Correction des TP N°2 et 3

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TP#N°2#et#3#:#RÉACTION#DE#CANNIZZARO#
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II.#Travail#préparatoire#TP#N°2#
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=4,7∙10!! 𝑚𝑜𝑙!
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mélange
réactionnel
solvant organique
(éther diéthylique)
mélange
biphasique
1 phase organique :
alcool benzylique
Ph-CH2-OH
dans l'éther
1 phase aqueuse :
ions benzoate Ph-COO−
+ ions HO−
dans l'eau
1 phase aqueuse acide
+
1 phase solide (acide
benzoïque Ph-COOH)
1 phase solide
(acide benzoïque
Ph-COOH)
impure
1 phase aqueuse
acide
Extraction et décantation
Acidification
Essorage sous vide
pH
C6H5COOH
prédomine
C6H5COO−
prédomine
4,2

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phase organique (alcool benzylique
dans l'éther diéthylique)
phase aqueuse (ions benzoate et
ions hydroxyde dans l'eau)

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IV.#Questions#supplémentaires#pour#le#compte-rendu#du#TP#N°3#
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Rf = 0.44
Rf = 0.55
Rf = 0.75
1 2 3 4 5
1 : Benzaldéhyde commercial
2 : Alcool benzylique commercial
3 : Acide benzoïque commercial
4 : Produit brut
5 : Produit purifié
Ligne de dépôt
Front de l'éluant

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Il#est#donc#nécessaire#de#manipuler#proprement#et#d'optimiser#chaque#étape#afin#de#perdre#le#moins#de#
produit#possible.#
%
Conclusion#:#%
#
Benzaldéhyde + ions HO−
Réaction de Cannizzaro
Alcool benzylique + ions benzoate
+ ions HO−
Extraction liquide-liquide
+ Décantation
Alcool benzylique
(phase organique)
Ions benzoate + ions HO−
Acidification
Acide benzoïque (s) +
phase aqueuse
Essorage sous vide Phase aqueuse
Acide benzoïque brut
Recristallisation
Traitement
Acide benzoïque purifié
Caractérisation et évaluation de la pureté
Mesure de la Tfus au banc Kofler
Chromatographie sur couche mince
Calcul du rendement : 78%
Purification
Traitement
Traitement