Question

Dehydration of glycerol gives:
A.Propane.
B.Propene.
C.Acrolein.
D.Benzene.

Answer 1

Hint: We know that when fats are heated strongly in the presence of a dehydrating agent such as potassium sulphate, the glycerol portion of the molecule dehydrates to form the unsaturated aldehyde; this is how we obtain acrolein from glycerol. This is a normal day to day phenomena taking place in our kitchens but we fail to notice it.

Complete answer:
Glycerol when heated alone or with dehydrating agents such as potassium hydrogen sulphate or phosphorous pentoxide or concentrated sulphuric, the elimination reaction takes place to give acrolein; glycerol (called glycerin) is a simple polyol compound. It is a colourless, odourless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in those lipids known as glycerides. Dehydration of glycerol gives acrolein.
Acrolein is mostly used to make acrylic acid. It is also used to control plant and algae growth in irrigation canals. Acrolein kills or controls microorganisms and bacteria in oil wells, liquid hydrocarbon fuels, cooling-water towers and water treatment ponds. In papermaking, acrolein is used to control slime. Acrolein test is used to detect the presence of glycerol or fat.
When glycerol is heated with sulphuric acid or \[KHS{{O}_{4}}\]it is followed by dehydration to give acrolein. Acrolein is a compound with bad odour. It is a detection test of glycerol.
\[\underset{Glycerol}{\mathop{\left( OH \right){{H}_{2}}C-CH\left( OH \right)-C{{H}_{2}}\left( OH \right)}}\,\xrightarrow[-2{{H}_{2}}O]{KHS{{O}_{4}}}\text{ }\underset{Acrolein}{\mathop{\left( OH \right)C-CH=C{{H}_{2}}}}\,\]

Therefore, the correct answer is Option C.

Additional information:
Glycerol is an essential sugar alcohol for many living things. For one, it is a component of lipids such as triglycerides and phospholipids along with fatty acids. Glycerol forms glycerides that can serve as an energy fuel. Triglycerides, for instance, is a major component of animal fats and vegetable oils.

Note:
Remember that glycerol is used in the food industry as a humectant. It is used as sweetening and a solvent for several beverages. It is also used in the pharmaceutical industry in treatment of wounds and burns. The glycerol dehydration is mainly carried out in gaseous phase in the presence of an acid catalyst such as protonated or metal-promoted zeolites, mixed metallic oxides, functionalized oxides.