Reaction of Aldehydes and Ketones with Naoh

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D. REACTIONS OF ALDEHYDES AND KETONES WITH SODIUM HYDROXIDE (By: Mary Deo Luigi J. Mabunay1N-3)

Objective:
To determine the reactions of Aldehydes and Ketones when combined with Sodium Hydroxide.

Process:
* Obtain 5 clean and dry test tubes
* Put 2mL of 40% NaOH solution to test tubes 1, 2 and 3 and on test tubes 4 and 5, put 10% NaOH solution * Add 10 drops of the following solution:
* Tube 1: formaldehyde
* Tube 2: benzaldehyde
* Tube 3: acetaldehyde
* Tube 4: acetaldehyde
* Tube 5: acetone
* Transfer all test tubes in a boiling water bath for 10 minutes * Record all observations

Results:
Sample| NaOH| Observations|
1. Formaldehyde| 40% NaOH| Alcohol-like odor|
2. Benzaldehyde| 40% NaOH| The color became yellow; immiscible| 3. Acetaldehyde| 40% NaOH| The color became dark orange; rubber-like smell| 4. Acetaldehyde| 10% NaOH| The color became orange|

5. Acetone| 10% NaOH| Viscous |

The table above shows the results of aldehydes and ketones as it reacts with sodium hydroxide (NaOH). There were two types of NaOH used, the 40% and the 10%. For sample 1, only the odor of the product formed was noted. For sample 2, the state and color were observed. For sample 3, the odor and color of the resulting solution were distinguished. For sample 4, only the color was noted while for sample 5, the consistency of the solution was identified.

Study Questions:
A. State the function of the sodium hydroxide in the test. * Sodium Hydroxide (NaOH) acts as a catalyst in the test. B. What are the principles involved in the test? What is its purpose? * Aldol-ketol Condensation

* Is an organic reaction in which an enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hyroxyketone, followed by dehydration to give a conjugated enone. (Acetaldehyde and ketone)

MECHANISM OF THE ALDOL CONDENSATION|

Step 1: 
First, an acid-base reaction. Hydroxide functions as a base and removes the acidic α-hydrogen giving the reactive enolate.| | Step 2: 
The nucleophilic enolate attacks the aldehyde at the electrophilic carbonyl C in a nucleophilic addition type process giving an intermediate alkoxide.| | Step 3: 
An acid-base reaction. The alkoxide deprotonates a water molecule creating hydroxide and the β-hydroxyaldehydes or aldol product.| | | |

MECHANISM OF THE ALDOL CONDENSATION OF A KETONE|

Step 1: 
First, an acid-base reaction. Hydroxide functions as a base and removes the acidic α-hydrogen giving the reactive enolate.| | Step 2: 
The nucleophilic enolate attacks the ketone at the electrophilic carbonyl C in a nucleophilic addition type process giving an intermediate alkoxide.| | Step 3: 
An acid-base reaction. The alkoxide deprotonates a water molecule creating hydroxide and the β-hydroxyketone, the aldol product.| | | |

* Cannizzaro Reaction
* ”Aromatic aldehydes (ArCHO), and other aldehydes that lack an α-hydrogen, undergo an unusual oxidation-reduction reaction when treated with a strong base such as sodium hydroxide (NaOH). Half of the aldehyde molecules are oxidized, and the other half are reduced. The products (after acidification) are a carboxylic acid and a primary alcohol.” -www.britannica.com

* (Formaldehyde and benzaldehyde)
* Mechanism:
Step 1: Nucleophilic Attack

The Nucleophile attacks the carbonyl carbon which is electron deficient due to the presence of the electron withdrawing O group. Step 2: Deprotonation and formation of Dianion

The proton is abstracted by the nucleophile and the di anion formation takes place simultaneously, resulting in a reactive intermediate. Step 3: Hydride ion transfer

Hydride ion is transferred from one molecule to another molecule and neutralization of charge results in the formation of a carboxylate ion and a alkoxide ion. Step 4: Formation of the salt and the...
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