248
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y A C T I O N O F SODIUM. C A R B O N A T E O N T E T R Y L
Having proved t h a t m-nitro-tetryl may be satisfactorily removed from tetryl by means of sodium carbonate, it appeared advisable to determine the effect of this alkali on tetryl itself. After a thorough laboratory investigation it was shown conclusively t h a t sodium picrate was the sole reaction product when sodium carbonate acted on tetryl. During the reaction the whole nitromethylamine radical is replaced by the ONa group, nitrous acid being evolved. As might be expected, this reaction takes place to a greater extent on boiling tetryl with caustic alkalies, sodium or potassium picrate being formed with the liberation of methylamine. With sodium carbonate solutions the rate of hydrolysis of tetryl is relatively slow. However, sufficient sodium picrate was prepared in this manner t o carefully study its properties and prove its identity. The picric acid after acidification and recrystallization melted a t 1 2 2 . 5' C. and showed a molecular weight of 1 2 9 , the theory for picric acid. D E T E C T I O N OF S O D I U M P I C R A T E I N T E T R Y L
Since sodium picrate is very soluble in water, i t appears t h a t any of this compound formed would be easily removed by the subsequent water washes after neutralization. To settle this point, a sensitive test for the determination of small quantit:es of sodium picrate in tetryl was developed and i t was found t h a t none:of this product could be detected in our finished tetryl nor in our second wash water after the alkali boil. This indicated t h a t any sodium picrate formed was removed by the first water wash. E F F E C T OF SODIUM P I C R A T E O N S T A B I L I T Y O F T E T R Y L
Since sodium picrate is a relatively stable explosive, i t is difficult t o conceive of its lowering the stability of tetryl and its complete removal seems of little importance. Varying mixtures of tetryl and sodium picrate have been carefully made up and the stability and sensitiveness determined. Even large quantities of sodium picrate were found t o affect the tetryl but slightly. The addition of I t o I O per cent sodium picrate t o tetryl has no effect on the drop test, the mixture giving a detonation in each case with a 4 oz. weight a t 14 in., the drop test for pure tetryl. Pure sodium picrate cannot be detonated with an 8 oz. weight a t 24 in. The addition of I O per cent of picrate to tetryl was found t o lower the melting point by only 0.6' C., while the presence of smaller amounts could hardly be detected from t h c drop in melting point, indicating t h a t the stability of the material was not impaired. ILloreover, the stability of mixtures of sodium picrate and tetryl gave approximately the same gas evolution test as pure tetryl. The decomposition in vacuo of a mixture containing I O per cent sodium picrate was less than t h a t for ordinary crude tetryl. CONCLUSIONS
It is hoped t h a t this discussion of the stability of tetryl has brought out the following points, most of
Vol.
12,
No. 3
which have been under more or less discussion since the outbreak of the war. I-As a n indication of t h e stability of tetryl, ordinary qualitative heat tests are of little value. 11-The Obermuller or gas evolution test in vacuo shows the true stability of tetryl t o be indicated by the melting point, t o which it is directly proportional. 111-The instability of ordinary tetryl is due t o a large extent t o the presence of tetranitrophenylmethylnitramine (m-nitro-tetryl). This impurity is formed by nitration of the monomethylaniline present in the dimethylaniline used. IV-The nitration of pure dimethylaniline under ordinary conditions gives no m-nitro-tetryl. V-m-Nitro-tetryl is unstable and its presence greatly decreases the stability of tetryl. VI-m-Nitro-tetryl may be removed from tetryl by boiling with water, by which i t is converted into soluble trinitromethylnitramidophenol, and more readily by a sodium carbonate solution, whereby the soluble sodium salt of styphnic acid (trinitroresorcinol) is formed. VII-Tetryl is slightly hydrolyzed by a dilute sodium carbonate solution t o sodium picrate. VIII-Sodium picrate is insensitive and stable and its presence does not lower the stability of tetryl t o any appreciable degree. IX-Sodium carbonate is a very satisfactory stabilizing agent for tetryl. It removes acidity and such impurities as m-nitro-tetryl. Any sodium picrate formed and not removed by washing is non-injurious t o the tetryl. THE MANUFACTURE OF TRINITROXYLENE FOR USE AS A SUBSTITUTE FOR TNT IN BURSTING CHARGES FOR HIGH EXPLOSIVE SHELL' By John Marshall EASTSRN LABORATORY, E. I . DU FONT DE
NEMOURS & CO.,
CHESTER,
PA.
