Category Archives: Spring 2013 Organic Chemistry Lab

Benz But Doesn’t Break. Part VI

I reported earlier that our attempts to run the thiamine catalyzed 4-methoxybenzaldehyde (anisaldehyde) coupling to 4,4’-dimethoxybenzoin (anisoin) did not appear to generate any products. I ended up pouring all the student prepared reaction mixtures into a 1 L Erlenmeyer flask and let it sit in my research lab. One day towards the end of August […]

Benz But Doesn’t Break. Part V

The third step of the modified benzilic acid synthesis project proceeded well under the same conditions as the benzil to benzilic acid rearrangement as outlined in a previous post. The products were characterized by melting point, UV absorption, IR, 1H and 13C NMR. The carboxylic acid products were not compatible with the GC column we […]

Benz But Doesn’t Break. Part IV

The second part of the modified benzilic acid synthesis project was as straightforward as the first part was complicated. The quantities of ammonium nitrate for the copper(II) acetate catalyzed oxidation were adjusted for the different molecular weight of the starting material. Other than that conditions were the same as for the benzoin to benzil transformation. […]

Benz But Doesn’t Break. Part III

The thiamine catalyzed coupling reaction of 4-methylbenzaldehyde created an off-white solid product. Upon analysis the product contained one to three different peaks in the GC-FID that corresponded to the coupled products. After the oxidation step was completed, one of the three peaks remained. It is reasonable to conclude that the peak after oxidation was 4,4’-dimethylbenzil. […]

Benz But Doesn’t Break. Part II

We set up the condensation reactions with the same molar quantities and under the same conditions as we had done the thiamine catalyzed benzoin reactions as few weeks before. It soon became apparent that the condensation of anisaldehyde was not occurring to any extent and the condensation of tolualdehyde was occurring much slower than it […]

Benz But Doesn’t Break. Part I

I wanted to do a variation of the Benzaldehyde to Benzilic Acid synthesis as our final project. The premise was simple: We would use derivatives of benzaldehyde for the reaction. This is a common way to explore synthetic reactions. Many articles that feature synthetic reaction have dozens of experiments done by varying the structural characteristics […]

A Case of the Benz. Part IV

Benzil to Benzilic acid The third step of the benzaldehyde to benzilic acid synthesis is the base catalyzed rearrangement of benzil to benzilic acid. An early study of this reaction was reported in a 1921 J. Am. Chem. Soc. article by Arthur Lachman. According to the procedure we followed, the reaction only required 15 minutes […]

A Case of the Benz. Part III

The second step of the benzaldehyde to benzilic acid synthesis is the oxidation of a benzylic alcohol to a ketone. This oxidation could likely be effected by dozens of different reagents. Some of the early experiments do this step with nitric acid. This seems like overkill. An alcohol in that position should be easily oxidized. […]

A Case of the Benz. Part II

The so-called condensation of benzaldehyde to benzoin was originally performed with a cyanide catalyst. The origins of this reaction go back as far as an 1832 report by Wöhler and Liebig. The reaction can be performed in a biomimetic manner with thiamine as a catalyst under basic conditions as proposed by Ronald Breslow in a […]

A Case of the Benz Part I

The following posts report on the three step synthesis of benzilic acid from benzaldehyde. The first step is the conversion of benzaldehyde to benzoin using a vitamin, thiamine, as a catalyst. In the second step, the benzoin is oxidized to benzil through the use of an oxidizing agent. The third step is the preparation of […]