TETRANITROMETHANE KARL F. HAGEK Ordnance Research and Development Division Subofice (Rocket), Fort Bliss, Tex.
Tetranitromethane has found scientific interest for its configuration, its formation of colored complex compounds with double bonds, as an intermediate to prepare nitroform (trinitromethane), as a mild nitrating agent which is less corrosive than nitric acid, as a highly explosive mixture with hydrocarbons, as an oxygen carrier of high specific gravity, and for its ability to increase the cetane number of Diesel fuel. A method promising technical applicability for manufacture of TNhI is presented in detail. It was based on w-ork done by Orton and RIcKie and improved in a continuous glass laboratory apparatus. This apparatus was designed for a capacity of 10 kg. per day with a possible increase up to 14 kg. Acetylene is allowed to react with nitric acid, producing nitroform. The mixture of nitroform and nitric acid is converted to TNM by means of sulfuric acid at elevated temperature. This continuous process 5 ields about 90% TNJI, based on the nitric acid consumed, when a11 waste gases have been reclaimed carefully. By this method TN31 should become a low-cost intermediate.
T
E T R A S I T R O M E T H A N E ( T A W ) is generated during the manufacture of trinitrotoluene as a n undesired by-product which can be separated b y means of its higher vapor pressure (11). It has the following physical properties: melting point, 14.2"C.; boiling point, 126" C.; specific gra,vily,1.65. Many publications concerning the preparation of T X l I have appeared sirice the beginning of the century. According to them, i t can be prepared by the reaction of nitroform and nitric acid (go), iodopicrin and silver nitrite (281, aromatic hydrocarbons and nitric acid (11), acetic anhydride and nitrogen pentoxide (79), acetic anhydride and nitric acid (6-9, 42, 47,72, 99),acetylene and nitric acid (58,68, 63), dinitrobenzene niid nitric acid (5Sj, ethylbenzene and nitric acid ( S 6 ) ,and acetic anhydride and acetylnitrite ( 7 3 ) . Only t F o of these reactions, however, seem practical for laboratory preparation of TI"M--acetic anliydride with nitric acid (8, 9) and acetylene Kith nitric acid (55,68, 69), although both methods have serious disadvantages for industrial application. The first method, nitration of acetic anhydride, involves the reclaiming of large amounts of waste liquids containing niistures of organic and inorganic acids (acetic and nitric acids), in addition to otlirr organic reaction products and nitrogen oxides. The yield is too small for economical operation, considering reaction tiriic aiid size of apparatus. T h e nitration of acetylene, hon-ever, d o i ~ xnot present the same problem of reclaiming various Fvaste liquids but docs require handling of large quantities of waste gases, especially nitrogen oxides and carbon dioxide. For these reasons no method was industrially availahle for producing TSX until about 1943.
Extensive work has been done on other properties, such as electrical properties in liquid ammonia (18)and in liquid sulfur d'ioaide : (SR), elcctron diffraction (SS), ultraviolet spectra ( I S , 21, 41 j, dipole monieiit (46,9 6 ) , Raman spectra (40, 56, 56,58,63j, parachor (84j, entropy of evaporation ( 2 3 ) , heat of combustion arid formation (781, vapor pressure (59),optical constants (3). and s-ray (45). REACTIOM. The ease of reaction uf one nitro group of T S M led to numerous experiments. Reaction in alkaline medium produces nitroform chiefly, especially b y means of potassium ethylate, bisulfite, or hydroxide ( 4 , 87, 64, 81, 86). Other invwtigations have been carried out as f o l l o w : reaction with ammonia, sodium ethylate, and hydrazine derivatives (18, 48, 60, 6 4 ) , action as nitrating agent (20, 82-84), reaction with metals and reducing agents ( 4 , 10, S I , SS), properties and determination (43,44,Y5j, and reaction with proteins (16). A reaction of special interest is the formation of bright colored coniplex compounds with unsaturated compounds. This reaction cnn serve as a test for ethylene bonds (13, 14, 16, 25, 26, 2.9, 37, 38, 49,51, 70, 71,86,97). EXPLOSIVE PROPERTIES.T h a t mixtures of T S S I with hydrocarbons like toluene arc highly esplosive is of special interest 111 the military field. Extensive reports have been pub1:shed OII t h e following phases: preparation and explosive properties (87-92 j , luminous phenomena and flame spectra (SO-SS), detonation luminosities, shock waves, and dependency of brisance upon ignition strength (66, 66, 6 7 ) , explosive properties ( 7 7 ) , and explosion accident in a chemical institute (1). TOXICITY.Some fatal cases of poisoning by trinitrotoluerla have been esplained by the presence of T N M ( 1 7 ) . Other workers also investigated this compound (39, 67, 74). Recent iuvestigation resulted in the following survey: T N M is locslly irritating, seldom to the skin but mostly t o the mucous tissue oi' the eges, nose, and respiratory passage. T h e initial poisoning is evidenced by strong saliva secretion, later by inflammation of tht, upper respiratory passage; inhaling small quantities of T S M ix sufficient for this irritation. Acute poisoning was seldom found. T h e general tosicitg of TNhf is shown by chronic s y m p t o r i ~ . such as regular headaches, weariness, sleepiness, slowing of the, pulse, formation of hemoglobin, disturbance of internal respiratiori, a11 of which show up in acute cases. After prolonged erposure to T S X , tire central nervous system and heart are ai"-fected. T S l i was sometimes thought t o have been the cause ot anemia. Experieiice, however, gained during several months of laboratory production of T X Y by the process to be described improvcd the picture. The sensitivity of workers to T N M varied greatly. Sormally, contact with the skin did not cause iriflammation; the effect on eyes, nose, and respiratory passage, disappeared soon after exposure t o fresh air. Prolonged inhaling of the vapor, horvever, caused headache and difficult breathing S o serious poisoning showed up.
