James A. Garrison State Universitv of N e w
York
Buffalo, N e w York 14214
I 1
lndene Reactions An organic chemistry laboratory problem Indene was treated with bromine in aqueous KBr solution to form the bromohydrin. This proved a good test of technique as too rapid addition or too little mixing results in an oily product probably due to formation of some 1,2-dibromoindan. After refluxing with water, good yields of the bromohydrin are obtained. The bromohydrin was treated with concentrated potassium hydroxide to obtain the epoxide (IV). The epoxide is a low melting solid which is best purified by distillation under reduced pressure. Treatment of the epoxide with 48% hydrogen bromide solution gave black tars; so we tried anhydrous HBr in anhydrous ether solution, but again only tars were obtained. Several other methods were nsed hut to no avail. The addition of HBr to the epoxide was not accomplished, nor was the formation of bromohydrin 111. We then shifted our attention to removal of the bromine and identification of the resulting alcohol. The bromohydrin was debrominated by hydrogenolysis in a Parr Hydrogenation apparatus using Raney Ni catalyst and magnesium hydroxide (6). Whitmore and Gebhardt report isolation of polymorphic forms of 1indanol (V) melting at 40.5 and 52.5. Our method of isolation gave only the higher melting form. For comparison purposes, 1-indanol could be made by reduction of 1-indanone (VII) with sodium horohydride and kindanol by the hydroboration-oxidation reaction with indene. Only the second reaction was done by the entire class. Infrared spectra and mixed melting points were nsed to show that debromination of the bromohydrin gave 1-indanol. While these reactions may not unequivocally prove the structure of the bromohydrin, they support strncture I1 in preference to structure I11 and have served the purpose of involving students in a real problem. The first response to the failure to synthesize I11 was a let down of morale. Recovery was quick, however, as other reactions worked and it became apparent that structure I1 should be assigned.
Interest in a problem-oriented organic chemistry lab has been growing during the past several years (1-3). This type of organic chemistry laboratory, which presents the student with a problem that he is capable of solving, has been used at the State University of New York at Buffalo with a class of 60 firstsemester sophomores (3 sections of 20 students). The problem selected necessarily involved the chemistry of rather simple systems. Only a knowledge of the chemistry of alkenes, alkyl halides, and alcohols was required with an awareness of the special properties imposed by the benzylic system. The problem was presented in the following way Indene (I)has an aromatic ring with an attached unsaturated, &membered ring. The double bond in the five membered ring is capable of most of the common resotiom of alkenes. In 1912, Pope and Read (4) reported that bromine in water reacted with indene to form a bromohydrin which was given the structure 11, 1-hydroxy-2-bromoindan. In Vol. 36 on page 764 of Chemical Abstracts there is the abstract of an article by P. Pfeifferand J. Hesse (6) in which the abstractor concludes that the addition of bromine in water leads to 111,2-hydroxy-1-bromoindan. The Problem: Who is right? Which compound is formed?
Several leading references were given (6-9) and the students were asked to recommend reactions and carry out those that helped establish the structures and, if possible, to synthesize both bromohydrins I1 and 111. There was much discussion about what reactions to try and what information would be gained from the reactions. These discussions involved everyone in the course; the instructor, the graduate assistant, and the students. The discussions were guided by the results obtained from some preliminary development experience with the reactions carried out in the summer of 1968 and during the early Fall semester of 1968. The reactions that were used are shown in the reaction scheme.
Experimental
IH
VI
300
V
/ Journal o f Chemical Education
-
v
V
-
W
P r e p a r d i a of I - h y d ~ o z y - 2 - b m d n(XI). Twenty grams of indene was suspended in 500 rnl of water in a one liter Erlenmeyer flask and enough detergent added to completely emulsify the indene. A mixture of 30 g of bromine in 300 ml of 10% KBr solution was added slowly enough, the bromohydrin separates as a solid. If the mix is not stirred or the bromine added too rapidly, a n oil sepma,tes. When the oil is refluxed with water for a short time, the bromohydrin is obtained. Yields Presented in part as Paper No. 14, Chemical Education Division. American Chemical Society National Meeting, April14, 1969, Minneapolis, ~ i n n e s o t a .
of product, mp 13(t131°C range from 50-80% after erystallieation from benzene. Prepamtion of I-Indanol ( V ) . To a solution of 5.6 g of magnesium chloride hexahydrate in 120 ml of 95% ethanol in a Paw Hydrogenation bottle was added 4.2 ml of 13 N potassium hydroxide and the mixture shaken to assure complete reaction. (11) and 3 g of Raney nickel Then 10 g of indenebr~moh~drin were added and the mixture :haken under n pressure of 50 psi of hydrogen until one equivalent of hydrogen had been absorbed. The mixture was filtered and the alcohol evaporated to a small volume. The alcohol mixture was diluted with 100 ml of water and extracted with ether. The ether extracts were dried over magnesium sulfate, filtered, and evaporated. The residual oil crystallized from petroleum ether, mp 5 2 3 % . Preparation of Z-Indanol ( V I ) . The method of Brown (10) was adapted as follows: Fifty ml of anhydrous tetrahydrofuran, 5 g of sodium borohydride, and 11.6 g of indene were mixed together in a 125 ml Erlenmeyer flask. To this was added a solution of 5.1 ml of boron trifluoride etherate in 10 ml of anhydrous THF, a t such a rate that the temperature did not rise above 25°C. After standing for about one hour, 10 ml of water was added to decompose the excess sodium borohydride. The reaction mixture was warmed to 40DC, 11 ml of 3 N sodium hydroxide was added followed by dropwise addition of 11 ml of 30% hydrogen peroxide solution. Finally, the reaction mixture wss saturated with sodium chloride, the layers separated, the organic layer dried over magnesium sul'ate, filtered, and evaporated. The oily, semisolid product was crystallized from petroleum ether (bp 3&60), mp 65-67'C. Preparatim of Indeneozide I V . The method of Whitmore and Gebhardt (6) was used and found to give good yields after distillation under reduced pressure.
Summary
This lab experience brought the student in contact
with vacuum distillation; recrystallization from a volatile solvent; handling of a low melting solid; the importance of reaction conditions to suecess of a synthesis; a hydroboration-oxidation reaction; a hydrogenolysis; a sodium borohydride reduction; a small ring compound; and, in the attempted addition of HBr to the epoxide, failure. All of which are part of the every day life of a working organic chemist. The lab was not an unqualified success. Some students did not like being "on their own," but the majority found the experience stimulating and felt they were really learning what organic chemistry was all about. Acknowledgment
The author wishes to thank the Division of Chemical Education of the American Chemical Society for a grant under the DuPont Small Grants Program to carry out the development of most of the experiments used in this work.
-
Literature Cited
(7) BUDOT, H., J ~ L I E NJ.,, llOR1) ~.""-,.
AND
L ~ B L A NE C...Bull. SOC.Chim. Fmnce, 41
(8) Smm, C. M., AND L m z , G . A.. J . Am. Chern. Sor., 60,1360 (1938). (9) Mouas~noa,M., Bull. Soc. Chim. Fvonce. I41 51,805 (1932). Bxown. H. C.. "Organic Reactions," John Wiley 6; Sons. Inc.. New Ymk. 1963, 13, P. 30.
(10)
vol.
Volume 47, Number 4, April 1 9 7 0
/
301
