Aldehydes and Ketones Name _____________________

Tollens’ Test (test for aldehydes)

I. Write an equation for the reaction of an aldehyde with Tollens’ reagent.

II. Clean 3 reaction tubes by adding a few milliliters of 10% NaOH to each and

heating in a water bath while preparing the Tollens’ reagent.

III. Write a flow chart for the preparation of Tollens’ reagent.

IV. Empty reaction tubes of NaOH and rinse.

V. Write a procedure for testing the three knowns (acetophenone, benzaldehyde,

and hexane) with Tollens’ reagent.

VI. Observations

Tollen’s reagent plus

acetophenone

benzaldehyde

hexane

VII. PROMPTLY DESTROY excess TOLLENS’ REAGENT with a few drops

of nitric acid. It can form an explosive fulminate on standing. A drop of

nitric acid can be used to remove the silver mirrors form test tubes.

Schiff’s Test (a very sensitive test for aldehydes)

I. Write an equation for the reaction of an aldehyde with Schiff’s reagent.

II. Write a procedure for testing the three known substances (acetophenone,

benzophenone, and hexane) with Schiff’s reagent.

III. Observations

Schiff’s reagent plus

acetophenone

benzaldehyde

hexane

VI. Clean up

Neutralize the solution with Na₂CO₃ and flush it down the drain.

Iodoform Test (test for methyl ketones)

I. Write an equation for the reaction of a methyl ketone to form iodoform.

II. Write a procedure for the iodoform test with

A. a water soluble substance:

B. a water insoluble substance:

III. Observations

Iodine solution plus

acetophenone

benzaldehyde

hexane

VI. Clean up

Combine all reaction mixtures in a beaker, add a few drops of acetone to

destroy any unreacted iodine in potassium iodide reagent, remove iodoform

by suction filtration, and place iodoform in the halogenated organic waste

container. The filtrate can be flushed down the drain after neutralization

(if necessary).

Bisulfite Test (test for unhindered aldehydes or ketones)

I. Write an equation for the reaction of an unhindered aldehyde or ketone

with a sodium bisulfite solution.

II. Write a procedure for the reaction of an unhindered aldehyde or ketone

with sodium bisulfite.

III. Observations

NaHSO₃ solution plus

acetophenone

benzaldehyde

hexane

IV. Clean up

Dilute the bisulfite solution with a large amount of water and flush the mixture

down the drain. The amount of organic material being discarded is negligible.

Part 2, Unknown

Your unknown may be acetophenone, benzaldehyde, n-butanal, cinnamaldehyde,

furfural, 2-heptanone, 3-heptanone, n-heptanal, or 2-octanone.

Aldehyde or ketone?

Run a Tollens’ or/and a Schiff’s Test to determine, if you have an aldehyde or ketone.

Tollens’ Test

I. Observations for unknown

Tollens’ reagent plus

acetophenone (or hexane)

benzaldehyde

unknown

II. DO NOT FORGET TO PROMPTLY DESTROY excess TOLLENS’

REAGENT.

Schiff’s Test

I. Observations for unknown

Schiff’s reagent plus

acetophenone (or hexane)

benzaldehyde

unknown

If you have a ketone, test to see if you have a methyl ketone

Results of Iodoform test: ___________________________________

Boiling point of unknown

You must determine the boiling point of your unknown. See Chapter 4, Boiling Points, In a Reaction Tube, page 75 for the procedure.

Boiling point of your unknown: _____________________________

2,4-dinitrophenylhydrazone or semicarbazone derivative

You must submit one derivative of your unknown (either a

2,4-dinitrophenylhydrazone or semicarbazone derivative). If the first derivative that you make is oily and won’t crystallize out, try making the second derivative. You need at least one good derivative to get a melting point.

I recommend doubling the quantities when making the derivatives.

I. Write a reaction for the preparation of the 2,4-dinitrophenylhydrazone or

semicarbazone derivative of an aldehyde or ketone.

II. Write a procedure for the preparation of the 2,4-dinitrophenylhydrazone or

semicarbazone derivative of an aldehyde or ketone.

III. Observations

Melting point of 2,4-dinitrophenylhydrazone or semicarbazone derivative

of your unknown: _____________

Turn in the 2,4-dinitrophenylhydrazone or semicarbazone derivative of your unknown with this experiment.

Conclusion

Unknown # _____ is _______________________________________________.

QUESTIONS

1. What is the purpose of making derivatives of unknowns.

2. Why are 2,4-dinitrophenylhydrazones better derivatives than phenylhydrazones?

3. Using chemical tests how you distinguish among 2-pentanone, 3-pentanone,

and pentanal?

4. Draw the structure of a compound, C₅H₈O, that gives a positive iodoform

and does not decolorize permanganate.

5. Draw the structures of three different compounds, C₅H₈O, that give a positive

Tollen’s test and do not react with bromine in dichloromethane.

6. Draw the structures of five different compounds, C₅H₈O, that react with

phenylhydrazine, decolorize bromine in dichloromethane, and do not give

a positive iodoform test.

7. Draw the structures of two geometric isomers, C₅H₈O, that give a positive

iodoform test.

9. Give the wavenumber (cm^-1) of the carbonyl peak in the IR in Figure 36.4 of

your lab text.

10. Assign various peaks in the ¹H NMR spectrum of 2-butanone to specific

protons in the following molecule (See Figure 36.6 in your lab text):

(a) (b) (c) quartet 2.4 PPM _______

CH₃-C-CH₂-CH₃

|| singlet 2.1 PPM ________

O

triplet 1.0 PPM ________

11. Assign various peaks in the ¹H NMR spectrum of crotonaldehyde to specific

protons in the following molecule (see Figure 36.7 in your lab text):

(a) (b) (c) (d) doublet 9.5 PPM _______

CH₃CH=CHCHO

sextet 6.9 PPM _______

quartet (doublet of doublets) 6.1 PPM _______

doublet 2.0 PPM _______