Editing Creosote (section)

==Creosote oils==
The term creosote has a broad range of definitions depending on the origin of the coal tar oil and end-use of the material.

With respect to [[wood preservation|wood preservative]]s, the United States Environmental Protection Agency (EPA) considers the term ''creosote'' to mean a [[pesticide]] for use as a wood preservative meeting the American Wood Protection Association (AWPA) Standards P1/P13 and P2.<ref>Communication between United States Environmental Protection Agency and the Creosote Council.{{Full citation needed|date=April 2019}}</ref> The AWPA Standards require that creosote "shall be a pure coal tar product derived entirely from tar produced by the [[carbonization]] of bituminous coal."<ref name="United States Environmental Protection Agency-2008"/><ref name=ReferenceA>{{cite book |publisher=American Wood Protection Association |title=2013 AWPA Book of Standards}}</ref>

Currently, all creosote-treated wood products—foundation and [[deep foundation#Timber|marine pilings]], lumber, posts, [[railroad tie]]s, timbers, and utility poles—are manufactured using this type of wood preservative. The manufacturing process can only be a pressure process under the supervision of a licensed applicator certified by the State Departments of Agriculture. No brush-on, spray, or non-pressure uses of creosote are allowed, as specified by the EPA-approved label for the use of creosote.<ref name="United States Environmental Protection Agency-2008"/>

The use of creosote according to the AWPA Standards does not allow for mixing with other types of "creosote type" materials—such as lignite-tar creosote, oil-tar creosote, peat-tar creosote, water-gas-tar creosote, or wood-tar creosote. The AWPA Standard P3 does however, allow blending of a high-boiling petroleum oil meeting the AWPA Standard P4.<ref name=ReferenceA/><ref name=MacLean1952/>

The information that follows describing the other various types of creosote materials and its uses should be considered as primarily being of only historical value.{{citation needed|date=December 2017}} This history is important, because it traces the origin of these different materials used during the 19th and early 20th centuries. Furthermore, it must be considered that these other types of creosotes – lignite-tar, wood-tar, water-gas-tar, etc. – are not currently{{when|date=December 2017}} being manufactured and have either been replaced with more-economical materials, or replaced by products that are more efficacious or safer.{{citation needed|date=December 2017}}

For some part of their history, coal-tar creosote and wood-tar creosote were thought to have been equivalent substances—albeit of distinct origins—accounting for their common name; the two were determined only later to be chemically different. All types of creosote are composed of [[phenol]] derivatives and share some quantity of monosubstituted phenols,<ref name=roscoe37/> but these are not the only active element of creosote. For their useful effects, coal-tar creosote relies on the presence of [[naphthalene]]s and [[anthracene]]s, while wood-tar creosote relies on the presence of methyl ethers of phenol. Otherwise, either type of tar would dissolve in water.

Creosote was first discovered in its wood-tar form in 1832, by [[Carl Reichenbach]], when he found it both in the tar and in [[pyroligneous acid]]s obtained by a [[dry distillation]] of beechwood. Because pyroligneous acid was known as an [[antiseptic]] and meat [[preservative]], Reichenbach conducted experiments by dipping meat in a dilute solution of distilled creosote. He found that the meat was dried without undergoing [[putrefaction]] and had attained a smoky flavor.<ref name=roscoe33/> This led him to reason that creosote was the antiseptic component contained in smoke, and he further argued that the creosote he had found in wood tar was also in coal tar, as well as amber tar and animal tar, in the same abundance as in wood tar.<ref name=schorlemmer152/>

Soon afterward, in 1834, [[Friedrich Ferdinand Runge]] discovered carbolic acid ([[phenol]]) in coal-tar, and [[Auguste Laurent]] obtained it from "phenylhydrate", which was soon determined to be the same compound. There was no clear view on the relationship between carbolic acid and creosote; Runge described it as having similar caustic and antiseptic properties, but noted that it was different, in that it was an acid and formed salts. Nonetheless, Reichenbach argued that creosote was also the active element, as it was in pyroligneous acid. Despite evidence to the contrary, his view held sway with most chemists, and it became commonly accepted wisdom that creosote, carbolic acid, and phenylhydrate were identical substances, with different degrees of purity.<ref name=schorlemmer152/>

Carbolic acid was soon commonly sold under the name "creosote", and the scarcity of wood-tar creosote in some places led chemists to believe that it was the same substance as that described by Reichenbach. In the 1840s, [[Eugen Freiherr von Gorup-Besanez]], after realizing that two samples of substances labelled as creosote were different, started a series of investigations to determine the chemical nature of carbolic acid, leading to a conclusion that it more resembled chlorinated quinones and must have been a different, entirely unrelated substance.

