carboxylic acids

CARBOXYLIC ACIDS

by Lily Haines and Nikole Watson

INTRO

DU

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Aldehydes and ketones with carboxylic acids are widespread in plants and animal kingdom. They play a significant role in biochemical processes of life. They add smell and flavour to nature, for example, the very pleasant fragrances of vanillin and cinnamaldehyde.

Introduction

INTRODUCTION Carboxylic acids are found in many

common household items: vinegar and salad dressing, citrus fruits, rhubarb, yogurt.

The feeling that you get in your legs after running for a long time is caused by the build up of the carboxylic acid, “lactic acid”

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GENERAL STRUCTURE Carboxylic acids contain a -COOH group

The “-COOH” attachment is also known as the carboxyl group.

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NAMING SCHEME The name counts the total number of

carbon atoms in the longest chain - including the one in the -COOH group.

If you have other groups attached to the parent chain, the carbon in the –COOH group is always counted as number 1 on the chain.

They are named by adding –oic acid onto the end of the carbon skeleton.

The substituents are named as in other aliphatic compounds.

Example 1:  Write the structural formula for 3-methylbutanoic acid.

This is a four carbon acid with no carbon-carbon double bonds. There is a methyl group on the third carbon (counting the -COOH carbon as number 1).

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Example 2:  Write the structural formula for 2-hydroxypropanoic acid (or lactic acid).

The hydroxy part of the name shows the presence of an -OH group. Normally, you would show that by the ending ol, but this time you can't because you've already got another ending. You are forced into this alternative way of describing it.

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Example 3:  Write the structural formula for 2-chlorobut-3-enoic acid.

This time, not only is there a chlorine attached to the chain, but the chain also contains a carbon-carbon double bond (en) starting on the number 3 carbon (counting the -COOH carbon as number 1).

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The general formula of a carboxylic acid is R-COOH, where R is the rest of the chain.

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SALTS OF CARBOXYLIC ACIDS

When the carboxylic acids form salts, the hydrogen in the -COOH group is replaced by a metal.

There is an ionic bond between the metal and the carboxylic group.

In the formula, the sodium is at the end, but appears first in the name.

Example:  Write the structural formula for sodium propanoate.

This is the sodium salt of propanoic acid - so start from that. Propanoic acid is a three carbon acid with no carbon-carbon double bonds.

In a shortened version, sodium propanoate would be written CH3CH2COONa or, if you wanted to emphasise the ionic nature, as CH3CH2COO- Na+.

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REACTION PROPERTIES Smaller carboxylic acids (1-5 carbons) are

polar or soluble with water. Carboxylic acids with higher numbers of carbons are less soluble due to increasing hydrophobic nature of the alkyl chain.

Higher boiling points than water (larger surface area)

Weak acids

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IN SOLUTION IN WATER, A HYDROGEN ION IS TRANSFERRED FROM THE -COOH GROUP TO A WATER MOLECULE. FOR EXAMPLE, WITH ETHANOIC ACID, YOU GET AN ETHANOATE ION FORMED TOGETHER WITH A HYDROXONIUM ION, H3O+.

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WORK CITED PAGE http://www.chemguide.co.uk/organicprops/aci

ds/background.html www.chatt.hdsb.ca/~smallbonel/.../

Carboxylic%20acids%20note.doc?... http://en.wikipedia.org/wiki/Carboxylic_acid http://

www.cliffsnotes.com/study_guide/Reactions-of-Carboxylic-Acids.topicArticleId-23297,articleId-23285.html

Corey, Paul F., «Carboxylic Acids and their Derivatives.», General Chemistry. New York: MacMillan Publishing Company, 1989.

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