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
FEBRUARY, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
reacts to form fluorosulfuric acid and liberate water. Phosphorus pentoxide reacts similarly. Calcium chloride reacts to liberate hydrogen chloride. It can, however, be dried by electrolysis, the conductivity diminishing as the water is eliminated. It is fortunate that for many reactions of industrial interest absolutely anhydrous material is not essential. Some reactions will tolerate a considerable percentage of water. I t has recently been found that hydrogen fluoride is a useful reagent for many organic chemical reactions. I n some of these it acts as a fluorinating agent, but in most of them the products formed contain no fluorine. For conducting these reactions on an industrial scale, hydrogen fluoride appears to have properties which should make it preferred over other reagents used to obtain the same products. The chemical properties which probably govern its action in organic reactions are its strong solvent property, its high acidity, its great dehydrating tendency, the insolubility of the other halogen halides in it, and its great tendency to combine with itself and other substances to form molecular complexes. Although the work relating to the use of hydrogen fluoride in organic chemical reactions is recent and few investigations have so far been published, it has already been shown to cause reactions which may be listed under the following headings-polymerization, alkylation, acylation, special reactions, and fluorination.
Polymerization Everyone who has worked with hydrogen fluoride has experienced its powerful action in polymerizing organic substances. Rubber in the form of rubber stoppers or tubes and also raw crepe rubber becomes a hard brittle mass when acted upon by hydrogen fluoride. All the synthetic or natural resins that I have tried are acted upon in some way. Unsaturated organic compounds are readily polymerized, particularly those containing the olefin linkage. Fredenhagen ( 7 ) listed the following substances as being polymerized by it: oleic acid, linseed oil, poppy-seed oil, castor oil, sunflower oil, soybean oil, amylene, butadiene, dipentene, indene, isoprene,
179
piperylene, pyrrole, thiophene, and thionaphthene. Grosse and Linn (10) also include ethylene, propylene, and cyclohexene. I n this laboratory we have found that acetaldehyde, furfural, and acetone (11) are polymerized. Klatt (12) believed that mesitylene is formed in the polymerization of acetone, but in most of our experiments an inseparable mixture of polymers was produced. A t 0 " C. the action on acetone is slow. I n contrast to certain other agents, hydrogen fluoride does not polymerize aromatic compounds such as benzene, toluene, naphthalene, etc.
Alkylation I n view of the great polymerizing power of hydrogen fluoride it is surprising that it can be used to prepare simple organic compounds in good yields and without the formation of any appreciable amount of unwanted polymers. This, however, is the case, and it will probably constitute the greatest industrial use of the material. The first report appeared in 1938 (17). As a catalyst for alkylation reactions, hydrogen fluoride has been used with alkyl halides, olefins, alcohols, esters, ethers, and with strained ring compounds. With alkyl halides (19,dO) the reaction follows the equation: RH
+ R'X +R-R' + HX
RH represents a great variety of substances, which includes the aromatic compounds. We may, for a simple example, consider it to be benzene. R' is almost any alkyl radical, and X may be chlorine, bromine, or iodine. If R' is tertiary, the reaction takes place rapidly a t 0" C.; if secondary, it reacts a t room temperature; but if primary, the reaction must be heated (100" C. is ample in most cases). The H X escapes as a gas in these reactions; and only a small amount of hydrogen fluoride is necessary, provided neither RH nor R'X contains oxygen. The reaction will proceed in the hydrocarbon phase, if some hydrogen fluoride gas is dissolved in it. With olefins @,SI18,20, SO) the reaction, RH
+ R'-CH=CH-R"
g' > CH--CH,-R"
takes place readily, usually a t 0" C., with relatively small amounts of catalyst. The olefin is added slowly, with stirring, to the substance to be alkylated which contains the hydrogen fluoride. This is to prevent the polymerization of the olefin, and under these conditions detectable amounts of the polymers are not found. I n this case, as in all cases of alkylation, a great excess of the material to be alkylated should be used to prevent polyalkylated products unless they are desired. R' and R" may be almost any radical, including hydrogen. A cyclic olefin such as cyclohexene may be used. With alcohols (3, BO, 22) the reaction, RH
