AMINATION IN THE HETEROCYCLIC SERIES BY SODIUM AMIDE K. NORRIS SHREYE, E. H. RIECHERS,‘ HARRT RUBENKOEKIG,U -IND A. H . GOOD3I.AS.
Purdoe I-niversit?, Lafalette. Tnd.
fairly simple to make and safe to ube. Sodium amide is employed on a large scale in the manufacture of indigo. .It o give made to revolve on hollow trunnions; one of them is blocked off from the reaction chamber and carries the driving pulley and well ?r’/\r\”Na f SaNH2-+ K a S H / ?;’ \SHh HINAS KH? f 2NaOH ,vith also the the t h ethermometer r m o m e t e r bulb
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against the cylinder wall, and held in place by copper turnings. The other hollow trunnion opens into the inside of the drum and connects through a packing gland to the stationary attachment to the reflux condenser. Thi3 nine . _ reflux also jerves as an
Sodium amide i. a dangerous reagent; disastrous ail11 fatal explosions having ensued from its storage and haw ([ling. Because of this fact sodium amide is being withdrawn from ordinary commerce. and the authorities recommend t’hat it be ma-de and used’at once. When st’oretl?oxidation has developed explosive impurities. However, wit>h the requisite apparatus and proper conditions sodium amide i.
ia
resent address, 830 Bauer Street, H a m , ~ o n d I, n d , 2
173
Present address. Willam S. Aferrill. Cincinnati. Ohio. Picsent address, American llaize Company, Roby. Ind
174
INDUSTRIAL AND ENGINEERING CHEMISTRY
exit for any gas, such as hydrogen. There is a connection for the inlet of any react,ing liquid, such as pyridine (Figure 2). The outside of the cylinder toward the outer periphery is provided with a 7/rincir (2.2-cui.) welded pipe connection which serves for thc screwing in of the ammonia delivery tube during the t,ime ammonia is being conducted into the metallic sodium for tlie preparation of the sodium amide, Before the ammonia is shut off, the cylinder is rotated until this '/&ch connection is above the liquid level. The ammonia delivery tube is ruiscrcwcd and replaced by a '/giricl~ iron plug, after no furthcr ammonia is needed for the amide or to keep out air. Figure 1 slious that the bottom housing is provided with a curvcrl slot and a replaceable cover to permit this ammonia delivery tube to be moved through a 90" turn to the low point. T o permit access to the drum, a 4-inch (10.Z-cm.) iron plilg is provided which can he screwed in and which is lubricated with ., eranhite. The cylinder is provided with ninety-eight steel balls (weighing 10.4 kg.) of tlie following sizes: eight, 2 inches ( 5 em.) in diameter; thirty, 1 inch (2.5 em.); and sixty, '/? inch (1.2i em.). (A steel explosion disk in the side opposite tlie 4-inch plug ~voulcl be an added safety device.) As Figure 1 shows, the drum revolves i n an insulated jacket consisting of a bottom and a removable top. Electrically heated Nichrome coils, connected through a variable-resistance rheostat, maintain the temperature at any point u p to about 400" C. The drum is revolved at 20 r. p. m. by means of a motor operatiiig through a speed reducer. However, while the sodium amide is tieing made, " 3 the drum is stationery; it is revolved only SUPRV to pulverize the solidifying amide and to facilitate its reaction with pyridine. This equipment must he thoroughly cleaned, dried, and inspected before use; t o remove all final traces of moisture anif air before the introduction of sodiiim, the cylinder must be heated to about 120' C.
.
