Question

Using your roadmap as a guide, show how to convert propane into butyronitrile. You must use propane and sodium cyanide as the source of all of the carbon atoms in the butyronitrile product. Show all reagents and all molecules synthesized along the way.

Short answer

Question: Provide a step-by-step solution to convert propane into butyronitrile using sodium cyanide as the source of carbon atoms in the final product. Answer: To convert propane into butyronitrile, the following steps must be followed: 1. Formation of 1-propanol by reacting propane with borane (BH3) and hydrogen peroxide (H2O2) using hydroboration-oxidation reaction. 2. Conversion of 1-propanol to propanal using PCC (pyridinium chlorochromate) as an oxidizing agent. 3. Reaction of propanal with sodium cyanide (NaCN) in a Strecker synthesis reaction to obtain 4-hydroxybutanenitrile. 4. Dehydration of 4-hydroxybutanenitrile to butyronitrile using H2SO4 (sulfuric acid) as a dehydrating reagent.

Step-by-step solution

Formation of 1-propanol

First, we need to convert propane into 1-propanol. We will do this by using hydroboration-oxidation reaction, which uses borane (BH3) and hydrogen peroxide (H2O2) as reagents. The reaction will proceed as follows: C3H8 + BH3 → C3H9B → C3H8O For this step, the reagents are: 1. BH3 (borane) 2. H2O2 (hydrogen peroxide)

Conversion of 1-propanol to propanal

Once we have obtained 1-propanol, we need to convert it to propanal. This can be done through the use of PCC (pyridinium chlorochromate) as an oxidizing agent. The reaction will proceed according to the following equation: C3H8O + PCC → C3H6O For this step, the reagent is PCC (pyridinium chlorochromate).

Reaction of propanal with sodium cyanide (NaCN) to form 4-hydroxybutanenitrile

Now we can react the propanal obtained in step 2 with sodium cyanide (NaCN) in a Strecker synthesis reaction to obtain 4-hydroxybutanenitrile: C3H6O + NaCN → C4H7NO For this step, the reagent is sodium cyanide (NaCN).

Dehydration of 4-hydroxybutanenitrile to butyronitrile

Finally, to obtain the desired compound, butyronitrile, we must dehydrate the 4-hydroxybutanenitrile. This is achieved by reaction with a dehydrating reagent such as H2SO4 (sulfuric acid), which will remove a water molecule from the 4-hydroxybutanenitrile: C4H7NO → C4H5N + H2O For this step, the reagent is H2SO4 (sulfuric acid). In summary, we have converted propane to butyronitrile using sodium cyanide as the source of carbon atoms in the final product. The reagents used along the way were BH3, H2O2, PCC, NaCN, and H2SO4, and the intermediate molecules synthesized during the reactions were 1-propanol, propanal, and 4-hydroxybutanenitrile.

Key concepts

Hydroboration-Oxidation Reaction

The hydroboration-oxidation reaction is a two-step process that transforms alkenes into alcohols. Interestingly, this reaction can also be applied to alkanes like propane using a radical initiated mechanism, although this is less common and not part of the traditional hydroboration-oxidation reaction. The reaction consists of the addition of borane (\textbf{BH\(_3\)}), a boron-hydrogen compound, to an alkene or alkane to form a trialkylborane. This is followed by oxidation with hydrogen peroxide (\textbf{H\(_2\)O\(_2\)}) which replaces the boron atom with a hydroxyl group (\textbf{-OH}), thus forming the alcohol.

In the context of our problem, where propane (\textbf{C\(_3\)H\(_8\)}) is the starting molecule, the result is 1-propanol (\textbf{C\(_3\)H\(_8\)O}). It's important to note that this reaction is stereospecific, usually yielding anti-Markovnikov products, meaning the hydroxyl group will attach to the less substituted carbon. As such, hydroboration-oxidation is valuable in organic synthesis for its ability to produce alcohols with high regio- and stereoselectivity.

Oxidation of Alcohols

The oxidation of alcohols is a fundamental reaction in organic chemistry used to convert alcohols into aldehydes, ketones, or carboxylic acids depending on the conditions and the type of alcohol. In the second step of our propane conversion, 1-propanol (\textbf{C\(_3\)H\(_8\)O}), a primary alcohol, is oxidized to an aldehyde known as propanal (\textbf{C\(_3\)H\(_6\)O}). Primary alcohols like 1-propanol can be oxidized to aldehydes using mild reagents such as pyridinium chlorochromate (\textbf{PCC}).

The choice of oxidizing agent is crucial. Stronger agents like potassium permanganate (\textbf{KMnO\(_4\)}) could further oxidize the aldehyde to a carboxylic acid, which is not the desired reaction in this case. PCC is therefore ideal for this controlled oxidation where further oxidation is undesired. The detailed mechanism of PCC oxidation involves the formation of a chromate ester intermediate, which facilitates the removal of hydrogen atoms, resulting in the formation of the carbon-oxygen double bond characteristic of aldehydes.

Strecker Synthesis

The Strecker Synthesis is a classic method for producing \textalpha-amino nitriles from aldehydes or ketones, which can then be hydrolyzed to \textalpha-amino acids. The key reactants in a Strecker Synthesis include an aldehyde or ketone, ammonia or an amine, and a cyanide source, typically sodium cyanide (\textbf{NaCN}).

In our exercise, the aldehyde, propanal (\textbf{C\(_3\)H\(_6\)O}), is reacted with sodium cyanide to form 4-hydroxybutanenitrile (\textbf{C\(_4\)H\(_7\)NO}). The cyanide acts as a nucleophile, attacking the electrophilic carbon of the carbonyl group in the aldehyde, followed by a series of steps leading to the substitution of the carbonyl oxygen for a cyano group (\textbf{-CN}), forming the \textalpha-amino nitrile. The Strecker Synthesis is an important reaction in organic synthesis because it offers a straightforward approach to the synthesis of amino acids and their derivatives.

Organic Synthesis Reagents

In organic synthesis, reagents are chemical substances used to affect transformations in organic molecules. Each reagent plays a specific role, often targeting particular functional groups to bring about significant changes in the structure of organic compounds.

In the conversion of propane to butyronitrile, several reagents play critical roles:

• Borane (BH\(_3\)): Initiates hydroboration, adding boron across a carbon-carbon bond.
• Hydrogen peroxide (H\(_2\)O\(_2\)): Oxidizes the borane complex to form an alcohol.
• Pyridinium chlorochromate (PCC): A mild oxidant that converts primary alcohols to aldehydes without further oxidation to acids.
• Sodium cyanide (NaCN): Acts as a source of the cyano group in Strecker synthesis, allowing the formation of nitriles.
• Sulfuric acid (H\(_2\)SO\(_4\)): A strong acid and dehydrating agent used in the final step to convert 4-hydroxybutanenitrile to butyronitrile by removing water.

Choosing the appropriate reagent is essential for the success of a reaction in organic synthesis. Knowledge of the reactivity, compatibility, and outcome of using each reagent allows chemists to carefully plan and execute synthetic routes to obtain desired products efficiently.