Courtesy, Harehaw Chemical Company
CONTROLBOARD FOR ROUTINQTHE FLOWOF HYDROQEN FLUORIDH~
+ R'OH
R-R'
+ HZO
takes place in a manner similar to the reaction of the alkyl halides. Tertiary alcohols react most readily, and primary least. For two reasons much more hydrogen fluoride is necessary in reactions using alcohols as the alkylating agent: All compounds that contain oxygen have a strong tendency to add to hydrogen fluoride, and this reduces the catalytic action. Also, since water is one of the reaction products, its formation dilutes the hydrogen fluoride and decreases the catalytic activity. With esters ( W ) the reaction,
INDUSTRIAL AND ENGINEERING CHEMISTRY
180
RH
+ R’-COzR” +R-R” + R’COzH
takes place readily a t 100” C. The reaction is similar to the reaction of alcohols. With ethers (3) the reactions, RH RH
++ R’-0-R +R-R” + R’OH R’OH +R-R’ + HzO
take place. The temperatures required and the amount of the second reaction depend upon the reactivity of the R’ and R ” groups. In general, the reactions follow the course of the reactions of alcohols. The strained ring compound, cyclopropane ( S I ) , was found to be an effective reagent to alkylate; it forms normal propyl compounds whereas primary propyl halides or alcohol forms chiefly isopropyl compounds. This, however, is true with other condensing agents. With hydrogen fluoride as the catalyst, the reaction proceeds rapidly and smoothly, and the yields are high. Typical alkylations catalyzed by hydrogen fluoride are given in the following equations, with benzene as the material to be alkylated:
+ CHaCH2CH2Br
--f
0
+ CHsCHdHz
+ CsHsOH
---+
very soluble in liquid hydrogen fluoride, the reaction probably takes place in the hydrogen fluoride liquid phase. Most of the reactions take place readily a t 80” to 100” C., but with very active reagents 0 to 20” C. can be employed. I n contrast to the similar use of aluminum chloride, the reactions take place with the carboxylic acid as readily as, or perhaps more readily than, with the acid anhydride or halide. With the acid halide the following rapid reaction occurs in the cold immediately upon mixing the reagents: RCOX
+ HF --3 RCOF + HX
With the acid anhydrides a similar reaction takes place: (RC0)ZO
+ HF +RCOF + RCOzH
In the use of esters the alkylation reaction takes place mure readily than the acylation, and alkylated products are formed in abundance. This may be related to the reactivities of the R’ and R ” groups, and perhaps the latter may be adjusted to favor a desired product; but this behavior has not yet been studied. Typical acylation reactions catalyzed by hydrogen fluoride are given in the following equations, with benzene as the substance to be acylated :
n
v
n-cHc:: v
v
3
-----f
-Cds
VOL. 33. NO. 2
+
CHsCOzH
d
+
CHsCOCl
+
-COCHa
+ HzO
-COCH,
+ HCI
+ CHsCOzH Special Reactions From the great variety of alkylations and acylations that hydrogen fluoride will promote, it would be expected to cause a number of related reactions. This has already been found true. It is effective in the Fries change (S4), for example, iii t,he following case,
‘d Hydrogen fluoride may be used to alkylate uunipoullds which are as difficult to alkylate as benzoic acid or aromatic compounds containing the nitro group. The reason probably is that it may be used a t relatively high temperatures for long periods of time without the formation of excessive amounts of tars.
Acylation The preparation of ketones can be readily accomplished by the use of anhydrous hydrogen fluoride. In these acylation reactions (6, t 3 , 29) the carboxylic acid, its anhydride, the acid halide, or the ester the acid may be used. Typical reactions are as follows
+
+ HzO + HX 1 + 5 HzO + R-R” +
RH R’COZH +R--CO-R’ RH + R‘COX +R--CO-R’ 1 RII + 3 (R’C0)zO +R-CO-R’ 2RH + R’C02R” + R-CO-R’
a
-02CCHs
-+ CHaCO--(rZ)-OH
It will also cause certain other rearrangements (24)-for ample : CH,
+
@OH
-+-
0
+ CH,-I-=--OH CHa
It
cause ring
(z, zO)-for
(? COCH4HCHs
Hz0
These reactions require a considerable excess of hydrogel1 fluoride; and since the oxygen-containing compounds art’
--f
ex-
lNDUSTRlAL AND ENGINEERING CHEMISTRY
FEBRUARY, 1940 OCH3
In these two examples, either the carboxyl or olefin group can be effective in such reactions. Rings can also be formed in cases where a compound having two reactive groups is caused to react with an aromatic compound. An example is: 0
li
H,C-CH~
Another interesting reaction has been found in rhich hydrogen fluoride is the reagent. The treatment of tert-amyl chloride with hydrogen fluoride (27) yielded tert-butyl chloride as well as a mixture of other chlorides, and tert-butyl chloride yielded tert-amyl chloride as one of the products.
