Textbook Question
Show how you might use SN2 reactions to convert 1-chlorobutane into the following compounds.
b. 1-fluorobutane
7. Substitution Reactions
Substitution Comparison
3:36 minutesProblem 81
Textbook Question
Alkylbenzyldimethyl ammonium chloride is a leave-on skin antiseptic used to treat such things as cuts and cold sores. It is also the antiseptic in many hand sanitizers. It is actually a mixture of compounds that differ in the number of carbons (any even number between 8 and 18) in the alkyl group. Show three different sets of reagents (each set composed of an alkyl chloride and an amine) that can be used to synthesize the alkylbenzyldimethyl ammonium chloride shown here.
Verified step by step guidance1
Step 1: Identify the structure of the target compound, alkylbenzyldimethyl ammonium chloride. It consists of a benzyl group attached to a nitrogen atom, which is further bonded to two methyl groups and an alkyl chain (with an even number of carbons between 8 and 18). The nitrogen carries a positive charge, and the chloride ion is the counterion.
Step 2: Understand the synthesis mechanism. The target compound can be synthesized via a nucleophilic substitution reaction (SN2) where an alkyl chloride reacts with a tertiary amine. The tertiary amine must contain a benzyl group and two methyl groups to form the desired quaternary ammonium salt.
Step 3: Select the alkyl chloride. Choose three different alkyl chlorides with even numbers of carbons in the alkyl chain (e.g., octyl chloride, decyl chloride, and dodecyl chloride). These will provide the varying alkyl groups in the final product.
Step 4: Select the amine. Use benzyl dimethyl amine as the amine reagent in all three cases. This amine contains the benzyl group and two methyl groups required for the quaternary ammonium structure.
Step 5: Combine the reagents. For each set of reagents, react the chosen alkyl chloride with benzyl dimethyl amine under appropriate conditions (e.g., heating in a polar solvent) to form the desired alkylbenzyldimethyl ammonium chloride. Ensure the reaction proceeds via SN2 to achieve the quaternary ammonium salt.
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3mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Quaternary Ammonium Compounds
Quaternary ammonium compounds are a class of chemicals that consist of a positively charged nitrogen atom bonded to four organic groups. In the context of the question, alkylbenzyldimethyl ammonium chloride is a quaternary ammonium compound where the nitrogen is bonded to two methyl groups, a benzyl group, and an alkyl group. These compounds are known for their antimicrobial properties and are commonly used in antiseptics and disinfectants.
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Alkyl Halides
Alkyl halides are organic compounds containing a carbon chain bonded to a halogen atom (such as chlorine, bromine, or iodine). In the synthesis of alkylbenzyldimethyl ammonium chloride, alkyl chlorides serve as the source of the alkyl group. The reactivity of alkyl halides allows them to participate in nucleophilic substitution reactions, which are essential for forming the desired quaternary ammonium compound.
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Nucleophilic Substitution Reactions
Nucleophilic substitution reactions involve the replacement of a leaving group in a molecule by a nucleophile. In this case, the amine acts as the nucleophile that attacks the alkyl halide, leading to the formation of an intermediate that can further react to yield the quaternary ammonium compound. Understanding the mechanisms of these reactions, such as SN1 and SN2 pathways, is crucial for predicting the outcomes of the synthesis described in the question.
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