Page 223 - PG 504-theoretical notes-phyto-1-2024-2025..

Clinical pharmacy PharmD program Third level Phytochemistry-1 (PG-504)

2.Reaction with neutral sodium sulfite (for aldehydes):
R- CHO + Na2SO3→ RCH(OH)SO3Na + 2NaOH

The produced NaOH titrated against standard HCl solution
• An equivalent amount of NaOH is liberated. The liberated NaOH must be neutralized
to push the reaction forward
• This method can avoid the lack of a definite end point by adding few drops of phenol
phthaline and could be used for small quantities but it is still slow.
• The neutral sulfite method could be used to estimate ketones containing α-β
unsaturation as carvone, pulugone and pipertone.
B. Condensation reactions:

1. Reaction with hydroxylamine HCl (for aldehydes and ketones)
Aldehyde + Hydroxylamine HCl → Oxime + HCl

R-CHO+NH2OH.HCl → RCH=N-OH+HCl+H2O

The produced HCl is titrated against standard KOH solution

1. Reaction with phenylhydrazine (for aldehydes)
Aldehyde + phenylhydrazine → hydrazone (crystalline product → m.p.)

RCHO+Ph-NH-NH2→RCH=N-NH-Ph +H2O

The excess phenyl hydrazine unreacted is back titrated against standard solution of HCI and the
% of aldehyde could be calculated
Notes:

*Hvdroxvl amine hydrochloride method:-

This is a universal method .

This method consider to be the best of all (WHY???)
1- It requires only little amount of oil (about 1ml),

2- The reaction time about 20 minutes

3- It is considered universal and valid for most aldehydes and ketones.
However, determination of individual component in the mixture is impossible but the total carbonyl
compounds will be determined.

*Phenyl hydrazine method: -
This method is used for estimation of aldehydes rather than ketones
CHO
1- Aldehydes

A- Aliphatic aldehydes 1- Citronellal

⚫ Occurrence: in Citronella and Eucalyptus citriodora oils. Citronellal
⚫ Isolation: by formation of crystalline bisulfite derivative and decomposed by alkali carbonate

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