A SIMPLE METHOD OF PREPARING TETRANITROMETHANE. 2099CCXX.-A Simple Method of Preparing Tetranit ro-waethane.By FREDERICK DANIEL CHATTAWAP.TETRANITROMETHANE can easily * be obtained without danger,and in almost theoretical amount, by allowing equal molecularamounts of nitric acid + and acetic anhydride to interact 1 at theordinary temperature for several days. Some heat is developed onmixing, and slight cooling is necessary during this part of theprocess, otherwise the action may become so vigorous that loss ofmaterial results, but, so far as the author’s experience goes, it neverbecomes explosive in character.IC The methods hitherto described for the preparation of tetraiiitromethane,namely, (1) nitrating nitroform (Schischkoff, Annalen, 1861,119, 247), (2) the actionof diacetylorthonitric acid on acetic anhydride (Pictet and Genequand, Bw., 1903,36, 2225), (3) distilling nitrobenzene with a large excess of a mixture of nitric andsulphuric acids containing sulphur trioxide (Claessen, D.R. -P. 184229), and (4)adding acetic anhydride to a mixture of nitrogen pentoxide and nitrogen peroxide(Schenck, D.R.-P. 211198, 211199), leave much to be desired in the way ofsimplicity.j- The use of more than the equiva ent amount of nitric acid is of noadvantage ; indeed, when an excess is added, the yield is seldom so good, as the acidordinarily employed always contains some small amount of water.$ On the 7th of July, since this paper was written, the Farbenfabriken vorm.F. Rayer & Go. published a method (D.R.-P.224057) of preparing tetranitromethnncexactly similar to that given above. As, however, this paper was read about a nionthearlier, namely, on June 16th (Proc., 1910, 26, 164), and as many details not to befound in the specification are given, it seems desirable that it should be publishedin full2100 CHATTAWAY: A SIMPLE METHOD OFThe action takes place almost quantitatively according to theequation :4CH3*C'O*O*C'O*CH3 + 4HN03 = C(NO,), + CO, + 7CH3*C02H.The tetranitromethane remains dissolved in the acetic acid, andseparates out as a heavy, oily layer on pouring the product intowater. Carbon dioxide is given off almost from the time of mixing,but the evolution is never rapid, and the tetranitromethane appearsonly to be formed gradually, as the yield is small unless themixture is kept for some days.When nitric acid attacks acetic anhydride, a mononitrederivativeis probably first produced, which is nitrated so much more readilythan the parent compound that action proceeds until the threehydrogen atoms of a methyl group have been replaced.Hydrolysisthen occurs, and the trinitroacetic acid formed slowly decomposesinto carbon dioxide and nitroform, which as soon as it is liberatedis converted by the remainder of the nitric acid into tetranitro-methane.The operations necessary in this method are so simple and so easilycarried out that the preparation is well adapted to take its placein any elementary course of practical organic chemistry to illustratethe ease with which aliphatic compounds can be nitrated, whilstthe materials employed are so cheap and the yield is so satisfactoryas to make tetranitromethane, which has hitherto been a somewhatunfamiliar substance, one of the most easily procurable of organiccompounds.Preparation of Tetranitromet hane.Thirty-one grams of nitric acid * (D*5 1-53) are placed in a 250 C.C.flask, and 50 grams of acetic anhydride are gradually added inquantities of about 2 C.C.at a time, the flask meanwhile beingcooled in water, as some little heat is developed. If the flask isnot cooled, action proceeds more and more vigorously as the tem-perature rises, and may, if unchecked, become violent. It isinadvisable therefore to allow the temperature to rise much aboveWhen all the anhydride has been added, the flask is coveredloosely by a watch-glass or inverted small beaker, and kept at theordinary temperature for about a week.As the reaction proceeds,carbon dioxide is continuously but very slowly evolved, and themixture, which at first is colourless, becomes brown, owing t o the* The anhydrous nitric acid required in the preparation is most ensily obtained byslowly distilling ordinary fuming nitric acid from its own bulk of concentratedsulphuric acid ; if ordinary