Cinnamaldehyde, cinnamic aldehyde or 3-phenyl-2-propenal is the major constituent of cinnamon oil, extracted from several species of Cinnamomum (C. verum, C. burmanii, C. cassia), under the family Lauraceae, a group of evergreen trees. Cinnamon bark (particularly C. verum) yields 0. 4-0. % oil, which contains 60-80% cinnamaldehyde, 4-5% sesquiterpenoids (? -humulene, ? -caryophyllene, limonene and others), eugenol, cinnamyl acetate, eugenol acetate, cinnamyl alcohol, methyl eugenol, benzaldehyde, benzyl benzoate, cuminaldehyde, monoterpenes (linalool, pinene, phellandrene and cymene), safrole and others (List and Horhammer; Masada; Ravindran qtd.
from Khan and Abourashed, 2011). Isolation of cinnamaldehyde from cinnamon oil of Cinnamomum sp. ark, called “quills”, “quillings”, “featherings” and “chips” depending on quality, was first done in 1834 by Dumas and Peligot (Attokaran, 2011). It has been proven that cinnamaldehyde from cinnamon oil has a very high potential in the pharmaceutical industry, aside from its well known role in the food preparation, specifically as spice, odorant and colorant. Several researches have proven the antimicrobial activity of cinnamaldehyde against Salmonella typhimurium and Bacillus subtilis (Council of Europe, 2008).
Also, cinnamaldehyde has been proven to inhibit microbial growth of opportunistic human pathogenic fungi, such as Aspergillus niger, Candida albicans and Rhizopus oligosporus, and various bacteria (Escherichia coli, Enterobacter cloacae, Micrococcus luteus, Staphylococcus aureus, Streptococcus faecalis, and others) (Khan and Abourashed, 2011). Several studies have also unraveled the hypoglycemic (insulin-like) and hypolipidemic properties of cinnamaldehyde since it can cause: elevated glucose oxidation and uptake, causing decrease in blood plasma glucose levels; decreased glycosylated hemoglobin, serum total cholesterol and riglyceride levels; increased plasma insulin, hepatic glycogen and high-density lipoprotein; and restored modified plasma enzyme concentrations to almost normal level (Babu, Prabuseenivasan and Ignacimuthu, 2006).
Though effective approaches in the isolation of cinnamaldehyde from cinnamon oil from quills, low amounts of pure cinnamaldehyde can only be obtained from effective separation processes.
Due to this demarcation in the discovery and investigation of other potential medicinal and non-medicinal values of cinnamaldehyde, chemists have also developed synthetic procedures to obtain high amounts of pure cinnamaldehyde, one of which is the mixed aldol condensation of benzaldehyde and acetaldehyde. Mixed aldol condensation is a reaction of different aldehydes or ketones leading to the formation of aldols (? -hydroxyaldehydes) or ketols (? -hydroxyketones), accompanied by the removal of water to result finally to enals (? , ? -unsaturated aldehydes) or enones (? , ? -unsaturated ketones).
Aldol additions are due to the reaction of enolate ions of carbonyl compounds (from the reaction of acidic ? -hydrogens of aldehydes and ketones with bases) with the electrophilic centers of other carbonyl compounds. Synthesized aldols and ketols can dehydrate spontaneously or can be dehydrated, especially when heated, to form enals and enone, the final product(s) of aldol condensations (Moore and Langley, 2010). Possible side reactions were the Canizzarro reaction of benzaldehyde and the self-condensation of acetaldehyde. Minimization of the possibilities of the stated reactions was done by following a special scheme of procedure.