VOL. 32, NO. 2
and swept out by a curreiit of pure ammonia. The top is removed, the 4-inch plug unscrewed, and the requisite amount. of metallic sodium introduced through t!iis opening. The sodium should be clean; if it has been kept under oil, tlie latter can be removed hy dipping into petroleum ether. The weight of sotliuirr for conversion into sodium amido must not be such that the total volume of the resiilting product. reaches the outlet of the trunnion. This varies according t o tlie product; 300 grams of sodium, when making aminopyridine, and 400 grams, when makingdiaminiipyridine, have been convenient quantities. 1,iehknccht (6) reports that sodium hydroxide was a favorable catalyst in the preparation of sodium amide; 2.9 per cent gave a yield of !IT per cent sodium amide, hut 0.25 per cent gave only a 59 per cent yield. The presence (if tlie grinding halls seriously limits the capacity of the equipment; on the other harid, its relatively small capacity is no serious handicap when we consider the safety undcr which this particulsr type of equipment can he operated. Afder the sodium is introiluced, the 4-inch plug is screwed i n and the cylinder rotated by hand until the '/rincli plug, carrying the ammonia delivery pipe, is on the bottom. The flow of ammonia is started gently and the temperatiire is raised by means of the electrical coils to 320-350' C . , as read OII the trunnion thermometer, which is somewhat lower ttian the actiral reaction zone. Under these conditions a vigorous reaction takes plact? as the ammonia is hubbled through the molten sodium. The progress of the reaction can be measured by a test 011 the exit gas. At tlie start t,his will tie practically all hydrogen, hut as the formation of sodium amide progresses the rate nf introduct.ioii of ammonia should be deereased. Aiter about 8 or 10 hours (overnight) the exit gas will consist of only about 10 per cent hydrogen hy volume. This generally mcans that all of the sodium has been converted. T o check this, the cylindcr is rntat.ed until the ammonia delivery tube no longer dips into the molten mass. Simultaneously the introduction of ammonia should he shut down almost completely. As soon as the drum is coded to about 250" C. the 4-inch plug should be unscrewed and a sample (1.5-3.00grams) of the molten product ladled out throiigh the porthole into a Pyrex glass weighing bottle for analysis. The Pyrex weighing bottle is then placed in a 250-ml. Kjeldahl flask, connected through a safety bulb to a condenser dipping into an
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,LUUPI)LO
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FIGURE 2. FLOW SHEETOF R A L ~ M I L REACTOR I.
INDUSTRIAL -4XD ENGINEERING CHEMISTRY
FEBRUARY, 1940
Erlenmeyer flask containing 1 S sulfuric acid. The Kjeldah1 flask is provided with a dropping funnel through which are slowly introduced 100 ml. of 90 per cent alcohol and then caut'iously 100 ml. of distilled water. The aqueous alcohol and the ammonia, evolved by the decomposition of the sodium amide, are distilled. The unneutralized sulfuric acid is titrated with 1 .I' sodium hydroxide, with methyl orange as indicat'or. From the titration the amount of animonia evolved can easily be calculated as well as the purit,y of the mlium amide. A purity of 95 per cent or better was considered satisfactory, especially since t'he possible errors in this analysis tend to lower the per cent of purity. If inspection and t'est show that the reaction is complete, the ammonia delivery tube is removed and the 7/g- and the 4-inch holes are closed with their respective plugs. K i t h the top off and the heat shut off, the mill is rotated during t'he cooling. This pulverizes the sodium amide safely and puts it in a condition for further reactions below its melting point.
recrystallization from benzene or toluene. The solubilities in ordinary solvents are as follows. Water a t room temperature will dissolve about 89 per cent of its weight in aminopyridine; 95 per cent alcohol, 170 grams in 100 ml. solvent at 27" C.; U. S. P. ethyl ether, 45.0 grams in 100 ml. solvent a t 25' C.; benzene, 19.1 grams in 100 ml. solvent a t 25" C.; toluene, 16.1 grams in 100 ml. solvent a t 25" C.; petroleum ether, 0.28 gram in 100 ml. solvent a t 25" C. It is not possible to determine these solubilities by evaporation because of the volatility of the 2-aminopyridine, and the figures are derived by titration with 1 S sulfuric acid, with modified methyl orange as the indicator. A sensitive test for aminopyridine i q the insoluble yellow precipitate given by picric acid. PREPARITIO?;. By adjusting the temperature of reaction and the relative proportions of pyridine to sodium amide, either 2-aminopyridine or 2,6-diaminopyridine is obtained. According to Chichibabin, the best procedure for making 2-aminopyridine seems to be reaction with sodium amide, followed by hydrolysis, as outlined under the reactions previously given. Chichibabin always used an indifferent solvent, such as xylene, toluene, or benzene. Dimethylaniline or diethylaniline has also been employed.
2-Aminopyridine PROPERTIES.2-Aminopyridine is volatile even a t room temperature. It is markedly hygroscopic and dissolves in water with appreciable absorption of heat. The solidifying point is 58.0" C. when 10 grams are heated slightly above this figure and then cooled t o crystal formation. Figure 4 gives the boiling point a t different pressures. 2-Aminopyridine can be purified either by vacuum distillation or by
REMOVABLE COVER FOR BOT# CHARGING AW U A N I N G
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175
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SECTION 00
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DETAILS O F DRUM
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HEATING COILS
SECTION A A 0 ASSEMBLY, WITH DRUM IN POSITION.
