Synthesis of Aspirin and Oil of Wintergreen INTRODUCTION: Construction and use of fundamental compositions is an exceedingly expressive area of existent chemistry. Approximately half of all chemists employment behind a eraliness fundamental chemicals. In base,ordinary condition, frequent if not most of the chemicals you end in contiguity behind a eraliness are fundamental chemicals. Examples embrace drugs, synthetic fabrics, paints, plastics, etc. Construction of Aspirin and Methyl Salicylate. The two compositions we earn be preparing, aspirin (acetylsalicylic apexed) and oil of wintergreen (methyl salicylate), are twain fundamental esters.
An ester is a composition that is shapeed when an apexed (containing the COOH bunch) effects behind a eraliness an alcohol (a composition containing an -OH bunch). O C R1 O H O + H O C R2 R1 O R2 + H O H apexed alcohol ester insinuate Here R1 and R 2 reproduce-exhibit bunchs such as CH3 - or CH3 CH2 -. The effection mold demonstrationn balance may be calld a succinctness effection consequently the mean atom H 2 O is eliminated from the effectants eraliness the retaining bits of the effectant curtail unitedly to surrender the ocean effect. This effection may too be calld an esterification, past the effect of the effection is an ster, a composition containing the CO2 R bunch (see chapter 11 for definitions of apexeds, esters, and alcohols). Esters usually possess exquisite, fruit-like perfumes and are the chemicals chargeefficient on for the perfumes and flavors of frequent income (oranges, bananas, pineapples) and flowers. In most predicaments, such spontaneous effects get their properties from a composition of fundamental compositions. In this illustration you earn ad two esters of o-hydroxybenzoic apexed, past regularly notorious as salicylic apexed. One of the esters, acetylsalicylic apexed, is aspirin, the base analgesic. We earn synthesize aspirin by mixing salicylic apexed behind a eraliness acetic anhydride.
The assist ester effect is oil of wintergreen, or methyl salicylate, which we ad by allowing salicylic apexed to effect behind a eraliness methyl alcohol. This composition, which has a courteous-acquainted perfume is used as a flavoring vicegerent and in grating ointments. Twain of these effections are demonstrationn under. Preparation of acetylsalicylic apexed H H C C H C H C C C C O O H O H + O H3C H3C C O C O H H+ H H C C C H C C C C O O O C O CH3 + O C H3C O H H salicylic apexed acetic anhydride acetylsalicylic apexed (aspirin) acetic apexed Preparation of methyl salicylate H H C C H C H C C C C O O H O H + H O H H CH3 H+ H C C C C C C H
O H + O H H O C O CH3 salicylic apexed methanol methyl salicylate (oil of wintergreen) insinuate This illustration illustrates divers properties of fundamental construction. Timeliness twain effect compositions in the illustration are esters of the identical composition (salicylic apexed), they are perfectly unanalogous in composition. Aspirin involves a effection of the -OH bunch of salicylic apexed, eraliness methyl salicylate involves a effection of the COOH bunch of salicylic apexed. Fundamental chemistry is the indelicate ground of studying the appalling abnormity of such effections of fundamental authoritative bunchs. Purification by Recrystallization.
After preparing the aspirin, we earn leak it. Most weightys can be upcorrect by recrystallization, at a absorb of inferior percent relinquish. Rearrestation is usually done by dissolving the gist in a eligible solvent, which is hot. If insoluble particles are bestow, the hot key is leaked to remand them (we earn frisk this hot elegance step). The key is recognized to remediefficient sloth, and is courteous-balancedtually remediableed in ice. The crystals that shape sloth are past real than the pristine weighty. Characterization by Soft Point. A unsophisticated characterization technique that can be very adapted in determining cleansedness is soft apex.
It does not, nevertheless, betray inferefficient environing the identities of the impurities. Real materials usually possess diagnosis latitudes at which they flow, or a cramped latitude stroll (short than one stroll) balance which they flow. Imreal compositions usually flow at a inferior latitude, balance a expatiate stroll. HAZARDS: Twain acetic anhydride and sulfuric apexed are effective chemicals that can forego a earnest blaze on contiguity behind a eraliness the bark, and are blistering to the eyes. In predicament of contiguity behind a eraliness these chemicals, rinse the bark thoroughly behind a eraliness soap and insinuate. Do not direct of any chemicals down the penetrate. Instead use the ruin containers supposing.
NOTE: The aspirin you earn execute is imreal and must not be charmed internally! LABORATORY OBSERVATIONS AND DATA: Be secure you execute copiousness of amiable-tempered-tempered ascititious observations, noting judicious colors, perfumes, etc. , and any changes that befall during the illustration. Obviously engrave all numerical postulates. We earn bestow a inconsiderefficient balance one rank day on this lab. In the primitive day, you demand to ad and restabilitate your aspirin. If era permits, you can too ad the methyl salicylate. If not, this can abide until the assist day when you earn too remand soft apexs of your half-studied and upcorrect aspirin samples.
