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Organic Acids

The organic acids are acids that has a carbon skeleton. Within these categories there are number of classes of neutral proton acids and bases. The three main types of neutral organic Bronsted Lowry acids are carboxylic acids, phenols, and alcohols. Each of these three functional groups has an –OH group. 

Each one of them could be attributed as acidic as the electronegativity difference between the oxygen and hydrogen involved in O-H bond. The difference in acid strength of the three functional groups are due to the difference in stability of the conjugate base. The most acidic of the three are carboxylic acids which is characterised by the presence of the carboxyl group R-COOH.

These carboxylic acids are among the most acidic of the neutral organic acids but they are rather weak acids as the pKa of acetic acid is 4.8 which indicates that only a small portion of the molecules of this acid ionize in an aqueous solution. Although carboxylic acids are weaker than mineral acids but are considered strongest amongst the neutral organic acids. 

Carboxylic Acid

The reason for the relative strength of carboxylic acids is the conjugate base which is resonance stabilized and makes it a weak base.

 

Organic Acids Definition

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Organic acids could be defined as organic compound with acidic properties. The most common organic acids in food are carboxylic acids which carboxyl group –COOH dissociates into a proton and conjugate base and endows acids with their acidic properties.

Organic acids partially dissociate in neutral aqueous solutions and are generally considered as weak acids. The deprotonation of the acid gives a carboxylate anion which is stabilized by resonance because the negative charge is delocalised between the two oxygen atoms eventually increasing the stability. 

The lower molecular weight organic acids are soluble in water while the higher molecular weight organic acids are less soluble due to increasing hydrophobic nature of the alkyl chain. The organic acids have higher boiling points than water as they could form stable dimer apart from greater surface area.

Organic Acids List

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Some of the common organic acids that we come across are as follows.

Acetic acid, L-ascorbic acid, Benzoic acid, Cinnamic acid, Citric acid, Formic acid, Fumaric acid, D-gluconic acid, D-lactic acid, malic acid, Propionic acid, tartaric acid and Gallic acid.

Organic acids and their respective pKa.

  Acid Name 
 pKa   Acid Name   pKa 
  Fromic acid  3.75  Acetic acid  4.76
 Propionic acid   4.87  Butanoic acid  4.82
 Pivalic acid  5.03  4-methylpentanoic acid  4.79
 Phenyl acetic acid   4.31  Benzoic acid  4.20
 Chloro acetic acid  2.87  Bromo acetic acid  2.90
 Iodo acetic acid  3.13  4-Nitro benzoic acid  3.44
 2-chloro Butanoic acid   2.88  2-methyl Butanoic acid 
 4.76

Organic Acids and Their Uses

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The organic acids and their derivatives extends to a wide range of substances. These are used in every type of chemically manufactured substances. These molecules are considered generally as irritant, the level of such irritant is decided partially by dissociation of acids along with their water solubility capacity. Some of these could result in severe burning or almost similar effects as the mineral acids. 

Many of these carboxylic acids are of immense importance because of their use in food and beverage industries along with drugs and other manufacturing processes. The most common organic acids which are used in such manufacturing are adipic acid, azelaic acid, Fumaric acid, maleic acid, malic acid, malonic acid, oxalic acid, succinic acid, tartaric acid and sebacic acid.

The saturated long chain of the monocarboxylic acids are basically fatty acids. These are the main chain resourced from various natural sources. Synthetic fatty acids could also be prepared by oxidation of paraffin using metals as catalysts. These could also be prepared by alcohol oxidation in presence of alkaline potassium di chromates. The commercial naphthenic acid are derived from cyclo-paraffins in petroleum, by oxidation.  

The organic acids are utilised in plastic making, tanning, textiles, paper, metal, pharmaceuticals, food industries, beverage making as well as and in manufacturing of cosmetics. These are also used in manufacturing of perfumes, herbal insecticides, colours and dyes, various lubricants and common household cleaners.

Formic Acid and Acetic Acid

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These are considered as major industrial chemicals amongst saturated monocarboxylic acids. While Formic acid is mainly used in textile and leather industry, acetic acid serves as intermediate chemical which acts as delimiting agent during leather tanning, serve as solvent, and also as oil well acidizer. Formic acid acts as dye exhausting agent in chrome dying and acts as a neutralizing agent in leather industries as well as coagulant.

Apart from these acetic acid acts as additive in many food products as well as a finishing agent in dye stuff, in pharmaceutical industries and textile industries.

Chloroacetic acid

The Chloroacetic acid is used in pharma industries, in dye stuff and in chemical industries as chemical intermediate. The salicyliclates are used as chemical intermediate in the manufacturing of aspirin formulations, rubber industries as well as dye stuff industries.

Benzoic acid, the ascorbates along with oleates are some other useful derivatives which are used in food, beverage and pharma industries.

Acids like palmitic and stearates are used in various industries like in soap industries, cosmetic preparation, the cleaning agents like detergents, machinery agents like lubricants, and hard protective coatings and other intermediate products.
  • Propionic acids are used in organic synthesis, used as various fungicides and also as food preserving chemical.
  • Acrylic acid, Meth acrylic acid, Crotonic acid are used in the manufacturing of resins, paper, plastics and pain industries.
  • The Crotonic acid is also used as softening agent in synthetic rubber manufacturing. 
  • Lactic acid is used in adhesive, plastics and textiles.
  • Glycolic acids are used in leather, textile, and electroplating, adhesive and metal cleaning industries.

Types of Organic Acids

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There are two types of organic acids. One derived from the -COOH group while the other from phenolic group or $C_{6}H_{5}OH$.

The dicarboxylic acids like the succinates, the fumarates and maleic acid along with tricarboxylic acid like citrates are very useful in food, beverage and pharma industries.
  • Succinic acid is used lacquers and dye manufacturing.
  • Maleic acid is used in synthetic resins manufacturing and also as preservatives for oils and fats.
  • Fumaric acid is used in the production of polyester resins, various ink and organic syntheses.
  • Adipic acid is used for the production of nylon, as well as synthetic lubricants, long chains of urethanes and food acidulates.
  • Oxalic acid is used for cleaning, textile finish, as well as household metal cleaning formulations. 
  • Oxalic acid is also used as bleaching agent of leather, and in syntheses.

Organic Acids and its Sources

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The acids which are produced by plants and animals are termed as organic acids. Many of these are found to be in living things. 

The list of such organic acids are as follows.


 Acids 
 Origin 
 Cirtric acid 
 Citrus fruits like oranges and lemons 
 Tartaric acid   Fruits like grapes and tamarinds
 Ascorbic acids   Present in citrus fruits as Vitamin C
 Methanoic acids  
 The sting of nettle, and ant sting
 Oxalic acids
 The juice of tomatoes
 Uric acids
 The urine discharge
 Lactic acids  When milk goes sour
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