Learning Objectives Compare the boiling points of esters with alcohols of similar molar mass. Compare the solubilities of esters in water with the solubilities of comparable alkanes and alcohols in water. Ester molecules are polar but have no hydrogen atom attached directly to an oxygen atom. They are therefore incapable of engaging in intermolecular hydrogen bonding with one another and thus have considerably lower boiling points than their isomeric carboxylic acids counterparts. Because ester molecules can engage in hydrogen bonding with water molecules, however, esters of low molar mass are somewhat soluble in water. Borderline solubility occurs in those molecules that have three to five carbon atoms. Table \(\PageIndex{1}\) lists the physical properties of some common esters. 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. Condensed Structural Formula Name Molar Mass Melting Point (°C) Boiling Point (°C) Aroma NaN methyl methanoate 60 −99 32 NaN NaN ethyl methanoate 74 −80 54 rum NaN methyl ethanoate 74 −98 57 NaN NaN ethyl ethanoate 88 −84 77 NaN NaN methyl butanoate 102 −85 102 apple NaN ethyl butanoate 116 −101 121 pineapple NaN pentyl ethanoate 130 −71 148 pear CH3COOCH2CH2CH(CH3)2 isopentyl ethanoate 130 −79 142 banana NaN phenyl ethanoate 150 −51 215 jasmine CH3CH2CH2COO(CH2)4CH3 pentyl butanoate 158 −73 185 apricot CH3COO(CH2)7CH3 octyl ethanoate 172 −39 210 orange Summary Esters have polar bonds but do not engage in hydrogen bonding and are therefore intermediate in boiling points between the nonpolar alkanes and the alcohols, which engage in hydrogen bonding. Ester molecules can engage in hydrogen bonding with water, so esters of low molar mass are therefore somewhat soluble in water. Concept Review Exercises Which compound has the higher boiling point— CH 3 -CH 2 -CH 2 -CH 2 -OH or ? Explain. Answers CH 3 -CH 2 -CH 2 -CH 2 -OH because there is intermolecular hydrogen bonding (There is no intermolecular hydrogen bonding in .) Exercises Which compound has the higher boiling point— CH 3 -CH 2 -CH 2 -COOH or ? Explain. Which compound is more soluble in water—methyl ethanoate or octyl ethanoate? Explain. Answer CH 3 -CH 2 -CH 2 -COOH because there is intermolecular hydrogen bonding and forms a dimer (There is no intermolecular hydrogen bonding between ethers .)