In the first step alcohol group of benzoin is oxidized to ketone group forming benzil in presence of concentrated nitric acid. Nitration of aromatic ring is not. BS (Hons) 2nd Semester. Organic Chemistry Practical Manual. Experiment Title: Preparation of benzilic acid from benzil. Chemicals required. Benzil KOH or. This experiment aims at the preparation of 2-hydroxyphenylbenzylic acid from benzil through a molecular rearrangement in basic medium.

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Benzilic acid rearrangement

Calculations show that an accurate description of the reaction sequence is possible with the participation of 4 water molecules taking responsibility for the stabilization of charge buildup. Once a proton was removed from thiamine hydrochloride, forming ylide, it acted as a nucleophile that allowed for the addition of the carbonyl group of benzaldehyde.

However, the following alternative incubation should be used, since it only required about minutes of total incubation time.

Home Synthesis of benzilic acid from benzoin. Let air be drawn through the filter before weighing to enhance the drying of your benzoin.

A novel benzil-benzilic acid. Dissolve the thiamine hydrochloride solid in 5.

Synthesis of benzilic acid from benzoin – Labmonk

However, your sample should be dry enough to proceed to the next experiment making benzil. The reaction is second order overall in terms of rate, being first order in diketone and first order in base. The picture below shows the bezil expansion of a cyclopentane to a cyclohexane ring as an example reaction.

Thiamine, vitamin Synthesus, will be used in the current experiment to convert benzaldehyde into benzoin. From Wikipedia, the free encyclopedia.

Part of the chemistry of thiamine is the acidic proton located on the carbon benxil the sulfur and nitrogen atoms. Overall, the spectra syhthesis the condensation of benzoin. From this data and the low percent yield, the rearrangement of benzil was not achieved successfully. The synthesis of barbituric acid is effected by condensation of diethyl malonate with urea in the presence The IR and 1 H NMR data displayed peaks that allowed for the distinction and identification of the different products that led to the ultimate synthesis of benzilic acid.


It has been found that aryl groups more readily migrate than alkyl groups, and that aryl groups with electron-withdrawing groups migrate the fastest. The reaction mechanism for thiamine catalysis is described above. This will provide enough solution for 8 student groups, assuming little solution is wasted. Use a procedure that will oxidize the benzaldehyde to benzoic acid.

To the yellow solution, add A peak acix 3. Do not confuse recrystallization with the formation of a solid e. Wash the crystals with mL of water to remove salts. Finally, a peak at cm -1 represented the carbonyl group and a peak at cm -1 accounted for the carbon-oxygen bond in both alcohol groups.

The only things that must be done are: The final mechanism, shown in scheme 3, involves the synthesis of the carboxylate salt intermediate, potassium benzilate, which drives the reaction to produce benzilic acid through workup. Calculations show that when R is methyl the charge build-up bnzil this group in the transition state can be as high as 0.

Multistep Reaction Sequence: Benzaldehyde to Benzilic Acid

To enhance reactivity, and to be stereoselective, enzymes are used to bind the substrate in a manner that allows only a single reaction, with stereoselectivity to occur. In most cases it is not necessary, just proceed with sytnhesis Part 2 experiment. For a synthetic organic chemist the product of one reaction is often used as the reactant in another. The reaction is an acylion condensation to benzaldehyde as an example, if you have The amount of the oxidizing agent e.


A peak at 3. The reaction is second order overall in terms feom rate, being first order in terms of alkoxide and first order scid terms of diketone. You might have a little reprieve, since other students will likely be requesting chemicals, and if you forgot, you can still use the chemicals on the cart, even if requested by another group.

As the reaction proceeds, the reaction product will turn brown and the solid may, or may not, be completely dissolved. To the yellow solution, add The benzoin produced will be used for the sequence of reactions which will be followed to produce benzil and benzilic synthedis.


Reflux for at least 30 minutes, or until no more NO 2 gas is being produced. The reaction is formally a ring contraction when used on cyclic diketones. Set up this reflux in the hood to vent NO 2 gas which is produced during the reaction.

Xcid the mixture has dissolved and heated for a few minutes, the mixture will turn blue-black in color. These new compounds can then be used in various different applications, some of which are for medicinal purposed. The first four lab periods are used to make the chemicals listed for those days. X g benzilic acid.

In addition, enzymatic reactions can be carried out in mild conditions and at moderate pH values. Benzilic acid was synthesized and the percentage yield was found to be………. Hence, a multi-step synthesis of different compounds. Baldania and Dimal A. The rest of the molecule is aynthesis biochemically, but it is not required for the reaction described here. There are five laboratory periods bsnzil to this experiment.