US3926953A - Process for producing 1,5-diacetyl-3,7-dinitro-1,3,5,7-tetraazacyclooctane - Google Patents

Abstract

Diacetyl pentamethylene tetramine in solution in acetic acid is converted to 1,5-diacetyl-3,7-dinitro-1,3,5,7-tetraazacyclooctane by nitrolysis in a mixture of nitric and sulfuric acid. The amount of nitric acid required for this purpose may be reduced to near-stoichiometric levels and a resultant hazardous exothermic reaction avoided by the addition of urea to the acetic acid solution of diacetyl pentamethylenetetramine before nitrolysis occurs.

Description

United States Patent [191 Coburn et al.

[ Dec. 16, 1975 PROCESS FOR PRODUCING 1,5-DIACETYL-3,7-DINITRO-1,3,5,7-

TETRAAZACYCLOOCTANE [75] Inventors: Michael D. Coburn, Los Alamos;

Theodore M. Benziger, Santa Fe, both of N. Mex.

[73] Assignee: The United States of America as represented by the United States Energy Research and Development Administration, Washington, DC. [22 Filed: Dec. 5, 1974 [21] Appl. No.: 529,988

[52] US. Cl. 260/239 BC [51] Int. Cl. C07D 257/02 [58] Field of Search 260/239 BC, 239 HM [56] References Cited OTHER PUBLICATIONS Yoshida et al., J. of Heterocyclic Chem., Vol. 10, pp.

Topchieu Nitration of Hydrocarbons and Other Organic Compounds, p. 62 perrnogen 1962.

Primary ExaminerDonald G. Daus Assistant ExaminerW. B. Springer Attorney, Agent, or FirmDean E. Carlson; Edward C. Walterscheid [5 7] ABSTRACT 4 Claims, 2 Drawing Figures BACKGROUND OF THE INVENTION I The invention described herein was made in the course of, or under, a contract with the US. ATOMIC ENERGY COMMISSION. It relates to high explosives andfmore particularly, to an' improved method'for' preparing l,5-diacetyl-3,7-dinitro-l,3,5,7-tetraazacyclooctane, an intermediate ina preferred synthesis of f the-high explosive cyclotetramethylenetetranitrarnine.-

Cyclotetramethylenetetranitramine (HMX) is apowerful high explosive possessing significant advantages in other explosives such as the widely used'cyclotrimethylenetrinitramine (RDX). Because of its high cost -3 to 4 times that of RDX) it typically finds use only in specialized ordnance such as shaped charges, where the explosive performance must be maximized. Presently, HMX is manufactured by a modified version of the Bachmann RDX process.

Another process has recently been developed, however, which results in substantially greater yields of HMX than can be obtained by the modified Bachmann RDX process, even though it uses essentially the same raw materials. -A mixture of hexamethylenetetramine (hexamine), acetic anhydride, and ammoniuni acetate tained by using a near-stoichiometric amount of nitric acid. In addition, a short reaction time is advantageous if a continuous rather than a batch process is to be used. The art discloses that good yields of high-purity DADN can be obtained but only through use of a tenfold excess of nitric acid and a reaction time of 100 minutes. A significant problem, however, is that if the nitric acid concentration is reduced to a near-stoichiometric level, a violent abrupt exotherm occurs toward the end of the reaction. Such an exotherm constitutes an intolerable hazard in any large-scale process.

SUMMARY OF THE INVENTION In accordance with the present invention, the violent exotherm which results from the nitrolysis of DAPT to DADN with near-stoichiometric concentrations of nitric acid may be completely eliminated by the addition of urea to the crude solution of DAPT in acetic acid prior to the nitrolysis. The urea addition not only avoids the production of the exotherm but also allows the temperature of the nitrolysis step to be increased and the nitrolysis to be completed in a substantially shorter time than is taught in the prior art.

both explosiveperformance and thermal stability over able that a good yield of high-purity DADN'jbeob-f BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a representative example of the exotherm which occurs during the nitrolysis of DAPT in acetic acid solution with a near-stoichiometric amount of nitric acid in the absence of urea.

FIG. 2 is a comparison of the yield of DADN produced during the nitrolysis of a standard DAPT feed 5 solution at 30C with and without the presence of urea.

Nitrolysis of DAPT to DADN The literature discloses that DADN may be prepared by the nitrolysis of DAPT to DADN using a mixture of nitric and sulfuric acids. See, e.g., Yoshida et a1., Synthesis of l,3,5,7-tetraazacyclooctane Derivatives, J. Heterocyclic Chem. 10, ,725 (1973). It is also known that hexamine, acetic anhydride, and ammonium acetate may be advantageously reacted to form DAPT in acetic acid solution. By way of example only, 0.1 mole of DAPT in solution in acetic acid may readily be prepared by blending 0.1 mole hexamine, 0.081 mole ammonium acetate, and 0.39 mole H O into a slurry in a 50-ml flask held at 5 to 10C and adding 0.3 mole acetic anhydride to the stirred slurry over a 60 min. period while holding the reaction temperature at 5 to 10C.

