Acetylsalicylic acid in ferric chloride test

[Fairway]

Homework Statement

In the reaction between salicylic acid and acetic anhydride, if you use a water bath at 90°C instead of 50°C. The final product (acetylsalicylic acid) was tested for the presence of phenols with ferric chloride. This test was negative (no color observed); however, the melting point of the dry product was 122-125°C.

Homework Equations

What are the reasons for these results?

The Attempt at a Solution

I'm not sure for the analytical reasons, but here what I thought. The product came out purity because it has no color on the test with ferric chloride. But the meltng point was lower than the tabulated melting point which is 135-136°C for pure Aspirin. It could be in result of high temperature of water bath, so the high temperature passed the right eqilibrium. Am I right? Please, if anyone knows the better answer, could you explain to me? I really appreciate it. Thank you in advance!

 

[chemisttree]

You have no 'phenol' (salicylate in this case) in the final product as evidenced by the negative ferric chloride test. The higher temperature of the reaction might affect the rate of reaction but does it affect the equilibrium distribution?

You also correctly identify the cause of the lower MP being related to purity and therefore your product isn't pure. How might cooking the reagents at a higher temperature affect purity? What impurity is likely to be present?

 

[Fairway]

Chemisttree, Thank you so much!
I agree with you it is impure due to the lower melting point. I was confuse with equlibrium. It was so helpful!