A STUDENT EXPERIMENT ON THE OLEFINE HYDROCARBONS: THE INTERCONVERSION OF ETHYLDIMETHYLCARBINOL AND AMYLENE; THE POLYMERIZATION OF AMYLENE W. M. LEE,SHARPLES SOLVENTS CORPORATION, AND E. C. WAGNER, UNIVERSITY
OF
PENNSYLVANIA. PHILADELPHIA, PENNSYLVANIA
The experiment described includes (1) dehydration of tertiary amyl alcohol to amylene, (2) polymerization of amylene, both indefinitely and to diamylene, and (3) hydration of amylene to tertiary amyl alcohol. A11 three reactions are induced by sulfuric acid of suitable cuncentrations and at suitable temperatures, the experiment affording the student a n illustration of the influence of conditions in determining the course of a reaction. The reactions involved are all of both theoretical and technical importance. Certain of the results are signij'icant with respect to the mechanism of hydration and polymerization of olefines, these panis being briefly discwsed. Intrinsically and through the extension possible by laboratory quizzing, the ex9erimmt possesses great teaching mlue.
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The exercise described below illustrates in a simple and striking way three important general reactions: (1) formation of olefines from alcohols by dehydration, (2) formation of alcohols from olefines by hydration, and (3) polymerization of olefines. The starting material is tertiary amyl alcohol (ethyldimethylcarbinol), now readily obtainable as a product derived from the pentanes.* An interesting feature of the experiment is the fact that all three reactions are produced by action of a single chemical, uiz., sulfuric acid of properly selected concentrations and at favorable temperatures, thus illustrating the influence of conditions in determining the course of a reaction. The chemical basis of tbe experiment, and of the brief discussion which follows, is to be found largely in papers by Brooks and Humphreys (3) and Norris and Joubert (4). Like other tertiary alcohols, ethyldimethylcarbinol is very easily dehydrated to olefine, in this case by merely warming with 50% sulfuric add; in the cold the reaction is reversible. Polymerization of the amylene obtained occurs actively and almost instantly by contact with concentrated sulfuric acid, and unless a very small amount of acid is used the product is an indefinite mixture of polyamylenes boiling from about 150' to over 300°, and containing usually but little diamylene (b. p. 155'). Hydration to tertiary amyl alcohol, and polymerization to diamylene, are effectedby initially dissolving amylene in cold 6&730/0 sulfuric acid. The solution contains tertiary amyl alcohol, which can be isolated by saturation of the * Tertiary amyl alcohol (as well as 5 other amyl alcohols) can he obtained from the Sharples Solvents Corporation, Philadelphia. For technical preparation of these alca hols from the pentanes, see A m s (I)and CL~RK (2). 941
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liquid with ammonium sulfate (the alcohol separates as an upper layer), or by dilution and extraction with ether. If, however, the acid solution is warmed, diamylene separates as an upper layer. The selective conversion of amylene (2-methylbutene-2) to diamylene or to tertiary amyl alcohol is therefore determined by a moderate temperature difference. There is no evidence here that the amyl hydrogen sulfate is intermediate in polymerization or hydration of the olefine. On the contrary i t appears that the hydration involves direct addition of the elements of water a t the double bond, probably due to the influence of the acid present, and that by warming the solution the alcohol is dehydrated in such way as to couple two molecules of amylene:
Norris and Joubert obtained indications of a similar mechanism for the polymerization of three other amylenes by somewhat diluted sulfuric acid. For such cases "the accepted explanation of the polymerization, namely, that it consists of the condensation of the alkyl sulfuric acid and the unsaturated hydrocarbon, does not appear to be correct, . . . . because these hydrocarbons can be made to pass completely into solution as the alcohol or acid ester before polymerization begins" (4). The older explanation, however, appears to be more reasonable for polymerization by concentrated sulfuric acid, for in this case the small amount of water present and the high concentration of the acid favor formation of alkyl hydrogen sulfate but not of alcohol. It should be made clear to students that, while the reactions illustrated in the experiment are "general" for alcohols and olefines, the degrees of readiness with which they occur depend in large part upon the structures and molecular weights of the compounds. The dehydration of alcohol to olefine is relatively easy with tertiary alcohols ( 5 ) , and less so with secondary and primary. Conversely the reactivity of olefines with sulfuric acid is greatest with those of relatively complicated structure and less with those of normal structure. In the experiment here described, if nprimary amyl alcohol were used as the starting material, the dehydration to pentene-I, the polymerization of this, and also its hydration to alcohol, would all require more severe conditions, e. g., stronger sulfuric acid or higher temperatures. With tertiary amyl alcohol, however, these reac-
VOL.8, No. 5 EXPERIMENT ON OLEFINE HYDROCARBONS
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tions all occur with exceptional ease and smoothness, which fact has determined the choice of this alcohol for the experiment. Procedures A-Amylene from Ethyldimethylcarbinol. In a 200-cc. flask mix 50 g. of ethyldimethylcarbinol and 50 cc. of 50% sulfuric acid ( a cooled mixture of 20 cc. of 1.835 acid and 35 cc. of water). Attach a short fractionation column,* and to i t a water-jacket condenser with adapter. Use as receiver a tared flask externally cooled. Heat the mixture gently until distillation of amylene begins, and then regulate the flame so that the product collects a t a rate of 60-90 drops per minute and the temperature remains below 40". When distillation can no longer be maintained below this temperature withdraw the heat. The product, boiling mostly 37" to 3g0, is fairly pure amylene. A little water is present, and may separate in drops on standing, but it does not interfere with subsequent use of the amylene. The yield is 85% or more. Keep the amylene in the tightly stoppered flask in a cool place. Test portions (1 or 2 drops) for unsaturation by bromine in carbon tetrachloride, permanganate, fuming sulfuric acid, fuming nitric acid, and Deniges' acid mercuric sulfate reagent. B-Polymerization of Amylene. (1) Extensive Polymerization with Concentrated Sulfuric Acid. Measure into a small (60 cc.) separatory funnel 5 cc. (3.3 g.) of amylene, and cool well under the tap. Add 0.5 cc. of concentrated sulfuric acid, quickly stopper the funnel, and cool well. Alternately shake and then cool the mixture, relieving the pressure occasionally. After several shakings the polymerization may be considered complete. Note that the characteristic odor of amylene is now absent. Allow the mixture to stand for about 10 minutes, and draw off and discard the lower acid layer. Wash the oily layer with dilute sodium hydroxide solution and then with saturated salt solution (water forms a stubborn emulsion), and dry in the funnel with several lumps of calcium chloride. Decant the dried liquid into a small (10 cc.) side-arm flask, and distil, noting the full boiling range. The product usually starts to boil around 150°, indicating the presence of some diamylene, but the temperature rises steadily, and the last distillable portion may boil above 300'. The yield is about 2 g. (60%). Test a drop of the product with bromine in carbon tetrachloride. (2) Formation of Dhmylene.** In a small stoppered flask shake together, with cooling, 5 cc. of amylene and 4 cc. of 73% sulfuric acid (a cooled mixture of 2 volumes of 1.835 acid and 1 volume of water), until a homo-
* A 3-ball Snyder column is recommended for this distillation and for that in Part C. ** The preparation of diamylene from 37-39'amylene. by a procedure almost identical with that used by Norris and Joubert. and described here, was effected in 1871 by Schneider (6).
