Qualitative Analysis of Unknown

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19 Apr 2012 4:30pm

Experiment #21: Qualitative Qualitative Analysis Analysis to to Identify Unknown #64: Maleic Acid Acid

Goal: To identify unknown #64 by comparing the results obtained in 1H NMR, 13C NMR, IR spectrogram, solubility tests, melting point analysis, and five chemical classification tests with those of known compounds. .

Physical Properties of Reagents: Reagent

Molecular Formula

Structural Formula

Molecular Weight

Melting Point

Boiling Point

18.015 g/mol

0˚C

100˚C

39.9971 g/mol

318˚C

1388˚C

(varies with concentration)

(varies with concentration)

Solubility Tests POLAR PROTIC SOLVENT:

water

H2O

STRONG BASE:

sodium hydroxide

NaOH

Na+ -OH

(5% solution used)  WEAK BASE:

sodium bicarbonate

NaHCO3

84.007 g/mol

(5% solution used) STRONG ACID:

hydrochloric acid

HCl

H⊕⊖Cl

-114.8˚C

-84.9˚C

(varies with concentration)

(varies with concentration)

98.079 g/mol

10˚C

337˚C

(varies with concentration)

(varies with concentration)

-96 – -94˚C

68-69 ˚C (varies

(varies with concentration)

with concentration)

-96.7˚C

39.6˚C

STRONG BASE:

sulfuric acid (concentrated solution used) NONPOLAR SOLVENT:

hexane POLAR APROTIC SOLVENT:

dichloromethane

C6H14

86.18 g/mol

CH2Cl2

84.93 g/mol

C2H6O

46.07 g/mol

-114˚C

78.37˚C

(varies with concentration)

(varies with concentration)

C4H10O

74.12 g/mol

-116.3˚C

34.6˚C

POLAR PROTIC SOLVENT:

ethanol (95% solution used) NONPOLAR SOLVENT:

diethyl ether

851˚C (varies with concentration)

36.461 g/mol

(5% solution used)

H2SO4

50˚C (varies with concentration)

Silver Nitrate Test for 3º, Allylic, & Benzylic Halides REACTS WITH 3°, ALLYLIC, & BENZYLIC HALIDES TO FORM WHITE PPT:

169.87 g/mol

212˚C

C6H5Br

157.01 g/mol

–30.8˚C

156˚C

C7H7Br

171.04 g/mol

–3.9˚C

198199˚C

silver nitrate  ARYL HALIDE (negative halide control con trol for silver nitrate test):

444˚C

AgNO3

(decomposes)

bromobenzene BENZYLIC HALIDE (positive control for silver nitrate test):

benzyl bromide

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19 Apr 2012 4:30pm

Experiment #21: Qualitative Qualitative Analysis Analysis to to Identify Unknown #64: Maleic Acid Acid  ACID THAT DOES NOT DISSOLVE SILVER S ILVER HALIDES:

HNO3

63.01 g/mol

–42˚C

83˚C

C2H6O

46.07 g/mol

-114˚C

78.37˚C

(anhydrous)

100110˚C

N/A

56.1056 g/mol

406˚C

1327˚C

H2SO4

98.079 g/mol

10˚C

337˚C

C7H7NO2

137.136 g/mol

53-54˚C

nitric acid ORGANIC SOLVENT (dissolves AgNO 3 & halide):

95% ethanol Ferrous Hydroxide Test for Nitro Compounds SOURCE OF FERROUS ION FOR FORMATION OF FERROUS HYDROXIDE:

284.05 g/mol

Fe(NH4)2(SO4)2

ferrous ammonium sulfate (5% aqueous) BASE SOURCE OF HYDROXIDE ION FOR FORMATION OF FERROUS HYDROXIDE:

KOH

2M potassium hydroxide (in methanol)  ACID THAT REACTS WITH KOH TO FORM HYDROXIDE ION:

K⊕⊖OH

2M sulfuric acid NITRO COMPOUND (positive control for ferrous hydroxide test):

p- nitrotoluene nitrotoluene

238˚C (flash point)

Baeyer Unsaturation Test for Non-Aromatic Alkenes & Alkynes REACTS WITH ALKENES & ALKYNES (nonaromatic) TO FORM BROWN PPT:

potassium permanganate (1% aqueous solution) CYCLOALKENE (positive control for Baeyer Unsaturation Test):

