Lab 5 Qualitative Analysis or Organic Compounds PDF

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Lab 5 Qualitative Analysis or Organic Compounds...

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3/8/20 Lab 5: Qualitative Analysis of Orgaic Compounds

Introduction:

To identify certain functional groups within an organic molecule, a series of tests can be conducted. The change into certain colors or formation of precipitate act as indictors that the functional group is present after a specific reagent is added. In this experiment, to test for carbonyl functional groups 3 different types of test were performed on 5 carbonyl compounds. All 3 tests were performed on heptanal, acetone, benzaldehyde, ethyl acetate, and benzoic acid Test A: 2,4-DNP Test for aldehydes and ketones Reaction: represents ketone as starting material but works with aldehyde as well

Mechanism:

Aldehydes and ketones yield a positive test result of colored precipitate ranging from red to orange to yellow. 2,4-DNP is able to give these positive results only for aldehydes and ketones because the nucleophilic attack and proton transfers occurring between 2,4 DNP and only an aldehyde or a ketone (good electrophiles) are able to yield the hydrazone imine. As seen in the mechanism above, 2,4-DNP reacted with sulfuric acid to give a 2,4-dinirophenylhydrazone. The formation of a red to yellow precipitate confirms that this reaction has successfully occurred confirming identity of the functional groups present.

Test B: Tollens Test for Aldehydes: Reaction:

Mechanism:

Tollens test gives positive results for aldehydes like benzaldehyde and heptaldehyde because aldehydes are much more readily oxidized that other carbonyl groups like ketones. The hydrogen attached to the carbonyl group plays a pivotal role in why tollens reagent can be exclusive towards identifying aldehydes.

Test C: Iodoform Test for Methyl Ketones: Reaction:

Mechanism

Only methyl ketones like acetone are able to yield a positive result for the iodoform reaction because the methyl group is necessary for proton transfers and nucleophilic attacks to occur to be later converted into iodoform. This yellow solid precipitate formed that the methyl ketone group is present.

Part B: Amines Hinsberg Test Reaction for primary amines: Acidic Hydrogen

O RNH2 + 1o Amine

S Cl O

OH

O H

O

S

S

O

NR

Na NR + NaCl + 2H2O

O Water Soluble salt HCl O S NR O H Insoluble

Mechanism:

Reaction for secondary amines: R

O

R NH +

S Cl

O R

OH

O

S N R O Water Insoluble HCl No reaction

Mechanism:

Reaction for Tertiarty amines O NR3 +

S Cl O

OH

O S O Na + NR3 + NaCl + H 2O O

insoluble H+ Cl

NHR3 Soluble

Mechanism:

Based on the mechanisms, primary, secondary, and tertiary amines are able to react with p-TsCl, and the addition of base. Whether or not a precipitate form and is able to remain or dissolve in water or acid dictates whether the amine is primary, secondary, or tertiary. Part C: Lucas Test on alcohol Reaction for tertiary alcohol

Mechanism for tertiary alcohol:

Chromic Acid Test: Reaction for secondary alcohol

Mechanism:

Primary and secondary alcohols yield positive result because only primary and secondary alcohols can be oxidized. Tertiary alcohols do not undergo oxidation and therefor give negative results in the chromic acid test. For Lucas test, benzylic, allylic, tertiary, and secondary alcohols yield positive result because they are able to undergo substitution. Part D: Phenols

Test for water soluble phenols Reaction:

Mechanism:

Ferric chloride reacts well with phenols because phenol is a very good nucleophile and Is water soluble. It is able to attack ferric chloride very well. Phenols work best in this reaction and therefore phenols exclusively yield a positive result.

Part E: Ferris hydroxide test for nitro groups Reaction:

Mechanism:

When nitro group successfully reacts with ferrous hydroxide, iron (III)hydroxide precipitate forms indicating presence of nitro group. Methods and Materials: Tests for carbonyl groups, amines, alcohols, phenols, and nitro groups were performed as described in Pavia, Lampman, Kriz and Engel, A Small Scale Approach to Organic Laboratory Techniques, Fourth Edition, Cengage Learning, 2015, pp 465-487. For the carbonyl compounds the iodoform test was performed in variation. In a test tube, 2mL of methanol was added with 3 drops of each carbonyl test compound along with 1mL of iodoform reagent. After 10 drops of 10% NaOH was added and mixed until change was observed.

Results and Observations: Overall reaction

Observation

Additional Comments

Carbonyl Tests A-(i): 2,4-DNP Test

yellow-orange-red precipitate for aldehyde and ketones. Clear orange solution for all other carbonyl compounds

Test compound 1: Heptaldehyde

(+) immediate yellow precipitate in clear solution (+) immediate yellow precipitate (+) Orange precipitate (-) yellow solution, no precipitate (-) yellow solution, no precipitate

some ketones give oils that won’t solidify. Some impure alcohols can contain ketones and aldehydes in them yielding positive result. No issues

Test compound 2: Acetone Test compound 3: Benzaldehyde Test compound 4: Ethyl Acetate Test compound 5: Benzoic Acid

No issues No issues

solid benzoic acid had to be dissolved in ethanol. Took time to dissolve fully.

