Chemistry Lab Manual

Activity Check-In and begin benzoin condensation, Dilantin and related compounds, continue dilantin lab pseudopelletierine, finish dilantin lab, finish pseudopelletierine, 5,5-dimethyl-1,3-cyclhexanone Diels-Alder Reactions, Fischer Indole Synthesis, lab checkout. Possibly a Written Laboratory Final Exam, other activity, review session, or nothing at all – Report Due benzoin dilantin and others pseudopelletierine dimedone Diels-Alder Fisher Indole (submitted in lecture).

Before starting the lab, you need to have a drawing in your notebook that shows each separate reaction to be performed. Below the reaction, list the chemicals and reagents to be used in columns. Include information such as molecular weight, equivalents, mmol, wt, density (if applicable), mL (if applicable), bp (if applicable), and mp (if applicable). Include a row for the product as well. Your lab report should be concise and include a copy of your lab notebook, copies of your spectra with interpretive comments, and a detailed reaction mechanism.

The notebook should display the calculation of the percent yield, mp, etc, and the procedure. Neatness is important. The procedure does not have to be written in complete sentences. Each spectra should have a neatly computer generated structure created using a program such as chemdraw or one of the free alternatives (see the course website under links), along with your name and your lab section. In this lab, you will submit the products you create, and both quality and quantity (determined visually and by NMR) are important. The initial plan is for the demonstrators to prepare the 1H NMR samples from the bulk material that you provide to them.

The 1H NMR spectra will be given to you the following week. The reports will be due one week after that. Chemistry 3373f, Fall 2007 Page 3 The Benzoin Condensation of Benzaldehyde Aromatic aldehydes, in the presence of catalytic cyanide ion, dimerize to form the corresponding ? -hydroxyketone (acyloin). This reaction, which is reversible, is referred to as the benzoin condensation. This “condensation” is somewhat incorrectly named since it is not truly a condensation reaction as no water or alcohol is produced but two species do come together.

The mechanism below illustrates the three different roles of cyanide as a catalyst in this process. First, the addition of the cyanide ion forms a cyanohydrin, which reverses the normal charge affinity of the carbonyl group, transforming the electrophilic aldehyde carbon into a nucleophile upon deprotonation. This newly formed carbanion can then be deprotonated by a strong base at the former carbonyl C-atom. Furthermore, a second equivalent of aldehyde can react with this carbanion. Finally, the catalyst is eliminated, regenerating the carbonyl compound by the end of the reaction.

Chemistry 3373f, Fall 2007 Page 4: The use of cyanide ion as a catalyst is limited to aromatic aldehydes because the carbanion is stabilized by both the cyano group and delocalization into the aromatic ring. However, one disadvantage of using cyanide as a catalyst is its toxicity, both in the form of cyanide and hydrogen cyanide (HCN). Proper precautions should be taken in handling and disposing of cyanide to avoid the production of volatile and poisonous HCN, which could occur if it is accidentally poured into a sink containing acid.

Thiamine (vitamin B1) is a crucial coenzyme with multiple biological roles. A simple Google search can confirm its significance. Thiamine, along with related thiazolium salts, acts as a catalyst for the acyloin condensation by facilitating the reaction with different types of aldehydes. The proton at C-2 has a relatively low pKa value of 12.7 due to the stabilization of the resulting carbanion by the neighboring positively charged nitrogen. This leads to the formation of a highly stable ylide. This ylide can then undergo a reaction with an aldehyde, resulting in the production of an enamine:

The enamine that will be obtained, utilizing benzaldehyde, has the ability to react with a second benzaldehyde molecule, resulting in the desired product. This reaction follows the acyloin condensation pathway that is described for cyanide. The experimental procedure involves the addition of 1.30 g of thiamine hydrochloride to a clean 50-mL R.B. flask, followed by the addition of a stir bar. The solid is dissolved in 4.0 mL of water through stirring. Subsequently, 15 mL of 95% ethanol is added and the solution is cooled in an ice bath for a few minutes. Cold 3 M NaOH is then added dropwise, ensuring that the temperature does not exceed 20 °C. Afterward, 7.0 mL of pure benzaldehyde is added to the yellow solution. The flask is equipped with a reflux condenser and secured using a blue keck clip. To prevent freezing, a small piece of Teflon tape is placed between the condenser and flask. The mixture is then heated at 60 °C for approximately 1.5 hours using a water bath created with a 250 mL beaker. It’s important to avoid refluxing the reaction by not overheating it. Once heated, the reaction mixture is cooled in an ice bath. If immediate crystallization does not occur, a drop of the solution can be withdrawn on a stirring rod and allowed to dry in order to produce a solid, which can then be rubbed against.

Chemistry 3373f, Fall 2007 Page 5 inside surface of the flask to induce crystallization. Collect the product by vacuum filtration and wash it free of any yellow mother liquor with a cold 1:1 mixture of 95% ethanol and water. It is in your best interest to recrystallize the moist product from 95% ethanol (~8 mL of ethanol per gram of product). The product should be colorless and of sufficient purity (mp 134-135oC) to use in subsequent reactions. Usual yield is about 5 – 6 g. Characterization of the Product: Your lab report should be quite brief.

The content that needs to be included in the notebook for this assignment includes a copy of your lab notebook, spectra with interpretive comments, and a detailed reaction mechanism using thiamine instead of cyanide. The lab notebook should also display calculations such as percent yield and mp, as well as the procedure. It is important to maintain neatness throughout.
To label each spectra, create a neatly computer-made structure using a program like Chemdraw or one of the free alternatives provided on the course website under links. Then, include your name and lab section on the printed label. Stick this label onto the spectra and submit a photocopy.

Please provide your demonstrator with a 15 mg sample of your benzoin product. Make sure to label it with your name and lab section. The next week, you will receive a 1H NMR of the sample. Save your benzoin for next week’s lab.

In the Synthesis of Dilantin and Related Compounds lab, benzoin, a keto-alcohol, can easily be oxidized to the yellow diketone, benzil. Both benzoin and benzil can be reduced to the diol, hydrobenzoin. By condensing benzil with urea in the presence of a base, dilantin, a heterocyclic derivative, is produced. Dilantin is useful in medicine due to its anticonvulsant properties and does not have sedative side-effects like phenobarbital.

Furthermore, condensing benzil with dibenzyl ketone in the presence of a base results in the formation of tetracyclone, an unusual deep purple compound. The reduction of benzil using sodium borohydride yields a mixture of diastereomers, racemic- and meso-hydrobenzoin. The meso diastereomer is dominant and can be isolated by crystallization from water, as it is less soluble than the racemic diastereomer.

To successfully complete this lab in one period, it is crucial to properly organize your approach as several operations need to be conducted.Immediately after preparing benzil by oxidizing benzoin, the dilantin preparation should be initiated. While waiting for the dilantin preparation to reflux for one hour, the second portion of benzil will be reduced and the third portion will be purified through recrystallization. At the beginning of the third hour, the aldol condensation of the fourth portion of benzil with dibenzyl ketone should be started.

Before starting the lab, it is required that you have a drawing in your notebook depicting the reaction to be performed. Below the reaction, list the chemicals and reagents to be used in columns, along with their molecular weight, equivalents, mmol, wt, density (if applicable), mL (if applicable), bp (if applicable), and mp (if applicable). Each reaction should be entered on a separate page in your notebook under Chemistry 3373f, Fall 2007. The procedure for the oxidation of benzoin will be followed for this experiment, using 4 grams of benzoin. If you have more than 4 g of benzoin, you can either scale up your reaction or share it with a friend.