Fluorination
1x1
and phosphoric acids, it also has properties somewhat related to aluminum chloride, boron fluoride, and the other metallic halide condensing agents. It seems to be able to catalyze most of the reactions promoted by any and all of these other substances. Why this should be is still a matter of speculation. Hydrogen fluoride might be expected to have properties closely related to hydrogen chloride and tu water, but they do not catalyze the Condensation reactions effectively A relation to these substances, however, is seen in the reactions of hydrogen fluoride with double-bonded organic com pounds and with acyl halides. Some striking differences exist between the use of hydrogen fluoride and sulfuric acid for condensation reactions which, from the point of view of industrial utilization, are in the favor of hydrogen fluoride. Sulfuric acid has a great tendency to sulfonate organic substances, particularly the aromatics, and undesired sulfonated residues are formed. I n spite of the fact that under suitable conditions hydrogen fluoride can add to organic compounds, it cannot react in a manner similar to sulfonation because it contains no oxygen. Also, in none of the condensation reactions has fluorine-containing products been found. Sulfuric acid is also an oxidizing agent, and the oxidation of strongly reducing organic compounds results in reduced yields of desired prodiicts and in obnoxious residues.
In addition to condensation reactions, hydrogen fluoride is an effective fluorinating agent in certain cases. It reacts readily with acid halides (7’) to form the acid fluoride and the hydrogen halide. Acetyl chloride and hydrogen fluoride rapidly form acetyl fluoride and hydrogen chloride. With acid anhydrides hydrogen fluoride forms the acid fluoride and the acid. Acet’ic anhydride does this readily. Alcohols do not react with hydrogen fluoride to form the alkyl fluoride and water a t low temperatures. I t is reported (14) that a t 140’ C. ethyl alcohol reacts with hydrogen fluoride to form ethyl fluoride. Benzotrichloride (28) reacts with liquid hydrogen fluoride a t 0” C. slowly and progressively to replacr the chlorine with fluorine. The final product i s benzotrifluoride : C&CC13
+ 3HF
C6HhCF3 + 3HCI
Similarly to the other halogen halides, hydrogen fluuridr can be caused to add to the double bond between two carbon atoms (10). In this way ethyl fluoride has been made from ethylene, isopropyl fluoride from propylene, cyclohexyl fluoride from cyclohexene, and n-propyl fluoride from cyclopropane. I n these reactions polymerization of the olefins also takes place, but conditions can be adjusted to favor one or the other of the reactions. Addition to the triple bond between carbon atoms has also been reported (9); and the following compounds have been made by this method: 1,l-difluoroethane, 2,2-difluoropropane, 2,2-difluorobutane, 2,2-difluoropentane, 2,2-difluorohexane, 3,3-difluorohexane, and 2,2difluoroheptane. Hydrogen fluoride is also used in conjunction with antimony fluoride, zinc fluoride, or other metallic fluorides as a catalyst to replace chlorine with fluorine in organic compounds. Dichlorodifluoromethane is made in this manner.
Chemical Properties From the condensation reactions caused by hydrogen fluoride it must be concluded that, although similarities are noted between it and other acidic condensing agents such as sulfuric
Courtesy, Harshaw Chemical C o m p a n y
CONTAINERS OF ASHYDROUSHYDROGEN FLUORIDE
On the basis of the structure of the molecules it is difficult to see any analogy between hydrogen fluoride and aluminum chloride, which would account for the fact that in condensation reactions hydrogen fluoride catalyzes those reactions promoted by aluminum chloride and boron fluoride. These two substances have (as in the case of boron fluoride) or are in equilibrium with (as in the case of aluminum chloride) molecules in which a n atom contains a valence shell of six electrons, and therefore has a tendency to attract and hold
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 32,NO. 2
TABLEI. PHYSICAL PROPERTIES OF COMMON CONDENSING AGENTSO Formula Weight t?roms
HF b
20
Freesing Point C. -83(16)
Boiling Point O
c.
