[CONTRIBUTION FROM
TEE RESEARCH LABORATORIES OF THE PRODUCTS COMPANY, RIVERSIDE,ILLINOIS]
UNIVERSAL OIL
THE ADDITION OF HYDROGEN FLUORIDE TO T H E DOUBLE BOND* ARISTID V. GROSSE
AND
CARL B. LINN
Received April 6, 19%
It is well known that the facility of addition of hydrogen halides to olefinic compounds decreases rapidly in the sequence hydrogen iodide, hydrogen bromide, and hydrogen chloride. Hydrogen fluoride has been reported as incapable of adding to olefins.’ Recent work in our laboratories by V. N. Ipatieff and one of the writers2 has demonstrated the direct addition of olefin to paraffin in the presence of such catalysts as boron fluoride with hydrogen fluoride. It has been assumed by us that the alkylation of paraffins involves an initial hydrohalogenation of the olefin, followed by a condensation of the paraffin with the alkyl halide, involving elimination of hydrogen halide. For instance,
+
CH2 = CH2 H F 4 CzH5F (CH&CH CzH5F + (CH3)3CC2&
+
+ HF
I n the investigation of this proposed mechanism it was discovered that the olefins studied readily add hydogen fluoride, according to the general scheme
I
/
-C=G
+ HF
-
I 1 I t
-C-C-.
H F The addition reaction is noncatalytic. It takes place equally as readily in the presence or absence of boron fluoride, and in steel, nickel, copper, aluminum, or paraffin vessels. The reaction is particularly suitable as a preparative method. It has been used successfully not only for hydrocarbons, but other compounds as well. The present study is devoted to the hydrofluorination of ethylene, propylene, and cyclohexene and the respective preparations of ethyl,
* Presented before the Organic Division of the American Chemical Society a t its ninety-fourth meeting, Rochester, N. Y., Sept. 6,1937. 1 See W. Bockenmueller, “Organische Fluorverbindungen,” Ferdinand Enke, Stuttgart, 1936,pp. 33 and 34. 2 IPATIEFF AND GROSSE, J . Am. Chem. SOC.,67,1616 (1935). 26
27
HYDROGEN FLUORIDE ADDITION
i-propyl and cyclohexyl fluorides. The formation of hitherto unknown tertiary alkyl fluorides, such as tert.-amyl and tert-butyl fluorides, was readily accomplished, but description is reserved for a subsequent publication. In view of the close chemical relationship of the lower cycloparaffins to olefins and the accomplishment of their catalytic addition to paraffinsa the reaction between cyclopropane and hydrogen fluoride, leading to n-propyl fluoride, was included in this investigation. In all cases studied a competing reaction is the formation of polymers (or hydrofluorinated polymers) , which under some conditions may predominate over simple addition. The polymers obtained, either directly during hydrofluorination, or by reaction of prepared fluorides, as well as the mechanism of polymerization, will be discussed in a separate publication. Suffice it to say here that all fluorides so far studied with the exception of ethyl fluoride are converted by excess of hydrogen fluoride more or less readily a t room temperature into polymers of the original olefin. In general the method employed for the gaseous olefins was to introduce the predetermined quantities of hydrogen fluoride into a bomb into which the olefin was then forced under pressure. Anhydrous hydrogen fluoride was used throughout this investigation. Fifty per cent. aqueous acid does not add to the olefins here described, but in some particular cases it may be used to advantage. With the exceptions noted in the experimental part the pressures used were about 10 atmospheres for ethylene and 3 atmospheres for propylene. 90" in the case of The temperatures employed ranged from - 60" to ethylene, and from 45" to 75' in the case of propylene. The yield of ethyl fluoride increased continuously with increase in temperature, but the opposite effect was observed in the cases of i-propyl and cyclohexyl fluorides. The length of contact time has no appreciable effect on the yield in the case of ethylene (see Table II), and only such effect as may be attributed to secondary polymerization in the case of propylene (see Table 111). The propyl fluoride obtained from propylene was that which would be predicted on the basis of Markownikoff's Rule and Kharasch's4 theory, namely i-propyl fluoride. The reaction of hydrogen fluoride with cyclopropane was conducted at 25" by successive additions of cyclopropane to a reaction system originally
-
+
+
s A. V. GROSSEAND V. N. IPATIEFF,reported before the Organic Division of the American Chemical Society a t its ninety-second meeting, Pittsburgh, Pa., Sept. 8, 1936; see Abstracts. 4 KHARASCH, ENGELMANN, AND MAYO,J. ORG. CHEM.,2,298 (1937).