concentrated nitric acid (D 1'41) is used, it is advisableto distil i t twice from sulphnric acid. It is not necessary, although advisable ifconvenient, to distil off the acid under diminished pressure.20-25OPREPARINU TETRANITROMETMAKG 2101formation, in small quantity, of oxides of nitrogen.After a week,the tetranitromethane which remains dissolved in the uetic acidmay be separated by pouring the mixture into about 150-200 C.C.of water. The bulk of the tetranitromethane subsides as a colour-less, heavy, oily layer, which can be removed by means of a separatingfunnel, whilst a small quantity still remaining dissolved in thedilute acetic acid may easily be separated by means of a current ofsteam. The tetranitromethane passes over with the first few C.C.of the distillate, and separates as a heavy globule.The tetranitromethane thus obtained may be freed from tracesof acid by washing with water, or even betker, although with slightloss, by distilling in a current of steam.* It is then separated anddried over fused calcium chloride.Tetranitromethane as thus prepared is a heavy, very fa.intlyyellow liquid.It can be distilled at 126O under the ordinarypressure, but the distillate is of a pale brown colour, due to oxidesof nitrogen formed by some slight decomposition which takes placeat this temperature, and still requires to be washed and dried toobtain it quite pure. If cooled a little below the ordinary tem-perature, it easily solidifies t o a mass of colourless crystals.The yield of tetranitromethane obtained is never quite thetheoretical one, although by careful working it cm be made toapproximate to it. The small loss cannot be entirely, or evenmainly, due to oxidation, as at no period of the action is there anyconsiderable liberation of nitrous fumes; it is probably caused bysome of the very heavy vapour being carried away in the escapingcarbon dioxide, and lost during the processes of separation.Using acid prepared as above, without removing the oxides ofnitrogen,? the yield is approximately 80 per cent.of the theoretical,about 18-20 grams of pure, dry tetranitromethane being obtainedfrom the weights of materials given.It is immaterial whether the acetic anhydride be added to thenitric acid, or the nitric acid to the anhydride, but the formerprocedure is preferable, as the evolution of heat then occurs mainlyduring the first few additions of anhydride, which can be addedmore rapidly afterwards.I n a set of experiments to ascertain the rate of formation, a* After distilling in a current of steam, the distillate containing the tetranitro-methane as well as the residue is always bright yellow in colour, owiiig to thepresence of dissolved nitroform, which is formed in small quantity when tetranitro-methane is allowed to come into contact with water or is heated with it.t There is no great advantage in freeing the anhydrous nitric acid from oxides ofnitrogen, as even if the acid is conipletely colourless on mixing aud the mixture iskept at 0" in a dry atmosphere it becomes coloured in a few days.The yield isslightly better if colourless anhydrous acid is employed, but the increased yielddoes not compensate for the extra labour involved in the preparatiou of the acid2102 CLAYTON : THE CONSTITUTION OF COUMARINIC ACID.number of similar mixtures of the above quantities were made, andthe amount of tetranitromethane formed was estimated afterdifferent intervals. After one day, 7.5 grams of tetranitromethanewere obtained; after t3wo days, 11.5 grams; after faur days, 14.5grams; after six days, 17 grams; and after eight days, 18.6 grams.After this, further keeping did not appreciably increase the yield.The process can be accelerated by heating the mixed liquidscautiously until the action becomes sufficiently rapid to cause thetemperature to rise even after removing the source of heat* andthen checking the action by cooling; when this has been doneseveral times, the liquid, which a t first cannot be heated with safetymuch above 30°, may be heated to 80-looo without any violentaction occurring, but on diluting the product the yield is not foundto be anyOhing like so good as when the mixture is simply allowedto remain at the ordinary temperature.OXFORD.UNIVERSITY CHEMICAL IAABORATORY