Alcohols and Phenols

LBYCH63, EA2, Group # 5

Experiment #8: Qualitative Analysis of Alcohols and Phenols Nicolas, Zophia Beatrice I. Instructor: Sir Glenn Tan Date Performed: November 14, 2014 Date Submitted: November 21, 2014 Abstract Qualitative analyses of the different types of alcohols and phenols were carried out. In the majority of experiment, four test samples were used namely: ethanol, isopropyl alcohol, alcohol, tert-butyl alcohol, and phenol. With these, the objectives of the experiment are to make an analysis of different types of alcohols and phenols using different methods namely: the use of sodium metal for the detection of acidic hydrogen in alcohols, the comparison of oxidizing conditions of a compound using different solutions, the comparison of oxi dation rates of the different types of alcohols using one medium, ceric nitrate test, chromic acid test, Lucas test, the comparison of the relative acidity of phenol with other compounds, phenol reaction with bromine water, and ferric chloride test; write the balanced chemical equations of the reactions; identify 1°, 2° and 3° alcohols; and disting uish alcohols and phenols from other compounds. In each test, different samples were used and each of their reaction was observed for any indications of a positive test. These can be helpful in analyzing and identifying unknown compounds by analyzing their properties. In some tests, several compounds experienced side reactions due to contam ination, unclean equipm ent, and poorly prepared reagents that might have been stored for a long time already. Moreover, most of the tests had limitations. With that, several other tests are recommended like iodoform test and interpretation of infrared spectra in order to aid the quantitative analysis and identification of organic compounds specifically alcohols and phenols.

I.

Introduction

One of the objectives of this experiment is to make qualitative analyses of the different types of alcohols and phenols using different methods namely: the use of sodium metal for the detection of acidic hydrogen in alcohols, the comparison of oxidizing conditions of a compound using different solutions, the comparison of oxidation rates of the different types of alcohols using one medium, ceric nitrate test, chromic acid test, Lucas test, the comparison of the relative acidity of phenol with other compounds, phenol reaction with bromine water, and ferric chloride test. Also, the experiment aims to write the balanced equations of the reactions observed in the laboratory, identify 1°, 2° and 3° alcohols, and distinguish alcohols and phenols from other compounds. These tests are used to make analyses using the properties of different alcohols and phenols in different reactions. They can aid in identifying alcohols and phenols from other compounds and can also be used together to identify an unknown type of alcohol by analyzing its different properties and interpreting them. Moreover, these tests are based on the concept of structural theory of organic chemistry. This means that these qualitative tests can help in the further understanding of the structural properties of both alcohols and phenols. Also, some have practical applications like detection of certain compounds in a sample. However, it is very important to note the

limitations of each test. Moreover, it is very important to make preliminary tests on a compound before a reaction such as noting the physical characteristics like its state, color and odor, solubilit y, and the acidity using litmus paper, depending on the type of test to be done. After the reaction, the same tests and observations should be done in order to check the changes in the characteristics of the compound. Different reactions have different effects on certain compounds. Alcohols (R-OH) are organic compounds with an aliphatic hydrocarbon group (R) that have a hydroxyl group (-OH) bonded to an sp 3 hybridized carbon atom. They “may be looked upon as derivatives of water, HOH” HOH” (Properties of alcohols and phenols, n.d.). Since only the H and C atoms are bonded to O and there are two non-bonded electron pairs, the shape around O is bent. Alcohols are colorless liquids with a faint smell, and they usually have relatively high boiling temperature and are soluble in water. The types of alcohol depend on the type of carbon atom the OH group is bonded. These types are the primary (1 °), secondary (2 °) and tertiary (3 °) alcohols. In this experiment, the primary alcohol to be tested is ethanol, isopropyl alcohol and tert-butyl alcohol for the secondary and tertiary alcohols. Different types of alcohols differ in numerous reactions. One factor is that its O atom has the ability to hydrogen bond with water. This ability depends on the length of the longest chain in the compound.

