Propyl hexanoate (C₉H₁₈O₂), also known as propyl caproate, is an

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides a ...

formed by the reaction of

propanol There are two isomers of propanol. *1-Propanol, ''n''-propanol, or propan-1-ol : CH3CH2CH2OH, the most common meaning *2-Propanol, Isopropyl alcohol Isopropyl alcohol (IUPAC name propan-2-ol and also called isopropanol or 2-propanol) is a c ...

with

hexanoic acid Caproic acid, also known as hexanoic acid, is the carboxylic acid derived from hexane with the chemical formula . It is a colorless oily liquid with an odor that is fatty, cheesy, waxy, and like that of goats or other barnyard animals. It is ...

. Although it is a completely different ester, propyl hexanoate shares the same chemical formula with methyl octanoate, ethyl heptanoate, butyl pentanoate, etc. because they all have the same total carbon chain length. The scent of this ester can be described as that of

blackberries The blackberry is an edible fruit produced by many species in the genus ''Rubus'' in the family (biology), family Rosaceae, hybrids among these species within the subgenus ''Rubus'', and hybrids between the subgenera ''Rubus'' and ''Idaeobatus' ...

pineapple The pineapple (''Ananas comosus'') is a tropical plant with an edible fruit; it is the most economically significant plant in the family Bromeliaceae. The pineapple is indigenous to South America, where it has been cultivated for many centuri ...

, cheese or

wine Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...

Properties

Due to the length of the carbon chain in this molecule, there are only minor

van der Waals forces In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and th ...

acting upon it, which is why propyl hexanoate appears as a liquid and not a solid.

Dipole-dipole forces In physics, a dipole () is an electromagnetic phenomenon which occurs in two ways: *An electric dipole deals with the separation of the positive and negative electric charges found in any electromagnetic system. A simple example of this system i ...

are present because of the polar covalent bonds between carbon and oxygen, while

hydrogen bonding In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...

only occurs with other molecules that can hydrogen bond.

Preparation

Propyl hexanoate is formed by the

condensation reaction In organic chemistry, a condensation reaction is a type of chemical reaction in which two molecules are combined to form a single molecule, usually with the loss of a small molecule such as water. If water is lost, the reaction is also known as a ...

(

esterification In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...

) of propanol and hexanoic acid. The hydroxyl group from the propanol reacts with the hydroxyl group from the hexanoic acid to produce water and leave an oxygen that the parent acid and alcohol chains bond to, creating the ester. For this reaction to occur, it requires an acid

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

, such as concentrated sulfuric acid, and heat. The esterification process can also be reversed (

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolys ...

) to get propanol and hexanoic acid back from propyl hexanoate. This reaction occurs between the ester and water in the presence of a dilute acid catalyst and heat.

Uses

Propyl hexanoate, being an ester, is generally used for replicating the scents or flavors of fruit such as blackberry and pineapple, then is added to things such as food or perfume. It also has the use as a solvent for polar

organic compounds In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The s ...

.Hughes, A. (2003)
Uses of Esters
''The Chemistry of Esters''

References

Caproate esters