If you do not have 4 grams, you can obtain some from the demonstrators. Take a 125 mL Erlenmeyer flask and add 14 mL of concentrated nitric acid to 4 g of benzoin. Close the flask with a cork and transport it to your work area. In order to carry off the harmful nitrogen oxides that are formed, you must perform this step in a hood. Remove the cork and gently heat the mixture on a hotplate for 12 minutes. Next, add 75 mL of water to the mixture and let it cool to room temperature. Then, neutralize the mixture by slowly adding drops of 30% aqueous sodium hydroxide. Swirl the flask for a few minutes before collecting the yellow solid product on a Buchner funnel.

Press out as much water as possible from the solid on the filter before determining the crude yield by weighing the dry solid product. Divide the product into four portions: 0.4 g for the dilantin preparation, 0.5 g for the reduction process, 2.1 g for the tetracyclone preparation, and whatever remains (weigh it) for purification and testing. In a minimum amount of hot 95% ethanol, dissolve 80% of the remaining product. Gradually add water to reach the cloud point and then let the mixture sit to allow for crystallization. Collect the crystalline material, let it dry, and determine its melting point.

The presence of unreacted benzoin in the remaining crude product and the recrystallized benzil can be tested by dissolving a small crystal in 0.5 mL of ethanol or methanol and adding one drop of 10% sodium hydroxide solution. If a dark reddish color develops, it indicates the presence of benzoin as it complexes with benzil under these conditions. If no color is observed, a small amount of benzoin can be added to observe the color.
To prepare dilantin, place the 0.4 g sample of crude benzil in a 25 mL round-bottomed flask with 0. g of urea, 6 mL of absolute ethanol, and 1.2 mL of 30% aqueous sodium hydroxide. Add a boiling chip and attach a condenser after wrapping the ground glass joint with Teflon tape. Heat the mixture on a sand bath under reflux for 1 hour. After cooling the reaction mixture, add 10 mL of water. If the solution is not clear, remove any suspended solids by filtration. Then, carefully acidify the clear solution with concentrated hydrochloric acid. Collect the product by vacuum filtration and wash it thoroughly with water. Recrystallize the product from ethanol, weigh it dry, and calculate the yield.

Use deuterated DMSO to prepare a sample for NMR. The procedure for reducing benzil is as follows: place 0.5 g of crude benzil in a small Erlenmeyer flask and add 5 mL of 95% ethanol. Swirl the flask to obtain a fine suspension of the solid before adding 0.1 g of sodium borohydride. After 10 minutes, add 5 mL of water and heat the mixture to boiling. If the solution is not clear, perform a hot filtration using fluted filter paper before diluting with water to the saturation (cloud) point; this should require approximately 10 mL of water.

Crystallize the product and separate meso-hydrobenzoin into thin lustrous plates. Determine the melting point and yield of the dry crystalline product. The procedure for preparing tetracyclone involves adding 2.1 g of crude benzil, 2 mL (2.2 g) of 1,3-diphenylacetone, and 15 mL of absolute ethanol to a 100 mL RB flask. Attach a reflux condenser and gently heat the flask on a sand-bath until the solids dissolve. Increase the temperature of the benzil/ketone solution to just below the boiling point and add the 3 mL of 10% KOH in ethanol solution slowly through the top of the condenser.

Reflex the reaction mixture for 15 minutes, shaking the flask multiple times. Afterwards, cool the reaction mixture to below 5 °C using an ice-bath. Collect the purple crystals through vacuum filtration. Rinse the crystals with three portions of cold 95% ethanol, each measuring 5 mL. Determine the weight of the dry product and calculate the yield. For characterization and reports, obtain a melting point (mp) and 1H NMR analysis of your products using no more than 15 mg. Submit the remaining materials, excluding the tetracyclone, to your demonstrator. Keep the tetracyclone for the Diels-Alder experiment.

Chemistry 3373f, Fall 2007 Page 9 Synthesis of an Alkaloid: Pseudopelletierine (two weeks)

One of the most amazing syntheses ever reported was the synthesis of the alkaloid tropinone in 1917 by Robert Robinson at the University of Liverpool. For this and many other accomplishments in organic chemistry, he was awarded the Nobel Prize in 1974.