KMnO4

158.034 g/mol

240˚C

N/A

C6H10

82.143 g/mol

-103.5˚C

82.98˚C

C2H6O

46.07 g/mol

-114˚C

78.37˚C

cyclohexene ORGANIC SOLVENT (dissolves cyclohexene):

95% ethanol

2,4-Dinotrophenylhydrazine Test for Conjugated Aldehydes & Ketones REACTS WITH CONJUGATED ALDEHYDES & KETONES TO GIVE AN ORANGE TO RED PPT:

C6H6N4O4

198.14 g/mol

2,4-dinotrophenylhydrazine

198– 202˚C

N/A˚C

(decomposes)

CONJUGATED ALDEHYDE (positive aldehyde control for 2,4-dinitrophenylhydrazine test):

C9H8O

132.16 g/mol

-7.5˚C

248˚C

C13H10O

182.217 g/mol

47.9˚C

305.4˚C

cinnamaldehyde CONJUGATED KETONE (positive ketone control for 2,4-dinitrophenylhydrazine test):

benzophenone (in 1mL of 95% ethanol)

Nitrous Acid Test for 1º, 2º, 3º, & Aromatic Amines SOURCE OF NITRITE ION FOR FORMATION OF NITROUS ACID:

sodium nitrate

NaNO2

68.9953 g/mol

271˚C (decomposes)

320˚C

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19 Apr 2012 4:30pm

Experiment #21: Qualitative Qualitative Analysis Analysis to to Identify Unknown #64: Maleic Acid Acid 1º ALIPHATIC AMINE [positive control for nitrous acid test (N 2 bubbles)]:

C4H11N

73.14 g/mol

-49˚C

77˚C

C6H5NH2

93.13 g/mol

-6.3°C

184.13° C

C7H9N

107.15 g/mol

-57˚C

194196˚C

H2SO4

98.079 g/mol

10˚C

337˚C

C10H8O

144.17 g/mol

123˚C

285˚C

39.9971 g/mol

318˚C

1388˚C

N-butylamine  AROMATIC AMINE [positive control con trol for nitrous acid test (N 2 bubbles) + diazo dye coupling reaction with β-napthol (beige ppt)]:

aniline 2° ALIPHATIC AMINE [positive control for nitrous acid test (nitroso compound – yellow oil/ppt):

N-methylaniline  ACID (proton source for nitrous acid f ormation + prevents diazo dye coupling reaction):

2M sulfuric acid DIAZO DYE COUPLING REAGENT:

-naphthol (in 10% NaOH aqueous solution) BASE CATALYST FOR DIAZO DYE COUPLING REACTION:

NaOH

Na⊕⊖OH

sodium hydroxide Ferric Chloride Test Reagents for Phenols BASE CATALYST FOR DIAZO DYE COUPLING REACTION:

306˚C

(anhydrous)

(anhydrous)

(anhydrous –  decomposes)

C6H6O

94.11 g/mol

40.5˚C

181.7˚C

C2H6O

46.07 g/mol

-114˚C

78.37˚C

116.07 g/mol

135˚C

N/A

2.5% ferric chloride solution PHENOL [positive control for ferric chloride test (red, blue, purple, or green color change)]:

315˚C

162.2 g/mol

FeCl3

phenol ORGANIC SOLVENT (dissolves phenol):

95% ethanol

Identity of Unknown #64 SYMMETRICAL CARBOXYLIC ACID WITH DOUBLE BOND:

C4H4O4

maleic acid

Reactions & Mechanisms: Solubility Testing & Flowchart  The main rule of thumb for solubility and solvents is “like dissolves like” meaning that nonpolar compounds  dissolve other nonpolar nonpolar compounds while polar compounds dissolve dissolve other polar compounds. compounds. Additionally, Additionally, solubility based on acid/base interactions depends on the acid/base strength of the compound to be dissolved  as well as the solvent – strong acids can dissolve weak bases that cannot be dissolved in weak acids, strong  bases can dissolve weak acids that cannot be dissolved in weak bases, weak acids dissolve strong bases, and  weak bases dissolve strong acids. Water (polar protic) – dissolves compounds with four or fewer carbons and also those containing • oxygen or nitrogen; dissolves ionic compounds 5% HCl (dilute acid) – dissolves basic compounds such as aliphatic amines that readily dissolve in acid • to form soluble HCl salts in aqueous solution