Characterization tests that were done in to confirm the identity of the products are boiling point determination, reactions with nitric acid and with sodium bisulfite and derivatization with 2,4-dinitrophenylhydrazine. In the experiment conducted, the objectives of the author were as follows: 1. To synthesize cinnamaldehyde from the base-catalyzed mixed aldol condensation of benzaldehyde and acetaldehyde; and 2. To characterize the synthesized product using its boiling point, results of simple chemical tests and derivatization reactions, along with the determination of the elting points of the hydrazones and comparison of the hydrazones using their RGB values. II. Materials and Methods A. Reagents The following are the reagents were used in the experiment: Benzaldehyde Acetaldehyde 15% sodium hydroxide solution Sodium chloride 95 % ethanol solution 40% sodium bisulfite solution 2, 4-dinitrophenylhydrazine Nitric acid Ice B. Apparatus and Equipment The following are the apparatus and equipment were used in the experiment: 50-mL round-bottom flask 50-mL beaker 10-mL graduated cylinder 10-mL pipet Pasteur pipet Micro distilling flask Test tubes Evaporating dish Thermometer Bunsen burner
Microreflux Watch glass Iron ring Iron clamp Iron stand Separatory funnel Wire gauze Hot plate Electronic top loading balance Fisher-Johns melting point apparatus III. Schematic Diagrams C. Synthesis of Cinnamaldehyde (in round-bottom flask) 3. 06mL – cool in ice bath + 3. 00mL 15% NaOH + 0. 50mL dropwise with swirling + 3. 00mL 15% NaOH + 0. 50mL dropwise with swirling + 3. 00mL 15% NaOH + 0. 68mL dropwise with swirling – reflux for 10-15 minutes – cool to room temperature – cool in ice bath – separate layers Organic layer , very minimal (in 10-mL graduated cylinder) Aqueous layer very minimal, unreacted
H2O with Na+ and Cl- Measure amount and save for characterization discard D. Characterization 1. Boiling Point Determination Product (in distilling flask) – distill Note temperature at which liquid starts to boil 2. Reaction with Nitric Acid (Test for presence of benzene ring) 1-2 drops of test compound1 (in test tube) + 1-2 drops HNO3 Observe visible changes and temperature changes 3. Reaction with Sodium Bisulfite (Test for presence of carbonyl compounds) 4. 0mL 40% NaHSO3 + 1. 0mL ethanol – filter Residue Filtrate Save and label “alcoholic NaHSO3” 1-2 drops of test compound1 (in test tube) + 1-2 drops alcoholic NaHSO3
Observe visible changes 4. Derivatization with 2, 4-Dinitrophenylhydrazine 1-2 drops of test compound1 (in test tube) + 4. 0mL ethanol + 3. 0mL – filter – recrystallize using 95% ethanol Colored hydrazone crystals Determine melting point and RGB values Compared appearance, melting points and RGB values with other hydrazones 5. Combustion Test 2-4 drops of test compound1 (in evaporating dish) – flame carefully using Bunsen burner flame Observe flammability, flame color and sootiness and compared with other test substances 1 Compounds to be tested are: cinnamaldehyde (product), benzaldehyde and acetaldehyde.
IV. Data and Results Table 1. Observations on the synthesis of cinnamaldehyde. Reagent/Action Taken| Observations| Benzaldehyde| Clear, colorless, dense liquid| Acetaldehyde| Clear, colorless liquid| Sodium hydroxide| Colorless liquid| Benzaldehyde + NaOH| White mixture| Mixture + dropwise addition of acetaldehyde| Yellow oil (upper layer) and off-white lower layer| Reflux| Dark brown, opaque, viscous liquid mixture| Cooling| Formation of layers| Extraction:| | Organic layer| (Upper) Dark brown, opaque viscous liquid with cinnamon scent| Aqueous layer| (Lower) Light brown, translucent liquid|
Product| Dark brown, opaque viscous liquid with cinnamon scent| Table 2. Percent yield of the synthesis of cinnamaldehyde. Compound| Amount (mL)| Benzaldehyde| 3. 06| Acetaldehyde| 1. 68| Cinnamaldehyde:| | Theoretical| 3. 78| Experimental| 3. 46| % Yield| 91. 6 %| Table 3. Boiling points of compounds used and synthesized in the experiment. Compound| Boiling point (oC)| Benzaldehyde| 179| Acetaldehyde| 65-82| Cinnamaldehyde:| | Theoretical| 250-252| Experimental| Decomposed| Table 4. Results of the characterization tests of the product and reactants. Compound| Reaction with HNO3| Reaction with NaHSO3| Observations| (+/-)| Observations| (+/-)| Benzaldehyde| Yellow-orange liquid;Heat production | + | White precipitate | + | Acetaldehyde| Clear, colorless liquid (N. R. ) | – | White precipitate | + | Cinnamaldehyde| Two layers: opaque, dark brown (upper) and translucent, chocolate brown (lower) | + | Brown precipitate | + | Table 5. Results of the derivatization with 2,4-DNP. Compound| Observations| Melting point of hydrazone (oC)| Mean RGB Values (in hexadecimal)| | | Theoretical| Experimental| | Benzaldehyde| Orange yellow solids| 255. 25| 218| E7B01A| Acetaldehyde| Crimson red solids| 221. 6| 174| C75B34| Cinnamaldehyde| Red orange solids| 267. 76| Decomposed| AF6D21| Table 6. Observations on the combustion test of the reagents and the product. Compound| Flammability| Flame color| Sootiness| Benzaldehyde| Flammable| Orange| Sooty| Acetaldehyde| Moderately flammable| Blue| Very sooty| Cinnamaldehyde| Very flammable| Orange| Extremely sooty with black residue| Sample Calculations: V benzaldehyde = mol benzaldehyde ? MW benzaldehyde ? 1/? benzaldehyde V benzaldehyde = (0. 03 mol)(106. 12 g/mol)(1. 00 mL/1. 0415 g) V benzaldehyde = 3. 06 mL V acetaldehyde = mol acetaldehyde ?