Page 1 of 9 Qualitative Analysis of Alcohols and Phenols

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According According to J. Smith, “an “a n organic compound is water soluble only if it contains one polar functional group capable of hydrogen bonding with the solvent for every five C atoms it contains” contains” (2011). (2011). A smaller atom has an OH group that can hydrogen bond in it, which means it is soluble in water. An example is the methanol that only has one carbon atom in its longest chain. This makes it completely soluble in water. On the other hand, longer chains m ake compounds more non-polar; therefore, they are more soluble in organic compounds than in water.

to identify the solution’s acidity before and after the reaction. Anhydrous magnesium sulfate (MgSO 4) is added to produce dry alcohol since it is hygroscopic and readily accepts water. It is used in the test because of the tendency of sodium metal to react violently with water. After the reaction, an alkoxide is formed and hydrogen gas is released. Alkoxide is the “organic functional group formed when a hydrogen atom is removed from a hydroxyl group of an alcohol when reacted with a metal” metal” (Helmenstine, n.d.).It n.d.).It can be observed in the reaction: Na(s) + ROH(l)

Figure 1. Ethanol, an example of alcohol with 2 carbon atoms in the longest chain

On the contrary, phenols (Ph-OH) are organic compounds that have a hydroxyl group bonded to an sp2 hybridized carbon atom attached to an aromatic ring (benzene). Just like alcohols, the solubility of phenols in water decreases with the attachment of non-polar groups to the aromatic ring.

The next one is the comparison of oxidizing conditions of a compound using different solutions. It tests whether oxidization is more favorable and more rapid in acidic, basic or neutral conditions. Each type of solution results in a unique color change. In an aci d medium, the resulting solution is light pink; in a basic medium, it turns to green, while in neutral medium, it remains unchanged. In acidic medium, MnO 4-, reduces to Mn2+, while in basic MnO4- reduces to MnO4. The rate of oxidation of alcohols and phenol can also be tested using one common medium, which is usually acidic. This is because permanganate is reduced to its greatest extent in acidic solutions and least in basic solutions. This means lesser amount of KMnO4 is needed since more electrons are transferred per mole KMnO4. An oxidized solution turns to green; otherwise, it remains yellow. It has a general chemical equation of: 3RCH2OH + Cr 2O72- + 8H+ 7H2O

Figure 2. Phenol

In both alcohols and phenols, the reactive site is the hydroxyl group due to the difference of electronegativity of oxygen and carbon and the nucleophilic state of oxygen. The hydroxyl group allows electric substitution to phenols. These differences can be observed using tests, and this is the goal of the experiment. One test uses sodium metal to detect the acidic hydrogen in a

RONa(l) + H2(g)

3RCHO + 2Cr 3+ +

One test is the ceric nitrate test that uses cerium ammonium nitrate [(NH4)2Ce(NO3)6], an oxidizing agent, in identifying whether an unknown compound is an alcohol or not. However, its limitation is that it can only test alcohols with carbons fewer than ten. An immediate formation of red color indicates a positive test for alcohols with the general chemical equation,






distinguished. However, the limitation of Lucas test is that the unknown should be soluble in the Lucas reagent, which means it should only have a maximum of six carbons. ZnCl2

For primary alcohols: R-CH2-OH + HCl R-CH2-Cl + H2O (clears up after 5 minutes) ZnCl2

For secondary alcohols: RR’CHOH + HCl RR’CHCl + H2O (after 5 mins) ZnCl2

For tertiary alcohols: RR’R’’COH + HCl RR’R’’CCl + H2O (instantaneous) Figure 4. Complete oxidation in ceric nitrate test (Practical organic chemistry, n.d.).

For identifying whether what type of alcohol a compound is, several tests are performed such as chromic acid test and Lucas test. Chromic acid test distinguishes tertiary alcohols from primary and secondary ones by oxidation. Chromic acid can be prepared by mixing sodium dichromate and sulfuric acid. It oxidizes primary alcohols to aldehyde, which oxidizes further to carboxylic acid (Experiment 6, n.d.).

Another test analyzes the relative acidity of phenols with other compounds such as glacial acetic acid and ethanol. Phenol reacts with a base to produce water and a phenoxide ion.