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19 Apr 2012 4:30pm

Experiment #21: Qualitative Qualitative Analysis Analysis to to Identify Unknown #64: Maleic Acid Acid • •

• • • •

5% NaHCO3 (weak base) – dissolves strongly acidic compounds Concentrated H2SO4 (strong acid) – dissolves weak bases that remain insoluble in weak acids including compounds with either nitrogen or oxygen that can be easily protonated by a strong acid leaving ions that are soluble in the solution media Hexane (nonpolar) – dissolves completely nonpolar organic compounds Dichloromethane (polar aprotic) – dissolves polar aprotic organic compounds Ethanol – dissolves polar protic compounds especially alcohols Diethyl ether – dissolves nonpolar organic compounds especially ethers

Solubility Flowchart 

BASES

NEUTRAL COMPOUNDS:

INERT COMPOUNDS:

STRONG ACIDS:

 WEAK ACIDS:

Chemical Classification Tests  1. Silver Nitrate (Ethanoic) Test for 3º, Allylic, & Benzylic Halides:

R–X + AgNO3 + HO–CH2CH3



R–OCH2CH3 + AgX(s) + HNO3

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19 Apr 2012 4:30pm

Experiment #21: Qualitative Qualitative Analysis Analysis to to Identify Unknown #64: Maleic Acid Acid 2. Baeyer Unsaturation Unsaturation Test for for Non-Aromatic Alkenes & Alkynes Alkynes

3. Ferrous Hydroxide Hydroxide Test for for Nitro Compounds

R–NO2 + 6 Fe(OH)2 + 4 H2O



R–NH2 + 6 Fe(OH)3 (s)) + MnO2 (s)

4. 2,4-Dinotrophenylhydrazine 2,4-Dinotrophenylhydrazine Test for Conjugated Conjugated Aldehydes & Ketones

5. Nitrous Acid Test for 1º, 2º, 3º, & Aromatic Amines •

1º Aliphatic Amine 

•

1º Aromatic Amine 

•

2º Amine 

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19 Apr 2012 4:30pm

Experiment #21: Qualitative Qualitative Analysis Analysis to to Identify Unknown #64: Maleic Acid Acid •

3º Aliphatic Amine 

•

Aromatic Amine 

6. Ferric Chloride Chloride Test Reagents for Phenols:

Procedures & Observations: Solubility Tests:  1. Added 1 mL of each of the following to different test tubes – water, 5% NaOH, 5% NaHCO 3, 5% HCl, concentrated H2SO4, hexane, dichloromethane, ethanol, and diethyl ether. 2. Added a small amount of solid unknown #64. Unknown #64 was insoluble in H2O, 5% HCl, concentrated H2SO4, hexane, dichloromethane, and diethyl ether but soluble in 5% NaOH, 5% NaHCO3, and ethanol. Silver Nitrate (Ethanoic) Test for 3º, Allylic, & Benzylic Halides:  1. Added 0.5 mL of a 2% ethanolic AgNO 3 to test tube. 2. Under the fume hood added 1 drop of unknown #64 to test tube. Covered test tube with parafilm. No white precipitate noted. 3. Placed the test tube in a hot water bath for 5 minutes. Noted the formation of a white precipitate in the test tube. 4. Allowed test tubes to cool. Then added 2 drops of dilute HNO3. The precipitate dissolved in the nitric acid. 5. Unknown #64 had a negative silver nitrate test suggesting that it is not a halide. Baeyer Unsaturation Test for Non-Aromatic Alkenes & Alkynes:  1. Added 5 drops of unknown #64 to a test tube.