COMPLETE BOX ASSEMBLY
FIGURE 3. DETAILSOF BALL-MILLREACTOR
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176
\ \ D EYGIXEERIhG CHEMISTRE
In the equipment of Figure 1, which we prefer for these reactions, about as good results have been obtained by omitting the indifferent solvent, The best procedure is, after making the sodium amide from
300 grams of sodium, to cool the drum and its contents to about 110' C. and then to start the addition of the molecular
equivalent of the pyridine during rotation. The speed of addition of pyridine should be governed by the rate of evolution of the hydrogen evolved, which can easily he seen by inspecting the bubbles in the exit line; these should pass out in a steady, even stream. During the addition of the pyridine the temperature of the rotating mill as read from the trunnion thermometer should gradually rise to about 120" C. After the addition of all the pyridine the temperature should be increased to about 130' C. and kept there until no further hydrogen is evolved. This will usually be not over an hour or two. When the reaction is ended, the cover is removed and the mill allowed to cool to 75" C.; then 2000 cc. of hot xater are added. Part of this water should be added from the central pipe. This water serves to hydrolyze the sodium derivative of the aminopyridine and thus to form sodium hydroxide and 2-aminopyridine. The 4-inch plug should be removed and the rest of the water added through this larger opening. By oscillating the drum a quarter turn in either direction, the water will dissolve the contents. This aqueous solution should then he sucked out and, while quite hot, filtered through a cloth into a bucket. Upon cooling, the solution separates into a strongly alkaline aqueous layer on the bottom and an oily layer which contains the product. The mill is finally washed with several small portions of hot water. The aqueous layer is extracted with ether or benzene; the benzene or ether is distilled, and some crude diaminopyridine is left which is added to the oily layer containing the main portion. By vacuum distillation the oily product furnishes the pure product. This vacuum distillation has been found more satisfactory than crystallization.
TABLE I. DIAMINOPYRIDISE NITROGEX B.~I..\scE NITROGEN I N RE.4SENTI USED
489 495
Yo Nitrogen
Grams Sitrogeii
174.0 17.7 87 3 Total nitrogen input 2 6 1 . 3 35,Y
~
S I T R O G E N I&- P R O D E C T S O f REACTIOh-
Nitrogen Content
Quantit? Ammonia in eas Crude diaminopyridine Mother liquor Wash water
Grams Nitrogen
Yo Total Nitrogen to Input
22 560.0 p. 2.84 1. 3 . 3 8 1.
28.557, 160.0 15.65 g.,'I. 44.4 1 . 5 7 &/I, 5.3 Total nitrogen found 2 3 1 . 7 ~
8.3 61.4 17.0 4.0 88.7
~
DIJTRIBUTION OF DIAYINOPYRIDINE
Crude diarninopyridine, grams Mother liquor. liters
Approved procedure is to react the pulverized sodiuni amide with almost (96 per cent) theoretical proportions of pyridine lvithout any oil or other indifferent solvent. The omission of the diluting oil previously employed, under the mechanical conditions prevailing in the ball mill reactor, gave as good yields as the presence of the oil, owing to the fine grinding of the sodium amide and the excellent mixing during the introduction of the pyridine. Without oil, the filtration and the working up of the diaminopyridine were much simplified. This approved procedure calls for the making of sodium amide in the same ball mill reactor (Figures 1, 2, and 3) except that the initial charge consists of 18 moles (415 grams) of metallic sodium with the later addition of 96 per cent of 9 moles (685 grams) of pyridine. In most experiments only 300 grams of sodium, with a proportionate decrease in pyridine, were charged.
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2ool 190
,601 170
/
I60
!
120
The boiling points of 2,6-diaminopyridine a t variou- prehsures are given in Figure 4. The diaminopyridine can be purified by distillation, but crystallization from benzene wa> preferable. The solubility of diaminopyridine is 0.45 gram in 100 ml. benzene a t 25" C. The melting point i5 121" C. PREPARATION. Evidence points to the introduction of one amino group into the pyridine first, followed by the second group. For instance, in the making of 2-aminopyridine, little or no diaminopyridine was obtained. Although we have no direct quantitative data, observations of the reactions, such as temperature required and time necessary, indicated a somewhat greater difficulty to cause the second amino group t o enter the pyridine ring than was the case with the first. l'arious mechanisms for this reaction and extensive refer-
Sodamide Pyridine
ences to the literature can be obtained from the review article by Bergstrom and Fernelius ( 1 ) .