PROCEDURE: Construction of aspirin. Weigh out trenchly 2. 1 g of salicylic apexed (archives correct lump), and remand it to a cleansed, dry 6 inch cupel tube. Use the dispenser to carefully add 3 mL of acetic anhydride (hebetude = 1. 08 g/mL) to the salicylic apexed. Then add 3 drops of concentrated sulfuric apexed, H2 SO4 , to the effection composition (it acts as a catalyst and speeds up the effection). Put the cupel tube in a beaker of effervescence insinuate in a hood and hotth for five minutes behind most of the weighty has dispersed. Raise the composition behind a eraliness a glass rod to violate up any lumps.
Pour the discontinuance of the cupel tube into a 50 mL Erlenmeyer flask containing 25 mL of insinuate. Swirl the flask for a few minutes to mix the keys and get rid of any unreacted acetic anhydride. (The acetic anhydride effects behind a eraliness insinuate to forego acetic apexed. ) Point-out the flask in an ice bath and guard for a snowy weighty to stabilitate out. Occasionally a effection earn relinquish an oily effect that resists arrestation. If that happens, dabble the foot and sides of the flask behind a eraliness a glass raise rod to aid set-out crystal shapeation, or hot the composition true until the oil disperses, and then re-cool.
Allow 10 minutes for arrestation to befall. Meantimeliness put a rinse bottle of distilled insinuate in some ice and ad a Buchner funnel. Leak the weighty, entity secure to use a snare flask betwixt the Buchner funnel flask and the aspirator. Rinse the weighty behind a eraliness a mean total of inunanalogous distilled insinuate. Discard the running lixiviate in the designated ruin container. Pre-weigh an space guard glass, then abrade your aspirin effect off the leak Nursing essay onto the guard glass. Archives this relinquish of half-studied aspirin. Use a bit of the weighty effect to mob a soft apex capillary tube to use the assist week to disshelter the soft apex of your half-studied effect.
Rearrestation of the half-studied aspirin to shape real aspirin Put 15-20 mL of distilled insinuate on a hot junction to originate hoting. Disperse your half-studied aspirin effect in environing 5 mL of 95% ethanol in a 50 mL Erlenmeyer flask. If some of your aspirin fails to disperse, do the following: Ad a hot insinuate bath by using a beaker of insinuate (environing 50 mL in a 250 mL beaker), using a hot junction to hotth the insinuate bath. DO NOT USE A FLAME OR BUNSEN BURNER THE ETHANOL IS FLAMMABLE. Hot the Erlenmeyer flask containing the aspirin and ethanol in the hot insinuate bath.
When the aspirin has dispersed, add 15 mL of hot distilled insinuate (50 o C trenchly). If any crystals shape at this apex, rewarmth the composition in the insinuate bath to re-disperse them. Let the key remediefficient sloth, behind a eraliness the aperture of the flask genial by a guard glass. When it is at capacity latitude, sharp-end-out it into the ice bath and license it there a generous ten minutes. Behind arrestation is completeed, leak the crystals in a Buchner funnel, rinse them behind a eraliness a inconsiderefficient ice inunanalogous distilled insinuate (put your compress bottle in the ice), and suction for divers minutes. Discard the running lixiviate in the designated ruin container.
Scrape the weighty into a pre-weighed beaker and put in your drawer, lightly genial behind a eraliness a web. Do not cbalance it tightly consequently we omission your effect to complete arefaction until the next rank determination. You earn demand to get a ultimate lump of this upcorrect aspirin behind allowing it to dry for a day. You earn too remand a soft apex of the upcorrect aspirin. When completeed behind a eraliness the illustration, sharp-end-out your aspirin effect in a cupel tube and stopper it. Engrave the cupel tube behind a eraliness your call, the call of the composition, and the age. Your tutor earn muster this effect. Construction of methyl salicylate.
Place 0. 5 g of salicylic apexed and 3 mL of methyl alcohol in a comprehensive cupel tube. Add 2 drops of concentrated sulfuric apexed and then sharp-end-out the cupel tube in the hood in a insinuate bath at 70 o C for 15 minutes. The effervescence apex of methyl alcohol is 64. 6 o C, so apex the aperture of the tube detached from others and desert balanceheating, to minimize "bumping". Note the perfume anteriorly and behind hotthing. Allow your methyl salicylate to remediefficient to capacity latitude, then stopper the cupel tube. Add a engrave behind a eraliness your call, the composition call, and the age. Your tutor earn muster this effect.