PROPERTIES
RECENT DEVELOPMEYT
( ~ O M P O S I T I O P i AKD PHYSICOCHEMICAL PROPERTIES. The fact that one of the four nitro groups reacts by preference was the basis of a theory of unsymmetrical configuration like trinitronietliyl nitrite, (K02)3C.0S0 (76, SI j, The investigation, however, by Lexis (46)and Mark (64)proved t h a t T K M has the symmetrical configuration C(SO*),.
During the last war, interest in TSM increased so t h a t a nex investigation of the possibility of developing production methody in Germany was undertaken. Reasons were the prospect of using TSM as a substitute for nitric acid in rockets and the observation t h a t a n addition of T N M t o Diesel fuel increased t h e cetane number. 2168
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1949
Tests showed t h a t the increase in Diesel cetane number varies with the original cetane number of the fuel. The following table shows that the higher the cetane number of the original fuel, the more this figure increased upon adding 5% T S l I : _ _ _Cetane ~ Pu-umber Without T S M
With Th-M
Increase in Cetane Kurnhei
47 105 274
1110
23 38
hddition of only 0.5 axd l.OY0 T S h i to thc Dieeel fuel i l l d its cetane uuniber 10 and 15 points, respectively. About 1043 the former I. G. Farbenindustrie a t FrankfurtHvcchst was commiesioned by thc government to manufacture a larger quantity of T X S I in a very short time pithout regard t o yield and cost, and to develop a method of technical applicability. These tasks were carried out and solved by Schultheiss, Schimmelechmidt, and Reuter. Their successful Fork, partly covered in P.B. reports (36)7 5 ) ,is eunimarized here. T h e method of Chattaway was chosen and improved t o maiiufacture t h e larger quantity of T S h l demanded. The waste liquids had not been reclaimed, and therefore about 10 tons of T X M could be produced in a few weeks. This method, reacting acetic anhydride with nitric acid, however, had not been used further because of its high cost disadvantage. The goal of low cost and large scale procedure, however, has been attained by further developmerit of the reaction used by Orton and SlcKie-that is, of acetylene with nitric acid. At the end of the Kar this process had reached the stage of large scale application in the laboratory, using a continuous glws apparatus; i t s output was about 10 kg. T S l I per day. ACETYLENE-NITRIC ACID PROCESS
In the first step acetylene is allowed to react n-ith highly concentrated nitric acid containing mercury nitrate. i l t first a solution of trinitroniethane in 85% nitric acid coritaining nitrogen dioxide results, while carbon dioxide and nitrogeii dioxide are generated as waste gases. I n the second step sulfuric acid is added t o the solution, and upon heating, the nitroform is converted t o TSM, which separates from the mixed acid because of its different specific gravity. T h e resulting T h X , containing some nitric acid and nitrogen dioxide, is purified largely by a sulfuric acid rinse. Its melting point of about 13.8" to 14.0' C. shows t h a t TSSI manufactured hy this process has a higher purity than the products described
2169
in the literature, with a melting point of about 13.0" C. The purest compound available by the new continuous method had a melting point of 14.2' C. After the separation of TXM, a mixed acid remains which contains sulfuric acid, nitric acid, mater, nitrogen dioxide, mercury sulfate, and some T N M . This mixture runs through a high concentration column, usual in nitric acid manufacturing, and is separated into highly concentrated nitric acid and dilute sulfuric acid. The former contains all the T X M and nitrogen dioxide, while mercury sulfate precipitates from the weak sulfuric acid and can be recovered and converted t o the nitrate t o be used again. T h e distillate, after addition of new nitric acid and mercury nitrate, is led back into the first step of the process. The diluted sulfuric acid is concentrated t o about 0,5.5% in a Pnuling column. The mercury sulfate separated in this process is alloyed t o go back into the process after suitable conversion. Highly concentrated sulfuric acid iu obtained from the Pauling column, and fresh acid is added t o compensate for the losses during circulation. This acid is then passed through the purification column and is then suitable for the second step of the process. The wmte gases, generated in the first step, consist m.tinly of carbon dioxide and nitrogen dioxide cnrrying some trace3 of acetylene, nitric acid, and T N M . These ga3es are allowed to run through a countcrflow spray column, in which they are viashed with hot, highly concentrated nitric acid coritainirig mercury nitrate to react with the traces of acetylene. Tile nitric acid used in this column is continuously put back iiito the first step of the process. The waste gases escaping from the hot spray column, which are free of acetylene, are allowed to ru11 through a fractionating column in which liquid nitrogen dioside is circulating and are condensed as far as possible by a deep cooling system. The nitrogen dioxide obtained is very pure and can be used as a raw material for concentrated nitric acid (reaction with mater and oxygen according to the common process). The unliquefied parts of the waste gases :Ire allowed to flow through another smaller spray column; here, however, they are rinsed with cold, highly concentrated nitric acid. The rest of the nitrogen dioxide is washed out in this column. Tile wash liquid, still containing nitrogen dioxide, is led back to the hot spray column where the nitrogen dioxide vaporizes again. T h e waste gases escaping from the cold spray column consist chiefly of carbon dioxide and a small amount of nitric acid, depending on the vapor pressure. This continuous process, therefore, is characterized by three closed circulations (Figure 1): 1. S i t r i c acid circulation: storage container, cold spray column, hot spray column, reaction with acetylene, boiling with sulfuric acid, separation and regeneration of mixed acid. 2. Sulfuric a c i d c i r c u l a t i o n : storage c o n t a i n e r , p u r i f i c a t i o n column, boiling with mixed acid, separation, regeneration of mixed acid, high concentration. 3. Nitrogen dioxide circulation: reaction vessel, hot spray column, cold spray column, condensation, conversion to nitric acid.