Independently, there were investigations into the chemical nature of creosote. A study by [[Friedrich Karl Völkel|F.K. Völkel]] revealed that the smell of purified creosote resembled that of [[guaiacol]], and later studies by [[Heinrich Hlasiwetz]] identified a substance common to guaiacum and creosote that he called creosol, and he determined that creosote contained a mixture of creosol and guaiacol. Later investigations by Gorup-Besanez, [[A.E. Hoffmann]], and [[Siegfried Marasse]] showed that wood-tar creosote also contained phenols, giving it a feature in common with coal-tar creosote.<ref name=schorlemmer153/>

Historically, coal-tar creosote has been distinguished from what was thought of as creosote proper—the original substance of Reichenbach's discovery—and it has been referred to specifically as "creosote oil". But, because creosote from coal-tar and wood-tar are obtained from a similar process and have some common uses, they have also been placed in the same class of substances, with the terms "creosote" or "creosote oil" referring to either product.<ref name=overton7/>

===Wood-tar creosote===
{| style="background:#F9F9F9; border:1px solid #AAA; padding:5px; float:right; margin-left:20px;"
|
{| style="font-size:12px; text-align:right;"
|+ style="text-align:left; padding-left:5px; padding-bottom:10px; font-size:13.5px;" | Constituency of distillations of creosote from different woods at different temperatures<ref name=allen353/><ref name=apa1073/><ref name=rcs294/>
! scope="col" style="font-size:13px;" |
! scope="col" colspan="2" style="font-size:13px; padding-left:20px; text-align:center; border-bottom:1px solid #AAA;" | [[Beech]]
! scope="col" style="font-size:13px; padding-left:20px; text-align:center; border-bottom:1px solid #AAA;" | [[Oak]]
! scope="col" style="font-size:13px; padding-left:20px; text-align:center; border-bottom:1px solid #AAA;" | [[Pine]]
|-
! scope="row" style="font-size:11px;" |
! scope="col" style="padding-left:20px;" | 200&ndash;220&nbsp;°C
! scope="col" style="padding-left:20px;" | 200&ndash;210&nbsp;°C
! scope="col" style="padding-left:20px;" | 200&ndash;210&nbsp;°C
! scope="col" style="padding-left:20px;" | 200&ndash;210&nbsp;°C
|-
! scope="row" style="text-align:left;" | [[Monophenols]]
| 39.0 %|| 39.0 %|| 55.0 %|| 40.0%
|-
! scope="row" style="text-align:left;" | [[Guaiacol]]
| 19.7 %|| 26.5 %|| 14.0 %|| 20.3%
|-
! scope="row" style="text-align:left;" | [[Creosol]] and [[Homologous series|homologs]]
| 40.0% || 32.1% || 31.0% || 37.5%
|-
! scope="row" style="text-align:left;" | Loss
| 1.3% || 2.4% || . . . || 2.2%
|-
|}
|}
Wood-tar creosote is a colourless to yellowish greasy liquid with a smoky odor, produces a sooty flame when burned, and has a burned taste. It is non-buoyant in water, with a [[specific gravity]] of 1.037 to 1.087, retains fluidity at a very low temperature, and boils at 205-225&nbsp;°C. In its purest form, it is transparent. Dissolution in water requires up to 200 times the amount of water as the base creosote.<ref name=nickels614/> This creosote is a combination of natural [[phenols]]: primarily [[guaiacol]] and [[creosol]] (4-methylguaiacol), which typically constitutes 50% of the oil; second in prevalence are [[cresol]] and [[xylenol]]; the rest being a combination of [[monophenols]] and [[polyphenol]]s.
{| style="background:#F9F9F9; border:1px solid #AAA; padding:5px; float:left; margin-right:20px;"
|
{| class="sortable" style="font-size:12px; text-align:right;"
|+ style="text-align:left; padding-left:5px; padding-bottom:10px; font-size:13.5px;" | Composition of a typical beech-tar creosote<ref name=allen353/><ref name=lee1483/>
! class="unsortable" style="text-align:left; padding-right:20px;" |
| class="unsortable" |
|
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | [[Phenol]]
| class="unsortable" style="text-align:left; padding-right:20px;" | {{chem2|C6H5OH}}
| 5.2%
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | [[o-Cresol]]
| class="unsortable" style="text-align:left; padding-right:20px;" | {{chem2|(CH3)C6H4(OH)}}
| 10.4%
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | [[m-Cresol]] and [[p-cresol]]
| class="unsortable" style="text-align:left; padding-right:20px;" | {{chem2|(CH3)C6H4(OH)}}
| 11.6%
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | [[2-Ethylphenol]]
| class="unsortable" style="text-align:left; padding-right:20px;" | {{chem2|C6H4(C2H5)OH}}
| 3.6%
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | [[Guaiacol]]
| class="unsortable" style="text-align:left; padding-right:20px;" | {{chem2|C6H4(OH)(OCH3)}}
| 25.0%
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | 3,4-[[Xylenol]]
| class="unsortable" style="text-align:left; padding-right:20px;" | {{chem2|C6H3(CH3)2OH}}
| 2.0%
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | [[3,5-Xylenol]]
| class="unsortable" style="text-align:left; padding-right:20px;" | {{chem2|C6H3(CH3)2OH}}
| 1.0%
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | Various phenols
| class="unsortable" style="text-align:left; padding-right:20px;" | {{chem2|C6H5OH}}&mdash;
| 6.2%
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | [[Creosol]] and [[Homologous series|homologs]]
| class="unsortable" style="text-align:left; padding-right:20px;" | {{chem2|C6H3(CH3)(OH)(OCH3)}}&mdash;
| 35.0%
|-
|}
|}
The simple phenols are not the only active element in wood-tar creosote. In solution, they [[coagulation|coagulate]] [[albumin]], which is a water-soluble protein found in meat, so they serve as a preserving agent, but also cause denaturation. Most of the phenols in the creosote are [[methoxy]] derivatives: they contain the [[methoxy group]] {{chem2|(\sO\sCH3)}} linked to the [[benzene]] nucleus. The high level of methyl derivates created from the action of heat on wood (also apparent in the methyl alcohol produced through distillation) make wood-tar creosote substantially different from coal-tar creosote. Guaiacol is a [[methyl group|methyl]] [[ether]] of [[pyrocatechin]], while creosol is a methyl ether of methyl-pyrocatechin, the next [[Homologous series|homolog]] of pyrocatechin. Methyl ethers differ from simple phenols in being less hydrophilic, caustic, and poisonous.<ref name=psgb468/> This allows meat to be successfully preserved without tissue denaturation, and allows creosote to be used as a medical ointment.<ref name=allen348/>
{| style="background:#F9F9F9; border:1px solid #AAA; padding:5px; float:right; margin-left:20px;"
|
{| style="font-size:12px; text-align:left;"
|+ style="text-align:left; padding-left:5px; padding-bottom:10px; font-size:13.5px;" | Derivation of wood-tar creosote from resinous woods<ref name=overton13/>
|
[[File:Derivation of wood-tar creosote.svg|frameless|upright=1.5]]
|}
|}
Because wood-tar creosote is used for its guaiacol and creosol content, it is generally derived from [[beech tree|beechwood]] rather than other woods, since it distills with a higher proportion of those chemicals to other phenolics. The creosote can be obtained by distilling the wood tar and treating the fraction heavier than water with a sodium hydroxide solution. The alkaline solution is then separated from the insoluble oily layer, boiled in contact with air to reduce impurities, and decomposed by diluted sulfuric acid. This produces a crude creosote, which is purified by re-solution in alkali, re-precipitation with acid, then redistilled with the fraction passing over between 200° and 225° constituting the purified creosote.<ref name=allen347/>