His synthesis of tropinone was notable not only because of its efficient (one step, high yield) formation of the bicyclic heterocyclic ring system, but also because it mimicked the process believed to be at work in the biosynthesis of the alkaloid in nature.

In 1924, Robinson and Menzies successfully synthesized the pomegranate alkaloid, pseudopelletierine. We will now replicate this synthesis using Robinson’s method. By combining glutaraldehyde, methylamine, and acetonedicarboxylic acid, we can create pseudopelletierine in one step. To generate the glutaraldehyde, we will hydrolyze a heterocyclic precursor called 3,4-dihydro-2-ethoxy-2H-pyran. The reaction process is as follows:

1) CH3NH2 CHO CHO CO2H CO2H O CH3NH3 (buffer)
2) More H3O+ ?
3) OH+ H3C N tropinone O
1) CH3NH2 CO2H CHO O CHO CO2H glutaraldehyde CH3NH3 (buffer)
2) More H3O+ ?
3) OH+

Treatment with aqueous KOH followed by acid results in a decarboxylation to give 5,5dimethyl-1,3-cyclhexanone (dimedone). Dimedone is a cyclic 1,3-diketone, and it exists in both enol and keto tautormers that can be observed spectroscopically.

O O EtO O OEt O + 4-methyl-3-pentene-2-one NaOEt A EtO O O Na diethyl malonate B – not isolated O O O EtO O Na O KOH (aq) then HCl (aq) O OH B dimedone

The dimedone can be condensed with an aldehyde, and this is illustrated in a separate step by reaction with formaldehyde.

O O H2CO O O dimedone

Your task is to prepare dimedone on a 20 mmol scale, based on 4-methyl-3-pentene-2-one.

In this lab, you will be provided with a 2.5 M solution of NaOEt in EtOH. However, the procedure lacks routine details, so it is your responsibility to figure them out. Before starting the lab, you must have a drawing in your notebook that shows the reaction to be performed. This drawing should include two separate reaction schemes on two separate pages. Below each reaction, create columns listing the chemicals and reagents to be used. Include information such as molecular weight, equivalents, mmol, wt, density (if applicable), mL (if applicable), bp (if applicable), and mp (if applicable).

Please consider the size and type of flasks you will use. In Chemistry 3373f, Fall 2007 Page 12, we will be synthesizing 5,5-dimethyl-1,3-cyclohexanone. Prepare a 50mL B19 Erlenmeyer flask and a water condenser from the oven. Place a stir bar and 8 g of NaOEt, which is a 2. 44M solution in EtOH (provided for you), into the flask. Use a small piece of Teflon tape to prevent the round bottom flask from sticking to the condenser. Attach the flask to the water-cooled condenser and set up the apparatus so that the hot plate / stirrer can be raised and lowered using a labjack. With rapid stirring, slowly add 3. g of diethylmalonate to the flask from the top of the condenser. Solid particles will form. Put a drying tube on top of the condenser and heat the reaction mixture for 5 minutes at reflux while continuing to stir rapidly. After heating, lower the stirrer and let the flask cool for 5 minutes. Gradually add 2.1 g of Mesityl Oxide from the top of the condenser, replace the drying tube, and reheat the mixture with rapid stirring to bring it to reflux for an additional 35 minutes (90-95? C). Solid particles will form and there may be slight boiling or bubbling. Be careful not to overheat the solids while ensuring that reflux takes place.

After stirring, lower the heater again to cool the mixture for 5 minutes. Then, take out the flask and cover it with a stopper. Move the mixture to the Roto-vap, where the water bath should be around 80°C, so that the liquid (mainly EtOH) can be removed. Next, introduce 13mL (or 15g) of a 3.5 M solution of KOH in water. Reinstall the condenser and with stirring, heat at reflux for 45 minutes. Once heating is complete, remove the heater and allow the mixture to cool down naturally to room temperature (using an ice bath). Slowly adjust the pH to 1 by adding approximately 5 mL of concentrated HCl. Then, heat at reflux again with rapid stirring for 15 minutes. Before reaching the point of reflux, expect a clear release of gas from the solution.

