Question

what is the process of synthesis soap ? why do we need to use sodium hydroxide? and what are the diagnostic peaks of soap that can be found in IR?

Answer 1

Soap is a salt of fatty acid. It can be prepared by saponification of triglycerides. Saponification will produce salt of fatty acid and glycerol. For this process NaOH is needed because triglycerides are esters, to get salt of fatty acid ester must be hydrolyzed. So ester hydrolysis can be done in presence of Base such as NaOH, then only we will get salt of fatty acid. If hydrolysis of triglycerides is done in presence of acid instead of base then we will get fatty acid instead of salt of fatty acid. So hydrolysis of triglycerides has to done in presence of NaOH.

IR spectral analysis  

1) Absorption peaks in the region 3000-2800 cm^-1 observed for C-H bonds in CH2 and R groups.

2) Absorption peaks in the region 1700-1500 cm^-1 observed for COONa group.