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  Alkanoates, Chemistry tutorial

Introduction:

The Alkanoic acids form a variety of significant derivatives one of which is the alkanoates. The common name for alkanoates is esters. Alkanoates are made up from alkanoic acids by substituting the - OH of alkanoic acids with -OR group (here R = alkyl group). They are symbolized by the general formula, RCOOR' or CnH2n+1 COOCnH2n+1 (here n ≥ 0).

The IUPAC nomenclature for the members of series is derived from the alkanols (R'OH) and the alkanoic acid (RCOOH) from which the alkanoates are made up of. The alkanol part R' is named first as alkyl and a space is left, that is followed by the alkanoic acid portion R'COO named as alkanoate. For illustration:

a) CH2CCOCH3 = methylethanoate pointing out that it is made up from methanol as the alkanol and ethanoic acid (as the alkanoic acid)

b) CH3CH2COOCH2CH3 = ethyl propanoate pointing out that it is produced methanol (as the alkanol and propanoic acid (as the alkanoic acid).

Naturally occurring esters are known as fats and oils, made from long chain alkanoic acids. If the esters are liquids at room temperature, then they are termed as oils, while if they are solids at room temperature they are termed as fats. Illustrations of these are the fats it allow from cows, cocoa butter from cocoa and palm oil from oil palm, groundnut oil from groundnut, castor oil from castor plant which are employed for cooking are the main source of energy and as well in the manufacture of soaps.

The lower alkanoates are recognized for their characteristic sweet strong aroma and are found in numerous flower, and fruits example: methyl butanoate in pineapple, pentyl ethanoate in banana. The aroma of alkanoate is at times employed to confirm their presence.

Preparation of Alkanoates: Esterification

The esterification process is the principal route for making alkanoates. The direct reaction of alkanoic acid and alkanols in the presence of catalytic of a mineral acid is termed as the esterification.

For illustration, ethyl ethanoate is made up by heating ethanoic acid and ethanol by concentrated tetraoxo sulphate (vi) acid as catalyst.

1369_Preparation of Alkanoates-Esterification.jpg

Fig: Preparation of Alkanoates-Esterification

Esterification is the equilibrium method, and for the production of ethyl ethanoate, the forward and backward reaction takes place at around the similar rate. A convenient process for making ethylethanoate in good yield is to run a mixture of ethanoic acid and ethanol to a hot mixture of ethanol (surplus) and concentrated tetraoxosulphate (vi) acid at similar rate as the alkanoate distills off. The solution obtained from the distillation is shaken by concentrated trioxocarbonate (iv) to eliminate acids, and with concentrated calcium chloride solution to remove the ethanol. The resulting solution is then dried over anhydrous calcium chloride, and the ethyl ethanoate is obtained pure via redistillation.

General features or Characteristics of Alkanoates:

Physical Properties:

Alkanoates are coldness lipids or solids, sparingly soluble in the water. Most of them encompass a characteristic fragrant odor or sweet smell and most of them take place naturally. The fragrances in flowers and fruits attract the insects and animals which are responsible for the pollination of flowers and disposal of seeds.

Chemical Properties:

Alkanoates are usually not very reactive however can be hydrolyzed to their precursor alkanoic acids and alkanols; and reduced to the primary alkanols.

a) Hydrolysis of alkanoates: Alkanoates are hydrolyzed very slowly through boiling with water to provide the component alkanoic acids and alkanols. The reaction can be made faster through catalyzing the hydrolysis with acids or bases.

CH3COOC2H5 + H2O ↔ CH3COOH + C2H5OH

The acid - catalyzed method is the reverse of esterification and, as it is reversible, a surplus of acidic solution is needed to give a good yield of alkanoates.

The base-catalyzed hydrolysis is a more efficient procedure for the alkanoate ion formed, doesn't react appreciably by alkanols so that the reaction goes nearly to completion example:

R - COOR' + OH- → R - COO- + R'-OH

Alkanoate     from       alkanoate

                     base         ion

This alkaline hydrolysis method generally known as saponification is employed for the conversion of naturally occurring esters (that is, alkanoates) into soaps.

b) Reduction of alkanoates: The Alkanoates can be reduced to primary alkanols more simply than alkanoic acid. Lithium aluminum hydride and catalytic hydrogenation are both efficient catalysts for reduction.

R-COOR' → (LiAlH4 or H2/Ni) → R-CH2OH + R'-OH

Alkanoate                                   Primary alkanol

CH3COOC2H5 + 4[H] → 2C2H5OH

                  From reducing agent

Uses of Alkanoates:

1) A large member of alkanoates is employed as perfume and flavorings. For illustration: ethyl methanoate obtained from rum; 3-methylbutyl ethanoate obtained from pear, and ethyl butanoate obtained from the pineapple are all employed in this manner for perfumes and for flavoring.

2) Ethyl ethanoate is a good solvent.

3) Certain helpful waxes are comprised mainly of alkanoates.

For example: beeswax, C15H31COOC31H63

4) Alkanoates of trihydric alkanols and alkanoic acids are of great significance in making soap and propane 1, 2, 3-triod (glycerol).

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