Che 325 acetal lab

Che 325 acetal lab - Chemistry 325 Reduction of Benzil to...

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Chemistry 325 Reduction of Benzil to Hydrobenzoin Using NaBH 4 Followed by Stereochemical Assignment via the Acetal (Part I) Introduction In this first part of a two-week lab, benzil will be reduced to the 1,2-diol (hydrobenzoin) using excess sodium boro- hydride. The product can exist as two possible diastereomers: the meso form or the d/l form (racemic form). The objective of the week 1 lab is to perform the reduction, crystallize the product from the reaction mixture, and then use mp to determine which diastereomer you obtained. During week two, the diol product will be converted to an acetal using acetone. The acetal, due to an interesting structural feature related to the two methyls, can then be ex- amined by 1 H-NMR spectroscopy to confirm the stereochemical assignment made using the mp data. This will be done by determining if the methyls of the acetal are equivalent or not. If they are equivalent, they will give only one signal in the NMR; if they are not equivalent, then they will give two signals in the NMR. Based on this informa- tion, you will be able to determine the stereochemical nature of your original hydrobenzoin product. Part I Prelab As usual, including safety information for sodium borohydride. Draw each of the 3 possible stereoisomers of hy- drobenzoin (i.e., the meso, the d and the l) in a Fisher projection (you will not be able to distinguish which is the d and which is the l; just call each of them “either d or l”). Also, label hydrobenzoins A and B in the second line reac- tion above, which are shown as perspective drawings rather than Fisher projections, as either meso or one of the d/l
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Che 325 acetal lab - Chemistry 325 Reduction of Benzil to...

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