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19 Apr 2012 4:30pm

Experiment #21: Qualitative Qualitative Analysis Analysis to to Identify Unknown #64: Maleic Acid Acid 2. Slowly added 1% aqueous solution of potassium permanganate drop by drop while shaking the test tube to mix. Allowed the solution to sit for 5 minutes and observed a brown precipitate. 3. Unknown #64 had a positive Baeyer test suggesting that it has a non-aromatic alkene or alkyne group. Ferrous Hydroxide Test for Nitro Compounds:  1. Added 1.5 mL of a 5% ferrous ammonium sulfate solution to test tube. 2. Added 1 drop of unknown #64 to test tube. Tapped to mix. 3. Added 1 drop of 2M sulfuric acid and then 1 mL of a 2M potassium hydroxide solution in methanol to test tube. Covered with parafilm & shook vigorously to mix. Noted an army green colored precipitate. 4. Unknown #64 had a negative ferrous hydroxide test suggesting that it is not a nitro compound. 2,4-Dinotrophenylhydrazine Test for Aldehydes & Ketones:  1. Added 5 drops of unknown #64 to a test tube. 2. Added 1 mL of 2,4-dinitrophenylhydrazine, covered with parafilm, and shook gently to mix. No precipitate formation noted. 3. Allowed test tubes to sit for 15 minutes and noted no changes. Gently heated test tubes #2 and #3 in a hot water bath for 10 minutes. Unknown #64 remained a golden yellow, clear liquid with no precipitate formation. 4. Unknown #64 had a negative 2,4-dinitrophenylhydrazine test suggesting that it is neither an aldehyde or a ketone. Nitrous Acid Test for 1º, 2º, 3º, & Aromatic Amines:  1. Added 2 mL distilled water to a test tube labeled #1. 2. Added 8 drops of concentrated H2SO4 to same test tube. Then added 6 drops of unknown #64. Sulfuric acid provides the proton for nitrous acid formation and also keeps the diazo dye coupling reaction from occurring prematurely. 3. Added 2 mL of a 10% aqueous sodium nitrite solution to test tube #2, and dissolved 0.1 g β-naphthol in 2 mL of aqueous 10% NaOH solution to test tube #3. The sodium nitrite will provide the nitrite ion to form nitrous acid. 4. Placed all 3 test tubes in an ice water bath at ~ 5˚C to stabilize the diazonium ion that can be formed by the reaction of 1º or aromatic amines with nitrous acid. 5. Added cold sodium nitrite solution dropwise to tube #1 and gently shook to mix. No precipitate, gas formation, or oily drops noted. 6. Poured half of the solution from test tube #1 into another test tube and allowed it to return to room temperature. No precipitate or gas formation noted. 7. Added 0.5 mL β-naphthol drop by drop to the solutions that remained in the ice bath. No precipitate formation. No sign of azo-dye coupling reaction. 8. Unknown #64 had a negative nitrous acid test suggesting that it is not a 1°, 2°, 3°, or aromatic amine. Ferric Chloride Test Reagents for Phenols:  1. Added a pea-sized amount of unknown #64 to a test tube. Dissolved in a small amount of ethanol. Covered with parafilm and shook gently to mix. 2. Added 7 drops of 2.5% ferric chloride solution to the test tube and shook gently to mix. No dramatic color change noted. 3. Unknown #64 had a negative ferric chloride test suggesting that it does not contain a phenol group.

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19 Apr 2012 4:30pm

Experiment #21: Qualitative Qualitative Analysis Analysis to to Identify Unknown #64: Maleic Acid Acid Melting Point, NMR, & IR Analysis:  1. Received 1H NMR and 13C NMR data from TA. See results section for analysis. 2. Performed melting point analysis. Melting point was 134-137°C. 3. Prepared KBr pellet per protocol. Ran IR spectrometry. spectromet ry. See results section for analysis.

Characterization & Results: Various observations noted during the experiment are delineated in the “Procedures and Observations” section above. The significant results of the solubility test and each of the six chemical classification tests are presented in the table below including findings related to unknown #64.

Physical Properties:  Physical state:  solid • Color:  white crystals ranging from small chunks to fine powder consistency • Odor:  very faint acidic odor • Melting point:  134-137 °C • Spectral Analysis:  1 H NMR: Showed a peak at 6.2ppm (consist with symmetrical alkene hydrogens). Peak for –OH •

•

•

hydrogens was off the scale of the spectrum at approximately 10 to 12ppm (consistent with aliphatic carboxylic acid hydrogens). See attached 1H NMR for analysis. 13 C NMR: Showed peaks at 135ppm (consistent with alkene carbons) and at 190ppm (consistent with carboxylic acid carbons). See attached 13C NMR for analysis. IR spectrum: Showed deep depression in 3300 to 2500cm-1 range (consistent with carboxylic acid). See attached IR spectrum for analysis.

