Methacrylic acid
- Methyl acrylic acid
- 2- methylpropenoic
- Alpha-methyl- acrylic acid
- Isobutensäure
- MAA ( Methacrylic acid )
Colorless liquid with a pungent odor
Liquid
1.02 g · cm -3
15 ° C.
161 ° C
87 hPa ( 20 ° C)
Miscible with water
1.4314 (20 ° C)
Risk
5 ml · m -3 or 18 mg · m-3
Template: Infobox chemical / molecular formula search available
Methacrylic acid is an unsaturated carboxylic acid, a so-called alkenoic acid, and is used as starting material for the production of plastics. The salts and esters of methacrylic acid are referred to as methacrylates.
History and habitat
Methacrylic acid was first obtained by Edward Frankland and Baldwin Francis Duppa in the form of its ethyl ester by the reaction of phosphorus pentachloride with an ester of isobutyric acid. The polymeric form of methacrylic acid was described in 1880 first. It comes as esters naturally in chamomile oil.
Production and representation
More than 3 million tons of methacrylic acid are produced annually, although a substantial proportion of syntheses of other chemical compounds also go via the intermediate methacrylic acid. Industrially it is made from isobutylene and tert- butanol, which is then further oxidized to methacrolein and this only to methyl methacrylate. It can also be synthetically prepared by the hydrolysis of acetone cyanohydrin, and subsequent elimination of water.
Properties
Physical Properties
Methacrylic acid is a colorless liquid with an unpleasant odor. The fumes of the methacrylic acid is heavier than air. Fixed methacrylic acid forms prismatic crystals.
Chemical Properties
Methacrylic acid dissolves in water, alcohol and ether; the aqueous solution is strongly acidic. You polymerizes very easily when heated, when exposed to light or in the presence of hydrochloric acid or peroxides to form highly polymeric products. The addition of stabilizers such as hydroquinone methacrylic acid may still be stored in monomeric form an extended period.
Use
In the preparation of synthetic resin dispersions by the emulsion polymerization, a small proportion of methacrylic acid is often copolymerized inter alia to increase the colloidal stability. In contrast to the acrylic acid, methacrylic acid is thereby evenly incorporated into the particles. Aqueous ( neutralized ) or methacrylic acid polymer solutions methacrylsäurehaltiger copolymers find use as wetting agents or thickeners, for example, in the manufacture of emulsion paints. However, it is also used for the preparation of other monomers (e.g., hydroxyethyl methacrylate, HEMA short, CAS: 868-77-9 ).
The esters of methacrylic acid ( esterification with butyl or long-chain alcohols ) may be used for the production of plastics. Important polymethacrylates ( polymethylmethacrylate or polymethacrylic ) are:
- Polymethyl methacrylate, polymethyl methacrylate, abbreviated as PMMA, acrylic glass of methyl methacrylate, the methyl ester of methacrylic acid
- Polymethacrylsäureethylester, short PMAA
- Polymethacrylsäurepropylester, short PMAP
- Polymethacrylsäureisopropylester
- Eudragit: The different variants of Eudragit are anionic copolymers of methacrylic acid and methyl methacrylate. They are insoluble in gastric juice and in pure water. In neutral to alkaline media they dissolve by salt formation with alkali and deliver enteric coatings and soluble in intestinal juice. In this way, one can well protected transport drugs through the stomach.
Safety
Methacrylic acid can be very violent, depending on conditions polymerize explosively and with decomposition in a Runaway Reaction spontaneously. Commercially methacrylic acid is therefore always mixed with a polymerization inhibitor. When storing, make sure that the acid does not freeze ( solidification temperature 15 ° C). The freezing of the inhibitor is depleted the crystallized methacrylic acid, and oxygen, as they turn out to some extent, so that also after thawing have a strong concentration gradient of the inhibitor can occur in the storage vessel. Frozen methacrylic acid must therefore be careful ( temperatures above 50 ° C should be avoided ), to be thawed slowly and with constant mixing. This should only be performed by a qualified person ( the manufacturer shall provide to the safety data sheet, a consulting opportunity, often with an emergency hotline available ). This is not the spot, then the crystallized methacrylic acid, acrylic or below the melting point, however, be stored below 0 ° C. In this state, methacrylic acid is not critical. Under no circumstances may be taken from partially frozen containers liquid acid, as this is a large part of the inhibitor is taken with and so no longer is available during remelting of the frozen part of the methacrylic acid.