1366 LUMSDEN CRITERIA OF THE DEGREE OF CXXT'III .- Criteria of the Degree Commercial Toluene. By JOHN SCOTT LUMSDEN. THE following investigation was undertaken o j Purity of for the Explosives Department of the Ministry of Munitions for the purpose of find-ing some easily applied method for estimating the degree of purity of commercial toluene and is published with the permission of the Department. Commercial toluene contains varying amounts of a liquid which cannot be nitrated and has distilled along with the toluene during rectification. This liquid has not been isolated but in the follow-ing tests the assumption is made that it may be represented by a paraffi mixture which boils close to the boiling point of toluene. By fractionation of petrol a quantity of such a liquid was obtained boiling at 108-112°.Estimation of Toluene b y Specific Gravity.-Pure toluene a t 1 5 O wa,s found to have D 0.8712; the p a r a f i mixture had D 0.743. Since there is no change in volume on mixing toluene and paraffin, a graph was prepared to show the density of mixtures. From this graph it mas found that the presence of 1 per cent. of paraffin produced a lowering of the density of 0.0013. Whilst such a graph may not be depended on to give the accurat PURITY OF COMMERCIAL TOLUENE. 1367 percentage of impurity present because the toluene may be moist and the impurity may not be like that assumed it is certainly useful in indicating poor samples. For example of two samples of commercial toluene (a) had D 0.872 and ( b ) 0'8613. Both were fractionated with the following results Sample (a) showed a trace of moisture then boiled steadily a t l l O o .All fractions right to the end had D 0.8716. This was therefore a very good sample of toluene. Sample ( b ) showed a little moisture and then boiled half a degree below alowly rising to half a degree above l l O o . The fractions had D 0.8623 0-8621 0.8622 0.8619 0.8612 0.8586 and 0.8570. The original low density and the decreasing density of the fractions pointed to a considerable admixture of paraffins; from the graph the indication is 7.7 per cent. Estimation. of Toluene b y Nitration.-To effect nitration, potassium nitrate and sulphuric acid were employed as described later. It was soon found that the nitration of toluene cannot be made to stop when the mononitro-compound is formed but that any excess of acid is used up producing the dinitro-compound; it was however proved as the result of many experiments that nitration stops quantitatively when all the toluene has been con-verted into the dinitro-compound.Using nitration as a means of estimating toluene there are obviously two methods which may be adopted namely by nitrating with a weighed excess of potassium nitrate and determining the weight of nitric acid remaining after nitration the amount of acid used is obtained and from that the weight of toluene nitrated, or by isolating and weighing the dinitro-compound. Adopting the first method it was found that the residual acid could be satis-factorily determined by the nitrometer but that by the second mekhod the dinitro-compound could not be completely recovered, because a small but definite amount remains in solution in the acid liquid from which the substance is filtered.A 100 C.C. flask is weighed, and into this is weighed accurately by dropping from a fine pipette 2 grams of the sample to be nitrated. Five grams of pure dry powdered potassium nitrate are weighed in a watch-glass or aluminium scoop and transferred with great care to the flask. The flask is cooled in water and 30 C.C. of pure concentrated sulphuric acid are poured in rapidly the flask being shaken con-tinuously to prevent the formation of solid lumps which if formed, take aome time to dissolve. When the action is over a pale yellow, homogeneous liquid is obtained. To cause the dinitro-compound t o separate about 60 C.C.of water are added the first few C.C. being dropped in alowly lest The nitration process is as follows 1368 LUMSDEN CRITERIA OF THE DEGREE OF the heat evolved should volatilise any nitric acid and at the same time the flask is cooled in water. The solid is obtained in soft flakee which are nearly white and when the contents of the flask are quite cold ihe separation may be considered complete. Filtration is effected by the aid of the pump; using a small porcelain funnel with a small filter paper ; the preparation flask is washed out with several small amounts of wabr which are poured through the funnel and the solid is washed free of acid. The filtrate is transferred to a graduated cylinder, and together with the washings of the filter flask is made up to exaotly 150 C.C.The whole operation of nitration prweds smoothly and the only point where care is needed is when adding water to the nitratad liquid great precautions being then necessary to avoid rise of temperature. Calculations C,H,-CH + 2KN0 5 C,H,(NOS),-CH,. 92 202.2 182.0 2 4.3956 3.95 (a) Two grams of toluene require for nitration 4.39 grams of potassium nitrate. One per cent. of this-0.0439 gram-remain-ing unused represents 1 per cent. of impurity in the toluene. 