Xylene



Xylene is an organic solvent which is miscible with alcohol and wax. In histochemistry alcohol is used to dehydrate tissue sections and then this alcohol is further replaced by xylene (being miscible with alcohol) in a process called as clearing. After this DPX is used to mount cover slips on the sections. One more use of xylene is to dissolve wax which is used to make sections of tissues. Hence, we see that xylene is a clearing agent capable of dissolving wax as well as alcohol. Xylenes are not highly toxic

** Xylene ** is an [|aromatic hydrocarbon], an [|organic compound] created along with its counterpart [|isomers] , [|benzene] and [|toluene] , by [|extraction] and [|distillation] in the [|petroleum] refining process known as [|catalytic reforming]. Xylene is also created from [|coal carbonisation] in the manufacture of [|coke fuel]. Representing about 0.5–1% of crude oil, depending on the source, xylenes are hence found in small amounts in [|gasoline] and [|airplane fuels]. Xylene is mainly produced as part of the [|BTX] aromatics (benzene, toluene and xylenes) extracted from the product of catalytic reforming known as "reformate". The mixture is a slightly greasy, colourless liquid commonly encountered as a [|solvent]. Several million tons are produced annually. [|[1]] In 2011, a global consortium began construction of one of the world’s largest xylene plants in [|Singapore]. [|[2]]

Properties
Xylene encompasses three isomers of dimethylbenzene. The isomers are distinguished by the designations //ortho//- (//o//-), //meta//- (//m//-), and//para//- (//p//-), which specify to which [|carbon] atoms (of the [|benzene ring] ) the two [|methyl] groups are attached. Counting the carbon [|atoms] from one of the ring carbons bonded to a methyl group, and counting towards the second ring carbon bonded to a methyl group, the //o//- isomer has the [|IUPAC] name of 1,2-dimethylbenzene, the //m//- isomer has the IUPAC name of 1,3-dimethylbenzene, and the //p//- isomer has the IUPAC name of 1,4-dimethylbenzene. Some chemical and physical properties differ from isomer to isomer. The melting point ranges from −47.87 °C (−54.17 °F) (//m//-xylene) to13.26 °C (55.87 °F) (//p//-xylene). The boiling point for each isomer is around 140 °C (284.00 °F). The density of each is around 0.87 g/mL (7.26 [|lb] /U.S. gallon or 8.72 lb/ [|imp gallon] ) and thus is less dense than [|water]. Xylene in air can be smelled at 0.08 to 3.7 parts of xylene per million parts of air (ppm) and can begin to be tasted in water at 0.53 to 1.8 ppm. Orthoxylene || //m//-Xylol; Metaxylene || //p//-Xylol; Paraxylene || [|3]  [|2]   0  || Solid, liquid, gas || hydrocarbons |||||||| toluene, [|mesitylene], benzene, [|ethylbenzene] || materials in their [|standard state (at 25°C, 100 kPa)] [|Infobox disclaimer and references] ||
 * ~ Xylene Isomers ||
 * ~ General ||
 * Common name || **Xylenes** || ** [|o-Xylene] ** || ** [|m-Xylene] ** || ** [|p-Xylene] ** ||
 * [|Systematic name] || Dimethylbenzenes || 1,2-Dimethylbenzene || 1,3-Dimethylbenzene || 1,4-Dimethylbenzene ||
 * Other names || Xylols || //o//-Xylol;
 * [|Molecular formula] |||||||| C8H10, C6H4(CH3)2 or C6H4C2H6 ||
 * [|SMILES] ||  || Cc1c(C)cccc1 || Cc1cc(C)ccc1 || Cc1ccc(C)cc1 ||
 * [|Molar mass] |||||||| 106.16 g/mol ||
 * Appearance |||||||| clear, colorless liquid ||
 * [|CAS number] || [1330-20-7] || [95-47-6] || [108-38-3] || [106-42-3] ||
 * ~ Properties ||
 * [|Density] and [|phase] || 0.864 g/mL, liquid || 0.88 g/mL, liquid || 0.86 g/mL, liquid || 0.86 g/mL, liquid ||
 * [|Solubility] in water |||||||| practically insoluble ||
 * Soluble in non-polar solvents such as [|aromatic] [|hydrocarbons] ||
 * [|Melting point] || −47.4 °C (−53.3 °F; 226 K) || −25 °C (−13 °F; 248 K) || −48 °C (−54.4 °F; 225 K) || 13 °C (55.4 °F; 286 K) ||
 * [|Boiling point] || 138.5 °C (281.3 °F; 412 K) || 144 °C (291.2 °F; 417 K) || 139 °C (282.2 °F; 412 K) || 138 °C (280.4 °F; 411 K) ||
 * [|Viscosity] ||  || 0.812 c [|P] at 20 °C (68 °F) || 0.62 c [|P] at 20 °C (68 °F) || 0.34 c [|P] at 30 °C (86 °F) ||
 * ~ Hazards ||
 * [|MSDS] || Xylenes [|[4]] || [|//o//-Xylene] || [|//m//-Xylene] || [|//p//-Xylene] ||
 * [|EU Classification] |||||||| Harmful (**Xn**) ||
 * [|NFPA 704] |||||||| [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/6/6f/NFPA_704.svg/75px-NFPA_704.svg.png width="75" height="75" caption="NFPA 704.svg" link="http://en.wikipedia.org/wiki/File:NFPA_704.svg"]]
 * [|Flash point] || 30 °C (86 °F) || 17 °C (63 °F) || 25 °C (77 °F) || 25 °C (77 °F) ||
 * [|R/S statement] |||||||| [|R10], [|R20/21] , [|R38] : [|(S2)] , [|S25] ||
 * [|RTECS] number ||  || ZE2450000 || ZE2275000 || ZE2625000 ||
 * ~ [|Supplementary data page] ||
 * [|Structure & properties] |||||||| [|//n//], [|//εr//] , etc. ||
 * [|Thermodynamic data] |||||||| Phase behaviour
 * [|Spectral data] |||||||| [|UV], [|IR] , [|NMR] , [|MS] ||
 * ~ Related compounds ||
 * Related aromatic
 * Related compounds |||||||| xylenols - types of [|phenols] ||
 * = Except where noted otherwise, data are given for

