The Oxidation of Terminal Alkenes by Permanganate A practical demonstration of the use of phase transfer agents Keith C. Brown, Victor S. Chang, . Fazal H. Dar, Shannon E. Lamb, a n d Donald G. Lee University of Regina, Regina, Saskatchewan, Canada S4S 0A2 The use of phase transfer agents to facilitate or accelerate chemical reactions has hecome an established practice, particularly in organic chemistry. A large number of review articles ( 1 ) as well as several hooks (21 on the suhiect have been published recenrly. The i m p o r m s e d t h e s e reaEtions suggests that a n effort should be made to develon tlndereraduate lah" oratory procedures which demonstrate the principles involved. This article describes one such orocedure that we have used with considerable success. The function of ohase transfer azents is to solubilize anions in organic solvenis by combining them with organophilic cations. For example, it is known that quaternary ammonium permanganates will readily dissolve in many organic solvents (3).Furthermore, it has been shown that permancanate ions will migrate from an aqueous or solid phase iutoan organic are solvent if tetraalkylammonium or phosphonium ions (Q+) present (eqn. [I]) (4). (A somewhat more elegant hut more expensive approach is to complex the potassium ion of KMn04 with a polyether (5)).
Phase Transfer Assisted Perrnanganate Oxidations ' Aikene
Product (Yield)
Characterization
Heneicosanaic acid (74%)
mp 70-75'. lit.
Nonedecanoic acid (72%)
mp 62-65', lit.
Heptadecanoic acid (64%)
mp 57-59-. lit.
Pemadecanoic acid (55%)
mp 49.5-50.2'. lit.
(12,75O
in 66-670
(13)60-61'
Nonanaic acid ( 7 ~ 5 % ) ~
( 13)53' mp 57.5-59.0°, lit. ( 13)58' bp. lit. (13) 121'14
Heptanoic acid (88%)
bp 106-1Io/5 ton. lit.
Tetradecanoic acid (68%)
tor, (13)115-116~111 Styrene
Benzoie acid (76%)
Undergradme sttdem resulU.
a me product was notdistllled. The yield rapcalculated onthe residua rematnlnganer
- .
.
In the oreanic nhase. where it exists as an ion nair (6).nermanganate will oxidize any reductant present. Compounds that have been successfullv oxidized usine this nrocedure include alkenes (7), alkynes-(7,8), alcohols-(9), aldehydes (5), and sulfides (10). . . Because of the intense color of permanganate solutions these reactions offer a unique opportunity for students to observe the phase transfer process. In the experiment we have used, students were asked to note the transfer of permaneanateiou from solid and aqueous phases into organic solvents containing phase transfer agents and then to carry out a typical oxidation reaction. The phase transfer agent that we have used is Adogen 464 (a trialkyl (Cs-Clo) methylammonium chloride). I t is quite inexpensive and functions very well with permanganate. The reaction that we have used is an oxidative cleavage of a terminal alkene to give the corresponding carhoxylic acid with one less carbon atom. In one narticular annroach we provided students in each section w i b a variety if'alkenes in order to make the purification procedures less routine. If more efficiency is required, it is recommended that l-eicocene or styrene he used. Both alkenes give solid products that are fairly easy to recrystallize. It was our experience that students could usually obtain the crude products in one laboratory oeriod. hut that nurification reauired Dart of a second neriod. kome bf the r e s h t s taken from' s t u d e k reports are s k m a rized in the table. Yields obtained by professional chemists have been reported elsewhere (11). Prior to the laboratory period each student was provided with a hand-out which summarized the hasic principles of phase transfer assisted reactions and contained the following experimental directions. Experimental Phase Transfer Demonstration Place about 6 mL of toluene and methylene chloride in twoseparate test tubes. Add a few milligrams of powdered potassium permanganate to each solvent. Shake and ohserve any changes in coloration.
696
Journal
of Chemical Education
lha aoivem had been euaoorated.