19.4
Heat of Reaction with Exoesa Water Cot. per formulo wt. 6,030(4. 86) 11,560 ($1) 12,000 17,800at 18’ C. Heat of Vaporiration
Density G./cc.
C. ( 8 6 ) HzSOI 9s. 1 IO.5 Decompn. 1.834 at 20° C. 116.1 8.62 290 HzS01.Hz0 ..... ...... 1.842 at ICa C. AlCla 133.3 194 183 27,500 78,000 2.44 at 2 5 O C. 67.8 -127 -101 .... 24,000 ..... BFa 0 Data obtained from the International Critical Tables unless otherwise noted. b Liquid hydrogen fluoride also has an extremely low surfaoe tension ( 8 6 ) and a high fluidity,
the valence electrons of other molecules. This has been held responsible for their property in causing condensation reactions. Although the structure of hydrogen fluoride is unknown, i t cannot be considered similar t o aluminum chloride. It does have great tendencies to combine with itself and other substances; but this alone cannot be entirely responsible for the effects, since water also has this property to a marked extent but is not known to be effective in promoting condensation reactions. There are some differences in the use of hydrogen fluoride and aluminum chloride which are greatly in favor of the industrial utilization of hydrogen fluoride. Aluminum chloride has a great tendency to couple aromatic compounds together and form tarry residues. Hydrogen fluoride does not do this. It also has much less tendency to cause rearrangement of aliphatic chains. There are other differences between the use of aluminum chloride and hydrogen fluoride, The former easily and readily causes acyl halides to react with aromatic compounds; the latter does this only a t higher temperatures and with more difficulty. The former can be used only with difficulty to cause carboxylic acids or alcohols (usually with the formation of a halide or complex halide first) to react with aromatic compounds; the latter does this readily. Certain reactions have already been found that are promoted by hydrogen fluoride but are not favorably catalyzed by any of the other condensing agents. , Although hydrogen fluoride causes the “ p e d ’ condensations (2) promoted by sulfuric acid, it also causes some which are not. For example, perylene was obtained from the reaction products after phenanthrene was condensed with acrolein in the presence of hydrogen fluoride. Isopropylnaphthols, isopropylnitronaphthalenes, isopropylhydroxynaphthoic acids, isopropyl hydroquinones, and isopropylbenzoic acid, as well as alkyl anthracenes and alkyl phenanthrenes, have been made with hydrogen fluoride. It is reported (3) that they have not been prepared with any other condensing agent. For intermolecular acylations (6) it has been found that certain of these compounds are caused by hydrogen fluoride that are not promoted by any other reagent. An example is given under the heading “special reactions”. Also, acenaphthene (6) acylates chiefly in the 1 position with acetic acid and hydrogen fluoride, whereas other reagents cause the acylation chiefly in the 3 position. As further work is done, other reactions specifically catalyzed by hydrogen fluoride will undoubtedly be found. The use of hydrogen fluoride to promote condensation reactions, although similar to the use of other reagents, is also different from any of them, as the above examples show. The syntheses promoted by it, therefore, cannot be considered as Friedel and Crafts reactions. This name is also usually restricted to condensations catalyzed by aluminum chloride or other metallic halides.