MW acetaldehyde ? 1/? acetaldehyde V acetaldehyde = (0. 03 mol)(44. 05 g/mol)(1. 00 mL/0. 788 g) V acetaldehyde = 1. 68 mL Theoretical yield = mol cinnamaldehyde ? MW cinnamaldehyde ? 1/? cinnamaldehyde Theoretical yield = (0. 03 mol)(132. 16 g/mol)(1. 00 mL/1. 05 g) Theoretical yield = 3. 776 mL %Yield = (3. 46 mL/3. 776 mL) ? 100% %Yield = 91. 6% Maximum loss by solvation V cinnamaldehyde = ? cinnamaldehyde ? solubility in H2O ? V water V cinnamaldehyde = (1. 00 mL/1. 05 g)(4. 09? 10-4 g/mL)[9. 00 mL+(0. 030 mol)(18. 016 g/mol)](1. 00 mL/g) V cinnamaldehyde = (1. 00 mL/1. 05 g) (4. 09? 0-4 g/mL)(9. 54 mL) V cinnamaldehyde = 3. 72? 10-3 mL %Loss by solvation = (V cinnamaldehyde lost/ Theoretical yield) ? 100% %Loss by solvation = (3. 72? 10-3 mL/3. 776 mL) ? 100% %Loss by solvation = 0. 098% V. Discussion Cinnamaldehyde, cinnamic aldehyde or 3-phenyl-2-propenal is the dominant component of cinnamon oil, extracted from several species of Cinnamomum (C. verum, C. burmanii, C. cassia), under the family Lauraceae, a group of evergreen trees. Cinnamon bark (particularly C. verum) yields 0. 4-0. 8% oil, which contains 60-80% cinnamaldehyde (List and Horhammer; Masada; Ravindran qtd. rom Khan and Abourashed, 2011), which was first isolated in 1834 by Dumas and Peligot (Attokaran, 2011). It has been proven that cinnamaldehyde from cinnamon oil has a very high potency in the field of medicine, aside from its well known role in the cooking and baking, specifically as spice, odorant and colorant. Several researches have explained and proven the anti-diabetic properties of cinnamaldehyde (Babu, Prabuseenivasan and Ignacimuthu, 2006); also, studies have shown the antimicrobial activity of cinnamaldehyde against Salmonella typhimurium and Bacillus subtilis (Council of Europe, 2008).
Cinnamaldehyde has been proven to inhibit microbial growth of opportunistic human pathogenic fungi and various bacteria (Khan and Abourashed, 2011). Though effective approaches in the isolation of cinnamaldehyde from cinnamon oil from quills, low amounts of pure cinnamaldehyde can only be obtained from effective separation processes. Due to this demarcation in the discovery and investigation of other potential medicinal and non-medicinal values of cinnamaldehyde, chemists have also developed synthetic procedures to obtain high amounts of pure cinnamaldehyde, one of which is the mixed aldol condensation of benzaldehyde and acetaldehyde.
The synthesis of cinnamaldehyde through mixed-aldol condensation was done by mixing, in a cooled microreflux, benzaldehyde, portions of 15% sodium hydroxide solution and acetaldehyde, added in a dropwise manner, and then refluxing the mixture for 15-20 minutes. Isolation of the synthesized cinnamaldehyde was done simply by separating the water insoluble cinnamaldehyde layer from the aqueous layer. Aldol condensation is the reaction of aldehydes and/or ketones leading to the formation of ? -hydroxyaldehydes (aldols) or ? hydroxyketones (ketols), also known as the aldol addition, accompanied by the removal of water molecule (dehydration) from these compounds result finally to enals (? , ? -unsaturated aldehydes) or enones (? , ? -unsaturated ketones) (Moore and Langley, 2010; McMurry and Simanek, 2008; Fox and Whitesell, 2004). Aldol additions are due to the reaction of enolate ions of carbonyl compounds (from the reaction of acidic ? -hydrogen atoms of aldehydes and ketones with bases) with the electrophilic centers of other carbonyl compounds.
