Metol is a trade name for the

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 OC₆H₄NH₂(CH₃)sub>2HSO₄. It is the

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...

salt of ''N''-methylaminophenol. This colourless salt is a popular

photographic developer In the Photographic processing, processing of photographic films, plates or papers, the photographic developer (or just developer) is one or more chemicals that convert the latent image to a visible image. Developing agents achieve this conversio ...

used in

monochrome photography Monochrome photography is photography where each position on an image can record and show a different ''amount'' of light (Value (color), value), but not a different color (hue). The majority of monochrome photographs produced today are black- ...

.Gerd Löbbert "Photography" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim.

Synthesis and degradation

Several methods exist for the preparation of ''N''-methylaminophenol. It arises by decarboxylation of ''N''-4-hydroxyphenylglycine ( Glycin). It can be obtained by reaction of

hydroquinone Hydroquinone, also known as benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, a derivative of benzene, having the chemical formula C6H4(OH)2. It has two hydroxyl groups bonded to a benzene ring in a ''para' ...

with

methylamine Methylamine, also known as methanamine, is an organic compound with a formula of . This colorless gas is a derivative of ammonia, but with one hydrogen atom being replaced by a methyl group. It is the simplest primary amine. Methylamine is sold ...

. Being an electron-rich arene, metol is readily degraded by

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

Application

Metol is an excellent developing agent for most continuous tone developer applications, and it has been widely used in published developer formulas as well as commercial products. However, it is difficult to produce highly concentrated developer solutions using Metol, and therefore, most Metol developers are supplied in dry chemical mix. A developer containing both Metol and

is called an MQ developer. This combination of agents provides greater developer activity since the rate of development by both agents together is greater than the sum of rates of development by each agent used alone (

superadditivity In mathematics, a function f is superadditive if f(x+y) \geq f(x) + f(y) for all x and y in the domain of f. Similarly, a sequence a_1, a_2, \ldots is called superadditive if it satisfies the inequality a_ \geq a_n + a_m for all m and n. The ...

). This combination is very versatile; by varying the quantities of Metol, hydroquinone, and restrainer, and adjusting the pH, the entire range of continuous tone developers can be made. A popular variation of this is known as 'Dr. Beers.' Two separate solutions are made up: one with Metol; one with hydroquinone. By mixing the two in vaying proportions, various levels of contrast can be obtained. Therefore, this form of Metol replaced most other developing agents except for hydroquinone, Phenidone (which is more recent than Metol), and derivatives of Phenidone. Notable formulas include Eastman Kodak D-76 film developer, D-72 print developer, and D-96 motion picture negative developer.

History

Alfred Bogisch, working for a chemical company owned by Julius Hauff, discovered in 1891 that methylated ''p''-aminophenol has more vigorous developing action than ''p''-aminophenol. Hauff introduced this compound as a developing agent. The exact composition of Bogisch and Hauff's early Metol is unknown, but it was most likely methylated at the ortho position of the benzene ring (''p''-amino-''o''-methylphenol), rather than at the amino group. Some time later, Metol came to mean the ''N''-methylated variety, and the ''o''-methylated variety fell out of use. Aktien-Gesellschaft für Anilinfabrikation (

AGFA Agfa-Gevaert N.V. (Agfa) is a Belgian-German multinational corporation that develops, manufactures, and distributes Analog photography, analogue and digital imaging products, software, and systems. The company began as a dye manufacturer in 1867 ...

) sold this compound under the trade name Metol, which became by far the most common name. Because it has been in use for this purpose for over 100 years, and often by amateur photographers, there is a substantial body of evidence regarding the health problems that contact with Metol can cause. These are principally local

dermatitis Dermatitis is a term used for different types of skin inflammation, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened ...

of the hands and forearms. There is also some evidence of sensitization dermatitis.

References

{{Reflist Photographic chemicals 4-Hydroxyphenyl compounds