Яблочная кислота: свойства, применение и получение

Carboxylic acid with chemical formula CH2(COOH)2
Chembox
| ImageFile = Malonsäure. svg
| ImageAlt = Skeletal formula of malonic acid
| ImageFile1 = Malonic acid molecule ball from xtal. png
| ImageAlt1 = Ball and stick model of the malonic acid molecule
| PIN = Propanedioic acid
| OtherNames = Methanedicarboxylic acid
|Section1=
|Section2=Chembox Properties
| C=3 | H=4 | O=4
| MeltingPtC = 135 to 137
| MeltingPt notes = (decomposes)
| Density = 1.619 g/cm3
| Solubility = 763 g/L
| BoilingPt = decomposes
| pKa = pKa1 = 2.83 pKa2 = 5.69 is a naturally occurring substance found in many fruits and vegetables. There is a suggestion that citrus fruits produced in organic farming contain higher levels of malonic acid than fruits produced in conventional agriculture. Malonic acid was first prepared in 1858 by the French chemist Victor Dessaignes via the oxidation of malic acid.

Malonic acid reacts as a typical carboxylic acid: forming amide, ester, anhydride, and chloride derivatives. Malonic anhydride can be used as an intermediate to mono ester or amide derivatives, while malonyl chloride is most useful to obtain diesters or diamides. In a well known reaction, malonic acid condenses with urea to form barbituric acid. Malonic acid may also be condensed with acetone to form Meldrum's acid, a versatile intermediate in further transformations. The esters of malonic acid are also used as a −CH2COOH synthon in the malonic ester synthesis.

Malonic acid is the starting substrate of mitochondrial fatty acid synthesis (mtFASII), in which it is converted to malonyl CoA by malonyl CoA synthetase (ACSF3). Additionally, the coenzyme A derivative of malonate, malonyl CoA, is an important precursor in cytosolic fatty acid biosynthesis along with acetyl CoA. Malonyl CoA is formed there from acetyl CoA by the action of acetyl CoA carboxylase, and the malonate is transferred to an acyl carrier protein to be added to a fatty acid chain.

Malonic acid is a key component in the Briggs–Rauscher reaction, the classic example of an oscillating chemical reaction.

In Knoevenagel condensation, malonic acid or its diesters are reacted with the carbonyl group of an aldehyde or ketone, followed by a dehydration reaction. When malonic acid itself is used, it is normally because the desired product is one in which a second step has occurred, with loss of carbon dioxide, in the so called Doebner modification. Thus, for example, the reaction product of acrolein and malonic acid in pyridine is trans 2,4 Pentadienoic acid with one carboxylic acid group and not two.

Carbon suboxide is prepared by warming a dry mixture of phosphorus pentoxide (|P4O10) and malonic acid. It reacts in a similar way to malonic anhydride, forming malonates.

Malonic acid is a precursor to specialty polyesters. It can be converted into 1,3 propanediol for use in polyesters and polymers (whose usefulness is unclear though). It can also be a component in alkyd resins, which are used in a number of coatings applications for protecting against damage caused by UV light, oxidation, and corrosion. One application of malonic acid is in the coatings industry as a crosslinker for low temperature cure powder coatings, which are becoming increasingly valuable for heat sensitive substrates and a desire to speed up the coatings process. The global coatings market for automobiles was estimated to be $18.59 billion in 2014 with projected combined annual growth rate of 5.1% through 2022. It is used in a number of manufacturing processes as a high value specialty chemical including the electronics industry, flavors and fragrances industry, Potential growth of these markets could result from advances in industrial biotechnology that seeks to displace petroleum based chemicals in industrial applications. In 2004, malonic acid was listed by the US Department of Energy as one of the top 30 chemicals to be produced from biomass. In food and drug applications, malonic acid can be used to control acidity, either as an excipient in pharmaceutical formulation or natural preservative additive for foods. including the flavor and fragrance compounds gamma nonalactone, cinnamic acid, and the pharmaceutical compound valproate. Malonic acid (up to 37.5% w/w) has been used to cross link corn and potato starches to produce a biodegradable thermoplastic; the process is performed in water using non toxic catalysts. Starch based polymers comprised 38% of the global biodegradable polymers market in 2014 with food packaging, foam packaging, and compost bags as the largest end use segments. Eastman Kodak company and others use malonic acid and derivatives as a surgical adhesive.

If elevated malonic acid levels are accompanied by elevated methylmalonic acid levels, this may indicate the metabolic disease combined malonic and methylmalonic aciduria (CMAMMA). By calculating the malonic acid to methylmalonic acid ratio in blood plasma, CMAMMA can be distinguished from classic methylmalonic acidemia.

Malonic acid is the classic example of a competitive inhibitor of the enzyme succinate dehydrogenase (complex II), in the respiratory electron transport chain. It binds to the active site of the enzyme without reacting, competing with the usual substrate succinate but lacking the −CH2CH2− group required for dehydrogenation. This observation was used to deduce the structure of the active site in succinate dehydrogenase. Inhibition of this enzyme decreases cellular respiration. Since malonic acid is a natural component of many foods, it is present in mammals including humans.