From its physical properties trinitroxylene, or T N X , would appear t o be most unfavorable for use as the bursting charge for high explosive shell. The melting point of the predominating isomer is very high, 182' C., making i t impossible t o load by direct casting. Moreover, this compound is almost insoluble in other lower melting nitro bodies a t low temperatures such as are preferable for casting, seemingly precluding the casting of such a mixture. It has not more t h a n 80 per cent the explosive strength of T N T , and it is much less sensitive t o detonation. The acute situation which developed in the T N T supply in the summer of 1917, however, made i t necessary t o consider the use even of materials which appeared unfavorable. About this time i t was suggested by a member of the du Pont Company's chemical department t h a t T N X might be used to advantage as a partial substitute for T N T b y casting a mixture of T N X suspended in molten T N T . Experiments were immediately started a t the Eastern Laboratory for the preparation of a few pounds of T N X for experimental purposes. The nitration process 1 Presented a t the 58th &Meetingo f the American Chemical Society, Philadelphia, Pa., September 2 to 6, 1919.
Mar., 1920
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
itself offered many difficulties, b u t a few pounds were prepared, and a study made of t h e use of t h e compound in a shell bursting charge. Rather t o t h e surprise of those concerned, T N X proved t o be almost ideal for the purpose. When 30 t o 50 parts of T N X were suspended in 70 t o 50 parts of TNT a t 100' C. a sufficiently fluid mass was obtained t o admit of direct casting without the use of any extruding mechanism. The castings when cooled proved t o be completely amorphous, resembling paraffin in texture. They showed no segregation of either component of t h e charge, were remarkably free from air holes, showed high and uniform densities, were non-hygroscopic, and showed no tendency t o become oily or leaky, even on storage a t elevated temperatures. They could be completely detonated with smaller primers of tetryl than could castings of T N T alone. They could be drilled with ease for booster cavities, and in fragmentation tests showed results approaching those obtained with refined T N T . Added t o these advantages, i t was found t h a t more satisfactory castings could be obtained with a mixture of crude T N X and crude T N T t h a n with refined materials, which in itself would produce a considerable saving in both operating and material costs. Since the potential supply of xylene in the country was a t least 20 per cent of the supply of toluene, t h e development of a manufacturing process for T N X was immediately advisable and t h e study was at once undertaken. The development of t h e manuf acturing process from t h e laboratory scale t o t h e design, construction, and operation of a large scale plant occupied more than a year and a half, and production was proceeding rapidly a t t h e time of t h e signing of the armistice. The details of t h e work done during this period are manifestly beyond the scope of this paper. I t will be attempted, therefore, only to outline t h e difficulties encountered and t h e methods used in surmounting them. Ordinary commercial xylene, boiling within a range of 4 ' t o 5' C., contains t h e three possible isomers, the amounts present varying with t h e source of t h e xylene. I n general, it appears t h a t such material contains 60 t o 7 0 per cent m-xylene, t h e remainder being made up of 0- and p-xylene with some ethylbenzene and usually small percentages of paraffins and naphthenes. All of t h e xylene isomers give trinitro derivatives, though it would naturally be expected t h a t the oand $-xylenes would nitrate t o t h a t stage with difficulty. The high melting trinitro-m-xylene is difficultly soluble in the other isomers, so in t h e nitration of the mixture we should expect t o obtain a final product containing crystals of trinitro-m-xylene together with lesser amounts of an oil of lower nitrogen content, composed of the various di- and tri-nitrated isomers. I n t h e preliminary experiments, using commercial xylene, this condition was found t o hold. The efficient production of a non-homogeneous material of this type appeared impractical for t h e following reasons: I-The control of t h e finafstage of the nitration was
249