Physical Properties Even if hydrogen fluoride had no advantages from a chemical point of view, such as improved yield, etc., but would
1 .Oat O n
nearly duplicate the action of other reagents, it would replace them in industrial use if its physical properties would lead to simpler and more economical processing. Table I gives simple physical properties of common condensing agents. Technical advantages for the use of hydrogen fluoride are immediately obvious from a consideration of its physical properties. Its low formula weight gives more effective chemical per pound than any of the other agents. It also has more formula weights per unit of volume. Both of these factors will result in smaller containers and equipment. With its low freezing point it need never be handled as a solid, regardless of how low the temperature required in the process may be. Its convenient boiling point near room temperature enables it to be handled as a liquid or gas. Its addition and removal from reaction and storage vessels can be done entirely through pipes and controlled by valves. It can be stored a t high concentration without excess pressure, such as must be used with boron fluoride. Even for reactions a t 100” C. it can be retained as liquid in the reaction vessel without abnormally high pressures. Its vapor pressure at 50’ C. is only about 2.5 atmospheres. The difficulties of handling a hygroscopic salt such as aluminum chloride will never be experienced with hydrogen fluoride. If it is necessary to add water a t any stage of the process, less heat will be evolved per formula weight in the case of hydrogen fluoride than with any of the other agents, and less cooling will have to be provided. If it is possible to remove the agent by vaporization, less heat will be required for hydrogen fluoride than for sulfuric acid or aluminum chloride. Its high fluidity and low surface tension will enable the liquid to flow rapidly, and smaller pipes and valves will be required for it than for sulfuric acid. Coupled with its chemical properties, its boiling and freezing point will result in further economies in industrial practice. The freedom from the formation of tarry residues and sludges and the complete liquid solution of the products in most reactions will enable them to be completely and clearly drained from the reaction vessel. I n the separation of the products from the reaction mixture when hydrogen fluoride is used, it will, in general, not be necessary to add water. Technical advantages of great importance will thus be obtained. The hydrogen fluoride will be removed by distillation in most cases. Its temperature of boiling is so low that it can be vaporized without injury to the desired product or the formation of obnoxious substances. This will undoubtedly result in further economies. Besides saving a number of steps in the total process, the hydrogen fluoride can, in most cases, be recovered for further use. This is not true for any other agent. In addition, distillable products can be separated in the same distillation. Should the starting substances be distillable and the reaction not go to completion, they can be recovered a t the same time. With most other condensing agents in most reactions, any of the starting materials not used are lost in the process. The over-all yields of desired products should therefore be greatly increased. With the ability to recover the starting materials and little loss of them in the formation of undesired residues, over-all yields of products should be extremely high.
INDUSTRIAL AND ENGINEERING CHEMISTRY
FEBRUARY, 1940
Materials of Construction of Equipment Although an aqueous solution is acidic, the anhydrous liquid when pure is without action on most metals. I n fact in this respect it is very similar to water. It reacts with the alkali metals but not with magnesium or aluminum. I n the absence of oxygen or other oxidizing agent there is no appreciable action on copper, iron, or nickel. Alloys such as stainless steel, Alone1 metal, etc., are quite resistant. Brass withstands the pure liquid or gas but is rapidly acted upon in the presence of water or oxygen. The same is true of lead, soft solder, etc. In laboratory condensation experiments reaction vessels have been made of copper, steel, stainless steel, nickel, platinum, etc. The most satisfactory is copper. When iron vessels are used, tarry residues are formed that are absent when copper vessels are used for the same reaction. We have concluded that the iron fluoride formed on the surface of the vessel promoted the undesired Friedel and Crafts type of reaction with the resulting formation of tar. This will probably be true of any iron- or nickel-containing reaction vessel. Steel containers, pipes, valves, etc., for anhydrous hydrogen fluoride are, however, satisfactory as long as the condensation reactions are not carried out in them. Commercial steel pipe may be used with screw joint fittings; if flanges are used, they should be made of forged steel. Welding is excellent for making connections provided slag-free welds are obtained. Cast iron cannot be employed or any material containing silica. Numerous difficulties have been encountered in the use of cast iron fittings. Many substances react vigorously with anhydrous hydrogen fluoride, and they should not be used a t any point where they come in contact with this substance. Glass, quartz, porcelain, refractories, and any silica-containing material are rapidly attacked. Cellulose-containing substances are dissolved with reaction, and wood will not withstand its action. All natural and synthetic resins, gums, plastics, etc., tried in this laboratory are attacked by the anhydrous material. Hydrogen fluoride is a relatively inexpensive chemical, when the number of formula weights per pound are taken into consideration. Today’s prices are approximately as follows: In small cylinders for experimental work the liquid is available a t $1.00 per pound in 6-pound quantities with a n extra charge of $10.00 for the cylinder. In 100-pound cylinders the price is 50 cents a pound. If there is demand for the material in large quantity, the price may go as low as 20 cents a pound. Table I1 compares the cost of hydrogen fluoride with that of sulfuric acid and aluminum chloride. On a formula weight basis this compares favorably with sulfuric acid and is much
TABLE 11. COSTCOMPARISON Price, Cents Formula Wt. per Lb. per Lb. Hydrogen fluoride Large quantitiea 100-lb. cylinder
20 50
1
Price, Cents per Formula Wt.