Dehydration, which can be spontaneous due to formation of a more conjugated system or promoted by heating, then leads to the generation of the ? , ? -unsaturated carbonyl compounds as the final product of the aldol condensation (McMurry and Simanek, 2008; Fox and Whitesell, 2004). Aldol condensations can be classified as simple and mixed-(or cross-) aldol condensation. The difference between the two classifications is that simple aldol condensation utilizes only one aldehyde or ketone substrate while the mixed-aldol condensation uses two different carbonyl compounds as the substrate for the reaction (Fox and Whitesell, 2004).
The mixed-aldol condensation was type of reaction employed in the experiment; however, simple aldol condensation, also known as self-condensation was one of the expected side reactions in the conducted study. The general equation for the synthesis of cinnamaldehyde was: The mechanism of the synthesis reaction can be proposed as: 6. Formation of ethenolate ion nucleophile 7. Aldol addition: Formation of 3-hydroxy-3-phenylpropanal 8. Dehydration: Formation of cinnamaldehyde The initial step done in the experiment was combining 3. 06 milliliter benzaldehyde with three 3. 0 milliliter portions of 15% sodium hydroxide with dropwise addition of 1. 68 milliliter acetaldehyde while swirling the mixture, which was in the microreflux, dipped in an ice bath. Benzaldehyde, followed by 3. 00-milliliter portion of 15% sodium hydroxide solution, was first put into the microreflux instead of the acetaldehyde to prevent acetaldehyde from undergoing self-condensation with the following general equation: Compared to acetaldehyde, benzaldehyde has no 3 ? -hydrogen atoms, which can react with the nucleophile, hydroxide ions, to form a strong nucleophile, the ethenolate ion.
Ethenolate ions can attack acetaldehyde instead of attacking benzaldehyde. Thus, benzaldehyde, which can remain as it is in sodium hydroxide, was put in first until the formation and attack of the nucleophile, which was formed right after acetaldehyde was dropped into the reaction mixture. The following is the mechanism of the self-condensation of acetaldehyde, which was minimized by the procedure carried out: Addition of 3. 00-milliliter portions of 15% sodium hydroxide solution, a dilute base, was done to compensate for the combination of benzaldehyde and sodium hydroxide, before adding acetaldehyde.
Benzaldehyde reacts with strong, concentrated bases to form benzenecarboxylate and hydroxymethylbenzene; this is known as the Canizzarro reaction. Canizzarro reaction (mechanism shown below) was minimized by the addition of the strong base in small portions, before adding the acetaldehyde, and using a dilute solution of it. Cooling of the mixture in ice bath was done to favor the reaction aldol condensation of benzaldehyde and acetaldehyde, a spontaneous reaction due to the higher degree of conjugation of the product, while disfavoring the self-condensation of acetaldehyde, a heat-requiring reaction (Fox and Whitesell, 2004).
Dropwise addition of the enolizable compound, acetaldehyde, was performed to minimize the drastic formation of ethenolate ions while unreacted acetaldehyde molecules still exist in the mixture. The phenomenon was prevented since it would have entailed the self-condensation of acetaldehyde, which could have caused lower yield in the experiment since the reagent would have been consumed in the unnecessary reaction just stated. The microreflux was shaken while the mixture was still being prepared to distribute the ethenolate ions formed though the mixture for them to react with the electrophile, benzaldehyde.
This procedure was also done to minimize the possibility of the self-condensation of acetaldehyde since the ethenolate ions generated were expected to have reacted with benzaldehyde since they were distributed with the aid by shaking before the next drop of acetaldehyde came in contact with mixture. Furthermore, since the reaction mixture was cold, the reaction was expected to be slow; thus, shaking can compensate for the slow movement of molecules and ions in the mixture by somehow supplying the energy needed for the slow-moving benzaldehyde molecules and ethenolate ions to collide.
