Determination of Water Content in Benzoylacetic acid ethyl ester Using Karl Fischer Titration

Product Group

Esters of carboxylic acids, Ketones

General Information concerning the product group

Esters of carboxylic acids

Esters of carboxylic acid can be analysed analogously to the hydrocarbons according to standard Karl Fischer methods. Long-chain compounds require the addition of solubilisers, e.g. long-chain alcohols or chloroform. Unsaturated compounds can usually be titrated in the same way. Recommended methods are both the volumetric titration with one or two component reagents, as well as the coulometric analysis. The latter is predominantly applied for low water concentrations (< 0.1 %).

Ketones

During water determination after Karl Fischer (KF) aldehydes and ketones cause side reactions with the normally utilised methanol. Both side reactions, i.e. the formation of acetals and ketals, as well as bisulphite addition, can often be recognised by dragging end points and lead to wrong results. During acetal or ketal formation water is released which simulates water contents that are too high. Bisulphite addition, however, consumes water, leading to results that are too low. The extent of the interferences depends on the reactivity of the substances as well as the reactivity of the utilised KF solutions. Through utilisation of specific KF reagents for aldehydes and ketones it is possible to largely suppress the side reactions. The coulometric method is not recommended.

Special Information concerning the sample and the methods

Aromatic ketones are less reactive than aliphatic ones. In the case of benzoylacetic acid ethyl ester the influence of disturbing side reactions is therefore relatively less characteristic. The KF titration is carried out with methanol-free reagents, whereby two alternatives are at hand: CombiTitrant 5 Keto + CombiSolvent Keto or CombiTitrant 2 + CombiSolvent.

Titration one component system

Reagents:

Titrant
188006 Aquastar™ - CombiTitrant 5 Keto - One component reagent for volumetric Karl Fischer titration of aldehydes & ketones, 1 mL = approx. 5 mg water
or
188002 Aquastar™ - CombiTitrant 2 - One component reagent for volumetric Karl Fischer titration, 1 mL = approx. 2 mg water

Solvent
30 mL 188007 Aquastar™ - CombiSolvent Keto - Solvent for volumetric Karl Fischer titration with one component reagents for aldehydes & ketones
or
30 mL 188008 Aquastar™ - CombiSolvent - Methanol-free solvent for volumetric Karl Fischer titration with one component reagents

Titration Parameters:
Titration settings for methanol-free solvents:
I(pol) = 20 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
10 mL

Procedure:
The titration medium is first placed into the cell and titrated dry by means of the titrant. Then the sample is added with a syringe (exact sample weight determination by weighing of syringe before and after injection) or volumetric pipette and the titration is started.

Materials

     
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