Figure 1.
Flow Sheet for Tetranitroniethane
The extraction of all TXM and the use of closed circulations in this process avoid any loss of TSM or of nitrogen dioxide and nitric acid. The necessity of reclaiming large amounts of nitrogen dioxide and of converting these gases into nitric acid, however, suggests that this TSJI production could be combined with nitric acid manufacture.
Vol. 41, No. 10
INDUSTRIAL AND ENGINEERING CHEMISTRY
2170
. .I b...
Figure 2.
Diagrarn of E:cluipriieiit for \Ial\ing 'Tetranitroillethatie
!
GLASS m P . m A m s
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Tile lahrat(Jr)' glass apparatus used cor1 parts (Figure 2 ) : (1) a circulating system, about G liters in c:ipacity and 2 yards in height, used as reaction vessel for the exothermic reaction of acetylene with nitric acid. By means of a cooling coil and a thermostat it is possible to keep the temperature constant, :in important fact in obtaining n smooth reaction; ( 2 ) tlirec nitrating towers connected in series, about 3-liter capacity, heated by a steam jacket; ( 3 ) a separator, capacity of about 2 liters; ( 4 ) a washing ton-er, 2 yards high, for purification of TS31; ( 5 ) a column to distill nitric acid; ( 6 ) an apparatus for nitrogen dioxide rectification arid concentration (correspoilding t o tlie above-mentioned hot arid cold spray columns); ( 7 ) apparatus suitable for measuring and conduit. To this apparatus 2.1 liters of nitric acid, cotisistiiig of q u a 1 parts of irePh 987, nitric acid and regeneratetl nitri containing 0.336 grain of mercury nitrate, wcre added. T h e cata1y.t solutioti was prepared by tlissolvirig 7 rurrcury in 98(r, nitric acid, adding 300 nil. of ivatcr, and making up to 1 liter v i t h nitric acid: 20 Inl. of thi5 catalyst d u t i o n \wro added to ever)- 10 liters of nitric acid fed. ;\cc~tylcric~wxs introciured a t tlie lowest point of this reaction 1)er hour: the acetylene had t o he introiiu Iiozzle a i d not through a gas distributor, sinrr. thc lut1r.r inc,tliotl Iiiis :in adverse effect on the product purit?. nrid ci .4s tlie follon-ing table shows, the flon- of 93.5 lite per hour was determined to be tlie optimum at the oi nitric acid (2.4 liters per liour) a s g i r m ahovc,: Acetylene €-Io\\., I.iters/Houi 80
8; 92 7 7
AIrltiiig
Point ,of T S l I , C. 13.0 13.: 13.t
.Icet,-lene Flo\v, Liter-. 110 I: r 95 100 1111
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I
120
I00
ac Lo J
i
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60
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40
20
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(91) Ibid., 37, 42-5 (19421. (92) I b i d . , 37, 62-4 (1942). (93) Btosick, -4. J., J . A m . Chem. Yoc., 61, 1127-30 (1939). (94) Teichfeld, .I., Z'rzemysl Chem.. 22, 500-8 (1938). (95) Trinh, X. Q . , C o m p t . rend., 218, 718-20 (1944). (96) Weissherger, .k., and Saengewald, R., Ber., 65B, 701-4 (IClL32). (97) Kerner, A . , Zbid., 42, 4324 (1909). (98) jviilataetter,and ~ ~B ~ ~37,, 1779 , ~ (1904). ~ (99) \Tyler, J., U. S. Patent 2,057,076 (July 6, 1936). R E C E I V E D.Jiine 2 2 , 1948.
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