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geneous liquid results. The odor of ethyldimethylcarbinol replaces that of amylene. With the flask unstoppered warm the liquid gently until the upper layer which separates no longer increases. Transfer the contents of the flaskto a small (60 cc.) separatory funnel, and draw off and discard the lower acid layer. Wash the oily liquid with dilute sodium hydroxide solution, then with water, and dry in the funnel with several lumps of calcium chloride. Decant the liquid into a small side-arm flask and distil, collecting a 10' fraction. Most of the product should distil 155-158' uncorrected, and is apparently in large part the diamylene 2,3,4,4-tetramethylhexene-2 (b. p. 155'). The yield is about 70%. Test a drop with bromine in carbon tetrachloride. C-Hydration of Amylene to Tertiary Amy1 Alcohol (Reverse of A). Transfer to a separatory funnel 20 g. of amylene and 25 cc. of cold 68% sulfuric acid (1 volume of 1.835 acid and 0.7 volume of water*). Shake the stoppered funnel, cooling well under the tap, and occasionally relieving the pressure. Do not allow the mixture to become warm. The amylene dissolves to a clear liquid. Add about 50 cc. of water, and (ignoring the stratification whichoccurs) extract three times with ether, using in all about 50 cc. of ether. Shake the combined ether extracts with saturated salt solution, and run the ether solution into a small dry Erlenmeyer flask. Dry over night with lump potassium carbonate (anhydrous), decant the liquid into a second dry flask, and repeat the potassium carbonate treatment. Filter the liquid through cotton into a small short-neck flask, add several small pieces of hard coal or brick, and attach a short fractionating column. Distil off most of the ether on a water-bath, and then seat the flask on a perforated asbestos board and distil fractionally. Collect fractions as follows: (1) up to 70°, which may be discarded, (2) 70-95O, (3) 95-100°, (4) 10C-104", the last in a tared bottle. If fractions 2 and 3 are suficiently large, redistil them. The final yield of alcohol, boiling 10&104", should be about 17.5 g. (70%). If considerable liquid boils between 87' and 100°, even after redistillation, this shows the alcohol to have been incompletely dried. ** D-Purification of Amylene. Any remaining amylene may be washed with dilute caustic soda solution, then with water, dried over calcium chloride, and distilled from a small flask. A sealing-bottle of suitable size may be used as receiver. It should be cooled in water, and connected with the condenser by means of an extemporized capillary adapter. The liquid boilswithin arangeof 2",andmost of it between37-38'. I t is apparently 2-methylbutene-2, h. p. 38.4". The other amylene derivable fromethylThis acid :water ratio is essential for, except when the tap-water is very cold, a stronger acid leads directly to polymerization. '* The eonstant-boiling mixture contains 22% of water, and boils at 87.2".
VOL.8, No. 5 EXPERIMENT ON OLEFINE HYDROCARBONS dimethylcarbinol (assuming
945
no isomerization) is 2-methylbutene-1, b. p.
32".
Literature Cited ( I ) A Y ~ E S"Amy1 , Alcohols from the Pentanes," Ind. Eng. Ckem., 21, 899-904 (Oct..
1929). (2) CLARK,"High-Boiling Solvents from Natural-Gas Pentanes," ibid., 22, 4 3 9 4 3 (May, 1930). (3) BROOKS AND HUMPHREYS, "The Action of Concentrated Sulfuric Acid on Olefines, with Particular Reference to the Refining of Petroleum Distillates," J , Am. C k m . Soc.. 40,822-56 (May, 1918). (4) NORRISAND JOWBERT, "The Polymerization of the Amylenes," ibid., 49, 873-86 (March, 1927). (5) DAVISAND MURRAY, "The Aliphatic Tertiary Alcohols and Their Industrial Possibilities," Ind. Eng. Chem., 18, 844-6 (Aug., 1926). (6) SCHNBIDER, "Studien uher die Constitution des Amylens." Ann., 157, 185-226 (1871). Preparation of diamylene on page 207. See also MICRAELAND BRUNEI., "On the Relative Ease of Addition in the Alkene Group," Am. Chem. J.,41, 1 1 W 8 (Feh.. 1909).