.,.A
Add 1-2 drops of Adagen 464 (a tetraalkyl ammonium chloride), shake. and eeain note anv ehanees in color. Placeatxut :( mLof tducne and methylme chloride in rwo separate test tubes. Add abour 3 1111. ~f watrrnnd a frw milliymm.iof powdercd putassiumpemnarlganatr toeach trst tuhr and ahckr well. Note thr location of the permanganate ion. Is it in the aqueous phase or the organic phase? Add 1or 2 drops of Adogen 464 to each test tube and shake again. Record your observations and conclusions. The Oxidation of a Terminal Alkene In a 500-ml.Krlrnmeyrr flask placr 0.0'2 molrs of a terminal alkene. 100 m l . disrillrd warrr, 2 ml. arrtic arid, 15 m l . 509 H,SOr, 0.5 g Adoern 4fi.I. and 100 ml. r~wthvlrncchloride. Add 0 062 rnolrs of K M ~ at O irate ~ of about 0.5 g every minute while swirling the flask frequently. Do not allow the temperature to rise above 30°; if it does, cool the flask in an ice hath for a few minutes. After all the KMnO4 has been added, heat the flask very gently on a steam hath while swirling continuously for 15min. If the solution is still purple, continue to heat the flask on the steam hath until the purple color disappears. Test the solution with pH paper. If it is not acidic, add 50% HzSOd dropwise until the solution is acidic. Cool the flask in an ice hath for a few minutes. Reduce the precipitated MnOa to soluble Mn++ions by adding 3 g of sodium bisulfite in small portions while swirling continuously.This should take about 10 min. Test the solution with pH paper again. Add 50% HzS04 dropwise to give a pH of 1-2. Decant the solution into a 500-mL separatory funnel and separate the two layers. Rinse thereaction flaskwith methylene chloride and extract the aqueous layer with 2 X 30 mL methylene chloride. Combine all the or~anic and extract with 2 X 30 mL distilled - ~ortions . water. Place theoreanic laver ina 250-mL beaker. Add boilineehios .. . and hem inn n rtenm hnrh uamg an inverted funnel cmnertecl r o a water aspirator u, remove the vapor. Continue m hear very gently until the volume uf the xdution has been reduced to abuut 4tl mL and then cool. Purify the product by recrystallization or vacuum distillation. Identify the product and calculate the yield.
Literature Cited i l l Gokel, G. W.and Web,,W.P , J Chem Educ..55,350,429 (1978).GokeI, G. W.and Dulmf H.D.Smlhesis, 1976.168 (19761.Jones,RA..Aldrichimico Acto.9.35 (197fil. Dahrnlow,E.V..Angew. Cham. I n l . Ed. Ewl., 13.170 119741; 16.493 (19771. (2) Web., W.P , and GokeI, G. W."Phase Transfer Catalysis in Organic Synthesis." Springer-Verlsg. New York, 1917. Starks, C. M. and Liotts, C., "Phase Transfer Catalysis. Principles and Techniques," Academic Press. New Yark, 1978. (31 Schmidt, H.J. and Schafer, H. JAnRem. Chem. Inf. Ed. Enel., 18.68 (19791. (41 Okimoto,T.andSwern. D. J Amer OilChrm. Sor.,S4,86ZA (1977).
(51 8srn.D. J. snd Sirnmons,H. E. J. A m r . Chem. See.,%. 4024 (19721. ~ e eD. , G. and Chan&V.S. J. OPE.Chom.,13,1532(1978). (6) R,dndrtrbm.A..Adu. Phys Olq. Chmt. IS,267 (1977). (71 Krapeho, A. P., Lsrson, J. R.,and F.ldridg8, J. M. J. Org, Chem., 1977, 42, 3749 (19771. (8) Lee, D. G. and Chsng, V. S., J. Oq. Chrm., 43,2726 (19791. (91 Herriott, A. W.and Picker, D.,Tetrahedron Lefterr. 1511 (197Q
Volume 59
Number 8
August 1982
697