Place an aluminum block on the heater plate of the stirrer to cool the surface faster. Meanwhile, cool the flask on ice for 10-15 minutes, continuously stirring. Use a Hirsch filter to collect the crystals. Rinse the crystals with approximately 20 mL of ice-cold H2O followed by 2 portions of Petroleum Ether (30-60) each, measuring about 6 mL. Let the crystals dry under vacuum. Recrystallize a portion using hot acetone and obtain your sample for NMR and melting point analysis. Note: Most reagents in this experiment are measured gravimetrically. Diethyl Malonate, Mesityl Oxide, and HCl can be obtained using disposable test tubes and corks.

Chemistry 3373f, Fall 2007 Page 13 Diels-Alder Syntheses of Polycyclic Compounds
In 1921, Otto Diels and Kurt Alder discovered that alkenes add to conjugated dienes to give cyclohexenes: C C C C C C
Similarly, alkynes add to conjugated dienes to give 1,4-cyclohexadienes: C C C C C C
The Diels-Alder reaction also provides a route to aromatic compounds through cycloadditions with “benzyne” as the dienophile.
This is a highly unstable and reactive fleeting intermediate which is generated in situ by elimination
(of ortho substituents from a suitable benzene derivative) and immediately trapped by Diels-Alder cycloaddition to a diene.

The lab involves the generation of benzyne by heating diphenyliodonium-2-carboxylate, which is a complex reagent, at 200 °C. This carboxylate salt is obtained from 2-iodobenzoic acid through oxidation using potassium persulfate to produce an iodonium sulfate. The resulting compound then undergoes electrophilic aromatic substitution with benzene. The diene used in a previous experiment, tetracyclone, will be used to trap the benzyne as it forms. At the reaction temperature, the Diels-Alder adduct that is formed is unstable and rapidly loses carbon monoxide, resulting in the formation of 1,2,3,4-tetraphenylnaphthalene. CO2H I K2S2O8 CO2H I OSO3 Ph Ph O Ph ? Ph Ph benzyne Ph Ph O ?

The procedure for preparing diphenyliodonium-2-carboxylate involves the following steps:

1. Begin by placing 8 mL of concentrated sulfuric acid in a 25 mL Erlenmeyer flask and cooling it in an ice-bath.

2. Take 2.0 g of 2-iodobenzoic acid and 2.6 g of potassium persulfate, mix them in a mortar, and crush them into small particles.

3. Transfer the mixture to a 125 mL Erlenmeyer flask.

4. Swirl the flask containing the sulfuric acid in the ice-bath for a few minutes and then dry it off.

5. Place the 125 mL flask in the ice-bath and carefully pour the cold acid down the wall of the larger flask to wash the solid to the bottom.

Swirl the larger flask in the ice-bath for 5 min to evenly disperse the particles in the liquid. Take the flask out of the ice-bath and record the time, then allow it to sit for 20 min. Swirl the flask in the ice-bath again for 5 min and cautiously add 2 mL of benzene. Keep swirling the flask until the benzene solidifies. Remove the flask from the bath, dry it off, and note the time when the benzene melts. Warm the flask with your hands and swirl it multiple times at room temperature over a 20 min period. Swirling is crucial to achieve complete reaction in the two-phase system.

During this period, chill three 50 mL Erlenmeyer flasks in the ice-bath. One flask should contain 19 mL of distilled water, the second flask should have 23 mL of 27% ammonium hydroxide, and the third flask should contain 40 mL of methylene chloride. After the 20-minute interval, thoroughly chill the reaction mixture in the ice-bath and place a small separatory funnel over the flask with the reaction mixture. Transfer the 19 mL of cold water into the funnel while swirling the reaction flask. Slowly add the cold water to the reaction flask until a solid substance separates. Take the chilled ammonia solution and pour it into the funnel, then transfer the cold methylene chloride into the reaction flask.

