Orgo 2 lab 4 - Lab report PDF

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Lab 4: Qualitative Organic AnalysisIntroduction: Classification tests are often used in order to quickly identify the different functional groups of an unknown compound. As different functional groups have different reactivities, a series of reactions can be conducted in order to identify their corr...

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Lab 4: Qualitative Organic Analysis Introduction: Classification tests are often used in order to quickly identify the different functional groups of an unknown compound. As different functional groups have different reactivities, a series of reactions can be conducted in order to identify their corresponding functional groups. Although these are helpful, they only provide a portion of the compound’s structure, and it is possible to obtain false positives. A method of confirmation is to conduct the compound’s IR, which would show if a functional group is actually present in the compound. There are several classification tests that can be conducted, some of which were performed in this lab. The classification tests in this experiment are:

1) 2,4-DNP Test: Mechanism:

This tests allows for the detection of aldehydes and ketones by reacting with them to form a colored precipitate. This is an intensely colored red/yellow precipitate. Carbonyls of ethers and carboxylic acid do not provide a positive result due to their highly resonance stable structures. The mechanism begins with the 2,4-DNP molecule acting as a nucleophile which attacks the oxygen of the carbonyl group. Next, there is proton transfer for negative charged oxygen and the positive nitrogen atom. The oxygen atom deprotonates the sulfuric acid, and the nitrogen atom is deprotonated by the base. Now the hydroxyl group is protonated again, and acts as a leaving group and leaves as a water molecule.

From left to right: Heptaldehyde (positive), Acetone(positive), Benzaldehyde(positive), Ethyl Acetate(negative), Benzoic Acid(negative)

2) Iodoform Test: Mechanism:

The Iodoform test indicates if there are methyl ketones present. Formation of a yellow precipitate is a positive test. The methyl ketone reacts with iodoform as methyl has three hydrogens present. The mechanism begins with hydroxide which deprotonates a hydrogen from the carbon. The carbon attacks the positively charged iodine, and this occurs three times. Afterwards, a hydroxide attacks the carbonyl, causing the oxygen to become negatively charged. Next, the CHI3 is deprotonated. This will form the products in the reaction above. If the R group is a di-ortho substituted aryl group, the test will not be positive.

From left to right: Heptaldehyde(Negative), Acetone(Positive), Benzaldehyde(Negative), Ethyl Acetate(Negative), Benzoic acid (Negative)

3) Tollen’s Test:

Mechanism:

From right to left: Heptaldehyde(Positive), Acetone(False positive), Benzaldehyde(Positive), Ethyl Acetate(Negative), Benzoic acid (Negative) The Tollen’s test is performed for aldehydes. The formation of a silver mirror on the and a precipitate indicates a positive test. The tollen’s reagent is water soluble in a basic solution. During the first step, the oxygen atom from the aldehyde attacks the silver atom, forming the oxonium intermediate. The carbon of the carbonyl is attacked by water and becomes electrophilic. The oxygen molecule that is positively charged is deprotonated using ammonia, and the deprotonated oxygen forms a hydroxyl. This hydroxyl attacks silver to become deprotonated by ammonia again. Proton transfer is able to occur between the oxygen molecule and the central carbon making it negative. Next, a lone pair moves to form a pi bond with the oxygen atom and leaves the molecule. Using this test, aldehydes are positive, but ketones are negative. Aldehydes are oxidized to carboxylic acid by the Tollen’s reagents, however some

compounds that are also easily oxidized can provide false positives. 4) Hinsberg Test:

Primary Amine:

Secondary Amine:

Tertiary Amine:

The Hinsberg test is used to identify amines. This is done by reacting amines with benzenesulfonyl chloride. Primary amines are dissolved in KOH, and the addition of HCl produces a precipitate. First, they react with benzenesulfonyl chloride in the presence of KOH. Then, the acidic hydrogen is deprotonated creating a water soluble salt. After reacting with HCl, it is protonated and becomes neutral, and water insoluble. Secondary amines form a precipitate when dissolved in KOH, and form a clear solution when they are dissolved in HCl. It undergoes the formation of a dialkyl benzene sulfonyl amine compound which is insoluble in water. Secondary amines lack an acidic hydrogen, they do not react with bases. In addition, since it is insoluble, it does not react with HCl and stays insoluble. When the benzenesulfonyl reacts with the KOH, it creates a salt. Tertiary amines form a precipitate when reacting with KOH, and also become clear when reacting with HCl. Tertiary amines do not react with benzenesulfonyl chloride; only the KOH will. This creates a salt, and the tertiary amine becomes acidic after reacting with HCl. Initially, it forms a precipitate, then dissolves after it reacts with HCl.