:::I/
2,6-Diaminopyridine
K t . Basis l o o % , Grams
F 01,. 32, NO. 2
yo of Sitrogen Content Due t o Nitrogen of Diaminopyridine
Diaminopyridine Content ,by hnalysis
Nitrogen Equivalent t o Diarniriopyiidiiie
362.0
139.4
87
43.1
16.6
37
PRESSURE, rnm 01 Hg
I10 0
IO0
200
300
400
YJO
600
700
FIGURE4. TEMPERATURE-PRESSURE DI.4GR.4M
.\iter the sodium amide had been made, it was cooled to ahout At this temperature the reaction was much more vigorous and the large heat of reaction was taken care of by the air-cooled refluxing of the pyridine as the react,ion proceeded. The speed of the addition of the pyridine was controlled, as in the case of aminopyridine, by watching the evolution of the hydrogen; the actual pyridine addition usually took 2 to 4 hours. The reactor was kept at approximately 170" C. during the addition of the pyridine and thereafter until the evolution of hydrogen ceased, which was generally ahout 6 to 8 hours after addition of the pyridine was started. During this entire time the reactor \?as kept revolving. After cessation of the hydrogen evolution, the top housing was removed from the apparatus and the temperature allowed to cool to 90" C. Three liters of very hot water were then added slowly through the central inlet tube, under continuous agitation. Hydrogen was again evolved and escaped. The &inch plug was removed and the hot solution sucked out at once into a flask and filtered by gravity into an enameled bucket through a cloth \vet Tvith hot water. One liter of hot water hhould be used to wash out the apparatus. Upon cooling, the diaminopyridine crystallized out in the form of plates. If the operation is performed quickly and the water is hot, little or no diaminopyridine will crystallize on the cloth. However, what does crystallize can he dissolved in the hot washings and these can be strained through the same cloth. The mother liquor is about 12 or 15 per cent sodium hydroxide in which the diaminopyridine is not very soluble. The diaminopyridine can he crystallized from benzene to give pure white flaky crystals. This reaction is vigorous, and the yields are only about 55 per cent of the theoretical amount based upon the sodium amide. Some of the pyridine is converted into an insoluble material which is caught on the filter cloth. 170' C.; then the addition of the pyridine was started.
SITROGEX BALASCE. Since the yields of pure diaminopyridine were never more than about 55 per cent, various rnodifications were tried to better these yields; a nitrogen
FEBRUARY, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
177
mitted; a high grade white medicinal mineral oil was used. Run 2, in Table 11, as well as a number of others made in these laboratories but not reported, exhibit practically the same yield whether oil was employed or not; consequently its use was abandoned because it interferes with the working up of the product. On the other hand, we have not completely investigated the conditions under which a diluent might or might not be advantageous in this reaction. Most of the previous workers state that the pyridine must be anhydrous, the object being to prevent the decomposition of the sodium amide with the formation of sodium hydroxide and ammonia. Consequently, the results obtained in runs 3 , 4, and 5 are surprising. The theory was that the addition of sodium hydroxide might help the reaction; therefore we added 56 grams of sodium hydroxide per 300 grams of sodium in several experiments. However, this addition did not seem to have any influence on yield. The temperature of the reaction (runs 6 to 18) is of the utmost importance. I n carrying out this reaction the authors are inclined to believe that with any new piece of equipment the runs should be made above and below what seems to be the most favorable temperature-namely, around 160-li0" C. Experimental Results -with the idea of ascertaining the best temperature for the particular conditions. Certaihy if the temperature is too The data in Table I1 summarize the diaminopyridine runs high, the sodium amide has a destructive action upon the made in the apparatus shown in Figures 1, 2 , and 3. I n pyridine. If the temperature is too low, mostly monoaminoreading this table, particularly in regard to the temperatures, pyridine is formed. I n considering the ratio of pyridine to it must be borne in mind that the apparatus used was essentially a pilot equipment and that the temperature mainsodium amide, when Table I1 refers to '(theory", it means tenance was not such that the apparatus could be held closer that for every molecule of sodium added, 0.96 molecule than 5' or 10' C. Since temperature has considerable inof pure pyridine (99f per cent) was used. I n making fluence upon yields, the yield figures may vary as much as the sodium amide from sodium, the average yield was 96 5 per cent in duplicates run as closely as could be managed per cent. with