Organic Acids and Bases

Acids and bases are obviously important because many organic and biological reactions are catalysed by acids or bases. Originally, a substance was identified as an acid if it exhibited the properties shown by other acids: a sour taste (the word acid is derived from the Latin acidus meaning ‘sour’) and the abilities to turn blue vegetable dyes red, to dissolve chalk with the evolution of gas, and to react with certain ‘bases’ to form salts. It seemed that all acids must therefore contain something in common and at the end of the eighteenth century, the French chemist Lavoisier erroneously proclaimed this common agent to be oxygen (indeed, he named oxygen from the Greek oxus ‘acid’ and gennao ‘I produce’).

Later it was realized that some acids, for example, hydrochloric acid, did not contain oxygen and soon hydrogen was identified as the key species. However, not all hydrogen-containing compounds are acidic, and at the end of the nineteenth century it was understood that such compounds are acidic only if they produce hydrogen ions H+ in aqueous solution—the more acidic the compound, the more hydrogen ions it produces. This was refined once more in 1923 by J.N. Brønsted who proposed simple definitions for acids and bases.

Brønsted definitions of acids and bases

• An acid is a species having a tendency to lose a proton

• A base is a species having a tendency to accept a proton

Every acid has a conjugate base

In water, hydrogen chloride donates a proton to a water molecule to give a hydronium ion and chloride on, both of which are strongly solvated.

Water can behave as an acid or as a base

If a strong acid is added to water, the water acts as a base and is protonated by the acid to become H3O+. If we added a strong base to water, the base would deprotonate the water to give hydroxide ion, OH–, and here the water would be acting as an acid. Such compounds that can act as either an acid or a base are called amphoteric.

Organic Acids and Bases
a. Organic Acid

Organic acids are characterized by the presence of positively polarized hydrogen atom. There are two kinds of organic acids, the first of a hydrogen atom attached to the oxygen atom, such as the metal of alcohol and acetic acid. Second, the hydrogen atoms attached to the carbon atoms in which the carbon atoms are bonded directly to the carbonyl group (C = O), such as acetone.

Methyl alcohol contains OH bonds and hence weak acid, acetic acid has acidic OH bond stronger. Acetic acid is a stronger acid than alcohol because the conjugate base metal formed can be stabilized through resonance, while the conjugate base of methyl alcohol is only stabilized by keelektronegativitasan of oxygen atoms.

The acidity of the conjugate base of acetone are shown in the form stabilized by resonance. And again, one of the form resonannya stabilize the negative charge by transferring the charge on the oxygen atom.

Compounds called carboxylic acids, has a-COOH group, are very much in living organisms and is involved in metabolic reaction pathways. Acetic acid, pyruvic acid, and citric acid is an example. It should be noted that the physiological pH is about 7.3, so the carboxylic acids are mostly found as the anion, the carboxylate anion,-COO-.

Examples of organic acids: acetic acid, pyruvic acid, citric acid
1) Acetic Acid
Acetic acid, ethanoic acid or acetic acid is an organic acid chemical compounds known as sour flavoring and aroma in food. Acetic acid has the empirical formula C2H4O2. This formula is often written in the form of CH3-COOH, CH3COOH, or CH3CO2H. Pure acetic acid (called glacial acetic acid) is a colorless hygroscopic liquid, and has a freezing point of 16.7 ° C.

Acetic acid is one of the simplest carboxylic acids, as formic acid. Solution of acetic acid in water is a weak acid, meaning that only partially dissociate into H + and CH3COO-. Acetic acid is a chemical reagent and industrial raw materials is important. Acetic acid is used in the production of polymers such as polyethylene terephthalate, cellulose acetate and polyvinyl acetate, as well as a wide range of fibers and fabrics. In the food industry, acetic acid is used as an acidity regulator. In households, diluted acetic acid is often used as a water softener. Within a year, world demand for acetic acid to 6.5 million tons per year. 1.5 million tons per year generated from the recycling, the remainder derived from the petrochemical industry as well as from biological sources.

