Which buffer system generally produces the fastest rate of formation of semicarb

Question

Which buffer system generally produces the fastest rate of formation of semicarbazones of aldehydes and ketones?

A. CH3CO2H/CH3CO2-

B. H2PO4-/HPO42-

C. H2CO3/HCO3-

This may help, that I read out of my book. But I am still confused as to which one. Phosphate system, the range is pH 6.1-6.2. By comparison, a carbonate/bicarbonate buffer system maintains a pH of 7.1-7.2. The maximum rates of the reactions of most aldehydes and ketones with semicarbazide occur in the pH range of 4.5-5.0. For the purpose of making derivatives of carbonyl compounds, semicarbazide is best used in an acetate buffer solution, which maintains a pH in the maximum rate range of 4.5-5.0.

I can't decide whether its the phosphate system, or acetate buffer.

Thanks all

Explanation / Answer

Answer:

The subtrate PH should be in range of the Buffer PH range. Here the semicarbazones of aldehydes and ketones PH is in the range of Acetate buffer.

Hence the Acetate buffer is the suitable buffer.

Note: Generally the Aldehydes and the ketones are weak acids, For the weak acids Acidic buffers are suitable.

Phosphate buffer also acidic buffer but the PH not matches with the Aldehyde and ketone with semicarbazide.

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