Refluxing was done to: (1) react the still unreacted benzaldehyde molecules and ethenolate ions; and (2) promote the dehydration of the 3-hydroxy-3-phenylpropanal to finally form the 3-phenyl-2-propenal or the cinnamaldehyde. Refluxing intimately mixes substances by increasing the contact between the reactant particles through boiling and evaporation, followed by the condensation in the reflux condenser (due to the removal of heat by the cold water flowing in the condenser) and restoration of the synthesized compound and the little (expected) amount of the unreacted reagents on their original vessel (Mayo, Pike and Forbes, 2001).
Refluxing the mixture was very advantageous to the conducted experiment since it ensured higher yield and faster dehydration of the 3-hydroxy-3-phenylpropanal, though the stated reaction was expected to be spontaneous due to the higher degree of conjugation of the product (3-phenyl-2-propenal) compared to the 3-hydroxy-3-phenylpropanal. The synthesized cinnamaldehyde was readily separable (solubility of cinnamaldehyde in water=4. 09? 10-4gram/milliliter) with the lower aqueous layer; however, cooling of the mixture was done first to decrease the solubility of the cinnamaldehyde to achieve higher recoverable amount of the product.
Liquid-liquid extraction to recover the solvated cinnamaldehyde was not done since the maximum amount of solvated cinnamaldehyde was just 0. 098% of the theoretical yield (see Sample Calculations), thus the recovery of such little amount of product would be wasteful in terms of effort and reagents. Graduated cylinder was used directly as the receiver of the organic layer separated to determine right away the amount of synthesized cinnamaldehyde. The determination of the amount of product in this kind of manner was performed to minimize the loss of products due to the adherence of the very viscous product on the sides of different containers.
The amount of the synthesized cinnamaldehyde was found to be 3. 46 milliliter, 91. 6% of the theoretical yield which was computed as 3. 776 milliliter. Possible sources of error in the experiment were: the losses of minimal amount of reagents due to their adherence on the sides of the Pasteur pipets and 50-milliliter beakers; and the losses of the synthesized cinnamaldehyde caused by its adhesion on the sides of the microreflux, surface of the boiling chip and the inside surface of the separatory, caused by the high viscosity of cinnamaldehyde.
The lack of further purification process on the cinnamaldehyde, which could still contain traces of benzaldehyde, acetaldehyde and other side products, could also be a factor, leading to the incorrectness of the results of the experiment. The synthesized cinnamaldehyde was expected to be constituted of the cis- and trans- diastereomers; however, it was expected that the trans-isomer was the major component of the product. The reason for the claim was that higher possibility of existence of its trans-isomer-forming transition state conformation compared to the cis-isomer-forming transition state conformation.
Elimination to a trans double bond from the staggered conformation of the 3-hydroxy-3-phenylpropanal transition state, wherein the carbonyl group and the phenyl group are in the anti position to minimize the steric effects on the molecule, was still favored, though the carbonyl group is relatively small, compared to the energetically less stable gauche conformation (due to steric interactions of the carbonyl group and the large phenyl group) of the 3-hydroxy-3-phenylpropanal, which can cause the cis-isomer formation (Carey and Sundberg, 2001). (a)(b) Figure 1.
Balls and sticks representation of 3-hydroxy-3-phenylpropanal in the conformations for the formation of (a) trans-cinnamaldehyde and (b) cis-cinnamaldehyde. Carbon 2 shadows carbon 3 to show the anti-conformation in (a) and the gauche conformation in (b) of the phenyl and the carbaldehyde groups. Further proof that the formation of the trans-cinnamaldehyde was favored in the reaction was the coplanar arrangement of the highly conjugated aldol condensation product. According to Fox and Whitesell (2004), extended conjugation of the benzene ring with the alkene double bond and carbon-oxygen double bond of the carbonyl group in the ? ? -unsaturated aldehyde product leads to the flat, coplanar arrangement of the product. The p orbital overlap of extensive ? system of the carbonyl group and the alkene is greatest as the ? systems arrange in a single plane, which leads to higher stability of the molecule in terms of the conjugation present. Having a flat product would cause the increased torsional strain on the molecule due to the very close distance of the carbonyl group and the benzene ring. Therefore, cis-benzaldehyde, given the stated situation, is highly unstable and is not preferentially formed over trans-benzaldehyde. (a) (b) Figure 2.
Balls and sticks representation of (a) trans-cinnamaldehyde and (b) cis-cinnamaldehyde, viewed at different perspectives to show the differences in the flatness of the two molecules that contribute to their stabilities. Possible side reactions in the experiment conducted were the self-condensation of acetaldehyde and Canizzarro reaction as previously stated along with the preventive measures exercised to minimize their occurrence. Self-condensation of acetaldehyde was expected to be greatly minimized by the procedure employed and the fact that it is energetically unfavorable, according to Fox and Whitesell (2004).