2) Citric acid
Citric acid is a weak organic acid found in the leaves and fruits of plants of the genus Citrus (orange-jerukan). This compound is a good preservative and natural, but used as a flavor enhancer sour on food and soft drinks. In biochemistry, citric acid is known as an intermediate in the citric acid cycle occurs in the mitochondria, which is important in the metabolism of living things. This substance can also be used as an environmentally friendly cleaning agent and as an antioxidant.

Citric acid is found in many fruits and vegetables, but has been found at high concentrations, which can reach 8% dry weight, the lemon and lime juice (such as lemon and lime).

Citric acid is the chemical formula C6H8O7 (structure shown in the tables of information on the right). Acid structure is reflected in its name IUPAC acid, 2-hydroxy-1 ,2,3-propanatrikarboksilat.

3) pyruvic acid
Pyruvic acid (CH3COCO2H) is an alpha-keto acid which has an important role in biochemical processes. Carboxylate anion of pyruvic acid called pyruvate

Pyruvic acid is a colorless liquid with an odor similar to acetic acid. Pyruvic acid mixed with water, and soluble in ethanol and diethyl ether. In the laboratory, pyruvic acid is made by heating a mixture of tartaric acid with potassium bisulfate, or by hydrolysis of acetyl cyanide, which is made by reaction of acetyl chloride and potassium cyanide:
CH3COCl + KCN → CH3COCN
CH3COCN → CH3COCOOH

Pyruvate is an important chemical compound in biochemistry. This compound is the metabolism of glucose is called glycolysis. A glucose molecule is split into two molecules of pyruvic acid, which is then used to generate energy. If there is enough oxygen, the pyruvic acid is converted to acetyl-CoA, which is then processed in the Krebs cycle. Pyruvate can also be converted into oxaloacetate by reaction anaploretik were then broken down into molecules of carbon dioxide. Cycle name is taken from the biochemist Hans Adolf Krebs, winner of the 1953 Nobel Prize in Physiology, as he managed to identify the cycle).

If there is not enough oxygen, pyruvic acid is broken down anaerobically, producing lactic acid in animals and humans, or ethanol in plants. Pyruvate is converted into lactate using the enzyme lactate dehydrogenase and the coenzyme NADH through lactate fermentation, or to acetaldehyde and then ethanol through fermentation alcohol.

Pyruvic acid can also be converted to carbohydrates via gluconeogenesis, to fatty acids or energy through acetyl-CoA, to the amino acid alanine and to ethanol.

Pyruvic acid derivatives, 3-bromopiruvat been studied for the treatment of cancer.
b. Organic Bases

Organic base is characterized by the presence of atoms with a lone pair of electrons that can bind protons. Compounds containing nitrogen atom is an example of an organic base, but the oxygen-containing compounds can also act as a base when reacted with a strong acid. It should be noted that compounds containing oxygen atoms can act as an acid or alkaline, depending on the environment. As acetone and methyl alcohol can act as an acid when it donates a proton, but as a base while receiving oxygen atom proton.

Examples of organic bases are: amine
1) amine

Amina has the molecular formula RNH2 (primary amine), R2NH (secondary amine) and R3NH (tertiary amine). Amina kwarterner NR4 + wherein R is alkyl or aryl group.
Because amine containing free electron pair on the nitrogen atom, the amine is alkaline (Bronsted - Lowry) and are nucleophiles. Basanya properties of aliphatic amines stronger than ammonia. Instead aromatic amines basanya properties lower than in ammonia. Amines react with mineral acids to form ammonium salts are soluble in water kwarterner.

Aromatic amine is insoluble in water, such as starch, N-methyl aniline. Ammonia and primary amine each containing an-NH2. In ammonia, this group is bound to a hydrogen atom, while the primary amine attached to an alkyl group or a benzene ring.