H2O

3RCH2OH + 2CrO3 + 3H2SO4 Cr 2(SO4)3 + 6H2O

3R-CHO +

Meanwhile, chromic acid oxidizes secondary alcohols to ketones, and unlike primary alcohols, it does not oxidize any further. H2O

3R2CHOH + 2CrO3 + 3H2SO4 Cr 2(SO4)3 + 6H2O

Figure 5. Reactions of phenols with bases (Reactions of aldehydes, ketones and phenols, 2011).

The next test distinguishes phenols from other compounds by reacting it with bromine water. A positive test shows a formation of white immiscible layer and an antiseptic smell.

3R-CRO +

The final solution turns to green and indicates a positive test. On the other hand, tertiary alcohols remain unreacted and the color remains unchanged. H2O

3R3COH + CrO3 + H2SO4

No Reaction

In order to distinguish the remaining types of alcohol namely, primary and secondary alcohols, Lucas reagent is reacted to them and produces alkyl chloride. Lucas reagent is a solution of anhydrous zinc chloride (ZnCl2) in concentrated HCl. Lucas reagent does not react with primary alcohols; however, it reacts with some secondary alcohols

Figure 6. Reaction of phenols with bromine water (Reactions of aldehydes, ketones and phenols, 2011).

Lastly, a test using ferric chloride can be made in order to distinguish phenols from most alcohols. Reactions of phenols and ferric chloride produce a pink, violet or green solution. The color depends on the structure of the phenol tested. 3ArOH + FeCl3

Fe(OAr)3 + 3HCl






ethanol (C2H6O). By adding MgSO 4, the water in the ethanol solution was removed. The solution was shaken and filtered using gravity filtration pr oducing a dry alcohol. A litmus paper test was carried out, and the red litmus paper remained red, while the blue one turned to red. The provided sodium metal (Na) in kerosene was wiped clean by putting it on a filter paper, folding the paper, and pressing the sodium metal inside. It is then reacted with the previously prepared dry alcohol. Upon doing this, the solution started to produce bubbles and the size of the sodium metal started to decrease. Also, the bottom part of the test tube became warmer. This continued on until the sodium metal completely disappeared. Another litmus paper test was done, and this time, red litmus paper turned to blue and the blue one stayed blue. The solution was disposed of after the sodium metal completely disappeared.

1 mL of ethanol, isopropyl alcohol, tert-butyl alcohol, and phenol were added. Then, 5 drops of 6M sulfuric acid were introduced together with 5 drops of 1% potassium dichromate. The rates of the reaction and the final colors were recorded. The ethanol solution turned to green with a few patches of yellow in it after 1 minutes and 40 seconds, the isopropyl solution turned to green after 3 minutes and 50 seconds, the phenol solution turned to brown instantly, and nothing happened to the tert-butyl solution. The fourth test was the ceric nitrate test. First, in t hree test tubes, 1 mL of ceric nitrate soluti on was added in each. In test tubes one, two and three, 10 drops of ethanol, isopropyl alcohol and tert-butyl alcohols were added respectively, and the solutions were covered and mixed. A fourth test tube was prepared containing 0.5 mL water and 1 mL ceric nitrate. All the resulting solutions had only one layer. The solutions in test tubes two and three turned to red-orange, wh ile that of test tube one turned to yellow-orange. The solution of the last test tube stayed yellow.

Figure 7. Reaction of sodium metal with alcohol.

The next test was the comparison of oxidation of a compound using solutions of different acidity: acidic, basic and neutral. Three test tubes each with 2mL water and 5 drops of ethanol alcohol were prepared. In the first test tube, a drop of t he 6M sulfuric acid was added, and a drop of 6M sodium hydroxide to the second one. Nothing was added to the third one. Then, two drops of 1% potassium permanganate were added to each of the three solutions. The times at which the resulting solution changed were recorded. Immediately, the solution in the first test tube turned from purple to peach. After 7 minutes and 43 seconds, the solution in the second test tube

Figure 8. Results of the ceric nitrate test (from left to right: ethanol, isopropyl alcohol, tert-butyl alcohol, water).

