[savoy8]

When starch is hydrolyzed with an acid (HCl) it forms monomers and disaccharides.  The hydrolysis is incomplete(~50%).  I'm trying to determine why this happens.  I know that starch is compose of amylose and amylopectin.  The alpha 1,4-glucosidic linkage is the most common with the alpha-1,6-glucosidic linkage involving branching.

Anyone have any suggestions why this happens?

[AWK]

Just partial hydrolysis happened

[savoy8]

Awk,
thank you for your reply.  What dictates partial hydrolysis vs. complete hydrolysis?  The acid is a hot diluted HCl(a strong acid).  The bonds that are broken are all the same.  Why do only half of the alpha 1,4-glucosidic linkages hydrolyze?  Is there an equilibrium that is met?  If the components are allowed to react, would they go through complete hydrolysis?

thanks

[mahesh]

You see, starch or cellulose like materials are sugars made from monomers like glucose, fructose etc. The acid hydrolysis will result in formation of monomers. The glucose monomer, further, will undergo the ring opening in the presence of the mineral acid. This will result in many competitive hydrolysis reactions in your reaction vessel, and the rates of these reactions are governed by the structure of the individual molecules (monomers, dimers, oligomers, etc) that undergo hydrolysis! This might be the reason for the hydrolysis of starch being partial.
I might be wrong, somebody correct me if it is so!!