Methacrylic acid

Methacrylic acid
Names
	IUPAC name Methacrylic acid
	Preferred IUPAC name 2-Methylprop-2-enoic acid
	Other names Methacrylic acid; 2-Methyl-2-propenoic acid; α-Methacrylic acid; 2-Methylacrylic acid; 2-Methylpropenoic acid
Identifiers
CAS Number	79-41-4 ;
3D model (JSmol)	Interactive image;
Abbreviations	MAA
ChEBI	CHEBI:25219 ;
ChemSpider	3951 ;
ECHA InfoCard	100.001.096
EC Number	201-204-4;
MeSH	C008384
PubChem CID	4093;
UNII	1CS02G8656 ;
CompTox Dashboard (EPA)	DTXSID3025542 ;
	InChI InChI=1S/C4H6O2/c1-3(2)4(5)6/h1H2,2H3,(H,5,6) Key: CERQOIWHTDAKMF-UHFFFAOYSA-N;
	SMILES CC(C(O)=O)=C;
Properties
Chemical formula	C4H6O2
Molar mass	86.09 g/mol
Appearance	Colorless liquid
Odor	Acrid, repulsive
Density	1.015 g/cm3
Melting point	14 to 15 °C (57 to 59 °F; 287 to 288 K)
Boiling point	161 °C (322 °F; 434 K)
Solubility in water	9% (25 °C)
Vapor pressure	0.7 mmHg (20 °C)
Hazards
NFPA 704 (fire diamond)	3 2 2
Flash point	77.2 °C (171.0 °F; 350.3 K)
	NIOSH (US health exposure limits):
PEL (Permissible)	none
REL (Recommended)	TWA 20 ppm (70 mg/m3) [skin]
IDLH (Immediate danger)	N.D.
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Methacrylic acid, abbreviated MAA, is an organic compound with the formula CH₂=C(CH₃)CO₂H. This colorless, viscous liquid is a carboxylic acid 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 esters, especially methyl methacrylate (MMA), and to poly(methyl methacrylate) (PMMA).

Production

In the most common route, methacrylic acid is prepared from acetone cyanohydrin, 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, 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 and ethylene. Yet a third route involves the dehydrogenation of Isobutyric acid.^[3]

Various green routes have been explored but they have not been commercialized. Specifically, the decarboxylation of itaconic acid, citraconic acid, and mesaconic acids affords methacrylic acid.^[4] Salts of methacrylic acid have been obtained by boiling citra- or meso-brompyrotartaric acids with alkalis.^{[citation needed]}

Pyrolysis of ethyl methacrylate efficiently gives methacrylic acid.^[5]

Uses and occurrence

The main use of methacrylic acid is its polymerization to poly(methyl methacrylate).^[6]

It is used in some nail primers to help acrylic nails adhere to the nail plate.^[7]

Copolymers 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, and thus extend or delay the release of the active ingredient.^[8]

MAA occurs naturally in small amounts in the oil of Roman chamomile.^{[citation needed]}

MMA is used in the synthesis of some vinyl ester resins.

Typical vinyl ester resin derived from bisphenol A diglycidyl ether and methacrylic acid.^[9]

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.^[6]

Methacrylic acid undergoes several reactions characteristic of α,β-unsaturated acids (see acrylic acid). 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.^[3] Sodium amalgam reduces it to isobutyric acid. A polymeric form of methacrylic acid was described in 1880.^[10]