Once again, mix the reaction flask in ice and carefully add the ammonia solution from the funnel. Take your time with this step, approximately 10 minutes. Ensure that the resulting mixture has a pH greater than 9 by testing for alkalinity. If necessary, add more ammonia solution. Transfer the reaction mixture into a separatory funnel and rinse the flask with a small amount of methylene chloride. Allow the layers to separate, and then remove the lower, organic layer through a filter paper cone that contains anhydrous sodium sulfate. Place the extracted layer into a 250 mL round bottom flask that has been weighed beforehand.

Extract the aqueous layer twice with 10 mL portions of methylene chloride, running the extracts through the drying agent into the tared flask. Use a roto-vap to remove the solvent. Weigh the crude iodonium carboxylate inner salt. The product should weigh approximately 2.5 g. Transfer the solid to a 50 mL Erlenmeyer flask. Add 14 mL of distilled water to the 250 mL flask, swirl the flask, and add its contents to the 50 mL flask before again adding 14 mL of water to the smaller flask. Heat the contents of this flask to boiling, then add a little charcoal for decolorizing, swirl, and filter at the boiling point through moistened filter paper in a stemless funnel which has been preheated on a steam-bath. The benzyne precursor, diphenyliodonium-2carboxylate, should crystallize in colorless, rectangular prisms. Weigh the dry crystalline material, and calculate the yield.

Procedure for the preparation of 1,2,3,4-tetraphenylnaphthalene: Place half of the diphenyliodonium-2-carboxylate and half of that weight of tetracyclone (that you prepared previously in the dilantin laboratory) in a 25 X 150 mm test tube.

Rinse the solids down the sides of the tube as you add 6 mL of triglyme. Clamp the test tube vertically, insert a thermometer, and heat the tube with a butane torch (ask your demonstrator for assistance with this). No open flames allowed outside of the hood, and when in use no flammable solvents are allowed in or near the hood. When the temperature reaches 200 °C, remove the flame, note the time, and, with intermittent heating, maintain the temperature near 205 °C until the purple color disappears and bubbling ceases. If the color persists for more than 3 min, add a little more of the benzyne precursor.

Chemistry 3373f, Fall 2007 Page 15 and heat the mixture until the solids are dissolved and the purple color disappears completely. Let the yellow solution cool down to 90 °C. In a separate flask, heat 6 mL of 95% ethanol until it boils. Transfer the yellow solution to a 25 mL Erlenmeyer flask, using small amounts of the hot ethanol to clean the test tube. Add the remaining ethanol to the yellow solution and heat it to boiling. Gradually add water until crystals start to form. Allow the mixture to cool to room temperature and then chill it to ice temperature.

Collect the product, weigh it dry, and determine its melting point and the yield. Chemistry 3373f, Fall 2007 Page 16 The Fischer Indole Synthesis: Preparation of 2-Phenylindole Indoles are among the most important of all biologically active organic compounds. The indole ring system is found in diverse naturally occurring molecules including tryptophan (an essential amino acid), 3-indoleacetic acid (the main plant growth hormone of higher plants), and serotonin (a bioregulator that plays an essential role in our mental health).