When ferric chloride is added to a dilute solution, it will turn green: a characteristic of ortho-oxy derivatives of benzene.<ref name=psgb468/> It dissolves in sulfuric acid to a red liquid, which slowly changes to purple-violet. Shaken with hydrochloric acid in the absence of air, it becomes red, the color changing in the presence of air to dark brown or black.<ref name=allen348/>

In preparation of food by [[smoking (food)|smoking]], [[guaiacol]] contributes mainly to the smoky [[taste]], while the dimethyl ether of [[pyrogallol]], [[syringol]], is the main chemical responsible for the smoky [[aroma]].

====Historical uses====

=====Industrial=====
Soon after it was discovered and recognized as the principle of meat smoking, wood-tar creosote became used as a replacement for the process. Several methods were used to apply the creosote. One was to dip the meat in pyroligneous acid or a water of diluted creosote, as Reichenbach did, or brush it over with them, and within one hour the meat would have the same quality of that of traditionally smoked preparations.<ref name=abel23/> Sometimes the creosote was diluted in vinegar rather than water, as vinegar was also used as a preservative.<ref name=letheby225/> Another was to place the meat in a closed box, and place with it a few drops of creosote in a small bottle. Because of the volatility of the creosote, the atmosphere was filled with a vapour containing it, and it would cover the flesh.<ref name=abel23/>

The application of wood tar to seagoing vessels was practiced through the 18th century and early 19th century, before the creosote was isolated as a compound. Wood-tar creosote was found not to be as effective in wood treatments, because it was harder to infuse the creosote into the wood cells, but still experiments<ref name=joerin767/> were done, including by many governments, because it proved to be less expensive on the market.<ref name=bradbury107/>

=====Medical=====
Even before creosote as a chemical compound was discovered, it was the chief active component of medicinal remedies in different cultures around the world.

