INDUSTRIAL A N D ENGINEERING CHEMISTRY
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1-01. 17. No. 11
Preparation of Hexachloroethane b y the Chlorination of Ethylene'"i3 By G . E. Miller CHEMICAL
\\'AXFARE
SERVICE, EDGEWOOD ARSENAL,
HLORINATION of ethylene offers a simple method for the preparation of hexachloroethane and is easily adaptable for large-scale production. The temperature required is comparatively low (300" to 350' C.) and the product obtained is unusually pure. The principal requirement for the successful operation of this method on a large scale is a sufficiently large and cheap source of ethylene. Jones and Allison4 sho-wed that chloroform, carbon tetrachloride, and hexachloroethane are formed by the direct chlorination of natural gas in the presence of a catalyst. The present work indicates that when pure ethylene is used with a small excess of chlorine, in the presence of activated charcoal as a catalyst, a yield of about 90 per cent hexachloroethane can be obtained. With this small excew of chlorine the hexachloroethane is practically free from lower chlorinated products. The following equation expresses the reaction:
C
CzH4
+ 5C12 = czcls + 4HC1 Apparatus
The difficulties encountered in this work were more mechanical than chemical. The first runs were made in a silica tube, heated in an electric furnace, but difficulty with leaky connections a t the ends of the tube, or clogging due t o condensation of the product when the t u b e p r o t r u d e d sufficiently from the furnace to be kept cool a t the ends, caused the abandonment of this type of apparatus in favor of an all-Pyrex glass system h e a t e d w i t h coils of nichrome wire. In the a p p a r a t u s shown in the diagram the reactor A consists of a Pyrex tube 38 mm. in diameter. B is a 16.5mm. tube sealed into the reactor to serve as a pyrometer sheath. The gas inlet tubes, C, 6.4 mm. in diameter, are sealed into the reactor about 50 mm. from the top. The tube D,also 6.4 mm. in diameter, is sealed into the top for charging and emptying the charcoal. A perforated glass plate, E , is sealed into the large tube 25.4 mm. below the pyrometer sheath, to support the charcoal. The lower part of the tube A is drawn down to about 19 mm. so that it will fit into a rubber stopper. The Received April 30, 1925. Published by permission of the Chief, Chemical Warfare Service a The work described herein was done a t various times by the following men: W. A. Taylor, E. M. Faber, G. M. Bartlett. S G Seaton, P. F . Stricker, F . M . Henley, and J. H Holden, from whose laboratory notes this article was compiled. 4 THISJOURNAL, 11, 639 (1919). I
a
?vfD
tube was first wound t o within 15.2 cm. of the bottom with No. 18 nichrome wire. Two 7.5-liter bottles in series were used as receivers. With this arrangement the lower part of the tube clogged, owing to condensation of hexachloroethane. I n order to prevent this a piece of large glass tubing was sealed onto the bottom of the reactor so as to turn back over it like a collar, as shown in the sketch. I n this way the winding can be carried to the bottom of the inner tube while the outer tube fits into a rubber stopper. Experimental
The charcoal used was the regular activated charcoal of commerce ordinarily used in gas masks and for the removal of gasoline from natural gas or for the recovery of volatile solvents. I n carrying out experiments with this apparatus it was found that with 200 grams of charcoal the maximum rate of flow of ethylene was approximately 60 cc. (25" C.) per minute. When the rate was increased above this amount ethylene was lost in the exit gas. A 10 per cent excess of theory of chlorine, based on the ethylene, mas used in all the runs. It was also found that the ethylene tended t o carbonize if allowed to mix with the chlorine before it entered the catalyst. Results
Eighteen runs were made with this apparatus. The data on these runs are given in the table. C h l o r i n a t i o n of E t h y l e n e
Run 1 2 3 4 5 6 7 8 9 10