22.7
Sulfurio acid
Technical, in quantity c. P., In carboys
Aluminum chloride Minimum Frequent
4.6
la
1
3.4
less than aluminum chloride. Since hydrogen fluoride can be recovered from a condensation reaction mixture, whereas both sulfuric acid and aluminum chloride cannot, it should be the least expensive reagent to use. This is in addition to the other advantages which the use of hydrogen fluoride seems
183
to promise, such as higher yields from a simplified and more economical technique. Caution The use of any powerful chemical is accompanied with danger. This is true of hydrogen fluoride, although the danger of handling it is probably overestimated. It is corrosive to living tissue and causes burns if allowed to come in contact with the skin. Inhaling the vapors is dangerous. However, the vapors are acidic, and are readily detected and easily neutralized. If contact is made with hydrogen fluoride, the parts should be immediately and thoroughly washed, since it absorbs rapidly and pain may not be experienced until 5 to 8 hours later. If the parts affected are small, calcium hydroxide paste should be immediately applied; it can be replaced later with a salve of calcium lactate or glutonate, magnesium oxide, or a combination of them. The salve should be kept moist and must contain no oil or grease. If the parts affected are large, an aqueous solution of ammonia can be used as a wash, to be followed by the calcium or magnesium salve. This treatment is based upon the principle that it is important both to neutralize the acid and precipitate the fluoride ion and to do these quickly. If so treated, wounds will not be severe and no great pain experienced. They will be milder than heat burns caused by hot sulfuric acid or hot salt. Because of the low boiling point, it is impossible to have hot liquid hydrogen fluoride. When properly understood, hydrogen fluoride is not as dangerous as many chemicals used on a large scale. In the use of aluminum chloride and also sulfuric acid there is considerable danger.
Acknowledgment Information concerning the industrial preparation, handling, and cost of hydrogen fluoride was supplied by the Harshaw Chemical Company, Cleveland, Ohio.
Literature Cited (1) Cady and Hildebrand, J . A m . Chem. Soc., 52, 3843 (1930). (2) Calcott, Tinker, and Weinmayr, Ibid., 61, 949 (1939). (3)Ibid., 61,1010 (1939). (4) Claussen and Hildebrand, Ibid., 56, 1820 (1934). (5) Davy, Trans. Rog. SOC.(London), 103,263 (1813). (6) Fieser and Hershberg, J . A m . Chem. Soc., 61, 1272 (1939). (7) Fredenhagen, 2.physik. Chem., A164, 190 (1933). (8) Fremy, Ann. chim. phys., [ 3 ] 47,5(1856). (9) Groase and Linn, Baltimore Meeting, A. C. S.,April, 1939. (10) Grosse and Linn, J . Org. Chem., 3,26 (1938). (11) Hughes, M.S. thesis, Penna. State Coll., 1939. (12) Klatt, 2. physik. Chem., A173, 115 (1935). (13) Margraff, “Memoires de Berlin”, p. 3 (1768). (14) Meslans, Compt. rend., 111,882(1890). (15) Simons, Chem. Rev., 8 , 213 (1931). (16) Simons, J . A m . Chem. Soc., 46, 2179 (1924). (17) Simons and Archer, Ibid.. 60, 986 (1938). (18)Ibid., 60,2952 (1938). (19)Ibid., 60,2953 (1938). (20) Ibid., 61,1521 (1939). (21) Simons, Archer, and Adams, Ibid., 60, 2955 (1938). (22) Simons, Archer, and Passino, Ibid., 60, 2956 (1938). (23) Simons, Archer, and Randall, Ibid., 61, 1821 (1939). (24)Ibid., to be published. (25) Simon8 and Bouknight, J . A m . Chem. Soc., 54, 129 (1932). (26)Ibid., 55, 1458 (1933). (27) Simons, Fleming, Whitmore, and Bissinger, Ibid., 60, 2267 (1938). (28) Simons and Lewis, Ibid., 60, 492 (1938). (29) Simons, Randall, and Archer, Ibid., 61,1795 (1939). (30) Spiegler and Tinker, Ibid., 61, 1002 (1939). (31) Wartenberg. von. and Fitaner. 2. amrg. allgem. Chem.. 151, 21 (1926).
INDUSTRIAL AND ENGINEERING CHEMISTH’I
Views of s p r a y - p a i n t i n g booths in the dope room of the Curtiss Aeroplane Division at Buffalo, N. Y. All b o o t h s h a v e a continuous water curtain at the back. operated in connection with the exhaust system, to remove any excess dnpe nr paint.
VOL. 32, NO. 2