In antiquity, pitches and resins were used commonly as medicines. [[Pliny the Elder|Pliny]] mentions a variety of tar-like substances being used as medicine, including ''cedria'' and ''pissinum''.<ref name=cormack58/> ''Cedria'' was the pitch and resin of the cedar tree, being equivalent to the oil of tar and pyroligneous acid which are used in the first stage of distilling creosote.<ref name=parr383/><ref name=pliny8/> He recommends cedria to ease the pain in a toothache, as an injection in the ear in case of hardness of hearing, to kill parasitic worms, as a preventive for infusion, as a treatment for [[phthiriasis]] and [[wikt:porrigo|porrigo]], as an antidote for the poison of the [[sea hare]], as a liniment for [[elephantiasis]], and as an ointment to treat [[ulcer]]s both on the skin and in the lungs.<ref name=pliny8/> He further speaks of cedria being used as the embalming agent for preparing mummies.<ref name=cormack58/> ''Pissinum'' was a tar water that was made by boiling cedria, spreading wool fleeces over the vessels to catch the steam, and then wringing them out.<ref name=berkeley9/><ref name=pliny290/>

[[File:John Smibert - Bishop George Berkeley - Google Art Project.jpg|thumb|left|upright|Portrait of [[George Berkeley|Bishop Berkeley]] by [[John Smybert]], 1727]]
The ''Pharmacopée de Lyon'', published in 1778, says that cedar tree oil is believed to cure vomiting and help medicate tumors and ulcers.<ref name=cormack59/><ref name=vitet427/> Physicians contemporary to the discovery of creosote recommended ointments and pills made from tar or pitch to treat skin diseases.<ref name=cormack59/> [[Tar water]] had been used as a folk remedy since the Middle Ages to treat affections like dyspepsia. [[George Berkeley|Bishop Berkeley]] wrote several works on the medical virtues of tar water, including a philosophical work in 1744 titled ''Siris: a chain of philosophical reflexions and inquiries concerning the virtues of tar water, and divers other subjects connected together and arising one from another'', and a poem where he praised its virtues.<ref name=cd300/> Pyroligneous acid was also used at the time in a medicinal water called ''Aqua Binelli'' (Binelli's water),<ref name=cormack59/> a compound which its inventor, the Italian Fedele Binelli, claimed to have [[Hemostasis|hemostatic]] properties in his research published in 1797.{{sfn|Tsiamis |Sgantzou |Popoti |Papavramidou |2020}} These claims have since been disproven.{{sfn|Tsiamis |Sgantzou |Popoti |Papavramidou |2020}}{{sfn|Simon|1833}}{{sfn|Dunglison|1846|pp=64–65}}

Given this history, and the antiseptic properties known to creosote, it became popular among physicians in the 19th century. A dilution of creosote in water was sold in pharmacies as ''Aqua creosoti'', as suggested by the previous use of pyroligneous acid. It was prescribed to quell the irritability of the stomach and bowels and detoxify, treat ulcers and abscesses, neutralize bad odors, and stimulate the mucous tissues of the mouth and throat.<ref name=king617/><ref name=taylor207/> Creosote in general was listed as an [[irritation|irritant]], [[styptic]], [[antiseptic]], [[narcotic]], and [[diuretic]], and in small doses when taken internally as a [[sedative]] and [[anaesthetic]]. It was used to treat ulcers, and as a way to sterilize the tooth and deaden the pain in case of a tooth-ache.<ref name=king617/>

Creosote was suggested as a treatment for tuberculosis by Reichenbach as early as 1833. Following Reichenbach, it was argued for by [[John Elliotson]] and Sir [[John Rose Cormack]].<ref name=king617/> Elliotson, inspired by the use of creosote to arrest vomiting during an outbreak of [[cholera]], suggested its use for tuberculosis through inhalation. He also suggested it for epilepsy, neuralgia, diabetes, and chronic [[glanders]].<ref name=whittaker77/> The idea of using it for tuberculosis failed to be accepted. Use for this purpose was dropped, until the idea was revived in 1876 by British doctor [[G. Anderson Imlay]], who suggested it be applied locally by spray to the bronchial mucous membrane.<ref name=king617/><ref name=imlay514/><ref name=dobbell315/> This was followed up in 1877 when it was argued for in a clinical paper by [[Charles-Joseph Bouchard|Charles Bouchard]] and [[Henri Gimbert]].<ref name=kinnicut514/> Germ theory had been established by [[Louis Pasteur|Pasteur]] in 1860, and Bouchard, arguing that a [[bacillus]] was responsible for the disease, sought to rehabilitate creosote for its use as an antiseptic to treat it. He began a series of trials with Gimbert to convince the scientific community, and claimed a promising cure rate.<ref name=contrepois211/> A number of publications in Germany confirmed his results in the following years.<ref name=kinnicut514/>

