Experiment 9 ESTERIFICATION OF SALICYLIC ACID: PREPARATION AND CHARACTERIZATION OF ASPIRIN AND OIL OF WINTERGREEN Bacuyag, Florence Mae S. Mendoza, Jillian Ela M. Munoz, Abel Christopher Valino, Angelica Faye Collee o! S"ien"e #ni$er%it& o! t'e P'ilippine% ()*io A+%tr)"t Esterification is the process of making an ester using carboxylic acid or its derivatives and catalysed by an acid. This experiment aimed to prepare and determine the percentage yield of the aspirin produced, characterize crude, recrystal recrystalliz lized, ed, and commercia commerciall aspirin, aspirin, and to synthesiz synthesize e and react react methyl methyl salicylate with FeCl . !reparation of aspirin involves esterification of salicylic acid, catalysed by phosphoric acid. The crude and recrystallized aspirin had a percentage yield of "#.$% and &$.'%, respectively. respectively. The melting point ranges were also determined. The crude aspirin had a lower melting point than actual( the recrystallized aspirin was considered pure since it is within the melting point range( range( the commer commercia ciall aspiri aspirin n yielde yielded d )#*C+ )#*C+)#" )#"*C *C melti melting ng point. point. Crude, Crude, recrystal recrystalliz lized, ed, and commercia commerciall aspirin aspirin were soluble in water, water, toluene, and a-C, but only crude and commercial aspirin tested positive in the test for phenolic group. /ethyl salicylate was also synthesized using salicylic acid, methanol, and concentrated - ' 0 '0 # as catalyst. The methyl salicylate produced was reacted with FeCl and produced a violet solution.
INTROD#CTION Carboxylic acid derivatives are compounds having an acyl group bonded to an electronegative atom or substituent that acts as a leaving group in the nucleophilic acyl substitution reaction. (McMurry, 2012).
Euation1. !ucleophilic "cyl #ubstitution $eaction (McMurry, (McMurry, 2012) %ne o& these these acid acid deriv derivati atives ves is ester ester.. Ester Esters s are derive derived d &rom &rom carbox carboxyli ylic c acids acids and their their derivatives. 'he hydrogen in the C%% group in carboxylic acid is being replaced by a hydrocarbon group, *hich can be aryl or al+yl, in esters. Esters are synthesied by an acid catalyed nucleophilic acyl substitution reaction. 'his process is called esteri&ication. 'he reaction involves alcohol and an acid catalyst (Clar+, 200-).
Euation2. Esteri&ication Mechanism sing Carboxylic "cid
#alicylic acid, (C /%-), also +no*n as orthohydroxybenoic acid is a *hite crystalline solid. t *as &irst prepared &rom salicylaldehyde but these days, it is already made o& sodium phenolate and carbon dioxide &ollo*ed by a treatment *ith acid. t is used in preparation to combat *arts, corns, calluses, and various s+in diseases. t also has its bad e&&ects, it is irritating to the lining o& the mouth, esophagus, and stomach, and can cause hemorrhaging o& the stomach lining. 'his is mainly because salicylic acid is diprotic acid, *hen dissolves in *ater, it releases t*o hydronium ions and ma+es the solution more acidic (3ro*n, n.d.). "cetyl salicylic acid, *as trademar+ed by the 3ayer as "spirin4. 'he 5a6 in the name 5"spirin6 comes &rom the root acetyl, 5spir6 &rom the 7ree+ root 5spirea6 (*illo* plant), and 5in6 is a common medical su&&ix to help ease o& pronunciation. ("li, 2018) #alicylic acid has a carboxyl and a hydroxyl group both attached to a benene ring. t is a di&unctional organic compound *hich can undergo esteri&ication in t*o di&&erent *ays, it can act as a carboxylic acid and an alcohol. #alicylic acid as an alcohol *ill react *ith acetic anhydride, (C 8%-), and sul&uric acid, ( 2#%8), as a catalyst &orming acetyl salicylic acid, (C 9:%8), or aspirin. 'he phenol group on the salicylic acid &orms an ester *ith the carboxyl group on the acetic anhydride.