Furthermore, even if the reaction took place, it would have been very minimal since it is a reversible reaction, which was competed with a more favorable reaction that is followed by an irreversible somehow spontaneous dehydration reaction. Depletion of the ethenolate ions (due to the consumption in the addition of benzaldehyde and ethenolate ions, then conversion of the intermediate to cinnamaldehyde) causes the competing self-addition of acetaldehyde to proceed backwards, forming back the acetaldehyde and ethenolate ions, which can be consumed in the aldol condensation of cinnamaldehyde and acetaldehyde.
Simple distillation was done to determine the boiling point of the synthesized cinnamaldehyde; however, decomposition was observed in the middle of the procedure, causing the failure of the melting point determination attempt; but supported that it was possible that cinnamaldehyde. The observed decomposition can be attributed to the instability of cinnamaldehyde, usually denoted by thickening and decomposition, when exposed for a long time to air at elevated temperatures but lower than its boiling point (>70°C) (Gholivand and Ahmadi, 2008).
Decomposition of natural cinnamaldehyde, however, is not observable in baking and cooking due to the presence of eugenol impurities on cinnamon oil, which has antioxidative properties that protect cinnamaldehyde from heat-induced decomposition (“Cinnamaldehyde Content”). The chemical tests performed were reaction with nitric acid, formation of the sodium bisulfite addition complex and derivatization with 2, 4-dinitrophenylhydrazine.
Reaction with nitric acid is a test for the differentiation of aromatic and aliphatic aldehydes. Aromatic aldehydes undergo nitration with concentrated nitric acid under normal conditions. Positive test results can are color changes and/or heat production. The general equation for the nitration of aromatic aldehydes is: Results of the reaction with nitric acid were shown in Table 4. Figure 3. Test results for the reaction of nitric acid with acetaldehyde (left), benzaldehyde (middle) and cinnamaldehyde (right).
Positive test results were observed with benzaldehyde and with cinnamaldehyde by the production of colored mixtures, yellow and brown, respectively, accompanied by heat production as shown by the following specific mechanism: 1. Formation of nitrosonium ion 2. Electrophilic addition of the nitrosonium ion to the aromatic aldehyde (a) Cinnamaldehyde Ortho attack Para attack (b) Benzaldehyde (Meta attack) (c) Acetaldehyde Reaction with alcoholic sodium bisulfite solution is a confirmatory test for aldehydes and ketones, having the following reaction and mechanism: Mechanism:
Results of the reaction of the compounds with alcoholic sodium bisulfite solution were listed in Table 4. Positive results were observed with acetaldehyde, benzaldehyde and cinnamaldehyde, which were denoted by the formation of transparent accumulation which turned to white precipitate, white precipitate and brown precipitate, respectively. Figure 4. Test results of the reaction of alcoholic sodium bisulfite with cinnamaldehyde (left), benzaldehyde (middle) and acetaldehyde (right). Sodium bisulfite addition complexes were the observed precipitates of the following reactions:
Derivatization with 2, 4-dinitrophenylhydrazine was done to support the identity of the cinnamaldehyde by the determination of the melting point of the hydrazone formed in the derivatization since the boiling point of the cinnamaldehyde was impractical to measure given that it is relatively high and the product, being impure can undergo decomposition. Derivatization with 2, 4-dinitrophenylhydrazine was performed by dissolving the test compound (cinnamaldehyde, acetaldehyde and benzaldehyde) in 4. 00 milliliter of ethanol and adding 3. 0 milliliter 2, 4-dinitrophenylhydrazine solution. The formed precipitate was then filtered and then recrystallized using minimum amount of 95% ethanol solution. The general equation and the mechanism of the reaction can be proposed as: Mechanism: Results of the derivatization, with 2, 4-dinitrophenylhydrazine, were shown in Table 5. The following are the equations for the derivatization of each aldehyde with 2,4-DNP in the experiment: Colors of the derivatives obtained were qualitatively different due to the differences in their degrees of conjugation.
