TETRA-NITRO-ANILINE[1] (T. N. A.)
Tetra-nitro-aniline (briefly designated as T. N. A.) is the latest explosive to claim marked attention in the field of military explosives. The term T. N. A. is probably familiar to nearly all of the officers of the naval service, yet the scarcity of literature regarding this substance, the difficulty of finding what little there is, and the technical form in which it is written, all lead the writer to attempt to present clearly some of the more important properties and probable uses of this promising explosive.
Tetra-nitro-aniline is the strongest solid explosive compound known and, as such, must claim the greatest attention and most careful consideration from a service which has so much at stake on the quality and strength of its explosives.
It is a tetra-nitro derivative of aniline, which in turn is a simple derivative of benzene, as shown by the graphic formulas below.
[IMAGE: BENZENE (C6H6). Anilene (C6H5NH2). Tetra-nitro-aniine (C6H NH2 (NO2)4).]
Tetra-nitro-aniline is prepared by the action of a mixture of nitric and sulphuric acids upon meta-nitro-aniline,[2] the graphical formula of which is here illustrated. Ortho-nitro-aniline and para-nitro-aniline, although having the same empirical formula as meta-nitro-aniline (C6H4NH2NO2), do not yield tetra-nitro- aniline when subjected to this same treatment.
[IMAGE: Meta-nitro-aniline (C6H4NH2NO2).
Meta-nitro-aniline Tetra-nitro-aniline is formed in yellow crystals, the exact size and hue of which varies with the method used in the preparation. Its melting point is 216-217° C., at which temperature it melts with decomposition.[3] If heated quickly, it will decompose at a lower temperature than that given above, but its decomposition due to heat alone is never explosive. Its ignition point is 220° C., which compares very favorably with that of tetryl, which is 186° C. under similar conditions. Its specific gravity is 1.867.
It is practically insoluble in water at ordinary temperatures; is slightly soluble in benzene, chloroform, or ligroin; is more soluble in acetic acid, nitrobenzene, acetone, etc.
Its deficiency in oxygen is less than that of any previously known aromatic nitro explosive, as is shown by the following table. Deficiency of oxygen is figured under the assumption that no deficiency would exist if the explosive contained sufficient oxygen to afford complete combustion.
| %N. | Grams of oxygen deficiency per 100 grams explosive for complete combustion |
Dinitrotoluene ...................................... | ..... 15.4 | 114 |
Dinitrobenzene ...................................... | ..... 16.7 | 95 |
Trinitrotoluene ...................................... | ..... 18.5 | 74 |
Trinitroanisol ...................................... | ..... 17.3 | 63 |
Hexanitrodiphenylamine ...................................... | ..... 22.3 | 53 |
Tetryl ...................................... | ..... 24.4 | 47 |
Picric acid ...................................... | ..... 18.3 | 45 |
Tetranitroaniline ...................................... | ..... 25.6 | 32 |
This table also shows that the percentage of nitrogen in tetra- nitro-aniline is greater than in any other of the explosives enumerated. Since oxygen, in pure nitro explosives, is present almost entirely in the nitro groups, a high nitrogen content will necessarily indicate a high oxygen content. For obvious reasons, a high oxygen content will indicate a low oxygen deficiency. The reverse of this reasoning does not always hold true, since there are cases (picric acid being a notable one) in which the oxygen deficiency is small while the nitrogen content is not large. In the case of picric acid, this is due to the fact that it has a molecule of oxygen in the OH group, thus increasing its oxygen content without correspondingly increasing its nitrogen content.
Tetra-nitro-aniline is the first nitro explosive in which four nitro groups have been attached directly to the carbon ring (as shown in the graphical formula), all efforts having failed heretofore to accomplish this result. In tetryl (tetra-nitro-methyl- aniline) there are four nitro groups, but one of them is in the side chain,[4] leaving only three directly attached to the ring. Due to this construction, tetryl has a smaller percentage of nitrogen than tetra-nitro-aniline.