0.004522 Gram of potassium nitrate gives 1 C.C. of gas in the nitro-meter ; 0.0439 gram therefore represents 9-72 C.C. Working with 2 grams of toluene 9-72 C.C. of gas in the nitrometer a t N.T.P. represent 1 per cent. of impurity.( 6 ) Five grams of potassium nitrate are used to nitrate 2 grams of toluene but only 4.3956 grams are required. This is an excess of 0.6044 gram which in the nitrometer would give 133.65 C.C. of gas. ( c ) Two grams of toluene give 3-95 grams of dinitrotoluene. One per cent. of this-0.0395 gram-as a deficit in the yield repre-sents 1 per cent. of impurity in the toluene. (a) Estimation by Nitrometer.Two grams of toluene were nitrahed with 5 grams of potassium nitrate. The liquid was made up to 150 c.c. and 15 C.C. were taken for the nitrometer estimation. (The 15 C.C. were measured from a small burette into the cup of the nitrometer and 10 C.C. of pure sulphuric acid were used to liberate the gas.) 19.8 C.C. of gas a t 16O were obtained or 18-71 a t N.T.P.For the whole 150 C.C. this was 187.1 c,c.; deducting the known excess used namely 133.65 c.c., leaves 53-45 C.C. As 9.72 C.C. represent 1 per cent. of impurity, 53.45 c,c. represent 5.5 per cent. of impurity. Examples of Nitration. The following are the results of other estimations PURITY OF COMME~IAL TOLUENE. 1369 Pure toluene. 150 C.C. liquid 16 C.C. taken. 13.27 C.C. g a ~ at N.T.P. 132.7~~. For 160 C.C. liquid, From excess taken 133.6 -. -0.9 C.C. - 0.9/9-72 = - 0.1 per Toluene 100-1 per cent. cent. Good toluene. 176 C.C. liquid 20 C.C. taken. 16.7 C.C. grts Elf N.T.P. 137.37 C.C. For 176 C.C. liquid, From exces8 133.65 3.72 C.C. 3.72/9.72 = 0.38 per Toluene 100 - 0-38 = cent. 99.62 per cent. Poor toluene. 160 C.C.liquid 15 C.C. taken. 18.64 C.O. g m at N.T.P 186-4 C.C. For 150 C.C. liquid, From excess 133.6 -62-8 0.0. 52.8/9.72 = 6.4 per Toluene 100 - 6.4 = cent. 94.6 per cent. The sample of pure toluene shows more than 100 per cent.; this is due to experimental loss. It will be realised that if the potassium nitrate is not pure and dry or if there is any loss before the filtrate is made up to a definite volume less nitric acid is found, and this is indicated as a small increase in the percentage of toluene. (b) Estimation by Weighing the Solid.-The solid dinitxo-com-pound is transferred from the filter funnel to a watch-glass and set in a desiccator over sulphuric acid or the watch-glass may be set over a beaker of boiling water when the solid melts to a clear liquid with water beneath it.On cooling the solid forms a firm mass from which water is readily removed by filter paper; then, after a much shorter time in the desiccator the weight becomes constant. It was found that when the volume after nitration was made up to 150 c.c. approximately 0.11 gram of solid remained in solu-tion and this amount is added to the weight found in the follow-ing examples. Two grams of “pure ” toluene gave 3.8337 grams of solid; add-ing 0.11 gram the total dinitro-compound was 3.9437 grams; 100 per cent. toluene should give 3.9564 grams therefore the deficit is 0*0127 gram. 0.0395 Gram deficit represents 1 per cent. of impurity and 0.0127 gram 0.32 per cent. The toluene was there-fore 100 - 0*32 = 99-68 per cent.Two grams of a poor sample of toluene gave a deficit of 0.2573 gram that is 0.2573/0*0395=6*5 per cent. The toluene was therefore 100 - 6.5 = 93.5 per cent. Estimation of Toluene by Miscibility with Acetic Acid. Whilst engaged on this investigation a report by Professor Orton was received describing the experimental work detailed in his recent paper (this vol. p. 1055). He there showed that whe 1370 LUMSDEN CRITERIA OF TEE DEQBEE OF 88 to 90 per cent. acetic acid is mixed with hluene m the propor-tions of 1 C.C. of acid to 0.8 C.C. of toluene tws layers are formed, and on raising the temperature a point of complete miscibility is reached which is definite for the same strength of acid and so sharply defined that it can be read to one-tenth of a degree. He showed also that the temperature of miscibility of toluene rises regularly with the dilution of the acetic acid and further that for a given strength of acid the temperature of miscibility of toluene containing paraffin rises in direct proportion to the amount of paraffin present.Working with two strengths of acetic acid 87.9 and 89.5 per cent. and using pipettes of certain volumes he prepared curves from which the percentage of a mixture of toluene and paraffin could be found when the temperature of miscibility with one of these acids had been determined. The method is susceptible of great accuracy but it is very troublesome to prepare acetic acid of a definite strength and almost impossible to keep a concen-trated acid without absorption of moisture from the air and more-over it requires so much care to carry out the process as set down by Professor Orton that it could scarcely be used as a commercial test.The folfowing modification consisting in the changing of an absolute t o a comparative method may