Question

Using your roadmaps as a guide, show how to convert propane into propyl propanoate. You must use propane as the source of all carbon atoms in the target molecule. Show all reagents needed and all molecules synthesized along the way.

Short answer

Question: Outline the steps to convert propane into propyl propanoate. Answer: To convert propane to propyl propanoate, the following steps are required: 1. Convert propane to propanol using potassium permanganate (KMnO4) in acidic conditions. 2. Oxidize propanol to propionic acid using potassium dichromate (K2Cr2O7) in acidic conditions. 3. Convert propionic acid to propionyl chloride using thionyl chloride (SOCl2). 4. Finally, convert propionyl chloride to propyl propanoate via esterification with propanol.

Step-by-step solution

Compare propane and propyl propanoate

Begin by comparing the structure of propane and propyl propanoate. Propane is a simple hydrocarbon with the formula C3H8. Propyl propanoate is an ester which has the formula C6H12O2. We can observe that propyl propanoate has twice as many carbon atoms, introducing oxygen and an ester functional group.

Convert propane to intermediate compound (propanol)

First, we need to introduce an alcohol (OH) group to propane so that it can react further. This can be done by treating propane with a strong base like potassium permanganate (KMnO4) in acidic conditions, forming propanol. Our reaction is: C3H8 + KMnO4 + H2O → C3H7OH Here, propane is converted into propanol.

Convert propanol to propionic acid

We will now oxidize propanol to propionic acid. This can be done by treating propanol with an oxidizing agent like potassium dichromate (K2Cr2O7) in acidic conditions. The reaction can be represented as: C3H7OH + K2Cr2O7 + H2SO4 → C2H5COOH Here, propanol is oxidized to form propionic acid.

Convert propionic acid to propionyl chloride

Next, we need to convert propionic acid to propionyl chloride, which can react further to form propyl propanoate. This can be done by treating propionic acid with thionyl chloride (SOCl2). The reaction can be represented as: C2H5COOH + SOCl2 → C2H5COCl + SO2 + HCl Here, propionic acid is converted into propionyl chloride.

Convert propionyl chloride to propyl propanoate

Finally, we will convert propionyl chloride to propyl propanoate by treating it with propanol. This reaction is an esterification. The reaction can be represented as: C2H5COCl + C3H7OH → C2H5COOC3H7 + HCl Finally, propionyl chloride reacts with propanol to form propyl propanoate. In conclusion, to convert propane to propyl propanoate, the following steps are required: 1. Convert propane to propanol (C3H8 + KMnO4 + H2O → C3H7OH) 2. Convert propanol to propionic acid (C3H7OH + K2Cr2O7 + H2SO4 → C2H5COOH) 3. Convert propionic acid to propionyl chloride (C2H5COOH + SOCl2 → C2H5COCl + SO2 + HCl) 4. Convert propionyl chloride to propyl propanoate (C2H5COCl + C3H7OH → C2H5COOC3H7 + HCl)

Key concepts

Propane to Propyl Propanoate Conversion

Propyl propanoate is a fascinating compound that can be synthesized starting from a simple molecule like propane. This conversion involves several key reactions that demonstrate the versatility of organic synthesis.

Step-by-Step Conversion: The process starts with the conversion of propane into propanol. This is achieved through an oxidation reaction using potassium permanganate (KMnO4) as the oxidizing agent in an acidic medium which introduces the alcohol functional group. Next, propanol is further oxidized to propionic acid, typically with potassium dichromate (K2Cr2O7) in acidic conditions. To make the molecule more reactive towards esterification, propionic acid is then converted into propionyl chloride using thionyl chloride (SOCl2). This reactive intermediate is then treated with propanol to form the desired ester, propyl propanoate, through a nucleophilic acyl substitution, a common mechanism in producing esters.

Understanding this conversion requires an appreciation of multiple chemical transformation steps, which collectively illustrate the power of organic synthesis in constructing complex molecules from simpler ones.

Organic Reaction Mechanisms

The core of understanding any organic synthesis, including the conversion of propane to propyl propanoate, lies in grasping the underlying organic reaction mechanisms. Mechanisms provide a step-by-step description of how bonds are broken and formed to convert reactants into products.

For a student, understanding the basic mechanisms involved in this conversion, such as oxidation and nucleophilic substitution, is critical. These are not random processes; they follow specific electron movement governed by the properties of the involved compounds. For instance, in the oxidation of propanol to propionic acid, the electron-rich alcohol group is transformed into a carboxylic acid through the loss of electrons. Similarly, in the last step of the synthesis, the nucleophilic oxygen in propanol attacks the electrophilic carbon in propionyl chloride, leading to the formation of propyl propanoate. Each step follows its own unique mechanism, which collectively lead to the successful synthesis of the target molecule.

Esters and Esterification

Esters like propyl propanoate have distinct odors and are often found in fragrances and flavorings. The formation of esters from an alcohol and a carboxylic acid (or carboxylic acid derivative) is known as esterification. Specifically, the conversion of propionyl chloride to propyl propanoate is an example of esterification through the reaction of an acid chloride with an alcohol.

The reaction involves the nucleophilic attack of the alcohol's oxygen atom on the acid chloride's carbonyl carbon, leading to the release of hydrogen chloride (HCl) and the formation of the ester linkage. This particular reaction is preferred in the industry because it tends to proceed quickly and with fewer by-products when compared to direct esterification of a carboxylic acid and an alcohol, especially since acid chlorides like propionyl chloride are highly reactive towards nucleophiles like alcohols.

Oxidation Reactions

Oxidation reactions are chemical processes that involve the transfer of electrons from one substance to another. In the context of organic chemistry, oxidations result in the increase of oxygen or the decrease of hydrogen in a molecule.

In our conversion of propane to propyl propanoate, two crucial oxidation steps are observed. The first oxidation step involves the transformation of propane to propanol, where an oxygen atom is added, and the second involves the conversion of propanol to propionic acid, where the alcohol is converted to a carboxyl group. These steps often require strong oxidizing agents like potassium permanganate (KMnO4) or potassium dichromate (K2Cr2O7). These reactions show the fundamental role of oxidation in organic synthesis, from simple hydrocarbons to more complex functional groups, setting the stage for further chemical transformations.