Download Carbonyl Classification Tests The samples to be tested in each of

Carbonyl Classification Tests
The samples to be tested in each of the following tests are:
.Your Sample
.Cyclohexanol
.Cyclohexanone
.Benzaldehyde
.Acetophenone
2,4-dinitrophenylhydrazine* Test
OH

R2C=O + H2NNH-C6H4(NO2)2*  R2C-NH-NH-C6H4(NO2)2  R2C=N-NH-C6H4(NO2)2 + H2O
2,4-dinitrophenylhydrazone
1.
Dissolve 1 - 2 drops of sample to be tested in 10 drops of 95% ethanol.
2.
Add this solution to 10 drops of 2,4-DNPH reagent.
3.
Shake the mixture vigorously, and if no precipitate forms almost immediately, allow the mixture to stand
for 15 minutes. A positive test is indicated by the presence of a precipitate the 2,4-dinitrophenylhydrazone of
your compound.
Dispose of test tube contents into the Recovered Organic Solvent Bottle.
Tollens' Test
RCHO + Ag(NH3)2 + 2 OH  2 Ag + RCO2NH + H2O + 3NH3
1.
Place 3 drops of sample into a test tube, followed by 10 drops Tollens' reagent. The formation of a silver
mirror, or a black precipitate constitutes a positive test.
2.
If no reaction occurs at room temperature, warm the solution in a beaker of warm tap water from one of the
hot water faucets at the front of the lab.
Dispose of contents into the sink and clean tubes CAREFULLY.
Chromic acid test See Alcohol Classification Tests Pg. 29.
H2CrO4
Primary alcohols and aldehydes: RCH2OH ------------> RCO2H
H2CrO4
Secondary alcohols: R2CHOH ------------> R2CO
Ketones: no visible reaction
Tertiary alcohols: R3COH do not react with H2CrO4
1.
To a test tube, add 20 drops acetone, 1 drop of sample, and 1 drop of chromic acid reagent.
2.
Shake the contents of the tube. A positive test is indicated by the disappearance of the orange color of the
chromic acid reagent and the formation of a green or blue-green precipitate or emulsion.
Primary and secondary alcohols and aliphatic aldehydes give a positive test within 5 minutes, while aromatic
aldehydes require up to 45 minutes.
Dispose of test tube contents into the Recovered Organic Solvent bottle.
Iodoform Test
When an aldehyde or ketone that has -hydrogens is treated with a halogen in basic medium, halogenation occurs at
the -carbon:
R1 O
X2, NOOH
R1 O
R2 - C - C - R(H) -----------> R2 - C - C - R(H)
H
X
If R1 and R2 = H, AND X = I
H O 3I2,4NaOH X O
I
O
HC-C-R(H)--------> X-C-C(H) ---> X-C-H(s) + Na+ -O-C-R(H)+3NaI
H
H2O
X
I
1.
To a test tube, add 10 drops dioxane, 2-3 drops of sample, and 10 drops 3M NaOH.
2.
To the tube now slowly add 15 drops of Iodine solution. A positive test is evidenced by the disappearance
of the brown iodine color and the separation of the yellow iodoform.
Dispose of test tube contents into the Recovered Organic Solvent bottle.
Pour the remainder of your product , if any, into the cyclohexanone recovery bottle at the front of the lab.
Laboratory Report. Write the name of each compound & the observation after mixing it with the reagent.
B. Mechanism of Halogenation Using H for R1 & R2 and I for X.
HO
HO
H OHC-C-R(H) + NaOH- ---> H2O + HC-C-R(H)  H-C=C-R(H) +Na+
H
HO
H O
HC-C-R(H) + I2 ---> HC-C-R(H) + NaI
I
HO
-O
OHC-C-R(H) + NaOH ---> HC-C-R(H)  HC=C-R(H) + H2O + Na+
I
I
I
-O
I O
HC-C-R(H) + I2 ----> HC-C-R(H) + NaI
I
I
Repeat this last step again to get
I
I-C-C-R(H) + NaI
I
Sum is
HO
IO
HC-C-R(H) + 3NaOH ---> I-C-C-R(H) + 3NaI
H
I
Now
IO
I OI O
I-C-C-R(H) + NaOH ---> I-C-C-R(H) --> I-C- + HOCR(H) + Na+
I
I OH
I
I
I
I-C- + H2O ---> I-CH(s) + OHI
I
O
O
Na+ + OH- + HO-C-R(H) ---> Na+  C-R(H) + H2O
O
O
Net Eq. CH3-C-R(H) + 4NaOH + 3I2 ---> I3CH + Na+ -OCR(H) + 3NaI + OHEXERCISE:
Write the equation of a positive test for test performed. Tell what you
observed that constituted a positive test.