Decomposition of the cinnamaldehyde hydrazone was observed, which hindered the determination of the melting point of the hydrazone. Deviations from theoretical melting point values of the two other hydrazones were observed on the experimental melting points gathered. The observed discrepancies maybe ascribed to the efficiency of the Fisher-Johns melting point apparatus and/or the quality of the reagents (benzaldehyde, acetaldehyde and 2, 4-dinitrophenylhydrazine) used.
To compensate for the failure in the melting point determination of the cinnamaldehyde hydrazone, the RGB (Red, Blue, Green) values or the web color keywords used by computer monitors to generate colors (McFarland, 2009), of the three hydrazones were determined and tested for significant differences using Analysis of Variance (ANOVA). Figure 5. Isolated and purified hydrazones of benzaldehyde (left), acetaldehyde (middle) and cinnamaldehyde (right). Mean RGB values obtained for cinnamaldehyde, acetaldehyde and benzaldehyde were shown in Table 5.
Results of the Analysis of Variance revealed significantly differences among the red values and among the green values of the three hydrazones and no significant differences among the blue values of the hydrazones. Having significantly different values on at least one of the RGB values proves that the composition of the hydrazones was significantly different, thus implying that the probable presence of benzaldehyde and acetaldehyde in the product was negligible and that cinnamaldehyde can be the compound present.
Results of the combustion test were shown in Table 6. Combustion is a chemical reaction between a substance and oxygen that proceeds with the evolution with heat and light as flame (Stoker, 2009). It can be complete, where all of the substance totally undergoes combustion with carbon dioxide and water as the product (general) or incomplete, caused by several factors, which brings about carbon monoxide and elemental carbon formation (soot).
Observed differences in the sootiness of acetaldehyde, benzaldehyde and cinnamaldehyde were due to the differences in the number of carbon atoms and the differences in the degrees of unsaturation of the molecules of each of the compounds. Incomplete combustion is generally observed in long chain hydrocarbons and other organic compounds given that oxygen is limited (Johnson, 1999; Macomber, 1996) since oxygen is consumed along with the carbon of the organic compound to produce carbon dioxide while hydrogen atoms are utilized, also along with oxygen, to produce water.
Furthermore, unsaturated organic compounds (having as much carbon-carbon double bond) favors incomplete combustion since the number of carbon atoms is relatively higher than the number of hydrogen atoms; excess carbon atoms cannot be used up in the combustion process to produce carbon dioxide (when oxygen supply limited) and thus soot forms (Lister and Renshaw, 2000). It has been show in the balanced equations of the combustion each compound that cinnamaldehyde requires the highest amount of oxygen, followed by benzaldehyde and, lastly, by acetaldehyde.
Given that, in the combustion test conducted, oxygen supply was almost uniform among the three, soot formation was predicted to be observed more prominently on cinnamaldehyde (product), followed by benzaldehyde and lastly by acetaldehyde due to the amount of carbon atoms and the relative number of unsaturations on each molecules. The same arrangement was also the experimental arrangement of the compounds with respect to the observed degrees of sootiness after the carried out combustion test.
The structure of cinnamaldehyde was supported by the positive reaction of cinnamaldehyde with nitric acid and with alcoholic sodium bisulfite. Though it can be inferred that the detected compound can also be benzaldehyde, the cinnamaldehyde color (yellow to brown), viscosity and the cinnamon aroma of the compound (which are qualitatively different from the color, viscosity and odor of benzaldehyde), the characteristic decomposition of cinnamaldehyde below its boiling point and the results of the combustion test can be used as further evidence of the identity of the compound produced.
Possible sources of error in the experiment were the quality of the reagents used, intervals of dropping acetaldehyde on the mixture, lack of further purification process, lack of more evident physical and chemical characterization method for the product, efficiency of the melting point apparatus utilized and the storage of cinnamaldehyde product for too long prior to derivatization. I. Summary and Conclusion
The special synthesis experiment, entitled “Mixed-Aldol Condensation: Synthesis of Cinnamaldehyde”, was conducted to synthesize cinnamaldehyde from the base-catalyzed mixed aldol condensation of benzaldehyde and acetaldehyde; and characterize the synthesized product using its boiling point, results of simple chemical tests and derivatization reactions, along with the determination of the melting points of the hydrazones and comparison of the hydrazones using their RGB values.
The synthesis of cinnamaldehyde through mixed-aldol condensation was done by mixing, in a cooled microreflux, benzaldehyde, portions of 15% sodium hydroxide solution and acetaldehyde, added in a dropwise manner, and then refluxing the mixture for 15-20 minutes. Isolation of the synthesized cinnamaldehyde was done simply by separating the water insoluble cinnamaldehyde layer from the aqueous layer. Determination of the volume of the synthesized substance was then performed.