Then, a chromic acid test was done by adding to test tubes one, two, three, and four 1 m L of reagent grade acetone and 4 drops of chromic acid in each. Ethanol, isopropyl alcohol, tert-butyl alcohol, and phenol were added respectively in the four test tubes. The solutions in test tubes one and two turned to bluegreen, while the third one did not react. The phenol solution turned brown afterwards.






and shook briskly. Immediately, the solution in the third test tube turned into a cloud, murk y solution. The same thing happened to the isopropyl solution af ter 7 minutes and 45 seconds. On the other hand, the solution in the first test tube remained unreacted.

Figure 10. Reaction of bromine water and phenols.

Figure 9. Results of the Lucas test (from left to right: ethanol, isopropyl alcohol, tert-butyl alcohol).

The seventh test was the comparison of the relative acidity of phenol with other compounds. In a test tube with 0.5 mL water, 5 drops of phenol were added. The resulting solution was tested with litmus paper. It turned the blue litmus paper to red, while the red one remained the same. The solution was then added into a 1 mL of 10% sodium bicarbonate solution. Another litmus paper test was done with the red litmus paper turning to blue and the blue one staying as it is. The same procedure was done to two different test tubes both containing 0.5 mL water and one containing 10 drops of glacial acetic acid, while the other contained the same number of drops ethanol. The initial litmus paper test resulted in the turning of the blue litmus paper in the glacial acetic acid to red and the red one was staying as it is, while both litmus papers in ethanol remained blue and red. After the addition of sodium bicarbonate, the litmus paper in the glacial acetic acid remained red, while the litmus papers in the ethanol remained unchanged. Also, a significant number of bubbles appeared. In the ethanol solution, the blue and red litmus papers did not change, and there was no production of bubbles. Afterwards, reaction of phenol with bromine water was done. In a test tube containing 5 drops of phenol, 10 drops of bromine were added. Immediately, a white cloudy precipitate was formed as seen in figure

The last test was the ferric chloride test for water soluble phenols. Six test tubes were prepared, each containing 1 mL of ethyl alcohol. In each test tube, a drop of a different solution was added namely, phenol, resorcinol, salicylic acid, hydroquinone, acetic acid, and ethyl alcohol. Four drops of 1% ferric chloride were added to each test tubes. The solutions containing phenol, resorcinol and ethyl alcohol turned from transparent to yellow. The acetic acid solution turned from colorless to dark orange. The solutions of hydroquinone and salicylic acid turned from orange to dark orange and colorless to violet respectively.

Figure 11. Results of the ferric chloride test.

III.

Results and Discussion

In the first test, the addition of sodium metal in the dry alcohol resulted in the formation sodium alkoxide as observed in the reaction:






of the ethyl alcohol. This resulted in the production of hydrogen gas. This displacement of H proves the existence of acidic hydrogen in the alcohol, and it explains the results of the litmus paper test wherein the solution was found out to have changed from acidic to basic. This can be further explained by the production of ethoxide ions (CH 3CH2O-), which have high pH. Also, the bottom part of the test tube became warmer because the reaction of sodium m etal and dry alcohol released heat and is exothermic. In comparing the oxidation of ethanol with potassium permanganate in solutions of different acidities, it was observed that oxidation was fastest in the basic medium (NaOH) rather than the acidic one (H 2SO4). The oxidation of ethanol in an alkaline medium has a balance equation of: 12H+ + 4MnO4- + 5C2H5OH 5CH3COOH + 11H2O

4Mn2+ +

The next one to oxidize was the isopropyl alcohol, a secondary alcohol, and it produce a ketone called acetone with the reaction: 3C2H5CH2OH + Cr 2O72- + 8H+ 2Cr 3+ + 7H2O

Unlike acetaldehyde and other aldehydes, ketone did not oxidize further since it contains two R’s attached to the carbonyl group (C=O). These two R’s cause steric hindrance which made it harder for the OH to attack the carbon atom since it had to push the two large groups. The resulting green color of the solutions in test tubes one and two was caused by Cr 3+. Tert-butyl alcohol, a tertiary alcohol, did not give a reaction because it only contains R groups and no better leaving group like H. C4H9OH+ Cr 2O72- + 8H+

Oxidation of ethanol and the reduction of potassium permanganate in H2SO4 produced acetic acid and Mn2+, which gave the pale pink color of the solution. The balanced chemical equation of oxidation of ethanol in acidic medium is: 4MnO4- + 3C2H5OH

