This document discusses various methods for preparing carboxylic acids, including the oxidation of primary alcohols, hydrolysis of nitriles, reaction of Grignard reagents with carbon dioxide, hydrolysis of esters, and the malonic ester synthesis. The malonic ester synthesis involves treating malonic ester with sodium ethoxide to form its salt, then reacting the salt with an alkyl halide to form a dialkyl malonic ester which decarboxylates to form a substituted acetic acid. Important carboxylic acids like acetic and benzoic acid are prepared industrially using these oxidation, nitrile hydrolysis, and substitution reactions.

1. Aromatic Acids*

2. Syllabus
• Preparation and reaction of Aromatic acid
• Acidity, and effect of substituents on acidity
• Important reactions of benzoic acid.

3. Carboxylic acid
• carboxylic acid molecules are polar, and like
alcohol molecules can form hydrogen bonds
with each other and with other kinds of
molecules.
• The alipliatic acids therefore show very much
the same solubility behavior as that of
alcohols
• First four acids are miscible with water, the
five carbon acid is partly soluble, and the
higher acids are virtually insoluble.

4. Carboxylic acid
Water solubility undoubtedly arises from
hydrogen bonding between the carboxylic acid
and water.
The simplest aromatic acid, benzoic acid,
contains too many carbon atoms to show
appreciable solubility in water.

5. odors of the lower aliphatic acids
• Lower aliphatic acids - sharp,
• Odors of formic and acetic acid –
irritating,
• Butyric, valeric, and caproic acids-
distinctly unpleasant odors
• The higher acids have little odor because
of their low volatility.

6. Acidity of Carboxylic acid
• Weaker than the strong mineral acids
(sulfuric, hydrochloric, nitric),
• The carboxylic acids are tremendously
more acidic than the very weak organic
acids (alcohols, acetylene)
• They are much stronger acids than water.

7. Aqueous hydroxides therefore readily
convert carboxylic acids into their
salts;

8. Acetic acid, by far the most important of all
carboxylic acids, is prepared by
air oxidation of acetaldehyde, which is readily
available from the hydration of
acetylene , or the dehydrogenation of ethanol.
Industrial source preparation of acetic acid.

9. Hydration of
acetylene

10. Dehydrogenation of Ethanol

11. Preparation of benzoic and phthalic
acid
• The most important of the aromatic carboxylic
acids, benzole acid and the phthalic acids, are
prepared by oxidation of alkylbenzenes.
• The toluene and xylenes required are readily
available from coal tar and, by catalytic reforming
of aliphatic hydrocarbons from petroleum;
another precursor of phthalic acid is the aromatic
hydrocarbon naphthalene, also found in coal tar.
• Cheap oxidizing agents like chlorine or even air (in
the presence of catalysts are used.

14. PREPARATION OF CARBOXYLIC ACID

15. 1.Oxidation of primary alcohol
Oxidation is the most direct and is generally
used when possible, some lower aliphatic acids
being made from the available alcohols, and
substituted aromatic acids from substituted
toluenes.

17. oxidation

18. 2.Cyanide on hydrolysis

19. Nitrile synthesis
Aliphatic nitriles are prepared by treatment
of alkyl halides with sodium cyanide in a
solvent that will dissolve both reactants; in
dimethyl sulfoxide, reaction occurs rapidly
and exothermically at room temperature.
The resulting nitrile is then hydrolyzed to
the acid by boiling aqueous alkali or acid.

20. The reaction of an alkyl halide with cyanide ion
involves nucleophilic substitution. The fact that
HCN is a very weak acid tells us that cyanide ion
is a strong base; as we might expect, this
strongly basic ion can abstract hydrogen ion and
thus cause elimination as well as substitution.
Tertiary halides elimination is the principal
reaction; even with secondary halides the yield
of substitution product is poor. Here again we
find a nucleophilic substitution reaction that is
of synthetic importance only when primary
halides are used.

21. • As already mentioned, aromatic nitriles are
made, not from the unreactive aryl halides,
but from diazonium salts

22. • Although nitriles are sometimes named as
cyanides or as cyano compounds,
• they generally take their names from the acids
they yield upon hydrolysis.
• They are named by dropping ~ic acid from the
common name of the acid and adding -nitrile;
• usually for euphony an "o" is inserted between
the root and the ending (e.g., acetonitrile).
• In the IUPAC system they are named by adding -
nitrile to the name of the parent hydrocarbon
(e.g., ethanenitrile).

23. Grignard reagent with carbondioxide
and acid

24. The Grignard synthesis of a carboxylic acid
is carried out by bubbling gaseous CO2 into
the ether solution of the Grignard reagent,
or by pouring the Grignard reagent on
crushed Dry Ice (solid CO2 ); in the latter
method Dry Ice serves not only as reagent
but also as cooling agent.

25. The Grignard reagent adds to the
carbon-oxygen double bond just as in
the reaction with aldehydes and
ketones. The product is the
magnesium salt of the carboxylic acid,
from which the free acid is liberated by
treatment with mineral acid.

26. The Grignard reagent can be prepared from
primary, secondary, tertiary, or aromatic halides;
the method is limited only by the presence of
other reactive groups in the molecule.

28. Hydrolysis of ester
When an ester is boiled with concentrated
aqueous NaOH sodium salt of the acid is
formed. This on treatment with dilute HCl gives
the corresponding carboxylic acid.

29. Malonic ester synthesis of carboxylic
acid
• Most valuable method of preparing carboxylic
acids makes use of ethyl malonate is called
malonic ester synthesis
The synthesis depends on
• The high acidity of the alpha hydrogens of
malonic ester.
• The extreme ease with which malonic acid
and substituted malonic acids undergo
decarboxylation.

30. • Malonic ester contains alpha
hydrogen that are particularly acidic :
they are alpha to two carbonyl
groups.
• When malonic ester is treated with
sodium ethoxide in absolute alcohol.
• It is largely converted into its salt
sodio malonic ester.

32. • This reaction involves the nucleophilic attack
on the alkyl halide by the carbanion
CH(COOC2H5)2.
• Highest yield with primary alkyl halide.
• Lower yield with secondary alkyl halide.
• Worthless for tertiary alkyl halide and for
aryl halide.
• The alkyl malonic ester still contain one
ionizable hydrogen and on treatment with
sodium ethoxide. It can be converted into its
salt.

33. • The salt can react with alkyl halide to yield
dialkyl malonic ester.
• In a similar way substituted malonic acid
readily lose CO2 to form substituted acetic
acid.
• A malonic ester synthesis yields an acetic acid
in which one or two hydrogen have been
replaced by alkyl group.

35. • When heated above its melting point malonic
acid readily loses CO2 to form acetic acid.