Left to right: N,N-dimethylaniline(Clear solution), N-ethylaniline(precipitate), Aniline(precipitate)

5) Lucas Test:

The Lucas test is able to identify alcohols. They are able to classify the different alcohols into primary, secondary, and tertiary. In step 1 of the mechanism, the oxygen is protonated by HCl. Then it acts as a leaving group, and water leaves. The tertiary carbocation is then attacked by the nucleophilic Chlorine anion. Primary alcohols should not have any reaction. Secondary alcohols should react within ten minutes, whereas tertiary alcohols react immediately. In order to react, the alcohol must be soluble in the reagent. As a result, alcohols with long carbon chains often can not be tested. Primary alcohols do not react due to the fact that they produce very unstable carbocations, whereas tertiary alcohols form very stable carbocations.

Benzyl Alcohol (Primary), 1-Butanol (Primary), Cyclohexanol(Secondary), Tert-butyl alcohol (Tertiary), Allyl Alcohol (Primary)

6) Chromic Acid Test:

The chromic acid test is used to identify primary and secondary alcohols or aldehydes. In this mechanism, an acid protonates the hydroxyl group, and an alcohol attacks the molecule, causing water to act as a leaving group. An oxonium ion is created, then deprotonated. The strong base deprotonates the carbon atom making a carbanion, and a resonance structure is formed which creates a pi bond instead of a negatively charged oxygen. The chromium complex leaves, creating a ketone. As tertiary alcohols do not contain hydrogens which are essential for deprotonation, they can not be oxidized. For this reason, the chromic acid test is negative for tertiary alcohols by remaining orange. The primary and secondary alcohols however change to a green color. Enols may give a positive result as well. Phenols, however, give a dark colored solution, which differs from the normal blue-green positive. This is able to differentiate aldehydes and ketones as well.

Left to right: Heptaldehyde(negative), 1-butanol(positive), Cyclohexanol(positive), Tert-butyl alcohol(negative)

7) Nitro group Test: Ferric hydroxamate tests identify the presence of nitro groups. If there is a nitro group, the ferrous hydroxide will be oxidized into ferric hydroxide. Following this, the nitro group is reduced into a primary amine. 2-Nitrotoluene contains a nitro group, and as such, is positive, with a red-brown precipitate.

2-Nitrotoluene (positive) 8) Test for Water-Insoluble Phenols:

The Iron (III) chloride test is used to identify if there are any water-soluble, or water-insoluble phenols present. When identifying water-soluble phenols, no pyridine is needed, however pyridine is required when checking for water-insoluble phenols. When pyridine is added to the test, mixing of the solution will cause a color to appear as it is able to aid the phenol in being dissolved.

Cyclohexanol (negative), Phenol (positive)

9) Beilstein Test: This test is able to detect halogens using flames from a bunsen burner. A copper wire is placed under fire with a portion of each sample. When a non-halide is placed on the copper wire, a red flame will be present. When a halogen is used, a green flame will be created, however, it does not provide a technique in distinguishing which halogens are present. Procedure: The procedure for the Iodoform test was altered in order to skip the heating step which would require 60°C water. The reaction mixture was altered, and the resulting test still tested positive for methyl ketones. Results and observations: Overall Reaction Carbonyl 2,4-DNP Test

Observation Positive tests create a colored precipitate Tests: that is orange-yellow. Allylic alcohols can be oxidized to aldehydes and cause a positive test.

Heptaldehyde: C 7 H 14 O+C 6 H 6 N 4 O 4 → H 2 O +C 13 H 18 N 4 O 4

Positive due to yellow precipitate formation

Acetone: C3 H 6 O+C 6 H 6 N 4 O 4 → H 2 O +C 9 H 10 N 4 O 4

Positive due to orange precipitate formation

Benzaldehyde: C 7 H 6 O+ C6 H 6 N 4 O 4 → H 2 O+ C13 H 10 N 4 O 4

Positive due to orange precipitate formation

Ethyl Acetate: No Reaction Occurs

Negative due to no precipitate formation

Benzoic Acid: No Reaction Occurs

Negative due to no precipitate formation

Carbonyl Iodoform Test

Positive tests create a yellow precipitate, Tests: indicating the presence of methyl ketones. Compounds that are easily oxidized may result in a positive test. If the R group is a di-ortho substituted aryl group, the test will be negative.

Heptaldehyde: No Reaction Occurs

Negative due to lack of yellow precipitate formation

Acetone: C3 H 6 O+ 3 I 2 +4 NaOH → 3 H 2 O +2 CH I 3 (s) −¿ ¿ +¿ 3 I ¿ +C 2 H 3 O 2 N a

Positive due to formation of yellow precipitate

Benzaldehyde: No Reaction Occurs

Negative due to lack of yellow precipitate formation

Ethyl Acetate: No Reaction Occurs

Negative due to lack of yellow precipitate formation

Benzoic Acid: No Reaction Occurs

Negative due to lack of yellow precipitate formation

Carbonyl Tollen’s Test

Heptaldehyde:

Positive tests create a silver mirror on Tests: the walls of the test tube, or a black precipitate, indicating the presence of aldehydes. Compounds that are easily oxidized may result in a positive test. Positive due to silver mirror formation

