Methacrylic acid

Structural formula
General
Surname	Methacrylic acid
other names	Methyl acrylic acid; 2-methylpropenoic acid; alpha-methyl acrylic acid; Isobutenic acid; MAA ( M eth a crylic a cid);
Molecular formula	C 4 H 6 O 2
Brief description	colorless liquid with a pungent odor
External identifiers / databases
EC number	201-204-4
ECHA InfoCard	100.001.096
PubChem	4093
Wikidata	Q165949
properties
Molar mass	86.09 g mol −1
Physical state	liquid
density	1.02 g cm −3
Melting point	15 ° C
boiling point	161 ° C
Vapor pressure	2.13 h Pa (30 ° C); 4.09 hPa (40 ° C); 7.75 hPa (50 ° C);
solubility	soluble in water (98 g l −1 (20 ° C)
Refractive index	1.4314 (20 ° C)
safety instructions
H and P phrases	H: 302 + 332-311-314-335
	P: 261-280-305 + 351 + 338-310
MAK	DFG / Switzerland: 5 ml m −3 or 180 mg m −3
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Methacrylic acid is an unsaturated carboxylic acid , a so-called alkenoic acid , and is used as a raw material for the manufacture of plastics . The salts and esters of methacrylic acid are known as methacrylates .

History and occurrence

Methacrylic acid was first obtained from Edward Frankland and Baldwin Francis Duppa in the form of its ethyl ester by reacting phosphorus pentachloride with an ester of isobutyric acid . The polymeric form of methacrylic acid was first described in 1880. It occurs naturally as an ester in chamomile oil .

Extraction and presentation

More than 3 million tons of methacrylic acid are produced annually, with a significant part of the synthesis of other chemical compounds also going through the intermediate stage methacrylic acid. It is produced industrially from isobutylene and tert-butanol , which are first oxidized to methacrolein and this is then further oxidized to methyl methacrylate. It can also be produced synthetically by hydrolysis of acetone cyanohydrin and subsequent elimination of water.

properties

Physical Properties

Methacrylic acid is a colorless liquid with an unpleasant odor. Methacrylic acid vapors are heavier than air. Solid methacrylic acid forms prismatic crystals. According to Antoine, the vapor pressure function results from log ₁₀ (P) = A− (B / (T + C)) (P in kPa, T in K) with A = 8.1, B = 2621 and C = −4.2 in the temperature range from 298 to 434 K. It dissolves in water, alcohol and ether; the aqueous solution reacts strongly acidic.

Chemical properties

Methacrylic acid polymerizes very easily when heated, when exposed to light or in the presence of hydrochloric acid or peroxides to form highly polymeric products. With the addition of stabilizers such as hydroquinone or hydroquinone monomethyl ether , methacrylic acid can still be stored in monomeric form for a longer period of time. The heat of polymerization is −64.5 kJ mol ⁻¹ or −749 kJ kg ⁻¹ .

When the aqueous solutions are neutralized with metal oxides, hydroxides or alcoholates, the corresponding metal acrylates are obtained in solution. To obtain the crystalline salts, the neutralization can be carried out, for example, in iso-propanol, in which the free acid is soluble but its salts are not.

Safety-related parameters

Methacrylic acid forms inflammable vapor-air mixtures at high temperatures. With a flash point of 68 ° C, the substance is considered flame-retardant. The explosion range is between 2.1 vol.% As the lower explosion limit (LEL) and 8.7 vol.% As the upper explosion limit (UEL). The ignition temperature is 385 ° C. The substance therefore falls into temperature class T2.

use

In the production of plastic dispersions by emulsion polymerization , a small proportion of methacrylic acid and the like is often used. a. copolymerized to increase the collidal stability. In contrast to acrylic acid , methacrylic acid is incorporated more evenly into the particles. Aqueous (neutralized) solutions of polymeric methacrylic acid or copolymers containing methacrylic acid are used as wetting agents or thickeners, e.g. B. in the production of emulsion paints . However, it is also used to produce other monomers (e.g. hydroxyethyl methacrylate , HEMA for short).

The esters of methacrylic acid (esterification with butyl or longer-chain alcohols ) are used in the manufacture of plastics . Important polymethacrylates (or polymethacrylic acid esters) are:

Polymethacrylic acid methyl ester , polymethyl methacrylate, PMMA for short , plexiglass made from methacrylic acid methyl ester , the methyl ester of methacrylic acid

Polymethacrylic acid ethyl ester, PEMA for short

Polymethacrylic acid propyl ester, PPMA for short

Butyl polymethacrylate , PBMA for short

Isopropyl polymethacrylate

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 through salt formation with alkali and provide coatings that are resistant to gastric juice and soluble in intestinal juice. In this way, medicines can be transported safely through the stomach.

safety instructions

Partially frozen methacrylic acid in an IBC .

