15.7 Physical Properties of Esters

Note

Esters are common solvents. Ethyl acetate is used to extract organic solutes from aqueous solutions—for example, to remove caffeine from coffee. It also is used to remove nail polish and paint. Cellulose nitrate is dissolved in ethyl acetate and butyl acetate to form lacquers. The solvent evaporates as the lacquer “dries,” leaving a thin film on the surface. High boiling esters are used as softeners (plasticizers) for brittle plastics.

Table 15.4 Physical Properties of Some Esters
Condensed Structural Formula Name Molar Mass Melting Point (°C) Boiling Point (°C) Aroma
HCOOCH3 methyl formate 60 −99 32
HCOOCH2CH3 ethyl formate 74 −80 54 rum
CH3COOCH3 methyl acetate 74 −98 57
CH3COOCH2CH3 ethyl acetate 88 −84 77
CH3CH2CH2COOCH3 methyl butyrate 102 −85 102 apple
CH3CH2CH2COOCH2CH3 ethyl butyrate 116 −101 121 pineapple
CH3COO(CH2)4CH3 pentyl acetate 130 −71 148 pear
CH3COOCH2CH2CH(CH3)2 isopentyl acetate 130 −79 142 banana
CH3COOCH2C6H5 benzyl acetate 150 −51 215 jasmine
CH3CH2CH2COO(CH2)4CH3 pentyl butyrate 158 −73 185 apricot
CH3COO(CH2)7CH3 octyl acetate 172 −39 210 orange

Concept Review Exercises

  1. Which compound has the higher boiling point: CH3CH2CH2CH2OH or CH3COOCH3? Explain.

  2. Which compound is more soluble in water—methyl propanoate or butyric acid? Explain.

Key Takeaways

  • Esters have polar bonds but do not engage in intermolecular hydrogen bonding and are therefore intermediate in boiling points between the nonpolar alkanes and the alcohols, which engage in intermolecular hydrogen bonding.
  • Ester molecules can engage in hydrogen bonding with water, so esters of low molar mass (3-5 C atoms) are somewhat soluble in water.

Exercises

  1. Which compound has the higher boiling point: CH3CH2CH2COOH or CH3CH2CH2COOCH3? Explain.
  2. Which compound is more soluble in water—methyl acetate or octyl acetate? Explain.