Later, a period of experimentation with different techniques and chemicals using creosote in treating tuberculosis lasted until about 1910, when radiation therapy seemed more promising. Guaiacol, instead of a full creosote solution, was suggested by [[Hermann Sahli]] in 1887. He argued it had the active chemical of creosote and had the advantage of being of definite composition and having a less unpleasant taste and odor.<ref name=kinnicut515/> A number of solutions of both creosote and guaiacol appeared on the market, such as ''phosphotal'' and ''guaicophosphal'', phosphites of creosote and guaiacol; ''eosot'' and ''geosot'', valerinates of creosote and guaicol; ''phosot'' and ''taphosot'', phosphate and tannophospate of creosote; and ''creosotal'' and ''tanosal'', tannates of creosote.<ref name=coblentz/> Creosote and eucalyptus oil were also a remedy used together, administered through a vaporizor and inhaler. Since then, more effective and safer treatments for tuberculosis have been developed.

In the 1940s, Canadian-based [[Eldon Boyd]] experimented with guaiacol and a recent synthetic modification—glycerol guaiacolate ([[guaifenesin]])—on animals. His data showed that both drugs were effective in increasing secretions into the airways in laboratory animals, when high-enough doses were given.{{citation needed|date=August 2020}}

====Current uses====

=====Industrial=====
Wood-tar creosote is to some extent used for [[wood preservation]], but it is generally mixed with coal-tar creosote, since the former is not as effective. Commercially available preparations of "[[liquid smoke]]", marketed to add a smoked flavour to meat and aid as a preservative, consist primarily of creosote and other constituents of smoke.<ref name=chenoweth206/> Creosote is the ingredient that gives liquid smoke its function; guaicol lends to the taste and the creosote oils help act as the preservative. Creosote can be destroyed by treatment with chlorine, either [[sodium hypochlorite]], or [[calcium hypochlorite]] solutions. The phenol ring is essentially opened, and the molecule is then subject to normal digestion and normal respiration.{{Citation needed|date=August 2019}}

=====Medical=====
The [[guaifenesin]] developed by Eldon Boyd is still commonly used today as an [[expectorant]], sold over the counter, and usually taken by mouth to assist the bringing up of phlegm from the airways in acute respiratory tract infections. Guaifenesin is a component of [[Mucinex]], [[Robitussin DAC]], [[Cheratussin DAC]], [[Robitussin AC]], [[Cheratussin AC]], [[Benylin]], [[DayQuil]] Mucous Control, Meltus, and Bidex 400.{{Citation needed|date=September 2021}}

[[Seirogan]] is a popular [[Kampo]] medicine in Japan, used as an anti-diarrheal, and has 133&nbsp;mg wood creosote from beech, pine, maple or oak wood per adult dose as its primary ingredient. Seirogan was first used as a gastrointestinal medication by the Imperial Japanese Army in Russia during the [[Russo-Japanese War]] of 1904 to 1905.<ref name=seirogan/>

[[Creomulsion]] is a cough medicine in the United States, introduced in 1925, that is still sold and contains beechwood creosote. Beechwood creosote is also found under the name ''kreosotum'' or ''kreosote''.