In a runaway reaction, methacrylic acid can spontaneously polymerize very violently, depending on the conditions, explosively and with decomposition. (see also Trommsdorff effect ) Commercially available methacrylic acid is therefore always mixed with a polymerization inhibitor. During storage, make sure that the acid does not freeze (solidification temperature 15 ° C). When freezing, the crystallized methacrylic acid is depleted in inhibitor and oxygen, since some of these fail, so that even after thawing, a strong concentration gradient of the inhibitor within the storage container can occur. Frozen methacrylic acid must therefore be thawed carefully (temperatures above 50 ° C should be avoided), slowly and with constant mixing. This should only be carried out by competent persons (the manufacturers provide advice on this in the safety data sheet, often also an emergency hotline). If this is not available, the crystallized acrylic or methacrylic acid can be stored below the melting point, but below 0 ° C. In this state, methacrylic acid is not critical. Under no circumstances may liquid acid be removed from partially frozen containers, as this would also remove a large part of the inhibitor and thus no longer be available when the frozen part of the methacrylic acid is melted again.

Detection and Analysis

The acid number can be determined traditionally volumetrically with sodium hydroxide solution against phenolphthalein and the water content according to Karl Fischer .

The pyridine sulfate bibromide method, which is based on bromination of the double bond and subsequent titration with sodium thiosulfate , can be used to determine the double bond content .

In addition to the wet chemical methods, classical physical methods can also be used for the analysis:

Individual evidence

↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o Entry on methacrylic acid in the GESTIS substance database of the IFA , accessed on September 24, 2018(JavaScript required) .
↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-326.
↑ Entry on methacrylic acid in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
↑ Swiss Accident Insurance Fund (Suva): Limit values - current MAK and BAT values (search for 79-41-4 or methacrylic acid ), accessed on November 2, 2015.
^ E. Frankland, BF Duppa: Investigations on acids from the acrylic acid series; 1) Conversion of the acids from the lactic acid series into those of the acrylic acid series . In: Annals of Chemistry and Pharmacy . tape 136 , no. 1 , 1865, p. 1–31 , doi : 10.1002 / jlac.18651360102 (here: p. 12).
↑ Rudolph Fittig, F. Engelhorn: II. Investigations on the unsaturated acids . In: Justus Liebig's Annals of Chemistry . tape 200 , no. 1-2 , 1880, pp. 21-96 , doi : 10.1002 / jlac.18802000103 (here: p. 65 ff.).
^ William Bauer, Jr. Methacrylic Acid and Derivatives in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi : 10.1002 / 14356007.a16_441 .
^ ^A ^b E. Brandes, W. Möller: Safety-related parameters - Volume 1: Flammable liquids and gases , Wirtschaftsverlag NW - Verlag für neue Wissenschaft GmbH, Bremerhaven 2003.
↑ Brandrup, J .; Immergut, EH; Grulke, EA; Abe, A .; Bloch, DR: Polymer Handbook , 4th Edition, Wiley-VCH 2003, ISBN 978-0-471-47936-9 , p. II / 369.
↑ ^a ^b Rauch Puntigam, Theodor Volker: Acrylic and methacrylic compounds . In: Chemistry, physics and technology of plastics in individual representations . tape 9 . Springer, Berlin, Heidelberg, New York 1967, ISBN 978-3-642-46058-6 .
↑ EUDRAGIT® L 30 D-55 (Evonik)

[GESTIS-1] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o Entry on methacrylic acid in the GESTIS substance database of the IFA , accessed on September 24, 2018(JavaScript required) .

[CRC90_3_326-2] David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-326.

[CLP_100.001.096-3] Entry on methacrylic acid in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .

[4] Swiss Accident Insurance Fund (Suva): Limit values - current MAK and BAT values (search for 79-41-4 or methacrylic acid ), accessed on November 2, 2015.

[5] E. Frankland, BF Duppa: Investigations on acids from the acrylic acid series; 1) Conversion of the acids from the lactic acid series into those of the acrylic acid series . In: Annals of Chemistry and Pharmacy . tape 136 , no. 1 , 1865, p. 1–31 , doi : 10.1002 / jlac.18651360102 (here: p. 12).

[6] Rudolph Fittig, F. Engelhorn: II. Investigations on the unsaturated acids . In: Justus Liebig's Annals of Chemistry . tape 200 , no. 1-2 , 1880, pp. 21-96 , doi : 10.1002 / jlac.18802000103 (here: p. 65 ff.).

[7] William Bauer, Jr. Methacrylic Acid and Derivatives in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi : 10.1002 / 14356007.a16_441 .

[Brandes-8] A ^b E. Brandes, W. Möller: Safety-related parameters - Volume 1: Flammable liquids and gases , Wirtschaftsverlag NW - Verlag für neue Wissenschaft GmbH, Bremerhaven 2003.

[Polymer_Handbook-9] Brandrup, J .; Immergut, EH; Grulke, EA; Abe, A .; Bloch, DR: Polymer Handbook , 4th Edition, Wiley-VCH 2003, ISBN 978-0-471-47936-9 , p. II / 369.

[:0-10] Rauch Puntigam, Theodor Volker: Acrylic and methacrylic compounds . In: Chemistry, physics and technology of plastics in individual representations . tape 9 . Springer, Berlin, Heidelberg, New York 1967, ISBN 978-3-642-46058-6 .

[11] EUDRAGIT® L 30 D-55 (Evonik)