✔ 最佳答案
NaBH₄ can reduce ketone groups (R-CO-R) and aldehyde groups, but cannot reduce carboxyl groups (-COOH), ester groups (-COOR) and amide groups (-CONH- or -CONH₂).
The structures of aspirin and paracetamol are :
https://c2.staticflickr.com/8/7234/27009408834_c71bc4ce61_o.png
In aspirin molecule, there is 1 carboxyl group and 1 ester group, but no ketone group or aldehyde group. Therefore, NaBH₄ would not reduce aspirin.
NaBH₄ is also a base. Although aspirin contains -COOH group, the solubility of aspirin is low (3 g/L). Therefore, when NaBH₄ is mixed with aqueous aspirin, NaBH₄ would rather react with water than aspirin.
In paracetamol, there is 1 amide group, but no ketone group or aldehyde group. Therefore, NaBH₄ would not reduce paracetamol.
The acidity of the phenol group in paracetamol is too low, and thus no neutralization occurs between NaBH₄ and paracetamol.