===Coal-tar creosote===
{| style="background:#F9F9F9; border:1px solid #AAA; padding:5px; float:right; margin-left:20px; width:375px"
|
{| class="sortable" style="font-size:12px; text-align:right;"
|+ style="text-align:left; padding-left:5px; padding-bottom:10px; font-size:13.5px;" | Composition of a typical coal-tar creosote<ref name=melber11/><ref name=speight456/>
! class="unsortable" style="text-align:left; padding-right:20px; width:230px" |
|
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | [[Aromatic hydrocarbons]]
<span style="font-weight:normal>Polycyclic aromatic hydrocarbons ([[Polycyclic aromatic hydrocarbon|PAHs]]), alkylated PAHs, [[benzene]]s, [[toluene]]s, [[ethylbenzene]]s, and [[xylene]]s ([[BTEX]])</span>
| 75.0–90.0%
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | [[Tar acids]] / [[phenol]]ics
<span style="font-weight:normal>Phenols, cresols, xylenols, and naphthols</span>
| 5.0–17.0%
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | [[Tar bases]] / [[nitrogen]]-containing heterocycles
<span style="font-weight:normal>Pyridines, quinolines, benzoquinolines, acridines, indolines, and carbazoles</span>
| 3.0–8.0%
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | [[Sulfur]]-containing [[heterocyclic compound|heterocycles]]
<span style="font-weight:normal>[[Benzothiophene]]s</span>
| 1.0–3.0%
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | [[Oxygen]]-containing heterocycles
<span style="font-weight:normal>Dibenzofurans</span>
| 1.0–3.0%
|-
! class="unsortable" style="text-align:left; padding-right:20px;" | [[Aromatic amine]]s
<span style="font-weight:normal>Aniline, aminonaphthalenes, [[diphenylamine]]s, aminofluorenes, and aminophenanthrenes, cyano-PAHs, benz acridines</span>
|0.1–1.0%
|-
|}
|}
Coal-tar creosote is greenish-brown liquid, with different degrees of darkness, viscosity, and fluorescence depending on how it is made. When freshly made, the creosote is a yellow oil with a greenish cast and highly fluorescent, and the fluorescence is increased by exposure to air and light. After settling, the oil is dark green by reflected light and dark red by transmitted light.<ref name=allen366/> To the naked eye, it generally appears brown. The creosote (often called "creosote oil") consists almost wholly of [[aromatic hydrocarbon]]s, with some amount of bases and acids and other neutral oils. The flash point is 70&ndash;75&nbsp;°C and burning point is 90&ndash;100&nbsp;°C,<ref name=bateman50/> and when burned it releases a greenish smoke.<ref name=nickels615/> The smell largely depends on the naphtha content in the creosote. If there is a high amount, it will have a naphtha-like smell, otherwise it will smell more of tar.

In the process of coal-tar distillation, the distillate is collected into four fractions; the "light oil", which remains lighter than water, the "middle oil" which passes over when the light oil is removed; the "heavy oil", which sinks; and the "[[anthracene oil]]", which when cold is mostly solid and greasy, of a buttery consistence. Creosote refers to the portion of coal tar which distills as "heavy oil", typically between 230 and 270&nbsp;°C, also called "dead oil"; it sinks into water but still is fairly liquid. Carbolic acid is produced in the second fraction of distillation and is often distilled into what is referred to as "[[carbolic oil]]".<ref name=philips255/><ref name=martin416/><ref name=nelson204/><ref name=noller185/>
{| style="background:#F9F9F9; border:1px solid #AAA; padding:5px; float:left; margin-right:20px;"
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{| style="font-size:12px; text-align:left;"
|+ style="text-align:left; padding-left:5px; padding-bottom:10px; font-size:13.5px;" | Derivation and general composition of coal-tar creosote<ref name=overton12/>
|
[[File:Derivation of coal-tar creosote.svg|frameless|upright=2]]
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Commercial creosote contains substances from six groups.<ref name=melber11/> The two groups occur in the greatest amounts and are the products of the distillation process—the "[[tar acids]]", which distill below 205&nbsp;°C and consist mainly of phenols, cresols, and xylenols, including carbolic acid—and [[aromatic hydrocarbon]]s, which divide into [[naphthalene]]s, which distill approximately between 205 and 255&nbsp;°C, and constituents of an [[anthracene]] nature, which distill above 255&nbsp;°C.<ref name=ec531/> The quantity of each varies based on the quality of tar and temperatures used, but generally, the tar acids won't exceed 5%, the naphthalenes make up 15 to 50%, and the anthracenes make up 45% to 70%.<ref name=ec531/> The hydrocarbons are mainly aromatic; derivatives of benzene and related cyclic compounds such as [[naphthalene]], [[anthracene]], [[phenanthrene]], [[acenaphthene]], and [[fluorene]]. Creosotes from vertical-retort and low temperature tars contain, in addition, some paraffinic and olefinic hydrocarbons. The tar-acid content also depends on the source of the tar—it may be less than 3% in creosote from coke-oven tar and as high as 32% in creosote from vertical retort tar.<ref name=greenhow58/> All of these have antiseptic properties. The tar acids are the strongest antiseptics but have the highest degree of solubility in water and are the most volatile; so, like with wood-tar creosote, phenols are not the most valued component, as by themselves they would lend to being poor preservatives.<ref name=arbba287/> In addition, creosote contains several products naturally occurring in coal—nitrogen-containing heterocycles, such as acridines, carbazoles, and quinolines, referred to as the "[[tar bases]]" and generally make up about 3% of the creosote—sulfur-containing heterocycles, generally [[benzothiophene]]s<ref name=orr39/>—and oxygen-containing heterocycles, dibenzofurans.<ref name=speight77/> Lastly, creosote contains a small number of [[aromatic amine]]s produced by the other substances during the distillation process and likely resulting from a combination of [[thermolysis]] and [[hydrogenation]].<ref name=orr255/><ref name=bateman47/> The tar bases are often extracted by washing the creosote with aqueous mineral acid,<ref name=greenhow58/> although they're also suggested to have antiseptic ability similar to the tar acids.

