Synthesis of Benzoic acid sytnhesis Benzaldehyde Each part will be performed on successive days. <> Add 180mL of water. Principle: The reaction between aromatic aldehyde and an aliphatic anhydride capable of providing an ‘active methylene‘ moiety in the presence of a basic catalyst, such as: acetate ion and a hydronium ion, which yields an α, β-unsaturated carboxylic acid and a mole of acetic acid i.e. When synthesizing complex organic molecules, it is common to have at least a dozen individual transformations whereby the product of one reaction is then used as the starting material for the next reaction. recrystallization %Recovery from 76.12% The melting point of this product was 92°C-94.3°C. REFERENCES Procedure: Using a 25 mL or a 50 mL Erlenmeyer flask, dissolve 0.50 g of benzil (weigh to the nearest hundredth of a gram) in 5 mL of warm 95% ethanol. You can use hot water from the faucets at the front of the lab. The crude product was recrystallized using 8.2mL of 95% The 13C NMR produced a peak at 192.0 ppm representing the two carbonyl groups. This reaction, which requires a catalyst, if often performed with cyanide ion. Four peaks appeared between 132.3 and 126.5 ppm accounting for the carbons within the aromatic ring and the alkene bonds. 13C NMR (CDCl3, 75Hz) δ: 199.2, 139.2, 139.1, 134.0, 129.2, 129.1, 128.7, 128.5, 127.8, 76.2 ppm. 0000008240 00000 n Through a multistep synthesis benzaldehyde was converted to benzilic acid. reaction mixture, after the NaOH was added to the thiamine and ethanol, was yellow in color. Decolorizing carbon was added to assist in separating the filtrate from Add 7.5 mL of 95% ethanol to the thiamine and cool the solution for several minutes in an ice bath. point values for benzoin is 135-137°C. It is also meant to demonstrate some general preparation methods, such as using a reflux apparatus, vacuum filter, and a hot gravity filter, plus determining melting point and titrating. 706. Aqueous sodium hydroxide (4.5 mL) was added and swirled until the solution appeared pale yellow. Take an IR of the product using a cast film technique as described in the lab textbook. Weigh your crude yield, break up any clumps of solid and recrystallize from hot 95% ethanol (8 mL per gram). Research has enhanced the sustainability, time efficiency, and design of multistep synthesis reactions to be utilized in many industrial situations.1. As the second step of the multistep synthesis, the alcohol group of benzoin must be oxidized. Benzoic acid was first synthesized in the 16th century . trailer In the first part of this multistep synthesis, benzaldehyde was converted to benzoin. Through recrystallization, a pure product of 2.07 g was collected, which produced a 44% yield. First, start by preparing the mixture. Finally, the IR spectra displayed a peak at 3403 cm-1 representing the C-H stretches, a peak at 3003 cm-1, accounting for the alcohol group, and a strong peak at 1761 cm-1 representing the carbonyl group. 0.371g 0.01764mol You may recrystallize a portion of the purple product using a 1:1 mixture of 95% ethanol and toluene (12 mL/0.5 g). Green chemistry was involved in the preparation of benzoin by the choice of catalysis, thiamine hydrochloride. mixture sat for 7 days in a cool room, the color noted was more of an orange color with white Overall, the spectra confirmed the condensation of benzoin. 5 = 14.66 g, Hence, Theoretical yield of Cinnamic Acid = 14.66 g, Then, Percentage Practical yield = Practical yield / Theoretical yield × 100, The percentage yield of the Cinnamic acid is about 64.8% of melting point 132 °C. You will have an opportunity to do a multistep synthesis starting with inexpensive, readily available benzaldehyde. 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. Experiment 4: Preparation of Benzoic Acid INTRODUCTION This experiment is designed both as a preparative and an investigative project. In your discussion, mention that three stereoisomers are possible and suggest why the meso isomer (lit mp 136-7 oC) predominates. reaction mixture, the progress of the reaction was determined. The melting point was determined and 0000003267 00000 n Weight into a flask (ground glass joints recommended) 16g of Potassium Permanganate. The more reactive hydride reducing agents can reduce other functional groups such as carboxylic acids, esters, epoxides, and nitriles. benzilic anion by the addition of an acid. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. The fumes are toxic and noxious so be certain that the fume hood safety shield is pulled down. from beginning After cooling, the recrystallized benzoin should be filtered, washed with a minimum of a cold 2:1 mixture of water and 95% ethanol, and air dried for 15 min or left until the next lab period. Record the mp; literature mp 219-220 oC). Amount benzil used 0.202g 0.000962mol to contamination or improper measurement of reactants added during the experiment. Mix the ingrediants by swirling, cover the beaker with a thin watch glass or appropriate microwave safe film (thick watch glasses often break in the microwave) and place it in the microwave oven. Amount benzilic acid Filter, dry, record the yield, and take the mp. Watch the recordings here on Youtube! The solution becomes milky but then clears*. After a total of 10 minutes, add 5 mL of water, heat to boiling on a steam bath, filter or decant if the solution is not clear. Your starting compound is a diketone so you need one mmol of borohydride for every two mmol of ketone . startxref Have questions or comments? xÚb``�a``~È N�¨€ˆY800¹8 Ë@1ƒ2§C³èCK�E•Ek=Vgc4c`¶×ÿtFeWoÂn�‚ïsmøÃ{Aª›‘�ÁM H3±³20„. 1 Bruggink, A.; Schoevaart, R.; Kieboom, T. Org. Multistep Reaction Sequence: Benzaldehyde to Benzilic Acid. Multistep synthesis is a sequence of reactions intended to produce a specific molecule as The ultimate products of ylide and benzoin are produced. The IR and 1H NMR data displayed peaks that allowed for the distinction and identification of the different products that led to the ultimate synthesis of benzilic acid. Set the oven at power level=6 for 5 minutes. 0000006192 00000 n Too much water will force benzaldehyde out of solution preventing an efficient reaction. To dissolve the solid effectively, the bigger clumps should be crashed by appropriate devices. The resulting benzil was treated with 0.9g of Cu(OAc) 2 and the mixture was refluxed for one hour. 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. crystals were already visible before placing the reaction mixture in an ice bath. Benzilic Acid: Benzil (2.10 g, 1.0 mmol), 95% ethanol (6 mL), and a boiling stone were added to a 25-mL round-bottom flask with a reflux condenser and heated until the solid benzil was dissolved. Raise the temperature to provide a slow reflux and add a solution of 0.1 g of potassium hydroxide (CAUSTIC) in 1 mL of absolute ethanol (this solution may be already prepared) dropwise through the top of the condenser. Introduction. This appeared to be less than the ideal melting point of 95 °C, which could account for the lack of purity. 0000012555 00000 n You should not have to filter the hot solution. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Vacuum filtration was used to collect the crude product. It is also used as a precursor of the sweetener, aspartame.1, Apparatus:        Double naked round-bottomed flask with guard tube system, Another 500 ml RBF with steam distillation system. The summarization of the results Some possible causes for impurity might be due to unclean glassware leading The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. a mixture of benzil, alcohol, and potassium hydroxide. was an incompletion of this reaction. 50 oC until the solution clears or for a maximum of 10 minutes. 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. synthesis, especially through the second part of this synthesis. Cyclopentadienone is a relatively unstable compound which will dimerize even at low temperature.