SolutionsPreparation
1. Saponification
Which products are obtained when tristearin (the triester of glycerin with stearic acid, C17H35COOH) is heated with aqueous NaOH? And after acidification?
Glycerin (1,2,3-propanetriol) and three molecules of sodium stearate, C17H35COO− Na+, which is a soap. On acidification, the stearate is protonated and stearic acid is obtained.
2. Two routes, one more carbon
Phenylacetic acid can be obtained from benzyl bromide (C6H5CH2Br) by two laboratory methods. Which ones?
- Substitution with cyanide (C6H5CH2CN) and hydrolysis of the nitrile.
- Grignard reagent (C6H5CH2MgBr), reaction with CO2 and acidification.
Both methods add one carbon atom to the chain: that of the cyanide or that of CO2.