Commercially used creosote is often treated to extract the carbolic acid, naphthalene, or anthracene content. The carbolic acid or naphthalene is generally extracted to be used in other commercial products.<ref name=mushrush115/> In the early 20th century, American-produced creosote oils typically had low amounts of anthracene and high amounts of naphthalene, because when forcing the distillate at a temperature that produces anthracene the soft pitch will be ruined and only the hard pitch will remain; this ruined it for [[Bituminous waterproofing|use in roofing purposes]] (which was common before widespread availability of cheap oil bitumen) and only left a product which wasn't commercially useful.<ref name=bateman47/>

====Historical uses====

=====Industrial=====
The use of coal-tar creosote on a commercial scale began in 1838, when a patent covering the use of creosote oil to treat timber was taken out by inventor [[John Bethell (inventor)|John Bethell]]. The "Bethell process"—or as it later became known, the [[full-cell process (wood processing)|full-cell process]]—involves placing wood to be treated in a sealed chamber and applying a vacuum to remove air and moisture from wood "cells". The wood is then pressure-treated to imbue it with creosote or other preservative chemicals, after which vacuum is reapplied to separate the excess treatment chemicals from the timber. Alongside the zinc chloride-based [[Sir William Burnett|"Burnett process"]], use of creosoted wood prepared by the Bethell process became a principal way of preserving railway timbers (most notably railway sleepers) to increase the lifespan of the timbers, and avoiding having to regularly replace them.<ref name=angier408/>

Besides treating wood, it was also used for lighting and fuel. In the beginning, it was only used for lighting needed in harbour and outdoor work, where the smoke that was produced from burning it was of little inconvenience. By 1879, lamps had been created that ensured a more complete combustion by using compressed air, removing the drawback of the smoke. Creosote was also processed into gas and used for lighting that way. As a fuel, it was used to power ships at sea and blast furnaces for different industrial needs, once it was discovered to be more efficient than unrefined coal or wood. It was also used industrially for the softening of hard pitch, and burned to produce [[lamp black]]. By 1890, the production of creosote in the [[United Kingdom]] totaled approximately 29,900,000 gallons per year.<ref name=nickels615/>

In 1854, [[Alexander McDougall]] and [[Robert Angus Smith]] developed and patented a product called [[McDougall's Powder]] as a sewer deodorant; it mainly consisted of [[phenol|carbolic acid]] derived from creosote. McDougall, in 1864, experimented with his solution to remove [[entozoa]] parasites from cattle pasturing on a sewage farm.<ref name=brock91/> This later led to widespread use of creosote as a cattle wash and [[sheep dip]]. External parasites would be killed in a creosote diluted dip, and drenching tubes would be used to administer doses to the animals' stomachs to kill internal parasites.<ref name=salmon7/>

[[File:Wood Pavers (36011657806).jpg|thumb|Wooden street pavers in Chicago]]
Creosoted wood blocks were a common road-paving material in the late 19th and early 20th centuries, but ultimately fell out of favor because they did not generally hold up well enough over time.<ref>{{cite web |title=Ames Street Paving |publisher=Ames History Museum |location=Ames, Iowa |url=https://ameshistory.org/content/ames-street-paving |access-date=2023-01-25}}</ref><ref>{{cite journal |title=(untitled advertisement) |journal=The Town Crier |volume=10 |issue=32 |page=7 |location=Seattle |date=1915-08-07 |url=https://commons.wikimedia.org/wiki/File:The_Town_Crier,_v.10,_no.32,_Aug._7,_1915_-_DPLA_-_9f439e1283fe9793c210a74b8e85dc66_(page_7).jpg |access-date=2023-01-25}}</ref><ref>{{cite web |last1=Reed |first1=Ryan J. |title=The Creosoted Wood Block: One Step in the Evolution of St. Louis Paving |publisher=Landmarks Association of St. Louis, Inc. |location=St. Louis, Missouri |url=https://www.landmarks-stl.org/news/the_creosoted_wood_block_one_step_in_the_evolution_of_st_louis-paving/ |access-date=2023-01-25}}</ref><ref>{{cite web |title=Historic Wood Paver from Galveston's Market Street |publisher=Rosenberg Library Museum |location=Galveston, Texas |url=https://www.rosenberg-library-museum.org/treasures/historic-wood-paver-from-galvestons-market-street |access-date=2023-01-05}}</ref>