; salicylic acid
acetic anhydride
2#%8 (catalyst)
; acetyl salicylic acid
carboxylic acid
Euation-. #ynthesis o& "cetyl #alicylic "cid ("spirin) "spirin is the most used medication globally. t is used to treat &ever, pain, and can act as anti in&lammatory agent. t is a nonsteroidal antiin&lammatory compound. n preparation o& acetyl salicylic acid, recrystalliation is involved. 'his process is an easy and e&&ective *ay to puri&y solid organic compounds as long as the solvent satis&ies the &ollo*ing criteria< t should readily dissolve the solute at elevated temperatures and sparingly at lo*er temperatures. t should dissolve the desired solute and not the impurities. t should dissolve the desired solute and not the impurities. t should be chemically inert to the solute. t should allo* the solute to give *ell&ormed crystals upon cooling. t should be highly volatile to permit easy removal &rom the pu ri&ied crystals. •
• • • •
$ecrystalliation is necessary because aspirin is crystalline at a room temperature but a solution at a higher temperature *hen synthesied. 'his process recrystallies the aspirin *hile the solid impurities *ill remain dissolved in the solution, thus, isolating it. t reuires the &ormation o& a &e* introductory crystals at the beginning. =ormation o& crystals can either be induced through seeding or scratching o& the *alls o& the container. #eeding involves the addition o& a pure solid compound *ith the same composition as that o& the compound to be crystallied. #olid aspirin is isolated through suction &iltration. 'his experiment aims to compute the percentage yield o& the crude and the recrystallied aspirin. 'he percent o& starting material that is converted to product in a chemical reaction is re&erred to as the percent yield. %rganic reactions typically do not give 100> yields, meaning not all o& the starting material is converted to the product. 'he percent yield can be calculated *ith the &ollo*ing in&ormation< • • • •
?eight o& the starting material limiting reagent (usually in grams or milligrams) Molecular *eight o& starting material (g@mol) ?eight o& product (in grams) Molecular *eight o& product (g@mol)
'his experiment also aims to determine some characteriations o& crude, recrystallied, and commercial aspirin such as their melting point, their solubility in *ater, ( 2%), sodium bicarbonate, (!aC% -), and toluene, (CAC-). "lso, test &or phenolic group is included. %n the other hand, salicylic acid as carboxylic acid reacts *ith methanol, (C -%), and *ith the presence o& acid catalyst sul&uric acid, it yields into methyl salicylate.
; salicylic acid
-C% methanol
2#%8 (catalyst)
; methyl salicylate
2% *ater
Euation8. #ynthesis o& Methyl #alicylate (%il o& ?intergreen) Methyl salicylate or 5oil o& *intergreen6 is used as a &lavoring agent such as in candies and &oods and is also used in per&umes. t is also used by athletes to soothe muscular aches and pains. t has a s*eet and &resh scent li+e mint, thus, it is also added in gums and toothpaste. 'his experiment includes the testing o& the reactivity o& methyl salicytate to &erric chloride, (=eCl -).
RES#LTS AND DISC#SSION ". Breparation o& Crude "cetylsalicylic "cid n this experiment, preparation o& crude "#" reuired three grams o& salicylic acid reacted *ith /.Am acetic anhydride and &ive drops o& :A> phosphoric acid. 'he salicylic acid reacted *ith excess acetic anhydride, *here phosphoric acid acted as a catalyst ("rias, 201). eat *as also reuired to be able to &orm the acetylsalicylic acid ("#") and acetic acid (C -C%%) (Eddy, n.d.). " sour smell given o&& by the reaction is due to the presence o& the acetic acid. 'his reaction is called an esteri&ication reaction since the hydroxyl group in the salicylic acid &ormed an ester in the "#" (Bavia, et.al., 200A).
Euation A. #ynthesis o& "cetylsalicylic "cid (retrieved &rom http<@@***.lahc.edu@) ?hile cooling the solution, more crystals started to &orm. 'his is due to the decreasing solubility o& "#", thus it is solidi&ying. ?ater decreases the solubility o& "#" so ice *ater *as added to maintain its temperature and solubility (Bavia, et.al., 200A). 'o induce crystalliation, the *alls o& the bea+er *ere scratched. Crystals &ormed are mainly "#" but some substances are also present. ?ater also mixes *ith the excess acetic anhydride and some other impurities thus ma+ing the "#" impure.
3. Breparation o& $ecrystallied "cetylsalicylic "cid 2.1A grams o& crude aspirin *as trans&erred to a 12Am E&las+ *ith a 10m each o& diethyl ether and petroleum ether. 'he &las+ *as then cooled and the crystals *ere collected through suction &iltration. 'he "#" acuired *as puri&ied by recrystalliation (Eddy, n.d.). n recrystalliation, the impure substance *as dissolved in a hot solvent and is cooled to induce crystalliation (#mart, 2002). "dding ether to the "#" crystals prevented the crystals to decompose. (Bavia, et.al., 200A). C. Mass Calculation 'able1. Mass in grams o& the samples used in the synthesis and recrystalliation o& aspirin. ?eighed #ample Mass (in grams) Mass o& &ilter paper
0.81
Mass o& &ilter paper ; crude aspirin
2.A
Mass o& crude aspirin
2.1A
Mass o& &ilter paper
0.81
Mass o& &ilter paper ; recrystallied aspirin
1./
Mass o& recrystallied aspirin
1.29
'able2. ?eight in grams and molecular *eight o& the starting material and product. ?eight o& the starting material limiting reagent -g (salicylic acid, C/%-) Molecular *eight o& starting material (salicylic acid, C/%-)
1-:.121g@mol
?eight o& product (aspirin, C9:%8)
2.1Ag
Molecular *eight o& product (aspirin, C 9:%8)
1:0.1A9g@mol
n solving &or the percentage yield o& the crude aspirin, the uantity in grams o& salicylic acid as the limiting reagent *as converted to moles<
-g C/%- D
1mol C9:%8 1-:.121g C9:%8
0.021/2mol C9:%8
'heoretical yield *as calculated (the number o& grams o& product that *ould &orm i& every mole o& limiting reagent *ere converted 100> to product). 0.021/2mol salicylic acid *ill yield to 0.021/2mol aspirin.
