The second name of malic acid is oxyantaric. It is a representative of the class of hydroxy-dicarboxylic acids. For the first time the compound was obtained by Karl Scheele (Swedish chemist) from immature apples (which determined its name) in 1785. Also in nature it is found in grapes, barberries, mountain ash, raspberries, etc. In the form of salts called malates, the substance is contained in tobacco. The maximum content of oxy succinic acid together with citric acid in immature green apples reaches 1.2%.
Apple acid: the formula
This chemical compound has the following formula:
Under normal conditions, malic acid is a colorless crystalline powder that dissolves well in alcohol (in 100 ml - 35.9 g) and in water (in 100 ml - 144 g). The molecular weight of the compound is 134.1 g / mol.
The picture below shows the spatial structure of the malic acid molecule. Carbon atoms are designated by black color, oxygen - red, hydrogen - white.
The malic acid exists in the form of a racemate (an optically inactive compound) and two stereoisomers. The latter are those compounds in whose molecules an identical sequence of chemical bonds is observed between the atoms, but there are differences in their location in space relative to each other. Stereochemistry deals in detail with this question. In the case of malic acid, the stereoisomer is two, it was in their example that P. Walden in 1896 first showed that interconversion of enantiomers is possible. The study of this phenomenon acted as a basis for the subsequent creation of the theory of the reaction of the so-called nucleophilic substitution at the carbon atom (saturated).
The substance is obtained in two ways: natural and chemical. The first offers an extraction of fruits and berries. Synthetic malic acid is produced as a result of several reactions:
1. Hydration of maleic or fumaric acid. A mandatory condition is a temperature of 100-150 ° C. The reaction equation is as follows:
HOOCCH = CHCOOH + H2O → HOOC-CH2 -CH (OH) -COOH
2. Hydrolysis of bromo- or chlorosuccinic acid. Apple acid is extracted using ether. In this case, plant material is used.
Apple acid. Interaction reactions
1. Oxidation with sulfuric acid (H2 SO4 ) with the formation of cumulic acid. The reaction takes place in two stages:
HOOS-CH2 -CH (OH) -COOH + H2 SO4 → HOOC-CH2 -CHO + HCOOH
As a result, aldehydomalonic and formic acids are formed. The last compound decomposes with the formation of carbon monoxide and water:
HCOOH → CO + H2O
Aldehydomalonic acid immediately transformed into kumalinovoy.
HOOS-CH2 -CH (OH) -COOH + HCl → HOOC-CH2-CHCl-COOH
The resulting substance is called 2-chlorohydrate.
3. Apple acid is susceptible to oxidation (in particular, when using KMnO4):
HOOS-CH2 -CH (OH) -COOH + KMnO4 → HOOC-CH2-CO-COOH
The resulting acid is called 2-oxo-succinic (oxalylacetic).
4. Interaction with acetyl chloride with the formation of 2-acetoxy-succinic acid:
HOOS-CH2 -CH (OH) -COOH + CH3COCl → HOOC-CH2-CH (OCOCH3) -COOH
With gradual heating, malic acid decomposes to form a series of intermediate products. At a temperature of 100 ° C, anhydrides are formed (they are similar to lactides). With an increase to 140-150 ° C, they are converted to fumaric acid. With a rapid increase in temperature to 180 ° C, maleic anhydride is obtained.
Summarizing all the data, we can say that the chemical properties of malic acid are the same as the other hydroxy acids.
Apple acid is involved in the Krebs cycle. It is the main stage in the respiration of all cells that use oxygen and is an intermediate link between glycolysis and the electrotransport chain. The main role of the tricarboxylic acid cycle (Krebs) is the synthesis of reduced coenzymes FAD * H2 and NAD * H. They are subsequently used to produce ATP, ADP and phosphate. Oxy succinic acid is formed as a result of hydration of fumaric acid. Its subsequent oxidation with NAD + completes the Krebs cycle. The catalyzing enzyme is malate dehydrogenase.
Spheres of use
Obtained on an industrial scale, malic acid is widely used:
- In the food industry, it is known as E296. The substance is used as a preservative, taste enhancer and acidity regulator. Main application: carbonated drinks, fruit juices, confectionery, wine, canned goods. It is worth emphasizing that in small amounts of malic acid has a positive effect on the body.
- In cosmetology. Oxy succinic acid has antioxidant, bleaching, exfoliating and moisturizing properties, which makes it suitable for use in anti-cellulite and bleaching agents for the skin, peelings. In addition, it is added to toothpastes and products that care for the oral cavity.
- In pharmacology, malic acid (the formula is given above) is used in the composition of expectorants and laxatives.