4MnO4+ 3CH3COOH + H2O

On the other hand, the production of MnO 2 together with acetic acid from the reaction of ethanol in a NaOH solution resulted in the green color of the solution. Oxidation did not happen in water since it is a neutral solution and did not cause redox reactions. In the following test, the rates of oxidation of different compounds using one common medium were observed, and it was noted that primary alcohols like ethanol oxidize first with the reaction: 3CH3CH2OH + Cr 2O72- + 8H+ 2Cr 3+ + 7H2O

3C2H5CHO +

No Reaction

The phenol gave negative results because it had a reaction different from oxidation since it turned brown. One possible source of this error is that phenol was oxidized by chromic acid producing quinones that give a dark color mixture. This is because chromic acid is strong enough to oxidize phenol. This might have been caused by the repeated use of test tubes for different kinds of tests specifically the chromic acid test. The ceric nitrate test produced positive results for all four alcohols: ethanol, isopropyl alcohol, tert-butyl alcohol. CH3CH2OH + [(Ce(NO3)6]2[(Ce(NO 3)5(OCH3CH2)]2- + HNO3 C2H5CH2OH + [(Ce(NO3)6]2[(Ce(NO3)5(OC2H5CH2)]2- + HNO3

3CH3CHO +

Ethanol oxidized to form acetaldehyde, an aldehyde. Aldehydes can be oxidized further to form carboxylic acids. One observation is the patches of yellow in the test tube that might be caused by excess addition of potassium dichromate. The primary alcohol oxidized sooner than other types because all the surrounding

C4H9OH + [(Ce(NO3)6]2[(Ce(NO3)5(OC4H9OH)]2- + HNO3 The oxidation reactions above formed a alkoxycerium compound [(Ce(NO3)5(OR)]2- from the red complex (NH4)2Ce(NO3)5(OR). This complex caused the red color upon the reaction of ceric nitrate with the alcohols. The fourth test tube containing water and








chromic acid to produce water, acetaldehyde, and chromium(III) sulfate [Cr 2(SO4)3].

butyl alcohol is a tertiary alcohol even without knowing initially what type of alcohols they are.

H2O

3CH3CH2OH + 2CrO3 + 3H2SO4 3CH3CHO + Cr 2(SO4)3 + 6H 2O Meanwhile, isopropyl alcohol reacted with chromic acid to produce water, acetone, and chromium(III) sulfate [Cr 2(SO4)3]. H2O

3(CH3)2CHOH + 2CrO3 + 3H2SO4 3CH3CH3CO + Cr 2(SO4)3 + 6H2O In both solutions, the chromium(III) sulfated is what caused the green color. Meanwhile, tert-butyl did not have a reaction with chromic acid because of the R groups surrounding it. (CH3)3COH+CrO3+H2SO4

No Reaction

Just like with the test on oxidation conditions, tertbutyl did not oxidize due to the R groups surrounding it which caused steric hindrance and made attacking the carbon atom more difficult. Another test is the Lucas test, which was used in identifying primary alcohols. Among all three samples, ethanol was the only one that did not react because ethanol is a primary alcohol and the least stable of all which means a greater amount of energy was required in its transition state. Therefore, the reaction took more time and cannot be observed during the limited time of experiment. ZnCl2

CH3CH2OH + HCl

CH3CH2Cl + H2O

Isopropyl alcohol reacted with Lucas reagent and formed water and ethyl chloride that caused the white, immiscible layer. Secondary alcohols are the

The next part tested the relative acidity of phenols with glacial acetic acid and and ethanol. In the initial litmus paper test, it was found out that ethanol is the least acidic of the three and can alm ost be considered negligible. In order to compare the remaining two samples, sodium bicarbonate was added and the final litmus paper test showed that glacial acetic acid is stronger than sodium bicarbonate since the solution remained acidic. NaHCO3 + CH3COOH

NaCH3COO + H2O + CO2

On the other hand, the solution of phenol turned basic, which means phenol is weaker than sodium bicarbonate. Ph-OH +NaHCO3

