IdentifyingIdentifyingan Unknown Alcoholan Unknown Alcohol

BackgroundBackground

Classification Tests are qualitative tests which can indicate the presence of a particular functional group, such as an aldehyde or an alcohol.

Two inviolable rules when performing classification tests:

1. Perform the test exactly as described.2. Always perform tests on known compounds, one

that will result in a positive test (known positive) and one that will result in a negative test (known negative) and then perform the tests on the unknown compound.

Experimental ProceduresExperimental Procedures

Do this experiment before finishing the Grignard purification. For all procedures in this lab, follow the lab manual exactly as written, but change the order. (Do Part 1 after Parts 2 & 3)

New experimental order: Part 2. Lucas Test Part 3. TCICA Test: use gloves Part 1. Derivative formation

Omit the refractive index and micro-boiling point sections.

Do not cross contaminate the contents of your test tubes.

There are three Waste Bottles: 1. Recovered Lucas Solutions 2. Recovered TCICA Solutions 3. Recovered Alcohols

Your lab report must state which type of alcohol is your unknown.

Experimental ProcedureLucas TestLucas Test

The Lucas reagent is a solution of zinc chloride (ZnCl2) in concentrated HCl. A positive test occurs when the alkyl halide formed in the reaction begins to separate from the aqueous solution to form a second layer. This test readily distinguishes between primary, secondary, and tertiary alcohol based on whether a reaction occurs and on the reaction time.

3°3° alcohol and alcohols that form resonance-stabilized carbocations react to form a cloudy mixture in less than 30 sec at room temperature.

R C

R

OH

R

ZnCl2

HCl/H2OR C

R

O

R

ZnCl

H

+ R C

R

R

+Cl-

R C

R

R

Cl

not soluble3° alcohol: water soluble

(SN1 reaction)Forms Carbocation

R C

R

OH

H

ZnCl2

HCl/H2OR C

R

O

H

ZnCl

H

+ R C

R

H

+Cl-

R C

R

H

Cl

not soluble2° alcoholwater soluble

2° alcohol can react in 3-10 min, but may need to be warmed.

1° alcohol requires more than an hour to react, if it reacts at all.

R C

H

OH

H

ZnCl2

HCl/H2O

NO REACTION in several hours

1° alcoholwater soluble

The rate of reaction is related to carbocation stability.

3° > 2° > 1° alcohol

Experimental – Lucas Test

Lucas TestLucas Test

Prepare 4 test tubes with 2 mL Lucas reagent, 4 drops alcohol, & mix. Record time until cloudy (how long does it take to form cloudy solution?).

TCICA TestTCICA Test

Experimental ProcedureExperimental Procedure

TCICA (1,3,5-trichloroisocyanuric acid) is a common source of chlorine used to disinfect swimming pools or as an additive in some kitchen cleansers.

OH

H

3 +N

N

NCl

Cl

Cl

O

O O

1 drop HCl(aq)3

ON

N

NH

H

H

O

O O

+ + 3 HCl

CH3CN

alcohol TCICAisocyanuric acid precipitate

Experimental - TCICA Test The time it takes for isocyanuric acid precipitate to appear is characteristic of the type of alcohol.

R C

OH

R R C

O

R

H

TCICA

HCl / CH3CN

N

N

NH

H

H

O

O O

+ + 3 HCl3 3

R C

OH

H

H

3TCICA

HCl / CH3CNR C

O

HN

N

NH

H

H

O

O O

+ + 3 HCl3

R C

OH

R

R

TCICA

HCl / CH3CN

2° alcohol

15 – 30 sec

1° alcohol

not soluble

3 – 7 min

3° alcohol

NO OXIDATION within 1 hr

ketone

aldehyde

The rate of isocyanuric acid precipitate appearance(cloudy solution): 2° > 1° > 3° alcohol

Experimental ProcedureExperimental Procedure

TCICA Test

Prepare 4 test tubes with 0.5 mL TCICA and 1 drop of 1M HCl, mix together. Add 1 drop of alcohol, each to its own test tube, and mix together. Record time until precipitate forms.

Derivative formationDerivative formation ( (only with unknownonly with unknown))

Unknown compounds can be reacted with various reagents to give new compounds called derivatives.

Stable, crystalline derivatives can be used to identify unknowns by comparing the derivative melting point with literature values. Several derivatives can be made to confirm an unknown alcohol.

Derivative FormationDerivative Formation

If 1° or 2° alcohol is suspected, follow A. If 3° alcohol (which is slow to react) is suspected, follow B (use catalyst).

R OH + ClNO2

NO2

O

8 drops

0.23 g

1) heat 10 - 15 min in water bath (almost boiling)

2) cool to RT. if NO precipitate, cool in ice bath3) neutralized with Na2CO34) filter5) recrystallize using EtOH

RONO2

NO2

O

Take melting point after recrystallizefrom EtOH (do not exceed 5 mL)

ONO2

NO2

O-

ClH

R+ O

NO2

NO2

O

H

R+

Cl-

AA:

3,5-dinitrobenzoyl chloride

+ ClNO2

NO2

O

0.23 g

1) 1 mL of acetone

2) 8 drops ROH

3) heat 10-15 min

4) cool

5) neutralized with Na2CO3

6) filter

7) recrystallize using EtOH

N

N

0.12 g

N

O

NO2

NO2

N

+

ROH

(tertiary alcohol)

N

O-

NO2

NO2

N

+

ORH

+

N

O-

NO2

NO2

N

+

Cl

Derivative FormationDerivative Formation

NO2

NO2

O

NO2

NO2

O+

R

NNH

RO

O

B:B:

Ester: take mp after recrystallization

NN+

better leaving group

4-dimethylaminopyridine (DMAP)

Triturate residue in distilling flask with cold petroleum ether (not diethyl ether).

"…to reduce to fine particles or powder by rubbing, grinding, bruising, or the like."

Decant petroleum ether (SAVE small sample of ether for TLC). Recrystallize from isopropyl alcohol to obtain the pure product.

Perform TLC on the crude product, petroleum ether extract, and pure

product by using ether to dissolve all solids and using petroleum ether

as eluent. Measure mass, mp and calculate %yield.

Have Fun!Have Fun!

Characterization of Your Product:

Last - Finish Grignard ReactionLast - Finish Grignard Reaction

Next week – Comprehensive Final !!!