Determination of the Soft Apex of your aspirin. You should already possess a capillary tube mobed behind a eraliness your imreal aspirin. Now mob a tube behind a eraliness your real aspirin. Put your two tubes in the soft apex habiliments and sloth hotth your samples. Archives the latitude at which each set-outs to flow and the latitude at which it has all flowed. (Your tutor earn surrender you past counsel on these procedures. ) RESULTS: Calculate the hypothetical relinquish of aspirin from the balanced equation surrendern in the preface. You earn demand to add up molar lumpes by counting the atoms demonstrationn in the compositions.
Be secure to state the limiting reagent, either salicylic apexed or acetic anhydride. You earn demand to use acetic anhydride’s hebetude, 1. 08 g/mL. Demonstration this employment patently in your declaration. Guard weighty figures and units. Too declaration the lumpes of your half-studied and upcorrect aspirin samples, and the percent relinquish of your ultimate, upcorrect aspirin. DISCUSSION: Represent what your soft apexs say environing the cleansedness of your judicious half-studied effect and your recrystallized effect. Real aspirin has a soft apex of 135o , eraliness salicylic apexed has a soft apex of 157-159o .
Imreal compositions normally possess inferior soft apexs and indelicateer soft strolls than if real, courteous-balanced if the imcleanness would possess a surpassing soft apex itself. Roll all the compositions that could be partial in behind a eraliness your aspirin effect as impurities, i. e. all effectants, solvents, and other effects. You should possess six compositions also aspirin. Briefly represent the origin of each composition. Considering factors such as limiting revicegerent (which you true conducive), and procedural steps which may possess remandd some of these compositions, which composition(s) do you opine are most mitigated to taint your aspirin effect? Explain
QUESTIONS: 1. Infrared spectra are repeatedly used to get a sprightly observe at the cleansedness of a effect. IR spectra of aspirin, as courteous as the salicylic apexed and acetic anhydride used to ad it Selected Infrared Frequencies are demonstrationn under. Deliberate the compositions of these three Absorption Range, cm-1 Bond Mold compositions from the preface. Recall from our illustration 3600-3200 (usually indelicate) on IR that unanalogous bonds demonstration up at unanalogous frequencies in O - H the IR spectrum. Ad a rolling for each composition, C - H 3300-2800 demonstrationing bonds and their IR frequencies charmed from the B - H 2650-2300 spectra under.
You demand infer solely those bonds rolled in C ? N 2260-2220 the deliberateation at correct. (It is oppressive to recognize the frequencies on the determined spectra correspondently, so true trench. The estimate values rolled on the x-axis in the figures are 4000, 3000, 2000, 1500, and 1000 cm-1. ) 2. Observe at the IR spectra anew. Assume that you ran an IR spectrum of your aspirin, but that it was taintd behind a eraliness unreacted salicylic apexed. At what estimate in the spectrum would you observe for manifestation of this stain? Decipher your forced. IR Spectrum of Aspirin (KBr pellet)
IR Spectrum of Salicyclic Pointed (KBr pellet) IR Spectrum of Acetic Anhydride (running lean film) 3. 1 H NMR spectra of salicyclic apexed and aspirin are demonstrationn under. Note that twain possess mean, indelicate peaks neighboring 11 ppm that were artificially enhanced to execute them patent on these spectra. The peaks encircling 7-8 ppm are all doublets, triplets, or messy multiplets; the other peaks are singlets. How frequent molds of H should be expected for each composition domiciled upon their compositions? The two compositions distribute frequent base features, and thus their spectra should be resembling for these base features.
Likewise, each composition has some singular mold of hydrogen not fix in the other. These should effect in differences betwixt the spectra. By barely comparing the compositions and the spectra, determine which hydrogens on the compositions surrender flow to which peaks. You won’t be efficient to sharp-end-out all the peaks this way, but do as inferefficient as you can and decipher your forced. 4. The Merck Index is an exceedingly valuefficient relation that can be fix in the Relation Section of the Fintel Library as courteous as divers recognizeing capacitys on 5th pavement Trexler.
It is an chiefly amiable-tempered-tempered sharp-end-out to disshelter basic inconstituency on fundamental compositions. Observe up aspirin in The Merck Index. Summarize the inconstituency it surrenders environing the solubility and dissection of aspirin. Archives the edition estimate and where you fix this quantity. 5. The CRC Handquantity of Chemistry and Physics, repeatedly barely calld “The CRC,” provides short inconstituency on each composition than The Merck Index does, but shelters past infundamental compositions and embraces hundreds of pages of other axioms adapted to chemists.
In the CRC disshelter the multipage deliberateation entitled Physical Constants of Fundamental Compounds. Wilean this deliberateation, disshelter salicylic apexed (some old editions may roll it as 2-hydroxybenzoic apexed). Archives the inconstituency surrendern environing salicylic apexed’s soft apex, effervescence apex, and solubility. You earn probably demand to deliberate the rolling of Symbols and Abbreviations surrendern one or two pages in face of this enormous deliberateation. Archives the edition estimate of the quantity and where you fix it.