0.021/2mol C9:%8 D
1:0.1A9g C9:%8 1mol C9:%8 -.91-0A g C9:%8 (theoretical yield)
Bercentage yield *as computed by dividing the actual yield, 2.1Ag o& aspirin, by the theoretical yield. 2.1A g C9:%8 -.91-0A g C9:%8 D 100 A8.:> (percentage yield) n the recrystalliation o& aspirin, 1.Ag o& the crude aspirin *as mixed *ith 1Aml each o& diethyl ether and petroleum ether. Crystalliation *as completed and crystals *ere collected by suction &iltration.
1.29g o& recrystallied aspirin *as collected. n computing &or the percentage yield, the mass o& the recrystallied aspirin *as divided by the mass o& the crude aspirin. 1.29g 1.Ag D 100 /:.2> (percentage yield) 'hus, the percentage yield &or the synthesis o& aspirin is A8.:> and the percentage yield &or the recrystalliation o& aspirin is /:.2>. F. Characteriation o& "spirin 'he melting point o& crude aspirin, recrystallied aspirin and commercial aspirin *ere determined and compared. 'he three +inds o& aspirin *ere pulveried on a *atch glass *ith the end o& a test tube one at a time and separately. 'he pulveried samples *ere then mounded. "&ter*ards, the open end o& the melting point capillary tube *as pressed into the samples against the sur&ace o& the *atch glass. 'he capillary tubes *ere lightly tapped on the sealed end o& the tube on the tabletop until the samples &illed about t*o to &our mm height. " 2Am o& oil *as placed in a A0m bea+er. " thermometer *as then inserted through a cor+ near the top o& the thermometer. 'he capillary tubes *ere separately attached *ith the samples by means o& a rubber band. 'he oil bath *as strong heated *ith constant stirring until the temperature is 101AGC belo* aspirinHs melting point, 1-AGC. "&ter*ards, a very lo* &lame *as utilied so that the temperature o& the bath rises at a rate o& -GC per minute. 'he temperature *as recorded as soon as a droplet o& liuid &ormed *hich is the start o& meltingI the second temperature reading *as also recorded as soon as the last trace o& solid liue&ied *hich is the end o& melting. 'he melting point o& the compounds can provide valuable in&ormation that can help in the identi&ication o& aspirin or to establish its purity. 'he melting point is the temperature at *hich the solid melts. 'he intermolecular &orces that hold the aspirin together li+e hydrogen bonding, dipoledipole &orces and ondon dispersion &orces have to be overcome &or melting to occur. 'hese &orces hold the molecules together in a crystal lattice. Bure, crystalline organic compounds usually have sharp and characteristic melting points. Compounds *ith minimal or large amounts o& impurities can have a lo*er melting point than the pure aspirin and increase in the melting point range. (%', n.d.) 'he rate o& heating should be slo* near the melting point (about -GC per minute) to guarantee that the increase rate o& temperature is not &aster than the ability o& the heat to be trans&erred to the sample. t is necessary that the thermometer bulb and the sample in the capillary tube be at thermal euilibrium. ("CC, 200A) 'he melting point o& acetylsalicylic acid or aspirin is 1-AGC. 'he melting point range o& crude aspirin is 10-GC120GC, *hich is signi&icantly lo*er than the actual melting point and has a *ide range o& melting point. 'his implies that the crude aspirin still contains some impurities since it melted in a long time. Bossible impurities are *ater, salicylic acid, acetic anhydride, and phosphoric acid. 'he recrystallied aspirin has a melting point o& 1-GC1-:GC. 'his implies that the recrystallied aspirin is pure since the melting point range is near the actual melting point and the range is sharp. 'he melting point range o& commercial aspirin is 1-8GC18AGC since more than 8mm *as applied in the capillary tube. #ince it has a *ide range o& melting point, this implies that the commercial aspirin has other ingredients other than aspirin itsel&. Bossible ingredients may be *ater, corn starch, &illers or diluents, and lubricants. 'he solubility o& crude aspirin, recrystallied aspirin, and commercial aspirin *ith *ater, sodium bicarbonate, and toluene *as also determined. 'he three compounds *ere pulveried and 0.1g o& each *as separately put in the test tubes. "&ter*ards, 2.Am o& *ater, sodium bicarbonate and toluene, respectively, *as added. "spirin is an aromatic compound *hich contains both a carboxylic &unctional group and an ester &unctional group. t is a *ea+ acid. #ince aspirin has a polar component in its carboxyl &unctional group and *ater is polar, aspirin is partially soluble in *ater. 'he aromatic ring it contains prevents it &rom being &ully soluble to *ater. Crude aspirin and commercial aspirin are also slightly soluble in *ater. "spirin is soluble in !aC%-. 'he process under*ent an acidbase reaction, giving a sodium carboxylate *hich is an ionic species o& aspirin. 'he sodium carboxylate can ma+e the aspirin more soluble in *ater. 'he sodium bicarbonate deprotonated the aspirin. ence, aspirin is soluble in !aC% -. "ll three compounds are soluble in !aC%-.
