Skip to main content
Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
All textbooksBruice 8th EditionCh. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblem 81
Chapter 10, Problem 81

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 guidance
1
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.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
3m
Was this helpful?

Key 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.
Recommended video:
3:26
Quaternary Protein Structure Concept 1

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.
Recommended video:
Guided course
01:52
How to name alkyl halides

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.
Recommended video:
Guided course
01:47
Nucleophiles and Electrophiles can react in Substitution Reactions.
Related Practice
Textbook Question

Fill in the squares in the following chemical equations:

a.

b.

1
views
Textbook Question

Draw the substitution products for each of the following reactions; if the products can exist as stereoisomers, show what stereoisomers are obtained:

e. 1-bromo-2-butene + CH3O−

f. 1-bromo-2-butene + CH3OH

4
views
Textbook Question

Draw the substitution products for each of the following reactions; if the products can exist as stereoisomers, show what stereoisomers are obtained:

c. benzyl chloride + CH3CH2OH

d. allyl chloride + CH3OH

1
views
Textbook Question

Fill in the squares in the following chemical equations:

c.

d.

1
views
Textbook Question

Would you expect methoxide ion to be a better nucleophile if it is dissolved in CH3OH or if it is dissolved in DMSO? Why?

1
views
Textbook Question

Draw the major product obtained when each of the following alkyl halides undergoes an E2 reaction:

a.

1
views