 1723. (13) Coker, W. P. Synthesis of Aziridines. French Patent 1,468,054, Feb 11, 1966. (14) Werner, F.; Blank, H. U.; Gramm, G.; Braden, R.; Ziemann, H. Neopentylamine. European Patent Application 22532, Jan 21, 1981. (15) Baiker, A. Supercritical Fluids in Heterogeneous Catalysis. Chem. Rev. 1999, 99, 453. (16) Anderson, W. S.; Hyer, H. J. JANNAF Propulsion Meeting Vol. 1, AD-A103 844. Chemical Propulsion Information Agency Publication 340; CPIA: Washington, DC, 1981. (17) Dunn, T. J.; Neumann, W. L.; Rogic, M. M.; Woulfe, S. R. Versatile Methods for the Synthesis of Differentially Functionalized Pentaerythritol Amine Derivatives. J. Org. Chem. 1990, 55, 6368. (18) Kolthoff, T. M.; Stenger, V. A. Volumetric Analysis; Interscience: New York, 1947; Vol. II. (19) Oyumi, Y.; Brill, T. B.; Rheingold, A. L.; Lowe-Ma, C. Thermal Decomposition of Energetic Materials. 2. The Thermolysis of NO3- and ClO4- Salts of the Pentaerythrityltetrammonium Ion, C(CH2NH3)44+, by Rapid-Scan FTIR Spectroscopy. The Crystal Structure of C(CH2NH3+)4(NO3-)4. J. Phys. Chem. 1985, 89, 2309.
Received for review November 8, 1999 Revised manuscript received March 30, 2000 Accepted August 6, 2000 IE990805J
