Question

Lidocaine (xylocaine) is used as a local anesthetic and cardiac depressant. CCCN(C)CC(=O)Nc1c(C)cccc1C Lidocaine (xylocaine) a. Draw the condensed structural formula of the amine salt formed when lidocaine reacts with HCl. b. Why is the amine salt of lidocaine used rather than the amine?

Short answer

a. (CH3)2N^+CC(=O)Nc1c(C)cccc1C Cl^- b. Amine salts are more water-soluble and stable.

Step-by-step solution

Identify the Functional Groups

Examine the chemical structure of lidocaine. Identify the amine group (N(CH3)2) and the rest of the molecular skeleton.

Understand the Reaction

Determine what happens when an amine (lidocaine) reacts with HCl. The reaction involves the amine group accepting a proton (H+) from HCl to form an amine salt.

Draw the Condensed Structural Formula of the Amine Salt

Draw the structure of lidocaine, but where the nitrogen atom is, show it with an additional proton and a positive charge (NH(CH3)2^+). Also, show the chloride ion (Cl^-) associated with the positive amine to complete the formation of the amine salt.

Explain the Use of Amine Salt over Free Amine

Explain that the amine salt form is more soluble in water and can be easily administered in aqueous solutions. It also tends to be more stable and less volatile than the free amine.

Key concepts

Amine Salt Formation

When different compounds react, changes in chemical structure can create useful new forms. One key concept in this exercise is the formation of an amine salt. Lidocaine contains an amine group, which includes nitrogen atoms that are able to accept protons. When lidocaine reacts with hydrochloric acid (HCl), the amine group accepts an additional proton (H+) from HCl. This reaction forms an amine salt.
The nitrogen in the amine group ends up with a positive charge due to the extra proton, making it a positively charged ion (NH(CH3)2^+). Meanwhile, the chloride ion (Cl^-) from HCl pairs with this newly formed positively charged amine, resulting in the complete amine salt, NH(CH3)2^+ Cl^-.
Amine salts tend to be more stable and more soluble in water compared to their parent amines. This makes them practical and effective for various applications in medicine and other fields.

Local Anesthetic

Lidocaine's primary use is as a local anesthetic. It helps to prevent pain by blocking the nerve signals in a specific area of the body. Here's how it works

• Prevents pain signals: Lidocaine interferes with the sodium channels in nerve cells, blocking the transmission of pain signals.
• Fast-acting: Lidocaine works quickly, providing relief soon after application.
• Temporary: Its effects are reversible and usually wear off after a few hours.

Besides its common use in minor surgical procedures and dental work, lidocaine can also function as a cardiac depressant. It's useful in treating certain heart conditions by slowing down or stabilizing the heart rate.

HCl Reaction with Amine

Understanding the chemical change when HCl reacts with an amine group is fundamental here. When hydrochloric acid (HCl) comes in contact with lidocaine's amine group, a proton transfer occurs. The nitrogen in the amine group, which has lone pairs of electrons, accepts a proton (H+).
This acceptance changes the nature of the amine group. The nitrogen, once neutral, now has an extra proton and acquires a positive charge, converting it to NH(CH3)2^+. The chloride ion (Cl^-) from HCl then associates with this positively charged amine to balance out the charge, forming the amine salt NH(CH3)2^+ Cl^-.

Condensed Structural Formula

Drawing condensed structural formulas is a way to simplify and clearly represent complex molecules. For lidocaine, its condensed structural formula highlights its chemical composition and arrangement of atoms in a streamlined way. The formula for lidocaine is:
N(CH3)2-C-C(=O)N-C6H4-CH3. Here's a breakdown:

• N(CH3)2: The amine group contains a nitrogen atom bonded to two methyl groups (CH3).
• C-C(=O)N: A carbon chain where one carbon is double-bonded to an oxygen (carbonyl group) and single-bonded to a nitrogen atom.
• C6H4: A benzene ring, indicating six carbon atoms forming a ring with alternating double bonds.
• CH3: A methyl group attached to the benzene ring, showing the structure's details compactly.

By drawing such formulas, chemists provide a quick yet detailed way to visualize and understand molecular structures.