How is this happening?!

[livingdeadbeat]

Hi,

 

In a test in our a-level class we had to use gelatine because we didn't have proline. We used acid hydrolysis to break down the polymer, which i believe has glycine and proline in it in roughly equal measures.

 

Then we added ninhydrin, which produced a yellowish colour. Now i know why proline doesn't produce the purple colour, but what i don't get is how come this works? Because Glycine is a primary amino and its also present in gelatine, so surely when we performed acid hydrolysis the result would be equal (roughly) amounts of proline and glycine. How come the glycine didn't react as well and turn the solution purple?

 

Thanks for any help.

[Horza2002]

Don't really understand what your asking, but ninhydrin will react with an N-H bonds in your molecule (whether they are primary/secondary amines or amides).