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.

 

Failure to properly dispose of your solutions will result in a 2 point deduction from your lab score,

FOR EACH INFRACTION

 

 

 

 

Tollens' Test

 

                                RCHO + Ag(NH3)2r + 2 OHs 6 2 Ag + RCO2sNHr + 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 Silver Recovery Bottle.  Rinse tubes with 5% HCl and add to

Silver Recovery Bottle.

 

Failure to properly dispose of your solutions will result in a 2 point deduction from your lab score,

FOR EACH INFRACTION

 

 

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.

 

Failure to properly dispose of your solutions will result in a 2 point deduction from your lab score,

FOR EACH INFRACTION

 

 

 

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.

 

Failure to properly dispose of your solutions will result in a 2 point deduction from your lab score,

FOR EACH INFRACTION

 

Pour the remainder of your product , if any, into the cyclohexanone recovery bottle at the front of the lab.

 

Failure to properly dispose of your product will result in a 2 point deduction from your lab score,

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.

 

 

   H O                                              H O                 H O-

HC-C-R(H) + NaOH- ---> H2O +  HC-C-R(H) X H-C=C-R(H)  +Na+

   H                                                  -  

 

   H O                         H  O

HC-C-R(H) + I2 ---> HC-C-R(H) + NaI

   -                               I

 

  H O                                  -  O                    O- 

HC-C-R(H) + NaOH ---> HC-C-R(H) W 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

 

 H   O                                   I  O

HC-C-R(H) + 3NaOH ---> I-C-C-R(H) + 3NaI

 H                                         I

 

Now

 

   I  O                                   I   O-                  I           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) + OH-

   I                        I

 

                           O                          O

Na+ + OH- + HO-C-R(H) ---> Na+ u C-R(H) + H2O

 

                     O                                                              O

Net Eq. CH3-C-R(H) + 4NaOH + 3I2 ---> I3CH + Na+ -OCR(H) + 3NaI + OH-

 

EXERCISE:

 

Write the equation of a positive test for test performed.  Tell what you

observed that constituted a positive test.