Editing Metol

{{short description|Reducing aromatic compound used as developing agent in black and white photography}}
{{Use dmy dates|date=July 2020}}
{{chembox
| verifiedrevid = 444014995
| Name = Metol
| ImageFile = Metol Structural Formula V2.svg
| ImageName = 
| IUPACName = 4-(methylamino)phenol sulfate
| OtherNames = ''N''-methyl-p-aminophenol sulfate, Pictol, p-(methylamino)phenol sulfate, monomethyl-p-aminophenol hemisulfate, Metol, Elon, Rhodol, Enel, Viterol, Scalol, Genol, Satrapol, Photol. 
|Section1={{Chembox Identifiers
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = D3W0VWG12M
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 55413
| SMILES = O=S(=O)(O)O.Oc1ccc(NC)cc1.Oc1ccc(NC)cc1
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 5717
| PubChem = 5930
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = C11206
| 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)
| InChIKey = ZVNPWFOVUDMGRP-UHFFFAOYAW
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 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)
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = ZVNPWFOVUDMGRP-UHFFFAOYSA-N
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 55-55-0
| RTECS = 
  }}
|Section2={{Chembox Properties
| Formula = (C<sub>7</sub>H<sub>10</sub>NO)<sub>2</sub>SO<sub>4</sub>
| MolarMass = 344.38 g/mol
| Appearance = 
| Density = 
| Solubility =
| MeltingPtC = 260
| BoilingPt = 
| pKa = 
| pKb = 
| Viscosity = 
  }}
|Section7={{Chembox Hazards
| ExternalSDS =[http://msds.chem.ox.ac.uk/ME/4-(methylamino)phenol_sulfate.html Oxford MSDS]
| MainHazards = 
| GHSPictograms = {{GHS08}}{{GHS07}}{{GHS09}}
| GHSSignalWord = warning
| HPhrases      = {{HPhrases|H302|H317|H373|H410}}
| PPhrases      = {{PPhrases|P260|P280|P301+P312+P330}}
| GHS_ref       = <ref>GHS: [https://gestis.dguv.de/data?name=022920 GESTIS 022920]</ref>
| FlashPt = 
}}
|Section8={{Chembox Related
| OtherAnions =
| OtherCompounds = 
  }}
}}
'''Metol'''  is a trade name for the [[organic compound]] with the formula [HOC<sub>6</sub>H<sub>4</sub>NH<sub>2</sub>(CH<sub>3</sub>)]<sub>2</sub>HSO<sub>4</sub>. It is the [[hydrogen sulfate|sulfate]] salt of ''N''-methylaminophenol. This colourless salt is a popular [[photographic developer]] used in [[monochrome photography]].<ref name=Ullmann>Gerd Löbbert "Photography" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. {{doi| 10.1002/14356007.a20_001}}</ref>

==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]] with [[methylamine]].<ref>{{cite journal | doi = 10.1021/ja01459a014 | year = 1919 | author = Harger, Rolla N. | journal = [[J. Am. Chem. Soc.]] | title = Preparation of Metol | volume = 41 | pages = 270–276 | issue = 2| url = https://zenodo.org/record/1428838 }}</ref>

Being an electron-rich arene, metol is readily degraded by [[hydrogen peroxide]].<ref>{{cite journal |doi=10.1016/s0043-1354(99)00339-5 |title=Degradation of Photographic Developers by Fenton's Reagent: Condition Optimization and Kinetics for Metol Oxidation |date=2000 |last1=Lunar |first1=L. |journal=Water Research |volume=34 |issue=6 |pages=1791–1802 }}</ref>

==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 ([[superadditive developer|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. 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|''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.

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.<ref>{{cite journal |doi=10.1021/tx060121y |title=Electrophilic Chemistry Related to Skin Sensitization. Reaction Mechanistic Applicability Domain Classification for a Published Data Set of 106 Chemicals Tested in the Mouse Local Lymph Node Assay |date=2007 |last1=Roberts |first1=David W. |last2=Aptula |first2=Aynur O. |last3=Patlewicz |first3=Grace |journal=Chemical Research in Toxicology |volume=20 |issue=1 |pages=44–60 |pmid=17226926 }}</ref>

==References==
{{Reflist}}

[[Category:Photographic chemicals]]
[[Category:4-Hydroxyphenyl compounds]]