Metol

Metol (or Elon) is a trade name for the organic compound with the formula [HOC₆H₄NH₂(CH₃)]₂HSO₄. It is the sulfate salt of N-methylaminophenol. This colourless salt is a popular photographic developer used in monochrome photography.

Metol

Names
IUPAC name 4-(methylamino)phenol sulfate
Other names N-methyl-p-aminophenol sulfate, Pictol, p-(methylamino)phenol sulfate, monomethyl-p-aminophenol hemisulfate, Metol, Elon, Rhodol, Enel, Viterol, Scalol, Genol, Satrapol, Photol.
Identifiers
CAS Number	55-55-0 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:55413 Y
ChemSpider	5717 Y
ECHA InfoCard	100.000.216
KEGG	C11206 Y
PubChem CID	5930
UNII	D3W0VWG12M Y
CompTox Dashboard (EPA)	DTXSID6025565
InChI InChI=1S/2C7H9NO.H2O4S/c2*1-8-6-2-4-7(9)5-3-6;1-5(2,3)4/h2*2-5,8-9H,1H3;(H2,1,2,3,4) Y Key: ZVNPWFOVUDMGRP-UHFFFAOYSA-N Y InChI=1/2C7H9NO.H2O4S/c2*1-8-6-2-4-7(9)5-3-6;1-5(2,3)4/h2*2-5,8-9H,1H3;(H2,1,2,3,4) Key: ZVNPWFOVUDMGRP-UHFFFAOYAW
SMILES O=S(=O)(O)O.Oc1ccc(NC)cc1.Oc1ccc(NC)cc1
Properties
Chemical formula	(C7H10NO)2SO4
Molar mass	344.38 g/mol
Melting point	260 °C (500 °F; 533 K)
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H317, H373, H410
Precautionary statements	P260, P280, P301+P312+P330
Safety data sheet (SDS)	Oxford MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Synthesis

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 with methylamine.

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 hydroquinone 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). 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. 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) sold this compound under the trade name Metol, which 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 substantial body of evidence regarding the health problems that contact with Metol can cause. These are principally local dermatitis of the hands and forearms. There is also some evidence of sensitization dermatitis, in which repeated exposure triggers a chronic condition that is resistant to medication. The use of Metol in highly caustic solutions and the presence of other materials in darkrooms that have been implicated in dermatitis—such as hexavalent chromium salts—may exacerbate some health impacts.