NEW LABORATORY PREPARATIONS FOR THE COURSE IN ORGANIC CHEMISTRY. II.* DECANE FROM N-AMYL BROMIDE BY THE WURTZ REACTION HARRY F. LEWIS? AND MARTHATRYON, OHIO WESLEYAN UNIVERSITY,DELAWARE,
OHIO
An important organic synthesis is that of the formation of higher aliphatic, mixed aliphatic-aromatic, or higher aromatic hydrocarbons by the reaction discovered independently by Wurtz (1)for the aliphatic compounds and by Fittig (2) for the mixed aliphatic-aromatic compounds. Student preparations, illustrative of this reaction, ordinarily require the presence of dry solvent ether. This necessitates operations involving the drying of ether; in addition, the presence of ether in the reaction mixture slows up the reaction so that one laboratory period is used in carrying on the condensation and much of the second period in recovering.the product from the reaction mixture. The author feels that there is just as much to be gained by a shorter preparation and is giving the laboratory details for the preparation of decane from n-amyl bromide as an illustration of such a preparation. The method for preparing the alkyl bromides by the action of concentrated sulfuric acid and sodium bromide on the alcohol, as outlined in "Organic Syntheses, Vol. I," has been modified and directions are also given for this reaction as a student preparation in place of the more common preparations of ethyl or butyl bromides.
Amy1 Bromides The alcohol used as a starting point in tfie synthesis is the n-amyl alcohol furnished by the Sharples Solvents Corporation. The material which is 80-90% n-amyl alcohol and contains as its chief impurity iso-amyl alcohol (3-methyl butanol-1), is satisfactory for general student use although if i t is desired to prepare a product of higher purity, this may be accomplished by careful fractionation. The alcohol as used in the following work boiled between 136-136.5'. The directions for a class for the preparation of amyl bromide (3) are as follows: Set up a 5W-cc , round-bottom, short-neck flask, condenser, and addition tube, with the condenser in the reflux position on the slanting arm of the addition tube. Fit a dropping funnel with a rubber stopper of such size as will he taken by the upright arm of the addition tube. Before putting in the dropping funnel add 27 cc. of water t o the flask and then follow this by stirring in 31 grams (0.3 mol) of finely powdered sodium bromide. This must he carried out as directed or the bromide will form a hard cake. Twenty-two grams (0 25 mol) of n-amyl alcohol are next added. Now connect the dropping funnel and condenser and run in through the dropping funnel, shaking the contents of the flask occasionally, 40 grams (about 0.4 mol) of concentrated sulfuric
* For I, see J. CHEM.Eouc., 7,856-8
(Apr., 1930).
t Now located a t The Institute of Paper Chemistry, Appleton. Wisconsin. 2712
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acid. Reflux the mixture for two hours, set the condenser for distillation, and distil until the distillate is free from oil. Separate this, wash with water, then with 20 grams of cold concentrated sulfuric acid and finally with a 5% sodium carbonate solution. Ihy thr amyl bromide over calcium chloridc and distil, collecting thc frnction hrterrn 12G-120" as amyl hmmidc. The yield will be about (i0'.& of the theoretiwl.
Decane The mechanism of the Wurtz reaction has been very thoroughly considered by Bachman and Clarke (4). The influence of operating conditions in the preparation of octane has also heen considered by Lewis, Hendricks, and Yohe (5). These papers should be consulted for details. Two reaction mechanisms are used to account for the products of a Wurtz condensation. One involves the formation of the sodium alkyl through the action of sodium on the alkyl halide. This condenses with the remaining halide to form the hydrocarbon (I). (I) R-X + 2Na +R-Na + NaX R-X + RNa --+ R-R + NaX In the second a free alkyl radical is formed by the action of sodium on the halide; two free alkyl radicals then may combine to form the hydrocarbon (11). (11) R-X + Na +R' + NaX R ' + R' +R-R
The reaction between n-butyl bromide apd sodium is too violent for general student use in the absence of solvent ether; n-amyl bromide will work rather well in the absence of the ether-hence it is possible to carry out the greater part of this preparation within one laboratory period. With n-amyl bromide the principal product is decane; in the presence of an excess of sodium very little unchanged amyl bromide remains and the fractionation proves to be rather simple. The directions for a class for the preparation of decane are as follows: Set up a 500cc. round-bottom, short-necked flask, condenser, and addition tube, with the condenser in the reflux position in the slanting arm of the addition tube. Select a tight-fitting rubber stopper for closing the straight arm of the addition tube. Now run in 30 grams (0.2 mol) of amyl bromide and then through the straight arm add slowly and in small pieces 7 grams (0.3 mol) of sodium. The sodium is added fast enough to keep the mixture rduxing; the neck of the addition tube is stoppered after each addition of sodium. Toward the end of the reaction the mixture becomes a pasty blue mass. After the sodium has all been added and the readion has moderated, cautiously warm t o a reflux temperature and maintain a t this point for 15 minutes additional. Now cool the flask in a water-bath and n m in 150 cc. of ether; this should cover the reaction mass. Replace the stopper in the upright arm of the addition tube with a 60-cc. dropping funnel and slowly add water a drop or two a t a. time to destroy the sodium. When the reaction is complete, the sodium will have disappeared and the sodium bromide will be completely dissolved in the lower aqueous layer. The decane i s found in the top ethereal layer. Separate this, dry with calcium chloride and fradion-
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ate, the portion distilling between 160-175' is collected as decane. On redistillation a product boiling between 170-174' (cor.) is recovered. The yield is about 55.65% based on amyl bromide.
Observations 1. The first piece of sodium added will become blue, begin to swell and then as the temperature of reaction causes it to melt will appear to erupt from within very much in the manner of popcorn. As soon as this has happened, it is safe to add the next piece of sodium. These should he no larger than a small pea. 2. The blue color (possibly due to an unstable modification of sodium bromide) remains throughout the condensation but rapidly disappears as water is added. 3. If water is not added too rapidly, this method for destroying sodium is safe. The senior author has used it on reacting masses in 5-liter flasks and considers it much more satisfactory for general use and much safer than the common practice of distilling from the reaction mass. Under some conditions this latter procedure is extremely hazardous. 4. The decane thus prepared, while containing small amounts of 2,7-dimethyl octane as an impurity, is satisfactory for many purposes, such as a material for use in testing properties of aliphatic hydrocarbons and as one component for a study of certain types of boiling-point curves. This method of preparation for decane has the advantages that no dried ether is required as a solvent and the reaction may he completed in one laboE ratory period.
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The author wishes to acknowledge the advice and help of the Sharples Solwen& Corporation i n connection with the prefiaration of a satisfactory n-amyl alcohol. Literature Cited (1) W m r z , Ann., 95, 365 (1855). (2) TOLLENS and F I T ~ Gibid., , 131,3031 (1864). (3) "Organic Syntheses." John Wiley & Sons, Inc., New York City, 1921, Vol. I, pp. P 5 . and CLARKE,3. Am. Chem. Sac.. 49,2089 (1927). (4) BACRMAN and YO=, ;bid., 50, 1993 (1928). ( 5 ) Lewrs, HENDRICKS,
Indian Hemp, Common Weed, Possible Source of Rubber. A victim of disparagement for many years, Indian hemp, a common weed, has a t last been given a place in the society of plants of economic value. Scientific research, according to the Missouri Botanical Garden Bulletin, has remaled that the weed, known scientifically as Apocynum, bas rich rubber content. "One of the most significant factors concerning the study of the latex of Apocynum," says the Bulletin. "is that the rubber content increases t o a large extent with drought and infertility of the soil."-Science Service