this equipment. Runs 19 to 25 were carried out to study further the influence of the ratio of pyridine to sodium amide. Results did I n a number of the runs oil was added as a diluent to be mixed with the sodium amide before the pyridine was adnot show any advantage in the use of pyridine with variations from theory. I n runs with more than the theoretical amount of pyridine (not recorded in Table TABLE 11. DIAYINOPYRIDIXE RUNE 11) the tendency was to form the Ratio, 'Temp. Temp. Purity Wt. of monoamine. Pyridine/ during after of Crude Pure Yield on Run Sodium Pyridine Pyridine Diamino- Diamino- Sodium Because of the destructive acNo. Amide Addition Addition pyridine pyridine Amide Ueiuark& tion of sodium hydroxide on these c. c. % Grama % 1 Theory 145-100 160-130 65 362 51 Standard run compounds, several runs were 2 Theory 175-120 170-120 66 338 48 Oil added as diluent made in which, when the sodium3 Theory 160-145 185-140 77 336 47 1% water t o pyridine water to pyridine pyridine compound was decom4 Theory 160-145 190-145 '76 400 .7 Theory 160-13.5 190-190 75 390 % water t o pyridine posed by water, an amount of Temperature of Reaction Varied ammonium chloride required to ti Theory 135-110 155-145 59 218 30.5 .... change the sodium hydroxide 7 Theory 145-100 16o-im 64.7 362 51 .... 8 Theory 160-i.in 160 73.4 323 45 .. into ammonia and sodium chlo9 Theory 160 160 66 340 48 . . 10 Theory 170 170 65 340 48 ... ride was added. However, there 11 Theory 170 170 71.5 347 49 ... was no appreciable effect on the 12 Theory 180 180 62.5 306 43 ... 13 Theory I80 I80 62.5 272 38 .. .. .. .. yield. 14 Theory I90 I90 47.5 262 3i balance was also made upon the input and output of the reaction, in order to follow the course of the reaction better. This nitrogen balance is summarized in Table I. Several nitrogen balances were made with about the same resultnamely, in accounting for about 90 per cent of the total input of nitrogen into products. The unaccounted percentage we believe to be due largely to ammonia that escaped during the various handling operations. By actual analysis, 22 grams of nitrogen were found in the form of ammonia in the evolved hydrogen. However, the mother liquors smelled strongly of ammonia, and some of this was lost in the manipulations. Apparently the sodium amide decomposes partially into ammonia, and it may also be that the sodium hydroxide converted a part of the ring nitrogen to ammonia. This ammonia was detectable in the gas by means of moist phenolphthalein paper a t all stages of the reaction between pyridine and sodium amide and also during the addition of water to decompose the sodium aminopyridine. At times the ammonia was as much as 10 per cent of the volume of hydrogen evolved. This ammonia evolution was also observed in the making of aminopyridine. Analysis showed no nitrogen in the waste gas. The analysis for nitrogen in the solids and liquids was carried out by the Dumas method. A few other nitrogen-containing compounds mere isolated from the diaminopyridine mother liquor. These were 4-aminopyridine and 4,4'-dipyridyl.
:%
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2n 21 22 23 24
25 0
Theory Theory Theory Theory lo%"
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Less than theory. On pyridine.
190
200 200
201)
160-135 155-135 155-135 195-195 160-140 160-140 im-14n
62 144 20 53 108 15 60 198 28 39 66 D Ratio of Pyridine t o Sodinin Amide Varied 190
200
zoo 200
155-130 160-130 145-140 150-140 155-130 140-140
145135
58
57 61 62 65 55
53
293 290 265 211 26'7 129 I27
41 41 3'7 30 38 18 18
...
....
., .. .. ..
46% yieldb 5 1 % ieldb 4 6 . 5 d yieldb 42% yieldb 54% yieldb 3 6 7 yieldb 36'% yinldh
2-Aminoquinoline Although 2-aminoquinoline was not made in the apparatus shown here, since only small quantities were wanted, this compound was obtained in a 32 per cent yield from quinoline. The reaction was carried out by boiling xylene with two moles of sodium amide in suspension, to which was added
178
INDUSTRIAL AND ENGINEERING CHEMISTRY
one mole of quinoline. (Equal moles of sodium amide and quinoline did not give such good yield.) This mixture was kept boiling and refluxing until hydrogen evolution became very small (about one hour). The sodium amide was divided by pouring fresh molten product through a screen into mineral oil. After the reaction the cooled mixture was treated carefully with water to decompose the sodium-quinoline compound. The xylene layer was reacted with concentrated hydrochloric acid to precipitate diquinolyl and diquinoline and to dissolve the aminoquinohe. The aqueous layer was made alkaline with sodium hydroxide and extracted with ether. The xylene and ether extractswere distilled and the residue was vacuumfractionated* The product coming Over around c*at 30 mm' was from The 2-aminoquino1ine was odorless and Sugar white, and Crystallized in IWdles at 130.0" C. (corrected).
