Chapter 17 Carboxylic Acids and Their Derivatives

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Chapter 17Carboxylic Acids and Their Derivatives
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• In this chapter we continue the study of
  compounds with the structure
• In the last chapter we studied aldehydes and
  ketones. In their case the -X group (either H or
  R) was a nonpolar group. In this chapter we
  cover the case when X is a polar group, namely
  OH, -OR or NH2 (and its variations).

• An acyl group is what remains when we remove the
  X group in the structure above.

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Properties of Acids

• Hydrogen of the carboxylic group (-COOH) is
  acidic.
• Able to form strong H-bonds (smallest carboxylic
  acid has B.P. of 101 oC).

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• Carboxylic Acids up to 9 carbons are liquids
  with strong, sharp odors. Larger size are waxy,
  odorless solids.
• Water-soluble up to 4 carbons. Solubility in
  water then decreases with the size of the R
  group.

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Naming of Carboxylic Questions

• IUPAC naming Replace the e of the alkane with
  the same number of carbons with oic acid. If
  numbering is required, then assign the C in the
  COOH group as carbon 1.

6 5 4 3 2 1
Propanoic Acid
3-ethyl-5-methylhexanoic Acid
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• Many carboxylic acids have common names as shown
  in the extract from table 17.1 from your book.
• Other than the first and last two, you do not
  need to memorize the names. If I use a common
  name I will tell you the number of carbons in the
  structure.

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• When using common names the carbons adjacent to
  the COOH group are named a, b, g, d, and so on
• Substituents are named as usual but using the
  greek letters instead of carbon numbers.

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d g b a
b a
a-aminopropionic acid (an a-aminoacid)
g-hydroxyvaleric acid
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• There are many dicarboxylic acids of biological
  importance. They are named by adding dioic acid
  to the name of the alkane with the same number of
  carbons. Notice that the e ending in the alkane
  name is kept.

ethanedioic acid (Oxalic acid)
butanedioic acid (Succinic acid)
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Some Common Carboxylic Acids

• Carboxylic acids are very common in plants and
  animals. Whole systems of enzymes and proteins
  are designed for their processing in biological
  systems.

Formic acid (from Latin formica ant) chemical
that produces the sting in ant bites.
Acetic acid (from Latin acetum vinegar) found
in vinegar and wine that has been exposed to air.
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Butyric acid (from Latin butyrum butter) gives
rancid butter its characteristic smell.
Lactic acid (from Latin lactim milk) gives
sour milk its characteristic taste.
Stearic acid one of the main components of
animal fat (saturated fat).
Citric acid gives its characteristic flavor to
lemons and other citric fruits. Used widely as
preservative (antioxidant) and as an additive for
tartness.
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Acidity of Carboxylic Acids

• Carboxylic acids are weak acids. In aqueous
  solutions they establish equilibria with
  carboxylate ions (RCOO-)
• Caboxylate ions are named by changing the ic
  ending in the name of the acid by ate. For
  example, the carboxylate ion from propanoic acid
  is propanoate.

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• At physiological pH (7.4) carboxylic acids exist
  mainly in their carboxylate form.
• As other acids, carboxylic acids will react with
  bases to produce salts
• Salts of acids are named by writing the cation
  and then the anion name the salt above is sodium
  acetate.
• As in the case of amines, salts of carboxylic
  acids are much more soluble than the acids
  themselves.

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A parenthesis a-hydroxy acids

• In the last few years a-hydroxy acids have
  become very popular because of their properties.
  They are used widely for treatment of diverse
  skin conditions ranging from acne to
  rejuvenating peelings.
• You can see many over-the-counter creams
  containing alpha-hydroxy as their main
  ingredient.
• a-hydroxy acids work by essentially burning an
  upper layer of skin. The dead cells are then
  replaced by new ones producing a fresh look.

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Glycolic acid In low concentrations is used in
mini-peelings. Higher concentrations used for
spot removal.
Lactic acid Present in many over-the-counter
creams for the removal of wrinkles.
Salicylic acid Seen the infomercial late at
night for magic acne creams? This is the main
ingredient in those preparations.