however be carried out in any commercial laboratory. A quantity of concentrated acetic acid of unknown strength is taken and with equal volumes of this the temperatures of misci-bility with equal volumes of pure toluene toluene with 5 per cent. of paraffins and the sample of toluene to be tested are found. Then since the percentage of paraffins is proportional to the increase in the temperature of miscibility the comparison of the rise of temperature of miscibility of the sample with that of the 5 per cent.paraffin mixture gives the paraffin content of the sample. To carry out the test there is required: (1) A quantity of pure toluene which need not be synthetically pure but might be considered as 100 per cent. quality. (2) A mixture of this toluene with 5 per cent. of paraffins made by mixing 95 grams of toluene with 5 grams of paraffins of the same boiling point prepared by the distillation of petrol. (3) Acetic acid prepared by taking 100 grams of glacial acetic acid adding a few C.C. of water and by trial with toluene in the proportions described below finding if two layers are formed and if the temperature of miscibility is somewhere between 25O and 30°. (4) The sample to be tested. The proportions of acetic acid and toluene found by Professo PURITY OF COMMERCIAL TOLUENE.1371 Orton as suibable for the test may be adhered to and two pipettes prepared one delivering 1 C.C. and the other 0'8 c.c. or quantitiea in these proportions but they need not be exact. The pipettes are made from narrow glass tubing and must have fine capillary points to deliver very slowly. A test-tube 1.2 cm. in diameter serves as a vessel in which the miscibility point is determined and while hhe test is being made it may for convenience be fixed to the thermometer by a rubber band. The test is carried out as follows. With the larger pipette acetic acid is run into the fest-tube and pure toluene is added from the smaller pipette. The tube is then fixed to the thermometer which must be graduated in tenths of a degree. Water is heated in a beaker holding about 2 litres the temperature being raised speedily and by stirring with the thermometer and tube an approximation t o the miscibility point is found by noting the temperature when the two layers disappear and a homogeneous liquid is obtained.A little cold water is then added t o the beaker the flame is turned very low the water thoroughly stirred and as the tempera-ture slowly rises the thermometer and tube are moved continuously in the water. As the miscibility point is approached the two layers disappear the liquid becomes opalescent and then auddenly becomes transparent. This is the point a t which the temperature is noted. By cooling the water in the beaker lo the test may be repeated. The same procedure is gone through with the 95 per cent.toluene and with the sample being examined the tube being washed out thoroughly each time and dried in an air-oven. The following are results obtained : Pure 95 Per cent. toluene. toluene. Sample. (1) The miscibility temperature wm 32.0' 38.3" 414O (2) Same sample on another day, the acid being different ............ 33.4 40.3 44.0 From (1) 38.3" - 32" = 6.3" and 41.4" - 32" = 9.4". A rise of 6.3" represents 5 per cent. of impurity 9.4" represents 7.4 per cant. From (2) 40.3" - 33.4" = 6.9" and 44.0" - 33.4" = 10.6'. A rise of 6.9" represents 5 per cent. of impurity 10.6" represents 7.6 per cent. It is seen that the strength of the acid does not require to be known it has only €b remain constant during the time that three portions are withdrawn and the pipettes do not require to be of any definite volume although they must deliver precisely the same volume each time.The three tests might be carried out simultaneously by having three test-tubes attached to the thermometer one with each mixture, VOL. cxv. 3 1372 BAXTER AND FARGHER 1 3-BENZODIAZOLEARSINIC and the three points of miscibility determined as the temperature of the water is raised. When the same sample of toluene was tested by the different methods the following results were obtained : From specific gravity curve .............................. 92.3 per cent. From nitrometer estimation after nitration ............ 92.9 ,, By weighing dinitro-compound ........................... 92.6 ,, By temperature of miscibility with acetic acid ...... 92.5 ,, Conclusions.-The specific gravity of commercial toluene gives a fair indication of the amount of impurity present; the estimation of the temperature of miscibility with acetic acid is quickly done, and although a comparative method if skilfully carried out is trustworthy; the nitration and estimation of the excess of nitric acid by the nitrometer is believed to be the most accurate test and indicates the total nitration which has taken place and the weighing of the solid after nitration gives the actual practical yield of nitro-compound . By none of the methods under ordinary conditions of working, can an accuracy closer than one-half per cent. be expected. THE TECHNICAL COLLEGE, DUNDEE. [Received October 16th 1919.