Chemical test carried out were test for aromatic ring (reaction with nitric acid), test for aldehydes (reaction with alcoholic sodium bisulfite) and derivatization with 2, 4-dinitrophenylhydrazine while the physical characterization test done were boiling point determination using simple distillation and melting point determination of the derivatized hydrazones. RGB values of the isolated and recrystallized hydrazones were obtained and tested for significant differences using Analysis of Variance (ANOVA). It was shown that positive test results were exhibited by cinnamaldehyde and benzaldehyde in their reactions with nitric acid.
It was also shown that positive test results were displayed by cinnamaldehyde, benzaldehyde and acetaldehyde in their reactions with alcoholic sodium bisulfite. The boiling point of the isolated product and the melting point of the cinnamaldehyde hydrazone were not obtained due to the decomposition of the stated compound. However, RGB values of the hydrazones were obtained. Results of the Analysis of Variance of the RGB values of the hydrazones revealed significantly differences among the red values and among the green values and no significant differences among the blue values of the hydrazones.
Based on the results, it can be concluded that that synthesized product was different from the starting materials and that it was possible that the product was cinnamaldehyde due to the highly colored hydrazone formed. Though chemical tests were successfully done, boiling point determination of the product and melting point determination of its hydrazone were unsuccessfully performed due to the decomposition of both product and its hydrazone; however, chemical tests done and physical properties exhibited by the compound were considerable as enough indicant of the identity of the compound.
Based on the readily perceivable physical characteristics of the compound produced and the results of the chemical tests performed and observed, it can be concluded that the synthesized compound was genuinely cinnamaldehyde. Based on the results of the experiment, it was proven that cinnamaldehyde, constituted primarily of trans-cinnamaldehyde, with a percent yield of 91. 6%, was successfully synthesized using the described procedure of the student.
Furthermore, the procedure constructed and performed was proven to have minimized the possible side reactions which could have impeded the yield, physical properties and authenticity of the executed chemical tests. Possible sources of error in the experiment were the quality of the reagents used, intervals of dropping acetaldehyde on the mixture, lack of further purification process, lack of more evident physical and chemical characterization method for the product, efficiency of the melting point apparatus utilized and the storage of cinnamaldehyde product for too long rior to derivatization. II. References ABOURASHED EA and KHAN IA. 2011. Leung’s Encyclopedia of Common Natural Ingredients: Used in Food, Drugs and Cosmetics. Germany: J. Wiley and Sons. ATTOKARAN M. 2011. Natural Food Flavors and Colorants. Germany: J. Wiley and Sons. BABU P, PRABUSEENIVASAN S and IGNACIMUTHU S. 2006. Cinnamaldehyde: A Potential Antidiabetic Agent. Phytomedicine. 1:15-22. CAREY FA and SUNDBERG RJ. 2001. Advanced Organic Chemistry Part B: Reactions and Synthesis. 4th Ed. USA: Plenum Publishers. COUNCIL OF EUROPE. 008. Natural Sources of Flavorings. France: Council of Europe. FOX MA and WHITESELL JK. 2004. Organic Chemistry. 3rd Ed. USA: Jones and Bartlett Publishers. GHOLIVAND MB and AHMADI F. 2008. Simultaneous Determination of Trans-Cinnamaldehyde and Benzaldehyde in Different Real Samples by Differential Pulse Polarography and Study of Heat Stability of Trans-Cinnamaldehyde. Analytical Letters. 41:3324-3341. JOHNSON W. 1999. Invitation to Organic Chemistry. USA: Jones & Bartlett Learning. LISTER T and RENSHAW J. 2000.
Understanding Chemistry for Advanced Level. China: Nelson Thornes. MACOMBER R. 1996. Organic Chemistry. USA: University Science Books. MAYO D, PIKE R. and FORBES, D. 2001. Microscale Organic Laboratory: With Multistep and Multiscale Syntheses. USA: John Wiley and Sons, Inc. MCFARLAND, DS. 2009. CSS: The Missing Manual. 2nd Ed. USA: O’Reilly Media Inc. MCMURRY J and SIMANEK E. 2008. Fundamentals of Organic Chemistry. 6th Ed. Singapore: Thomson Learning. MOORE JT and LANGLEY RH. 2010. Organic Chemistry II for Dummies.