C9:%8 ; !aC%- J C::%2C%%!a; ; C%2 ; 2% Euation . $eaction o& "spirin *ith #odium 3icarbonate "cetyl salicylic acid is soluble in toluene. 3ecause both toluene and aspirin have a nonpolar aromatic ring, aspirin is soluble *ith toluene. "ll three compounds are soluble *ith toluene. 'he three compounds *ere also tested &or phenolic group. =e* crystals &rom each compound *ere separately dissolved in &ive m o& *ater. "&ter*ards, a drop o& 1> =eCl- solution *as added the color *as noted. =erric chloride &orms highly colored complexes &rom red to violet *ith phenolic compounds. #olutions containing the phenolic group are dar+ purple and ones *ithout are a yello* color. 'he &erric chloride test *as used to compare the commercial aspirin, crude aspirin and recrystallied aspirin and to chec+ the purity o& the product. pon the addition o& &erric chloride to each compound, there *as a &ormation o& violet solution in crude aspirin, yello* solution in recrystallied aspirin, and light violet solution in commercialied aspirin. 'he violet solution indicates the presence o& phenol. 'he crude aspirinHs &ormation o& violet solution implies that there is still a presence o& phenol group, salicylic acid, ma+ing the crude aspirin impure. 'he light violet solution o& commercialied aspirin accounts &or the possible phenol group in the ingredients or components &urther added in the pure aspirin. 'he &ormation o& the yello* solution in the recrystallied aspirin indicates its purity. 'he yello* solution implies that there is no phenolic group in the recrystallied aspirin and no excess salicylic acid in the compound. (%dinity, 2018) E. #ynthesis o& Methyl salicylate n a test tube, 1g o& salicylic acid *as placed. "&ter*ards, Am o& methanol - drops o& conc. 2#%8 (serving as an acid catalyst) *ere added respectively. 'he mixture produced *as transparent.
Euation /. $eaction o& Methy #alicylate *ith Methanol 'his mixture is then heated &or at least 1A minutes, having been activatedI the mixture produced a s*eet scent similar o& that to commercial products such as 5E&&icascent oil6 and 5Casino alcohol6 *hich indicates the &ormation o& ester. 'his mixture *as stored &or a couple o& minutes and it thus produced crystals *hich *ere very much &ine and condensed and had a *ebli+e aesthetic. =erric Chloride *as dropped into the solution, &orming a violet complex due to the reaction o& the phenolic (%) character o& the methyl salicylate. ?hen aspirin comes into contact *ith air moisture, the compound *ill have a bac+*ard reaction and it *ill go bac+ to its original &orm. 'he aspirin loses its strength *hen hydrogen atoms and reverts bac+ to its original composition, salicylic acid and acetic acid. "cetic acid is also the same component &ound in vinegar, *hich accounts &or the vinegar smell o& aspirin. (?hy, 2010)
CONCL#SION Esters are derived &rom carboxylic acids and their derivatives. 'he hydrogen in the C%% group in carboxylic acid is being replaced by a hydrocarbon group, *hich can be aryl or al+yl, in esters. Esters are synthesied by an acid catalyed nucleophilic acyl substitution reaction. 'his process is called esteri&ication. 'he reaction involves alcohol and an acid catalyst. #alicylic acid, (C /%-), also +no*n as orthohydroxybenoic acid is a *hite crystalline solid. t *as &irst prepared &rom salicylaldehyde but these days, it is already made o& sodium phenolate and carbon dioxide &ollo*ed by a treatment *ith acid. 3y means, o& suction &iltration "#" *as prepared, on the other hand, methanol *as added to salicylic acid *ith an acid catalyst ( 2#%8) and *as heated to produce methyl salicylate. 'he physical characteristics o& the three types o& aspirin *ere observed, in addition, the reaction o& methyl salicylate *ith =eCl - yielded a violet solution. 'he obKectives *ere success&ully achieved.
REFERENCES
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