NEW LABORATORY PREPARATIONS FOR THE COURSE IN ORGANIC CHEMISTRY. I. DIETHYL. CARBINOL FROM ETHYL. FORMATE BY THE GRIGNARD REACTION HARRY F. LEWIS,OHIO WESLEYAN UNNRRSITY,DELAWARE, OHIO Although a large number of teachers of organic chemistry use a formal, printed laboratory manual in their laboratory work, many prefer to select their own preparations from the material available in the various textbooks and in the chemical literature. Laboratory directions are handed out by them to the students in the form of looseleaf sheets which may he altered from year to year and which permit a certain flexibility in regard to the introduction of new material as it seems desirable. The author is strongly in favor of the latter method. One important advantage to he gained by this method of laboratory instruction is the opportunity it affords to tie up the interests of the organic student with the research interests of the instructor or with the newer developments in the organic chemical literature of the present day. This may be accomplished either through a class preparation run parallel to similar work in the research lahoratory or through the use of methods which illustrate current work in the research laboratory. At the same time, it may furnish the instructor with a source of his research intermediates. The development of such an interest in research at this time in the edncational growth of the student is often of lasting value. As a by-product of these attempts to relate the teaching and research functions, several uncommon or verfr satisfactory lahoratory preparations for general student use have been worked out and the first of these is described in this report. Preparation of Diethyl Carbinol One of the research problems being carried on in the laboratory of the author is connected with the mechanism of the action of sodium on secondary and tertiary alkyl halides. The sources of these halides are the corresponding alcohols and in the case of the secondary alcohols of higher molecular weight, it is necessary to synthesize these. The most satisfactory method in general is the Grignard reaction. Thus diethyl carbinol can be prepared by the action of ethyl magnesium bromide and ethyl formate. Since the materials are inexpensive and the yields good, the method was turned over to the undergraduate class for study. General Directions.-The method used is essentially that of Grignard,' who treated two equivalents of ethyl magnesium bromide in ether with one equivalent of ethyl formate in ether, and decomposed the intermediate compound with a dilute acid solution. 1
Grignard, Comfit. rend., 132,336 (1901); Ann. Chim., 24,433 (1901). 8j6
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Materials Used.-Ethyl bromide, EK, dried over calcium chloride; ethyl formate, EK, dried over "dry" potassium carbonate; diethyl ether. CP, dried over calcium chloride and then over sodium; magnesium turnings. Directions for the Student.-To a 500-cc. round-bottom, short ringneck flask containing 12 grams (0.5 mol) of dry magnesium turnings, attach your addition tube equipped with a dropping funnel and a long r d u x condenser (20-24 inches). The dropping funnel is closed a t the top with a calcium chloride tube to prevent the entrance of moisture and for the same reason the inner tube of the condenser must he perfectly dry. After adding 60 cc. of dry ether to the magnesium in the flask, place a solution of 45 cc. (0.6 mol) of ethyl bromide and 30 cc. of ether in the funnel, close the funnel with the drying tube and add the mixture slowly to the contents of the flask. The reaction should start after the addition of a small amount of the mixture; in case it does not, add a crystal of iodine. It may be necessary to slow up the reaction by immersing the flask in a cold water bath. After the reaction is well started, add 125 cc. of ether carefully through the condenser. Since an excess of ethyl bromide is used, the magnesium should go completely into solution. When this is the case, cool the contents of flask with a cold water- or ice-bath, and add cautiously, and with shaking after each addition, a solution of 20 cc. (0.25 mol) of ethyl formate and an equal volume of ether. The reaction is complete in a short time to give a bluish grey, viscous solution. + Now cautiously decompose the addition product by adding slowly through the funnel 50 cc. of water; shake well while adding. Then slowly add a cooled solution of 16 cc. (0.3 mol) of concentrated sulfuric acid in 100 cc. of water. When all the acid solution is added and the greyish precipitate largely dissolved, separate the ethereal layer, dry with "dry" potassium carbonate and fractionally distil, taking the fractions (1) up to 50°, (2) from 5&100°, and (3) from 100-116°. Determine the refractive indices of these fractions and compare with those found or listed for the materials used and the one listed in the Critical Tables for diethyl carhinol. (Wbat substances may be in these fractions?) Redistil the last fraction, taking the diethyl carbinol between 113-116°. Calculate your yield from the ethyl formate used. Discussion of Results Twenty student preparations and three by the instructor using identical directions resulted in yields running from 37-71 per cent. The yield depends largely on two factors: the dryness of apparatus and materials and care used in fractionation. The average for the class was 57% and for the instructor, 70%. Careful fractionation of the ether recovered in
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all the preparations, using a five-foot special column, gave up sufficient diethyl carbinol to bring up the average yield of each group 8%. The diethyl carbinol thus prepared has a boiling point of 113-115°, and ng of 1.4110. Ether for use in this preparation may be prepared from the laboratory CP grade by drying over calcium chloride and then over sodium. There is some advantage to be gained in distilling this last product over phosphorus pentoxide. Good results are obtained with the halide dried over calcinm chloride and decanted and with ester dried over "dry" potassium carbonate and decanted and distilled. The main student difficulty added to these two factors appears to be a lack of sufficient agitation during the addition of the ester solution. The lighter ester tends to collect and float unless shaken after each addition; if enough thus collects, it reacts with violence when the mixture is next agitated and some material will be lost through the condenser.
The Mechanism of the Reaction Grignard in his early articles1 has postulated the reaction as taking place in three steps.
The by-product in (2) is C2Hs-OMgBrand in (3) is Mg(0H)Br. (Sulfuric acid is added to dissolve this latter.) These equations will he found in a number of textbook^.^ Reformatsky3 and a number of others have more recently suggested that in this reaction an aldehyde or ketone is formed as an intermediate product and that the alcohol results from this by hydrogenation. %Porter,"Carbon Cpmpounds," rev. ed., p. 417. Cnhen, "Organic Chemistry," 1919, pt. I, p. 211. a Reformatsky, J. Russ. Phys. C h a . Soc., 37, 881 (1905). Stadnikoff, Rer., 47, 2133 (1914); 57, 1-8 (1924). Boyd and Hatt, J. Chem. Soc.. 1927,898-1109.
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