Overall reaction

Observation

Additional Comments

Carbonyl Tests B-(i): Tollens Test

Formation of silver mirror around test tube indicates positive test for aldehydes

Test compound 1: Heptaldehyde

(+) silver mirror with some black interlayered, took few minutes for silver mirror to develop (-) dark black solution

important not to add too much ammonia solution when trying to dissolve dark precipitate made from mixing Tollens A and B. Reagent prepared must be used immediately after. Not full silver mirror occurred because test tube could have been dirty or it wasn’t used fast enough not aldehyde, so no reaction

Test compound 2: Acetone Test compound 3: Benzaldehyde

Test compound 4: Ethyl Acetate Test compound 5: Benzoic Acid

(+) silver mirror with some black interlayered, took few minutes for silver mirror to develop (-) dark black solution (-) dark black solution

Not full silver mirror occurred because test tube could have been dirty, or it wasn’t used fast enough not aldehyde, so no reaction solid benzoic acid had to be dissolved in 1,2-dimethoxy ethane.

Overall reaction

Observation

Additional Comments

Carbonyl Tests C-(i): Iodoform Test mixing test compound with methanol, iodoform reagent and 10% NaOH base to yield iodoform precipitate (CHI3) if test compound is methyl ketone.

light yellow precipitate in clear solution for methyl ketones. Clear brown- orange solution for all other carbonyl compounds.

different procedure was followed. Test will not be positive if the R-group is diortho substituted aryl group.

Test compound 1: Heptaldehyde

(-)no precipitate, brown/yellow spotty solution (+) immediate light yellow precipitate with clear solution (-) no precipitate, brown solution

Test compound 2: Acetone Test compound 3: Benzaldehyde

Test compound 4: Ethyl Acetate

(-) no precipitate, brown solution,

separation between brown and clear solutions started to occur. separation between brown and clear solutions started to

occur. Test compound 5: Benzoic Acid

(-) no precipitate, brown solution.

Overall reaction

Observation

Additional Comments

Amines (ii): Heinsberg Test

primary amines- dissolve in base and precipitate in acid is positive test. Secondary aminesprecipitate from base and no change from addition of acid is positive test tertiary amines- precipitate in base and dissolve in acid is positive test.

test tubes had to be warmed on steam bath

Test compound 1: aniline

(+) clear solution with white precipitate formed

Test compound 2: N-ethylanilne

(+) foggy solution with white precipitate

Test compound 3: N, Ndimethylaniline

(-) clear light blue solution with white precipitate.

aniline was primary amine, able to precipitate after the addition of acid N-ethylanilne was secondary amine, precipitate formed from addition of base but did not dissolve upon addition of water precipitate did not fully dissolve upon addition of acid but it should have, a possible error could have occurred of not adding enough acid to dissolve precipitate.

Overall reaction

Observation

Additional Comments

Alcohols (iii): Lucas Test

immediate to 2-3 minutes positive test (cloudiness) for benzylic, allylic, and tertiary alcohols. Secondary alcohols: 5-10 minutes reaction time for positive test. Primary alcohols give

alcohols being tested must be soluble in reagent for test to work

mixing 1,2,3 amines

benzylic, allylic, and tertiary alcohols converted to chlorides and water when reacted with HCl and ZnCl2

test with pH paper after adding base to make sure the solution is saturated enough in base. precipitate formed may be unreacted p-TsCl leading to confusing results.

Test compound 1: Benzyl alcohol Test compound 2: 1-butanol Test compound 3: cyclohexanol

Test compound 4: tert-butyl alcohol Test compound 5: Allyl alcohol

negative test (clear) (+) immediate cloudiness, no precipitate (-) clear solution, no precipitate (+)cloudy solution, no precipitate (+) cloudy solution, no precipitate (-) clear solution, no precipitate

benzyl alcohol yields positive test fast primary alcohol yields positive test fast secondary alcohol works but takes 5-10 mintues logner to react. tertiary alcohol yields positive test fast primary alcohol does not react with Lucas reagent, yields negative test.

Overall reaction

Observation

Additional Comments

Alcohols (iii): Chromic Acid Test

aldehydes, primary and secondary alcohols yield immediate green/blue color (+). Tertiary alcohols remain orange in solution

disregard changes after 15 seconds. enols can also give positive test. Can use this test to distinguish between aldehydes and ketones as well.

Test compound 1: Heptaldehyde

(+) cloudy light green color

Test compound 2: 1-butanol

(+) cloudy blue color

Test compound 3: cyclohexanol

(+) cloudy blue color

Test compound 4: tert-butyl alcohol

(-) orange solution, no precipitate.

No issues, aldehyde tested postive No issues, primary alcohol tested positive No issues, secondary alcohol tested positive tertiary alcohols do not react with chromic acid. Negative test.

Overall reaction

Observation

Phenols (iv): Iron (III) chloride Test for water-soluble phenols.

water soluble phenols produce intense red, blue purple or green color for positive test.

alcohols react with CrO3 (orange) with sulfuric acid to yield carboxylic acid (for priamry alcohol) or ketone (for secondary alcohol)with water and Cr2(SO4)3 (green color).

phenols react with ferric chloride(FeCl3) to get a colored complex of Fe(OAr)3

Additional Comments

Test compound 1: phenol Test compound 2: cyclohexanol

(+) intense orange solution with red patches (-) clear solution on top with small amounts of light orange on the bottom

phenol yields positive result and is indeed water soluble not a phenol, so yielded negative result

Overall reaction

Observation

Additional Comments

Nitro Groups (v): Ferris hydroxide Test for 2-nitrotoluene

positive test yielded through formation of red-brown precipitate of iron (III) hydroxide. negative test indicated by greenish precipitate

all nitro groups give positive test in 30 seconds, speed at which nitro group is reduced depends on its solubility. Iron (III) hydroxide produced through oxidation of iron (II) hydroxide.

(+) brown precipitate forms on the bottoms and separates from clear solution in about 30 seconds.

2-nitrotoluene contains nitro group yielding positive result.

Nitro group reacts with Ferris hydroxide and water to yield RNH2 and Fe(OH)3

Test compound 1: 2-nitrotoluene...