28
ARISTID V. GROSSE AND CARL B. LINN
containing an excess of hydrogen fluoride. The product consisted of normal propyl fluoride, containing small amounts of the is0 fluoride. Under proper reaction conditions the olefins reacted to completion. The maximum yields obtained equalled 80-90 per cent. of the olefin charged. The analyses and some physical constants of the fluorides prepared, determined with the help of Mr. R. C. Wackher, are recorded in Table I. The fluorine determinations were made by burning the substance in excess air in a platinum tube and titrating the hydrogen fluoride produced. An exception was ethyl fluoride; it was analyzed by the more intricate Meslans6 method. A detailed description of the analytical method and more complete data on physical properties will be described in a separate publication.
ANALYS~S AND
TABLE I SOMEPHYSICAL CONSTANTS OF FLUORIDES
FLUORIDE
M.P.
Found
Cala'd
38 30.4 30.2 18.3
39.6 30.6 30.6 18.6
-143.2 - 159 -133.4 +13.0
B.P.
(780 mm.)
-37.7 - 3.2 -10.1 71.2 (300 mm.)
REFRACTIY E INDEX
n-'," n-: n-: n
1.3057 I .33% 1.3240 1.4147
:
EXPERIMENTAL
Description of apparatus-The hydrofluorinations of ethylene and propylene were carried out, unless otherwise indicated, in an Allegheny metal autoclave of 1200 cc. capacity, fitted with a mechanical stirrer and a pressure gage. The autoclave contained a close fitting nickel liner; the inlet and exit tubes, as well as the stirrer, were also of nickel. The reaction with cyclopropane was carried out in a duraluminum bomb of 250 cc. capacity. When superatmospheric pressures are not necessary the hydrofluorinations are best carried out in a copper flask or cylinder, fitted with copper stirrer and tubes. Isolation of reaction products.-The reaction products were usually siphoned over under pressure into a copper receiver, cooled with dry ice-acetone mixture to from -70" to -80". This receiver contained an excess of finely crushed ice to combine with the unchanged hydrogen fluoride; a line led from there through a soda-lime tower into a glass trap cooled t o about -80", and from there into a gas collecting bottle. The contents of the copper receiver were allowed to warm u p to room temperature during which time the gaseous fluorides boiled out and were recondensed in the glass trap. The polymers were separated from the aqueous acid in the copper 6
MESLANS, BUZZ.soe. chim., [a], 9, 109 (1893); 2.anal. Chem., 33,470 (1894).
29
HYDROGEN FLUORIDE ADDITION
receiver. The crude fluoride usually had a purity of over 95%. One Podbielniak distillation of the crude material gave a very pure product. Sources of reagents.-Hydrogen fluoride, obtained from the Harshaw Chemical Company, Cleveland, Ohio, was a C.P. product. It was water-white, and contained 0.1% or less of water. On evaporation it left a residue of less than 0.04%, containing some iron and copper. Ethylene, from the Ohio Chemical and Manufacturing Company, was over 99.5% pure. Propylene, from The Matheson Company, was !19% pure; 1.3640. Cyclohezene, c.P., from Eastman Kodak Company, n: 1.4457. Cyclopropane, from The Mallinckrodt Chemical Works, 99% pure, n;424 1.3799. BoronJEuoride, was originally prepared in our own laboratory, but was later obtained, compressed in cylinders, from the Harshaw Chemical Company. The C.P. product solidified to perfectly white crystals and contained only traces, if any, of silicon fluoride. Addition o j hydrogen fluoride to ethylene.-(A) Experiments in Allegheny metal autoclave.-In all experiments 10 g.-moles (200 g.) of anhydrous hydrogen fluoride TABLE I1 PREPARATION OF ETHYLFLUORIDE MOLE Mom '~~~~ HF:CzHd BFs:HF BATIO,
BXPT. NO.
BATIO,
m "D OF POLYYEBB
-__
6 7 8 9
81 45 49 55 27 22 0 49 22
100 92 97 100 95 100
