The solution becomes milky but then clears*. When you are satisfied that you have the product you want, the filtrate can be neutralized with dilute aqueous HCl and flushed down the drain. After addition of the base, allow the mixture to reflux for 15 minutes while periodically shaking the flask. The 13C NMR spectra displayed a weak peak at 175.8 ppm, which accounted for the carbonyl group within the carboxylic acid. The second filtrate (from recrystallization) can be flushed down the drain with water. The student can research their ultimate uses to observe that no chemical synthesis is for naught. 36 0 obj <>stream Overall, the spectra confirmed the condensation of benzoin. 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. 1H NMR (CDCl3, 300 MHz) δ: 7.47 (m, 6H), 7.26 (s, 4H), 2.18 (s, 1H) ppm. benzaldehyde usedAmount of 1mL 1.044g 9.84 x 10- This indicates that there was a slight impurity to the However, the solution process is not immediate. Finally, a peak at 82.0 ppm represented the carbon attached to the alcohol group. Kar Ashutosh, Advanced Practical Medicinal Chemistry, New Age International (P) Limited Publication, New Delhi, Page No. Too little water prevents the thiamine hydrochloride from dissolving. Ethanol from the recrystallization goes to the non-halogenated waste container. Such hydrides react violently with water releasing hydrogen gas and must be handled very carefully. The third step is a condensation reaction of benzil with dibenzyl ketone (1,3-diphenyl-2-propanone) to produce tetraphenylcyclopentadienone. Melting point 132.3°C-134.9°C, g mol xÚb``�a``~È N�¨€ˆY800¹8 Ë@1ƒ2§C³èCK�E•Ek=Vgc4c`¶×ÿtFeWoÂn�‚ïsmøÃ{Aª›‘�ÁM H3±³20„. in order to precipitate it. Am. there was still a presence of benzil in the reaction mixture. 6. By utilizing crystallization, pure solid products of each step were collected and analyzed through IR, NMR spectroscopy, and other physical properties. The melting point of this product was 92°C-94.3°C. A mixture of ethyl benzoate (2 ml) and sodium hydroxide solution (15 ml, 10%) is refluxed in a round bottomed flask fitted with a water condenser on a water bath (temp. The ultimate products of ylide and benzoin are produced. 0000002511 00000 n 66 x 100 = 64.8%. By monitoring the retention factor (Rf) value of the Add 7.5 mL of 95% ethanol to the thiamine and cool the solution for several minutes in an ice bath. You will have an opportunity to do a multistep synthesis starting with inexpensive, readily available benzaldehyde. Therefore, 10mL of 0000006572 00000 n ��4N����BR`������oʵSS���'S�}so�]C��7��uu7_��x��3:FHR.x̄����ai�������M��y6��h�;8�"�ٕX�)�AI�vo�S�,G��؞�6���}vȺ�({g���%=�֩���s���u�����2C2�|\�����9�Hc�E�p��.8�nD�� ���S�����[ ! 0000003860 00000 n used to monitor the reaction and the melting point and refractive index was determined. The second part of this multistep synthesis of benzilic acid involved the conversion of You can use hot water from the faucets at the front of the lab. 0000008991 00000 n Some of the base reacts with the thiamine hydrochloride to produce thiamine which is the active catalyst. Amount benzilic acid %PDF-1.5 filtrated. After preparing the mixture, set up an apparatus for simple reflux. catalytic copper(II) acetate is used as the oxidizing agent, with ammonium nitrate used to The reaction mixture should be a golden color which cools to colorless crystals. 90-100 oC) for about 30 minutes till the ester layer disappears. Multistep Reaction Sequence: Benzaldehyde to Benzilic Acid. determined to further classify the product. If you do not have more than 0.7 g, save 100 mg of the benzil for a mp, IR, and to hand in and use the rest for this next step, altering the procedure to scale or obtaining additional benzil from your instructor. The final product of benzoin contained 13C NMR peaks at 199.2 ppm accounting for the carbonyl group and eight peaks in the range of 139.0-127.8 ppm representing the alkene bonds as well as the carbons of the aromatic rings. Staudt, M., Stranz, M. Chemistry 2011 Cengage Learning: Ohio, 2011; p 65-87. yield Soc., 1922, 44, 330-340. When you are satisfied that you have the product you want, you may dispose of the first filtrate by neutralizing with dilute HCl, then flushing the aqueous layer down the drain with plenty of water. When the crystals are dry (which may take until the next lab period), weigh, record the yield and the percentage yield . 106.12 g of Benzaldehyde yields Cinnamic Acid = 148.16 g, 10.5 g of Benzaldehyde shall yield Cinnamic Acid = 148. regenerate the catalyst. Each reaction produces a product that is used in the next reaction, until the An impurity of ethanol appeared at 4.42 ppm. The resulting benzil was treated with The first reaction produced benzoin by using the thiamine hydrochloride catalyst, followed by an oxidation reaction to produce benzil, and a rearrangement to synthesize benzilic acid. Product obtained, after Klien, D Organic Chemistry; John Wiley &Sons, Inc.: New Jersey, 2012; p 940, 946. Product obtained, Set the oven at power level=6 for 5 minutes. Step 1: Converting benzaldehyde to benzoic acid. trailer The crystals were isolated through vacuum filtration and washed with 4-mL portions of cold 95% ethanol. CAUTION: Concentrated Nitric Acid is extremely caustic and will burn exposed skin. The crude product was then recrystallized with 3.0mL of 95% ethanol as the boiling Advanced Organic Chemistry: Reaction Mechanisms by Reinhard Bruckner, Published by Harcourt Academic Press: 2002; Page No. 0000001192 00000 n Conclusion Through the multistep reaction, a 44% yield of benzoin, a 77% yield of benzil, and a 17% yield of benzilic acid were obtained. The literature value melting point of benzoin The stoichiometry of the typical borohydride reaction is: \[\ce{4 R_2C=O + NaBH_4} \rightarrow \ce{(R_2CHO)_4B}^-\ce{Na+}\], \[\ce{(R_2CHO)_4B}^-\ce{Na+} + \ce{H_2O} \rightarrow \ce{4 R_2CHOH}\]. from amount benzoin of the reaction mixture. 0.371g 0.01764mol This reaction is a classic--the conversion of two molecules of an aldehyde to an alpha-hydroxy ketone. A peak at 5.82 ppm accounted for the hydrogen attached to the carbon containing the alcohol group. Part 4 is a “self-designed” experiment where you brnzil a protocol to follow to prepare and purify benzoic acid from benzaldehyde. 12 x 10. It may take a few hours to see crystals. Add 20mL of Toluene. You will reduce the diketone, benzil, using sodium borohydride. Benzilic acid can be synthesized by a couple of common methods. It is also used as a precursor of the, 10.5 g of Benzaldehyde shall yield Cinnamic Acid =, Practical yield / Theoretical yield × 100. When you are satisfied that you have the product you want, you may dispose of the filtrate by first neutralizing with sodium carbonate, diluting with water, and flushing down the drain. The final product is separated from the byproduct by addition synthesis, especially through the second part of this synthesis.
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