N H 3 ¿2 OH → 2 Ag+3 N H 3 +H 2 O C 7 H 14 O+2 Ag ¿ +¿ H4 O−¿ 2 N¿ +C 7 H 13 ¿ Acetone: No Reaction Occurs

False positive due to formation of black precipitate

Benzaldehyde: N H 3 ¿2 OH → 2 Ag+3 N H 3 + H 2 O C7 H 6 O+ 2 Ag ¿ +¿ H4 −¿ O2 N ¿ +C 7 H 5 ¿

Positive due to silver mirror formation

Ethyl Acetate: No Reaction Occurs

Negative due to no precipitate formation

Benzoic Acid: No Reaction Occurs

Negative due to no precipitate formation

Observations Tests Hinsberg Test

for

Amines:

Primary Amine:

Positive tests create a clear solution and a precipitate after an acid is added.

Aniline: C6 H 5 N H 2 +C 7 H 7 S O 2 Cl+ 2 NaOH → + ¿+ NaCl + 2 H 2 O ¿ −¿ N a C13 H 12 S O 2 N ¿

Positive due to formation of clear liquid after addition of base, then formation of a precipitate after addition of acid.

Secondary Amine:

Positive tests are created by a formation of no precipitate, and no change after addition of acid.

N-ethylaniline: C 8 H 11 N +C 7 H 7 S O 2 Cl+ NaOH → C 15 H 17 S O 2 N + H 2 O + NaCl

Positive due to formation of a precipitate which remains after base is added.

Tertiary Amine:

Positive tests create a precipitate after addition of base, and then dissolve after

addition of acid. N,N-dimethylaniline: C8 H 11 N +C 7 H 7 S O 2 Cl+NaOH → C 8 H 11 N +¿+ NaCl+H 2 O ¿ −¿ N a ¿ C 7 H 7 S O2

Positive due to precipitate formation after addition of a base, and then a clear liquid after addition of acid.

Test for Water-Insoluble Phenols

Positive tests result in a red, blue, green or purple color after addition of pyridine, indicating the presence of phenols or enols.

Cyclohexanol: No Reaction Occurs

Negative due to formation of orange color.

Phenol

Positive due to formation black/purple color.

Lucas Test Primary Alcohol Secondary Alcohol Tertiary Alcohol

Positive tests result in no change and remain clear. Positive tests result in cloudiness or precipitate within 5-10 minutes. Positive tests result in immediate cloudiness of precipitate.

Benzyl Alcohol (Benzylic) C7 H 8 O+ HCl→ C 7 H 7 Cl+ H 2 O

Positive due to immediate cloudiness.

Tert-butyl Alcohol (Tertiary) C 5 H 12 O + HCl →C 5 H 11 Cl + H 2 O

Positive due to immediate formation of precipitate.

Allyl Alcohol (Allylic) C3 H 6 +HCl →C 3 H 5 Cl+ H 2 O

Positive due to formation of cloudiness within a minute.

Cyclohexanol (Secondary) C 6 H 12 O + HCl →C 6 H 11Cl + H 2 O

Positive due to formation of cloudiness after 6 minutes.

1-butanol (Primary) C 4 H 10 O +HCl→ C 7 H 9 Cl+ H 2 O

Positive due to clear liquid formation

Chromic Acid Test

Positive tests result in the formation of a bluegreen color, indicating primary, secondary alcohols and aldehydes.

Tert-butyl Alcohol: No Reaction Occurs

Negative due to retention of orange color.

Heptaldehyde: No Reaction Occurs

Negative due to retention of brown color.

Cyclohexanol: 3 C6 H 12 O +H 2 C r 2 O 7 +3 H 2 S O 4 → S O 4 ¿3 + 4 H 2 O 3 C6 H 11 COOH +C r 2 ¿

Positive due to blue-green color formation.

1-Butanol: 3 C4 H 10 O+H 2 C r 2 O 7 +3 H 2 S O 4 → S O 4 ¿3 + 4 H 2 O 3 C4 H 9 COOH + C r 2 ¿

Positive due to blue-green color formation.

Test for Nitro groups:

Positive tests result in the formation of a redbrown precipitate, indicating the presence of a nitro group.

2-Nitrotoluene:

Positive due to formation of a red-brown precipitate.

Beilstein Test

Positive tests result in a formation of a green flame, indicating the presence of a halogen.

1-bromobutane

Positive due to the presence of a green flame.

1-Butanol

Negative due to the presence of an orange flame.

1-Chlorobutane

Positive due to the presence of a green flame.

Reference: 1) Lancashire, Robert John. “Qualitative Analysis of Organic Compounds.” Qualitative Analysis of Organic Compounds., 2005, wwwchem.uwimona.edu.jm/lab_manuals/c10expt25.html. 2) Pavia, Donald, et al. A Small Scale Approach to Organic Laboratory Techniques. 4th ed., Cengage, 2016. Print...