Tetra-nitro-aniline is a neutral compound,[5] and would therefore not be expected to show any action on metals. Comparative tests have been carried out by placing 0.2 gm. of tetra-nitro-aniline, tetryl, and picric acid on sheets of various metals in the open air. Each of the compounds was moistened with water once every 24 hours for 14 days. A blank experiment was simultaneously carried out in which the metal alone was moistened with water. The results are given in the following table:[6]
| Steel | Iron | Tin | Copper | Brass | Lead | Aluminum | Zinc |
Water alone | Dark brown | Brown | Unchanged | Less than Tetryl | Unchanged | White stain | Unchanged | Very light brown |
Tetryl | Brown | Brown | Unchanged | Slight darkening | Unchanged | Unchanged | Unchanged | Unchanged |
T.N.A. | Dark brown | Dark brown | Slight grey color | Slight darkening | Unchanged | Unchanged | Unchanged | Very light brown |
Picric acid | Dark brown | Black | Metal attacked | Yellowish brown | Yellowish brown | Dark brown | Brown ring | Dark brown |
The hygroscopicity of tetra-nitro-aniline is very small, so small that it may be considered as practically non-hygroscopic. The manufacturers state that when exposed to an atmosphere of 85 per cent saturation, at ordinary temperature, for one week, the material showed an increase in weight of only 0.12 per cent. Recrystallized tetra-nitro-aniline, under the same conditions, showed an increase of only 0.023 per cent in weight.
The stability of the pure compound in excellent.[7] Het tests have given the following results. After being stored for three months at atmospheric temperature, a heat test of 50 minutes at 65.5° C. was obtained. A small sample which had been stored for three months at atmospheric temperature was heated to 100° C., held there for 15 minutes, and then given the regular KI test. This sample still gave a test of 50 minutes at 65.5° C.[8]
Dr. Flurscheim states in his patent[9] “that tetra-nitro-aniline" is characterized by the remarkable facility with which its nitro group in the 3 position may be replaced by other groups.” Up to the present time investigations of this particular feature have not progressed sufficiently far so that a definite opinion may be expressed as to whether or not this remarkable facility of replacement will prove a deterrent to the use of this explosive for military purposes.
As previously stated, tetra-nitro-aniline is the strongest known solid explosive compound. The following comparative brisance[10] or force tests were obtained by using 10 gm. of the explosive designated. A No. 8 fulminate detonator was used.[11]
Lead Block (International Standard) | Trinitrotoluene | Picric acid | Tetryl | Gun cotton | Tetra-nitro- aniline | Standard dynamite (75% N. G. 25% Guhr) |
Cc net expansion per 10 gm | 254 | 297 | 375 | 290 | 430 | 300 |
Ballistic pendulum ft. lbs. per 10 gm | 719 | 808 | 951 | 923 | 1056 | 900 |
These tests may be supplemented by the comparative brisance tests of tetra-nitro-aniline and trinitrotoluene given below.[12]
Lead Block | Trinitrotoluene | Tetra-nitro-aniline |
(International Standard) | (average) | (average)' |
Cc net expansion per 10 gms | 216 | 315 |
Although, at first glance, it would seem that there is a very great difference between the values of the brisance of tetra-nitro-aniline as given in these two tables, this difference is very much diminished by comparing the figures for tetra-nitro-aniline and trinitrotoluene in each case. In the first case that we have the brisance of tetra-nitro-aniline is 1.693 times as great as that of trinitrotoluene, while in the second case it is 1.458 times as great. It is noted that this discrepancy is not such that it should be classed as unreasonable.
It should be remembered that the lead block test is a comparative test only, and that the actual enlargement of cavity obtained in one series of tests, for any given explosive, can hardly be expected to agree with the results for the same explosive obtained in another series of tests. The ratio existing between the brisance of two explosives in one test is, however, comparable to the ratio existing between the brisance of the same two explosives in another test.
From a consideration of the above, it seems safe to assume that the brisance of tetra-nitro-aniline is about 1.5 times that of trinitrotoluene.
In order that the reader may not get a false impression of the value of such data as that given above, the following quotations from eminent authorities are given: Brunswig[13] says: “ It is yet an open question how far these and other similar empirical methods for measuring the relative brisance of various explosives are to be relied upon.” Gutmann [14] says: “ Although this apparatus[15]and Guttmann’s give very valuable assistance in judging explosives, the reader is warned against relying upon them entirely for drawing absolute conclusions as to the suitability of various explosives for any specific purpose.”