VOL. 32, NO.
2
Acknowledgment It is a pleasure to acknowledge the considerable help that was obtained from the &Iallinckrodt Chemical Works of St. T,ouis and which enabled this investigation to be pursued. Literature Cited (1) Bergstrom, F. W., and Fernelius. W. C . . Chem. Rev., 12,64 (1933).
ii; I g b ~ ~ ~ 2 ~ f 5 ~ . e t , ~ ~ ~ 0 ~ ~ g a 3 ~ ~ . S y n t h e s i s , , ,
vel. I , p. 74, New York, McGraw-Hill Book Co., 1939. (4) Chichibabin, A. E., and Zeide, 0. A,, J . RUES. Phys. Chem. SOC.. 46, 1216-34 (1914). (5) Gilbert, H . N., Scott, N. D., Zimmerli, W. F., and Hansley. V. L.,IND. ENQ.CHEM.,25,73541 (1933). (6) Liebknecht, O., U. S. Patent 1,359,080(Nov. 16, 1920).
ABSTRACTED from the Ph.D. thesis of E. H. Reiohers and the M.S.theses H~~~~ Rubenkoenig end A. H. Goodman. The final paragraphs on 2aminoqiiinoline were abstracted from the M.S. thenin of R. B. Bennett. of
POTENTIAL USE OF HYDROGEN FLUORIDE IN ORGANIC CHEMICAL PROCESSES J. H. SIMONS
Hydrogen fluoride promises to be of extensive use in organic chemical processes. Fortunately it can be made available in large quantities. Present indications are that it will displace other condensing agents in reactions for which they are used and will also enable new reactions to be carried out not possible with the other agents. Higher yields are to be expected both because obnoxious by-products such as tarry residues and sulfonated sludges are not formed and because the starting materials not used can be recovered. Its physical properties should result in more efficient processing, and greater ease and less cost in the design and use of equipment. It should be recoverable from reaction vessel for subsequent use. Equipment can be made of common materials of engineering construction. In the near future it will probably become one of our more widely used industrial chemicals.
KHYDROUS hydrogen fluoride has been made available commercially within the past ten years. It can now be obtained on the market in steel cylinders or in tank cars. Kewer developments indicate that it will find ex-
A
tensive large-scale uses. Until the recent industrial preparation, the anhydrous material was obtainable only by laboratory methods. Hydrogen fluoride was discovered by Margraff (13) in 1768, but
Pennsylvania State College, State College, Penna.
Davy (6) in 1813 first obtained a sample of the anhydrous liquid by the electrolysis of an aqueous solution until it would no longer conduct the current. Fremy (8)made it by heating carefully purified and dried potassium hydrogen fluoride. This method was used by all subsequent workers until Simons (16) in 1924 modified it by purifying and drying the salt by electrolysis. The laboratory methods are slow and require considerable technical skill, but they must be used for material of the highest purity. The industrial method consists of a carefully controlled reaction between calcium fluoride and sulfuric acid a t an elevated temperature, followed by a distillation of the gaseous products of this reaction. I n tbis process steel equipment is used throughout. The liquefied gas is stored in steel storage tanks. Pipes, fittings, and valves are all made of steel. The commercial material contains less than 0.5 per cent water, the average being 0.1 to 0.2 per cent. Silicon fluoride is less than 0.1 per cent and often as low as 0.01 per cent. It contains a small amount of sulfur dioxide which can be removed if required. Anhydrous hydrogen fluoride forms a liquid of high dielectric constant, which is a good ionizing solvent for many salts. In addition, it is a good solvent for many organic substances, particularly those containing oxygen such as alcohols, carboxylic acids, ethers, ketones, etc. That many of them form highly conducting solutions is probably due to the strong acidity of the solvent (16). Aromatic compounds are appreciably soluble in it, and it is in them. A useful property is that the other halogen halides are not soluble in it to any appreciable extent. Hydrogen chloride is so slightly soluble that a saturated solution of it, when dissolved in water, fails to give a chloride ion test with silver nitrate. Anhydrous hydrogen fluoride is a powerful dehydrating agent. It reacts with water with the evolution of considerable heat, A number of hydrates are known (1). No chemical reagent so far tried can be added to it to dry it. Sulfuric acid