Solubility Test  Test Reagent H2O

Unknown # 64 Insoluble (white powder remains)

5% NaOH

Soluble

Results & Conclusions Not a low MW amine, low MW neutral compound, or low MW carboxylic acid Organic acid. Could be a carboxylic acid or phenol

(clear liquid – no white powder)

5% NaHCO3

Soluble

Strong organic acid. Could be carboxylic acid or a phenol.

(clear liquid – no white powder)

5% HCl

Concentrated H2SO4 Hexane

Insoluble

Not a neutral compound (alkene, alkyne, alcohol, ketone, aldehyde, nitro compound,

(white powder remains)

ester, ether, or amide)

Insoluble

Not an inert compound (alkane, alkyl halide, aromatic compound) Not a basic compound.

(white powder remains)

Insoluble

Not a nonpolar compound

(white powder remains)

CH2Cl2

Insoluble

Not a polar protic compound

(white powder remains)

Ethanol

Soluble

Compound is polar aprotic

(clear fluid – no white powder)

Diethyl Ether

Insoluble (white powder remains)

Not a nonpolar compound

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19 Apr 2012 4:30pm

Experiment #21: Qualitative Qualitative Analysis Analysis to to Identify Unknown #64: Maleic Acid Acid Chemical Classification Tests:  Chemical Classification Test Silver Nitrate (Ethanoic) Test for 3º, Allylic, & Benzylic Halides:

Control(s)

Unknown #64

Identity of Unknown #64

BENZYLIC HALIDE – (+) white ppt

(–) white ppt

 ARYL HALIDE – (–) white ppt (soluble in HNO 3)

(soluble in HNO 3)

NONAROMATIC ALKENE – (+) brown ppt

(+) brown ppt

NITRO COMPOUND - (+) rust color ppt

(–) army green ppt

Not a nitro compound

CONJUGATED ALDEHYDE: (+) orange red ppt CONJUGATED KETONE: (+) orange ppt UNCONJUGATED ALDEHYDE/KETONE: (+) yellow ppt

(–) no ppt

Not a ketone or aldehyde

(–) no ppt, no gas, no azo dye

Not a 1º, 2°, 3°, or aromatic amine

(–) no color change

Not a phenol

Baeyer Unsaturation Test for Non-Aromatic Alkenes & Alkynes Ferrous Hydroxide Test for Nitro Compounds 2,4Dinotrophenylhydrazine Test for Conjugated Aldehydes & Ketones

Not a halide

ALKENE or ALKYNE

---------------1º ALIPHATIC AMINE---------------

(+) N2 gas: gas bubbles (+) azo dye: bright yellow ppt (with addition of β-naphthol) ---------------1º AROMATIC AMINE---------------

Nitrous Acid Test for 1º, 2º, 3º, & Aromatic Amines

(+) N2 gas: gas bubbles (when heated) (+) diazonium ion: beige ppt (+) azo dye: orange ppt (with addition of β-naphthol) ---------------2ºº AMINE-----------------------------2

(–) N2 gas: no gas bubbles (+) nitroso compound: brown-yellow oily ppt (+) azo dye: orange ppt (with addition of β-naphthol)

Ferric Chloride Test Reagents for Phenols:

(+) Phenol: color change to dark purple

Conclusions: The experiment was completed per protocol with observations as noted. Specific results have been presented in tabular format in the “Results” section. The solubility tests showed that unknown #64 was a polar aprotic compound and a strong organic acid. Using the solubility flowchart, it was determined that unknown #64 was a carboxylic acid or perhaps a phenol. Chemical classification tests showed that unknown #64 was an alkene or alkyne and that it was not a phenol; therefore, unknown #64 was determined to be a carboxylic acid with a double or triple bond. Both NMRs showed that the molecule was symmetrical with analysis presented on attached spectra. IR analysis showed a deep depression in 3300 to 2500cm-1 range that is consistent with a carboxylic acid. Melting point allowed for the identification of unknown #64 as maleic acid. UNKNOWN #64 is MALEIC ACID.

Post-Lab Questions: The information requested on the “Results and Data sheet” must be fully completed in order to receive full credit.

Sources: •

http://en.wikipedia.org/wiki/

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19 Apr 2012 4:30pm

Experiment #21: Qualitative Qualitative Analysis Analysis to to Identify Unknown #64: Maleic Acid Acid • •

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• • •

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