difficult owing t o t h e viscous nature of t h e charge in t h e nitrator. 2-It was necessary t o separate the crystalline product from the spent acid by filtration, followed by a secondary separation of the oily products not held by t h e filter. 3-The yield of desirable product was greatly lowered owing t o t h e loss of material in the form of oil, which obviously could not be used in shell loading. &--When washing the oil-contaminated crystals with boiling water in t h e neutralizing process, there was a tendency for the crystals t o cement together in small lumps, which included small quantities of acid from the wash waters. This acid could be finally removed only with great difficulty. The first requirement was therefore t h e production of a homogeneous material, and for this three methods of procedure were open: first, by using pure m-xylene; second, by increasing the severity of nitrating conditions t o the point of partial oxidation of t h e 0 - and +isomers and more complete nitration of t h e unoxidized residue; and third, b y controlling t h e composition of the raw material so as t o partially exclude the undesirable isomers. T H E N I T R A T I O N O F P U R E "-XYLENE
Pure m-xylene is easily prepared by the partial sulfonation of t h e mixed xylenes, followed by steam distillation of t h e sulfonated product for the regeneration of t h e m-xylene. m-Xylene thus prepared, having a boiling range of 0.4' C., was subjected t o a three-stage nitration and gave an almost pure trinitroxylene melting above I 7 5 ' C. It was found, however, t h a t t h e solid product was precipitated in the final nitration in a very finely divided crystalline form t h a t made t h e charge extremely viscous. This could not be overcome except by using prohibitive amounts of nitrating acid t o obtain the necessary fluidity. Also, as before mentioned, i t was found t h a t pure T N X of this character could not be used in castings t o as good advantage as the crude material, and the use of pure m-xylene was therefore abandoned. NITRATION O F T H E MIXED ISOMERS
The study of the nitration of t h e mixed isomers was continued while the foregoing work was in progress, and the following methods developed: The xylene was nitrated in three stages, separation of spent acid being made after each stage. The mononitration was carried out by adding t o the xylene a t 5 5' t o 60' C. 2 l / 2 parts of a nitrating acid containing 38 per cent "03, 5 2 per cent HzS04, and I O per cent water, followed by a brief period of agitation. The bi-nitration was made by adding the same ratio of the same mixed acid to t h e mono-nitrated oil a t 80' C. The tri-nitration was carried out by adding the acid bi-nitrated oil t o 4 parts (based on xylene) of a mixed acid containing z j per cent H N 0 3 and 7 5 per cent HzS04 a t go' C., followed by a continued agitation a t g s ' t o 1 0 j O C. This method was used both on the laboratory and the semi-works scale with good results. It gave a homogeneous product, and
250
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
one of sufficiently large crystal structure for convenient filtration and handling. With the xylene in use a t t h e time, however, satisfactory neutralization of the T N X could not be obtained owing t o t h e previously mentioned cementing together of the crystals on t h e treatment with hot water and consequent inclusion of acid. This was doubtless due t o the high content of isomeric compounds. STUDY O F R A W M A T E R I A L S
I n order t o overcome this difficulty a study $as made of the rectification of solvent naphtha, and of t h e results obtained b y nitration of various ranges of the xylene fraction. Rectifications for this purpose were first carried out a t the Deepwater Point Works of the du Pont Company, and later a t the Frankford plant of the Barrett Company. The Barrett Company cobperated in all the later portions of this study, and the successful outcome of the work was in large measure due t o their assistance in settling this very vital phase of the problem. A comparison of the physical properties of xylenes from different portions of the range with the results obtained on nitration brought out the following points: I-The boiling range and specific gravity of t h e xylene do not offer a satisfactory control of t h e charact e r of the raw material, and the final value of t h e xylene for use in the manufacture of T N X can be established with satisfaction only by a nitration test carried out in a manner comparable with the plant method. 2-In general, T N X of the most satisfactory freezing point and in the best yields, is obtained from a xylene meeting the following boiling point specifications : Range, 1st drop to flask dry 3’ C. First drop, between 137.2O and 139.2’ C. Flask dry, between 138 5O and 140.5’ C.