It is desirable to be able to perform the nitrolysis of the DAPT using the acetic acid solution rather than pure DAPT. A preferred procedure for doing this in the rior art is indicated by the following example. A mixed acid is prepared from 1.0 mole of 99% HNO and 2.26 moles of 96% H The crude DAPT in solution in acetic acid prepared in accordance with the foregoing example is added dropwise to the acid mixture over a period of 50 min. with the reaction temperature held at 18 to 20C and the resultant reaction mixture aged for 20 min. at 20C. The reaction mixture is then quenched with 1,000 g of ice and the DADN precipitated with the addition of 1,500 ml of water. The filtered product consists of 0.095 mole DADN which is a 95% yield. The reaction is:

It isto be noted that in thisexample of the preparation of DADN, a substantial excess of HNO has been used, the reaction temperature has been kept at 20C or less, and the reaction timeis of the order of 70 minutes. When the concentration-of HNO is reduced to near-stoichiometric levels, the exotherm shown in FIG. 1 results. Although the nitrolysis of dry DAPT can be accomplished without a delayed exotherm, the yield is lower than when water and acetic acid are present.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 2 and Tables I through 111. These data are obtained using a DAPT feed solution prepared by adding 0.25 mole acetic anhydride to a slurry of 0.10 mole hexamine and 0.082 mole ammonium acetate in 0.139 mole (2.5 ml) water. The nitrolysis medium is made up of 0.33 mole HNO and 2.25 mole 98% H SO The DAPT feed solution is added to the nitrolysis medium over a 6-r'riiii. period with the temperature during and 35C with TABLE I DADN Spent Acids Time Yield Purity CH O HNO HNO (min) (moles) (moles) (moles) (moles) TABLE II DADN Spent Acids Time Yield Purity CH O HNO HNO, (min) (moles) (moles) (moles) (moles) TABLE Ill DADN Spent Acids Time Yield Purity C11 0 HNO HNO: (min) (moles) (moles) (moles) (moles) As is shown by FIG. 2 and Table l, increasing the reaction temperature to 30C without adding urea to the DAPT feed solution increases the rate of nitrolysis but at the expense of a significant decrease in the DADN yield. Without the presence of urea, a 90C exotherm also occurs at 19 minutes. The addition of either 0.05 mole (FIG. 2 and Table ll) or 0.1 mole (Table III) of urea effectively prevents the exotherm and permits rapid nitrolysis at 30C. A mild, easily controlled exotherm occurs when the urea is reduced to 0.02 mole. At 40C, using 0.05 mole of urea, no exotherm is observed and the reaction is complete within 10 min. after the addition of the DAPT solution is initiated. No reduction in yield occurs under the latter conditions.

The manner in which the urea acts to prevent the exotherm while allowing the higher DADN yield at the faster reaction rate permitted by the higher reaction temperatures is not completely understood. It appears, however, that the exotherrn is produced by the abrupt oxidation of a substantial amount of the formaldehyde generated as a byproduct during the nitrolysis. As is indicated in Tables II and III, the addition of urea prevents the destruction of formaldehyde and retards the reduction of nitric acid. When 0.1 mole of urea (Table III) is added to the DAPT feed solution the conversion of nitric to nitrous acid is completely inhibited, while with the addition of 0.05 mole of urea (Table II) this conversion is essentially complete in 60 min. The mode of action of urea in preventing the destruction of formaldehyde does not appear to be related to its ability to destroy nitrous acid, but it may be protecting the formaldehyde by forming an adduct, such as dimethylol urea.

What we claim is:

1. ln a method for preparing l,5-diacetyl-3,7-dinitrol,3,S,7-tetraazacyclooctane by the nitrolysis in mixed HNO H SO of diacetyl pentamethylenetetramine in solution in acetic acid, the improvement comprising the addition of urea to said acetic acid solution of diacetyl pentamethylenetetramine before said nitrolysis.

2. The method of claim 1 wherein the concentration of said HNO is slightly in excess of the stoichiometric amount required for said nitrolysis.

3. The method of claim 2 wherein said nitrolysis occurs at about 40C.

4. The method of claim 2 wherein said urea is added in an amount sufficient to react completely with the formaldehyde formed during said nitrolysis.

Claims (4)

1. IN AMETHOD FOR PREPARING 1,5-DIACETYL-3,7-DINITRO1,3,5,7-TETRAAZACYCLOOCTANE BY THE NITROLYSIS IN MIXED HNO3-H2SO4 OF DIACETYL PENTAMETHYLENETETRAMINE IN SOLUTION IN ACETIC ACID, THE IMPROVEMENT COMPRISING THE ADDITION OF UREA TO SAID ACETIC ACID SOLUTION OF DIACETYL PENTAMETHYLENETETRAMINE BEFORE SAID NITROLYSIS.

2. The method of claim 1 wherein The concentration of said HNO3 is slightly in excess of the stoichiometric amount required for said nitrolysis.

3. The method of claim 2 wherein said nitrolysis occurs at about 40*C.

4. The method of claim 2 wherein said urea is added in an amount sufficient to react completely with the formaldehyde formed during said nitrolysis.

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