Safety
Xylenes are not highly toxic as indicated by the high values of the [|LD50], which range from 200 to 4000 mg/kg for animals. The principal mechanism of detoxification is oxidation to [|methylbenzoic acid] and hydroxylation to hydroxylene. [|[1]] However, the material safety data sheet (MSDS) rating assigned is for a moderate hazard, indicating safe handling precautions should include goggles, __protective clothing__, ventilation, and proper gloves, with storage of the material in a cool, dry, well-ventilated location since it is highly [|flammable]. [|[4]] **Physical Information** Name: XyeleneUse: [|solvent], cleaning agent, paint thinner; used in printing, rubber, leather industries; found in airplane fuel and gasolineSource: petroleum, coal tarRecommended daily intake: noneAbsorption: dermal, inhalationSensitive individuals: humans and animalsToxicity/symptoms: headaches, lack of __muscle__ coordination, dizziness, confusion, change in sense of balance; skin, eyes, nose, and throat irritation; breathing difficulties; stomach discomfort, possible changes in lung and kidney; death at very high exposure levels (in humans) user:benson7280.csu CNS __depression__ and irritation of eyes and skin (in animals)Regulatory facts: EPA limit = 10ppm drinking water; OSHA 8-hr TWA = 100ppm air Chemical Description

Xylene (in commercial use) is mixture of three isomers: (1.) ortho-xylene, and (2.) meta-xylene are clear, colorless, flammable, sweet-smelling liquid, while (3.) para-xylene, at low temperatures, appear like clear, colorless plates ( [|OSHA] ).



Terephthalic acid and related derivatives
//p//-Xylene is the principal precursor to [|terephthalic acid] and [|dimethyl terephthalate], both [|monomers] used in the production of [|polyethylene terephthalate] (PET) plastic bottles and [|polyester] clothing. 98% of p-xylene production, and half of all xylene, is consumed in this way. [|[7]][|[8]] //o//-Xylene is an important precursor to [|phthalic anhydride]. The demand for [|isophthalic acid] is relatively modest so//m//-xylene is rarely sought (and hence the utility of its conversion to the //o//- and //p//-isomers).

Solvent applications
Xylene is used as a solvent. In this application, the mixture of isomers is often referred to as **xylenes** or **xylol**. Solvent xylene often contains a small percentage of [|ethylbenzene]. Like the individual isomers, the mixture is colorless, sweet-smelling, and highly flammable. Areas of application include [|printing], [|rubber] , and [|leather] industries. It is a common component of ink, [|rubber], adhesive, [|[9]] and [|leather] industries. In thinning [|paints] and [|varnishes], it can be substituted for [|toluene] where slower drying is desired, and thus is used by [|conservators] of art objects in solubility testing. [|[10]] Similarly it is a [|cleaning agent], e.g., for [|steel] , [|silicon wafers] , and [|integrated circuits]. In dentistry, xylene can be used to dissolve gutta percha, a material used for endodontics (root canal treatments).

Laboratory uses
It is used in the laboratory to make baths with dry ice to cool reaction vessels, and as a [|solvent] to remove synthetic [|immersion oil] from the microscope [|objective] in [|light microscopy]. [|[11]] In histology, xylene is also used for clearing the tissues following dehydration in preparation for paraffin wax infiltration. It is also used after sections have been stained to make them hydrophobic so that a coverslip may be applied with a resin in solvent.

Precursor to other compounds
Although conversion to [|terephthalic acid] is the dominant chemical conversion, xylenes are precursors to other chemical compounds. For instance [|chlorination] of both methyl groups gives the corresponding xylene dichlorides (bis(chloromethyl)benzenes).