Methacrylic acid, abbreviated MAA, is an
organic compound
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
with the formula CH
2=C(CH
3)CO
2H. This colorless, viscous liquid is a
carboxylic acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...
with an acrid unpleasant odor. It is soluble in warm water and miscible with most organic solvents. Methacrylic acid is produced industrially on a large scale as a precursor to its
ester
In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
s, especially
methyl methacrylate (MMA), and to
poly(methyl methacrylate)
Poly(methyl methacrylate) (PMMA) is a synthetic polymer derived from methyl methacrylate. It is a transparent thermoplastic, used as an engineering plastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and bran ...
(PMMA).
Production
In the most common route, methacrylic acid is prepared from
acetone cyanohydrin
Acetone cyanohydrin (ACH) is an organic compound used in the production of methyl methacrylate, the monomer of the transparent plastic polymethyl methacrylate (PMMA), also known as acrylic. It liberates hydrogen cyanide easily, so it is used as a ...
, which is converted to methacrylamide sulfate using sulfuric acid. This derivative in turn is hydrolyzed to methacrylic acid, or esterified to methyl methacrylate in one step. Another route to methacrylic acid starts with
isobutylene
Isobutylene (or 2-methylpropene) is a hydrocarbon with the chemical formula . It is a four-carbon branched alkene (olefin), one of the four isomers of butylene. It is a colorless flammable gas, and is of considerable industrial value.
Product ...
, which obtainable by dehydration of
''tert''-butanol. Isobutylene is oxidized sequentially to
methacrolein and then methacrylic acid. Methacrolein for this purpose can also be obtained from
formaldehyde
Formaldehyde ( , ) (systematic name methanal) is an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as ...
and
ethylene
Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...
. Yet a third route involves the
dehydrogenation of
Isobutyric acid
Isobutyric acid, also known as 2-methylpropanoic acid or isobutanoic acid, is a carboxylic acid with structural formula ( CH3)2CH COOH. It is an isomer of butyric acid. It is classified as a short-chain fatty acid. Deprotonation or esterificati ...
.
Various green routes have been explored but they have not been commercialized. Specifically, the
decarboxylation
Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is ...
of
itaconic acid,
citraconic acid, and
mesaconic acids affords methacrylic acid. Salts of methacrylic acid have been obtained by boiling citra- or meso-brompyrotartaric acids with
alkali
In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The a ...
s.
Pyrolysis of
ethyl methacrylate efficiently gives methacrylic acid.
Uses and occurrence
The main use of methacrylic acid is its polymerization to
poly(methyl methacrylate)
Poly(methyl methacrylate) (PMMA) is a synthetic polymer derived from methyl methacrylate. It is a transparent thermoplastic, used as an engineering plastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and bran ...
.
It is used in some nail primers to help
acrylic nails adhere to the nail plate.
Copolymers
In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are som ...
consisting partially of methacrylic acid are used in certain types of tablet coatings in order to slow the tablet's dissolution in the
digestive tract
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...
, and thus extend or delay the release of the
active ingredient
An active ingredient is any ingredient that provides biologically active or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease or to affect the structure or any function of the body of humans or animals.
...
.
MAA occurs naturally in small amounts in the oil of
Roman chamomile.
MMA is used in the synthesis of some
vinyl ester resins.
:
Reactions
For commercial applications, MAA is polymerized using
azobisisobutyronitrile as a thermally activated free-radical catalyst. Otherwise, MAA is relatively slow to polymerize thermally or photochemically.
[
Methacrylic acid undergoes several reactions characteristic of α,β-unsaturated acids (see ]acrylic acid
Acrylic acid (IUPAC: prop-2-enoic acid) is an organic compound with the formula CH2=CHCOOH. It is the simplest unsaturated carboxylic acid, consisting of a vinyl group connected directly to a carboxylic acid terminus. This colorless liquid has ...
). These reactions include the Diels–Alder reaction and Michael additions. Esterifications are brought about by acid-catalyzed condensations with alcohols, alkylations with certain alkenes, and transesterifications. Epoxide ring-opening gives hydroxyalkyl esters.[
Sodium amalgam reduces it to ]isobutyric acid
Isobutyric acid, also known as 2-methylpropanoic acid or isobutanoic acid, is a carboxylic acid with structural formula ( CH3)2CH COOH. It is an isomer of butyric acid. It is classified as a short-chain fatty acid. Deprotonation or esterificati ...
. A polymer
A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...
ic form of methacrylic acid was described in 1880.[{{cite journal, author=F. Engelhorn, journal = Justus Liebigs Annalen der Chemie, year= 1880, volume= 200, page= 70, title=II. Untersuchungen über die ungesättigten Säuren. Zur Kenntnis der Methacrylsäure , trans-title=II. Investigations on the unsaturated acids. On the characterisation of methacrylic acid., doi=10.1002/jlac.18802000103, url=https://zenodo.org/record/1655491 , editor=Rudolph Fittig.]
See also
* Lactic acid
Lactic acid is an organic acid. It has the molecular formula C3H6O3. It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as wel ...
References
Carboxylic acid-based monomers
Alkenoic acids
Foul-smelling chemicals