Skatole (3-methylindole), which comes from the digestion of proteins, produces the unpleasant smell of feces. However, when it is in a more diluted form, skatole has a pleasant floral fragrance and is commonly used in perfumes! CH3 CO2H N H indole N H skatole N H 3-indoleacetic acid NH2 CO2H N H tryptophan HO N H serotonin NH 2 Indoles, including indomethacin and indoxole, are used as medicinal drugs. Indomethacin is an anti-inflammatory, antipyretic, and analgesic similar to aspirin. Indoxole is also an anti-inflammatory and antipyretic medication. The Fischer indole synthesis is commonly used to synthesize many of these drugs. In this laboratory experiment, we will use this reaction to create a compound closely related to indoxole called 2-phenylindole. ) Psilocybin and psilocin are the main and secondary active substances found in the hallucinogenic sacred mushroom of the Aztecs, referred to as teonanacatl (“flesh of the gods”). Today, native peoples in the southwestern United States and Mexico still use this mushroom in religious ceremonies. Chemistry 3373f, Fall 2007 Page 17 O CH 3 CO 2 H CH 3 O CH 3 N O indomethacin N Cl H indoxole O O P O HO H N O CH 3 N OH CH 3 CH 3 CH 3 CH 3 N H psilocin N H psilocybin

In this experiment, the preparation of 2-phenylindole will be conducted through the acid-catalyzed rearrangement of acetophenone phenylhydrazone, resulting in the elimination of ammonia. The mild acid, acetic acid, catalyzes the formation of phenylhydrazone from acetophenone and phenylhydrazine. However, the Fischer indole synthesis of 2-phenylindole from the phenylhydrazone requires a much stronger acid. In this case, “polyphosphoric acid” (PPA) will be utilized, which is created by heating a mixture of phosphoric acid and phosphorus pentoxide. PPA is composed of approximately 55% triphosphoric acid and 45% other polyphosphoric acids.

O OH O CH3 PhNHNH2 EtOH HOAc ?

H 3C N H N PPA ? N H 2-phenylindole O OH O triphosphoric acid OH HO P O P O P OH Procedure for the preparation of acetophenone phenylhydrazone Dissolve 1. 2 g (10 mmol) of acetophenone in 5 mL of 95% ethanol in a test tube. Carefully stir in 1. 0 g (10 mmol) of phenylhydrazine [Toxic liquid and vapor! A station to weight out these reagents will be set up in the dispensing hood. Work or in hood! Wear gloves! ] and then 2 drops of glacial acetic acid. Return to your work area add a boiling chip, and heat the mixture gently on a sand bath for 15 min, adding more ethanol if it boils away.

To cool the mixture and allow the product to crystallize, place it in an ice bath. If necessary, scratch the mixture to encourage crystallization. Then, use a Buchner funnel to filter and collect the phenylhydrazone.
Wash the crystals with a few mL of 1 M aqueous hydrochloric acid, followed by a few mL of ice cold 95% ethanol. Allow the crystals to air dry on the filter. For maximum dryness, press the crystals between two large pieces of filter paper. Remember to wear gloves!
This is the procedure for preparing 2-phenylindole: Using a poly squeeze bottle, weigh 20 g of syrupy polyphosphoric acid into a dry 50 mL beaker.

Place the beaker on a steam bath and secure a thermometer in a way that it can measure the temperature of the liquid near the beaker wall. Heat the acid until it reaches 50 °C and slowly mix in the acetophenone phenylhydrazone, being careful not to touch the thermometer bulb with the stirring rod. (Do not use the thermometer as a stirring rod!) Once the addition is complete, continue stirring and strongly heat the mixture on the steam bath for 15 minutes while stirring. Carefully transfer the hot mixture into 30 mL of ice and water, rinsing the beaker with a few mL of water. Stir until all the acid dissolves in the water.

Collect the precipitated crude product on a Buchner funnel, wash it with cold methanol, and let it air dry on the filter. Recrystallize the crude product from a mixture of ethanol and water, using approximately 0.1 g of decolorizing carbon. (First dissolve the crude product in hot ethanol, then add the activated carbon and filter while still hot. Heat the filtrate to boiling, and add water until it becomes cloudy. Dissolve the fine cloudy precipitate by adding a few drops of ethanol, and let the solution cool undisturbed. Gather the crystals on a Buchner funnel, and let them air dry at room temperature.) Determine the weight of the product, calculate the yield, and obtain the final result.