The sensitiveness of tetra-nitro-aniline to shock has been established by comparative drop tests. The results obtained in some of these tests are given below. The fall in each case is for a two kilogram hammer.
Table I[16]
| 1st Series | 2nd Series | 3rd Series | Average |
Tetryl | 25 cm. | 50 cm. | 35 cm. | 36.66 |
Tetra-nitro-aniline | 45 cm. | 60 cm. | 50 cm. | 51.66 |
Picric acid |
| 35 cm. |
| 35 |
Table II[17]
Tetra-nitro-aniline | 7 inches (17.78 cm.) |
Trinitrotoluene | 11 inches (27.94 cm.) |
Table III[18]
Picric acid | 35-95 cm. |
Tetryl | 40-65 cm. |
Trinitrotoluene | 57-9 cm. |
These three tables were, of course, obtained under different conditions and could not be expected to agree in detail. They furnish a means of obtaining a fair comparison of the sensitiveness of tetra-nitro-aniline with that of other explosives which are now in common use. From a study of them, the writer draws the conclusion that the sensitiveness of tetra-nitro-aniline toward shock is of a degree about similar to that of tetryl; that it is somewhat greater than that of trinitrotoluene; and that is somewhat less than that of picric acid.
Since tetryl, picric acid and trinitrotoluene have all been accepted as military explosives for some time, it would seem that tetra-nitro-aniline is sufficiently insensitive to shock to meet the ordinary military requirements. Its sensitiveness may be greatly reduced by using it in combination with paraffin, as will be noted later.
Up to this time it has not been possible to detonate tetra-nitro- aniline by friction.
Careful tests (made for the purpose of establishing the suitability of tetra-nitro-aniline for a booster for military purposes) have shown that it is very sensitive toward fulminate detonators.
Its degree of sensitiveness toward such detonators is about the same as that of tetryl, which is known to make a very good booster.
The brisance and the sensitiveness to shock of certain mixtures of tetra-nitro-aniline with other substances are given below.[19]
Composition. | Lead block (International Standard) CC. net expansion per 10 gm. | Drop test, inches 2 kilogram hammer |
25% T. N. A | 221 |
|
75% D. N. B. | ||
33% T. N. A | 240 |
|
67% D. N. B. | ||
40% T. N. A | 255 |
|
60% D. N. B. | ||
50% T. N. A | 277 |
|
50% D. N. B. | ||
95% T. N. A | 290 | No detonation in 5 drops. Limit 28 inches. |
5% Paraffin | ||
90% T. N. A | 215 |
|
10% Paraffin | ||
T. N. A. (pure) | 315 | 7 |
T. N. T. (pure) | 216 | 11 |
T. N. A., tetra-nitro-aniline; T. N. T., trinitrotoluene; D. N. B., dinitrobenzene. The mixtures of tetra-nitro-aniline and dinitrobenzene were prepared by stirring the T. N. A. into the molten D. N. B. The paraffin compositions were obtained by coating T. N. A. with paraffin dissolved in varnolene, with the subsequent evaporation of the solvent.
Military Applications[20]
It is the purpose of the writer to merely mention some of the various military uses for which this explosive may prove useful. Only by experiments, carried out with the material itself and under as nearly service conditions as possible, can it be definitely determined whether or not anything could be gained by substituting tetra-nitro-aniline for the explosives now in use.
Bursting Charge for Projectiles.—The writer considers that pure tetra-nitro-aniline is too sensitive to shock to warrant it being used as a shell filler. By using a coating of paraffin (95 per cent T. N. A., 5 per cent paraffin) its sensitiveness to shock is much reduced and it still retains a brisance considerably greater than that of trinitrotoluene, picric acid, or ammonium picrate. It is true that it cannot be fused and then poured into the cavity of the projectile (there to be allowed to cool and solidify), but trinitrotoluene is about the only high explosive, suitable for military purposes, with which this can be safely done. It may also be stated that fused trinitrotoluene is very nearly as sensitive to shock as is pure tetra-nitro-aniline.
