Metol
Encyclopedia
Metol is the chemical compound with the name monomethyl-p-aminophenol hemisulfate. It is a developing agent used in black & white photographic developer
s. In its pure form, it is a solid
rather light-sensitive chemical which is the half sulfate
(hemisulfate) salt
of N-methyl-p-aminophenol.
with methylamine
, followed by neutralization with sulfuric acid
.
is called an MQ developer. This combination of agents provide greater developer activity since the rate of development by both agents together is greater than the sum of rates of developments by each agent used alone (superadditivity
). This combination is very versatile; by varying the quantities of Metol, hydroquinone, restrainer, and adjusting the pH, the entire range of continuous tone developers can be made. Therefore, 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.
Because it has been in use for this purpose for over 100 years and often by amateur photographers, there is a wide body of evidence about the health problems that contact with Metol can cause. These are principally local dermatitis
of the hands and fore-arms as well as some evidence of sensitization dermatitis in which subsequent exposure triggers of a chronic condition that is resistant to medication. The use of Metol in highly caustic solution
s and the presence of other materials in darkrooms that have been implicated in dermatitis such as Cr(VI) salts
may exacerbate some health impacts.
Photographic developer
In the processing of photographic films, plates or papers, the photographic developer is a chemical that makes the latent image on the film or print visible. It does this by reducing the silver halides that have been exposed to light to elemental silver in the gelatine matrix...
s. In its pure form, it is a solid
Solid
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...
rather light-sensitive chemical which is the half sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
(hemisulfate) salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
of N-methyl-p-aminophenol.
Synthesis
Metol has been prepared by the reaction of hydroquinoneHydroquinone
Hydroquinone, also benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, having the chemical formula C6H42. Its chemical structure, shown in the table at right, has two hydroxyl groups bonded to a benzene ring in a para position. It is a white granular solid...
with methylamine
Methylamine
Methylamine is the organic compound with a formula of CH3NH2. This colourless gas is a derivative of ammonia, but with one H atom replaced by a methyl group. It is the simplest primary amine. It is sold as a solution in methanol, ethanol, THF, and water, or as the anhydrous gas in pressurized...
, followed by neutralization with sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
.
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 hydroquinoneHydroquinone
Hydroquinone, also benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, having the chemical formula C6H42. Its chemical structure, shown in the table at right, has two hydroxyl groups bonded to a benzene ring in a para position. It is a white granular solid...
is called an MQ developer. This combination of agents provide greater developer activity since the rate of development by both agents together is greater than the sum of rates of developments by each agent used alone (superadditivity
Superadditive developer
Photographic developer solutions may contain more than one developing agents, such as Metol and hydroquinone, or Phenidone and hydroquinone. This is because they work together to a synergistic effect, called superadditive development.-Definition:...
). This combination is very versatile; by varying the quantities of Metol, hydroquinone, restrainer, and adjusting the pH, the entire range of continuous tone developers can be made. Therefore, Metol replaced most other developing agents except for hydroquinone, Phenidone
Phenidone
Phenidone is an organic chemical compound whose primary use is as a photographic developer. It has five to ten times the developing power as Metol. It also has low toxicity and, unlike some other developers, does not cause dermatitis upon skin contact.Phenidone is Ilford's trademark for this...
(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 discovered in 1891 that methylated p-aminophenol has more vigorous developing action than p-aminophenol, and Julius Hauff introduced this compound as a developing agent. (Hauff operated a chemical business for which Bogisch worked.) Exact description of Bogisch and Hauff's early Metol is indefinitive, but it is most likely methylated at the ortho position of the phenol group (p-amino-o-methylphenol), rather than at the amino group. Some time after, Metol became to mean N-methylated variety and o-methylated variety had fallen out of use. Aktien-Gesellschaft fuer Anilinfabrikation (AGFA) sold this compound under trade name Metol and it became by far the most common name, followed by Eastman Kodak's trade name Elon.Because it has been in use for this purpose for over 100 years and often by amateur photographers, there is a wide body of evidence about the health problems that contact with Metol can cause. These are principally local dermatitis
Dermatitis
-Etymology:Dermatitis derives from Greek derma "skin" + -itis "inflammation" and genetic disorder.-Terminology:There are several different types of dermatitis. The different kinds usually have in common an allergic reaction to specific allergens. The term may describe eczema, which is also called...
of the hands and fore-arms as well as some evidence of sensitization dermatitis in which subsequent exposure triggers of a chronic condition that is resistant to medication. The use of Metol in highly caustic solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
s and the presence of other materials in darkrooms that have been implicated in dermatitis such as Cr(VI) salts
Hexavalent chromium
Hexavalent chromium refers to chemical compounds that contain the element chromium in the +6 oxidation state. Virtually all chromium ore is processed via hexavalent chromium, specifically the salt sodium dichromate. Approximately of hexavalent chromium were produced in 1985...
may exacerbate some health impacts.