Classical Analysis: Determination of Codeine Phosphate in Tablets Flashcards
(20 cards)
functional groups present in codeine
- ether
- aromatic
- cyclic ether
- tertiary amine
- secondary alcohol
- alkene
Which functional group in codeine is basic and why?
the tertiary amine as it has a lone pair of electrons available to accept a proton
Why was the codeine soluble in aqueous sulfuric acid? (when rinsed with h2so4)
the codeine was protonated increasing its polarity and therefore its water solubility
-> Bases are protonated in acidic conditions when the pH is sufficiently low
An excess of ammonia was used to ensure that the filtrate became alkaline. What was the form of the codeine after addition of the ammonia?
no charged ions present in the structure, look at the lt
The next step in the assay was the extraction of the codeine into chloroform. The alkaline filtrate was extracted THREE times with 25 mL of chloroform, washing each chloroform extract with the same 10 mL of water.
Why was it necessary to make the filtrate alkaline with ammonia BEFORE extraction?
to ensure the codeine was unionised, decreasing its polarity and increasing its solubility in chloroform
This is a back titration; the number of moles of codeine is equivalent to
(cHCl ×VHCl) – (cNaOH × VNaOH).
BP requirements, which specify that the content of codeine phosphate hemihydrate tablets should be between
99.0% and 101.5%
(1) Accurately weigh 10 codeine phosphate tablets, crush to a fine powder and record the
average mass of a tablet.
(2) Accurately weigh (by difference) the powder into a small vial. Transfer the powder to a
beaker and dissolve as completely as possible in what
0.25 M H2SO4 (20 mL).
once we dissolve the codeine phosphate tablets in H2SO4, what do we do with the solution
(3) Filter the solution through a small plug of cotton wool directly into a separating funnel,
washing the cotton wool with a small amount of 0.25 M sulfuric acid.
what do we was the cotton wool with
sulfuric acid
(4) Make the filtrate alkaline - how?
with 5 M ammonia solution
(CAUTION: FUME CUPBOARD).
(5) Extract this alkaline solution - how?
with 25 mL of chloroform in a separating funnel, making sure to shake well.
what do we do with the chloroform layer?
Remove the chloroform (lower layer) to another separating funnel containing 10 mL of water. Mix well and remove the chloroform layer to a B24 alkaloid flask.
(6) Repeat Step (5) TWICE more. Use the same 10 mL of water each time for washing the chloroform. You should now have approximately 75 mL of chloroform extract in the B24 flask
(7) what do we then use a rotary evaporator to do
Evaporate the chloroform
(8) Dissolve the residue in
ethanol (5mL)
what do we do after we dissolve the residue in ethanol
add precisely 10 mL of 0.1000 M hydrochloric
acid and 10 mL of water and titrate the excess acid with 0.1000 M sodium hydroxide
using methyl red solution as indicator.
what do we use as an indicator
methyl red solution
h2so4 : ammonia ratio in a reaction
1:2
h2so4 + 2nh3 -> (nh4)2so4
codeine and HCl stoichometry
1:1 ratio
HCL and NaOH stoichiometry
1:1