Mine and Torpedo Charges.—Tetra-nitro-aniline should be particularly suited for use as the bursting charge in a mine or a torpedo. In this class of military work the explosive is not subjected to the great shocks received by the bursting charge of a projectile. It would seem that its great brisance, coupled with its inertness toward metals, reasonable insensitiveness toward shock, and ease of detonation, would all be favorable for this class of work.
Aeroplane Bombs.—The properties of tetra-nitro-aniline would seem to indicate that it would be very suitable for aeroplane bombs. The use of such bombs, having a total weight of 22 pounds each and carrying 12 pounds of tetra-nitro-aniline per bomb, has recently been mentioned in the European press.[21]
Fuses and Detonators.—The use of tetra-nitro-aniline for the charges of fuses and detonators would do away with the necessity of using a priming charge, of either tetryl or picric acid, to inaugurate the detonation of main charge of the fuse or detonator, as it is necessary to do in many fuses at the present time.
In conclusion, it may be said that tetra-nitro-aniline may prove itself useful in many other ways than those mentioned above. Considering all things, it would seem that it is a sufficiently promising explosive to warrant considerable experimentation to determine in just what way it may be of use to the naval service.
[1] Since this article was written, the Bureau of Ordnance has concluded a series of experiments with tetra-nitro-aniline to determine its suitability for adoption as a service explosive. T. N. A. in the unmodified state has been found to have a serious tendency to decompose when in contact with moisture, even at ordinary temperatures. Although this disadvantage may be overcome to some extent by water-proofing, the explosive force of the material has not been found superior to T. N. T., the suitability of which as a military explosive is well known.
[2] U. S. Patent No. 1045011, dated Nov. 19, 1912. Bernhard Jacques Flurscheim, Ph. D., inventor.
[3] This melting point is for an elevation of temperature of 5°C. per minute, for the pure product. The melting point as given in Dr. Flurscheim’s patents is 210-212°C.
[4] The placing of one of the nitro groups in the side chain in the case of tetryl is illustrated by the use of t he graphical formulas for the side chains in the I position of tetryl and of tetra-nitro-aniline as shown below. [IMAGE: Tetry. Tetra-nitro-aniline.
[5] Z. ges. Schiess-Sprengstoffw 8, 185-8. Chemical Abstracts 7 (1913). 2685
[6] From literature of the Verona Chemical Company. The chemical action of picric acid on some metals is well known. The table shows what may be expected from picric acid under conditions which are favorable for such action. It would have been most interesting if T. N. T. had been included in this table in order that its well-known inertness might have been used as a criterion.
[7] Les Poudres et Explosives (L. Vennuir et G. Chesnau, 1914), says of this explosive: "C'est un explosif trés stable qui parait trés intéressant."
The first lots of this material tested in this country (by recognized government authorities) gave very unsatisfactory results in the stability tests. T. N. A. received at a later date has given results fully confirming the statement made here.
[8] From tests made at Picatinny Arsenal. Published by permission.
[9] U. S. Patent No. 104,5011, page 2, lines 83-85.
[10] We speak of the brisance of an explosive reaction when the surrounding inert substances, which a relatively slowly increasing pressure (of explosion) would have moved forward as a whole, or in large pieces, and in the prescribed direction, lose their form entirely and are blown to fragments . . . . The range of the effects of brisance is supposed to be largely confined to the immediate neighborhood of the explosion and it therefore exerts its greatest influence upon the medium with which it is in direct contact.” Explosives, Brunswig (Monroe and Kibler), page 111.
[11] Z. ges. Schiess-Sprengstoff 8, 185-8.
[12] From tests made at Picatinny Arsenal.
[13]Explosives, Brunswig (Monroe and Kibler), page 116.
[14] The Manufacture of Explosives, Guttmann, Vol. II, page 368.
[15] Referring to the Trauzl Lead Bock Test.
[16] From the Verona Chemical Co., North Newark, N. J.
[17] From tests made at Picatinny Arsenal.
[18] Explosives, Brunswig (Monroe and Kibler), page 27. Results obtained under different experimental conditions, such as moist or dry, in powdered form or pressed, etc.
[19] From tests made at Picatinny Arsenal.
[20] For inventor’s claims and formulas, see U. S. Patent No. 1045012, dated Nov. 19, 1912.
[21] The London Illustrated News, Dec. 26, 1914.