11
12 13 14 15 16 17 18
-EthyleneCc./min. Grams 58 4.81 58 to 60 8.03 16.97 58 t o 60 26.1 60 24.9 58 21.3 46 to 50 22.49 58 to 60 23.12 58 to 60 22.02 58 to 60 19.96 58 to 60 20.20 58 t o 60 20.60 58 t o 60 19.47 58 to 60 17.26 68 t o 60 16.59 58 to 60 15.68 58 to 60 19.36 58 t o 60 19.45 58 to 60
Chlorine Cc./min. 320 to 345 320 t o 350 315 t o 410 320 to 375 315 to 335 250 to 280 325 to 345 330 to 355 325 to 350 325 to 350 326 to 365 330 to 355 326 to 345 315 to 335 325 t o 340 335 t o 345 335 t o 345 325 to 350
Hexachloroethane Yield Per cent Time Temperature based on Hours C. Grams CzH4 54.1 1.2 288 to 308 22 60.5 2.0 285 to 292 41 92.1 132 292 to 300 4.2 86.6 6.3 191 283 to 290 90.4 6.3 189 283 to 297 80.7 6.3 145 285 to 292 5.5 195 to 207 110 6 0 . 1 74.3 5 . 8 201 to 205 140 72.6 130 348 195 to 205 358 5.5 95.3 155 5.0 81.1 131 5 . 0 345 to 365 70.8 119 5 . 0 350 to 355 152 92.5 6.0 340 tD 350 75.0 110 330 345 to 360 350 4.5 85.7 120 4.2 85.4 113 4 . 0 325 to 360 91.8 150 340 to 360 5.0 92.0 151 335 to 352 5.0
The first six runs were made a t approximately 300" C. I n the first two the yields were very low because the heating coils were not continued to the bottom of the reactor. This not only prevented the efficient recovery of all the product, but caused clogging, which made it necessary to stop the runs before a sufficient time had elapsed to give accurate results. The average yield on the remaining four runs was 87.5 per cent of theory, based on the ethylene used. The next three runs (7, 8, and 9) were made a t about 200" C., t o determine the effect of a lower temperature on the reaction. It is obvious from the yields, the average of which is 69 per cent, that this temperature is too low. The remaining nine runs were made a t about 350' C. The average yield was 84.4 per cent, the highest being 95.3 per cent. I n two of the runs, 12 and 14, the yield was low. No
I S D USTRIAL A S D EA'GINEERIKG CHEMISTRY
November, 1925
explanation is offered for the failure of these two runs; however, if they are omitted from the calculation of the average yield of runs a t 350" C., the remaining seven show a yield of 89.1 per cent. From these runs i t is apparent that variation of the temperature from 300" to 350" C. does not materially affect the yield or the quality of the hexachloroethane. At 200" C. the yield is considerably decreased.
1183
Conclusions
Hexachloroethane can be produced by direct chlorination of ethylene with chlorine using activated charcoal as a catalyst. . The principal advantages of this method are the high purity of the product, the comparatively low temperature (300 O to 350" C.) a t which the reaction takes place and the high yield (90 per cent) of hexachloroethane obtained.
The Evaluation of Chlorates' A Comparison of Seven Selected Methods Applied to a Single Lot of Potassium Chlorate of High Purity By E. C. Wagner LNIVERSXrY OF PEENSYLVANIA, PHILADELPHIA, P A .
URITY requirements for chlorates are sometimes high.
P
During the war government specifications for primer chlorate called for a purity of 99.85 per cent.2 Satisfactory analysis of such material requires a method the degree of accuracy of which is definitely known. Descriptions of methods in the literature or in the manuals often include no information as to accuracy, or give information which is of doubtful value. Comparisons of seven selected methods applied to the evaluation of a single lot of chlorate of very high purity was therefore undertaken in the hope of revealing their important merits or demerits. d further improvement in Bunsen's evolution method is effected by use of a new receiver. M e t h o d s Investigated
Volumetric Methods (1) Bunsen's evolution method (2) Method of Ditz
(3) Method of Kolb and Davidson (4) Ferrous sulfate excess method Note-Knecht's titanous chloride method [J. SOC. C h e m I n d . , 27, 434 (1908)]was not subjected to trial. Mohr's and Volhard's titrations, for determination of chloride formed b y reduction, are referred to under ( 7 ) .
