Examples of carboxylic acid in the following topics:
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- Carboxylic acids are a class of molecules which are characterized by the presence of one carboxyl group.
- As proton donors, carboxylic acids are characterized as Brønsted-Lowry acids.
- Salts and esters of carboxylic acids are called carboxylates.
- Generally, in IUPAC nomenclature, carboxylic acids have an "-oic acid" suffix, although "-ic acid" is the suffix most commonly used.
- Upon exposure to a base, the carboxylic acid is deprotonated and forms a carboxylate salt.
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- Carboxylic acids are widespread in nature, often combined with other functional groups.
- Simple alkyl carboxylic acids, composed of four to ten carbon atoms, are liquids or low melting solids having very unpleasant odors.
- As shown in the following table, these long-chain carboxylic acids are usually referred to by their common names, which in most cases reflect their sources.
- Interestingly, the molecules of most natural fatty acids have an even number of carbon atoms.
- The following formulas are examples of other naturally occurring carboxylic acids.
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- The carbon atom of a carboxyl group has a high oxidation state.
- Two other useful procedures for preparing carboxylic acids involve hydrolysis of nitriles and carboxylation of organometallic intermediates.
- The hydrolysis may be either acid or base-catalyzed, but the latter give a carboxylate salt as the initial product.
- The initial product is a salt of the carboxylic acid, which must then be released by treatment with strong aqueous acid.
- An existing carboxylic acid may be elongated by one methylene group, using a homologation procedure called the Arndt-Eistert reaction.
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- The carboxyl functional group that characterizes the carboxylic acids is unusual in that it is composed of two functional groups described earlier in this text.
- As with aldehydes, the carboxyl group must be located at the end of a carbon chain.
- The characteristic IUPAC suffix for a carboxyl group is "oic acid", and care must be taken not to confuse this systematic nomenclature with the similar common system.
- Substituted carboxylic acids are named either by the IUPAC system or by common names.
- Simple dicarboxylic acids having the general formula HO2C–(CH2)n–CO2H (where n = 0 to 5) are known by the common names: Oxalic (n=0), Malonic (n=1), Succinic (n=2), Glutaric (n=3), Adipic (n=4) and Pimelic (n=5) Acids.
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- In this section similar reactions of carboxylic acid derivatives will be examined.
- Acid-catalyzed alpha-chlorination and bromination reactions proceed more slowly with carboxylic acids, esters and nitriles than with ketones.
- This may reflect the smaller equilibrium enol concentrations found in these carboxylic acid derivatives.
- This difference may be used to facilitate the alpha-halogenation of carboxylic acids.
- To see a mechanism for the acyl halide-carboxylic acid exchange, view the second diagram below.
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- The table at the beginning of this page gave the melting and boiling points for a homologous group of carboxylic acids having from one to ten carbon atoms.
- In the table of fatty acids we see that the presence of a cis-double bond significantly lowers the melting point of a compound.
- Thus, palmitoleic acid melts over 60º lower than palmitic acid, and similar decreases occur for the C18 and C20 compounds.
- Carboxylic acids have exceptionally high boiling points, due in large part to dimeric associations involving two hydrogen bonds.
- A structural formula for the dimer of acetic acid is shown in the first diagram below.
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- Carboxylic acids are an important subclass of organic oxoacids, characterized by the presence of at least one carboxyl group.
- Carboxylic acids are the most common type of organic acid.
- Acids with two or more carboxyl groups are called dicarboxylic, tricarboxylic, etc.
- Salts and esters of carboxylic acids are called carboxylates.
- Carboxylate ions are resonance stabilized, and this increased stability makes carboxylic acids more acidic than alcohols.
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- The pKa 's of some typical carboxylic acids are listed in the following table.
- When we compare these values with those of comparable alcohols, such as ethanol (pKa = 16) and 2-methyl-2-propanol (pKa = 19), it is clear that carboxylic acids are stronger acids by over ten powers of ten!
- Furthermore, electronegative substituents near the carboxyl group act to increase the acidity.
- The resonance effect described here is undoubtedly the major contributor to the exceptional acidity of carboxylic acids.
- In the case of carboxylic acids, if the electrophilic character of the carbonyl carbon is decreased the acidity of the carboxylic acid will also decrease.
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- Sodium borohydride, NaBH4, does not reduce carboxylic acids; however, hydrogen gas is liberated and salts of the acid are formed.
- Partial reduction of carboxylic acids directly to aldehydes is not possible, but such conversions have been achieved in two steps by way of certain carboxyl derivatives.
- In the first, bromine replaces the carboxyl group, so both the carboxyl carbon atom and the remaining organic moiety are oxidized.
- Lead tetraacetate will also oxidize mono-carboxylic acids in a manner similar to reaction #1.
- Also, various iodide derivatives may be prepared directly from the corresponding carboxylic acids.
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- Acid or base-catalyzed hydrolysis yields the component fatty acid, some examples of which are given in the following table, together with the alcohol component of the lipid.
- These long-chain carboxylic acids are generally referred to by their common names, which in most cases reflect their sources.
- Natural fatty acids may be saturated or unsaturated, and as the following data indicate, the saturated acids have higher melting points than unsaturated acids of corresponding size.
- The trans-double bond isomer of oleic acid, known as elaidic acid, has a linear shape and a melting point of 45 ºC (32 ºC higher than its cis isomer).
- Because of their enhanced acidity, carboxylic acids react with bases to form ionic salts, as shown in the following equations.