The Preparation,
Oxidation
and Characterization of an Unknown Secondary Alcohol
In an effort to blend a sequential set of reactions and elements of qualitative organic analysis, we have designed the following experiment. The experiment is assigned for the last three to four 3-hr laboratory periods of the first term of the beginning organic chemistry course. The fourth period is necessary if spectroscopic data are collected. Because of the time factor, we have usually obtained only the infrared spectrum of the alcohol or ketone primarily for additional student exposure to the technique and for s check on the purity of either product. Each student is given a measured amount of an unknown alkyl bromide which he is to convert to the eorresponding Grignard reagent. To insure the formation of enough Grignard reagent for complete reaction with an unknown aliphatic aldehyde, the student is given about twice as much alkyl bromide (-0.50 mole) as aldehyde (0.25 mole). One full lahoratorv. oeriod is necessarv for the completion of the Grignard portion of the sequence. During the next labora. tory period the student purifies hrs alruhol by disrillatiun, prepares a derivative of the alrohol and oaldues a portion of the aln,hul to the corresponding ketone. The third lahnrarury period is devoted to the irolation and purification of the ketone and tu rhe preparation of the ketone derivative. Standard procedures for carrying out there reactions can be found in most organic laboratory manuals. alkvl bromides and aldehydes are chosen such that The -~ the boiling points of the alcoholand the corresponding keTable Possible Secondary and Precursors tone alone do not allow identification. Thus, the preparation ~ ~ 8 . 5of- solid derivatives of both compounds is necessary far conclusive identification. Possihle secondary alcohols and their ~kyl~mmide ~Idehyde ~'AIwhol ~p. w a w precursxs are Listed in Table 1 and the corresponding kes7 tones in Table 2. There are, of course, other combinations, Ropanal 3.Pcntanol Bromoethana i - ~ ~ m o p r n p m e Ethansl* 2-Penfanal la 61 such as aromatic aldehydes and bromides, which could he l-Bmmopmpane Ethansl' 3-Methyl-2113 76 used, ~
dE:m-
,,,
butenmi ~ I 1ammobutme ~ t h ~ ~ ~ Pi .a H ~ ~ ~ ~ 138 Bromefhane Butanal 3-Heranol 135 iammopropane PmpanaL l - ~ ~ ~ o p m p Butsnel ~ ~ e 4-Heptsnol 166 1-Bmmopentanc Ethanaia 2-Heptanol 159 Bromwthans Pentsnal 3-Heptsnol 156 1-~romobutsne Propaoal
38 77O M
49
Table 2. Ketones from the Oxidation of the Alcohols in Table 1
2'Almhol Ketone " ~ e l t i n gpoinu and boilin& ointa arefmm Shiner! RalphL., Fu~un,?emold 3-Pentanone C. and Curtin. David Y., $he Systematic ldent~fieatm 01 02gans Com- 3-Pentand 2-Penfanone . pp. 316 362, and 2-Pentsnol p&nd6- (5th ed.1. ~ o h nwliey & sons. ~ n c ~. e r ~v o r k 1%4, 3-Mathyl-2Com- 3-Methyl-2. horn h n k e l M ~ X .and patal ssd. ."~ahlasfor identification of or& hufanano butanol b ciove~snd, e ~ ohio, 1964, pp. 38-41, pounds,. (2nd ed.1, =he c h o m i a i ~ ~ b CO., 2.Hoxanal ?-Herenone 93-96. 3-Hexanone dresdy dissolved in ether to 3-Heianol ameefhanal can be distributed to the reduce its volatility. 4-Hoptsnol 4-Heptanone 3-Hepfam~e E T ~ is~the S melting point recorded in Shriner. e m n and Cvrtm, while in tho 3-Heptanol 2-Hepfanone cnc Tables, it is recorded 97. l'he melting pomt observed by our students .Z-Hopfasol has beenaround 77. a See ainTable 1. d Nthough no malting point is mmrded in atepdard fables. it may be Lnd ~ h melting e point of thesemiearbamne. rtrvcfive for the student to yy toprepare thederivatlve.
BpO
Mp 2,l-dinitzopheoylhydrswne'
102 102 94
156 143 120
126 125 144 148 I51
106 130 75
10P 89
If the instructor so chooses, the identification of the alcohol and ketone can be done by using the pmr spectra and by comparison of the infrared spectra to those in compilations such as the "Aldrich Library of Infrared Spectra"' and the Sadtler collection.2 Once the student has identified his alcohol and ketone, he can write the equation (or equations if more than one set of precursors is possible) for the preparation of the alcohol and far the subsequent reactions. We have found student response to the experiment to he high. Since there are a number of reactions and purifications to be carried out, the student must plan his work well and use his time efficiently. Since successful identification depends upon obtaining pure products and derivatives in reasonable yields, the student must carry out the reactions and purification steps skillfully. 1 Pouchert.
Charles J., "The Aldrich Library of Infrared Spectra," Aldrich Chemical Company, Milwaukee, Wis.,
1970.
"The Sadtler Standard Spectra," Sadtler Research Laboratories, Inc., Philadelphia, Pa. J o h n W. Chittum LeRoy W. Haynes
The College of Wooster Wwster. Ohio 44691
Volume 5 1 , Number 1, January 1974
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