PhO-Na+ + H2CO3

Ultimately, this means that phenol ( pKa = 9) is weaker than glacial acetic acid (pKa = 4.6) but is stronger than ethanol (pKa = 9.5), an alcohol (Acidity, Basicity and pKa, n.d.). This can be proven by comparing their pKa or acid dissociation values. The compound having the lowest pKa is the most acidic. The following reaction is that of bromine water and phenol that yielded hydrogen bromide and 2,4,6tribromophenol, a white compound that is insoluble in water. The ring electrons of the benzene ring undergoes electrophilic substitution. This made it attractive to electrophiles like bromine as observed in the reaction:






included with both turning to violet, while acetic acid should produce a negative result. This could be caused by contaminations among the reagents that might have been poorly prepared or stored for a long time already. Here are the reactions for the phenols: For phenol: FeCl3 + 6C6H5OH + 3HCl

H3[Fe(C6H5O)6]

For salicylic acid: FeCl3 + 3HOOCC6H4OH (HOOCC6H4O-)3Fe + 3HCl For resorcinol: FeCl3 + C6H6O2 FeCl2 + HCl

C6H4O2 +

For hydroquinone:

Figure 13. Hydroquinone reaction with FeCl 3 (Redox Reactions, 2009).

Theoretically, reactions of phenols with ferric chloride result in the OH group by the detection of ferric chloride in the phenol and the formation of coordination complexes with iron. They came from electrophilic substitution of the phenols. These complexes produce the intense colors in the resulting solutions. The shade of the color depends on the structure of the phenol. In the case of acetic acid, an aliphatic acid, and ethanol, the solutions turn yellow because of the lack of aromatic ring. For acetic acid: 3CH3COOH + FeCl3 Fe(CH3COO)3 + 3HCl For ethyl alcohol: 6C2H5OH + FeCl3

bromine water, and ferric chloride test. In this experiment, it was noted that a combination of tests is sometimes needed in identifying unknown types of compounds. One source of errors in the experiment was the reaction of the samples with contaminations. Another might be from the repetitive use of test tubes and pipettes in the laboratory. Also, poorly prepared reagents that might have been stored for a long time already might have been a factor. Since some qualitative tests have limitations and have results that are too general, other more specific tests are recommended like the iodoform test and infrared spectroscopy. Iodoform test specifically identifies secondary methyl alcohol and forms a yellow precipitate with a positive result. Meanwhile, interpreting interpreting infrared spectroscopy “involves “ involves the correlation of absorption bands in the spectrum of an unknown compound with the known absorption frequencies for types of bonds” bonds ” (Interpretation of Infrared Spectra, n.d.). This is sometimes used in detecting traces of alcohol in the body and relies on the intensity, shape and position of bonds. References Acidity, Basicity and pKa. [Online], http://www.columbia.edu/~crg2133/Files/CambridgeI A/Chemistry/AcidityBasicitykPa.pdf (accessed Nov. 21, 2014). Alkoxide definition. http://chemistry.about.com/od/chemistryglossary/fl/Al koxide-Definition.htm (accessed Nov. 18, 2014). Experiment 6. [Online], p 1. http://myweb.brooklyn.liu.edu/swatson/Site/Laborato






Properties of alcohols and phenols. [Online], p 1. http://myweb.brooklyn.liu.edu/lawrence/che4x/e3alc ohol.pdf (accessed Nov. 15, 2014). Reactions of aldehydes, ketones and phenols. (2011). [Online], http://1chemistry.blogspot.com/2011/09/reactions-ofaldehydes-ketones-and.html (accessed Nov. 20, 2014). Redox Reactions: Dihydroxybenzene Isomers with Ferric Chloride. (2009). [Online], http://chem2all.blogspot.com/2009/03/redoxreactions-reaction-of.html (accessed Nov. 21, 2014). Smith, J. Organic Chemistry, 3rd ed.; McGraw-Hill: New York, 2011. “I hereby certify that I have given a substantial contribution to this report and I did not copy and/or quote from any resource material unless being cited as reference. I am make known that failure to accomplish the second clause would be grounds for plagiarism and a failing grade for my final laboratory report.”

________ _______________ _______________ NICOLAS, ZOPHIA BEATRICE I.

Alcohols and Phenols

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