Two later methods for creosoting wood were introduced after the turn of the century, referred to as [[empty-cell process]]es, because they involve compressing the air inside the wood so that the preservative can only coat the inner cell walls rather than saturating the interior cell voids. This is a less effective, though usually satisfactory, method of treating the wood, but is used because it requires less of the creosoting material. The first method, the "Rüping process" was patented in 1902, and the second, the "Lowry process" was patented in 1906. Later in 1906, the "Allardyce process" and "Card process" were patented to treat wood with a combination of both creosote and zinc chloride.<ref name=angier408/> In 1912, it was estimated that a total of 150,000,000 gallons were produced in the US per year.

=====Medical=====
Coal-tar creosote, despite its toxicity, was used as a stimulant and [[escharotic]], as a [[corrosive substance|caustic]] agent used to treat ulcers and malignancies, cauterize wounds, and prevent infection and decay. It was particularly used in dentistry to destroy tissues and arrest necrosis.<ref name=farrar412/><ref name=farrar1/><ref name=pease/>

====Current uses====

=====Industrial=====
Coal-tar creosote is the most widely used wood treatment today; both industrially, processed into wood using pressure methods such as "full-cell process" or "empty-cell process", and more commonly applied to wood through brushing. In addition to toxicity to fungi, insects, and marine borers, it serves as a natural [[water repellent]]. It is commonly used to preserve and waterproof [[railroad tie]]s, pilings, telephone poles, power line poles, marine pilings, and fence posts. Although suitable for use in preserving the structural timbers of buildings, it is not generally used that way because it is difficult to apply. There are also concerns about the environmental impact of the [[#Release into environment|leaching of creosote into aquatic ecosystems]].

Due to its [[carcinogen]]ic character, the European Union has regulated the quality of creosote for the EU market<ref name=cec2001/> and requires that the sale of creosote be limited to professional users.<ref name=cec2007/><ref name=hse2011/> The [[United States Environmental Protection Agency]] regulates the use of coal-tar creosote as a wood preservative under the provisions of the [[Federal Insecticide, Fungicide, and Rodenticide Act]]. Creosote is considered a restricted-use pesticide and is only available to licensed pesticide applicators.<ref name=creosotecouncil/><ref name=ibach141/>

===Oil-tar creosote===
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Oil-tar creosote is derived from the tar that forms when using petroleum or shale oil in the manufacturing of gas. The distillation of the tar from the oil occurs at very high temperatures; around 980&nbsp;°C. The tar forms at the same time as the gas, and once processed for creosotes contains a high percentage of cyclic hydrocarbons, a very low amount of tar acids and tar bases, and no true anthracenes have been identified.<ref name=voorhies/> Historically, this has mainly been produced in the United States on the Pacific coast, where petroleum has been more abundant than coal. Limited quantities have been used industrially, either alone, mixed with coal-tar creosote, or fortified with [[pentachlorophenol]].<ref name=hunt88/>

===Water-gas-tar creosote===
Water-gas-tar creosote is also derived from petroleum oil or shale oil, but by a different process; it is distilled during the production of [[water gas]]. The tar is a by-product resulting from enrichment of water gas with gases produced by thermal decomposition of petroleum. Of the creosotes derived from oil, it is practically the only one used for wood preservation. It has the same degree of solubility as coal-tar creosote and is easy to infuse into wood. Like standard oil-tar creosote, it has a low amount of tar acids and tar bases, and has less antiseptic qualities.<ref name=overton12/> Petri dish tests have shown that water-gas-tar creosote is one-sixth as anti-septically effective as that of coal-tar.<ref name=stimson626/>

===Lignite-tar creosote===
Lignite-tar creosote is produced from [[lignite]] rather than bituminous coal, and varies considerably from coal-tar creosote. Also called "lignite oil", it has a very high content of tar acids, and has been used to increase the tar acids in normal creosote when necessary.<ref name=richardson103/> When it has been produced, it has generally been applied in mixtures with coal-tar creosote or petroleum. Its effectiveness when used alone has not been established. In an experiment with southern yellow pine fence posts in Mississippi, straight lignite-tar creosote was giving good results after about 27 years exposure, although not as good as the standard coal-tar creosote used in the same situation.<ref name=hunt97/>

===Peat-tar creosote===
There have also been attempts to distill creosote from [[peat]]-tar, although mostly unsuccessful due to the problems with winning and drying peat on an industrial scale.<ref name=eb821/> Peat tar by itself has in the past been used as a wood preservative.