Gravimetric Methods ( 5 ) Reduction to chloride by ignition with ammonium chloride
(6) Reduction to chloride by evaporation with hydrochloric acid ( 7 ) Reduction t o chloride by sulfurous acid, and precipitation as silver chloride M a t e r i a l Analyzed
The potassium chlorate used for the comparisons had been crystallized four times from hot filtered solution. Each crystallization was analyzed for chloride and bromate, using the methods previously d e ~ c r i b e d . ~The product of the fourth crystallization, dried a t 100" C., was found to contain 0.013 per cent chloride (KC1) and 0.0009 per cent bromate (KBr03). I t s purity may be assumed to be not less than 99.98 per cent. Bunsen's Evolution M e t h o d
The procedure described previously4 was for these trials improved by use of a new receiver, whose design obviates Received February 14, 1925. A t present the requirement is only 99.35 per cent; U. S. Army Ordnance Specification 50-11-11. * THISJOURNAL, 16, 616 (1924). ' For two investigations of Bunsen's method not cited in the previous paper, see Topf, Z . anal. Chem., 26, 295 ( 1 8 8 i ) , and Jander and Beste, C. A , , 18, 1625 (1924). 1
the need to transfer the liquid to another vessel for titration of iodine. There are thus eliminated both the "oxygen error" and loss of iodine by volatilization-two sources of possible error in the usual procedure. APPARArus-The appearance of the assembled apparatus is shown by Figure 1. The construction of the new receiver is more clearly indicated in Figure 2. PROCEDCRE-The analysis was conducted essentially as described previously. Samples were taken as 10-ml. aliquots of a 1 per cent solution, and decomposition was effected by means of 5 ml. of 40 per cent hydrobromic acid, and in'a continuous stream of oxygen-free carbon dioxide. Into the bottle, A , of the receiver were introduced 40 ml. of 10 per cent potassium iodide solution and 100 ml. of water. The trap, C, was charged with 10 ml. of 10 per cent potassium iodide solution. The receiver was placed in a 2-liter beaker containing cold water. When the distillation was ended, the receiver was disconnected and rotated to dissolve solid iodine. The trap was connected a t f with the carbon dioxide generator (Figure l), the cap B was slightly lifted, and the contents of the trap were forced into A by pressure of carbon dioxide. The trap was washed out with several portions of water, introduced through f (the stopper e being removed), using the procedure just described. The cap B was then lifted out, held above A , and the internal surface of the cap and the inlet tube, b, were washed with water. The free iodine was titrated at once with 0.1 N thiosulfate, added from a weighing buret. Blank analyses were conducted in the same way. All the blank analyses made in this apparatus gave a result of zero-i. e., the liquid gave no color on addition of starch indicator.
ANALYTICAL REsuLTs-The last series of trials yielded the following results: 99.91, 100.00, 99.99, 99.96, 99.94 per cent, average 99.96 per cent. The t'ime required for an analysis, exclusive of the preparation of the sample, was somewhat less than an hour. This time can be reduced, without sensible loss in accuracy, by use of a volume buret. Iodometric M e t h o d of D i t z j
The chlorate is brought into contact with potassium bromide and hydrochloric acid in an all-glass apparatus consisting of a 1500-ml. bottle with attached addition-funnel and a trap for potassium iodide solution. After reaction is complete the liquid is diluted, potassium iodide solution added, the contents of the trap washed into the bottle, and the free iodine titrated with thiosulfate. Fifteen results reported by Ditz ranged from 99.81 to 100.17 per cent, and averaged 6 Chem. Zlg., 26, 727 (1901); 2. anal. Chem., 46, 532 (1906); Classen, "Ausgewahlte Methodeu der analytischen Chemie," Vol. 11, 1903 p. 370. Cf. Rupp, Z . anal. Chem. 66, 580 (1917); Moerck, J. A m . Phorrn'l A S S O C . , a, 155 (1913).
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