LABORATORY PREPARATION OF NORMAL ALKYL BROMIDES1 LIONEL JOSEPH, MELVYN K. ROSS, and WILLIAM G. VULLIET San Diego State College, San Diego, California
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preparation of normal alkyl bromides is generally included in manuals of organic laboratory practice (1-3). The examples chosen are usually ethyl bromide and n-butyl bromide. In one case (1) the statement is added that other normal alkyl bromides may be prepared in a similar manner provided that appropriate changes are made in the procedure. The present work has two objects: first, to investigate the conditions for the preparation of n-butyl bromide with a view to modifying the procedure as commonly given in laboratory manuals; second, to determine the conditions for the preparation of normal alkyl bromides other than ethyl bromide and n-butyl bromide. For the accomplishment of these objectives, directions for the preparation of n-butyl bromide were selected from a standard manual (1). In these directions n-butyl alcohol is boiled for a period of two hours with a slight excess of potassium bromide and sulfuric acid. The original directions call for the addition of two-thirds of the acid a t the commencement of the experiment and the remainder after thirty or forty minutes. In the present work the acid was added in one portion a t the beginning of the experiment. Table 1 gives the yields of n-butyl bromide obtained when the period of boiling was varied. The n-butyl alcohol used was Baker & Adamson, Reagent Grade. Each run was carried out on a scale of one-half mol of the alcohol. TABLE 1 n-BUTYL BROMIDE Boiling Range 99.6-100.6'C.
Reflux time (hours) Yield (grams) Yield (per cent)
(Urn.); na0n 1.4334
*
g
0.25
0.50
0.75
1.00
1.50
2.00
52 76
57 83
58 85
59 86
59 86
58 85
and the fraction boiling between 134135°C. was used. The data obtained from these alcohols are shown in Tables 2 and 3. TABLE 2 n-PROPYL BROMIDE Boiling Range 70--71.5'C.
Reflux time (hours) Yieldbarns) Yield (per cent)
(Urn.); nSon 1.4330
0.25
0.50
0.75
1.00
1.50
2.00
47 77
51 83
53 86.5
53 86.5
53 86.5
53 Xfi.5
These values show that the maximum yield of npropyl bromide was obtained in three-quarters of an hour and that a satisfactory yield, about ten per cent lower, was obtained in fifteen minutes.
Boiling Range lZ?6-ld7"C. (Une.); nWln 1.4443
Reflux time Ihm>x\
Yield (grams) Yield (per oent)
0.25 50 66
0.50 0.75 55 56 73 74.5
1.00 59 78
L
Z?
1.50 59 78
2.00 59 78
These values show that the maximum yield of namyl bromide was obtained in one hour. A satisfactory yield, twelve per cent lower, was obtained in fifteen minutes. In half an bour of boiling the yield was only five per cent lower than the maximum yield. From the results obtained in this work it can be concluded that, for the normal alcohols studied, reasonable yields are obtainable in fifteen minutes. This agrees essentially with the statement of Kamm and Marvel (4) that such yields are obtainable in this period. However, highly satisfactory yields can be obtained in thirty minutes. It is believed that, from a teaching standpoint, a period of boiling longer than this is unsatisfactory. Ordinarily the student remains idle during a period of reflux and the slight additional yield obtained from a longer reflux period is of little educational value. In addition a shorter reflux time permits the student to complete the experiment in a three-hour laboratory period.
These results show that the maximum yield of 1 ~ butyl bromide was obtained in one bour and that a satisfactory yield, only ten per cent lower, was obtained in fifteen minutes. The same procedure was carried out using n-propyl alcohol (Eastman Kodak Co. No. 848) and n-amyl alcohol (Eastman Kodak Co. No. 568). The n-amyl alcohol was distilled through an 18-in. Vigreux column LITERATURE CITED 'Presented before the Division of Chemical Education at the 115th meeting of the American Chemical Soeiety in San Francisco, March 2eApril 1, 1949.
&(I) ROBERTSON, G . R., "Laboratory Practice of Organic Chemistry," Rev. ed., Macmillm Company, New York, 1943. PORTER, C . W., AND T. D. STEWART, "Organic Chemistry
330 for the Laboratory," Ginn & Company, New York, 1943. (3) COGEILL, R. D., AND J. M. STURTEVANT, "An Introduction to the Preparation and Identification of Organic Corn-
JOURNAL OF CHEMICAL EDUCATION pounds," 1st ed., McGraw-Hill Book Company, Inc., New York, 1936. (4) B u r r , A. H., "Organic Syntheses," 2nd ed., John Wiley & Sons, New York, 1944, Vol. 1, p. 32.