3-Xylenes taken from the p-xylene range will nitrate satisfactorily and give good freezing points, b u t yields will be low. +--Xylenes taken from the o-range, i. e., high in @-xylene, will give difficulty in nitration, with low yield and freezing point of product. 5-TNX samples having freezing points of 161.5 C. or better showed no tendency t o agglomeration of .crystals when treated with hot water. They could be neutralized without difficulty. I n addition t o t h e above points, i t was found t h a t t h e value of a xylene for the preparation of T N X depended in large measure upon the source of t h e xylene; for example, the coke-oven by-product xylene always gave a more satisfactory T N X t h a n xylene with a n identical boiling range from other sources, such as water-gas t a r , or drip oil. No satisfactory explanation has been found for this. Water-gas xylene and drip-oil xylene as a rule contain relatively high percentages of hydrocarbons (members of the paraffin a n d naphthene series, and usually designated“paraffins” for convenience) which resist sulfonation and nitration, and for a time these compounds were considered -responsible. However, on isolation of these com-
Vol.
12,
NO. 3
pounds from water-gas xylene b y sulfonation of t h e xylenes and separation of t h e unsulfonated residue, followed by nitration of mixtures of this material and coke-oven xylene, there was no effect shown on the freezing point of the resulting T N X , and no greater effect on yield was shown t h a n could be accounted for by the actual “paraffins” added. On t h e other hand, when water-gas xylenes of similar properties, but with varying “parafin” contents, were nitrated, there was a reduction in freezing point of T N X approximately proportional t o the “paraffin” content, and a reduction in yield greater t h a n could be explained on the ground of “paraffins” alone. These results apparently indicate t h a t “paraffins” are not responsible for the difference between cokeoven and water-gas xylene, and possibly indicate the presence of unidentified compounds in the watergas xylenes other t h a n “paraffins,” but appearing coincidentally with them. LARGE SCALE
OPERATIONS
As soon as progress had been made on the subject of specifications for t h e raw material, active operation was started in a semi-works plant constructed for the purpose, and i t was here demonstrated t h a t xylene of t h e type specified gave satisfaction on the larger scale operation. Final d a t a were also obtained in this work for the design of a large scale plant, and construction of this plant, with a potential capacity of 3,000,000 lbs. T N X per month, was a t once started. The first unit was completed August I , 1918, and operations were started a t once, and a t t h e time of the signing of the armistice two of the five units were in full production of a satisfactory product, with the other units nearing completion or in partial operation. NOTES ON DOUBLE POLARIZATION METHODS FOR THE DETERMINATION OF SUCROSE AND A SUGGESTED NEW METHOD By Geo. W. Rolfe and L. F. Hoyt CAMBRIDGE, MASSACHUSETTS Received August 30, 1919
The well-known principles and methods of double polarization applied in t h e analysis of commercial sugar products need not be detailed here. The methods in use depend on the assumption t h a t t h e change in optical rotation of a sugar solution, which is the measure of the sucrose, is the result of t h e inversion of the sucrose only. One of t h e chief objections t o the original method of Clerget and Herafeld arises from the fact t h a t the direct reading is made on a practically neutral solution and t h e invert reading on a strongly acidulated one. Much work has been done in developing improved methods of procedure t o prevent or a t least mitigate the errors which are introduced under these conditions, especially in sugar estimations of low-grade products where the change in acidity causes changes in the optical rotation of the sugars, other t h a n sucrose, which are present. Those who are interested in these investigations may be I
